Subependymal Layer Research Articles

Effects of withdrawal from chronic exposure to cigarette smoke on hypothalamic and preoptic catecholamine nerve terminal systems and on the secretion of pituitary hormones in the male rat.

A 48 h but not a 72 h or 7 day withdrawal from chronic exposure to cigarette smoke was associated with increased noradrenaline levels (quantitative histofluorimetry) in the subependymal layer (SEL) of the median eminence, the anterior periventricular hypothalamic region (PV I) and the parvocellular part of the hypothalamic nucleus (PA FP) and an increased noradrenaline utilization (tyrosine hydroxylase inhibition by alpha MT) in the SEL and the PV I. Following a 48 h or 72 h but not a 7 day withdrawal from chronic exposure to cigarette smoke an increased catecholamine utilization was found in the medial palisade zone (MPZ) of the median eminence. Reduced serum prolactin, FSH and corticosterone levels were found following a 48 h withdrawal from chronic exposure to cigarette smoke. Following a 72 h withdrawal from chronic exposure to cigarette smoke a reduced concentration of serum prolactin was noted. Chronic exposure to cigarette smoke reduced serum TSH levels and lead to a tolerance development with regard to noradrenaline levels and utilization within the preoptic region with the exception of the periventricular preoptic region. The finding of special interest in the present study is the demonstration of a highly significant lowering of corticosterone serum levels despite maintained blood levels of ACTH as seen 48 h following withdrawal. It is suggested that this type of endocrine change may lead to changes in fear-motivated behaviour and contribute to behavioural withdrawal reactions. The maintained reductions of serum prolactin levels found after 48 h and 72 h of withdrawal from cigarette smoke exposure (cf. Andersson et al. 1985a) is discussed in terms of an increased catecholamine utilization in the medial palisade zone of the median eminance. This activation is suggested to be caused by the development of a prolactin receptor supersensitivity within the medium eminence. The present evidence indicates withdrawal effects mainly in the noradrenaline nerve terminals of the subependymal layer of the median eminence, the anterior periventricular hypothalamic region and the parvocellular part of the paraventricular hypothalamic nucleus which inter alia are involved in regulation of ACTH secretion (cf. Andersson et al. 1985a).

Immunohistochemistry of human malignant astrocytoma cells xenografted to rat brain: apolipoprotein E.

Fresh xenografted human malignant astrocytoma cells migrate throughout the host rat brain. Cells from three Grade 3 human malignant astrocytomas were prelabeled with Phaseolus vulgaris leucoagglutinin (PHAL) and then xenografted into implantation pockets in rat host cerebral cortex. The human malignant astrocytoma cells in the host brain were immunocytochemically double-labeled for the presence of PHAL, which is used as a marker for graft derived cells, and either glial fibrillary acidic protein (GFAP), a specific marker for astrocytes and astrocytoma cells, or apolipoprotein E (APOE) 7 days, 14 days, 21 days, and 1 month later. Fresh human malignant astrocytoma cells (Grade 3 and 4) contained APOE and GFAP. The xenografted cells preserved APOE and GFAP in the host. PHAL double-labeled human malignant astrocytoma cells were found on the glia limitans along the entire circumference of the brain, in the corpus callosum, internal capsule, entopeduncular nucleus, optic tract, and median eminence. In addition, astrocytoma cells were observed in the cingulum, habenula, arcuate, and supraoptic nucleus. Astrocytoma cells entered the space of Virchow-Robin, migrated along parenchymal blood vessels and between the ependymal and subependymal layers of the third and lateral ventricles. APOE was a consistent marker for the migrating human malignant astrocytoma cells, but not an exclusive marker of the xenografted cells, since host rat reactive astrocytes also expressed APOE.

Distribution and possible metabolic role of class III alcohol dehydrogenase in the human brain

In human brain, the sole alcohol dehydrogenase (ADH) present in significant quantity has been shown to be Class III (χ) ADH and this ADH is ineffective in generating potentially toxic and reactive acetaldehyde from ethanol at concentrations attainable in living brain tissue. We have extended this finding to show that Class I ADH potentially present is undetectable even when concentrated several hundred-fold. Purified Class III ADH from human brain is identical in its pattern of tryptic peptides and in other properties to Class III ADH from human liver. Immunohistochemical staining and western immunoblots using polyclonal antibodies reveal that Class III ADH is widely distributed in brain and most concentrated in the subependymal layer and perivascular areas. Class III ADH closely resembles ω-hydroxyfatty acid dehydrogenase and a possible role for the brain enzyme is in the oxidization of long chain fatty alcohols and ω-hydroxyfatty acids.

