Connectivity of fetal neocortical block transplants in the excitotoxically ablated cortex of adult rats

Fetal neocortical block grafts placed into new-born recipients are able to exchange axonal projections with the host central nervous system, as shown in several previous experiments. The present study examined the connectivity of fetal neocortical block transplants placed into the excitotoxically ablated cortex of adult rats. Young adult rats received injections of the excitotoxic amino acid N-methyl-D-aspartate into the sensorimotor cortex area 1 week prior to receiving a fetal (E14–15) neocortical transplant. Afferent and efferent connections of these grafts were examined 3–6 months after transplantation by injecting the transplants with the fluorescent retrograde tracers fast blue and diamidino yellow or with the anterograde tracer Phaseolus vulgaris leucoagglutinin. Retrogradely labeled neurons were observed within several host brain regions including the ipsilateral neocortex, several thalamic nuclei, subcortical areas such as claustrum and lateral hypothalamus, nucleus basalis, dorsal raphe nuclei and locus coeruleus. Fibers labeled with Phaseolus vulgaris leucoagglutinin were found extending throughout the transplants, but with rare exceptions fibers were not observed within the host brain. The experiments showed that neocortical block grafts placed into the excitotoxically ablated neocortex receive afferent input from areas in the host brain that normally innervate the sensorimotor cortex. The extensive Phaseolus vulgaris leucoagglutinin-positive axonal labeling found within the grafts demonstrated the ability of the grafted neurons to establish extensive intrinsic graft connections. Their failure to project out of the grafts suggests that the mature host brain does not provide a permissive environment for neurite extension.     

Organization of identified fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study

The fimbria is a major route for afferent and efferent fibers of the hippocampal formation. However, little is known about the intrinsic organization of the fimbria-fornix complex. In this study, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used to analyze the ultrastructure and topography of identified fiber tracts within the fimbria-fornix. Septo-hippocampal fibers are loosely distributed throughout the fimbria-fornix. Commissural fibers cross the midline in the ventral hippocampal commissure and form a tight fiber bundle in the fimbria. Crossed entorhino-hippocampal fibers cross the midline in the ventral hippocampal commissure rostral to the commissural fiber bundle, and crossed entorhino-entorhinal fibers pass through the dorsal hippocampal commissure. This suggests a topographical organization of fiber tracts within the fimbria-fornix that reflects the laminar organization of the hippocampal target structure: fibers of the diffusely terminating septohippocampal projection are loosely distributed throughout the fimbria-fornix, while those projections that are known to terminate in specific laminae of the hippocampal formation (commissural projection, crossed entorhino-hippocampal projection) form fiber bundles within the fimbria and the ventral hippocampal commissure.Abbreviations A Astrocyte - CA1, CA3 hippocampal subfields - CC corpus callosum - D dendrite - DG dentate gyrus - DHC dorsal hippocampal commissure - Fi fimbria - LS lateral septal area - LV lateral ventricle - O oligodendrocyte - SFO subfornical organ - VHC ventral hippocampal commissure     

The ultrastructure of the olivary pretectal nucleus in rats. A tracing and GABA immunohistochemical study

 The olivary pretectal nucleus is a primary visual centre, involved in the pupillary light reflex. In the present study an ultrastructural analysis was made of the olivary pretectal nucleus by means of separate, anterograde and retrograde tracing techniques and immunohistochemistry of gamma-aminobutyric acid. Large-projection neurons and two types of gamma-aminobutyric acid-immunoreactive (GABA-ir) neurons are observed in the olivary pretectal nucleus. The primary dendrites of the projection neurons have a dichotomous appearance, the secondary dendrites a multipolar appearance. At the ultrastructural level the projection neurons have well-developed Golgi fields, abundant rough endoplasmic reticulum and the nucleus is always heavily indented. Numerous small GABA-ir neurons and a few medium-sized GABA-ir neurons are found. The small GABA-ir neurons contain a few stacks of rough endoplasmic reticulum and the nucleus is oval-shaped. The medium-sized GABA-ir neurons have well-developed Golgi fields, a moderate number of rough endoplasmic reticulum stacks and an indented nucleus. GABA-positive dendritic profiles containing vesicles also are observed. In the neuropil of the olivary pretectal nucleus, retinal terminals are found that contain round clear vesicles and electron-lucent mitochondria. They make asymmetric synaptic contacts (Gray type I) with dendritic profiles and with profiles containing vesicles. Terminals originating from the contralateral olivary pretectal nucleus exhibit small, round clear vesicles, electron-dense mitochondria and make asymmetric synaptic contacts (Gray type I) mainly with dendritic profiles. Two types of GABA-ir terminals were found. One type is incorporated in glomerulus-like arrangements, whereas the other type is not. GABA-ir terminals contain pleomorphic vesicles, electron-dense mitochondria and make symmetric synaptic contacts (Gray type II). Retinal terminals, terminals originating from the contralateral olivary pretectal nucleus and GABA-ir terminals are organized in glomerulus-like structures, in which dendrites of the large projection neurons form the central elements. Triadic arrangements are observed in these structures; a retinal terminal contacts a dendrite and a GABA-ir terminal and the GABA-ir terminal also contacts the dendrite. The complexity of the synaptic organization and the abundancy of inhibitory elements in the olivary pretectal nucleus suggest that the olivary pretectal nucleus is strongly involved in processing visual information in the pupillary light reflex arc. Received: 17 July 1996 / Accepted: 24 September 1996     

