State-dependent effects of some neuropeptides and neurotransmitters on neuronal activity of the medial septal area in brain slices of the ground squirrel, Citellus undulatus

Neuronal activity of the medial septal area was recorded extracellularly in brain slices taken from hibernating (winter) and waking (summer) ground squirrels. The effects of neuropeptides identified in the brain tissue of hibernators (Thr-Ser-Lys-Tyr, Thr-Ser-Lys-Tyr-Arg and Asp-Tyr) on the background activity and responses to electrical stimulation of the median forebrain bundle were analysed. For comparison, the effects of bath application of noradrenaline and serotonin were also tested. Spontaneous activity in half of all neurons (47-56%) was changed under the influence of neuropeptides in hibernating ground squirrels, while in waking ground squirrels the proportion of responsive neurons was significantly lower (25-30%). The tendency for higher efficacy in hibernating ground squirrels was observed for serotonin; only noradrenaline was equally effective in both groups of animals. Electrically evoked responses of the medial septal nucleus-nucleus of the diagonal band neurons were also strongly modulated by neuropeptides; their changes could occur in the absence of shifts in the level and pattern of spontaneous activity. All three neuropeptides had differential action on the level of spontaneous activity, as well as on inhibitory and excitatory components of electrically evoked responses. Thus, the character and distribution of the effects were state dependent and differed greatly in hibernating and waking ground squirrels. The experiments confirmed that medial septal nucleus-nucleus of the diagonal band neurons have higher excitability and responsiveness to some neuropeptides and neurotransmitters in hibernating ground squirrels.The data obtained suggest an increased latent excitability and responsiveness of septal neurons during hibernation and their possible active participation in urgent arousal under the influence of sensory signals.     

Neuropeptide Modulation of Evoked Responses of Neurons in the Medial Septal Region of Hibernating Ground Squirrels in Conditions of Chronic Isolation of the Medial Septal Region from Preoptic-Hypothalamic Structures

Septal slices from hibernating ground squirrels were initially (for two weeks) subjected to basal separation of the septal region and were then used for studies of the effects of neuropeptides extracted from the brains of hibernating animals (TSKYR, TSKY, and DY) and monoaminergic neurotransmitters (noradrenaline and serotonin) on neuronal responses evoked by intraseptal electrical stimulation. Despite removal of a large complex of afferent connections and direct contacts with the preoptic region, the neurons retained their normal reactivity and the normal distribution of response types. Neuropeptides efficiently modulated responses, and had strong facilitatory effects on oligosynaptic short-latency responses consisting of single spikes. In most cases (78% of tests), effects on evoked activity were independent of effects on baseline discharge frequency. These data lead to the suggestion that neuropeptides have two influences on septal neurons: a direct, non-synaptic influence on the pacemaker potential responsible for baseline activity, and modulation of synaptic processes. Analysis showed that retention of descending septohippocampal connections was not critical for entry into hibernation and the tonic maintenance of this state. The effects of preoptic-hypothalamic mechanisms of hibernation determine the paradoxical latent excitability of septal cells, allowing the septohippocampal system to filter external signals and provide for urgent arousal of the forebrain during hibernation.     

Paradoxical state-dependent excitability of the medial septal neurons in brain slices of ground squirrel, Citellus undulatus

