Metabolic rates associated with distress and begging calls in birds.

Rates of oxygen consumption during begging behaviour in nestlings of seven species and distress call behaviour in adults of eight species of Australian birds were measured. A transparent mask coupled to an open-flow respirometry system was used, and calling was elicited by the presentation of food or by the perceived threat of a predator. Distress calling significantly increased oxygen consumption above the measured resting levels in six of the species of birds tested. The factorial increase in oxygen consumption during distress calling was independent of body mass. In most cases, begging behaviour in juvenile birds caused a significant increase in metabolic rate, with some individuals showing factorial increases over fourfold. There was a significant negative correlation between body mass and the factorial cost of begging behaviour.

Neurogenesis in septum, amygdala and hippocampus in the marsupial brushtailed possum (Trichosurus vulpecula).

The times of origin of neurons in the septum, amygdala and hippocampus of the marsupial brushtailed possum, Trichosurus vulpecula, were determined with 3H thymidine autoradiography. The long time period for neurogenesis in the brushtailed possum facilitated analysis of neurogenetic gradients in the brain. A series of 20 possums were injected with 3H thymidine from postnatal (P) days 5-95 and were allowed to survive until brain cytoarchitecture was mature. Our results indicate that septal neurogenesis was complete by P21 (38 days after conception) with a medial to lateral gradient of neurogenesis evident in the lateral septal division. Neurogenesis in the amygdala was complete in the basal, central and medial amygdaloid nuclei by P21, and in the lateral amygdaloid nucleus by P46, with a medial to lateral gradient of neurogenesis evident in basal, central and lateral amygdaloid nuclei. In the hippocampus, neurogenesis of pyramidal cells was complete in field CA3 by P50, and in field CA1 by P55. Early forming pyramidal cells (P5-12) were distributed adjacent to the stratum oriens in fields CA1 and CA3, with later forming pyramidal cells distributing in the middle of the stratum pyramidale (P21-32) and on the edge adjacent to the stratum radiatum (P46). Neurogenesis of dentate granule cells extended over a long period of time, from P5, at least until P82, with the earliest forming granule cells (P5-12) distributed adjacent to the stratum moleculare, and the latest forming granule cells (P82) adjacent to the hilus.

The correlation of elevated levels of an index of lipid peroxidation (MDA-TBA) with adverse outcome in the very low birthweight infant.

The objective of this study was to examine the relationship between malondialdehyde-thiobarbituric acid (MDA-TBA) levels, as a measure of lipid peroxidation, in very low birthweight (VLBW) infants and outcome measures. A prospective observational longitudinal study was carried out in two level III neonatal units in the South Island of New Zealand measuring MDA-TBA levels in 61 VLBW infants in 1993. MDA-TBA levels were measured in (i) maternal plasma within 48 h of parturition, (ii) cord plasma, and (iii) infants' plasma at 2, 7, 14 and 28 days of age and correlated with antenatal and postnatal factors. Elevated levels of plasma MDA-TBA at 7 days were associated with adverse respiratory and ophthalmological outcome in the VLBW infants. Elevated MDA-TBA levels were measured at sample times close to the time of death in the infants who died. These results substantiate previously reported preliminary observations and support the hypothesis that oxidative injury, particularly within the first 7 days of life, is associated with the development of the long-term complications of the pre-term infant. MDA-TBA levels appear to be a useful measure to continue to explore the role of free radical mediated disease in the VLBW infant.

Lipid peroxidation of circulating low density lipoproteins with age, smoking and in peripheral vascular disease.

