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I Divac

Publications and source records attributed to I Divac.

At least 73 records · Page 4Linked to original sources
PubMed1980

Functions of the neostriatum: cortex-dependent or autonomous?

Studies of animals with ablations of varying amounts of the neocortex, the neostriatum, or both, are reviewed in an attempt to establish to which extent functions of the neostriatum are dependent on its cortical input. Scarce and inconclusive evidence does not allow firm conclusions. It seems well established that the neostriatum shares some functions with the neocortex. In the rat and infant monkeys these striatal functions appear to be cortex-independent, whereas in cats and adult monkeys they seem to be more cortex-dependent. It is possible, and even likely, that the neostriatum also has functions which are not shared with the cortex and which are cortex-independent. The degree to which the neostriatum is able to contribute to the integration of behavior in the absence of its cortical input is species- and age-specific.

Animals↗
PubMed1979

Cortical afferents to the prefrontal cortex of the cat: a study with the horseradish peroxidase technique.

Following horseradish peroxidase (HRP) injections into different areas within the prefrontal cortex (PFC) of the cat, labeled neurons were found in the cingulate and insular cortex. These results demonstrate that the cat's prefrontal cortex is reached directly from these cortical regions, and that the observed cortical projections are similar to those detected in the monkey's prefrontal cortex.

Animals↗
PubMed1978

Behavioral and anatomical consequences of small intrastriatal injections of kainic acid in the rat.

The effects of bilateral injections of kainic acid into the anteromedial neostriatal region were examined behaviorally and anatomically in two groups of rats. Behaviorally, kainic acid injections resulted in a severe impairment of delayed alternation retention, while the ability for visual discrimination remained unaffected. Anatomically it was found that axons traversing the injected area remain able to transport horseradish peroxidase. Furthermore, histological examinations of the injected regions revealed a heavy loss of neurons and a decrease of histochemical staining for specific acetylcholinesterase. Silver impregnation showed slightly disorganized, but continuous, axons in bundles of the capsula interna. On the other hand, the axonal network throughout the neuropil of the injected area was markedly diminished. No conspicuous change was found in myelin staining or in the intensity or catecholamine fluorescence. The anatomical results suggest that kainic acid appears to affect only perikarya of the neostriatum and the axons originating from these perikarya, whereas passing axons seem to remain intact. Thus, the observed behavioral impairment must be attributed to changes in the neostriatum itself. It is concluded that the neostriatum has 'complex' or 'cognitive' functions and that some mental symptoms in Huntington's chorea may be attributed to a dysfunction of this part of the brain.

Animals↗
PubMed1978

The prefrontal cortex of the cat: anatomical subdivisions based on retrograde labeling of cells in the mediodorsal thalamic nucleus.

Different areas of the frontal cortex of the cat were injected with small amounts of horseradish peroxidase. The region of labeled cells in the mediodorsal nucleus of the thalamus (MD) were related to the injected areas. Distinct relations between subdivisions of MD and of the prefrontal cortex were established: a rather large central sector of MD projects to the gyrus proreus and the anterior parts of the gyri sigmoideus, rectus, and frontalis. A narrow lateral band of anterior MD neurons projects predominantly to an area on both sides of the sulcus praesylvius, whereas a postero-lateral band sends fibers to a region on the ventral anterior sylvian gyrus. The area between the presylvian sulcus and the sylvian gyrus is apparently free of MD afferents, but not of other thalamic afferents. A fourth sector of MD, situated dorsomedially, projects to the middle parts of the gyri rectus and frontalis. And a fifth sector, located ventrally to the dorsomedial MD sector, projects to the ventral part of the gyrus rectus. The established subfields of MD and of the prefrontal cortex are discussed with respect to previous anatomical research in the cat.

Afferent Pathways↗
PubMed1978

Converging projections from the mediodorsal thalamic nucleus and mesencephalic dopaminergic neurons to the neocortex in three species.