Spontaneous and evoked neuronal activity of the medial septum-diagonal band complex was investigated extracellularly in slices, taken from the brain of the three groups of animals: hibernating ground squirrels, waking ground squirrels, and guinea-pigs. All slices were incubated at 31-32 degrees C. The slices of the ground squirrels' brain were retested after keeping them for 15-36 h in the refrigerator at 2-4 degrees C. In all experimental groups the majority of the medial septum-diagonal band complex neurons had high regular or rhythmic burst spontaneous activity, which in half of the neuronal population persisted in conditions of synaptic blockade. The low-frequency irregular activity of the surrounding structures (lateral septum, caudate, accumbens, medial preoptic area) was completely suppressed in these conditions. The density of the spontaneously active neurons in the slices, as well as the mean frequency of discharges in the medial septum-diagonal band complex of hibernating ground squirrels, was significantly higher than that in waking ground squirrels and guinea-pigs. Stimulation of the medial forebrain bundle evoked initial suppression of activity in majority of the medial septum-diagonal band complex units; in many of them the suppression was followed by a burst discharge. The neurons with background rhythmic burst activity always responded by resetting the spontaneous bursts. In total, about 50-60% of the medial septum-diagonal band complex neurons of waking ground squirrels and guinea-pigs responded by post inhibitory bursts to the stimulation of medial forebrain bundle, while in hibernating ground squirrels such responses were observed in nearly all neurons. The threshold values of the stimulating current were significantly lower in the hibernating ground squirrels' group, the mean duration of the initial suppression was shorter, the intraburst density of spikes and/or duration of the bursts was increased. Thus, evaluation of spontaneous and evoked activity on the basis of various criteria revealed surprising similarity between the two groups of active animals, while the activity and excitability of the medial septum-diagonal band complex neurons was approximately doubled in the hibernating animals. This difference between active and hibernating ground squirrels was preserved during retesting after deep and prolonged cooling of the slices. The experiments demonstrate paradoxical stable increase of activity and excitability of the medial septum-diagonal band complex neurons in the hibernating ground squirrels.(ABSTRACT TRUNCATED AT 250 WORDS)     

State-dependent and state-independent effects of thyrotropin-releasing hormone on medial septum neuronal activity in the brain slices of waking and hibernating ground squirrels

Effects of thyrotropin-releasing hormone on spontaneous activity and responses to medial forebrain bundle stimulation were tested in the units of the medial septum-diagonal band complex in slices taken from the brain of hibernating and waking ground squirrels.

Administration of thyrotropin-releasing hormone (0.1 μM) into the flow of incubating medium increased the frequency of spontaneous activity of all the medial septum-diagonal band complex neurons in hibernating ground squirrels and of the majority of neurons in the waking ground squirrels. However, in the septal slices of hibernating ground squirrels this increase was significantly more pronounced. In addition, the neuropeptide slightly increased the frequency of bursts in the majority of cells with rhythmic burst activity. The excitatory influence of thyrotropin-releasing hormone on the units was preserved in conditions of synaptic blockade. In neurons from other structures (lateral septum, medial preoptic area, hippocampus) in the brain slices of both hibernating and waking ground squirrels, thyrotropin-releasing hormone did not usually affect the level of spontaneous discharges.

When studying the responses of the medial septum-diagonal band complex neurons to electrical stimulation of medial forebrain bundle it was found that application of thyrotropin-releasing hormone (0.1 μM) led to the disappearance of responses in 50 and 44% of units in the hibernating and waking ground squirrels, respectively; in the rest of the neurons a disturbance of stability and probability of responses was observed.

The existence of a modulatory thyrotropin-releasing hormone system which participates post-, and, probably, presynaptically in the regulation of the medial septum-diagonal band complex neuronal activity is suggested. The role of thyrotropin-releasing hormone and of medial septum-diagonal band complex in the neural control of hibernation/euthermic waking cycle is discussed.     

Functional stability of the brain slices of ground squirrels, Citellus undulatus, kept in conditions of prolonged deep periodic hypothermia: electrophysiological criteria

The brain of hibernating animals, controlling the physiological functions during the hibernation cycles, is itself subject to deep cooling during bouts of hibernation. This suggests its high tolerance to deep hypothermia. Effects of prolonged deep cooling were investigated in hippocampal and septal slices, taken from the brains of three groups of animals: hibernating ground squirrels, actively waking ground squirrels, and guinea-pigs. The slices were kept at a low temperature (2-4 degrees C) for various periods of time (from several hours up to six days) and periodically tested in warm (31 degrees C) incubation medium. The hippocampal field potentials (mainly of field CA1), as well as spontaneous activity of single neurons of hippocampus and medial septum were recorded. For comparative purposes mean amplitudes of population spikes and mean frequency of spontaneous neuronal discharge were used. Significant differences between the experimental groups were observed in recovery of functional activity of the slices after their dissection from the brain, as well as after deep cooling. In both cases re-establishment of neuronal activity in ground squirrels occurred more rapidly, than in guinea-pigs. The most dramatic was the difference in maximal time of survival of the slices under conditions of deep cooling. Independently of periodicity of the electrophysiological testing in warm medium, the slices taken from hibernating squirrels retained their activity for seven to nine days, the slices of waking ground squirrel hippocampus survived up to six to seven days, while those of guinea-pis did not recover their functional activity after cooling for more than one to two days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal involution of gut-associated lymphoid tissue of the european ground squirrel