In this study, lipid peroxides in plasma and the low density lipoprotein (LDL) fraction and plasma concentrations of vitamin E, lipids and lipoproteins were measured in 22 smokers (mean age 35 years), 26 non-smoking patients with peripheral vascular disease (PVD), mean age 66 years), and 23 younger (ages < or = 55 years) and 26 older (ages > 55 years) healthy subjects. Plasma lipid peroxide concentrations in the PVD patients (105.9 +/- 20.6 vs. 91.8 +/- 15.8 ng malondialdehyde (MDA)/ml plasma, mean +/- S.D.) and the smokers (94.1 +/- vs. 74.0 +/- 13.9 ng MDA/ml plasma) were significantly elevated compared with levels in the appropriate control subjects and levels were significantly higher in older compared with younger control subjects. Plasma LDL lipid peroxides were also significantly raised in patients with PVD and smokers compared with control values (PVD): 37.1 +/- 7.7 vs. 26.3 +/- 4.1 ng MDA/ml plasma; smokers: 30.4 +/- 6.9 vs 24.9 +/- 7.5 ng MDA/ml plasma). The ratio of LDL lipid peroxides: LDL-cholesterol was significantly higher in the smokers, and plasma cholesterol and LDL-cholesterol were significantly higher in patients with PVD compared with other groups of subjects. The ratio of vitamin E: total lipid was not significantly different between the study groups. These data show that lipid peroxide levels in the plasma LDL fraction are elevated along with raised circulating levels in patients with PVD and smokers but that LDL lipid peroxide concentrations were independent of age in the healthy subjects. Elevated LDL lipid peroxide concentrations may may be mainly due to abnormally high LDL levels in PVD patients, whereas in smokers, the concentration of lipid peroxides in the LDL particles is raised and might render the lipoprotein more atherogenic.

Biphasic retinal neurogenesis in the brush-tailed possum, Trichosurus vulpecula: further evidence for the mechanisms involved in formation of ganglion cell density gradients.

We investigated cell generation in the retina of the brush-tailed possum (Trichosurus vulpecula) by using tritiated (3H)-thymidine labelling of newly generated cells. Animals aged between postnatal day (P) 5 and 85 each received a single injection of 3H-thymidine. Following autoradiographic processing, maps of labelled cells were constructed from retinal sections. Retinal cell generation takes place in two phases, the first is concluding in the retinal periphery at P53 as the second is seen to commence in midtemporal retina. In the first phase, cells in central retina are generated earlier than those in peripheral regions. In the second phase, cells complete their final division in midtemporal retina first and in the periphery last. Cells generated in the first phase comprise virtually all cells in the ganglion cell layer, amacrine cells, horizontal cells, and cones. Ganglion cells are produced at a slightly earlier stage than displaced amacrine cells, horizontal cells, or cones. Amacrine cells in the inner nuclear layer are the final cells produced in the first phase. When ganglion cells and amacrine cells are pooled, their combined rate of production matches that of the other cell types. These data indicate that the ratio of displaced amacrine cells: horizontal cells: cones: combined ganglion cells and amacrine cells does not change throughout development. However, the ratio of ganglion cells:macrines changes steadily as development proceeds to favour amacrine cells. In the second phase, sparse numbers of nonganglion cells in the ganglion cell layer and large numbers of bipolar and Müller cells are produced along with all rods. The two phases in the possum are similar to those seen in the wallaby, the quokka. However, fewer cells are added in central retina in the possum than in the quokka and cell addition continues for a more extended period in the periphery in the possum. We suggest that this difference in cell addition could account for the development of a more pronounced visual streak of retinal ganglion cells in the possum than in the quokka. A comparison of possum retinal cell generation with that of other marsupials adds support for the "homochrony theory."

Prosencephalic connections of striate and extrastriate areas of rat visual cortex.

Afferent connections of rat primary visual cortex (area 17 or V1 area) and the rostral and caudal parts of areas 18a and 18b were studied, by placing in each of the areas, small electrophoretic injections of enzyme horseradish peroxidase (HRP) or wheat germ agglutinated-HRP. The results indicate that: 1) each of the areas has a distinct pattern of distribution of afferent neurons in the ipsilateral visual thalamus - area 17 receives its principal thalamic input from the dorsal lateral geniculate nucleus, the caudal parts of areas 18a and 18b receive a major thalamic input from the lateral posterior nucleus and a minor input from the posterior nucleus, while the rostral parts of areas 18a and 18b receive a major input from the posterior nucleus, and a minor projection from the lateral posterior nucleus; 2) the rostral and caudal parts of areas 18a and 18b each receive an associational input from area 17; 3) the rostral parts of areas 18a and 18b each receive associational input from three different extrastriate regions, the caudal part of the same extrastriate area, and the rostral and caudal parts of the other extrastriate area, whereas the caudal parts of areas 18a and 18b receive associational inputs only from one or two extrastriate regions; 4) area 17, area 18b and rostral area 18a each receive a substantial associational input from lamina V of the caudal part of the frontal eye field (FEF) in the motor cortex; however the input from the FEF to caudal area 18a (if present) is very small; 5) The extrastriate areas studied receive associational input from the restrosplenial cingulate area 29d; however, the input from area 29d to area 17 appears to be very small. The distinct patterns of distribution of prosencephalic afferents suggest to us that multiple retinotopically organized areas described previously in the rat cortex (cf Montero 1981; Espinoza and Thomas 1983) represent functionally distinct areas.

