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Biomedical subjects

I Divac

Publications and source records attributed to I Divac.

At least 19 recordsLinked to original sources
PubMed1995

Parcellation of the frontal cortex of the New World monkey Callithrix jacchus by eight neurotransmitter-binding sites.

The most extensive development during primate brain evolution involves the cortex of the frontal lobe, especially its prefrontal region. The distribution of neurotransmitter receptors is unknown in this part of the cortex of New World monkeys. The respective distributions of eight different receptors for the transmitters L-glutamate (L-glu and NMDA), gamma-amino-butyric acid (GABAA), noradrenaline (alpha 1), acetylcholine (M1 and M2) and serotonin (5-HT1 and 5-HT2) were therefore studied in cortical areas of the frontal lobe of the lissencephalic New World monkey, Callithrix jacchus. The results are compared to earlier data on Old World monkeys in order to obtain insight into evolutionary trends at the level of chemical neuroanatomy. Our results indicate that the density and laminar pattern of some receptors change precisely at the cytoarchitectonic boundaries between different cortical areas, while some other receptors do not exhibit measurable changes. For example, the premotor area 6 can be distinguished from prefrontal areas by its high concentration of adrenergic alpha 1 receptors as labelled with [3H] prazosin, with only the cingulate area 24 showing higher values. In other cases, the receptor distribution changes within a cytoarchitectonically homogeneous area. Thus, area 8 can be subdivided into dorsal and ventral regions on the basis of the distribution of GABAA, muscarinic and serotonin receptors. Comparison of these results in a New World monkey with receptor distributions in other primate species reveals much larger interspecies differences in the areas of the frontal lobe than e.g. in the primary visual cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Afferents to different layers of the dorsolateral isocortex in rats.

Fluorescent somatopetal tracers were used to infiltrate, by diffusion rather than injections, the dorsolateral cortex of one hemisphere in rats. In different animals the tracers penetrated into the cortex to different depths. We found several interesting features of the commissural system: first, there were no areas without commissural neurons. At least a few labelled cell bodies were present in a single-cell layer also in "acallosal" cortical areas. Secondly, there is a considerable variety of laminar distribution patterns of labelled perikarya in different areas. Thirdly, some cortical fields, which cytoarchitecturally appear uniform, can be subdivided according to different distributions of cell bodies with commissural projections. Fourthly, when only supragranular layers were infiltrated, labelled cell bodies were present mainly in the supragranular layers of the contralateral cortex. Infiltration of the first layer alone did not label any neurons in the contralateral cortex but did label neurons in layer VIb ipsilaterally. In the subcortex, the labelled perikarya were found in the structures already known to project directly to the cortex. In rats with the tracer restricted mainly to the supragranular layers, a conspicuously reduced labelling was found in the basal forebrain and the thalamus. In the thalami of those animals, labelled neurons were found only in paralamellar nuclei. The high sensitivity of the tracer used, together with infiltration of the entire dorsolateral cortex, allows us to conclude that probably all sources of innervation of the isocortex in rats have been seen.

Afferent Pathways↗
PubMed1995

Quantitative receptor autoradiography of eight different transmitter-binding sites in the hippocampus of the common marmoset, Callithrix jacchus.

The regional and laminar distributions of eight different transmitter-binding sites were measured in the marmoset hippocampus by means of quantitative in vitro receptor autoradiography. Receptors for 5-HT1, L-glutamate, N-methyl-D-aspartate (NMDA) and GABAA were similarly distributed. The highest concentrations of these receptors were found in the pyramidal layer of CA1 and the molecular layer of the dentate gyrus. The 5-HT2 receptors showed the highest concentrations in the oriens layer of CA2. The highest concentrations of muscarinic M1 receptors were seen in the pyramidal layer of CA1. Muscarinic M2 receptors were most densely concentrated in the pyramidal layers of CA1, CA2 and CA3. The noradrenergic alpha 1 receptors were most densely packed in the radiatum-lacunosum-molecular layer of CA2 and the molecular layer of the dentate gyrus. Statistically significant co-distributions of serotoninergic, glutamatergic and GABAergic receptors point to possible interactions between these receptor systems in the same hippocampal regions and layers. Comparisons of marmoset distribution patterns for GABAA, NMDA, L-glutamate and 5-HT1 receptors with those in human hippocampi and those of other primates showed similarities between them. Clear differences in the patterns of alpha 1, M1, M2 and 5-HT2 receptors could be seen between marmoset and human hippocampi, indicating a high degree of species specificity in a presumably "conservative" brain region. More similarities, however, could be found between marmoset and human hippocampi than between those of rat and human brains, especially in relation to 5-HT1 and GABAA receptors and L-glutamate-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Improved contrast in histochemical detection of cytochrome oxidase: metallic ions protocol.

