Corticofugal influences on pontine unit activity

Unit responses of the nuclei pontis (NP) and reticular pontine nuclei (RPN) to stimulation of the frontobasal cortex (proreal, orbital, and basal temporal regions) and of the dorsal hippocampus were studied in cats. Stimulation of the various cortical structures was found to induce phasic and (less frequently) tonic responses in neurons of NP and RPN. The main type of unit response in RPN was primary excitation, whereas in NP it was primary inhibition. The largest number of responding neurons in the pontine nuclei was observed to stimulation of the proreal gyrus. In the cerebro-cerebellar relay system neurons of the reticular tegmental nucleus and ventromedial portion of NP showed the highest ability to respond. In the oral and caudal reticular pontine nuclei the regions of predominant influence of cortical structures were located in zones of these nuclei where neurons with rostral and (to a lesser degree) caudal projections were situated.M. Gorkii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 358–367, July–August, 1980.     

Hypothalamic influences on unit activity in the cat sensomotor cortex

Experiments on unanesthetized, immobilized cats showed different effects of individual hypothalamic nuclei on spontaneous unit activity in the sensomotor cortex. Compared with the posterior hypothalamic nucleus (PHN) and its anteromedial region (AMH), in response to stimulation of the lateral hypothalamic nucleus (LHN) changes in spontaneous activity were more frequently found. The ratio between activation and inhibitory responses was 36 and 36% for AMH, 51 and 30% for LHN, and 47 and 28% for PHN. An approximately equal number of sensomotor neurons (27–34%) gave tonic responses. Phasic changes in spontaneous activity were observed more often in response to stimulation of LHN, less frequently to stimulation of AMH and PHN. Responses of "nonpyramidal" neurons to stimulation of AMH and LHN were identical. "Pyramidal" units were more sensitive to LHN stimulation. Variations in hypothalamic effects depending on the type of response of sensomotor neurons to sensory stimuli were detected. Cells with tonic responses were more susceptible to influences of LHN and AMH than cells which responded by phasic changes in spontaneous activity to sensory stimuli. Fewer still positive responses were recorded in areactive neurons.Medical Institute, Chita. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 115–122, March–April, 1972.     

Hypothalamic influences on unit activity in the cat superior colliculus

Experiments on immobilized unanesthetized cats showed that hypothalamic stimulation effectively modified spontaneous unit activity and activity evoked by photic stimulation in the superior colliculus. Long-latency responses, often with a tonic type of formation, were predominant. Meanwhile, definite differences were found in the character of influences from different regions of the hypothalamus. Stimulation of the anterior hypothalamic region and lateral hypothalamus led more frequently to inhibition of spontaneous activity, often expressed as the development of initial inhibition, especially during stimulation of the lateral hypothalamus. Definite modulation of spontaneous activity of cyclic type also developed. Influences from these structures on activity evoked by photic stimulation were chiefly facilitatory and modulating in character. Stimulation of the ventromedial nucleus could produce inhibitory and facilitatory effects equally on activity of tectal neurons, with a tendency for the frequency of manifestation of facilitation to increase when a series of stimuli was used. The mechanisms of triggering and realization of hypothalamic influences on activity in the superior colliculus are discussed.Ivano-Frankovsk State Medical Institute, Ministry of Health of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 560–568, November–December, 1979.     

Corticofugal influences on reticulospinal neurons of the gigantocellular nucleus in cats

It was shown by intracellular recording that stimulation of the motor cortex evokes E PS Ps and I PS Ps in reticulospinal neurons of the gigantocellular nucleus of the cat medulla. The E PS Ps appeared in 94.3% and the I PS Ps in 5.7% of neurons tested. Analysis of the presynaptic pathway showed that 77.4% of E PS Ps studied arose through monosynaptic, and 22.6% through polysynaptic corticoreticular connections. By their latent period, duration, and rise time up to a maximum the monosynaptic E PS Ps were divided into two groups: "fast" and "slow." It is postulated that "fast" E PS Ps are generated in reticulospinal neurons which are activated by fast-conducting fibers and "slow" E PS Ps by slowly conducting corticobulbar fibers. I PS Ps were recorded from reticulospinal neurons that also were inhibited by stimulation of the ventral columns of the spinal cord. The hypothesis is put forward that cortical motor signals in cats can be transmitted to the spinal cord via monosynaptic and polysynaptic connections of "fast" and "slow" pyramidal neurons with reticulospinal neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 250–257, May–June, 1976.     

