Electrographic manifestations of "falling asleep" in isolated cat cortex]

Experiments were conducted on unrestricted cats; a study was made of the electrical activity of the neuronally isolated cortex during the wakeful hours and sleep. Transition from wakefulness to sleep was accompanied in the isolated cortex by the manifestations of drowsiness accompanied by the corresponding changes in the electrocorticogram of the isolated hemisphere. Electrographic manifestation of drowsiness in the isolated cortex depended on the time lapse after the operation and was mostly pronounced during the late period after the isolation of the cortex.     

Evoked impulse activity in neuronally isolated cortex

The reactions of neurons of the isolated cortex of one hemisphere to direct cortical stimulation were investigated in cats under Nembutal anesthesia. Isolation of the cortex was carried out by Khananashvili's method [10]. It is shown that phasic reactions develop in the isolated cortex in response to such stimulation: initial discharge, initial pause, first after-discharge, first after-pause, late after-discharges and pauses, as well as reactions of presumably inhibitory neurons. A majority of the cells (85%) which manifest background activity respond to direct electrical stimulation, and the frequency of the late after-reactions is twice as great as in the intact cortex. It is concluded that cortical elements of the isolated cortex retain their principal neurophysiological properties.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 236–244, May–June, 1971.     

Manifestation of integrative activity in the neuronally isolated cortex]

By the slow bioelectrical activity parameter, with vector representation of experimental data, an attempt was made to reveal elements of integrative activity in the neuronally isolated cortex at early stages after its isolation from subcortical formations. Animals with an intact cerebral cortex were used as controls. It has been found that in spite of isolation of the cerebral cortex from synaptic influences of the subcortical structures, it possesses even at early stages after isolation (10--17th day) its own mechanisms of integrative activity, providing for the organization of background and evoked activity which are gradually normalized by the 30th to 40th day, without however reaching the level of activity of the intact cerebral cortex.     

Regional variations in spontaneous unit activity in the neuronally isolated cortex

Unit activity of the visual, auditory, and association areas of the neuronally isolated cortex of one hemisphere was studied in acute experiments on cats (the method was described previously [5]). A few hours after operation, the same types of spontaneous unit activity are observed in the isolated cortex as in the intact cortex under identical experimental conditions. Unlike in the normal cortex, most cells in the neuronally isolated cortex discharge regularly. Spontaneously active cells are two or three times fewer in the isolated cortex than in the intact. The distribution of active cells by depth in the neuronally isolated cortex varies from one region to another.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 475–481, September–October, 1970.     

Dynamics of axonal degeneration in the neuronally isolated cerebral cortex]

The brains of 11 cats were studied after unilateral isolation of the cortex after M. M. Khananashvily (1961) by means of resection of the projection fibres connecting the cortex with subcortical formations. The character and peculiarities of axonal degeneration in the large hemisphere cortex, were investigated after Nauta and Fink--Heimer. It was found that distribution of degenerating terminals in every layer depended on the time when the material was taken for investigation. Maximal concentration of the degenerating fibres was observed 3--5--10 days after the operation, then a gradual decrease in density of degeneration in every cortical layer was observed. By the 9th month after the operation, the processes of axonal degeneration completely came to their end. The problem of retrograde and anterograde nature of the axonal degeneration in the cortex of the large hemispheres was discussed in the article and it was demonstrated that in the field 4 of the neuronally isolated cortex it is of mixed nature.     

Asymmetry of the electroencephalographic manifestations of REM and slow-wave sleep in the cat

Studies were carried out on cats by bipolar electrodes implanted into symmetrical points of somatosensory cortical areas, caudate nuclei, hippocampus, lateral geniculate bodies, reticular formation of the midbrain after section of the half of midbrain tegmentum and commissural systems of the brain. Animals with sections usually have asymmetry of sleep EEG. The phenomenon is revealed of the coexistence of slow-wave and paradoxal sleep in different brain halves.     

Regional features of background electrical activity and of direct cortical response by the intact or neuronally isolated cortex

Background electrical activity and thresholds for the appearance of direct cortical responses (DCR) were studied in acute and chronic experiments on cats in some gyri of the intact and neuronally isolated cortex (the whole cortex was subjected to neuronal isolation [10]). It was determined that in intact animals the suprasylvian gyrus, particularly its central part, differs by its higher electrical activity and lower DCR thresholds from the ectosylvian gyrus. These differences are retained after neuronal isolation of the cortex from the subcortical structures. Hence the differences found in the neurophysiologic characteristics of the gyri under study reflect specific properties and are not mediated by subcortical neural effects.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 52–58, January–February, 1970.     

Cholinergic neurons in an association cortex slab chronically isolated from the cat

Small numbers of short- and long-axon cholinergic interneurons were revealed on a slab of association cortex three weeks after (neuronal) isolation from the cat by means of a histochemical acetylcholinesterase reaction. Short-axon neurons are located at layers II–VI and take the form of mainly spindle-shaped medium sized cells with their axons forming synaptic terminals on pyramidal and stellate neurons of the isolated section. Typical positioning of cholinergic terminals on the perikaryon and proximal portions of cholinoceptive neuron dendrites was noted. Pyramidal cholinoceptive cells may be classed as noncholinergic cells, whereas stellate cells may be either cholinergic or noncholinergic. Long-axon cholinergic interneurons of different shapes and sizes are situated at layers I and VI. Neuronal axons located in these layers run within fibers of the first and subcortical layers, establishing intracortical connections beyond the confines of the isolated section.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 60–66, January–February, 1989.     

The effects of sleep on neurons in isolated cerebral cortex.

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8--12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural discharge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the model interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.     

Neuronal responses in an isolated slab of the cat auditory cortex to intracortical stimulation

Neuronal responses in an isolated slab (area AI) to intracortical pulsed electrical stimulation at the level of layer IV were investigated extracellularly in acute experiments on cats immobilized with D-tubocurarine. Responding neurons were found in all layers of the slab. The character of their distribution by depth in the slab depended on the distance between recording and stimulating electrodes. The latent period of responses of different neurons ranged from 0.8 to 25 msec. With interelectrode distances of 0.5–2 mm most neurons responded mono- and disynaptically. However, responses of many neurons had a latent period of over 4 msec, i.e., they were polysynaptic. This indicates the complex character of interneuronal interactions, even in a limited area of the cortex. After intracortical stimulation no after-discharges with a latent period of over 40 msec could be recorded in the isolated slab of auditory cortex.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 85–93, January–February, 1982.