Polygenic risk for neuropsychiatric disease and vulnerability to abnormal deep grey matter development.

Neuropsychiatric disease has polygenic determinants but is often precipitated by environmental pressures, including adverse perinatal events. However, the way in which genetic vulnerability and early-life adversity interact remains obscure. We hypothesised that the extreme environmental stress of prematurity would promote neuroanatomic abnormality in individuals genetically vulnerable to psychiatric disorders. In 194 unrelated infants (104 males, 90 females), born before 33 weeks of gestation (mean gestational age 29.7 weeks), we combined Magnetic Resonance Imaging with a polygenic risk score (PRS) for five psychiatric pathologies to test the prediction that: deep grey matter abnormalities frequently seen in preterm infants are associated with increased polygenic risk for psychiatric illness. The variance explained by the PRS in the relative volumes of four deep grey matter structures (caudate nucleus, thalamus, subthalamic nucleus and lentiform nucleus) was estimated using linear regression both for the full, mixed ancestral, cohort and a subsample of European infants. Psychiatric PRS was negatively associated with lentiform volume in the full cohort (ß = -0.24, p = 8 × 10-4) and a European subsample (ß = -0.24, p = 8 × 10-3). Genetic variants associated with neuropsychiatric disease increase vulnerability to abnormal lentiform development after perinatal stress and are associated with neuroanatomic changes in the perinatal period.

Prenatal methamphetamine exposure is associated with reduced subcortical volumes in neonates.

OBJECTIVES: Prenatal exposure to methamphetamine is associated with a range of neuropsychological, behavioural and cognitive deficits. A small number of imaging studies suggests that these may be mediated by neurostructural changes, including reduced volumes of specific brain regions. This study investigated potential volumetric changes in the brains of neonates with prenatal methamphetamine exposure. To our knowledge no previous studies have examined methamphetamine effects on regional brain volumes at this age. STUDY DESIGN: Mothers were recruited antenatally and interviewed regarding methamphetamine use during pregnancy. Mothers in the exposure group reported using methamphetamine≥twice/month during pregnancy; control infants had no exposure to methamphetamine or other drugs and minimal exposure to alcohol. MRI scans were performed in the first postnatal month, following which anatomical images were processed using FreeSurfer. Subcortical and cerebellar regions were manually segmented and their volumes determined using FreeView. Pearson correlations were used to analyse potential associations between methamphetamine exposure and regional volumes. The associations between methamphetamine exposure and regional volumes were then examined adjusting for potential confounding variables. RESULTS: Methamphetamine exposure was associated with reduced left and right caudate and thalamus volumes. The association in the right caudate remained significant following adjustment for potential confounding variables. CONCLUSIONS: Our findings showing reduced caudate and thalamus volumes in neonates with prenatal methamphetamine exposure are consistent with previous findings in older exposed children, and demonstrate that these changes are already detectable in neonates. Continuing research is warranted to examine whether reduced subcortical volumes are predictive of cognitive, behavioural and affective impairment in older children.

Nuclear receptor COUP-TFII-expressing neocortical interneurons are derived from the medial and lateral/caudal ganglionic eminence and define specific subsets of mature interneurons.

Neocortical GABAergic interneurons in rodents originate from subpallial progenitor zones. The majority of mouse neocortical interneurons are derived from the medial and caudal ganglionic eminences (MGE and CGE, respectively) and the preoptic area (POA). It is controversial whether the lateral ganglionic eminence (LGE) also generates neocortical interneurons. Previously it was shown that the transcription factor COUP-TFII is expressed in the CGE; here we show that COUP-TFII is also expressed in the dorsal MGE, dorsal LGE (dMGE and dLGE, respectively), and POA. In the adult neocortex, COUP-TFII+/somatostatin (SOM)+ interneurons are mainly located in layer V. Using a genetic fate-mapping approach (Shh-Cre and Nkx2.1-Cre), we demonstrate that the POA and ventral MGE do not give rise to COUP-TFII+ neocortical interneurons, suggesting that the dMGE is the source of COUP-TFII+/SOM+ neocortical interneurons. We also observed a migratory stream of COUP-TFII+/Sp8+ cells emanating from the dLGE and CGE to the neocortex mainly through the subventricular zone at later embryonic stages. Slice culture experiments in which dLGE progenitors were labeled with BrdU provided additional evidence that the dLGE generates neocortical interneurons. While earlier-born dMGE-derived COUP-TFII+ interneurons occupy cortical layer V, later-born dLGE- and CGE-derived COUP-TFII+ ones preferentially occupy superficial cortical layers. A similar laminar distribution was observed following neonatal transplantation of embryonic day (E)14.5 dMGE and E15.5 dLGE. These results provide novel information about interneuron fate and position from spatially and temporally distinct origins in the ganglionic eminences.