Fetal neocortical transplants grafted to the cerebral cortex of newborn rats receive afferents from the basal forebrain,locus coeruleus and midline raphe

Summary Fetal cerebral neocortex (E15–17) was grafted into the cerebral hemisphere of newborn (0–1 day old) rats. Grafts were placed into cortical aspiration lesion cavities made immediately prior to grafting. At maturity, transplant afferents were examined by injecting the retrogradely transported fluorescent dyes diamidino yellow and fast blue into the grafts. Retrogradely-labeled neurons were histologically observed within several regions of the host brain including the basal forebrain, locus coeruleus and dorsal raphe areas. The topographical distribution within these areas resembled the normal labeling patterns described in previous reports.     

A comparative study of cholinergic systems of the neocortex and hippocampus in rats with low and high resistance to hypoxia

Synaptic structures in the neocortex and hippocampus of the intact brain were compared between rats with low and high resistance to hypobaric hypoxia. Activities of choline acetyltransferase, acetylcholinesterase, Na,K-ATPase, and the portion of protein in the light and heavy synaptosome fractions and subfractions were measured. A discrepancy in cholinergic metabolism molecular mechanisms between high and low resistance animals have been found in the heavy somatosoma fraction from the neocortex. Activities of choline acetyltransferase, acetylcholinesterase, and Na,K-ATPase in the synaptolemmal subfraction of low resistant rats were much lower than in high resistant rats. This implies a less effective synaptic transmission in proper cholinergic neurons in the low resistance animals and, therefore, specifically changed neuron functioning in the circulation control. No differences in the cholinergic components of either neocortical light synaptosome fraction or hippocampal light and heavy synaptosome fractions were found between low and high resistance rats. Translated fromByulleten' Eksperimental'noi Biologii I Meditsiny, Vol. 125, No. 5, pp. 521–525, May, 1998     

Characterization of peptidergic efferents from the lateral parabrachial nucleus to identified neurons in the rat dorsal raphe nucleus

The peptidergic content of the lateral parabrachial nucleus (LPB) efferents to the dorsal raphe nucleus (DRN) was studied by combining visualization of the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin within fibers that were immunocytochemically stained for neurotensin (NT), calcitonin gene-related peptide (CGRP) or galanin (GAL). The identity of DRN target neurons was determined with simultaneous immunocytochemical labelling for serotonin, the major transmitter within the nucleus. Within the DRN, we estimated that about two-thirds of the anterogradely labelled fibers arising from the LPB also showed peptidergic immunoreactivity. NT was the most commonly observed neuropeptide in LPB neuronal efferents directed to the DRN, followed by CGRP and GAL. The peptidergic afferents in the DRN were oriented preferentially in the dorsoventral plane. Peptidergic fibers from the LPB possessed varicosities (diameters not exceeding 3 microns) and were apposed on serotoninergic neuronal somata. Some of the anterogradely labelled peptidergic fibers were not associated with cells showing immunoreactivity for serotonin. The present results suggest that NT-ergic, CGRP-ergic and GAL-ergic neurons within the LPB are in contact with serotoninergic and non-serotoninergic neurons within the DRN. Since the DRN is known to project to the LPB, it is likely that bi-directional interconnections between these nuclei exist. Such linkages may provide anatomical substrates for coordinated autonomic responses.     