Human malignant astrocytoma xenografts migrate in rat brain: a model for central nervous system cancer research.

Fresh cells from two grade 3 human malignant astrocytomas were prelabeled with Phaseolus vulgaris leucoagglutin (PHAL) and then xenografted into freshly made implantation pockets in rat host cerebral cortex. Animals were sacrificed at 7, 14, 21 days, and 1 month postimplantation (DPI). Paraffin sections were double-labeled for the presence of glial fibrillary acidic protein (GFAP), a specific marker for astrocytes and differentiated astrocytoma cells, and PHAL, utilized as a marker for graft-derived cells. Grafted human astrocytoma cells were found on the glia limitans along the entire circumference of the brain, in the corpus callosum, internal capsule, entopeduncular nucleus, optic tract, and median eminence. In addition, astrocytoma cells were observed in the cingulum, habenula, arcuate, and supraoptic nucleus. Astrocytoma cells entered the spaces of Virchow-Robin, and migrated along parenchymal blood vessels and between the ependymal and subependymal layers of the third and lateral ventricles. The corpus callosum was a major migration route for the astrocytoma cells. The presence of basal lamina or parallel nerve fiber bundles was a common factor for these migration routes. The migration of the human astrocytoma xenografted cells in the rat brain followed the spread of human malignant astrocytomas in the human brain and is a valuable basic science tool in brain cancer research.

Distribution of epithelial membrane antigen in normal and neoplastic human ependyma.

The ependyma and choroid plexus of 23 normal brains and 20 ependymal tumors were examined immunohistochemically for expression of epithelial membrane antigen (EMA) using a specific monoclonal antibody. The ependyma of normal brains showed three patterns of immunoreactivity: membrane immunoreactivity confined to the luminal surface; irregular punctate intracytoplasmic immunoreactivity in the subependymal layer; and spherical and ring-like intracytoplasmic immunoreactivity in the subependymal layer. Of 13 differentiated ependymomas 11 reflected the immunoreactive patterns of normal ependyma. The anaplastic ependymomas and ependymoblastomas had no immunoreactivity. Our results indicate that EMA has a highly selective distribution in the ependyma, and is a marker for differentiated ependymoma.

Distribution of the pro-opiomelanocortin-derived peptides, alpha-melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH), and beta-endorphin in the brain of the dogfishScyliorhinus canicula: An immunocytochemical study

The occurrence and distribution of the pro-opiomelanocortin (POMC)-derived peptides alpha-MSH, ACTH, and beta-endorphin in the brain of the dogfish Scyliorhinus canicula were investigated by immunocytochemistry using the indirect immunofluorescence and the peroxidase-antiperoxidase procedures. Immunoreactive perikarya were found in distinct regions of the hypothalamus. Alpha-MSH-like containing neurons were confined mainly in the dorso-caudal area of the hypothalamus within the nucleus tuberculi posterioris and the nucleus sacci vasculosi. A small number of immunoreactive cells were localized in the nucleus periventricularis. The hypothalamic dorso-caudal region contained a rich network of fine immunopositive fibers extending in the whole tuberculum posterioris toward the saccus vasculosi. Very few fibers were found coursing ventrally toward the nucleus periventricularis and within the thalamus and the basal mesencephalon. In the pituitary gland, only the melanotropic cells of the neurointermediate lobe were stained by the alpha-MSH antiserum. ACTH-like-containing neurons and fibers were identified in the nucleus lateralis tuberis. Many of these cells appeared to be of the liquor-contacting type. Some immunoreactive cells were also found within the subependymal layers of the nucleus lobi lateralis. At the pituitary level, ACTH-positive cells were located in the rostral lobe of the pars distalis. Beta-endorphin-like immunoreactive cells were seen mainly within the preoptic nucleus, bordering the ventral side of the anterior preoptic recess, and in the nucleus lateralis tuberis. Most of these immunoreactive cells were of the liquor-contacting type. Beta-endorphin immunoreactive fibers were found coursing through the lateral post-chiasmatic region and the hypothalamic floor. Scattered fibers were also found in the basal telencephalon. Occasionally, some positive cells were identified in the nucleus lobi lateralis. Beta-endorphin-positive cells were located in the neurointermediate lobe of the pituitary. These findings indicate that substances related to POMC-derived peptides are located in distinct neuronal centers of the hypothalamus of Scyliorhinus. The differential distribution of POMC-related peptides suggests that α-MSH may act as a neurotransmitter or neuromodulator, whereas β-endorphin and ACTH might also exert neuroendocrine (i.e., hypophysiotropic) functions.

