A critical maturational period of reduced brain vulnerability to injury. A study of cerebral glucose metabolism in cats.

We have developed a feline cerebral hemispherectomy model as an analog to the surgical procedure used in pediatric intractable epilepsy. Previous work with this model has shown a remarkable plasticity associated with an early period of brain development, which we have defined using morphological, cerebral metabolic and behavioral methods. However, the important functional-metabolic bracketing of this period has not yet been performed. We have conducted the present study to answer questions raised by our previous findings using [14C] 2-deoxy-D-glucose autoradiography but only including animals lesioned at day 10 postnatally (P10) or in adulthood. The questions were; (a) is there any age better than P10 for an optimal metabolic outcome?, and (b) can we determine a cutoff point for the beneficial effects of the young age-at-lesion? Twenty-one adult cats were studied. Seven cats served as intact controls, five received a left hemineodecortication at P30, three at P60, three at P90 and three at P120, respectively. Histological analysis indicated that the extent of the lesion was similar between the age groups. Local glucose metabolic rates (LCMR(glc)) were measured in 50 structures bilaterally and used to calculate overall LCMR(glc) for seven grouped sites within the cerebral cortex, thalamus, basal ganglia, mesencephalic tegmentum (and tectum), limbic system and cerebellum. Results indicated a widespread bilateral depression of LCMR(glc) in all age-at-lesion groups. The depression in overall LCMR(glc) across all structures measured in each hemisphere was significant (P<0.05) for the P120 group relative to intacts for both ipsilateral (left) and contralateral (right) sides of the brain. The ipsilateral thalamus was the region most effected by the injury, with significant losses for all age-at-lesion groups. In addition, while there were widespread depressions for all lesion groups, these losses were significant for the P120 group in five groups of structures ipsilaterally (thalamus, basal ganglia, tectum, limbic system, cerebellum) and in three contralaterally (thalamus, tectum, cerebellum). In contrast, significant depressions for the earlier age-at-lesion groups (P30, P60, P90) were found only in the ipsilateral thalamus and bilaterally in the tectum. These results, together with our previous results for the P10 group, indicate a relative sparing of LCMR(glc) after hemineodecortication during the first 60 days of life, with gradually decreasing plasticity thereafter, such that there is some residual sparing at 90 days of age, and afterwards an almost complete loss of metabolic plasticity, with lesions at P120 producing a dismal outcome. These results complement earlier morphological and behavioral studies and support the concept of a 'Critical Maturational Period' of reduced vulnerability to developmental injury.

Sleep-waking states develop independently in the isolated forebrain and brain stem following early postnatal midbrain transection in cats.

We report the effects of permanently separating the immature forebrain from the brain stem upon sleeping and waking development. Kittens ranging from postnatal 9 to 27 days of age sustained a mesencephalic transection and were maintained for up to 135 days. Prior to postnatal day 40, the electroencephalogram of the isolated forebrain and behavioral sleep-wakefulness of the decerebrate animal showed the immature patterns of normal young kittens. Thereafter, the isolated forebrain showed alternating sleep-wakefulness electrocortical rhythms similar to the corresponding normal patterns of intact, mature cats. Olfactory stimuli generally changed forebrain sleeping into waking activity, and in cats with the section behind the third nerve nuclei, normal correlates of eye movements-pupillary activity with electrocortical rhythms were present. Behind the transection, decerebrate animals showed wakefulness, and after 20 days of age displayed typical behavioral episodes of rapid eye movements sleep and, during these periods, the pontine recordings showed ponto-geniculo-occipital waves, which are markers for this sleep stage, together with muscle atonia and rapid lateral eye movements. Typically, but with remarkable exceptions suggesting humoral interactions, the sleep-waking patterns of the isolated forebrain were dissociated from those of the decerebrate animal. These results were very similar to our previous findings in midbrain-transected adult cats. However, subtle differences suggested greater functional plasticity in the developing versus the adult isolated forebrain. We conclude that behavioral and electroencephalographic patterns of non-rapid eye movement sleep and of rapid eye movement sleep states mature independently in the forebrain and the brain stem, respectively, after these structures are separated early postnatally. In terms of waking, the findings strengthen our concept that in higher mammals the rostral brain can independently support wakefulness/arousal and, hypothetically, perhaps even awareness. Therefore, these basic sleeping-waking functions are intrinsic properties of the forebrain/brain stem and as such can develop autochthonously. These data help our understanding of some normal/borderline sleep-waking dissociations as well as peculiar states of consciousness in long term patients with brain stem lesions.

Soma size of substantia nigra neurons increases after a prenatal neocortical lesion in cats.

