Search PubMed⌕ Search

Biomedical subjects

I Divac

Publications and source records attributed to I Divac.

At least 55 records · Page 3Linked to original sources
PubMed1987

Architectonics of the thalamus in the echidna (Tachyglossus aculeatus): search for the mediodorsal nucleus.

Architectural characteristics of the thalamus in echidnas and rats were compared in sections stained to reveal cell bodies, myelin, acetylcholinesterase, succinate dehydrogenase and cytochrome oxidase. Numerous species differences were noticed: in general, the thalamus is architecturally more homogeneous in echidnas than in rats, especially anteriorly. In this report we emphasize the presence of a relatively large structure localized in the anteromediodorsal part of the thalamus in echidnas. This structure, previously shown to project to the frontal cortex, contains very small amounts of acetylcholinesterase and the oxidative enzymes; in this respect it resembles the mediodorsal nucleus of rats. The same properties make this formation different from the anterodorsal and anteroventral nuclei in rats, the equivalents of which could not be identified in echidnas. The anteromediodorsal region of the thalamus in echidnas consists chiefly of two cytoarchitecturally different regions: the medial, 'polymorphic' part contains relatively small, densely packed, multiform perikarya, whereas the lateral, 'monomorphic' part is characterised by larger, sparse neurons with little cytoplasm and round, large, empty-looking nuclei in which the nucleolus is clearly seen. We conclude tentatively that this brain structure of echidnas corresponds to the mediodorsal nucleus in placental species. Further studies of connections and chemical properties will be essential to determine the degree of correspondence of the presumed 'frontal lobe system' in echidnas to that in other mammals.

Animals↗
PubMed1987

Neostriatal lesions impaired rats' delayed alternation performance in a T-maze but not in a two-key operant chamber.

Rats with lesions in the neostriatal region that belongs to the prefrontal system were trained in two versions of delayed alternation. They performed as proficiently as intact animals in a two-key operant chamber. The same operated rats took many more trials to reach criterion when subsequently compared with the same control group in a T-maze. This finding demonstrates that variants of delayed alternation are not equivalent for animals with lesions in the prefrontal system. Observations suggested that delayed alternation in the operant chamber may be mastered by positional mediation.

Animals↗
PubMed1985

The prefrontal 'cortex' in the pigeon. Biochemical evidence.

Concentrations of dopamine and noradrenaline were determined in 6 regions of the telencephalon and in the cerebellum of the pigeon. Noradrenaline was rather evenly distributed. A significant variation was found of the dopamine-noradrenaline ratio (DA:NA), a measure which makes it possible to distinguish dopamine found in dopaminergic fibers from dopamine which is precursor of noradrenaline. The highest ratio was found in the anteroventromedial region (containing the presumed homologue of the mammalian neostriatum), and the next highest in the posteroventrolateral region (containing the archistriatum). Like in mammals, the lowest concentration of the non-precursor dopamine in the pigeon brain seems to be contained in the cerebellum. Among the regions which show physiological and anatomical similarities with the mammalian cerebral cortex, the DA:NA ratio was significantly higher in the posterodorsolateral, than in the posterodorsomedial and anterodorsomedial regions. The two dorsomedial regions contain the equivalents of the hippocampus and sensory cortical areas of mammals. The strong dopamine innervation of the posterodorsolateral region is comparable to that of the mammalian prefrontal cortex.

Animals↗
PubMed1985

The prefrontal "cortex" in the pigeon catecholamine histofluorescence.

The prefrontal cortex of mammals is densely innervated with dopaminergic fibers. We report a comparable, dense network of catecholamine (probably dopamine)-containing fluorescent fibers in the posterodorsolateral neostriatum of the pigeon. This region is clearly separable from paleostriatum augmentatum, lobus parolfactorius, posterior archistriatum, posteromedial corticoid and septum, all of which also show strong catecholamine fluorescence. Parallel biochemical, anatomical and neurobehavioral data support the suggestion that posterodorsolateral neostriatum in the pigeon may be comparable to the mammalian prefrontal cortex. Thus the telencephalic tissue represented as the prefrontal cortex in mammals and the posterodorsolateral neostriatum in the pigeon, may turn out to be a phylogenetically ancient neural device.

Animals↗
PubMed1984

Focal cortical seizures prevent HRP and HRP-WGA labeling only in neurons bidirectionally connected to the cortex.

Intracortical implants of polyacrylamide gel containing horseradish peroxidase labeled cortical efferents and perikarya in some cortical areas and a number of subcortical formations. When epileptogenic penicillin was added to the gel, no labeling was seen in the efferents and cell bodies of the cortex, thalamus, or claustrum, whereas the magnocellular nuclei of the basal forebrain, raphe nuclei and locus coeruleus did contain the label.

Animals↗
PubMed1984

The monocular and binocular subfields of the rat's primary visual cortex: a quantitative morphological approach.

Primary visual cortex in the rat was studied by a variety of methods: transsynaptic transport of labelled amino acids, 2-deoxyglucose, and staining for perikarya, myelin, and acetylcholinesterase. The analysis was aided by a computer-controlled television image analyzer. The results obtained with different methods agree with one another in describing the position and extent of the entire primary visual cortex as well as its monocular (medial) and binocular (lateral) subareas.

Acetylcholinesterase↗
PubMed1984

Catecholamine microfluorometry of nigral perikarya and tyrosine hydroxylase assay in some telencephalic structures of rats exposed to different behavioral situations.

