Thalamic relay of somatic and visceral signals to the orbital cortex

We investigated the role of different thalamic nuclei in the relaying of afferent signals into the anterior section of the coronary gyrus and into the orbital gyrus, using the evoked-potentials method, in delicate experiments on cats under Nembutal or Nembutal-chloralose narcosis, and also in experiments on cats not anesthetized but immobilized by injection of succinyl choline. Specific projection zones of the lingual, vagus, and glosso-pharyngeal nerves have been charted in the anterior coronary gyrus. The thalamic relay for that region is the medial pole of the ventral posterior nucleus. The orbital gyrus contains associative projections of both somatic and visceral nature. The relay for signal transmission in this region is also located in the ventral posterior nucleus. Relaying takes place, however, not in the central parts of the nucleus, where projections of the corresponding receptor zones have been charted, but nearer its lower medial surface. There is also an indirect route for associative projections, passing through the medial center and the intralaminar nuclei. That route emerges into the cortex through the ventral anterior and reticular nuclei. A feature of the projections of the vagus nerve in the orbital cortex is the existence of a supplementary region that exhibits responses, lying along the sulcus rhinalis. It was found that relaying for that region takes place in the ventral medial and submedial nuclei of the thalamus.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 65–72, July–August, 1969.     

Unit responses of the cat lateral geniculate bodies to visceral and somatic stimulation

Acute experiments on cats anesthetized with pentobarbital and immobilized with Diplacin or Listhenon showed that electrical stimulation of the vagus, splanchnic, pelvic, and sciatic nerves and also of the mesencephalic reticular formation induces either a prolonged change in the frequency of unit activity or phasic responses of single units of the lateral geniculate body. During stimulation of the visceral nerves tonic changes in unit activity were predominant, whereas phasic responses were found more often during somatic stimulation. Most neurons tested responded to all types of stimulation used and only 15–18% responded only to the specific stimulus: photic stimulation of the receptive field. The results suggest that interaction of visceral, somatic, and sensory-specific excitation takes place on single neurons of the lateral geniculate body.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Ivano-Frankovsk Medical Institute. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 246–252, May–June, 1973.     

Habituation in the somatosensory cortex

Responses of neurons without spontaneous activity ("silent") to prolonged stimulation of the mesenteric nerves were studied in cats anesthetized with chloralose (65–70 mg/kg) and immobilized with flaxedil. The results showed that neurons of the association and primary projection areas are characterized by habituation to prolonged stimulation of visceral nerves. The rate of development of habituation depends on the parameters of stimulation and on the cortical region studied. Habituation developed more rapidly in the association area and was slower to develop at the focus of maximal activity of the second somatosensory area. The special features of cortical habituation during visceral stimulation are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 412–418, September–October, 1979.     

Organization of the visceral afferent representation in the cerebral cortex

In experiments on cats which had been narcotized with chloralose and immobilized with myo-relaxants, we have studied cerebral cortical responses to stimulation of the visceral system. A peculiarity of the visceral afferent representation is the fact that the convergence of visceral and dermomuscular impulses is achieved with predominance of somatic signals in the cortical zones of visceral representation, with the exception of the focus of maximal activity (FMA). A second peculiarity is the fact that the visceral afferent systems develop habituation to prolonged stimulation. The principles of this development are similar to the general principles described in the literature for other sensory systems.     

Topical organization of somatic projections in the fur seal cerebral cortex

To map somatic projections in the cerebral cortex of the fur sealCallorhinus ursinus multiple spike activity of cortical neurons evoked by tactile stimulation of different parts of the body surface was recorded in acute experiments. The region of somatic representation is bounded rostrally by the postcruciate and coronal sulci, caudally by the anterior suprasylvian sulcus, and dorsomedially by the ansate sulcus. The somatotopic map is oriented so that the projection of the head faces ventrolaterally, and that of the caudal part of the trunk faces dorsomedially; the projection region of the forelimb is buried in the coronal sulcus. The projection area of the head occupies the greatest area, and in it, the greatest area is occupied by the region of the superior labial vibrissae.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 344–351, May–June, 1985.     