Persistent effects of neonatal toluene exposure on regional brain catecholamine levels and turnover in the adult male rat

Effects of neonatal toluene exposure (80 ppm, day 1–7, 6 h/day) have been studied on regional brain catecholamine levels and utilization, and on serum levels of hypophyseal and adrenocortical hormones in the adult male rat. Catecholamine levels were measured by quantitative histofluorimetry in the forebrain and hypothalamus and by high pressure liquid chromatography with electrochemical detection in the substantia nigra. Catecholamine utilization was evaluated from the decrease in catecholamines seen after tyrosine hydroxylase inhibition using α-methy- p-tyrosine methyl ester hydrochloride (αMT, 250 mg/kg, i.p., 2 h). Serum levels of thyroid stimulating hormone, corticosterone, aldosterone, prolactin and luteinizing hormone were measured by radioimmunoassays. Neonatal toluene exposure produced a reduction of dopamine levels and utilization selectively in the olfactory tubercle and substantia nigra of the adult rat. Furthermore, neonatal toluene exposure produced a significant reduction in the noradrenaline levels and utilization in the substantia nigra and an increase of noradrenaline utilization selectively in the subependymal layer of the median eminence and of the magnocellular part of the paraventricular hypothalamic nucleus. The serum hormone levels were not significantly influenced by neonatal toluene exposure as evaluated in adulthood. However, the αMT induced increase in serum prolactin levels was reduced following neonatal exposure to toluene. Neonatal toluene treatment was also found to alter the responses of the catecholamine neurons to subacute toluene exposure in adulthood. In some of the dopamine nerve terminal systems of the forebrain and in the dopamine cell body containing area of the substantia nigra neonatal toluene exposure appears to have made the dopamine neurons insensitive to adult subacute toluene exposure. In the hypothalamic noradrenaline nerve terminal systems, there were even reversed responses to subacute toluene exposure. The present results indicate that neonatal toluene exposure in doses at the threshold limit value produces persistent changes in dopamine and noradreneline neurons of the forebrain, hypothalamus and substantia nigra in the presence of a relatively intact neuroendocrine system. In addition, neonatal toluene exposure appears to diminish or even counteract the responses to subacute toluene treatment in adulthood.

Aromatic l-amino acid decar☐ylase-immunoreactive neurons in and around the cerebrospinal fluid-contacting neurons of the central canal do not contain dopamine or serotonin in the mouse and rat spinal cord

Using a specific antibody against each of the 4 catecholamine-synthesizing enzymes, dopamine or serotonin, we compared the localization of these substances in rat and mouse spinal cord with two kinds of fixative, such as paraformaldehyde and glutaraldehyde, and two types of sectioning techniqye, i.e. cryostat and microslicer. In this study, we demonstrated aromatic l-amino acid decar☐ylase (AADC)-like immunoreactivity (LI) in cerebrospinal fluid (CSF)-contacting neurons for the first time in the mouse. These cells and some AADC-immunoreactive cells localized outside the subependymal layer of mouse and rat spinal cord did not show tyrosine hydroxylase-, serotonin- and dopamine-LI with and without colchicine treatment.