Gradients of neurogenesis in possum neocortex.

Gradients of neurogenesis in neocortex of the brushtailed possum were determined with [3H]thymidine autoradiography, using data taken from 16 possums injected with [3H]thymidine between postnatal (P) days 5-68, and allowed to survive until brain cytoarchitecture was mature. Gradients of neurogenesis shown in neocortex were: (a) an inside-out radial gradient within cortical areas with neurogenesis beginning around P5 in layer 6 and concluding between 1 and 2 months later in layer 2, and (b) a single, simple, regional gradient across all neocortex. On the lateral surface of the hemisphere neurogenesis runs anteroventrolateral to posterodorsomedial, and on the medial surface neurogenesis runs anteroventral to posterodorsal. When plotted for the whole neocortex, the two regional gradients from the lateral and medial surfaces of the hemisphere are seen as parts of the one simple pattern. The time duration of neurogenesis in possum cortex is 1-2 months, and is similar to that seen in monkeys.

Neurogenesis in a marsupial: the brush-tailed possum (Trichosurus vulpecula). I. Visual and auditory pathways.

The times of origin of neurons in the visual and auditory systems were studied in a marsupial, the brush-tailed possum, using tritiated thymidine autoradiography. Within the subcortical visual pathways, most neurons are generated between postnatal days 5 and 21, and the neurons of the primary visual cortex up to postnatal day 68. In the subcortical auditory pathways, most neurons are generated between postnatal days 5 and 28, and all auditory cortex neurons have appeared by postnatal day 46. Neurons in a single layer of cerebral cortex are generated during a period of about 2 weeks. Thus cortical neurogenesis in marsupials extends over a period similar to that seen in primates.

Neurogenesis in a marsupial: the brush-tailed possum (Trichosurus vulpecula). II. Sensorimotor pathways.

The times of origin of neurons in sensorimotor pathways of the marsupial brush-tailed possum were determined with 3H-thymidine autoradiography. A series of 20 possums were injected with 3H-thymidine from postnatal days 5-95 and were normally allowed to survive until the brain cytoarchitecture was mature. Brain stem and spinal sensorimotor regions were not labelled in our study and presumably form before birth in order to enable the newborn young to make the journey from the birth canal to the pouch on its own. Neurogenesis in thalamic sensorimotor nuclei probably begins about the time of birth and continues into the 2nd week of postnatal life. Formation of neurons in the sensorimotor cortex and the basal ganglia occurs during the first 2 months of postnatal life and in the cerebellum during the first 3 months. This protracted postnatal development of telencephalic and cerebellar sensorimotor regions offers great advantages for developmental studies.

Retinal projections in two Australian polyprotodont marsupials: kowari, Dasyuroides byrnei, and fat-tailed dunnart, Sminthopsis crassicaudata (Dasyuridae).

Retinal projections were examined in two small dasyurids, the kowari and the fat-tailed dunnart, following injections of 3H-proline into one eye. In both animals retinal fibres terminate in the dorsal and ventral lateral geniculate nuclei (LGd, LGv), the lateral posterior nuclear complex, the pretectum, the superior colliculus, the suprachiasmatic nucleus of the hypothalamus and the nuclei of the accessory optic system. The lateroposterior thalamic complex and the accessory optic nuclei receive projections from the contralateral eye only; the remaining centres receive bilateral inputs. Both LGd contain an undifferentiated beta or medial segment and an alpha or lateral segment that comprises further cellular sublaminae, 4 in the kowari and 3 in the dunnart. There is substantial overlap of crossed and uncrossed terminals in both segments, though in each animal a narrow cell lamina next to the optic tract receives only crossed projections and the lateral part of the beta segment receives only uncrossed projections. There is a cell-sparse zone within the alpha segment that receives a predominately uncrossed projection in the kowari and a crossed projection in the dunnart. In both marsupials the density of crossed and uncrossed terminals is equal, a feature of dasyurid quolls but not of another dasyurid, the Tasmanian devil. Additionally, retinal terminals do not form dense clusters within the LGd neuropil. This feature is characteristic of quolls, but not of other mammals, marsupial or placental, all of which display LGd terminal clusters. These findings suggest that the functional organisation of the LGd in these dasyurids may differ from that found in other marsupials.

