Postsynaptic potentials in cat abducens motoneurons evoked by stimulation of cortical eye fields.

Intracellular recordings were carried out on abducens motoneurons of encephale isole cats in order to analyse synaptic influences of cortical areas engaged in control of saccadic eye movements. It was found that, in addition to the "frontal eye field" (FEF), eye movements containing a contraversive component may be triggered by electrical stimulation of the 1st and the 2nd sensorimotor areas (SM). Correspondingly, sustained postsynaptic responses (EPSPs) and rhythmic firing of abducens motoneurons could be reliably induced by prolonged stimulus trains. In this respect, the efficiencies of FEF and SM were about the same. They appeared to be higher than the efficiency of excitatory pyramidal actions on spinal motoneurons as reported by others. EPSPs elicited from both regions by short stimuli were, on the major part, polysynaptic. Quite complex multineuronal chains appeared to be stronger engaged in the transmission of FEF effects. EPSPs of SM origin contained a disynaptic fraction which could not be reliably identified in FEF responses. Recipocal innervation of abducens nuclei on both sides was found to be reflected in the asymmetry of excitatory and inhibitory influences from two hemispheres: EPSPs predominated in responses to contralateral, IPSPs and mixed PSPs - to ipsilateral stimulation.     

Postsynaptic potentials of facial motoneurons evoked by afferent and corticofugal impulses

Postsynaptic potentials of motoneurons in the facial nerve nucleus, evoked by stimulation of the cranial nerves (trigeminal, hypoglossal, facial) and of the sensomotor cortex were investigated in cats anesthetized with chloralose and pentobarbital. Two functionally opposite groups of motoneurons were found to exist in the facial nucleus. Stimulation of the afferent nerves and cortex evoked the appearance of EPSPs in the first of these groups and IPSPs in the second. The latency and duration of the PSPs indicate that afferent and corticofugal impulses reach the facial motoneurons along polysynaptic pathways. Interneurons on which wide convergence of influences travelling along afferent fibers and of the cortex, were found in the region of the facial nucleus. The possible neuronal pathways concerned with the transmission of afferent and corticofugal impulses to the facial motoneurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 391–400, July–August, 1972.     

Components of synaptic potentials of cat rubrospinal neurons evoked by corticofugal impulsation

EPSPs of rubrospinal neurons evoked by stimulation of the sensorimotor area of the cortex were studied in cats anesthetized with pentobarbital by means of intracellular recording. The involvement of corticospinal input in generating the EPSP was assessed by selective activation of corticospinal fibers at medullary pyramid level and by studying how they interact under the effects of cortical stimulation. It was shown that predominantly corticospinal and corticorubral neurons with slow-conducting axons are involved equally in the genesis of the first two components of complex EPSP. The cellular composition and mechanisms of corticofugal influences on red nucleus neurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 692–700, September–October, 1985.     

Postsynaptic potentials of neck muscle motoneurons evoked by horizontal semicircular canal stimulation in cats

Postsynaptic potentials evoked by stimulation of ipsilateral and contralateral horizontal semicircular canals in motoneurons of muscles tilting and turning the head were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Stimulation of the ipsilateral canal evoked EPSPs with latent periods varying from 1.8 to 10.0 msec in 25 of these motoneurons and IPSPs with latent periods varying from 1.9 to 3.9 msec in 10 of them. Calculation of the impulse conduction time from the ipsilateral semicircular canal through Deiters' nucleus to the cervical motoneurons indicates that EPSPs with latent periods of under 3.8 msec may be regarded as disynaptic, and those with latent periods of over 3.8 msec as polysynaptic. Stimulation of the contralateral canal evoked EPSPs with latent periods varying from 1.8 to 6.0 msec in 19 motoneurons and IPSPs with latent periods varying from 3.2 to 3.9 msec in two cells. The possible pathways of transmission of these influences and their functional role are discussed.     

A biphasic excitability change in hindlimb motoneurons evoked by stimulation of the nucleus raphes magnus in the cat

1. The influence of electrical stimulation of the nucleus raphes magnus (RM) on spinal segmental systems were examined. 2. RM stimulation produced an initial increase and a subsequent suppression of the amplitude of both fiextor and extensor lumbar monosynaptic reflex potentials (MSRs). 3. Intracellular recordings were made from alpha-motoneurons of the common peroneal nerve (flexor) and the tibial nerve (extensor). RM stimulation evoked postsynaptic potentials with a time course similar to that of MSR facilitation. 4. RM stimulation inhibited the aggregate excitatory synaptic potential (EPSP) evoked by stimulation of group I afferent fibers without apparent changes in the motoneuronal membrane potential. 5. These data suggest that the RM-evoked biphasic effect on MSR consists of early facilitation due to EPSP, and late inhibition possibly due to presynaptic inhibition of group I afferent fibers.     

Spatiotemporal characteristics of evoked potentials in the posterior ventrolateral nucleus of the cat thalamus

Evoked potentials (EPs) in the posterior ventrolateral nucleus (VPL) of the thalamus in response to electrical stimulation of the skin of the contralateral forelimb were studied. It was shown that they are formed by superposition of several electrical dipoles, one of which lies with two poles in VPL while the rest have one pole in VPL and the other in more caudal zones of the somatosensory system. The first phase of the EP in VPL consists of two components with different amplitude—frequency characteristics. The lability of the second component is low and it disappears if the frequency of stimulation rises above 20 Hz. The focus of maximal activity during contralateral stimulation of the skin of the forelimb occupies the same topographical position in VPL during development of the positive and negative phases of the EP. The steepness of rise of the ascending phase and the amplitude of the positive phase of the EP are greatest at the focus of maximal activity; in other regions the lines of equal steepness need not necessarily coincide with the equipotential lines; differences are especially noticeable in the sagittal plane.Institute of the Brain, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 439–446, July–August, 1972.     

