Synaptic processes evoked in red nucleus neurons by stimulation of the substantia nigra in cats

Synaptic processes in red nucleus neurons evoked by stimulation of different parts of the substantia nigra and nucleus interpositus of the cerebellum were investigated by an intracellular recording method in acute experiments on cats. Stimulation of this sort was shown to induce mono- and polysynaptic activation of rubrospinal neurons. Monosynaptic cerebellar and nigral excitatory influences were found to be very similar. These influences were shown to converge on the same rubrospinal neurons. The functional significance of inputs from the substantia nigra to the red nucleus for movement performance is discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 149–158, March–April, 1981.     

Effect of epidural spinal cord stimulation on the activity of lateral vestibular nucleus neurons in the cat

The activity of neurons in Deiters' lateral vestibular nucleus was recorded in decerebrate cats before, during and after spinal cord stimulation. An almost equal number of units were inhibited and excited early during stimulation. Later during stimulation the majority of units was inhibited. Early after cessation of stimulation an ever larger number of units were inhibited to an even larger extent (for about 2 imp/s on the average). Later after stimulus cessation the predominant inhibitory effect could still be noted, as well as excitation in some units. The results could support the hypothesis that the inhibition of Deiters' neurons during and for some time after epidural cord stimulation may play a part in the decrease of limb spasticity. The mechanism of inhibitory and excitatory unitary responses, side effects during stimulation and differences between the experimental model and human state are discussed.     

Acetyl—DL—leucine对猫单侧前庭神经切断后运动平衡能力和前庭外…

本文观测了Ａｃｅｔｙｌ－ＤＬ－ｌｅｕｃｉｎｅ对猫单侧前庭神经切断后前庭代偿的影响。结果显示;ＡＬ加快术后猎在转动横梁测试中运动平衡能力的恢复,但抑制去传入前庭外侧核神经元静息自发放电频率的恢复。ＡＬ促进放电活动与头部左右动体位相关的神经元数量和比例的恢复,从术后的第１周的１０％,逐渐提高到术后第３周的６０％。第５周的７５％。     

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.     

Multicomponent synaptic potentials in rubrospinal neurons of cat brain evoked by corticofugal impulses

The compound nature of EPSP occurring in response to stimulation of the sensorimotor area of the cerebral cortex and the association area of the parietal cortex was shown during acute experiments on cats anesthetized by pentobarbital using an intracellular recording technique. The monosynaptic nature of the two first components of EPSP produced by corticofugal impulses spreading at the average rate of 18.5 and 7.5 msec, respectively, was established. It is postulated that these EPSP components are produced by activating the slow conducting pyramidal and corticorubral neurons. In a portion of rubrospinal neurons the first component of EPSP produced by corticofugal impulses was marked by a fast-rising phase and reflected electrophysiological activation of axosomatic synapses. Findings are discussed with regard to mechanisms reorganizing cortical synaptic inputs to the red nucleus neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 665–672, September–October, 1985.     

Changes in receptive field of tectal neurons evoked by vestibular and acoustic stimulation in pigeons

Responses to visual, acoustic, and vestibular stimuli were studied in neurons of the middle and deep layers of the tectum in the pigeon. Changes in the receptive field (RF) were assessed from comparison of unit responses to isolated movement of a shaped visual stimulus with responses to movement of a stimulus during simultaneous action of a vestibular or acoustic stimulus. Changes in RF of the neuron could be observed during the action of both a vestibular and an acoustic stimulus. These changes affected the identification of the predominant direction of movement of the stimulus, the position of the maximum in the response histogram, and the duration and number of spikes in the response. The direction of change in RF of the neuron was found not necessarily to coincide with the sign of the response to the same neuron to isolated presentation of a vestibular or acoustic stimulus. It is postulated on the basis of the results and data in the literature that the tectum transforms the flow of impulses arriving from the retina depending on the nature of the information received by it from other sensory systems.     

Synaptic processes in pericruciate cortical neurons evoked by pyramidal tract stimulation in cats

In cats anesthetized with chloralose and pentobarbital and immobilized with D-tubocurarine activity of 423 pericruciate cortical neurons was recorded (342 extra- and 81 intracellularly); 78 neurons had spontaneous activity. Stimulation of the pyramidal tract evoked antidromic action potentials in the pyramidal neurons with a latent period of 0.5–16.0 msec. Recurrent and lateral PSPs also developed both in pyramidal and in unidentified neurons in all layers of the cortex; IPSPs were recorded in 46.7% of neurons, EPSPs in 21.0%, mixed reponses in 26.0%, and no visible changes were found in 6.3%. The latent period of the IPSPs was 1.5–14.0 msec, their amplitude 1.3–17.0 mV, their rise time from 4 to 18 msec, and their duration 18–120 msec (sometimes up to 250–500 msec). In 30% of cases in which IPSPs appeared, their course was divided into two phases: fast (duration 10–20 msec) and slow. EPSPs developed after a latent period of 2.6–29.0 msec; their amplitude was 1.0–7.8 mV and their duration from 10.0 to 50.0 msec. In 51.2% of spontaneously active neurons the antidromic volley inhibited their activity in the course of 200–400 msec, in 19.5% it stimulated their activity, in 7.4% it had a mixed effect, and in 21.9% no visible change took place in their activity. The role and participation of axon collaterals of pyramidal neurons and of the interneuronal system in the formation of these processes are discussed.     