Cortico-cortical connections of the motor cortex in the brushtailed possum (Trichosurus vulpecula).

Cortico-cortical connections of motor cortex in the marsupial brushtailed possum were traced by making injections of horseradish peroxidase (HRP) into two parts of motor cortex: the rostral agranular part which does not overlap somatosensory cortex, and the caudal part which does. Following injections in motor cortex, labelled neurons were observed on the same side of the brain within somatosensory areas 1 and 2 and in parietal cortex just caudal to S1, with most neurons in cortical Layers 2-4. Commissural connections were found in half of the experiments, with many labelled neurons in cortical Layer 5. We have compared the pattern of cortico-cortical connections in the possum with those seen in some other mammals, which appear generally similar.

Retinogeniculate patterns in diprotodont marsupials.

The pattern of retinogeniculate connections has been examined in a range of diprotodont marsupials, including wallabies, possums, forest wombat and koala. The lateral geniculate nucleus (LGd) in most species has alternating bands of ipsilateral and contralateral retinal terminal fields, with considerable interspecific variability. The number of terminal bands of retinogeniculate input varies from eight to eleven in most species, with little binocular overlap. By contrast in one species, the feather-tailed glider, the most significant feature of LGd organisation is binocular overlap. No relationship is apparent between LGd organisation and the life-style of the animals.

The dorsal lateral geniculate nucleus of macropodid marsupials: cytoarchitecture and retinal projections.

The anatomy of the dorsal lateral geniculate nucleus (LGd) is described in five macropodid species, including two rat kangaroos (bettong and potoroo), two wallabies (pademelon and tammar), and the large grey kangaroo. The distribution of retinal terminals in the LGd was examined following intraocular injections of tritiated amino acids. There are considerable differences in both LGd cytoarchitecture and the patterns of retinal terminations among the five species. Cytoarchitecture in the bettong LGd is relatively simple, displaying a minimal regional differentiation. In contrast, the potoroo LGd is quite complex and displays several well-defined cell laminae, each of which is associated with input from a single eye. Both rat kangaroos display the same basic pattern of retinal termination with three bands of terminals from the contralateral eye and four from the ipsilateral eye. The bands are less sharply defined in the bettong, in which terminals from each eye overlap to a greater extent than is seen in the potoroo. The wallabies and kangaroos display a more complex LGd architecture and patterning of retinal terminal bands. Bilateral retinal projections within the same LGd lamina are unusual in these large macropodids. The number of terminal bands reaches ten in the grey kangaroo--four from the contralateral eye and six from the ipsilateral eye. The pademelon LGd is unusual in that it shows intraspecies variation with some animals displaying five ipsilateral terminal bands and others only four. The results are discussed in comparison with the patterns of LGd organisation observed in other mammalian lines, placental and marsupial. We conclude that LGd lamination and the segregation of retinal inputs to the LGd in marsupials are likely to be the result of evolutionary factors which differ from those which have produced ocular segregation and complex lamination in several lines of placental mammals.

Reevaluation of motor cortex and of sensorimotor overlap in cerebral cortex of albino rats.

The organization of motor cortex and the sensorimotor overlap zone was examined by in-depth electrical stimulation using micromapping procedures in rats. The cutaneous somatic sensory, as well as the efferent motor projections to the hindlimb and forelimb sensorimotor overlap zone were studied in the same animals. Low-threshold movements were elicited from portions of 3 architectonic areas: the lateral agranular, dysgranular and granular areas. Cutaneous light touch projections occur only within the granular area. Cutaneous projections to, and motor projections from individual punctures in the granular overlap zone did not always involve homologous body parts. The total motor cortex exhibits a general musculotopic pattern of organization.

Patterns of afferent projections to transitional zones in the somatic sensorimotor cerebral cortex of albino rats.