The standard current technique for demonstration of cytochrome oxidase (CyOx) provides low-contrast diaminobenzidine (DAB) polymer. In order to enhance the contrast with divalent metalic ions, we have screened a number of buffers and found that Hepes, Mops and cacodylate neither precipitate these ions nor inactivate CyOx in a concentration of 0.1 M. Staining thus obtained shows a broad range of gradations between black and white. With fresh tissue the resulting image is superior to that obtained with the brown DAB product, even if a recommended blue filter or printing on very hard paper are used. The technique is as simple as the one which is currently standard. Fixed tissue, cut either in a cryostat or vibratome, can be stained well when floating but not when mounted on slides. The stained floating tissue can be used for electron microscopy, but has no advantage over the standard method.

Animals↗
PubMed1995

Synaptic reorganisation of the mediodorsal thalamic nucleus in adult rat following chronic prefrontal cortical lesions.

Chronic changes in the thalamic mediodorsal nucleus (MD) after unilateral lesions of the prefrontal cortex were studied with the aid of quantitative light, and electron microscopic immunohistochemistry. Three months after the lesions, although the size of MD ipsilateral to the lesion did not change considerably, the neuronal density was significantly reduced. Conversely, as demonstrated by quantitative electron microscopy, the density of GABA immunostained axon terminals significantly increased in the lesioned side. It is suggested, that as MD does not contain GABA cells, the reactive hyperinnervation of the MD by GABA-containing axons is of extrinsic origin. This finding is also the morphological evidence of the potential of GABA-ergic nerve cells for reactive (induced) axonal sprouting.

Animals↗
PubMed1994

Anti-inflammatory drugs suppress injury-induced NADPH-d activity in CA1 pyramidal neurones.

Inducibility of NADPH-diaphorase (NADPH-d) or nitric oxide synthase (NOS) has been demonstrated in pyramidal neurones of the hippocampus, but the mechanisms of this induction are not known. The present study aimed to assess the role of anti-inflammatory drugs in injury-induced production of NADPH-d/NOS in CA1 pyramidal neurones. We found that either a steroid, dexamethasone or a non-steroid, indomethacin, prevents induction of these enzymes. We also found that NO is not necessary for the induction. None of the three drugs used had detectable effect on the neurones which contain constitutive NADPH-d/NOS.

Animals↗
PubMed1994

Retention and relearning of spatial delayed alternation in rats after ablation of the prefrontal or total non-prefrontal isocortex.

In the present study we addressed the question whether, within the isocortex, the prefrontal area of the rat is uniquely involved in mediation of delayed alternation. In one group of rats the dorsolateral isocortex, from the dorsomedial shoulder to the dorsal lip of the rhinal sulcus was removed bilaterally in a single surgical session. In these rats delayed alternation in a T-maze was significantly less impaired than in rats with one stage bilateral removal of the medial prefrontal cortex. The prefrontal cortex seems not to depend crucially on isocortical input for its medication of delayed alternation.

Animals↗
PubMed1994

Absence of transsynaptic transport in cerebello-thalamo-cortical path of the rat.

Attempts to visualize the cerebello-thalamo-cortical path in the rat were made with different approaches. We tried (1) double labelling with somatopetal tracing from the motor cortex and somatofugal from the cerebellar nuclei, (2) transmembrane labelling by depositing biocytin or wheat germ agglutinin (WGA) into the motor cortex or cerebellum. WGA was either iodinated with 125I or conjugated with horseradish peroxidase (HRP). The double labelling technique showed an overlap of the tracers in the same thalamic region but no evidence of transsynaptic transport in either direction was obtained. Our results indicate a difference in the organization of this system in primates and rodents, since transsynaptic labelling in the cerebellar nuclei after injections of WGA-HRP conjugate in the monkey motor cortex has been found.

Animals↗
PubMed1994

A Combined golgi and postembedding GABA and glutamate electron microscopic study of the nucleus dorsomedialis thalami of the rat.

The synaptic organisation of neurons in the nucleus medialis dorsalis (MD) was investigate by combined Golgi, and post-embedding gamma-aminobutyric acid (GABA) and/or glutamate (GLU) immunogold methods. The morphological features of the impregnated neurons in the MD (detailed by Kuroda et al. 1992a) were similar to thalamocortical relay cells present in other thalamic nuclei. GABAergic cell bodies could not be found. Distal dendritic branches of gold toned neurons established synaptic contacts with small and medium size glutamate as well as GABA-immunoreactive axonal endings. Large glutamate and GABA-positive axon terminals formed synaptic contacts with proximal dendrites. GABAergic axon terminals exhibited symmetric synaptic contacts and contained pleomorphic vesicles. Glutamate immunoreactive terminals formed asymmetric synapses and contained spheroid vesicles, although, some large glutamate immunoreactive endings contained pleomorphic vesicles. Synaptic glomerulus-like complexes could also be observed with the participation of glutamate-, and GABA-positive large axon terminals synapsing with Golgi impregnated proximal dendrites.