Ultrastructure of giant and small thalamic terminals of cortical origin: a study of the projections from the barrel cortex in mice using Phaseolus vulgaris leuco-agglutinin (PHA-L)

Summary By means of tracing with the lectin Phaseolusvulgaris leucoagglutinin (PHA-L), we examined in the thalamus of the mouse, the axon terminals of fibers originating in the barrel cortex. Vibratome sections of the brain were subjected to PHA-L immunocytochemistry and processed for light and electron microscopy. We observed small (0.5–0.8 m in diameter) varicosities of labeled fibers in the nucleus ventrobasalis (VB) and the nucleus posterior (PO) as well as labeled giant terminals (3–5 m in diameter) in PO. The analysis involved examination of serial sections and computer-aided reconstruction of several terminals. The small varicosities in VB appear to be small axon terminals forming distinct asymmetric synapses with small dendritic profiles. Some labeled terminals are apposed to, but not synaptically related with, the cell bodies of neurons in VB that are retrogradely labeled with PHA-L. The small varicosities seen with the light microscope in PO are terminals forming asymmetric synapses with dendritic shafts. The giant terminals in PO appear as large, vesicle-filled profiles forming part of synaptic glomeruli, i.e. complexes of one corticothalamic terminal engulfing several excrescences of a single dendrite. A giant terminal forms several asymmetric synapses (about 8) with these excrescences, as well as numerous (up to 15) puncta adhaerentia. The glomeruli are enveloped in glial lamellae, and they are often found at the bifurcations of primary dendritic segments. We suggest that the small terminals in VB are in the service of feedback signalling from the barrel cortex to its principal thalamic relay nucleus; the functional importance of this projection may reside in increased spatio-temporal discrimination. We interpret the giant terminals in PO as elements serving feed-forward processing, allowing the barrel cortex to influence, via PO, parts of the motor pathway modulating the animal's ongoing behavior.     

Experimental study of the possibility of metabolic correction of maternal, fetal, and newborn hypoxia in rats using a new amino acid composition MR-33

The status of pregnant rats, their fetuses, and progeny exposed to oxygen insufficiency are compares. By the end of pregnancy the resistance to hypoxia markedly decreases. Newborn rats during nursing are highly resistant to hypoxia. When nursing period is over, the resistance to hypoxia drops, but later is gradually restored. MR-33 preparation produces a pronounced antihypoxic effect. Administration of the drug to pregnant rats not only appreciably improves their resistance to oxygen insufficiency, but also promotes adaptation and compensatory mechanisms in the progeny, thus helping the progeny to better tolerate hypoxia, particularly when its probability is particularly high. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 10, pp. 451–454, October, 1997     

The projections of the retrorubral field A8 to the hippocampal formation in the rat

The dopaminergic neurons in the midbrain of the rat are located in three groups: the ventral tegmental area (VTA-A10), substantia nigra (SN-A9), and retrorubral field (RRF-A8). We have recently examined the organization of the projections from the VTA and the SN to the hippocampal formation (HF) in the rat. In the present study we characterize the projections of the RRF to the HF by using anterograde tracing, retrograde tracers, and tyrosine hydroxylase (TH) immunohistochemistry. Following iontophoretical injections of Phaseolous vulgaris leucoagglutinin (PHA-L) into the RRF, anterograde labeling was observed primarily in the ipsilateral subiculum and adjacent CA1 cell field. Sparse labeling was also observed in the CA3 cell field and dentate gyrus. The distribution of RRF neurons projecting to the HF was examined by injecting retrograde fluorescent tracers (fluorogold, fast blue, and nuclear yellow) into several hippocampal areas. The retrograde tracer findings indicate that the medial aspects of the RRF project to the subiculum and adjacent CA1 cell field of both the septal and temporal HF. In order to evaluate the percentage of dopaminergic cells of the RRF projecting to the HF, the retrograde neuronal tracer fluorogold was used in combination with TH immunohistochemistry. The quantitative evaluation of retrograde labeled and TH-immunoreactive (IR) cells showed that RRF projections to the HF are partially (10–18%) dopaminergic. The findings suggest that the general pattern of distribution and organization of the RRF-A8 projections to the HF is similar to that observed in our previous studies examining hippocampal afferents from the VTA and SN. The data also suggest a crude topographical organization of RRF afferents to the HF and a more prominent input to the temporal than to the septal HF.     

Effect of bromantane,a new immunostimulating agent with psychostimulating activity,on the release and metabolism of dopamine in the striatum of freely moving rats. A microdialysis study

It is demonstrated that bromantane induces a pronounced and prolonged (8 h) increase in the release of dopanime. Tetrodotoxin (10⁻⁶ M) perfused via a microdialysis probe partially inhibits the bromantane-induced release of dopamine. The extracellular content of the dopamine metabolites 3,4-dioxyphenylacetic and homovanillic acids is slightly decreased. The possible mechanisms of action of bromantane on the dopamin- and serotoninergic systems of the brain are discussed. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o . 3, pp. 302–304, March, 1995 Presented by M. D. Mashkovskii, Member of the Russian Academy of Medical Sciences