Seeking an explanation for an increase in volume of the caudate nucleus in adult cats that had sustained a fetal unilateral neocortical lesion, we investigated possible morphological changes in the reciprocally interconnected substantia nigra. In fetal-lesioned cats the cross-sectional area of neuronal somata in substantia nigra, pars reticulata was 33% larger than in control cats (P<0.05), while in pars compacta there was a marked tendency to an increase (25%, P<0.06). This size increase might have caused the survival of a larger number of caudate nucleus neurons during development, and thus contributed to the reported increase in caudate nucleus volume.

The growth of the feline brain from late fetal into adult life. I. A morphometric study of the neocortex and white matter.

We measured the growth of the neocortex (NCx) and telencephalic white matter (WM) in the brain of 64 cats allocated to the following 11 age-groups: fetal (E) 59 days (birth is at E63-65), postnatal (P) days 1, 7, 15, 30, 45, 60, 90, 120, 180, and adult. There were six subjects per group (except for E59, n=4). Using a projection microscope and cytochrome oxidase-stained coronal sections, a total of 4300 and 4325 sections at left and of 4282 and 4264 sections at right were drawn for the NCx and for the WM, respectively. With computer assistance, the drawings were digitized to calculate mean cross-sectional area and then the mean volume of each structure per age-group. The two structures grew heterochronously. In terms of percentage of the adult volume, for the left side (both side grew at a similar rate), the size of the NCx grew very fast from a 15.7% at E59 to an adult-range value of 93.7% at P30. In contrast, the WM grew slowly. Starting at a larger volume of 55%, the WM was only 72. 5% of the adult size at P30 reaching an adult-range value only by P180 (94.7%). After P30, both structures showed a small, albeit consistent, left versus right asymmetry with the right size been larger at all (but fetal) ages by a margin ranging between 0.4 and 4. 1%. In addition, after P30 the NCx tended to overgrow with all groups showing higher values relative to adult cats, and reaching significance at P60 (volume higher by 19.2%, P<0.01) and at P180 (higher by 14.5%, P<0.05). For the NCx there were no within group correlations between volume of the structures and the subjects' body weight, while a positive correlation was present for four of the WM postnatal groups. There were no correlations between the size of the structures and the sex of the cats. The data is discussed in the context of the extant human and animal literature and, in the ensuing paper, also within the context of growth of subcortical structures.

The growth of the feline brain from fetal into adult life. II. A morphometric study of subcortical nuclei.

As a continuation of the morphometric studies on the preceding paper, here we report on the rate of growth of the caudate nucleus (n.), thalamus, red n., and the substantia (s.) nigra using, with few exceptions, the same cohort of cats. The same previously used brains (n=64 cats) were allocated to the following age groups: fetal (E) 59 days, postnatal (P) days 1, 7, 15, 30, 45, 60, 90, 120, and 180. Sixteen additional cats, interspersed within the groups, were substituted for the red n. and s. nigra studies. There were six subjects per group (except for E59, n=4). Using a projection microscope and cytochrome oxidase-stained coronal sections, a combined (left plus right sides) total of 4693, 3822, 1636, and 1180 sections were drawn for the caudate, thalamus, s. nigra, and red n., respectively. With computer assistance, the drawings were digitized to calculate mean cross-sectional areas and then the mean volume of each structure per group. The growth time tables for the caudate n., thalamus and s. nigra were fairly synchronous. In terms of percentage of the adult volume, for the left side (both sides grew at a similar rate), the three structures grew at a fast pace between E59 and P30. Thus, at E59 their respective percentages relative to adult volume were 23.7, 29.8 and 22.6% and by P30 the percentages were within adult range (85.2, 115.1 and 87.5%, respectively). Starting at P30, for the thalamus and at P45 for the caudate n., there was a consistent tendency to an overgrow which ranged between 4.3 and 30.9% (at P180, P<0.5) for the caudate and between 0.3 and 15.1% for the thalamus. In addition, starting at P30, the right thalamus tended to be consistently larger than the left by a margin ranging between 0.5 and 11.2% (P120, P<0.05). The red n. grew at a different, slower pace. Starting from a fetal volume equivalent to an 18.6% of adult size, its volume was only a 61.0% of the adult value at P30 and came within range of adulthood size only by P60 (81. 3%). Neither the s. nigra nor the red n. showed any consistent tendency to overgrow or to asymmetry. These findings are discussed in the context of the literature. Furthermore, we discuss general conclusions and considerations pertaining to both papers as well as draw comparisons with the maturational time tables of other developmental landmarks in cats. Finally, in a comparison with growth of human brain structures, we point at the limitations and complexities involved in studying human material and, noting interspecies similarities, we propose that the present data from an advanced gyrencephalic mammal may form the bases for a model of structures maturation in humans.

Developmental neuroplasticity in a model of cerebral hemispherectomy and stroke.