Small intestine-associated lymphoid tissue of immature, male ground squirrels of the genus was studied histologically throughout the annual cycle. Circannual morphological changes of the lymphoid cells in the lamina propria of the mucosa as well as of the Peyer's patches in the submucosa, were established. The changes consisted mainly in a gradual decrease in the proliferative activity of the cells in the autumn and in arrest of this activity in hibernating animals during the first phase of hibernation. An involution of the follicles and their germinative centres, as well as lymphocyte depletion in the Peyer's patche parenchyma, and a marked increase in the lymphocyte number of the lamina propria in hibernating ground squirrels were found. It was shown that the activation of the lymphoid cell proliferation in both compartments of the small intestine begins in hibernating animals in January.     

Anorexia, food deprivation and hibernation

Two experiments examined the relationship between food eaten and the lenghts of bouts of continuous hibernation of golden-mantled ground squirrels, Citellus lateralis, kept at 5 ± 4°C. The first experiment showed that food deprivation at the start of the hibernation season increased the hibernation bout lengths compared to a control group given food ad lib. The second experiment showed that animals without food at the end of the hibernating season decreased bout lengths to near to 4 days; they continued to hibernated in this manner until refed at which time hibernation soon stopped altogether. Factors other than food intake contributed toward determining bout lengths since progressive changes in durations of continuous hibernation occurred at different times of year even in food deprived animals. It was argued that if high food intakes are incompatible with staying in a torpid state for many days on end, then set points for body weight must necessarily be lowered over the hibernation season.     

Hibernation induces immune changes in the lung of 13-lined ground squirrels (Ictidomys tridecemlineatus)

During hibernation, significant changes occur in the systemic and intestinal immune populations. We found that the lungs of hibernating 13-lined ground squirrels (Ictidomys tridecemlineatus) also undergo shifts in immune phenotype. Within the population of mononuclear cells, the percentage of T cells increases and the percentage of CD11b/c⁺ cells decreases in hibernators. E-selectin, which promotes endothelial attachment, increases during arousal from torpor. Levels of the anti-inflammatory cytokine interleukin (IL)-10 in the lung are lower during hibernation while levels of the pro-inflammatory cytokine, tumor necrosis factor (TNF)-α remain constant. Expression of suppressor of cytokine signaling (SOCS) proteins is also decreased in torpid hibernators. Our data point to a unique immune phenotype in the lung of hibernating ground squirrels in which certain immunosuppressive proteins are downregulated while some potentially inflammatory proteins are maintained or amplified. This indicates that the lung houses an immune population that can potentially respond to antigenic challenge during hibernation.     

Hibernation, a model of neuroprotection

Hibernation, a natural model of tolerance to cerebral ischemia, represents a state of pronounced fluctuation in cerebral blood flow where no brain damage occurs. Numerous neuroprotective aspects may contribute in concert to such tolerance. The purpose of this study was to determine whether hibernating brain tissue is tolerant to penetrating brain injury modeled by insertion of microdialysis probes. Guide cannulae were surgically implanted in striatum of Arctic ground squirrels before any of the animals began to hibernate. Microdialysis probes were then inserted in some animals after they entered hibernation and in others while they remained euthermic. The brain tissue from hibernating and euthermic animals was examined 3 days after implantation of microdialysis probes. Tissue response, indicated by examination of hematoxylin and eosin-stained tissue sections and immunocytochemical identification of activated microglia, astrocytes, and hemeoxygenase-1 immunoreactivity, was dramatically attenuated around probe tracks in hibernating animals compared to euthermic controls. No difference in tissue response around guide cannulae was observed between groups. Further study of the mechanisms underlying neuroprotective aspects of hibernation may lead to novel therapeutic strategies for stroke and traumatic brain injury.     