Subcortical and cortical structural central nervous system changes and attention processing deficits in preschool-aged children with prenatal methamphetamine and tobacco exposure.

OBJECTIVE: To examine the independent contributions of prenatal methamphetamine exposure (PME) and prenatal tobacco exposure (PTE) on brain morphology among a sample of nonalcohol-exposed 3- to 5-year-old children followed prospectively since birth. STUDY DESIGN: The sample included 20 children with PME (19 with PTE) and 15 comparison children (7 with PTE), matched on race, birth weight, maternal education and type of insurance. Subcortical and cortical volumes and cortical thickness measures were derived through an automated segmentation procedure from T1-weighted structural magnetic resonance images obtained on unsedated children. Attention was assessed using the computerized Conners' Kiddie Continuous Performance Test Version 5 (K-CPT™ V.5). PME effects on subcortical and cortical brain volumes and cortical thickness were tested by general linear model with type III sum of squares, adjusting for PTE, prenatal marijuana exposure, age at time of scan, gender, handedness, pulse sequence and total intracranial volume (for volumetric outcomes). A similar analysis was done for PTE effects on subcortical and cortical brain volumes and thickness, adjusting for PME and the above covariates. RESULTS: Children with PME had significantly reduced caudate nucleus volumes and cortical thickness increases in perisylvian and orbital-frontal cortices. In contrast, children with PTE showed cortical thinning in perisylvian and lateral occipital cortices and volumetric increases in frontal regions and decreases in anterior cingulate. PME was positively related and caudate volume was inversely related to K-CPT reaction time by inter-stimulus interval, a measure of the ability to adjust to changing task demands, suggesting that children with PME may have subtle attentional deficits mediated by caudate volume reductions. CONCLUSIONS: Our results suggest that PME and PTE may have distinct differential cortical effects on the developing central nervous system. Additionally, PME may be associated with subtle deficits in attention mediated by caudate volume reductions.

Prenatal stress changes learning strategies in adulthood.

It is well known that stressful experiences may shape hippocampus-dependent learning and memory processes. However, although most studies focused on the impact of stress at the time of learning or memory testing, very little is known about how stress during critical periods of brain development affects learning and memory later in life. In this study, we asked whether prenatal stress exposure may influence the engagement of hippocampus-dependent spatial learning strategies and caudate nucleus-dependent response learning strategies in later life. To this end, we tested healthy participants whose mothers had experienced major negative life events during their pregnancy in a virtual navigation task that can be solved by spatial and response strategies. We found that young adults with prenatal stress used rigid response learning strategies more often than flexible spatial learning strategies compared with participants whose mothers did not experience major negative life events during pregnancy. Individual differences in acute or chronic stress do not account for these findings. Our data suggest that the engagement of hippocampal and nonhippocampal learning strategies may be influenced by stress very early in life.

Shh signaling guides spatial pathfinding of raphespinal tract axons by multidirectional repulsion.