Animals↗
PubMed1994

Dopaminergic innervation of the brain in pigeons. The presumed 'prefrontal cortex'.

In the postero-dorso-lateral neostriatum (PDLNS) of the pigeon we found a high density of tyrosine hydroxylase and perineuronal nests of fibres labelled with anti-dopamine antibody. These data confirm our earlier indirect evidence that PDLNS receives a dense dopaminergic innervation and therefore can be compared with the mammalian prefrontal cortex.

Animals↗
PubMed1994

Cortical area in the rat that mediates visual pattern discrimination.

In Experiment I, bilateral ablations of the caudolateral cortex involving Krieg's area 36 impaired discrimination of visual patterns but not delayed alternation. In Experiment II, the same type of lesions retarded postoperative learning to discriminate embedded visual patterns. In rats from the Experiment II tracers of axonal transport gave no signs of damage of the connections of the primary visual cortex. In agreement with this, Nissl stain of the dorsal lateral geniculate nuclei showed no neuronal loss or gliosis. These results suggest that caudo-lateral cortex in rats corresponds to the inferotemporal cortex of primates.

Animals↗
PubMed1993

NOS neurones lie near branchings of cortical arteriolae.

We show that numerous neurones labelled for NADPH-diaphorase, which synthetize nitric oxide, lie near branching points of the arteriolae which descend through the cerebral cortex from its pial surface. This spatial relationship suggests the possibility of neural control of cortical blood flow by the NADPH-diaphorase neurones, possibly mediated by the rapid action of nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1993

Retention and relearning of spatial delayed alternation in rats after combined or sequential lesions of the prefrontal and parietal cortex.

Lesions of the medial prefrontal cortex strongly impaired rats' delayed alternation behaviour in a T-maze, both when the lesion was inflicted after the initial acquisition of the task and when the lesion was added after criterion performance had been reattained following an ablation of the parietal cortex. Lesions of the parietal cortex did not impair this behaviour, either when the parietal lesion was inflicted after the initial acquisition of the task or when it was added to a prefrontal lesion after criterion performance had been reattained. Combined, one stage, parietal and prefrontal lesions did not have stronger effect on delayed alternation than did prefrontal lesions alone. These results indicate that in spite of the strong anatomical connectivity between the prefrontal and parietal "association" cortex the latter is not necessary for the recovery of delayed alternation after prefrontal lesions. In comparison with the parietal cortex, the prefrontal cortex seems to be uniquely involved in mediation of delayed alternation.

Animals↗
PubMed1993

Cortical projections of the thalamic mediodorsal nucleus in the rat. Definition of the prefrontal cortex.

Deposits of somatopetal tracers, that filled the entire dorsolateral cortex of one hemisphere, labelled only a few cell bodies in the thalamic mediodorsal nucleus (MD). Further experiments served to confirm the existence of strong projections from MD to the mesial and suprarhinal areas of the frontal cortex. Thus, only a very small proportion of the MD neurones in the rat projects outside the cortical areas described first by Leonard (1969). We conclude that at least in the rat, cortical projections of the MD are selective enough to be used as the basis for definition of the prefrontal cortex.

Animals↗
PubMed1992

Bilateral thalamocortical projection in hedgehogs: evolutionary implications.

In adult hedgehogs with large unilateral cortical deposits of fluorescent somatopetal tracers, labelled perikarya were found not only in the ipsilateral but also contralateral thalamus. An exceptionally large number of contralaterally labelled neurons was seen in the ventrolateral nucleus, also at a considerable distance from the midline. Deposits of one of two different tracers in the frontoparietal cortex of each hemisphere appear to label different perikarya in each ventrolateral nucleus. This projection to the contralateral cortex in hedgehogs does not resemble thalamo-cortical connections in either adult or developing brains of other mammalian species. Among amniotes, only in pigeons have contralateral projections from the thalamus to the telencephalon been described. The somatosensorimotor system of hedgehogs may be the only known mammalian remnant of primitive vertebrate thalamocortical organization. Whether primitive or derived, the bilateral thalamocortical projection in hedgehogs shows that hedgehog brains cannot be uncritically taken to represent brains of primate ancestors.

Animals↗