Seasonal effects of Selank on the behavior of hibernating animals

We studied the seasonal effects of peptide preparation Selank on orientation and exploratory activity in 36 arctic ground squirrels Citellus undulatus in the open-field and hole-board tests. Selank most significantly increased behavioral activity of hibernating animals in the spring and fall. The test peptide had no effect on locomotor activity of animals. The selective stimulatory effect of Selank on exploratory behavior of hibernating animals was season-dependent. The maximum effect was observed under conditions of seasonal depression-like state. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 140, No. 12, pp. 658–660, December, 2005     

Reversible reduction in dendritic spines in CA1 of rat and ground squirrel subjected to hypothermia-normothermia in vivo: A three-dimensional electron microscope study

A study was made at electron microscope level of changes in the three-dimensional (3-D) morphology of dendritic spines and postsynaptic densities (PSDs) in CA1 of the hippocampus in ground squirrels, taken either at low temperature during hibernation (brain temperature 2-4 degrees C), or after warming and recovery to the normothermic state (34 degrees C). In addition, the morphology of PSDs and spines was measured in a non-hibernating mammal, rat, subjected to cooling at 2 degrees C at which time core rectal temperature was 15 degrees C, and then after warming to normothermic conditions. Significant differences were found in the proportion of thin and stubby spines, and shaft synapses in CA1 for rats and ground squirrels for normothermia compared with cooling or hibernation. Hypothermia induced a decrease in the proportion of thin spines, and an increase in stubby and shaft spines, but no change in the proportion of mushroom spines. The changes in redistribution of these three categories of spines in ground squirrel are more prominent than in rat. There were no significant differences in synapse density determined for ground squirrels or rats at normal compared with low temperature. Measurement of spine and PSD volume (for mushroom and thin spines) also showed no significant differences between the two functional states in either rats or ground squirrels, nor were there any differences in distances between neighboring synapses. Spinules on dendritic shafts were notable qualitatively during hibernation, but absent in normothermia. These data show that hypothermia results in morphological changes which are essentially similar in both a hibernating and a non-hibernating animal.     

Responses of barrel cortex neurons in awake rats and effects of urethane anesthesia

Summary A barrel is an interconnected network of layer IV neurons that is an important component of a functional cortical column in the whisker area of the rodent primary somatosensory cortex. The present study was undertaken in order to resolve apparently conflicting findings from single-unit studies of barrel neurons conducted in rats maintained under different anesthetic conditions. Multiunit responses to controlled deflections of mystacial vibrissae were recorded from the whisker/ barrel cortex of awake, undrugged rats, and responses at the same recording site were reexamined after the animal was anesthetized with urethane. In contrast to the awake condition, stimulus-evoked responses under urethane were characterized by a large late component. Such effects were more pronounced for deflections of noncolumnar or adjacent whiskers than for the the columnar whisker. Latencies to peak responses were virtually identical for the columnar whisker in awake and urethane states (11.9 vs 11.8 ms) but were considerably longer for adjacent whisker deflections in urethane-anesthetized animals (15.5 vs 29.0 ms). The magnitudes of adjacent whisker responses, relative to the response evoked by the columnar whisker, varied with the laminar location of the recording site in awake but not in urethane-anesthetized animals; in awake rats, receptive fields were clearly smallest in the layer IV barrels. Results in the awake condition confirm those of previous studies conducted in unanesthetized or lightly sedated animals, and data obtained with urethane are comparable to others' results in urethane-anesthetized rats. The former have important implications for how barrel cortex processes information in behaving animals.     

The role of dermorphin in the regulation of the processes of Hibernation in mammals

Data are presented in this paper regarding the influence of the opioid peptide, dermorphin, and its conjugate on the conditioned reflex activity of sousliks. The administration of dermorphin (0.1 /g, subcutaneously) is accompanied by a fall in body temperature, slowing of the baseline vegetative indices, and the sinking of the animal into a sleep-like state. A substantial disturbance of conditioned reflex activity was identified in the late period (delayed effects). Immunization of the hibernating sousliks with a conjugate of dermorphin leads to a gradual awakening of the animals from hibernation, to the normalization of conditioned reflex activity, and to the appearance of the motoric component of a conditioned defense reaction. The question of a possible specific role of dermorphin in the mechanisms of hibernation is discussed.Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 78, No. 4, pp. 1–13, April, 1992.     

