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.     

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.     

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.     

Postsynaptic potentials of motoneurons evoked by rubrofugal impulsation in the hypoglossal nucleus of the cat

The effect of stimulation of the ipsilateral and contralateral red nuclei on motoneurons of the hypoglossal nucleus was studied in cats anesthetized with chloralose and pentobarbital. In 35 (69%) of the 51 motoneurons tested, PSPs were generated in response to stimulation of the red nuclei by series of 3 to 5 stimuli of threshold strength and with a frequency of 500–600/sec. Of this number, 33 motoneurons responded to stimulation by EPSPs, whose latent periods varied from 3.5 to 14.0 msec (mean value for the ipsilateral red nucleus 5.7±0.75, for the contralateral nucleus 6.8±0.8 msec), whereas two motoneurons responded (after 6.2 msec) by IPSPs. Of the 35 motoneurons responding to stimulation of the red nuclei, stimulation of the lingual nerve evoked EPSPs in 31 and IPSPs in 4 (two of them were inhibited by rubrofugal impulses). IPSPs were generated as a result of stimulation of the lingual nerve in 16 motoneurons which did not respond to rubrofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 62–66, January–February, 1978.     

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.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Increased efficacy of antidromic and orthodromic activation of cat alpha motoneurons upon arrival of coerulospinal volleys

The present study demonstrates the enhanced efficacy of impulse initiation among the hindlimb alpha motoneurons of flexor and extensor origins (n = 35) upon electrical stimulation of the locus coeruleus (LC) in decerebrate cats. When combined with the LC-evoked excitatory postsynaptic potential (EPSP), intracellular hyperpolarization-induced partial and total blocks of antidromic invasion were overcome, resulting in full-spike generation in all cells (n = 21). In three other cells, partial blocks, representing the motoneuron refractoriness resulting from double stimulation at close intervals, were relieved by the concomitant LC-EPSP. When an antidromic volley occurred at a time when the somadendritic (SD) membrane was near threshold, LC stimulation was shown to increase the probability of full-spike initiation as well as to shorten the initial segment (IS)-SD delay, suggesting a coerulospinal enhancement of the safety factor for IS-SD impulse conduction. When coincident with the LC-EPSPs, group Ia EPSPs of flexor and extensor origins were demonstrated to reach the threshold of discharging the cells (n = 4). In those cells exhibiting prominent depolarizing synaptic noise (n = 10), LC stimulation was sufficient to cause the cell to fire action potentials presumably by interacting with concomitant excitatory synaptic drive. The present results advocate that the descending LC excitatory drive has engaged in the action potential initiation process of the alpha motoneuron, facilitating its reaching the firing threshold during concurrent depressed membrane excitability as well as subthreshold converging inputs.     

Effects of 5-hydroxytryptamine on cat spinal motoneurons

The effects of 5-hydroxytryptamine (5-HT) on spinal motoneurons were examined in pentobarbital-anaesthetized cats and in nonanaesthetized decerebrate cats by intracellular recording and extracellular iontophoresis of 5-HT. 5-HT first induced a depolarization and then a long-lasting hyperpolarization (up to 60 min) with unchanged input resistance. The slow hyperpolarization was prevented by the 5-HT antagonists ketanserin (5-HT2), methysergide, and spiperone (5-HT1,2) and mimicked by the agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (5-HT2). The post-spike after hyperpolarization was enhanced after application of 5-HT. A depolarization was induce by the 5-HT agonists (+/-)-8-hydroxy-(2)-(di-n-propylamino)tetralin (5-HT1A) and 1-(2-methoxyphenyl)piperazine (5-HT1). Possible mechanisms for the 5-HT-induced hyperpolarization and its intracellular medication are discussed. The present data suggest multiple effects of 5-HT on cat spinal motoneurons.     

The lateral cervical nucleus in the cat

Summary Profiles of 14 neurons all sectioned through the nucleolar plane and 87 isolated dendritic profiles have been analyzed with respect to the surface area covered by boutons and astroglial processes. This analysis has revealed two different types of neurons within the lateral cervical nucleus (LCN) of the cat. The cell types also differ in other ultrastructural respects. One type, which probably consists of projection neurons, is characterized by a rather large size, a relatively small nucleus, numerous mitochondria, well developed granular and agranular endoplasmic reticulum. The cell membrane of these cells shows somatic spines and the perikaryon is covered with boutons to a mean extent of 42%. The other cell type, which probably is internuncial, is smaller, has a proportionally larger nucleus, few mitochondria and a poorly developed granular and agranular endoplasmic reticulum. These cells show no somatic spines and the perikaryal membrane is covered with boutons to an extent of about 10%. Also the bouton populations contacting the two cell types differ from one another. The proportion of internuncial neurons within the LCN has been estimated to about 8%. The internuncial neurons seem to have no preferential localization.The primary dendrites of the projection neurons have a bouton covering of about 48%. No proportional differences in covering could be revealed between different sizes of dendrites.The results are discussed in relation to what is known about the anatomical and physiological organization of the LCN, and also compared with the results obtained in other similar investigations on other parts of the central nervous system.The author is grateful to fil.kand. Göran Engholm for his help with the statistical considerations.This work was supported by grants from Anders Otto Swärds Stiftelse, Stiftelsen Lars Hiertas minne, Åhlén och Holms stiftelse, Åke Wibergs stiftelse and the Swedish Medical Research Council (Project No B70-12X-2710).     