Cerebral hemispherectomy, a last resort treatment for childhood epilepsy, is a standard procedure which dramatically illustrates the resilience of the brain to extensive damage. If this operation, also mimicking long-term, extensive unilateral capsular stroke, is performed in postnatal cats of up to 60 days of age, there is a remarkable recovery/sparing of neurological functions that is not seen when the lesion occurs during late fetal life or in adulthood. A long-term effect at all ages is loss of neurons in bilateral brain areas remote from the resection site. This is pronounced in adult cats and shows intriguing, paradoxical features in fetal animals, but is substantially attenuated in neonatal cats. Similarly, large-scale reinnervation of subcortical sites (sprouting) by neurons of the remaining, intact hemisphere is prominent in young cats, but not in fetal or adult animals. These and other restorative processes (described herein) in young postnatal animals are matched by relatively higher rates of local cerebral glucose utilization, supporting the notion that they underlie the improved behavioral outcome. Thus, during a critical, defined stage of maturation, presumably common to higher mammals including humans, the brain entirely remodels itself in response to extensive but focal injury. Perhaps the molecular environment allowing for rescue of neurons and enhanced reinnervation at a specific developmental stage could be recreated in subjects with brain lesions at less favorable ages, thereby helping to restore circuitry and spare neurons. However, replacement via transplantation of neurons eliminated by the damage appears to be crucial in attempts to further preserve cells located remotely but yet destined to die or decrease in size. This article presents abundant evidence to show that there is a surprisingly comprehensive long-term morphological remodeling of the entire brain after extensive unilateral damage and that this occurs preferentially during a discrete period of early life. Additional evidence strongly suggests that the remodeling underlies the outstanding behavioral and functional recovery/sparing following early cerebral hemispherectomy. We argue that this period of reduced brain vulnerability to injury also exists in other higher mammals, including man, and suggest ways to enhance restorative processes after stroke/hemispherectomy occurring at other ages.

Regional age-dependent effects of hemineodecortication upon contralateral neocortical thickness: comparison with other measures of cortical size.

This study investigated age-dependent changes in regional neocortical thickness after hemineodecortication in cats and compared the results to previously reported volumetric and cross-sectional data. Subjects sustained hemineodecortication on postnatal days (P) P10, P30, P60 or in adulthood. Neocortical thickness was quantified at 115 sites along 20 stereotaxic coronal anterior-posterior (AP) planes using defined sites of the main cerebral sulci for the measurements. The analysis established significantly lower thickness values for adult-lesioned as compared to (a) P30, P60 and control groups at AP +14, (b) P30 group at 7 planes along a range of AP +9 to AP +3, and (c) P10 and P60 groups at AP +6. Both the P10 and the P30 groups presented a significantly thicker neocortex than controls at select coronal planes clustering behind AP +10 (parietal and temporal cortices). When analyzed by sulcus, results once again reflected significant advantages for the early-lesioned cats with a significantly thicker cortex found at 4 of the 8 sulci examined. Again, significant advantages were also discovered for early-lesion subjects compared with control cats (splenial, cruciate sulci). Overall, the range of significant effects (from AP +14 to AP 0) and the direction of the means suggested that there was a significant, age-dependent (P10-P60), regional sparing of neocortical thickness with a peak effect occurring at P30. We concluded that: (a) there was a regional sparing/increase of neocortical thickness suggesting that discrete cortical areas are selectively involved in the resistance to structural atrophy following hemineodecortication in young cats (P10-P60) and (b) the global loss of neocortex volume found in our previous study was not apparent using the present thickness measurement. It is suggested that both of these measurements must be taken into account when assessing morphological effects upon the neocortex either in human pathology (i.e. hemispherectomy, intractable epilepsy) or in animal models.

Effects of a restricted unilateral neocortical lesion upon cerebral glucose and oxidative metabolisms in fetal and neonatal cats.

The present study was designed to measure cerebral glucose and oxidative metabolisms and to assess relationships with previously identified morphological changes in adult cats with a unilateral, restricted neocortical lesion sustained either during fetal life or neonatally. Local cerebral metabolic rates for glucose (LCMR(glc)) were measured using the [14C]2-deoxy-D-glucose (2 DG) autoradiography method and oxidative capacity was determined using cytochrome oxidase histochemistry (C.O.). Only glucose metabolism in the fetal-lesioned cats was affected substantially. There was a global decrease (31.0% relative to controls) of the LCMR(glc) for both cerebral hemispheres while focal decreases were seen mainly in thalamic and neostriatal nuclei (and reaching declines of over 50%). Cats with a neonatal lesion showed only a tendency to such declines (19.5% and 22.0% for the right and left hemispheres, respectively). C.O. values were not affected significantly either globally or locally in any of the age-at-lesion groups. In previous work using fetal animals with similar lesions, morphological evidence of subcortical neuropile degeneration was not observed; instead, a marked decrease in size of the ipsilateral remaining neocortex and a pronounced distortion of gyri and sulci patterns bilaterally were found. In this context, we propose that in the fetal-lesioned cats, there was a widespread lesion-induced decrease in corticofugal (and transcortical) synaptic inputs which was responsible for a decline in functional (synaptic) activities, and that this, in turn, caused a downturn in glucose utilization. In the neonatal cats minor degeneration, coupled with lack of reinnervation, would account for the tendency to 2 DG declines. These results indicate that the long-term metabolic response of the fetal brain to injury is also less adaptive than that of the neonatal brain. Since standard methods are available to measure cerebral metabolism in humans, our studies in animal models may help understanding the long term physiological consequences of developmental focal brain damage in patients as well as to predict the relationships between cerebral metabolism and the underlying long-term morphological effects of such lesions.

