Morphological characteristics of callosal neurons of the cat primary auditory cortex (AI)

Cortical stratification of neurons forming callosal projections to the primary cortical area (AI) was investigated in cats using horseradish peroxidase axonal transport techniques. The population of area AI callosal neurons was found to be composed of several groups of cells. The group comprising around 60% of all callosal neurons of this area consists of large layer III pyramidal neurons. Callosal neurons belonging to this layer have a mean perikaryon profile area of 261.8±8.2 µm²; they account for 22% of all cells found in the layer. The second group, comprising 27% of all area AI callosal neurons, was largely made up of large layer V and VI cells; these could not be classed as pyramidal neurons due to the shape of their somata and the geometry of their dendritic arborization. Perikaryon profile in these nonpyramidal neurons occupied an area of 250.3±8.4 µ². No callosal neurons were observed in layer I. These account for 6 and 7% of total numbers of callosal neurons of area AI in layers II and IV. Callosal neurons were found to form projections to all layers of area AI in the contralateral hemisphere. Highest density of callosal fiber endings was observed in layers II and III.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 249–256, March–April, 1990.     

Nitric oxide contributes to the spinal nociceptive processing

NADPH-diaphorase-containing neurons (it is supposed that this enzyme is a form of NO-synthase, NOS) were histochemically identified in the spinal cord of rats. In another set of the experiments, we identified neurons -sources of spinothalamic and spinomesencephalic pathways - by their retrograde labelling with Fluoro-Gold (FG) injected into the thalamus and periaqueductal gray substance. It was shown that NOS-containing spinal cells are, as a rule, propriospinal intersegmental or intrasegmental interneurons. We discuss the possible involvement of these cells in the “inhibition-of-inhibition” processes and in potentiation of the synaptic transmission in spinal neurons under conditions of the development of tonic or chronic pain. In rats, the number of NOS-containing neurons, which are also retrogradely labelled with FG after dye injection into the thalamus and midbrain, Is rather limited.     

Caudatonigral projections under normal conditions and after an MPTP-induced lesion of the cat nigrostriatal system: Quantitative ultrastructural analysis

Ultrastructural and morphometric studies of caudatonigral synapses located on the nigrothalamic neurons were carried out on intact and N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated adult cats. Three types of synapses with different ultrastructural features were found. Morphometric analysis showed that 11.3% of analyzed junctions were caudatonigral synapses; 5.9% and 5.4% of them were located on the somata of nigrothalamic neurons and on their dendrites respectively. Among axo-somatic synapses, the caudatonigral ones amounted to 11.9%: 7.6% were type-I synapses and 4.3% belonged to type-III synapses. Both types had symmetrical contacts and could be considered inhibitory. Caudatonigral axodendritic synapses amounted to 10.6%: 3.2% were of type I; 4.2%, of type III; and 3.2%, of type II synapses with asymmetric contacts. The labelled type-II synapses were found exclusively on the nigrothalamic dendrites. The ultrastructural changes and the statistically significant decrease in the size of caudate axon terminals following the MPTP treatment took place only in the type I exosomatic synapses. It is suggested that the development of motor disorders in the cat after experimentally induced striatal dopamine insufficiency is due to the decrease in the efficacy of caudatonigral influences, which causes disinhibition of GABA-ergic inhibitory nigrothalamic neurons, and to enhanced influences of the latter on the cells of the motor thalamic nuclei.Neirofiziologiya/Neurophysiology, Vol. 26, No. 2, pp. 150–156, March–April, 1994.     

Distribution of horseradish peroxidase-labeled neurons giving rise to descending fiber systems in the basal ganglia and hypothalamus in cats

The distribution of neurons giving rise to various descending fiber systems to brain-stem structures in the basal ganglia (including amygdaloid nuclei) and hypothalamus of the cat was studied by the retrograde axonal transport of horseradish peroxidase method. Neurons in the medial part of the central nucleus and of the magnocellular part of the basal nucleus of the amygdaloid group were shown to send axons to the dorsal hippocampus, substantia nigra, lateral part of the central gray matter, and the mesencephalalic reticular formation and also to the region of the locus coeruleus and the lateral medullary reticular formation at the level of the inferior olives. The predominant source of projections to the hypothalamus and brainstem structures is the central amygdaloid nucleus, which also sends projections to the nucleus of the tractus solitarius, the dorsal motor nucleus of the vagus nerve, and the superior cervical segments of the spinal cord. Uncrossed fiber systems descending from the basal ganglia terminate at the level of the pons, whereas uncrossed and crossed fiber systems descending from the dorsal and ventromedial hypothalamus can be traced into the spinal cord. The possible role of nuclei of the amygdaloid group, the hypothalamus, and their efferent projections in the regulation of somatic and vegetative functions and also of complex behavioral reactions is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 14–23, January–February, 1981.     

