Cortical cyto- and chemoarchitecture in three small Australian marsupial carnivores: Sminthopsis macroura, Antechinus stuartii and Phascogale calura.

The cyto- and chemoarchitecture of the cerebral cortex has been examined in three small (mouse-sized) polyprotodont marsupial carnivores from Australia (the stripe-faced dunnart, Sminthopsis macroura; the brown antechinus, Antechinus stuartii; and the red-tailed phascogale, Phascogale calura) in order to compare the cortical topography of these marsupials with that of diprotodontids, didelphids and eutherians. All three species studied had similar cortical cytoarchitecture. The isocortical surface was dominated by primary somatosensory (S1) and visual (V1) areas. Putative secondary sensory areas (S2, V2M, V2L) were also identified. The primary somatosensory cortex demonstrated clumps of granule cells in the presumptive mystacial field, whereas the primary visual area showed a distinctive chemical signature of intense calbindin immunoreactivity in layer IV. On the other hand, the primary auditory area was small and indistinct, but flanked by a temporal association area (TeA). A cytoarchitecturally distinct primary motor cortex (M1) with prominent pyramidal neurons in layer V and poor layer IV was identified medially to S1, and at rostral levels a putative secondary motor area was identified medial to M1. Transitional areas between isocortex and allocortical regions showed many cyto- and chemoarchitectural similarities to those reported for eutherian (and in particular rodent) cortex. Medially, two cingulate regions were found at rostral levels, with dysgranular and granular 'retrosplenial' areas identified caudally. Laterally, granular and agranular areas surrounded the rostral rhinal fissure, to be replaced by ectorhinal and perirhinal areas caudally. The findings indicate that the cyto- and chemoarchitectural features which characterize the iso- and allocortex in these small marsupial carnivores are similar to those reported in didelphids and eutherians and our findings suggest the existence of putative dedicated motor areas medial to the S1 field.

Organisation and maturation of the human thalamus as revealed by CD15.

The distribution of the CD15 antigen (CD15, 3-fucosyl-N-acetyl-lactosamine, Lewis x) has been studied immunohistochemically in the fetal human thalamus. Its changing patterns could be related to three successive, but overlapping, periods primarily due to its association with radial glial cells, neuropil, and neural cell bodies, respectively. From 9 weeks of gestation (wg), a subset of CD15-positive radial glial cells distinguished the neuroepithelium of the ventral thalamus, a characteristic also seen in the developing mouse. Distal processes of the radial glial cells converged at the root of the forebrain choroid tenia, which was also CD15 positive. From 13 wg until approximately 20 wg, CD15-positive neuropil labeling marked the differentiation areas of prospective nuclei within the dorsal thalamus and progressively outlined their territories in a time sequence, which appeared specific for each nucleus. CD15 labeling of differentiating nuclei of the ventral, medial, anterior, and intralaminar thalamic divisions showed a transient topographic relationship with restricted areas of the ventricular wall. After 26 wg, CD15 immunoreactivity was observed in subpopulations of glial cells and neurons. Transient CD15 immunoreactivity was also found in delimited compartments within the subventricular region. The time of CD15 expression, its location, and cellular association suggest that CD15 is involved in segmentation of diencephalon, in the specification of differentiating nuclear areas and initial processes regarding the formation of intercellular contacts and cellular maturation.

Bcl-x and Bcl-2 immunoreactivity in postnatal mouse barrel fields.

BcL-xL and Bcl-2 proteins were identified by paraffin section immunohistochemistry in the neuropil core of the barrelettes of the caudalis spinal trigeminal nucleus 6 h after birth. They were subsequently identified at progressively more rostral levels of the trigeminal pathway, peaking in barreloid neuropil cores in the ventral posterior thalamic nucleus at postnatal day (P)4.5, and in cortical barrel cores at P7. Labelling was confined to the cores of barrel-like structures surrounded by immunonegative shells and became progressively less distinct at all levels from P8. These protein products, which are usually considered to control the onset of apoptosis, may serve other functions in the axon terminal fields of the trigeminal pathway.

Differential distribution of immunohistochemical markers in the bed nucleus of the stria terminalis in the human brain.

A variety of histochemical findings have contributed to a more differentiated architectonical description of the bed nucleus of the stria terminalis (BNST) in the mammalian brain. However, in the human brain investigations of the chemoarchitecture of this nucleus have been rare. Therefore we chose this region in six human autopsy brains in order to map the distribution patterns of 13 immunohistochemical markers for neurotensin (NT), neuropeptide Y (NPY), somatostatin (SOM), enkephalins (ENK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurophysins (NPH), glial fibrillary acid protein, 3-fucosyl-N-acetyl-lactosamine epitope, myelin basic protein (MBP), calbindin (CAB), synaptophysin (SYN) and chromogranin-A (CHR-A). Three chemoarchitectonically distinct areas could be defined. The lateral subdivision of the BNST contained high amounts of NPY and SP-fibre immunoreactivity and was further characterized by the occurrence of neurons labelled for NPY. The central subdivision of the BNST appeared as a histochemically clearly circumscribed compartment with massive fibre immunoreactivity for SOM, ENK, VIP, SYN, CHR-A, CAB as well as SOM, ENK, NT and CAB positive cells but lacked cytosolic or fibre-like immunolabel for NPY and SP. This structure was also ensheathed by myelinated fibres identified by means of MBP immunohistochemistry. The medial subdivision of the BNST showed moderate to high SP and NPY fibre immunoreactivity but lacked immunolabelled neurons and was only scarcely supplied with varicose or punctiform ENK immunoproduct. In the most posterior levels of our sections a cell group labelled for NPH was located lateral to the fornix columns. The lateral subdivision of the BNST (with NPY, SYN) and mainly the central BNST (with SOM, ENK, VIP, SYN and CHR-A) contributed to ventrolateral extensions of dense patchy fibre immunoreactivity throughout the basal forebrain region.