Relatively little is known about the molecular mechanisms underlying spatial pathfinding in the descending serotonergic raphespinal tract (RST) in the developing spinal cord, one of the most important nerve pathways for pain, sensory and motor functions. We provide evidence that ventral floor plate-secreted Sonic hedgehog (Shh) is responsible for the establishment of decreasing gradients in both the anterior-to-posterior (A-P) and the medial-to-lateral (M-L) directions in the ventral spinal cord during serotonergic RST axon projection. Downstream components of the Shh pathway, Patched 1 (Ptch1) and Smoothened (Smo), were expressed in the serotonergic caudal raphe nuclei and enriched in the descending serotonergic RST axons. Diffusible Shh repulsion of serotonergic RST axons was shown to be mediated by Shh-Ptch1 interactions and derepression of Smo. Using a co-culture assay, we showed that A-P graded repulsion mediated by Shh signaling pushed the serotonergic axons caudally through the ventral spinal cord and M-L graded repulsion mediated by Shh signaling simultaneously restricted the serotonergic axons to the ventral and ventral-lateral funiculus. Prominent pathfinding errors of serotonergic RST axons were observed in various Shh, Ptch1 and Smo mutants. We conclude that Shh signaling-mediated multidirectional repulsion is required to push descending serotonergic RST axons in the A-P direction, and to restrict these axons to the ventral and ventral-lateral funiculus in the M-L direction. This is the first demonstration that Shh signaling-mediated multidirectional repulsion of serotonergic RST axons maintains spatial axon pathfinding in the developing spinal cord.

[Fusion of brain neurons in rat embryos].

Syncytial interneuronal connections were studied in the sensomotor cortex and caudate nucleus of twenty 14-22 day rat embryos. It was shown that with the extremely weak development of glial processes, many neuronal bodies and their processes were in the direct contact with each other. The contacting membranes in these areas formed oblong and dot-like contacts resembling gap and tight junctions. As a result, the intercellular cleft experienced varicose-like deformations. In the area of contacts, barely visible membrane pores were formed that broadened to form large perforations. The perforation margins presented the rounded shape of fused plasma membranes of adjacent neurons. Inside the perforations, residual vesicular membranous bodies were formed. The areas of the paired membranes between perforations were fragmented, thus increasing the number of residual vesicles, until the neurons fused with each other completely by unifying the neuroplasm of contacting cells. The results of these studies suggest that that the fusion of neurons in vertebrate brain cortex and brainstem nuclei could occur not only in pathology, but also in normal animals at the stage of embryonic development.

Neonatal exposure to citalopram selectively alters the expression of the serotonin transporter in the hippocampus: dose-dependent effects.

Infants born to mothers taking selective serotonin reuptake inhibitors (SSRIs) late in pregnancy have been reported to exhibit signs of antidepressant withdrawal. Such evidence suggests that these drugs access the fetal brain in utero at biologically significant levels. Recent studies in rodents have revealed that early exposure to antidepressants can lead to long lasting abnormalities in adult behaviors, and result in robust decreases in the expression of a major serotonin synthetic enzyme (tryptophan hydroxylase) along the raphe midline. In the present investigation, we injected rat pups with citalopram (CTM: 5 mg/kg, 10 mg/kg, and 20 mg/kg) from postnatal Days 8-21, and examined serotonin transporter (SERT) labeling in the hippocampus, ventrobasal thalamic complex, and caudate-putamen when the subjects reached adulthood. Our data support the idea, that forebrain targets in receipt of innervation from the raphe midline are particularly vulnerable to the effects of CTM. SERT-immunoreactive fiber density was preferentially decreased throughout all sectors of the hippocampal formation, whereas the subcortical structures, each supplied by more lateral and rostral aspects of the raphe complex, respectively, were not significantly affected. Reductions in SERT staining were also found to be dose-dependent. These findings suggest that SSRIs may not only interfere with the establishment of chemically balanced circuits in the neonate but also impose selective impairment on higher cortical function and cognitive processes via more circumscribed (i.e., regionally specific) deficits in 5-HT action.

Caudate asymmetry: a neurobiological marker of moderate prenatal alcohol exposure in young adults.