Cerebral metabolism following neonatal or adult hemineodecortication in cats: effect on oxidative capacity using cytochrome oxidase histochemistry.

In order to determine the degree and extent of changes in cerebral oxidative capacity following cerebral hemineodecortication, adult cats which had undergone surgery early postnatally (mean age: 11.4 days) or during adulthood were studied using cytochrome oxidase histochemistry. A total of 18 animals were employed and 50 brain regions were quantified bilaterally using optical densitometry. Although many subcortical regions exhibiting extensive degenerative features revealed lower levels of cytochrome oxidase (C.O.) activity, this reduction was relatively unremarkable compared to intact controls. Nevertheless, it was interesting that this decrease (down to 66-89%) of normal was more pronounced in neonatal-lesioned cats, reaching significance in a number of ipsilateral thalamic nuclei, compared to adult-lesioned animals (91-100% of normal), suggesting a contribution of glial cells to the density of C.O. staining in the latter cats. Regions of the brain spared from degeneration exhibited a bilateral increase in C.O. activity which may reflect the demands for energy to support the anatomical reorganization which is prevalent in these animals. Surprisingly, such increases were more robust within spared regions of the adult-lesioned brain, reaching significance in four ipsilateral and nine contralateral areas with the density of the reaction attaining levels over 125% of control. This may indicate different demands for oxidative metabolism in the adult-lesioned cats. These results enhance our understanding of the mechanism(s) underlying the greater extent of functional sparing or recovery in cats sustaining injury to the cerebral cortex early vs. late in life. In addition, the findings complement our previous companion report on glucose metabolism supporting the concept of energy compartmentalization, which reflects the dynamic interaction between anatomical and functional changes in this age-at-lesion model of recovery.

A critical maturational period of reduced brain vulnerability to developmental injury. I. Behavioral studies in cats.

Groups of cats with resection of the neocortex of the left cerebral hemisphere at postnatal (P) ages (in days) 5-15 (P10), 30 (P30), 60 (P60), 90 (P90), 120 (P120), and in adulthood, were compared using a comprehensive battery of 16 neurobehavioral tests administered when they were at least 6 months post-lesion. For all behaviors, except 3 (including the paw contact placing reaction which never recovered), the performance was significantly better for the cats lesioned between P10 and P30 compared to cats lesioned at older ages. For 10 of the behaviors, the transition from age-at-lesion P30 to P60 was rather abrupt and characterized by a significant increment in impairments. However, cats with the resection at ages P90 and P120 still showed some behavioral advantage over the adult-lesioned animals. Overall, for most of the behaviors tested, there was a significant linear trend for an increase in the magnitude of impairments across the entire age-at-lesion range. We previously reported that cats with a unilateral frontal cortical lesion sustained during the late fetal life showed substantial behavioral impairments, while animals with a similar resection sustained early postnatally exhibited minimal abnormalities. These findings, together with the present results, indicate that the long-term behavioral outcome of neocortical injury is best when the lesion is sustained during a discrete period of the life of the cat. This period extends from about fetal age 55 days (the oldest lesion age in our fetal studies) to about P60, as shown in the present paper. For these reasons, we propose that there is a Critical Maturational Period (CMP) for optimal post injury brain and behavioral restoration. We hypothesize that this span of reduced vulnerability is linked to specific developmental morphological events which occur during the same time period. Since, as discussed, such ontogenetic events also occur in other mammal species (albeit at different chronological ages), we further propose that the timing of the CMP as delineated in cats, can be extrapolated to other higher mammals species including humans.

A critical period for reduced brain vulnerability to developmental injury. II. Volumetric study of the neocortex and thalamus in cats.