Pattern of brain glucose utilization following magnetic stimulation.

The 2-deoxy-D-(14C) glucose technique was used for autoradiographic mapping of the local cerebral glucose utilization in pigeons which were exposed to a periodically inverted artificial magnetic field in the Earth's field range. Stimulation during daytime resulted in increased values particularly in primary or secondary visual structures. Stimulation during nighttime resulted in increased values in the optic tectum and within the nucleus isthmi. In both situations decreased values were determined in the hypothalamus and increased values in the pineal gland. The results support the concept that magnetic information is transduced by magnetoreceptors and is relayed to structures of the visual system. Moreover, it is suggested, that magnetic stimulation exerts suppressive metabolic effects on the basal hypothalamus.

Contribution to the amygdaloid projection field in the rat. A quantitative autoradiographic study.

Light microscopic autoradiography and quantitative photometric studies of autoradiographs were performed subsequent to injection of tritiated amino acids into various parts of the amygdala of the rat. The course of amygdalofugal fibers in the stria terminalis (bilaterally), longitudinal association bundle, medial amygdalo-hypothalamic pathway, and medial forebrain bundle is described. Evidence is provided for both additional transcapsular and paracapsular fibers and early descending stria terminalis fibers. Labeling of the ipsilateral main olfactory bulb and the bilateral acessory olfactory bulb was observed following injection into the cortical amygdaloid subnucleus. The termination of amygdalofugal fibers in the preoptic area and especially the subnucleu of the ventromedial and premamillary hypothalamic nuclei bilaterally were analysed by photometric measurement. A caudal amygdaloid projection system arises from the central amygdaloid nucleus. This system extends to the substantia nigra, lateral terminal nucleus of the accessory optic tract, central grey in the midbrain, and to the parabrachial nuclei, nucleus of the mesencephalic trigeminal tract, nucleus of the solitary tract in the hindbrain.

Distribution of retinal axons within the lateral hypothalamic area.

Intraocular injections of tritiated leucine were performed in normal and in unilaterally enucleated adult albino rats. Light microscopical evaluation of the autoradiograms revealed evidence for retinal afferents to distribute within a rather circumscribed area of the lateral hypothalamus. The silver grains were consistently, however, observed only in the group of enucleated animals, indicating differential transport under basic and experimental conditions.

Evidence for amygdaloid projections to the contralateral hypothalamus and the ipsilateral midbrain in the rat.

Light microscopic autoradiography was performed subsequent to injection of tritiated amino acids into various parts of the amygdaloid body of the rat. Evidence is provided for two hitherto unreported projections of the amygdala: from the medial amygdaloid nucleus to the contralateral premamillary nuclei and from the central amygdaloid nucleus to the mesencephalic central grey. The functional implications of these findings are discussed.

The accessory optic system and the retino-hypothalamic system. A review.

The introduction of new techniques in neuroanatomy has helped to clarify a number of important issues on the nature of the accessory optic and retino-hypothalamic system. In this study, an effort was made, to collect all data obtainable, and to arrange them on the basis of some common parameter, so that the various results may be directly compared. These data were then interpreted on specific issues, although only limited coverage has been given to functional aspects, as described in older publications. The absence of a universally accepted concept of the function of both systems to date suggests the need for a thorough analysis of both contemporary and older literature dealing with a characterization of the structural components of the accessory optic and the retino-hypothalamic systems. On the basis of these anatomical studies it is concluded that the accessory optic system (AOS) is much more complex than formerly believed. Its development in various vertebrae classes is quite different. Among the mammals, the AOS is very well established in rodents but in primates and man its anatomical and functional role seems markedly reduced. In the rodents it consists of both superficially and deeply arranged axons which are in close topical relation to the cerebral peduncles. The axons not only supply the classic accessory otpic terminal nuclei but also the subthalamic nucleus and the substantia nigra. The secondary projections have not yet been established. The retino-hypothalamic system (RHS) mainly but not exclusively supplies the suprachismatic nucleus (sc). Crossed as well as uncrossed retinal fibres project to the ventro-lateral and to the posterior part of this nucleus. The cells within the sc combine both secretory and neuronal properties. The possible functions exerted are discussed. Both, the AOS and the RHS, are so closely related within the suprachiasmatic area that most methods fail in correlating experimental results with either system. The numerous problems which still remain to be clarified are also discussed.

Quantitative autoradiographic light- and electron microscopic studies on the retinohypothalamic connections in the rat.

Light microscopic autoradiography performed subsequent to intraocular injection of 3H-leucine revealed silver grains (SG) above axons of the optic tract which could be followed into the ventral and caudal portion of the suprachiasmatic nuclei (SCN) and above the contralateral anterior hypothalamic nucleus (AHN). By high resolution photometric measurement and computer processing the labelled areas were analysed, thus yielding statistical data of the relative grain distribution. The highest SG density was found in the ventrolateral part of both SCN (SCvl), confirming earlier reports concerning retinohypothalamic connections. That area exhibiting a cytoarchitecture different from the remaining nucleus was traversed, however, by numerous labelled axons. In the caudal part of both SCN a specific projection field of retinal fibres could be located. Here, almost no traversing fibres contribute to the rather circumscribed marked area. In the ventral part of the contralateral AHN, diffuse labelling well above background levels could be observed. Distinction between bypassing and terminating fibres within the SCvl could not be made using light microscopy. Analysis of SG distribution of the SCvl with electron microscopic autoradiography revealed a specific localization of SG within presynaptic terminals containing clear vesicles and pale mitochondria.