Monosynaptic excitory postsynaptic potentials in thoracic motoneurons under reticulospinal influences

We studied synaptic processes in motoneurons of thoracic segments (T_IX-T_XI) evoked by stimulation of the medial area of the giant-cell reticular nucleus in decerebrated cats. Monosynaptic EPSP were recorded in the majority of investigated motoneurons upon activation of the most rapidly conducting reticulospinal fibers. In some cells, such monosynaptic EPSP were accompanied by late EPSP or IPSP. Amplitude of monosynaptic EPSP attained 5 mV, but this value usually was insufficient for development of an action potential. Upon summation of single monosynaptic EPSP, the membrane potential reached the critical level and an action potential arose in the motoneuron. The efficiency of summary processes evoked by stimulation of the reticular formation exceeded the intensity of synaptic processes that arise in thoracic motoneurons on stimulating the nucleus of Deiters. Functional characteristics of reticular and vestibular monosynaptic EPSP are discussed in the work.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 243–252, November–December, 1969.     

Analysis of spontaneous unit activity in the cat pyramidal tract

For a statistical analysis of spontaneous activity of cortical pyramidal neurons (PN) of the cat, recordings were obtained from axons of those neurons descending in the lateral pyramidal tract in lumbar segments of the spinal cord. Spontaneous activity of all investigated PN is not random in sequence but has a complex temporal structure. Three types of spontaneous activity were distinguished by the character of distribution of the interspike intervals (ISI); the degree of grouping of the spikes into volleys separated by long intervals increases from type I to type III. Type III is more often found in PN with fast-conducting axons. As a rule the number of volleys in the spontaneous activity differed from that expected by the hypothesis of random spike sequence. In some cases repetition of volleys with an identical, or nearly identical, temporal structure was observed. It is postulated that the type of spontaneous activity is determined by the functional state of the neuron and by its morphological properties. Experiments were carried out on two groups of animals: 1) briefly anesthetized a long time before the recording was obtained, and then immobilized; 2) anesthetized with chloralose and Nembutal. The differences between the character of spontaneous PN activity were mainly in the degree of grouping of the spikes (which was greater in the second group). Significant positive correlation was found between the velocity of conduction along the PN axon and the mean ISI of the spontaneous activity.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 3–11, January–February, 1972.     

Effectiveness of ascending synaptic influences from various spinal funiculi on reticulospinal neurons in cats

Activity of reticulospinal neurons evoked by stimulation of the ventral, ventrolateral, dorsolateral, and dorsal funiculi of the spinal cord was recorded extracellularly in cats anesthetized with chloralose. Responses of 57 reticulospinal neurons, of which 22 projected into the ventral funiculus, 20 into the ventrolateral, and 15 into the dorsolateral, were studied. The functional properties (conduction velocity and refractory period) and the location of the neurons of the above-mentioned groups in the medulla did not differ appreciably. The most effective synaptic activation of all neurons was observed during stimulation of the dorsal and dorsolateral funiculi. Responses to stimulation of the dorsal funiculus had the lowest threshold. These responses arose in reticulospinal neurons of the ventral and ventrolateral funiculi after the shortest latent period. The effectiveness of synaptic influences from the dorsal and dorsolateral funiculi was identical in the group of neurons of the dorsolateral funiculus. Correlation between activity evoked by stimulation of the dorsal funiculus in reticulospinal neurons and peripheral nerves indicated that the responses appeared in these cells to stimulation of muscular (groups I and II) and cutaneous (group II) afferent fibers. The results indicate that impulses from low-threshold muscular and cutaneous afferents, which effectively activate reticulospinal neurons, are transmitted along ascending pathways of the dorsal funiculi.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 254–263, May–June, 1979.     

