Tongue-muscle-controlling motoneurons in the Japanese toad: topography,morphology and neuronal pathways from the ‘snapping-evoking area’ in the optic tectum

As a step to clarifying the neural bases for the visually-guided prey-catching behavior in the toad, special attention was paid to the flipping movement of the tongue. Tongue-muscle-controlling motoneurons were identified antidromically, and their topographical distribution within the hypoglossal nucleus, the morphology, and the neuronal pathways from the optic tectum including the 'snapping-evoking area' (see below) to these motoneurons were investigated in paralyzed Japanese toads using intracellular recording techniques. The morphology of motoneurons innervating the tongue-protracting or retracting muscles (PMNs or RMNs respectively) was examined by means of intracellular-staining (using HRP/cobaltic lysine) and retrograde-labeling (using cobaltic lysine) methods. Both PMNs and RMNs showed an extensive spread of the branching trees of dendrites; 4 dendritic fields were distinguished: lateral/ventrolateral, dorsal/dorsolateral, medial, and in some motoneurons, contralateral dendritic fields, although there was a tendency for the dorsal/dorsolateral dendritic field to be less extensive in the PMNs than in the RMNs. The axons of both PMNs and RMNs arose from thick dendrites, ran in a ventral direction without any axon-collaterals branching off, and then entered the hypoglossal nerve. The PMNs and RMNs were distributed topographically within the hypoglossal nucleus; the RMNs were located rostrally within the nucleus, whereas the PMNs were located more caudally within it. In about 3/4 of the RMNs tested, depolarizing potentials [presumably the excitatory postsynaptic potentials (EPSPs)], on which action potentials were often superimposed, were evoked by electrical stimuli applied to the nerve branch innervating the tongue protractor. These EPSPs were temporally facilitated when the electrical stimuli were applied at short intervals (10 ms). Both PMNs and RMNs showed hyperpolarizing potentials (IPSPs) in response to single electrical stimuli of various intensities (10-200 microA) applied to the 'snapping-evoking area' (lateral/ventrolateral part of the optic tectum) on either side. These IPSPs were facilitated after repetitive electrical stimulations at short intervals (10 ms) and of weaker intensities (down to 10 microA); i.e., a temporal facilitation of the IPSPs was observed. On the other hand, large and long-lasting EPSPs which prevailed over the underlying IPSPs were evoked after repetitive electrical stimulations (a few pulses or more) at short intervals (10 ms) and of stronger intensities (generally 90 microA or more); thus, a temporal facilitation of the EPSPs was also observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

An intracellular study of pudendal afferent inputs onto tail motoneurons in the spinalized cat

Postsynaptic potentials, elicited by stimulation of the sensory pudendal (SPud) and superficial perineal nerves (SPeri) on both sides, were recorded from motoneurons innervating tail muscles in the non-anaesthetized and spinalized cat. The stimulation of SPud and SPeri on both sides predominantly produced excitatory postsynaptic potentials (EPSPs) in all kinds of tail motoneurons (70-95%). The inhibitory postsynaptic potentials (IPSPs) were often observed in motoneurons innervating ventral tail muscles (30-33%). The means of averaged central latencies of EPSPs and IPSPs ranged from 4.3 to 7.3 ms, and from 4.6 to 8.4 ms, respectively. The findings suggests that polysynaptic neuronal pathways from pudendal nerve to tail motoneurons produce tonic activities of all tail muscles to raise the tail in micturation, defecation and sexual movements which are induced by stimulation of pudendal nerves.     

蟾蜍伸舌肌和缩舌肌运动神经元的双侧投射──荧光染料逆行标记

本实验将荧光染料固兰（ＦａｓｔＢｌｕｅ,ＦＢ）和核黄（ＮｕｃｌｅａｒＹｅｌｌｏｗ,ＮＹ）分别注入蟾蜍颏舌肌（Ｍ．ｇｅｎｉｏｇｌｏｓｓｕｓ）和舌骨舌肌（Ｍ．ｈｙｐｏｇｌｏｓｓｕｓ）,通过边行标记技术研究了伸舌肌和缩舌肌运动神经元（ＰＭＮＳ和ＲＭＮｓ）在延髓舌下核内的分布,结果表明ＰＭＮｓ和ＲＭＮｓ均位于延髓舌下核的背内侧核（ＤＭＮ）内,并发出侧投射支配舌肌,且其部分神经元为双标神经元。     

Corticospinal transmission to motoneurons in cervical spinal cord slices from adult rats

Cervical spinal cord slices were prepared from adult rats. Intracellular recordings from motoneurons revealed that electrical stimulation of the ventralmost part of the dorsal funiculus (which contains primarily descending corticospinal axons) elicited EPSPs in 75% of the neurons. The latencies of these EPSPs tended to be shorter than those elicited by dorsal horn gray matter stimulation. Pairs of subthreshold dorsal funiculus stimuli were able to elicit action potentials in motoneurons. These data are consistent with previous morphological and electrophysiological studies indicating that cervical motoneurons receive both mono-and polysynaptic corticospinal inputs. In addition, motoneurons were markedly depolarized by iontophoretic application of AMPA or KA (7 out of 7 neurons), but only weakly depolarized by NMDA (1 out of 6 neurons). CNQX (but not AP-5) blocked EPSPs elicited by dorsal funiculus stimulation. Thus, corticospinal transmission to motoneurons is mediated primarily by non-NMDA glutamate receptors.     