This study identified structural changes in the caudate nucleus in offspring of mothers who drank moderate levels of alcohol during pregnancy. In addition, the effect of duration of alcohol use during pregnancy was assessed. Young adults were recruited from the Maternal Health Practices and Child Development Project. Three groups were evaluated: prenatal alcohol exposure (PAE) during all three trimesters (3T), PAE during the first trimester only (1T), and controls with no PAE (0T). Magnetic resonance images were processed using the automated labeling pathway technique. Volume was measured as the number (gray+white) and relative percentage (caudate count/whole brain count x 100) of voxels. Asymmetry was calculated by subtracting the caudate volume on the left from the right and dividing by the total (L-R/L+R). Data analyses controlled for gender, handedness, and prenatal tobacco and marijuana exposures. There were no significant differences between the groups for whole brain, left, or right volumes. There was a dose-response effect across the three exposure groups both in terms of magnitude and direction of asymmetry. In the 3T group, the left caudate was larger relative to the right caudate compared to the 0T group. The average magnitude of caudate asymmetry for the 1T group was intermediate between the 0T and 3T groups. Subtle anatomical changes in the caudate are detected at the moderate end of the spectrum of prenatal alcohol exposure.

Effect of delta-sleep-inducing peptide on activity of enzymes of biogenic amine metabolism in the brain of Wistar and August rats.

Activity of enzymes catalyzing synthesis and degradation of serotonin and dopamine in brain structures of Wistar and August rats was measured biochemically under normal conditions and after short-term exposure to delta-sleep-inducing peptide. The effects of the test peptide manifested in activation of the serotoninergic system and inhibition of the dopaminergic system, particularly in the caudate nucleus. These changes were most pronounced in the brain of Wistar rats.

Morphological study of the perireticular nucleus in human fetal brains.

Abstract The perireticular nucleus consists of scattered neurons that are located in the internal capsule. The presence of perireticular neurons in the rat, ferret, cat and human has been described previously. Evidence suggests that the perireticular neurons in various species decrease in number with increasing gestation, but in humans this finding has not been supported by quantitative data. This study aimed to investigate (1) the morphology of the human fetal perireticular neurons, (2) the average number of perireticular neurons within the anterior and posterior crus of the internal capsule per unit area, and (3) the magnitude and the stage of neuronal loss in the human perireticular nucleus subsequent to maturation. Nissl-stained sections of the internal capsule of human fetal brains of 24, 26.5, 32, 35, 37 and 39 weeks of gestation showed a number of clearly distinguishable large perireticular and small microglia cells. A regular increase of both perireticular and microglial cells was observed up to 32 weeks of gestation, after which a dramatic reduction in the number of both perireticular and microglia cells was observed. The average number of perireticular and the microglia cells per unit area, located within the posterior crus, was more than in the anterior crus of the internal capsule. In the adult, no perireticular neurons were detected within the internal capsule. The results show that perireticular neurons are not restricted to the region lateral to the thalamus and medial to the globus pallidus (posterior crus) but are also present at the region lateral to the caudate nucleus and medial to the globus pallidus (anterior crus).

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.

Effect of antenatal betamethasone treatment on microtubule-associated proteins MAP1B and MAP2 in fetal sheep.

Betamethasone has been used extensively to accelerate fetal lung maturation, yet little is known of its effects on neuronal morphogenesis in the developing fetus. Microtubule-associated proteins (MAPs) are a diverse family of cytoskeletal proteins that are important for brain development and the maintenance of neuroarchitecture. Vehicle (n = 7) or betamethasone (10 ug h-1, n = 7) was infused I.V. to fetal sheep over 48 h beginning at 0.87 of gestation (128 days of gestation), producing fetal plasma betamethasone concentrations resembling those to which the human fetus is exposed during antenatal glucocorticoid therapy. Paraffin sections of the left hemisphere were stained with monoclonal antibodies against MAP1B and the MAP2 isoforms MAP2a,b,c and MAP2a,b. The level of the juvenile isoform MAP2c was determined by comparison of the two MAP2 immunostainings. We were able to detect MAP1B and MAP2 immunoreactivity (IR) in the fetal sheep brain. MAP2c was the major MAP2, constituting 90.2 % of the total MAPBetamethasone exposure diminished MAP1B IR in the frontal cortex and caudate putamen (P < 0.05) but not in the hippocampus. A decrease of MAP2 IR was found in the frontal cortex, hippocampus and caudate putamen (P < 0.05). Loss of MAP2 IR was mainly due to the loss of MAP2c IR. Haematoxylin-eosin staining did not demonstrate irreversible neuronal damage. Regional cerebral blood flow determined using coloured microspheres was significantly decreased by 28 % in the frontal cortex and by 36 % in the caudate putamen but not in the hippocampus 24 h after the onset of betamethasone exposure (P < 0.05). The loss of MAP1B and MAP2a,b,c IR showed a significant correlation to the cerebral blood flow decrease only in the frontal cortex (P < 0.05). These data suggest that mechanisms other than metabolic insufficiency caused by the decreased cerebral blood flow may contribute to the loss of MAPs. The results suggest that clinical doses of betamethasone may have acute effects on cytoskeletal proteins in the fetal brain.