In an earlier attempt to detect biochemical changes in the prefrontal system of rats performing a task sensitive to prefrontal damage, significant changes in amount of synaptic proteins were found only in the prefrontal cortex and only in the yoked control group. In a similar experimental paradigm, we measured presently activity of tyrosine hydroxylase in several telencephalic formations and intensity of dopamine fluorescence in neurons of the substantia nigra. The neurons in the medial and anterior portion of the substantia nigra of all experimental groups fluoresced significantly stronger than those in the lateral and posterior portions. The activity of tyrosine hydroxylase was 3-4 times higher in the medial prefrontal area than in the occipital cortex. No significant behavior-induced changes were detected in either of these variables. These results-in turn (1) demonstrate an unexpectedly strong dopamine concentration in the nigral neurons which innervate the prefrontal target of the neostriatum; (2) support the evidence of a strong dopaminergic innervation of the prefrontal cortex; and (3) indicate that the dopaminergic transmission in the prefrontal system was not affected by presumed activation of the system to a degree detectable by the presently used methods.

Animals↗
PubMed1984

The neostriatum viewed orthogonally.

The work described in this paper suggests that: (1) the neostriatum (a tier of the forebrain) is functionally heterogeneous, i.e. different neostriatal regions mediate responses in different situations; (2) regional specialization may be attributed to selective cortico-neostriatal connections, as indicated by anatomical and neurobehavioural evidence and studies with 2-deoxyglucose; (3) cortical areas and their corresponding principal neostriatal regions are organized 'in series'; (4) small lesions which cause severe but specific 'cognitive' effects do not induce movement disorders; (5) the transmitter of the cortico-neostriatal connections is glutamate. This work and other evidence suggests that the forebrain consists of systems that each contain a 'specific' thalamic nucleus and its associated cortical area and neostriatal region. This view, with three additional assumptions, can tentatively explain not only experimental neurobehavioural results but also certain symptoms of diseases involving the neostriatum.

Animals↗
PubMed1984

Neostriatal participation in prosencephalic systems: evidence from deoxyglucose autoradiography.

Epileptic foci, produced by small intracortical injections of penicillin, increased the uptake of 2-DG not only in the injected cortical area but also in a number of other formations. Each cortical focus coactivated specific portions of the striatum and thalamus. In certain instances, activation was found also in some other formations. These data suggest that each cortical area is related to a separate subcortical system consisting at least of specific parts of the striatum and the thalamus. The cortex-related heterogeneity of the striatum has been previously demonstrated in neurobehavioral experiments.

Animals↗
PubMed1983

Two levels of functional heterogeneity of the neostriatum.

Autoradiography following administration of 2-deoxy-[14C]glucose has shown that penicillin-induced epileptic foci in the cerebral cortex selectively coactivate associated neostriatal regions. The present material demonstrates that this coactivation may appear in patches in the rat neostriatum. Activity from a cortical area seems to spread first to islands of the associated neostriatal region and may either spread gradually to the surrounding 'matrix' or not involve the 'matrix' for tenths of minutes. The regionally restricted functional patchiness lends additional support to the notion that the neostriatum, like the neocortex, can be divided into regions which consist of modules.

Animals↗
PubMed1983

Activity of the auditory system in rats habituated to a test chamber: a 2-deoxyglucose study.

In a number of species, quantitative 2-deoxyglucose method revealed that the auditory system is much more active than any other-neural system. We tested the hypothesis that stressful experimental conditions may be responsible for this hyperactivity. Three rats received transcatheteral injections of [14C] 2 deoxyglucose while exposed to a wide band noise in a sound-shielded chamber in which they had previously spent 17 habituation sessions. In autoradiograms of these animals the auditory system appeared as intensely labelled (active) as in control animals. We conclude that the high activity of the auditory system in the rat does not seem to result from presumably stressful normal laboratory conditions.

Animals↗
PubMed1982

Synaptic proteins in frontal and control brain regions of rats after exposure to spatial problems.

Synaptic proteins D1, D2, D3, synaptin and 14-3-2, as well as the glial protein glutamine synthetase, were measured by crossed immunoelectrophoresis in the anteromedial (prefrontal) cortex, occipital (visual) cortex and the anterior and posterior parts of the neostriatum of rats. The 3 experimental groups consisted of rats trained to criterion in a spatial delayed alternation, those run as yoked controls and, finally, rats kept in individual cages and not subjected to any training. Statistical analysis showed that two variables: behavioral procedures and brain regions, had a significant effect. Their interaction was also significant. Further analysis revealed that only in the prefrontal cortex of the yoked control animals was there a significant decrease of the synaptic membrane proteins D1, D2 and D3. Thus, particular behavioral treatment seems capable of affecting synapses in a specific 'association' cortical area. The change is more easily related to the amount of 'work' than to formation of 'memory trace' within the critical area.

Animals↗
PubMed1982

The prefrontal 'cortex' in the pigeon. Behavioral evidence.

In 3 pigeons ablation of the posterodorsolateral neostriatum impaired delayed alternation without affecting visual discrimination. In mammals the same selective deficit is produced by lesions in the prefrontal system. The presently ablated neostriatal region resembles the mammalian prefrontal cortex also by being richly innervated with dopaminergic fibers. This region is clearly separated from paleostriatum augmentatum and archistriatum which also have a strong dopaminergic innervation. The presence of a prefrontal cortex-like formation in a bird species raises the possibility that all higher vertebrates are equipped with this neural device.

Animals↗
PubMed1982

Activation pattern in the prefrontal system of kainic acid-pretreated rats.

The aim of the present experiment was to find out whether lesions in the prefrontal system, produced with kainic acid (KA) would disrupt the pattern of activation of the prefrontal system, determined by the deoxyglucose technique. The activation was induced by injections of penicillin into the prefrontal cortex. There was no difference between the pattern previously described in rats with intact brains and that seen in the present animals pretreated with kainic acid. Thus, the doses of KA which destroy some neurons in the prefrontal system do not interfere with the spread of epileptic activity throughout this system.

Animals↗