Brainstem neurons projecting to the ampullae of anterior, lateral, and posterior semicircular canals in the guinea pig

Neurons projecting to the ampullae of anterior, lateral, and posterior semicircular canals were identified in the guinea pig brainstem using horseradish peroxidase labeling techniques. Two groups of neurons forming bilateral connections were found, one located dorsally and the other ventrally to facial nerve trajectories. The dorsal group of vestibular efferent neurons projecting to all three canals was detected in the subependymal granular layer of the floor of the 4th ventricle lateral to the facial nerve genu and in the abducent nerve nucleus. Efferent neurons belonging to the ventral group were unevenly distributed through different areas of the parvocellularis nucleus and the rostral portion of the pontine caudal reticular nucleus. The morphological characteristics and distribution pattern of these cells are taken as confirmation of their heterogeneity of neuronal and functional organization in the vestibular efferent system of semicircular canal ampullae.

Fetal cortical astrocytes migrate from cortical homografts throughout the host brain and over the glia limitans.

The cerebral cortices from 14-day gestation rat embryos were prelabeled with Phaseolus vulgaris leucoagglutin (PHAL) and then homografted into freshly made implantation pockets in the host cerebral cortex. Animals were sacrificed at 30 and 60 days postimplantation (DPI). Paraffin sections were double labeled for the presence of glial fibrillary acidic protein (GFAP), a specific marker for astrocytes, and PHAL, utilized as a marker for transplant-derived cells. Transplant-derived astrocytes were found on the glia limitans along the entire circumference of the brain, in the hippocampal commissure, corpus callosum, internal capsule, entopeduncular nucleus, habenular commissure, brachium of the superior colliculus, optic tract, optic chiasm, and sensory root of the trigeminal nerve. Transplanted astrocytes entered the spaces of Virchow-Robin, and migrated along parenchymal blood vessels and between the ependymal and subependymal layers of the third and lateral ventricles. The presence of basal lamina or parallel nerve fiber bundles was a common factor for these migration routes.

Ultrastructural characterization of exocytotic release sites in different layers of the median eminence of the rat.

The release of neuronal secretory products by exocytosis in different layers of the median eminence of the rat was investigated ultrastructurally after perfusion with Ringer solution containing tannic acid. Exocytotic images were observed in all layers studied. Neurohaemal release sites were found in the pars externa of the palisade layer, where they occurred not only against the basal lamina of the pericapillary space, but also opposite, adjacent to neuronal and glial elements. In the lateral portion of the pars externa of the palisade layer most release sites were separated from the pericapillary space or the pial surface by ependymal or glial processes. In the pars interna of the palisade layer, and in the reticular, fibre and subependymal layers, release was observed in different types of axonal processes without morphological synaptic specializations. We suggest that products released in the pars externa of the palisade layer are destined to reach the capillaries of the primary portal plexus. Although the non-vascular release sites may serve a similar hormonal function, they may alternatively represent the morphological correlate of axo-axonal contacts or of paracrine, non-synaptic release sites.

Development of macroglial cells in rat cerebellum II. An in situ immunohistochemical study of oligodendroglial lineage from precursor to mature myelinating cell

Using immunofluorescence with a panel of antibodies that recognize antigens expressed by oligodendroglia, the myelin-producing cells of the CNS, at different stages of differentiation from precursor to mature cell, we have investigated the development of cells of this lineage in cryostat sections of rat cerebellum. Our results are consistent with the view that glial precursors, identified by their expression of the ganglioside GD3, arise in the subependymal layers of the 4th ventricle and migrate to their final position in the cerebellum via the superior medullary velum, and to some extent the peduncles. As the cells reach their final destination they make the transition to recognizable galactocerebroside (GC)-expressing oligodendroglia, via a GD3+/GC+ intermediate. The myelin-associated protein 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) appears at the same time as GC, whereas myelin basic protein (MBP) is expressed 2-3 days after GC and CNP, immediately prior to myelin formation. A very clear progression of oligodendroglial differentiation was observed from the SMV into the base of the cerebellum, up into the white matter (WM) tracts of the folia, and then away from this central white matter into the granule cell and Purkinje cell layers, and finally the molecular layer. The time delay between the expression of GC, CNP and MBP was the same for oligodendroglia in all of these layers, suggesting the presence of an intrinsic clock controlling the initial expression of these myelin components. The early appearance of CNP in oligodendroglia suggests a role for this protein in the early stages of myelinogenesis.