Morphofunctional characteristics of the accessory structures of the cat lingual receptors

By means of scanning electron microscopy detailed topographic map of the cat tongue was made. It was demonstrated that besides three types of chemoreceptor formations, the dorsal surface of the cat tongue possess the same amount of additional mechanoreceptor structures. By means of registration of afferent impulses, from the lingual nerve fibres at their adequate stimulation, it was possible to determine functional role of some of them.     

Afferent connections of the cat lateral vestibular nucleus

Location within the brain of HP-labeled neurons (origins of projections to the lateral vestibular nucleus) was investigated by iontophoretic injection of this enzyme. Bilateral projections to the following midbrain structures were revealed: the field of Forel, interstitial nuclei of Cajal, oculomotor nerve nuclei, and the red nucleus — to all parts of the lateral vestibular nucleus. Bilateral projections were also shown from more caudally located structures, viz. the superior, medial and inferior (descending) vestibular nuclei, Y groups of the vestibular nuclear complex, facial nucleus and hypoglossi, nucleus prepositus nervi hypoglossi and caudal nuclei of the trigeminal tract; ipsilateral projections from crus IIa of lobulus ansiformus of the cerebellar hemisphere; contralateral projections from the bulbar lateral reticular nucleus and Deiter's nucleus. A tonic organization pattern of afferent inputs from a number of brainstem formations to the dorsal and ventral lateral vestibular nucleus is revealed and trajectories of HP-labeled fiber systems projecting to Deiter's nucleus described.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 494–503, July–August, 1988.     

Monosynaptic excitation of facial motoneurons during electrical stimulation of the red nucleus

Synaptic effects of the red nucleus on motoneurons of the facial nucleus were studied in cats. Impulses from the red nucleus activate motoneurons innervating the auricular, buccal, and orbicularis oculi muscles. Monosynaptic EPSPs appeared in all motoneurons which responded to stimulation. Their mean latent period was 1.5±0.04 msec, duration 12.3 ± 0.34 msec, and rise time between 1.5 and 3.2 msec. Repetitive stimulation of the red nucleus led to marked facilitation of the testing EPSP. Facilitation was maximal when the interval between stimuli was 3.5 msec; it was reduced by either a decrease or an increase in the interval. The functional role of the monosynaptic connections of neurons of the red nucleus and of the facial motoneurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 272–279, May–June, 1972.     

Projections from neurons of the medial terminal nucleus of the accessory optic tract to the caudate nucleus in the cat revealed by combining techniques of retrograde axonal transport and experimentally induced degeneration

Neurons of the medial terminal nucleus of the accessory optic tract receiving direct retinal inputs were shown to project to the heat and body of the caudate nucleus in the cat using techniques of retrograde horseradish peroxidase axonal transport and experimentally induced degeneration. These primarily ipsilateral projections are evenly distributed throughout the aforementioned areas of the nucleus. Neurons of the medial terminal nucleus forming synaptic connections with caudate nucleus cells are distinguished by their varied shapes and sizes, ranging from 20 × 10 to 37.5 × 18 µm and are located in both the ventral and dorsal subdivisions of the nucleus. The supposed functional significance of these projections for the regulation of muscle tonus tension is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 214–219, March–April, 1986.     

Classification of vestibulo-spinal neurons of the cat Deiters' nucleus

Antidromic excitation of neurons of the lateral vestibular nucleus of Deiters in cats in response to stimulation of the vestibulo-spinal tract in the cervical segments of the spinal cord was studied by intracellular microelectrode recording. Individual components of the antidromic action potential and accompanying after-potentials were analyzed and fast and slow neurons distinguished. The vestibulo-spinal neurons were differentiated on the basis of after-potentials accompanying the antidromic action potential. The ratio between fast and slow neurons differed in individual groups. The parameters of the depolarization after-potentials were directly proportional to the duration of the refractory period of the neurons studied. An attempt was made to correlate differences in the responsiveness of neurons with an identical conduction velocity along their axons with the characteristics of the depolarization after-potential.     

Effects of inositol, 1,4,5-trisphosphate injections into cat spinal motoneurons

Inositol 1,4,5-trisphosphate (IP3) was injected iontophoretically into cat spinal motoneurons in pentobarbital-anaesthetized cats and nonanaesthetized, decerebrate cats. Injections of IP3 induced a long-lasting, reproducible hyperpolarization without consistent change in input resistance. The peak amplitude of post-spike afterhyperpolarization (AHP) was significantly increased by IP3 when the membrane potential was adjusted to the control level. Intracellular injections of Ca2+ chelators, which depressed the Ca2(+)-activated AHP, prevented the IP3-induced long-lasting hyperpolarization, suggesting that IP3 acts by a Ca2(+)-dependent mechanism. Intracellular injections of myo-inositol did not consistently induce hyperpolarizations. Also intracellular injections of Li+, which blocks IP3 catabolism, did not prevent the IP3-evoked hyperpolarization. These data suggest that IP3 itself, rather than its breakdown product myo-inositol, is mainly responsible for the hyperpolarizing effect. Possible mechanisms for the IP3-induced hyperpolarization are discussed.