Ventilatory pattern and chemosensitivity in unanesthetized,hypothermic ground squirrels (Spermophilus lateralis)

The present study examined the effects of severe hypothermia in the absence of anesthesia on breathing pattern, ventilatory control and chemosensitivity in a cold tolerant species capable of seasonal hibernation. Hypothermia was induced in ground squirrels and ventilation and heart rate were recorded in animals breathing air at a body temperature (Tb) of 5 and 10 degrees C. The animals were then exposed to hypercapnic (2, 4 and 6% CO(2)) and hypoxic (12, 10, 8 and 4% O(2)) gas mixtures. We found that severe hypothermia in ground squirrels caused the breathing pattern to change from a continuous pattern to patterns that are commonly observed during hibernation. This suggests that temperature and metabolism alone are important factors in producing these patterns. The relative ventilatory sensitivity to hypercapnia was retained in the ground squirrel during hypothermia while ventilatory sensitivity to hypoxia was totally abolished. This is in contrast to hibernation where a small but significant hypoxic ventilatory response is present along with an enhanced relative response to hypercapnia. This suggests that changes in Tb alone can not account for the changes seen in ventilatory sensitivity during hibernation.     

Theta modulation of neurons of the hippocampus of the rabbit and its interrelationship with other parameters of spontaneous and evoked activity

The reliability of the existing functional criteria of the differentiation of pyramidal (neurons with complex spikes) and inhibitory (theta neurons) cells of the hippocampus is examined on the basis of a statistical analysis of the spontaneous and evoked activity of neurons of the hippocampus of the awake rabbit. The analysis shows that the parameters of average frequency, the presence of theta modulation of activity, the behavior of the neurons in situations evoking theta rhythm in the EEG of the hippocampus (inhibition or activation during the effect of sensory stimuli), and the character of the influences of stimulation of the medial septal region of the internal connections of the hippocampus do not permit the reliable identification of different types of neurons of the hippocampus in the awake rabbit. The available data on the functional classification of neurons of the hippocampus are discussed in connection with notions regarding their state in situations associated with the generation of theta rhythm.Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 42, No. 1, pp. 95–111, January–February, 1992.     

Sensory evoked neuronal activity in the hippocampus before and after lesions of the medial septal nuclei

The evoked activity of 142 single neurons in the hippocampus of 44 rats was recorded following presentation of one of several modalities of peripheral stimulation. In the intact rat, 41% of the neurons encountered showed some period of inhibition of neuronal firing following peripheral stimulation. In subjects that had received lesions of the medial septal nuclei, only 21% of the cells encountered showed such inhibition. Medial septal lesions were made in 23 animals while recording the activity of cells which exhibited inhibition following stimulation. Of these 23 cells, only 5 continued to exhibit response inhibition after the lesion, while 13 displayed only response excitation, and 5 showed a complete loss of responsiveness. These findings suggest that the integrity of the medial septal nucleus is necessary for the inhibition of neuronal firing observed in many hippocampal neurons following peripheral stimulation.     

Neuropeptide Y localization in telencephalic and diencephalic structures of the ground squirrel brain

The distribution of neuropeptide Y-immunoreactive (NPY-IR) perikarya, fibers, and terminals was investigated in the brain of two species of hibernatory ground squirrels, Spermophilus tridecemlineatus and S. Richardsonii, by means of immunohistochemistry. In the telencephalic and diencephalic structures studied, distinct patterns of NPY-IR were observed which were essentially identical in male and female animals of both species. No differences in amount or distribution of NPY-IR structures were observed between animals which had been in induced hibernation for several months before sacrifice in March/April and those sacrificed one week after their capture in May. In some brain structures (e.g., the hypothalamic arcuate nucleus), IR cell bodies were observed only after pretreatment with colchicine. NPY-IR perikarya and fibers were found in the cerebral cortex, caudate nucleus-putamen, and dorsal part of the lateral septal nucleus. Dense fiber plexuses were seen in the lateral and medial parts of the bed nucleus of the stria terminalis. The numbers of IR perikarya observed in the medial part of the nucleus increased following intraventricular colchicine injections. The accumbens nucleus exhibited few IR cells and many fibers. Claustrum and endopiriform nuclei showed a considerable number of stained cells and fibers that increased in number and staining intensity in colchicine-treated ground squirrels. The induseum griseum showed a small band of IR cell bodies and varicose fibers. Bipolar of multipolar IR cells and varicose fibers were found in the basal nucleus of the amygdala. Dense fiber plexuses as well as IR terminals were seen in the median, medial, and lateral preoptic areas of the hypothalamus. Terminals and relatively few fibers were located in the periventricular, paraventricular, and supraoptic nuclei. The anterior, lateral, dorsomedial, and ventromedial hypothalamic nuclei contained relatively large numbers of terminals and fibers. In the suprachiasmatic nuclei, dense terminals were distributed mainly in the ventromedial subdivision. In the median eminence, immunoreactive terminals were concentrated in the external layer, with fibers predominant in the internal layer. NPY-IR perikarya were observed only in the arcuate nucleus of the hypothalamus and only following colchicine treatment. In the epithalamus (superficial part of the pineal gland and habenular nuclei), varicose fibers appeared mainly in perivascular locations (pineal) or as a dense plexus (habenular nuclei). These results from ground squirrels are discussed in comparison to those obtained in other species and with regard to considerations of the physiological role of NPY.     