Antenatal betamethasone treatment reduces synaptophysin immunoreactivity in presynaptic terminals in the fetal sheep brain.

Knowledge of morphofunctional effects on the fetal brain induced by exogenous glucocorticoids is limited. Recently, we reported alterations of both the neuronal cytoskeleton and electrocortical function in the ovine fetal brain after antenatal betamethasone treatment in doses used in perinatal medicine. In the present study we examined whether these changes are accompanied by morphological alterations of synapses. Chronically instrumented fetal sheep at 0.87 of gestation were treated either with isotonic saline (n=7) or 10 microg/h betamethasone (n=7) over 48 h administered directly to the fetal jugular vein. Paraffin sections of the frontal neocortex, caudate putamen and hippocampus were stained with a monoclonal antibody against synaptophysin, a specific membrane protein of presynaptic vesicles and quantified morphometrically. Synaptophysin-like immunoreactivity (synaptophysin-LI) showed a widespread granular pattern in the neuropil. Betamethasone exposure reduced synaptophysin-LI in the frontal neocortex, caudate putamen and hippocampus by 46.9, 41.0 and 55.4%, respectively, (P<0.05) that was not accompanied by irreversible neuronal damage. These results suggest that clinical doses of betamethasone have acute effects on presynaptic terminals in the fetal sheep brain that could contribute to the altered complexity of electrocortical function that we have shown previously to occur following fetal exposure to betamethasone.

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.

Changing distribution patterns of synaptophysin-immunoreactive structures in the human dorsal striatum of the fetal brain.

Within the striatum two compartments, matrix and patches, can be distinguished by differences in the expression of neuroactive substances, afferent and efferent connections and time of neurogenesis. The present study was done to demonstrate the pattern of synaptophysin (SYN) expression which is indicative of synaptogenesis in the human fetal striatum (15th-32nd weeks of gestation) with special reference to developmental changes. From the 15th to the 22nd gestational weeks an intense diffuse SYN immunolabelling of striatal patches is observed. In the matrix SYN-immunoreactive fiber bundles are seen until the 20th week. Thereafter, the matrix is nearly devoid of SYN-immunoreactive structures. From the 28th week of gestation the matrix contains diffuse SYN immunoreactivity which gradually becomes as intense as that of the patches. The latter, thus, can no longer be delineated in the 30th week. The results show that fibrous SYN immunolabelling most probably indicating intra-axonal transport of synaptic vesicles can only be observed during the first half of gestation. Moreover, it becomes obvious that the patch compartment can selectively be visualized by anti-SYN until the 28th week. This pattern may correspond to the early dopaminergic innervation from the substantia nigra which is known to reach the developing patches. From the 28th week a transition from patchy to diffuse immunolabelling is seen. The increase in matrix labelling may be due to the occurrence of new neuronal contacts. The changeover from patchy to homogeneous SYN immunolabelling takes place distinctly earlier than changes in the distribution of other neuroactive substances described before.

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.

Species-specific patterns of glycoprotein expression in the developing rodent caudoputamen: association of 5'-nucleotidase activity with dopamine islands and striosomes in rat, but with extrastriosomal matrix in mouse.