D1 receptor mechanisms in the median eminence and their inhibitory regulation of LHRH release

D1 receptor mechanisms in the median eminence have been studied by means of immunocytochemistry using antisera against dopamine and cyclic AMP-regulated phosphoprotein-32 (DARPP-32) and tyrosine hydroxylase (TH) and by autoradiography using the iodinated analogue of the D1 receptor antagonist SCH-23390. The co-distribution of DARPP-32 and TH immunoreactivity (IR) and of DARPP-32 and luteinizing hormone releasing hormone (LHRH) IR was analysed in the median eminence by means of computer-assisted morphometry and microdensitometry. Functional analysis involved studies on the role of D1 receptors in the regulation of LH serum levels in rats treated with nicotine in the absence and presence of the D1 receptor antagonist. LH serum levels were measured by means of radioimmunoassay procedures. The results on the co-distribution of TH and DARPP-32 IR in the median eminence which were obtained both by analysis of adjacent sections and by two-colour immunocytochemistry on the same section, demonstrated a high degree of overlap of TH and DARPP-32 IR nerve terminals and tanycytes within the medial and lateral palisade zone. Furthermore, studies on LHRH and DARPP-32 IR nerve terminals and tanycytes in the median eminence with the same methodologies demonstrated preferential overlaps within the lateral palisade zone. The overlap area was about 50% of the LHRH or DARPP-32 immunoreactive area in this region. Density maps were also obtained on the distribution of LHRH and DARPP-32 immunoreactive profiles at various rostrocaudal levels. Correlation studies demonstrated a significant and positive co-distribution of LHRH and DARPP-32 immunoreactive terminals and tanycytes within the lateral palisade zone and the subependymal layer (when all DARPP-32 positive squares were considered) of the median eminence. Instead within the medial palisade zone a significant negative correlation coefficient was found, when all the LHRH positive squares were considered. In the receptor autoradiographical analysis a weak-to-moderate labelling was obtained of the part outside the mediobasal hypothalamus using the D1 receptor radioligand [(125)I]SCH-23982, while hardly any labelling was found within the median eminence and the arcuate nucleus. SCH-23390 was found to counteract, in a dose-related way, the inhibitory effects of intermittent nicotine treatment on serum LH levels. The D2 receptor antagonist raclopride in a dose of 1 mg/kg did not counteract the inhibitory effects of nicotine on serum LH levels. The present immunocytochemical, autoradiographic and functional studies suggest the existence of a D1 receptor in the median eminence which can be blocked by the D1 receptor antagonist SCH-23390 in behaviourally relevant doses and which is masked under basal conditions in the male rat. It is proposed that one type of median eminence D1 receptor is located on the axon terminals, not linked to DARPP-32, and which may make possible a rapid regulation of hypothalamic hormone release, e.g. LHRH release from the nerve terminals in the lateral palisade zone as indicated in the present morphological and functional experiments. The other type of median eminence D1 receptor may be located on the tanycytes and linked to DARPP-32. It is suggested that this D1 receptor is responsible for a long-term regulation of hypothalamic hormone release inter alia LHRH release from the terminal and preterminal parts of the LHRH axons in the lateral palisade zone and subependymal layer, respectively.

A study on causative factors of newborn intraventricular hemorrhages. An ultrastructural investigation on changes in the subependymal layer of the rat fetus

A study on causative factors of newborn intraventricular hemorrhages. An ultrastructural investigation on changes in the subependymal layer of the rat fetus

Immunohistochemical study of a dopaminergic system in the spinal cord of the ray, Raja radiata

Using a specific antibody we have demonstrated the presence of an intrinsic dopamine (DA)-containing system in the spinal cord of a cartilaginous fish. The DA neurons are distributed throughout the spinal cord in the subependymal layer that surrounds the central canal. These cells extend a thick process into the canal and thinner neurites throughout the gray matter; they resemble the liquor-contacting neurons reported for a range of vertebrates.