The hippocampal control of neuronal discharges in the septum of the rat

1. Records of field potentials and of the firing patterns of single neurones evoked by stimulation of the fimbria and fornix have been obtained from the septal nuclei of the rat.2. Fimbrial stimulation caused orthodromic activation of lateral septal neurones which was followed by a lengthy inhibition. In the medial septum such stimulation could elicit an antidromic response; but inhibition whose duration depended upon whether the neurones were firing irregularly or in synchronized bursts was obtained without prior activation.3. Stimulation of the medial septum evoked an antidromic response in the lateral septal neurones, which was followed by inhibition.4. For all of these inhibitory phenomena, bursts of action potentials of small amplitude and correlated with the start of the inhibitory periods were observed, and are believed to indicate the firing of inhibitory interneurones.5. Stimulation of the fornix caused excitation of medial septal neurones but was without effect on those in the lateral septum.6. A scheme is proposed in which the direct inhibition of medial septal neurones from the fimbria is suggested to act as a ;reset' mechanism, while the phasic input from lateral septum resulting from the recurrent inhibitory pathways regulates the frequency of bursting in the medial septum.     

Topochemical aspects of nucleic-acid and protein metabolism within the neuron-neuroglia unit of the hypothalamic supraoptic nucleus

The RNA and both the total and basic protein content of individual cells were determined by cytospectrophotometry in neurons and perineuronal oligodendroglia of the hypothalamic supraoptic nucleus in rats subjected to various stresses, as well as in ground squirrels during natural hibernation. Barbiturate narcosis and deep cooling, which induced a decrease in body temperature in rats and hibernation in squirrels, caused a marked decrease of all macromolecular constituents in neurons. A similar decrease was found in the perineuronal oligodendroglia in rats, but an increase was observed in ground squirrels. After cessation of cooling, while the body temperature of the animals returned to normal, the neurons, but not the oligodendroglia, of rats showed a significant accumulation of RNA, while RNA accumulated in both neurons and perineuronal oligodendroglia in ground squirrels. Milder cooling of rats, which did not lower their body temperature, induced reciprocal changes in basic-protein content in neuronal and glial cell nuclei, with the accumulation of protein occurring initially in neurons, and subsequently in glia. When cold adaptation was accomplished, the basic protein content of neurons and glial cells returned to the control level. Four days after adrenalectomy in rats, the RNA content decreased in oligodendroglia but not in neurons of the supraoptic nucleus. This effect was completely abolished by daily injections of cortisol in the adrenalectomized animals. The data obtained indicate the existence of differences in metabolic responses to stress between neurons and glial cells of the supraoptic nucleus of the hypothalamus.     

Spontaneous and evoked activity of neurons in deep structures of the brain during their anodal polarization

The influence of anodal polarization on the spontaneous activity of neurons in the caudate nucleus, medial geniculate body, and the median center of the thalamus and on the evoked impulse activity of neurons in the medial geniculate body was investigated during auditory stimulation. The impulse activity was recorded extracellularly with glass and metallic microelectrodes. Nichrome polarizing electrodes of 0.2 mm diameter with an uninsulated tip of 0.3 mm were inserted into the foregoing structures in a packet. Current parameters evoking the reversible suppression of spontaneous and evoked neuronal activity were determined: 300–500 A during exposure for 1–3 min at a distance of up to 3 mm from the polarizing electrode. After the cessation of polarization, a prolonged aftereffect was observed: The inhibition of evoked discharges lasted 4–10 min, and the evoked impulse responses disappeared for 5–20 min.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 71, No. 6, pp. 681–687, June, 1985.