Tranformation of long reticulofugal spike trains by interneurons connected monosynaptically with the reticulospinal tract

Characteristics of transmission of activity evoked by stimulation of the reticular formation through interneurons located in the ventromedial zones of the gray matter of the lumbar division of the spinal cord and connected monosynaptically with reticulospinal fibers were investigated in cats. Responses of the neurons to relatively low-frequency (not exceeding 80–100/sec) stimulation consisted mainly of stationary discharges; with a further increase in frequency the response became nonstationary (the initial, relatively high-frequency discharge was followed by partial or complete suppression of the discharge). The maximal frequency of the initial phase of the response to high (over 400/sec) frequencies of stimulation was 180–230 spikes/sec. The "transmission factor" (ratio between the frequency of spikes in the response to the frequency of stimulation), calculated for stationary discharges, reached 0.7–0.8 at low frequencies of stimulation, and then decreased significantly. On the basis of the statistical characteristics of the stationary portions of the evoked activity and analysis of these data by the use of a mathematical model, indirect estimates were obtained of the parameters of processes lying at the basis of the transforming properties of this cell population.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 278–286, May–June, 1978.     

Alarm reaction in the crucian carp is mediated by the medial bundle of the medial olfactory tract

Experiments were performed to determine which bundles of the olfactory tracts were essential for mediating alarm reaction in crucian carp (Carassius carassius L.). The fish were maintained in physiological saline after surgery to preserve the remaining tracts and postoperative inspections revealed the functionality of the intact tracts. Operations on the tracts were performed symmetrically on both sides. Sham-operated and non-operated fish showed the typical alarm behaviour of fast swimming to the bottom, dashing movements and aggregation when exposed to skin extract which contain alarm substance. Fish with only the medial bundle of the medial olfactory tract intact also displayed the alarm behaviour upon exposure; however, these fish did not react to the amino acid, L-alanine with either feeding response or alarm reaction. Crucian carp which had the medial bundle of the medial olfactory tract cut, leaving both the lateral bundle of the medial olfactory tract and the lateral olfactory tract intact, did not display any alarm reaction to skin extract; however, these fish reacted to exposure to L-alanine with feeding behaviour. There were statistically significant differences between the behaviour scores for the fish subject to different treatments. The present study demonstrates that the medial bundle of the medial olfactory tract appears to be both necessary and sufficient for mediation of the alarm reaction. The results also show that the sensory neurons which respond to alarm substance terminate and make synaptic connections with the secondary neurons that make up the medial bundle of the medial olfactory tract; thereby demonstrating the specificity of the spatial aspect of olfactory processing. The results are discussed with respect to the spatial aspect of organization within the olfactory system, the pattern of generalization across orders of fish, and the functional implications of the spatial arrangement of information transmission between the peripheral olfactory organ and the brain.     

Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Reflex discharges in intercostal nerves and activity of reticulospinal fibers of the ventral and lateral funiculi, evoked by stimulation of the reticular formation and of the splanchnic and intercostal nerves were investigated in cats anesthetized with chloralose (50 mg/kg). Brain-stem neuronal structures participating in the "relaying" of spino-bulbo-spinal activity were shown to lie both in the medial zones of the medullary and pontine reticular formation and in its more lateral regions; they include reticulospinal neurons and also neurons with no projection into the spinal cord. Structures whose stimulation led to prolonged (300–800 msec) inhibition of reflex spino-bulbo-spinal activity were widely represented in the brain stem, especially in the pons. Analogous inhibition of this activity was observed during conditioning stimulation of the nerves. Reticulospinal fibers of the ventral (conduction velocity 16–120 m/sec) and lateral (17–100 m/sec) funiculi were shown to be able to participate in the conduction of spino-bulbo-spinal activity to spinal neurons. In the first case fibers with conduction velocities of 40–120 m/sec were evidently most effective. Evidence was obtained that prolonged inhibition of this activity can take place at the supraspinal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 373–383, July–August, 1976.     

Environmental influences on the activity of captive apes

Forty-one zoological gardens in seven European countries were visited to investigate activity level in captive environments for great apes. Forty-three groups of gorillas and 68 groups of orangutans were observed. The seven factors quantified for each of the environments were size of the enclosure, usable surface area, frequency of feeding, number of animals, and number of objects (stationary, temporary, and movable). Activity level of each group was measured by instantaneous scan sampling for one hour on two consecutive days. For both species, the factors most highly related to activity level were number of animals, and stationary, temporary, and movable objects. The usefulness of these variables for predicting group activity level was different for the two species, however. Factors important for gorillas were stationary and temporary objects, while stationary and movable objects were significant for orangutans. These findings suggest that objects within environments may be more important for captive apes than the size or construction of the enclosure. Also, the types of objects that need to be included in environments may be related to the natural behavior of the individual species.     

