Electrophysiological features of facial motoneurons in cats

Antidromic activation of facial motoneurons in cats during stimulation of different branches of the facial nerve was studied by intracellular recording. Time and amplitude characteristics of individual components of the antidromic action potentials were analyzed and fast and slow after-potentials distinguished. Correlation was found between the duration of the descending phase of the SD spike, duration of its after-hyperpolarization, and the spike conduction time along the axon. Data were obtained to show absence of a recurrent collateral pathway in motoneurons of the facial nucleus. The functional significance of the after-potentials is discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 261–270, May–June, 1978.     

Populations of motor units of the human soleus muscle supplying H reflex generation: Electrophysiological analysis

Variations in the amplitude of H and M responses of them. soleus related to the variation in intensity of stimulation of then. tibialis comm. were evaluated in five persons with different ratios of the maximum H and maximum M response amplitudes (from 0.27 to 0.75). A decrease in amplitude of the H reflex accompanied by an increase of M response is supposed to be determined by collision of ortho- and antidromically conducted spikes in motoneuronal axons; this makes it possible to quantify the participation of various motoneuronal populations differing in activation thresholds of their axons in H reflex generation. The H response in individuals with a low ratio of the maximum H and M response amplitudes was shown to be due primarily to the involvement of high-threshold motoneurons. When the ratio between the above-mentioned maximum EMG potentials was high, all populations of motoneurons, except very low-threshold ones, participated in the H reflex generation. In all cases, only a portion of high-threshold motoneurons was involved in H activity, which contradicts the so-called size principle.Neirofiziologiya/Neurophysiology, Vol. 25, No. 6, pp. 417–420, November–December, 1993.     

Typological characteristics of conditioned reflex learning in monkeys

Three types of conditioned learning dynamics were singled out in males of the rhesus monkeys by the speed of formation of a positive motor instrumental reflex and differentiation. Type I is characterized by the fastest mastering of separate subprograms and of the whole test program of conditioned behaviour, by optimal functional characteristics in the process of learning and by a high adaptivity in new conditions. The most prolonged formation of the conditioned reflexes occurs in monkeys of the III-d type; 50% of them do not master the whole learning program; monkeys with such type of learning dynamics have no adaptation of previously acquired conditioned stereotype to new environmental conditions. Monkeys of the II-nd type of learning dynamics possess intermediate characteristics. A notion is substantiated of interconnection of higher nervous activity properties with typological characteristics of conditioned learning dynamics in monkeys.     

Physiological analysis of the relation between the conditioned reflex and image memory in monkeys and preschool children

Interaction of short-term and long-term memory processes is subjected to phylo- and ontogenetic changes. Progressive development includes differentiation and independent manifestation of these memory forms together with formation of a more complex pattern of interaction between the latter.     

Electrophysiological study of 5,6-dihydroxytryptamine effect on defensive reflex conditioning in the snail

The role of serotonin in expression of membrane properties of identified neurons was studied during defensive reflex conditioning using the neurotoxic analogue of serotonin 5,6-dihydroxytryptamine (5,6-DHT). The defensive reflex conditioning in snails was destroyed on the second day after second injection of 5,6-DHT. Through the 1st weeks after second injection of 5,6-DHT the snails were learned but worse than snails after injection of saline solution. This result shows the recovery of snail's learning ability within 2 weeks after the second injection of 5,6-DHT. It was found that injection of 5,6-DHT prevented the decrease of membrane and threshold potentials of command neurons during defensive reflex conditioning as compared with the snails injected with 5,6-DHT without learning.     

Electrophysiological analysis of the effect of cortisone on the rat neuromuscular apparatus]

The influence of cortisone (1.5 mg per 100 g of body weight, daily, for 10 days) on the neuro-muscular system was studied in rats in situ. The action potentials of the nerve and muscle were recorded with the extracellular electrodes. The rest potentials (RP) of the muscle fibers and the miniature end-plate potentials (MEPP) were recorded with the intracellular glass microelectrodes. A decrease of the RP and the MEPP amplitude, and an increase of the MEPP frequency and prolongation of the neuromuscular transmission time were revealed in rats given daily doses of cortisone, 1.5 mg/100 g of body weight, during 10 days; reliability of the neuro-muscular transmission (acceleration of the fall of the muscle action potential amplitude during tetanus) proved to decrease under the action of cortisone.     

Underbite and the scaling of facial dimensions in colobine monkeys.

This investigation was concerned with the dimensions of the facial skeleton and the incidence of underbite in colobine monkeys. Standard craniofacial dimensions and the notation of the presence or absence of underbite were recorded for skulls of 308 adult, wild-caught colobines belonging to 10 species. Underbite was noted in all species examined, ranging in frequency from 10% in Colobus polykomos to 100% in 2 species of Presbytis. Univariate statistics indicate that species with high frequencies of underbite tend to have shorter, broader maxillary dental arches, shorter faces and rostrums, and longer mandibular dental arches. A multivariate discriminant analysis supported the univariate statistics. Interspecific allometric analysis of facial measurements against a constructed size variable indicated that maxillary dimensions scale in a strongly positive manner in relation to size. However, mandibular dimensions tend to scale isometrically. This pattern of facial scaling indicates that the tendency toward underbite should increase as overall size decreases. This would explain why smaller species have higher frequencies of underbite than larger species and why females often have a higher incidence of underbite than conspecific males. Zingeser has suggested that the high incidence of underbite in colobine and some cebid monkeys is an adaptation to folivory. The results of this study support an alternative hypothesis that the high incidence of underbite in colobine monkeys is related to the pattern of facial scaling with size in combination with relaxed selection on the anterior dentition.     

Electrophysiological analysis of corticopontine connections

In acute experiments on cats anesthetized with pentobarbital and chloralose, the method of recording focal responses was used to study projections of various parts of the orbito-frontal and basal temporal cortex and also of the hippocampus in the region of the pons. Different formations of the fronto-basal zones of the neocortex were shown to have local projections in the rostral zones of the pons and relatively diffuse projections in its caudal zones. Projections of the hippocampus in structures of the pons are less well marked than those of the fronto-basal zones of the neocortex and their focal responses are more diffuse in character. Representation of all the structures studied is found only in the nuclei of the gray matter of the pons. The orbito-insular zone of the orbito-frontal cortex is not represented in the caudal zones of the reticular formation; the basal temporal cortex has no projection in the middle cerebellar peduncles.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 347–354, July–August, 1977.