Features of the organization of the cerebral cortex bioelectric potentials and visceral state in neurotic depression

Studies were conducted with the participation of 20 patients with different classical variants of neurotic depression. The spatial organization of the bioelectrical activity of the brain was studied with the method of cross-correlation and coherent analysis. The autonomic-visceral state was assessed by the results of the auricular cryoreflex test (measurement of the cold sensibility of auricular points). The clinical picture of neurotic depression was shown to be reflected in the structure of the EEG spatial organization, which is modified depending on the degree of neurotic depression and the concomitant anxiety and asthenic syndromes. In the group with depressive syndrome without concomitant asthenic or anxiety manifestations, most changes were revealed in the right frontotemporal-left posterotemporal region. A cross-correlation and coherence decrease in the frontotemporal regions of both hemispheres and markedly increased cross-correlations in the right posterotemporal region were revealed in the depression + associated anxiety group. In the group where the depressive and anxiety syndromes were associated with marked asthenic manifestations, decreased cross-correlation and coherent relations in the frontotemporal regions of both hemispheres were observed. The clinical picture of neurotic disorders is reflected in a specific pattern of variations in the spatial organization of electrical activity of the cerebral cortex and in variations in the autonomic visceral state parameters. The development of negative emotional states in humans is accompanied by changes in the visceral functions. Variations in the central brain structures involve the zones of representation of emotional reactions and the zones of cortical representation of the organs. Insignificant central variations may cause autonomic dysfunction.     

Adenosine-receptor-mediated stimulation of low-Km GTPase in guinea-pig cerebral cortex.

Inhibition of receptor-coupled adenylate cyclase by hormones is proposed to be associated with GTP hydrolysis. Since adenosine inhibits cerebral-cortical adenylate cyclase via A1 adenosine receptors, the present study attempts to verify this mechanism for A1-selective adenosine derivatives. In guinea-pig cortical membranes N6-(phenylisopropyl)adenosine (PIA) increased the Vmax. of the low-Km GTPase, with an EC50 (concentration causing 50% of maximal stimulation) of about 0.1 microM, and the stimulatory effect was competitively antagonized by 5 microM-8-phenyltheophylline. The rank order of potency of the stereoisomers of PIA and of 5-(N-ethylcarboxamido)adenosine (NECA) to stimulate GTPase correlated with their ability to inhibit adenylate cyclase activity (R-PIA greater than NECA greater than S-PIA). Competition binding studies with (-)-N6- ([125I]iodo-4-hydroxyphenylisopropyl)adenosine suggest that adenylyl imidodiphosphate (p[NH]ppA), an essential component of the GTPase assay system, is a more potent A1-receptor agonist than ATP, with an IC50 (concentration giving half-maximal displacement of radioligand binding) of 7.9 microM. On the basis of the p[NH]ppA concentration used in the GTPase assay (1.25 mM), enzyme stimulation by adenosine seems to be highly underestimated. Nevertheless, adenosine-induced GTP hydrolysis reflects an increased turnover of guanine nucleotides at the Ni regulatory site and appears to be a crucial step in the sequence of events processing the inhibitory signal to adenylate cyclase.     

Habituation rules for a theory of the cerebellar cortex

A quantitative model of cerebellar cortical function is described with a complete formalization based on (i) the topology of cerebellar cortical neuronal network, (ii) some particular synaptic properties of cell classes in cerebellum cortex, and (iii) the dynamics of excitation in this network. For (i), a construction of functional classes around one Purkinje cell is given and their existence is discussed. For (ii), as in Marr-Albus model, the modifiability of synapses between parallel fibres and Purkinje cell is assumed. But the formalization permits to consider the consequences of such a property at the level of glomerulus (with granule cells) which is known as a complex transformation system. For (iii) habituation rules are assumed. It is shown that this method leads to some interesting properties in the functioning of cerebellar cortex. Particularly, emitting frequency along a Purkinje cell axon results from a discrimination by the system between transformed input signals and an external noise due to all other contexts, and learning could be considered as the result of a conflict between a set of patterns and the transformed input signals. This model could be a basis for future numerical simulations.     

Habituation in the rabbit visual cortex during development and after septal ablation

In chronic experiments on adult rabbits with injury to the septum pellucidum and on newborn rabbits the dynamics of evoked responses to repeated flashes was studied. Experimental blocking of the hippocampal theta-rhythm by electrolytic destruction of the medial septum is followed by marked facilitation of habituation of the primary responses. This process takes place twice as fast in rabbits with damage to the septum as in intact animals. Very rapid habituation of the primary responses was observed in newborn rabbits before acquiring vision and in rabbits with vision but under the age of 15–16 days, after 10–20 presentations of the stimulus. When the animals reached this age the time required for habituation increased sharply. Starting from the age of 17 days, the primary responses of the animals were just as stable as in normal adult rabbits. The significance of the hippocampal theta-rhythm as a factor preventing the development of habituation is discussed.Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 123–129, March–April, 1972.