Groups of young adult cats with a left hemineodecortication at postnatal (P) ages (in days) 5-15 (P10), 30 (P30) 60 (P60), 90 (P90), 120 (P120) and in adulthood, were used to measure the volume of the thalamus, bilaterally, and of the remaining neocortex (right hemisphere). The same subjects were employed for the behavioral studies reported in the preceding paper. There was a bilateral, age-dependent, thalamic volume decrease. Ipsilateral to the resection, the thalamic shrinkage was the largest for the adult-lesioned cats (by 56.7%) and it was the smallest for the P30 group (43.4%), with a tendency towards a greater atrophy as the age at lesion increased. A similar pattern of atrophy was seen for the contralateral thalamus but the volume reduction was much less pronounced such that it was significant only for the four older age-at-lesion groups (ranging from 18.2% to 11.2% for the P120 and P90 groups respectively). Once again, the shrinkage was the smallest for the P30 group (5.3%). The remaining neocortex also shrunk in these animals, but the volume decrease was significant only for the adult-lesioned (17.8%) and the P120 group (15.4%), while the P30 group had practically no shrinkage (2.4%). The frontal cortex had no atrophy or it was minimal but the shrinkage gradually increased caudally such that all lesioned groups had some size reduction of the occipital cortex. The present results, together with the main conclusion of the preceding paper, indicate that there is a critical maturation period (CMP) of reduced forebrain vulnerability to neocortical injury which, in cats, tends to end between 30 to 60 days postnatally. The implications for developmental brain damage in other higher mammal species as well as the possible morphological ontogenetical underpinnings of this period are discussed.

Differences in D2 dopamine receptor binding in the neostriatum between cats hemidecorticated neonatally or in adulthood.

In order to study differences in response to neocortical injury sustained at different ages at the neurotransmitter level, we examined the density in D2 dopamine receptors in the neostriatum of cats hemidecorticated neonatally (N = 4) or in adulthood (N = 4), as well as in intact brains (N = 6). Receptor densities were measured using quantitative autoradiography and [3H]-spiperone binding in 12 regions of the neostriatum and nucleus accumbens septi. We found that the anterior lateral caudate nucleus on both sides of the brain contained a higher D2 receptor density in neonatal-lesioned as compared to adult-lesioned brains. Ipsilateral to the lesion, the increase was 101% (P < 0.05) and contralaterally it amounted to 77% (P < 0.05). Moreover, this region of the ipsilateral caudate nucleus of neonatal-lesioned cats tended to be more densely labeled than that of intact brain by 58% (P < 0.1). D2 receptor densities in adult-lesioned cats did not differ from that of intact controls. Comparison of these data with those of a former morphological study using the same animals suggested that this bilateral elevation of D2 receptor density in neonatally lesioned brains represents a higher mean density of binding sites per neuron. The elevation in the neonatal-lesioned cats might be a response of the striatum to neuroplastic changes in the striatal neuropil, including the corticostriatal afferents, since such changes are different in neonatal- as compared to adult-lesioned cats.

The effect of neocortical lesions on the number of cells in neonatal or adult feline caudate nucleus: comparison to fetal lesions.

After a unilateral resection of the frontal cortex in fetal cats the volume of the caudate nucleus increases while the packing density of neuronal and glial cells does not change. In the present report we address the questions of whether a similar lesion sustained neonatally or a more extensive neodecortication sustained neonatally or in adulthood may have the same unusual effect. Stereological methods were used to determine bilaterally the volume of the caudate nucleus as well as to estimate the total number and packing density of neurons and glial cells in the caudate nucleus ipsilateral to the lesion. Comparisons between each of three experimental groups and intact animals were made at a time when all animals were young adults. In cats with a unilateral frontal cortical lesion performed between postnatal days 8 and 14, none of the measured parameters changed significantly compared to intact controls. In cats with removal of the entire left neocortex in adulthood, the ipsilateral caudate nucleus volume decreased by 18.1% and by 21.5% relative to intact and to neonatal hemidecorticated cats respectively (P < 0.05), with no change in the contralateral caudate. In the ipsilateral caudate the total number of neurons decreased by 21.8% (P < 0.05) compared to controls while the number of glial cells did not change significantly. In the same caudate the packing density of neurons did not change significantly (except for a 17.1% decrease, P < 0.05, relative to frontal-lesioned cats) while that of glial cells increased by 19.9% and by 24.7% compared to intact and neonatal neodecorticated cats respectively (P < 0.05). In adult cats in which a similar hemineodecortication was performed between postnatal days 8 and 13, the only significant changes were a 25.8% (P < 0.05) and a 30.6% (P < 0.05) decrease in neuron packing density compared to intact and frontal-lesioned cats, respectively. In summary, a restricted unilateral neocortical resection in neonatal cats did not induce any morphological changes in the caudate nucleus that we could detect with the methods employed. In contrast, an extensive neodecortication sustained in adulthood produced ipsilateral caudate shrinkage with substantial neuron loss and increase in packing density of glial cells, while a similar lesion but sustained neonatally only altered substantially the packing density of glial cells (decreased). Therefore, we concluded that (i) the caudate nucleus hypertrophy which we reported after a unilateral discrete cortical removal during the prenatal period is a unique phenomenon which is peculiar to the cat brain during the last third of gestation; (ii) the caudate nucleus changes seen in the cats with hemineodecortication in adulthood are degenerative in nature and closely resemble those which we reported for other subcortical nuclei following a similar lesion; and (iii) the animals with neonatal hemidecortication are relatively spared from these degenerative effects. Overall, these results indicate that, as for other structures, the morphological changes of the caudate nucleus following neocortical damage depend on the maturational state of the brain at the time of the injury and on the size of the lesion, and support the notion that the consequences of cerebral cortex lesions upon subcortical brain nuclei are of a different nature when sustained in prenatal as compared to postnatal cats.