Previous studies in the rat have shown that the neocortical dopaminergic afferents, originating in the mesencephalon, terminate in those areas of the frontal lobe which receive projections from the mediodorsal thalamic nucleus i.e., the prefrontal cortex. In order to clarify whether this overlap is accidental for the rat or a consistent feature of several species we have compared the projection areas of the ventral tegmental area and the mediodorsal thalamic nucleus in three species, rat, opossum and tree shrew, using HRP injections in combination with glyoxylic acid histofluorescence method. The results have shown, first, that the area innervated by the mediodorsal nucleus of the thalamus is localized in a different part of the frontal lobe in each species: dorsolateral in the opossum, anteromedial, polar and suprarhinal in the rat and frontopolar in the tree shrew. Secondly, this area alone in each species receives projections from the ventral tegmental area. Thirdly, this area alone receives a dense innervation in the deep cortical layers by fluorescent fibres probably containing dopamine. The neighbouring neocortical areas receive afferents neither from the mediodorsal nucleus of the thalamus nor from the ventral mesencephalic tegmentum; their catecholamine innervation is mainly confined to the superficial layers and appears to be of noradrenergic nature. Although the techniques used did not allow a precise determination of the borders of the two projection areas and, therefore, the exact degree of overlap, it appears that mesencephalic dopaminergic innervation is a characteristic feature of the prefrontal cortex in the mammalian brain.

Animals↗
PubMed1977

Heterogeneous afferents to the inferior parietal lobule of the rhesus monkey revealed by the retrograde transport method.

The sources of afferent connections to the inferior parietal lobule (rostral part of the area 7 of Brodman; PF and rostral part of PG of von Bonin and Bailey) were examined with the retrograde transport method in infant and adult rhesus monkeys. Two to 3 days after injections of horseradish peroxidase (HRP) into the cortex, the animals were anesthetized, and the brains fixed and processed for the histochemical demonstration of the enzyme marker. Labeled neurons were found in layer III in the ipsilateral prefrontal, parietal, occipital and temporal cortices, notably in areas 5, 19, 22 and 46 of Brodmann, and in area 7 of the contralateral parietal cortex. In the thalamus, HRP-positive cells were located ipsilaterally in the medial pulvinar nucleus in the nuclei centrum medianum and parafascicularis, as well as in the rostral thalamus, lateral and medial to the mammillothalamic tract, in the nucleus ventralis anterior and nucleus paracentralis. Numerous labeled cells were also identified in the magnocellular nuclei of the basal forebrain, in the dorsal and medial raphe nuclei, and in the locus coeruleus. Most of the cells in these regions were located in the hemisphere ipsilateral to the injections, but a number of them were also found in the contralateral hemispher. In adult monkeys, brownish granules in the cytoplasm of some cells were interpreted as endogenous pigment or due to various pigment precursors. However, all 14 locations listed above were identified in the infant monkey in which endogenous pigment was not a confounding factor.

Animals↗
PubMed1977

Possible pathogenesis of Huntington's chorea and a new approach to treatment.

Recent identification of glutamate as a transmitter in neocortical efferents and discovery of toxic effects of excessive amounts of extra-cellular glutamate or its analogues on some brain neurons offer an explanation of the pathogenesis of Huntington's chorea. Cell death as well as consequent biochemical changes and clinical symptoms in this disease possibly result from excessive excitation of the neostriatal, and of some other neurons by glutamate released from neocortical axon terminals. If so, the development of Huntington's chorea could be prevented or arrested by blockers of glutamate transmissions, and folate should be reduced to the minimum in the diet of the genetically marked families.

Brain↗
PubMed1976

Time-discrimination performance in cats with lesions in prefrontal cortex and caudate nucleus.

Cats were trained on a time-discrimination task in which different periods of bodily confinement served as discriminanda for go-left/go-right responding. Lesions of gyrus proreus or the associated anteroventral part of nucleus caudatus impaired relearning in this situation. After reacquisition, animals with caudate lesions received proreal ablations and animals with cortical damage received caudate lesions; both additional lesions caused reappearance of the deficit. The absence of external stimuli to signal locus of reinforcement at the moment of spatial choice may have been crucial for eliciting the deficit. The data support the notion that the prefrontal cortex and the anatomically related part of the caudate nucleus participate in similar behaviors.

Animals↗
PubMed1976

Discrimination of time intervals in cats.

Fourteen cats were trained to discriminate between 5 and 20 s periods of confinement as evidenced by differential responding to two feeders. In a subsequent titration procedure the cats discriminated 5 from 10 or even 8 s. Positional mediation of correct responses was observed only in some animals. The present task may complement the classical and operant conditioning situations in which the temporal distribution of responses reflects the animals' abilities for both time discrimination and response inhibition.

Animals↗