Autoradiographic mapping of [mono[ 125I]iodo-Tyr 10, MetO 17]vasoactive intestinal peptide binding sites in the rat brain

The distribution of vasoactive intestinal peptide binding sites in the rat brain was examined by in vitro autoradiography on slide-mounted sections. A fully characterized monoiodinated form of vasoactive intestinal peptide (M-[ 125I]VIP) previously shown 47 to maintain in the central nervous system the full biological activity of native vasoactive intestinal peptide was used for this study. In initial kinetic and pharmacological experiments the binding of M-[ 125I]vasoactive intestinal peptide to slide-mounted sections was shown to be time-dependent, saturable and reversible. Association of M-[ 125I]VIP specific binding was maximal within 90–120 minutes. Specific binding, corresponding to approximately 50% of total binding was saturable, of high affinity ( K d of 76.6 pM) and low capacity (fmol/mg prot range). Dissociation of M-[ 125I]VIP was maximal at 10 minutes. Unlabeled vasoactive intestinal peptide and the two structurally related peptides “peptide-histidine-isoleucine” (PHI) and secretin competed in a concentration-dependent manner for sites labeled by M-[ 125I]vasoactive intestinal peptide with the following rank order of potencies: vasoactive intestinal peptide > PHI > secretin. Vasoactive intestinal peptide receptors, as revealed by quantitative autoradiography, are present at various levels of the neuraxis. High densities were observed in olfactory bulb, cerebral cortex (highest in layers I, II, IV and VI), dentate gyrus, subiculum, various thalamic and hypothalamic nuclei, superior colliculus, locus coeruleus, area postrema, subependymal layer and pineal gland. Intermediate densities were found in the amygdala, nucleus accumbens, caudate-putamen, septum, bed nucleus of the stria terminalis, CA1 to CA4 fields of the hippocampus and central gray. No specific binding of M-[ 125I]vasoactive intestinal peptide was observed in white matter tracts such as corpus callosum, anterior commissure, medial forebrain bundle and fornix. The mapping of M-[ 125I]vasoactive intestinal peptide binding sites as revealed by autoradiography on slide-mounted sections indicates an association, although not exclusive, of vasoactive intestinal peptide receptors with brain regions involved in the processing of specific sensory inputs.

Golgi studies on the development of granule cells of the rat olfactory bulb with reference to migration in the subependymal layer.

The morphology and the development of the cells in the subependymal layer and of granule cells of the olfactory bulb were examined by Nissl and Golgi staining in postnatal rats. The subependymal layer around the anterior lateral ventricle extends into the center of the olfactory bulb. The mitotic indexes in the subependymal layer are high at the level of the anterior horn of the lateral ventricle and very low inside the olfactory bulb during the first 3 weeks after birth. Golgi-stained subependymal cells are classified into two main groups. One group consists of smoothly contoured bipolar cells with leading processes tipped by large growth cones and with trailing processes. They make up a majority of Golgi-stained subependymal cells during the first 3 weeks of age, and smaller numbers of them continue to exist at 37 and 60 days. They migrate with their growth cones oriented toward the olfactory bulb from the level of the anterior lateral ventricle into the granular layer of the olfactory bulb, where they differentiate into the definitive granule cells: their somata enlarge; the leading processes elongate, branch, sprout many gemmules, and become the peripheral processes; and the trailing processes become the basal dendrites. The other group contains relatively large cells with many cytoplasmic processes that are considered to belong to the glial cell line.

Distribution of tyrosine-hydroxylase (TH)-immunoreactive neurons in the diencephalon of the pigeon (Columba livia domestica).