Innervation of the caudate nucleus, thalamus and red nucleus by the remaining sensorimotor cortex in cats with fetal or neonatal unilateral frontal cortex removal.

We studied the projections to the caudate nuclei, thalami and red nuclei from the remaining sensorimotor cortex in adult cats that had sustained a unilateral frontal cortex resection prenatally or neonatally. Four cats had the lesion at age E 50-55 and six animals sustained the ablation at age P 8-14 (seven cats were intact controls). All cats grew to young adulthood and then received injections of tritiated leucine-proline in the remaining sensorimotor cortex. Injection sites and axon terminal fields were reconstructed using autoradiography-processed tissue. In all cats the label filled a similar extent of the right pericruciate cortex. Terminal field densities in the subcortical nuclei were estimated using computer-based video software. Three medial-lateral sectors at five coronal levels were examined in the caudate nucleus. Three nuclear groups were analyzed in the thalamus (intralaminary, ventralis lateralis and ventrobasal complex). For the red nucleus, the four quadrants were examined at four coronal levels. The main goal of the study was to assess possible changes in the cortical innervation of the nuclei ipsilateral to the lesion. Therefore, the mean particle counts per nucleus (and per area or sector of nuclei) and per animal group were used to calculate percentage values for the decussated (crossed, or contralateral to the injection site) as a function of the non-decussated (uncrossed, or ipsilateral to the injection site) innervation. The percentage values for the crossed projections were: (a) for the entire caudate nucleus, 61.3% for the intact. 56.7% for the fetal-lesioned and 42.7% for the neonatal-lesioned cats, with no statistical differences between groups; (b) for the thalamus the proportion of crossed projections was minimal fluctuating between a low 0.06-0.16% for the nucleus ventralis lateralis and a high of 2.01-3.46% for the intralaminary nuclei, with the highest values belonging to the lesioned groups but with no significant differences between groups: (c) for the entire red nucleus, 1.98%, 12.74% (P < 0.05) and 6.76% for the intact, fetal- and neonatal-lesioned cats respectively. In the lesioned cats, the topography of the distribution of the axon terminals was bilaterally the same as in the controls. In conclusion, only the red nucleus of the frontal-lesioned cats showed an increased crossed innervation from the remaining sensorimotor cortex but this was relatively weak and statistically significant only for the fetal-lesioned animals. These results as well as the literature suggest that: (a) the crossed corticorubral projections in fetal cats may represent true reinnervation (i.e., newly originated, no preexisting terminals); (b) the relative paucity of the crossed projections in the present cats as compared to the extensive reorganization of subcortical terminals seen after cerebral hemispherectomy (our original postnatal lesion model) may be due to the much smaller size of the present cortical lesion which presumably induced only a limited amount of subcortical nuclear deafferentation.

Cerebral metabolism following neonatal or adult hemineodecortication in cats: I. Effects on glucose metabolism using [14C]2-deoxy-D-glucose autoradiography.

In the cat, cerebral hemispherectomy sustained neonatally results in a remarkable degree of recovery and/or sparing of function as compared with the effects of a similar lesion but sustained in adulthood. We have proposed that this effect is due to a combination of reduced neuronal loss within partially denervated structures and a lesion-induced reorganization of corticofugal projections arising from the remaining intact hemisphere in the neonatally lesioned animal. The current study was designed to assess the physiological consequences of these anatomical changes utilizing [14C]2-deoxy-D-glucose autoradiography. A total of 17 adult cats were studied. Seven animals served as intact controls, five received a left cerebral hemineodecortication as neonates (NH; mean age 11.4 days), and five sustained the same lesion in adulthood (AH). Histological analysis indicated that the lesion was very similar between the two age groups and essentially represented a unilateral hemineodecortication. Local CMRglc (LCMRglc; mumol 100 g-1 min-1) values were calculated for 50 structures bilaterally and indicated that in the remaining intact contralateral (right) cerebral cortex (including all areas measured), AH cats exhibited a significantly (p < 0.05) lower level of LCMRglc (ranging from 20 to 72 mumol 100 g-1 min-1) than NH (ranging from 49 to 81 mumol 100 g-1 min-1). In comparison, the rates of NH cats within the cerebral cortex were very similar to those seen in intact animals (ranging from 48 to 119 mumol 100 g-1 min-1). Ipsilateral to the lesion in AH cats, the structures spared by the resection, including the basal ganglia and thalamus, exhibited LCMRglc rates of between 23 and 69 mumol 100 g-1 min-1, which were significantly lower (p < 0.05) than in NH cats (range 47-72 mumol 100 g-1 min-1). Considering all structures, both age-at-lesion groups exhibited a lower level of metabolism compared with similar measurements for intact control animals (LCMRglc range 45-75 mumol 100 g-1 min-1). However, this depression of glucose metabolism was more pronounced in the AH cats (p < 0.05). These results indicate that following neonatal hemineodecortication, LCMRglc is maintained at a higher level in many regions of the brain than in animals that sustain the same resection in adulthood. This higher level of glucose metabolism in NH animals suggests that the lesion-induced anatomical reorganization of structures not directly injured by the lesion plays a functional role that is probably responsible for the greater degree of recovery and/or sparing of function in these early lesioned cats.