The glycoprotein 5'-nucleotidase is a cell surface phosphatase and represents a new marker for striosomes in the adult rat caudoputamen. We report here on its developmental expression in the rat and mouse striatum, and show an unexpected converse 5'-nucleotidase chemoarchitecture of the caudoputamen in these closely related species. In the rat, 5'-nucleotidase activity was first visible as neuropil staining in tyrosine hydroxylase-positive dopamine islands of the midstriatum on postnatal day 1, and by the end of the first postnatal week, 5'-nucleotidase-positive dopamine islands also appeared rostrally. This compartmental pattern persisted thereafter, so that in adult animals, in all but the caudal caudoputamen, zones of enhanced 5'-nucleotidase staining were restricted to calbindin-D28k-poor striosomes. Weak 5'-nucleotidase activity also emerged in the matrix. In striking contrast, in the mouse striatum, enhanced 5'-nucleotidase activity was preferentially associated with extrastriosomal tissue. Enzymatic reaction first appeared on embryonic day 18, and developed over the first postnatal week into a mosaic pattern in which the matrix was stained but the dopamine islands were unstained. The matrix staining itself was heterogeneous. After the second postnatal week, most of the caudoputamen was stained, and in adult mice only rostral striosomes expressed low 5'-nucleotidase activity. We conclude that in rats, 5'-nucleotidase represents one of the few substances that maintains a preferential dopamine island/striosome distribution during striatal development. In mice, 5'-nucleotidase activity is expressed preferentially in the matrix during development, and its compartmental pattern is gradually lost with maturation, except very rostrally. These findings do not suggest an instructive role of the enzyme in striatal compartment formation in either species, but do suggest the possibility that 5'-nucleotidase contributes to the differentiation of striatal compartments during development.

Haloperidol effects on the developing dopamine system: conflicting results and implications for neurobehavioral teratology research.

In an attempt to further develop basic principles to guide research in neurobehavioral teratology, six experiments were conducted to examine the effects of prenatal haloperidol (a D2 dopamine antagonist) exposure on striatal D1 and D2 binding sites. Another laboratory has repeatedly reported that prenatal exposure to this dopamine antagonist reduces striatal dopamine binding sites in exposed offspring. Our initial studies were successful in replicating and extending these previously reported reductions in D2 dopamine binding sites in caudate of rats exposed prenatally to haloperidol. However, additional experiments in our laboratory, in which pups were exposed to a range of haloperidol doses over gestational periods when the dopamine system has been reported to be most vulnerable to prenatal haloperidol exposure effects, have repeatedly failed to replicate our initial findings. Three other laboratories have also failed to duplicate this effect. The results of these studies suggest that beyond "standard" confounding variables, neurobehavioral teratologists are faced with as yet poorly understood factors that influence replication of findings within and between laboratories. These findings also emphasize the importance of within- and between-laboratory replication of experimental findings.

Developmental regulation of phosphoprotein gene expression in the caudate-putamen of rat: an in situ hybridization study.

The regional and cellular ontogeny of the mRNA encoding the dopamine- and cAMP-regulated phosphoprotein, DARPP-32, has been studied in rat striatum by quantitative in situ hybridization histochemistry. The mRNA for DARPP-32 exhibited a characteristic developmental profile. The hybridization signal was first visible on the day of birth, at which time DARPP-32 mRNA was concentrated in patches in the caudate-putamen. By the end of the first postnatal week, the majority of neurons in the caudate-putamen expressed the DARPP-32 message. Levels of mRNA per cell increased markedly during the second postnatal week, and peaked around the beginning of the third week. The adult level of DARPP-32 mRNA was lower than that observed at the apex of mRNA expression, on a per cell basis, while the proportion of neurons expressing detectable levels of message remained relatively constant. In the nucleus accumbens and olfactory tubercle, DARPP-32 mRNA development lagged somewhat behind that observed in the caudate-putamen, but was similar in other respects. A non-quantitative study employing an oligonucleotide probe complementary to the mRNA encoding another cAMP-regulated phosphoprotein, ARPP-21, revealed a similar developmental sequence to DARPP-32. The present results suggest that for DARPP-32 mRNA, genetic and, possibly, environmental factors play a role in determining the developmental patterns observed.