Convergence of corticofugal impulses on pontine neurons

Convergence of corticofugal impulses in reticular and intrinsic pontine nuclei during stimulation of the frontobasal cortex (proreal, posterior orbital, and basal temporal regions) and also of the dorsal hippocampus was studied in acute experiments on cats anesthesized with a mixture of pentobarbital and chloralose. Three foci of convergence of corticofugal impulses were found in these structures: one in the reticular formation and two in the intrinsic nuclei—in their medial and lateral portions. Neurons with an excitatory type of response were shown to predominate in the reticular formation and neurons with an inhibitory or mixed type of response of neurons activated antidromically by stimulation of one brain region and synaptically during stimulation of another, that the pontine nuclei play an integrative role in the functional unification of structures of the frontobasal zones of the neocortex and hippocampus.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 472–480, September–October, 1980.     

Convergence of autonomic,somatic, and vestibular afferent impulses on single units of the medullary vasomotor center of the cat

Responses of vasomotor neurons of the cat medulla to electrical stimulation of the depressor nerve and of mixed nerves of the limbs and to adequate stimulation of the vestibular apparatus were investigated. Evoked unit activity was demonstrated as groups of action potentials followed by inhibition of spontaneous activity. Three types of unit responses to stimulation of the depressor nerve and somatic afferent fibers and changes in unit activity in response to vestibular stimulation are described. The features distinguishing the convergence of afferent impulses on vasomotor neurons are discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 460–467, September–October, 1973.     

Interaction of heterosensory afferent impulses on neurons of thalamic associative nuclei

The character and particular features of interaction between visual, auditory, and electrodermal afferent impulses on neurons of the pulvinar, posterolateral, and mediodorsal thalamic nuclei were studied in acute experiments on cats anesthetized with a mixture of pentobarbital and chloralose. Interaction discovered on cells of both groups of structures was of two types. In the first (the one most frequently found) only inhibition was observed or inhibition followed by facilitation of the response to testing stimulation; in the second type only facilitation or facilitation followed by inhibition of unit activity was found. Overall ability for interaction to take place on neurons of the mediodorsal nucleus was weaker than on cells of the pulvinar-posterolateral complex (P<0.05). Interaction was strongest on trisensory cells; it was also observed on monosensory cells or on cells which did not respond to isolated stimulation.Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 478–485, September–October, 1978.     

MPTP-induced suppression of corticofugal influences on neurons of the cat caudate nucleus

In acute experiments on cats, we demonstrated that the relative number of neurons of the caudate nucleus responding to stimulation of the motor cortex with latencies shorter than 8.0 msec significantly decreased, as compared with the control, after destruction of the nigro-striatal dopaminergic system caused by a series of injections of the neurotoxin MPTP. Within 1.5 months, the number of these cells gradually recovered. We conclude that in the norm dopamine exerts an inhibitory effect on glutamatergic cortico-striatal impulsation. We hypothesize that the blockade of transmission through cortico-striatal synaptic connections under conditions of dopamine deficiency is realized due to the toxic effect of glutamate released in excessive amounts on the corresponding receptors in the above synapses. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 287–291, July–August, 2006.     

Convergence of afferent impulses from individual semicircular canals of pontine reticular units.

The effect of afferent impulses on single pontine RF units was recorded by means of tungsten microelectrodes in 22 curarized guinea pigs followed thermic stimulation of individual semicircular canals. The labyrinthine stimulation consisted of short-lasting circumscribed heating (45 degrees C) of the canals through a silver thermode. Unitary response to labyrinthine stimulation was characterized by excitation and inhibition of rest discharge rate. Out of 86 units, 66 received bilateral labyrinthine influences responding in greatest number (20 units) to four semicircular canals. Only two units were unaffected. No significant difference in RF responses was noticed between concordant and antagonistic canals. Reticular formation units showed great degree of facilitation of response and convergence of impulses from the single six semicircular canals.     

Monosynaptic excitation of motoneurons of the accessory nerve nucleus by reticulofugal impulses

Acute experiments on cats anesthetized with chloralose and pentobarbital showed that excitation of fast-conducting (130 m/sec) reticulospinal fibers, arising during stimulation of the ipsilateral medullary reticular gigantocellular nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nerve nucleus. The EPSPs had latent periods of between 0.6 and 1.0 msec (mean 0.7 msec), they reached their maximal amplitude (4.0 mV) after 2.0–2.5 msec, and lasted about 10 msec. The EPSPs underwent only weak potentiation through the different types of stimulation of the gigantocellular nucleus and were not transformed into action potentials.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 62–66, January–February, 1980.     

Convergence of impulses on anterior hypothalamic neurons during local temperature stimulation of the skin

Unit responses in the medial preoptic region of the anterior hypothalamus and septum to local temperature stimulation of various parts of the skin were studied in chronic experiments on rabbits. The temperature of an area of skin on the back (zone I) and head (zone II) was altered by means of thermodes: heated to 38–40°C and cooled to 22–26°C. Of 111 neurons tested 21 responded to a change of skin temperature (mainly to cooling). Temperature-sensitive hypothalamic neurons were shown to react to temperature stimulation of both skin zones stimulated. The types of the responses recorded are described.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 365–370, July–August, 1981.     

Nociceptive afferent blockade by percutaneous peripheral stimulation in the cat]

Experiments have been performed in order to study the effects of percutaneous peripheral stimulation (PCPS) both on the transmission of messages elicited by recruiting sensory units of the tooth pulp at the thalamic Centrum Medianum Level and on the jaw opening reflex (JOR). Both evoked potentials and JOR were inhibited by stimuli applied to the limbs by means of percutaneous (needle) electrodes. Observed inhibitory effects were not immediate: there was a latency period and progressive induction of these phenomena. The site of the inhibition is still unknown, nevertheless, the demonstration that PCPS was able to inhibit both evoked potentials in Centrum Medianum and JOR support the hypothesis that the analgesic effects may be due to descending inhibition blocking transmission of nociceptive information through the spinal cord.     

Activation of cat pontine nuclei neurons produced by cortico- and cerebellofugal impulses

Extracellular recording techniques were used on cats anesthetized with Nembutal to illustrate antidromic activation of pontine neurons produced by stimulating the medial and occasionally the superior cerebellar peduncle, the cerebellar central nuclei, pyramidal tract, and sensorimotor region of the cortex. Of the pontine nucleus projection, that extending to the lateral cerebellar nucleus was the most clearly defined. Stimulation of the pyramidal tract, central cerebellar nuclei and the superior cerebellar peduncle was found to produce monosynaptic excitation of pontine neurons. The significance and special features of the connections identified are discussed in connection with cortico-pontocerebellar system function.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Amenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 38–48, January–February, 1988.