Excitation of accessory motoneurons by stimulation of Deiters' nucleus in the cat

Acute experiments on cats under chloralose-pentobarbital anesthesia showed that application of single stimuli to Deiters' nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nucleus. Latent periods of EPSPs ranged from 1.3 to 2.3 msec (mean 1.8±0.3 msec), their rise time was 0.5–1.0 msec, and their duration 7–10 msec. During repetitive stimulation the EPSPs were weakly potentiated, but with an increase in the strength of stimulation applied to Deiters' nucleus they readily changed into action potentials. In some motoneurons polysynaptic EPSPs with latent periods of the order of 6.0 msec appeared on the descending phase of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 515–519, September–October, 1981.     

Rubrofugal activation of motoneurons of the cat accessory nucleus

Postsynaptic potentials evoked in accessory nerve motoneurons by stimulation of the ipsilateral and contralateral red nuclei were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Polysynaptic EPSPs with latent periods of 5.2 to 16 (mean 9.1 ± 0.7) msec and from 5.5 to 18 (mean 10.3 ± 0.9) msec, respectively, appeared in motoneurons of the accessory nerve in response to stimulation of the contralateral and ipsilateral red nuclei. A minimum of two or three stimuli was necessary to produce EPSPs in these motoneurons. In response to single stimulation of the contralateral and ipsilateral red nuclei EPSPs appeared in four motoneurons of the trapezius muscle with latent periods of 2.5 to 5.0 and 3.0 to 5.2 msec, respectively. An increase in the number of stimuli led to action potential generation by motoneurons. The functional role of such activation is discussed.A. A. Bogomolets Institue of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 532–536, September–October, 1982.     

Synaptic processes in facial motoneurons evoked by stimulation of the caudal trigeminal nucleus

Field potentials and postsynaptic potentials of facial motoneurons evoked by stimulation of the caudal trigeminal nucleus were investigated in acute experiments on cats by extra- and intra-cellular recording. Pre- and postsynaptic components of field potentials were found. Four types of motoneuron response were distinguished: EPSP with generation of single action potentials; a gradual shift of depolarization inducing grouped action potentials; a rhythmic discharge of action potentials arising at a low level of depolarization; and EPSPs or EPSP-IPSP sequences. The monosynaptic and (chiefly) polysynaptic nature of these responses was demonstrated. The possible mechanism of afferent control over facial motoneurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 272–282, May–June, 1980.     

Pharmacological modification of evoked caudate nucleus potentials

To stimulation of the Substantia nigra the nucleus caudatoputamen of the rat responds with the release of a short-latent sum action potential that may serve to characterize the interaction between the two nuclear areas. The partly conflicting results reported in the literature about drug effects on this potential prompted us to examine the effectiveness of dopaminergic and cholinergic substances or their antagonists following systematic administration. Chloropromazine increases the amplitude of the potential, while apomorphine has a distinct antagonistic effect. Interesting appear to be the analogical effects of Tricuran, arecoline and apomorphine, and the furtherance of the chloropromazine effect by arecoline.     

Neurophysiology of the motoneurons of the external oculomotor nucleus in the waking cat

The spontaneous and visually induced activity of abducens motoneurons has been recorded in the alert cat. Motoneurons were identified by their antidromic activation from the ipsilateral abducens nerve. All identified motoneurons appeared related to both the position and velocity of the eye in the horizontal plane, although distributed in a wide range. Neural time constants were also measured, showing a mean value similar to that of the mechanical time constant of the oculomotor plant. According to present results, abducens motoneurons of cats and monkeys are very similar, notwithstanding some differences in their activities during saccadic movements.     

Dynamic characteristics of evoked potentials in the cat superior colliculus

Evoked potentials in the superior colliculus during monocular presentation of short flashes to the dark- and light-adapted eye were studied in experiments on cats anesthetized with pentobarbital. On insertion of the recording electrode deep into the superior colliculus simultaneous nonspecular inversion of the second and third components of the evoked potential was observed. The first component was not inverted. During stimulation of the retina by pairs of flashes the second response appeared when the interval between them was 70 msec. The amplitudes of the second and third components of the evoked potential decreased with an increase in the frequency of stimulation. Suggestions regarding the genesis of the various components of the evoked potential are put forward.Institute of the Brain, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 21–27, January–February, 1973.     

Action potentials of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cats

In cats anesthetized with chloralose and pentobarbital stimulation of the infraorbital nerve by a volley of 3 or 4 stimuli 1.2 times stronger than the threshold for excitation of A-fibers caused the generation of action potentials in motoneurons of the masseter muscle if the frequency of stimuli in the volley exceeded 300/sec. Paired stimuli with a strength of 2.0 thresholds, and with an interval of 1.3–4.0 msec between stimuli, led to generation of an action potential by the motoneurons. If the interval exceeded 4 msec stimulation with a strength of 1.2–2.0 thresholds caused biphasic facilitation of the second EPSP with a facilitation factor of between 0.2 and 1.0. The small number of stimuli, combined with their high frequency in the volley, required for action potential generation by masseter motoneurons suggests that they are due to activation of A-fibers of the infraorbital nerve connected with fast-adapted receptors of the vibrissae.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4 pp. 385–389, July–August, 1978.