Few neocortial and thalamic morphological changes after a neonatal frontal cortical ablation contrast with the effects of a similar lesion in fetal cats.

To further understand the neuroanatomical consequences following perinatal brain injury, quantitative morphometric analysis was performed on the brain of cats receiving a unilateral frontal cortical ablation between postnatal days (P) 9 and P 14 and intact control cats. In all cats, the volume of the neocortex and thalamus was measured bilaterally and that of the thalamic ventrobasal complex (VBc) was measured ipsilaterally. In addition, using stereology, the neuronal and glial (presumably) cell packing densities (CPD) and the total number of neurons and glial cells (TCN) were measured in the ipsilateral VBc. The neuronal and glial cell cross-sectional areas (CSA) were also measured in the ipsilateral VBc. The mean ipsilateral and contralateral neocortex volumes were similar between the two animal groups. There was a statistically significant 14% and 13% reduction in mean ipsilateral and contralateral thalamic volumes, respectively for the lesioned animals, while the VBc shrank by 16% relative to intact controls. The mean neuronal and glial CPD were similar between the two groups. The mean neuronal TCN was reduced by 10% in the neonatal-lesioned cats, while the mean glial TCN was reduced by 31% in the same animals, however neither value reached significance. Lastly, the mean CSA of neurons and glial cells showed a tendency to be smaller in the lesioned cats by 8% and 9%, respectively. These results: (a) indicate that the neonatal lesion caused only minor morphological brain alterations and this sharply contrast with the marked changes previously reported in cats with a similar lesion sustained prenatally; (b) suggest that the enhanced behavioral recovery and/or sparing reported for the present cats compared to fetal-lesioned animals is at least partially due to the morphological sparing reported here; (c) together with previous findings in fetal cats, support the hypothesis that the morphological changes after a neonatal neocortical lesion are qualitatively different and may depend on different mechanisms as compared to those occurring after similar damage sustained prenatally.

Development of a crossed corticotectal pathway following cerebral hemispherectomy in cats: a quantitative study of the projecting neurons.

A hypothetical mechanism for the partial sparing of visual function in the contralateral visual field following cerebral hemispherectomy early in life is the formation of a new corticotectal pathway arising from the remaining primary visual cortex (areas 17 and 18) that projects to the contralateral superior colliculus. To test this hypothesis, the left superior colliculus of intact adult and neonatal (5-15 days old) cats and of adult cats with a left cerebral hemispherectomy sustained neonatally (7-9 days old) or in adulthood, was injected with WGA-HRP and the brains were processed for combined TMB/DAB histochemistry. The primary visual cortex was examined, labelled neurons were counted and the cross sectional area of their somata was measured. The left primary visual cortex of intact adult animals exhibited a mean of 959.68 labelled cells +/- 406.5 (S.E.), with a mean soma size of 366.7 microns2 +/- 131.2. For the neonatal intact cats, there was a mean of 75.31 +/- 21.08 cells within the left primary visual cortex which exhibited a mean soma size of 249.56 microns2 +/- 68.18. The peak cell size distribution for both intact groups was similar at 300 microns2. Virtually no labelled neurons were detected in the right primary visual cortex of intact animals (neonatal or adult). For neonatal-hemispherectomized cats, the remaining right primary visual cortex exhibited a mean cell count of 351.09 +/- 126.3 cells, with a mean soma size of 436.1 microns2 +/- 131.5, and a peak cell size distribution of 400 microns2. Finally, for adult-hemispherectomized animals, the contralateral primary visual cortex exhibited 68.27 +/- 20.13 neurons having a mean soma size of 486.6 microns2 +/- 143.2 with a peak cell size distribution of 500 microns2. These results indicate that reorganization of the corticotectal pathway occurs in both adult- and neonatal-hemispherectomized cats but is more pronounced in neonatal-lesioned animals. In addition, the cells of origin of this reorganized pathway tended to be larger, perhaps in response to a greater axonal arborization.