The organization of somatosensory projections to the dysgranular areas of somatic sensory cortex was mapped in albino rats. Receptive fields that activate layer IV granule cells in these dysgranular zones were: cutaneous and deep (including muscle), roughly somatotopic, larger, and required stronger stimulation (tap) than the cutaneous light touch RFs of the adjacent granule cell zones.

Primary visual cortex in the brushtailed possum: receptive field properties and corticocortical connections.

The corticocortical connections and receptive field properties of primary or striate visual cortex of the brushtailed possum, Trichosurus vulpecula, have been examined. In this Australian marsupial species primary visual cortex has connections with four other visual areas in the occipital lobe. In these adjacent visual areas fibers from striate cortex terminate mainly in layers 3 and 4 and in some cases also in layers 1 and 2. In all four areas return connections to striate cortex originate predominantly in layers 2 and 3, and to a much lesser extent in layers 5 and 6. Interhemispheric connections of striate cortex are limited to the boundary of striate and peristriate cortex. In addition to its cortical connections, striate cortex makes reciprocal connections with the claustrum. Most neurons in striate cortex are highly binocular. Of our sample of 113 visually responsive neurons, only 30% were orientation selective. On the basis of these observations we have compared striate cortex of the marsupial brushtailed possum with striate cortices of the American marsupial opossum and those of placental mammals.

Postnatal development of retinal projections in the brushtailed possum, Trichosurus vulpecula.

The postnatal development of retinal projections was studied in the brushtailed possum, Trichosurus vulpecula. [3H]proline was injected into one eye of 13 young possums aged 24-84 days in order to trace retinal pathways. The dorsal lateral geniculate nucleus (LGNd) can be identified in Nissl material at 19 days but not at 9-10 days. By 40 days some cytoarchitectural lamination of the LGNd is apparent and by 71 days the adult pattern of cell layers is present. At 24 days retinal fibers occupy by lateral part of the LGNd on both sides of the brain. By 38-40 days the retinal fibers fill be contralateral LGNd and the binocular part of the ipsilateral LGNd and there is a beginning of the segregation of retinal fibers into left and right eye territories. By 49-50 days a partial segregation is achieved, and complete segregation by 71 days. At 9-10 days the superior colliculus is not differentiated into layers and there is a thick zone of cell proliferation around the ventricle. By 23 days the superior colliculus has well-defined cell layers and there is still some indication of cell proliferation around the ventricle. By 40 days, the superior colliculus shows little evidence of cell proliferation. At 24 days retinal fibers fill the superficial layers of the contralateral optic tectum and are lightly distributed through the superficial layers of the rostral half of the ipsilateral tectum. By 38 days the ipsilateral retinal input is restricted to the deeper layers of the tectum. These results show that the adult pattern of retinal projections to the LGNd and optic tectum develops a number of weeks before eye opening occurs (at 90-120 days).

Relationships of the visual cortex in the marsupial brush-tailed possum, Trichosurus vulpecula, a horseradish peroxidase and autoradiographic study.

The ascending and descending relationships of visual cortex in Trichosurus were determined using HRP and autoradiographic methods. The visual thalamus, LGNd and LP, was found to project to three cytoarchitecturally distinct areas of cortex with each of these regions displaying differing patterns of connectivity with other centres. The striate and peristriate cortices received homotypically organized projections from LGNd as well as projections from both divisions of LP. The posterior parietal cortex received projections from both LGNd and LP as well as from the latero-intermediate, posterior, ventroanterior and intralaminar thalamic nuclei. The cortical projection fields of LGNd and LP were co-extensive. Descending projections to thalamic centres were reciprocal with the exception of a descending only projection to the thalamic reticular nucleus. The striatogeniculate projection was homotypically organized as was the striatocollicular projection which extended only to the superficial layers of that nucleus. The posterior parietal projection to the superior colliculus involved the deeper layers of that nucleus. The entire visual cortex projected to the pretectum and to the pontine nuclei. The organization of visual cortex in Trichosurus differs from that reported in the American marsupial, Didelphis, in that the LGNd and LP complexes possess a very broad and co-extensive cortical projection, a finding substantially different to what has been reported in placental mammals as well. The organization of thalamic relationships with the posterior parietal cortex would also appear to be unusual with this region receiving convergent projections from at least seven separate thalamic nuclei.