Afferent connections of the cat caudate nucleus studied by the retrograde axonal transport method

Sources of direct and indirect afferent connections of the caudate nucleus were investigated in cats by the retrograde axonal transport of horseradish peroxidase method. Different parts of the neocortex were shown to form different types of projections to the caudate nucleus; the sources of these projections have a laminar organization. Connections of the globus pallidus with the caudate nucleus, not previously described, were found. Among the sources of the thalamo-caudate projections, besides nuclei of the intralaminar complex, an important place is occupied by the ventral anterior and mediodorsal nuclei. After injection of horseradish peroxidase into the caudate nucleus, retrograde axonal transport of the enzyme was observed in the caudal direction, as far as cells of the locus coeruleus. ON the basis of these results a general scheme of afferent projections to the caudate nucleus is drawn up, including its connections with the spinal cord mediated by the thalamic nuclei and mesencephalic reticular formation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 146–154, March–April, 1980.     

Morphology of the cat auditory cortex

The ultrastructural features of the primary auditory cortex of the cats and the character of the endings of geniculo-cortical afferent fibers in the early stages of experimental degeneration evoked by destruction of the medial geniculate body were studied. In all layers of the cortex asymmetrical synapses with round synaptic vesicles on dendritic spines and on thin dendritic branches of pyramidal and nonpyramidal neurons are predominant. Symmetrical synapses with flattened or polymorphic vesicles are distributed chiefly on the bodies of the neurons and their large dendrites. Because there are few symmetrical synapses which could be regarded as inhibitory it is postulated that inhibitory influences may also be transmitted through asymmetrical synapses with round vesicles. Other types of contacts between the bodies of neurons, dendrites, and glial processes also were found in the auditory cortex. Degenerating terminals of geniculo-cortical fibers were shown to terminate chiefly in layer IV of the cortex on pyramidal and nonpyramidal neurons. Degeneration was of the dark type in asymmetrical synapses with round vesicles. The results are dicussed in connection with electrophysiological investigations of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 519–524, September–October, 1973.     

Effect of Inhibition of NO Synthases on Cardiogenic Depressor Reflexes in Different Animal Species

We studied the role of the nitric oxide (NO) system in the realization of cardiogenic depressor reflexes evoked by stimulation of cardiac receptors by veratrine (reproduction of the Bezold–Jarish reflex). Acute experiments were performed on anesthetized dogs and rats: we tested the effects of inhibition of dissimilar isoforms of NO synthase (NOS) and paid special attention to possible species-related differences in realization of the reflex responses. We found that systemic inhibition of NOS by L-nitro-N-arginine (L-NNA, 30 mg/kg, i.v.) significantly decreased the depressor reflex reaction in dogs. Vasomotor dilatatory reactions of the peripheral vessels underwent considerable modifications and in some cases were converted into vasoconstrictory responses. Selective inhibition of neuronal NOS (nNOS) by 7-nitroindazole (7-NI, 25 mg/kg, i.p.) exerted no effect on the development of cardiogenic depressor reflexes in dogs. At the same time, systemic inhibition of NOS in the course of reproduction of cardiogenic depressor reflexes in rats resulted in intensification of depressor responses, while inhibition of nNOS decreased these reactions. Thus, we first demonstrated the role of NO in the realization of cardiogenic depressor reflexes under in vivo conditions and described species-related peculiarities of the involvement of the NO system in the development of these reflexes. We also demonstrated the dependence of formation of cardiogenic depressor reflexes on the predominant involvement of one NOS type or another.     

Operant reflexes and expression of the <Emphasis Type="Italic">c-fos</Emphasis> gene in the amygdalar nuclei and insular cortex of rats

We studied manifestations of increased neuronal activity in the limbic structures of the rat brain related to realizations of operant reflexes by the animals. After rats had performed repeated operant foodprocuring movements, the mean numbers of Fos-immunoreactive neurons within sections of the central and basolateral amygdalar nuclei, insular cortex, substantia innominata, and paraventricular hypothalamic nucleus significantly exceeded the control values. In the ipsilateral (with respect to the working forelimb) central nucleus of the amygdala, the mean number of such neurons within a 40-μm-thick slice was nearly an order of magnitude greater than in the control (42.2 ± 2.4 and 4.5 ± 0.4 labeled units, respectively). In the agranular insular and granular/disgranular cortical zones at the contralateral site, the numbers of labeled neurons exceeded control values by about three times (94.6 ± 8.2 vs 31.6 ± 2.2 and 103.5 ± 4.5 vs 39.6 ± ± 2.4 immunopositive cells, respectively). These findings confirm the hypothesis on the direct involvement of the subcortical structures and limbic cortex zones in the control of somato-cardiovascular integration during the performance of operant reflexes by the animals.     

Discovery of the sources of some descending forebrain systems by the retrograde axonal transport of horseradish peroxidase method

The location of neurons forming fiber systems descending into the brain-stem reticular formation, red nucleus, and relay nuclei of the dorsal columns was studied in cats by the retrograde axonal transport of horseradish peroxidase method. The cortical projection regions, structures of the limbic system, and the hypothalamus were shown to form fiber systems that descend to the brain stem, whereas the orbito-frontal cortex is the chief source of cortico-reticular projections. The possible functional role of these descending systems in the central control of somatic and visceral functions is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 218–226, May–June, 1979.