Morphological changes in the thalamus and neocortex of the cat brain after a restricted unilateral fetal neocortical lesion.

In order to study the response of the brain to injury during early development, the neocortex of ten fetal kittens was lesioned at age E43-48, in either the frontal (n = 8) or parieto-occipital (n = 2) areas. The thalamus and neocortex of the lesioned animals were analyzed using quantitative morphometry and compared to intact control cats (n = 10). Ipsilaterally, the volumes of the remaining neocortex and of the thalamus were 26.5% and 25.7% smaller, respectively (P < 0.05). Contralaterally, the neocortex did not change in volume, whereas the thalamus tended to be smaller by a mean of 11.1%. Ipsilaterally, in all four thalamic nuclei studied, the neuronal and glial cell packing densities (NCPD and GCPD) and the cross sectional area of neuronal somata did not differ between lesioned and intact animals except for the principal ventromedial nucleus, where the GCPD was significantly lower (P < 0.05) in lesioned animals. Contralaterally, the NCPD and GCPD did not show any differences between groups, except for the principal ventromedial nucleus, in which the GCPD was lower in lesioned cats (P < 0.05). Furthermore, in the contralateral basal ventromedial nucleus, the cross sectional area of the neuronal somata was smaller in lesioned than in intact animals (P < 0.01). These results indicate loss of neurons and glia in the ipsilateral thalamus and probably in the neocortex. Since, at the time of the cortical resection, transient reciprocal thalamosubplate connections have been established in the cat, the lesion-induced deprivation of subplate target neurons and cortical inputs probably precluded the survival of a substantial number of developing thalamic neurons. In the cortex the hypothetical loss of neurons may, at least partly, be attributed to lesion-induced elimination of target neurons before establishment of corticocortical connections.

Neurological and behavioral effects of a unilateral frontal cortical lesions in fetal kittens. I. Brain morphology, movement, posture, and sensorimotor tests.

Nine fetal kittens sustained removal of the left frontal cortex during the last third of gestation (E 43-55) and were compared to animals sustaining a similar lesion postnatally (P 8-14) as well as to littermate controls. Starting after 6 months of age the animals received a comprehensive battery of movement, posture and sensorimotor tests. The prenatal-lesioned cats performed worse in practically all 15 tests applied (significantly in 13 of them) compared to the neonatal-lesioned cats. Impairments included contralateral paresis of the limbs and face, defective limb placing reactions (with almost absence of the contact components) and a slight extensor hypertonus; tactile hypoesthesia in the contralateral face and hind paw; a bias not to use the contralateral forepaw in a food retrieval task, and an ipsilateral body turning bias. The neonatal-lesioned animals only showed minor defects in the contact components of the limb placing reactions and a tendency to a body turning bias. Morphologically, the brains of the prenatal-lesioned cats, but not of neonatal-lesioned or intact control cats, showed bilateral disruption of the cortical sulcal and gyral patterns, shrinkage of the ipsilateral hemisphere, and reduction in volume of the ipsilateral thalamus and cortex. We concluded, contrary to expectations, that the consequences of a prenatal brain lesion in the cat are worse than when a similar lesion is sustained neonatally.

Neurological and behavioral effects of a unilateral frontal cortical lesion in fetal kittens. II. Visual system tests, and proposing an "optimal developmental period" for lesion effects.

Nine fetal kittens sustained removal of the left frontal cortex during the last third of gestation (E 43-55) and were compared to animals sustaining a similar lesion postnatally (P 8-14) as well as to intact littermates. Beginning after 6 months of age, the animals' visual field and depth perception were assessed. In addition, pupil size as well as eye alignment were measured. On two visual field tests the fetal-lesioned cats showed test dependent decrements for some angles of vision. In terms of depth perception, only the prenatal-lesioned animals showed a higher binocular threshold; they also showed ocular misalignment which may have contributed to their depth perception impairment. Moreover, these animals had a larger ipsilateral pupil. The neonatal-lesioned animals were like normal cats for all tests and measurements. We conclude that, as for the tests reported in the preceding paper, the outcome for visual related behaviors of a prenatal frontal cortical lesion in the cat is also worse than that of a similar lesion sustained neonatally. Dysgenetic anatomical changes of the visual system induced indirectly by the frontal lesion are proposed as a possible explanation for these age-at-lesion differences. Based on the present work as well as on the literature, we propose the existence of an "optimal developmental period" for the best behavioral and anatomical outcome of perinatal brain lesions. We argue that this concept fits contemporary data and can better explain the different age-at-lesion effects of brain injury across animals species than the "Kennard Principle" (or "infant-lesion effect").