Summation of motor unit forces in rat medial gastrocnemius muscle

The summation of contractile forces of motor units (MUs) was analyzed by comparing the recorded force during parallel stimulation of two and four individual MUs or four groups of MUs to the algebraic sum of their individual forces. Contractions of functionally-isolated single MUs of the medial gastrocnemius muscle were evoked by electrical stimulation of thin filaments of the split L5 or L4 ventral roots of spinal nerves. Additionally, contractions of large groups of MUs were evoked by stimuli delivered to four parts of the divided L5 ventral root. Single twitches, 40 Hz unfused tetani, and 150 Hz fused maximum tetani were recorded. In these experimental situations the summation was more effective for unfused tetani than for twitches or maximum tetani. The results obtained for pairs of MUs were highly variable (more- or less-than-linear summation), but coactivation of more units led to progressively weaker effects of summation, which were usually less-than-linear in comparison to the algebraic sums of the individual forces. The variability of the results highlights the importance of the structure of the muscle and the architecture of its MUs. Moreover, the simultaneous activity of fast and slow MUs was considerably more effective than that of two fast units.     

Spatial analysis of motor unit potentials of the rat medial gastrocnemius

The spatial analysis of the potentials of single motor units of the rat medial gastrocnemius muscle evoked by stimulation of the fibres of split ventral roots was carried out with a bipolar electrode moving in the direction perpendicular to the longitudinal axis of the muscle fibres. During this movement of the electrode a variability was observed in the time of the biphasic potential from its maximum to minimum, and in the peak-to-peak amplitude of these potentials. The potentials recorded outside the territory of the motor unit had a lower amplitude in relation to the potentials from the territory of the unit. This made localization of the motor unit on the cross-section of the muscle possible. Differences in the duration of the potential from maximal to minimal amplitude (maximum-minimum amplitude time--M-MAT) of each investigated motor unit from successive recording sites reflected the number of fibres contributing to the action potential and the distance of the recording surface of the electrode from the zone of the motor end-plates of this motor unit. The greatest diameter of the territory of the observed motor units reached 2.5 mm.     

Corticofugal influences on the activity of vestibular nuclei units in the cat

Neuronal responses to stimulation of vestibular motor and orbital cerebral cortex were recorded by extracellular techniques in the lateral and medial vestibular nuclei of the bulbar complex during experiments on unanesthetized, immobilized cats. Both phasic and (mostly) tonic response of predominantly inhibitory type were observed. Horseradish peroxidase was injected into the aforementioned nuclei of the vestibular complex during the course of morphological experiments. Labeled neurons were found in the anterior supra- and ectosylvian cerebral gyri, the region of the cruciform sulcus, and that of the orbital cerebral cortex. Findings are discussed from the aspect of corticovestibular interaction.Ivano-Frankovsk Medical Institute, Soviet Ministry of Health. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 802–809, November–December, 1987.     

Investigation of pallidofugal influences on hypothalamic activity

In chronic experiments on nine cats electrical stimulation of the posterior zones of the lateral hypothalamus led to reproduction of a conditioned food-getting reflex produced previously in response to clicks. During stimulation of the globus pallidus a food-getting reflex also appeared in 3 of 10 zones studied, but it did so only irregularly. In response to combined stimulation of the hypothalamus and these three zones of the globus pallidus facilitation of this reflex was observed: its intensity was increased and its latent period shortened. Stimulation of other areas of the globus pallidus inhibited the food getting reflex of hypothalamic origin on account of the intensification of purposeless motor responses. Stimulation of the globus pallidus evoked desynchronization of spontaneous hypothalamic electrical activity. After bilateral electrolytic destruction of the globus pallidus and its principal efferent pathway (the ansa lenticularis) no conditioned food-getting reflex was reproduced during hypothalamic stimulation. After pallidectomy the amplitude of the spontaneous waves and evoked potentials was reduced by a statistically significant degree in the hypothalamic zones tested. The results are evidence of the existence of regulatory functional influences of the globus pallidus on the lateral hypothalamus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 6, No. 6, pp. 592–601, November–December, 1974.