The distribution of tyrosine-hydroxylase (TH)-immunoreactive cell bodies and fibers in the diencephalon has been investigated with immunohistological techniques in the pigeon. The results suggest that TH is present in a number of morphologically distinct neuronal systems. Preoptic and hypothalamic TH neurons were subdivided into a medial periventricular and a lateral group. The medial group starts with a rostral collection of small cells in the preoptic region. A significantly larger collection of TH neurons occupies the paraventricular nucleus (PVN) (stratum cellulare internum) and mainly consists of large multipolar cells. Further caudally, the main concentration of cells is in the hypothalamic posteromedial and the periventricular regions of the tuberoinfundibular (arcuate) nucleus. No TH neuron was found in the ventral and lateral parts of the tuberoinfundibular region, suggesting that the prominent tuberoinfundibular dopaminergic system described in mammals is absent in the pigeon. This further substantiated by the relative scarcity of TH immunoreactive fibers and varicosities in the neurohemal zone of the median eminence (ME). The caudalmost components of the medial group appear to be continuous with the large population of TH neurons distributed in the midline of the mesencephalon. Tyrosine-hydroxylase-immunopositive cells have not been found in the paraventricular organ. The lateral group consists of TH neurons loosely arranged in the lateral hypothalamus, including regions of the supraoptic nucleus and hypothalamic posterolateral nucleus. Tyrosine-hydroxylase containing neurons vary widely in size, shape, and dendritic arborization in each diencephalic region. However, it is possible to distinguish two main cell types. Small bipolar neurons with two simple arborizing dendrites were concentrated in the medial periventricular system. The second type of cell is large, multipolar with four to five branching dendrites. This latter cell type occurs mainly in the lateral system and in the PVN. Major fiber bundles containing TH immunoreactivity were identified in the lateral and periventricular hypothalamus. The paraventricular organ and the organum vasculosum laminae terminalis contained the densest arborization of fibers and varicosities. In the ME, dense innervation was found in the subependymal layer. Dense arborizations of TH positive fibers and varicosities were located in the septal nuclei and the paleostriatum augmentatum.

The cytoarchitecture of the torus semicircularis in the teleost Barbus meridionalis.

The torus semicircularis of Barbus meridionalis is composed of two nuclei, the nucleus centralis and nucleus lateralis. Its cytoarchitecture was studied in sections stained by Nissl and Golgi-Colonnier techniques. In the nucleus lateralis two portions were identified: the 'pars lateralis' and the 'pars medialis.' Cytoarchitecturally, both portions are identical. They exhibit a layered structure in which there is an alternation of cell-poor and cell-rich laminae designated as: (1) the subependymal layer; (2) the layer of small cells; (3) the fibrillar layer; and (4) the layer of disperse cells. The subependymal layer consists of fine fibers and some small rounded-ovoid cells whose dendritic prolongations course horizontally or ventrally. The second layer has small, densely-packed cells with rounded-ovoid and triangular somata and a main dendritic trunk that courses ventrally. The third layer contains dendritic fields of the cells of layer two and of cells from layer four. The fourth layer is composed of fusiform neurons with two dendritic trunks of equal thickness, rounded-ovoid neurons with one or two main dendritic trunks and multipolar triangular stellate neurons with equal dendritic trunks. The nucleus centralis comprises a fibrillar cortex with a structure identical to that of the subependymal layer. There is also a cellular region with the same cell types as those found in the nucleus lateralis. These two nuclei thus compose the torus semicircularis of the barbel. They exhibit the same cytological characteristics and both are differentiated by their cytoarchitectural and functional orders.

Microglia in the hypendyma of the rat subcommissural organ following brain lesion with serotonin neurotoxin.

The population of microglial cells in the subependymal layer of the subcommissural organ is sparse in normal adult rats. The number of microglial cells was substantially increased in this area following intraventricular injection of the serotonin neurotoxin 5,6-dihydroxytryptamine (5,6-DHT). In sections of plastic embedded material, 1 micron thick, the majority of phagocytic cells scattered in the subependymal layer had an appearance similar to that described in classical studies of microglial cells. At the electron microscopic level microglial cells exhibited the characteristic elongate nucleus with peripheral chromatin condensation. The perikaryon was scanty, containing strands of rough endoplasmic reticulum. The abundant organelles in the processes included Golgi complexes, mitochondria, rough and smooth endoplasmic reticulum as well as dense and multivesicular bodies. In addition, the processes contained phagocytosed axon terminals originating from the dense serotoninergic input to the subcommissural organ, which had degenerated on accumulating the serotonin neurotoxin. A fraction of the phagocytosed material was contained in subependymal subcommissural organ cells, astrocytes and oligodendrocytes. At the light microscopic level the phagocytosed terminals were visualized histochemically with Schmorl's reaction, which resulted in Prussian Blue precipitates. This allowed screening of microglial cells in complete series of sections through the well-defined subependymal layer of the subcommissural organ.