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.     

PKC-epsilon translocation in enteric neurons and interstitial cells of Cajal in response to muscarinic stimulation

Interstitial cells of Cajal in the deep muscular plexus (ICC-DMP) of the small intestine express excitatory neurotransmitter receptors. We tested whether ICC-DMP are functionally innervated by cholinergic neurons in the murine intestine. Muscles were stimulated by intrinsic nerves and ACh and processed for immunohistochemistry to determine these effects on PKC-epsilon activation. Under control conditions, PKC-epsilon-like immunoreactivy (PKC-epsilon-LI) was only observed in myenteric neurons within the tunica muscularis. Electrical field stimulation or ACh caused translocation of neural PKC-epsilon-LI from the cytosol to a peripheral compartment. After stimulation, PKC-epsilon-LI was found in spindle-shaped cells in the DMP. These cells were identified as ICC-DMP by Kit-LI and vimentin-LI. PKC-epsilon-LI in ICC-DMP and translocation of PKC epsilon-LI in neurons were blocked by tetrodotoxin or atropine, suggesting that these responses were due to activation of muscarinic receptors. Western blots also confirmed translocation of PKC-epsilon-LI. In conclusion, PKC-epsilon translocation is linked to muscarinic receptor activation in ICC-DMP and a subpopulation of myenteric neurons. These studies demonstrate that ICC-DMP are functionally innervated by excitatory motoneurons.     

Pacemaker potentials generated by interstitial cells of Cajal in the murine intestine

Pacemaker potentials were recorded in situ from myenteric interstitial cells of Cajal (ICC-MY) in the murine small intestine. The nature of the two components of pacemaker potentials (upstroke and plateau) were investigated and compared with slow waves recorded from circular muscle cells. Pacemaker potentials and slow waves were not blocked by nifedipine (3 µM). In the presence of nifedipine, mibefradil, a voltage-dependent Ca²⁺ channel blocker, reduced the amplitude, frequency, and rate of rise of upstroke depolarization (dV/dt_max) of pacemaker potentials and slow waves in a dose-dependent manner (1–30 µM). Mibefradil (30 µM) changed the pattern of pacemaker potentials from rapidly rising, high-frequency events to slowly depolarizing, low-frequency events with considerable membrane noise (unitary potentials) between pacemaker potentials. Caffeine (3 mM) abolished pacemaker potentials in the presence of mibefradil. Pinacidil (10 µM), an ATP-sensitive K⁺ channel opener, hyperpolarized ICC-MY and increased the amplitude and dV/dt_max without affecting frequency. Pinacidil hyperpolarized smooth muscle cells and attenuated the amplitude and dV/dt_max of slow waves without affecting frequency. The effects of pinacidil were blocked by glibenclamide (10 µM). These data suggest that slow waves are electrotonic potentials driven by pacemaker potentials. The upstroke component of pacemaker potentials is due to activation of dihydropyridine-resistant Ca²⁺ channels, and this depolarization entrains pacemaker activity to create the plateau potential. The plateau potential may be due to summation of unitary potentials generated by individual or small groups of pacemaker units in ICC-MY. Entrainment of unitary potentials appears to depend on Ca²⁺ entry during upstroke depolarization. pacemaker activity; slow waves; gastrointestinal motility; calcium channel     

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.     

The contribution of the lateral semicircular canal to the short latency vestibular evoked potentials in cat

Short latency vestibular evoked potentials (VsEPs) to angular acceleration impulses (maximal intensity 20,000°/sec², rise time 1.5–3 msec) were recorded by skin electrodes in cats before and after various surgical procedures. Under general anesthesia, the animals underwent unilateral labyrinthectomy and the VsEPs in response to stimulation of the remaining inner ear in the plane of the lateral semicircular canal (SCC) with the head flexed 20°–25° were recorded as a baseline. The lateral SCC was then selectively obliterated near its ampulla. This induced major changes in the VsEPs recorded in response to stimulation of the remaining inner ear in this plane: the first 2 VsEP waves were absent, and only longer latency, smaller amplitude waves were present in response to both clockwise and counterclockwise stimulation. On the other hand, obliteration of the anterior and posterior SCCs and, in addition, destruction of both maculae were without major effects on the first 2 VsEP waves in response to excitatory stimulation. The results confirm that when the head is flexed 20°–25° and stimulated with angular acceleration impulses in the horizontal plane, the major site of initiation of the VsEPs in cats and probably in man is the crista ampullaris of the lateral SCC.