Synaptic nature of the principal components of the evoked potential in the general cortex of the turtle forebrain

The nature of the principal components of the evoked potential of the general cortex of the turtle forebrain was studied in response to electrical stimulation of the contralateral optic nerve. Comparison of these components with postsynaptic potentials of the neurons of this structure showed that the four fast negative waves of the evoked potential correspond to fast EPSPs, which are independent of one another. The positive wave of the evoked potential is the sum of several IPSPs. The slow negative and, to some extent, the positive wave are a reflection of the slow EPSP. It is shown that early EPSPs are generated on portions of the apical dendrites which are further from the soma than those generating late fast EPSPs and also the IPSP and slow EPSP. Axo-somatic contacts are perhaps also concerned in the generation of the last-named potential.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No.3, pp.261–271, May–June, 1973.     

Statistical analysis of mediator release from the cyto-neural junction of the posterior canal of the labyrinth isolated from the frog]

The transmitter release mechanism was investigated at the cyto-neural junction of the frog labyrinth posterior canal. Low frequency (less than 100/s) non overlapping EPSPs were intracellularly recorded both at rest and during inhibitory mechanical stimulation of the canal (2-8 deg/s2). Recordings were obtained: in control solution; in the presence of increased external Ca2+ (9 mM); in Ca-free EGTA (5 mM) solution and during electrical activation at 50 Hz of the posterior canal inhibitory efferent system. Individual synaptic potentials were digitized and their peak amplitudes, their time integrals as well as the time intervals between them were evaluated. The time intervals proved to be exponentially distributed, suggesting a random EPSP occurrence. The analytical reconstruction of the EPSP waveform indicated that a gamma- function fitted reasonably well both the single and averaged events. As regards the averaged event, despite the scatter in the values of the gamma-function exponential factor (range 1.1-2.2), in the EPSP time-to-peak (0.6-1.2 ms) and peak amplitude (0.9-2.7 mV) displayed by the units, no significant differences were observed in the same fibre between control and test conditions. Moreover, the event peak amplitude distribution represented by cumulative plots or amplitude histograms was fitted by a lognormal function. The distributions obtained for the same unit in control solution proved to be not significantly different from those successively obtained under test conditions. The unimodal and continuous EPSP distributions, together with the unvarying characteristics of the single events, strongly suggest that the observed potentials are true mEPSPs due to the release of single quanta of transmitter.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Rubrospinal synaptic influences on the lumbar motoneurons of the rat

Intracellular recording was employed in experiments on rats with the nervous system intact and after acute pyramidotomy to study the postsynaptic effects produced in the lumbar motoneurons on stimulation of the nucleus ruber. Stimulation of this nucleus with single stimuli and with a short series of stimuli caused excitatory and inhibitory postsynaptic potentials (EPSP and IPSP) to develop in the motoneurons. Most of the EPSP recorded were disynaptic, but response development involved a monosynaptic segmental delay in five of the 124 cells that exhibited EPSP. A capacity for high-frequency potentiation was a characteristic feature of the disynaptic excitatory and inhibitory effects. Transmembrane polarization of the motoneurons had a marked influence on the amplitude of the disynaptic EPSP and IPSP. The properties of the disynaptic rubrospinal influences were similar to those described for the cat.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 266–273, May–June, 1971.     

Postural interneurons in the abdominal nervous system of lobster

The nature of the synaptic relationship between 7 identified postural interneurons and 5 pairs of superficial motoneurons was examined by obtaining dual intracellular recordings from interneuron-motoneuron pairs in the lobster 2nd abdominal ganglion. For six different interneuron-motoneuron pairs EPSPs recorded from motoneurons occurred with a short (1 to 3 ms) fixed latency following each presynaptic spike recorded from the interneuron. This suggests that there is a monosynaptic relationship between these interneurons and motoneurons. Monosynaptic pathways accounted for 27% of all excitatory connections. Preliminary evidence indicates that the monosynaptic potentials are mediated by an excitatory chemical synapse since: all IPSPs occurred with latencies greater than 5 ms, there was no evidence for electrical coupling, and one of the interneurons produced facilitating PSPs. A majority of all monosynaptic connections were made by two of the flexion producing interneurons (FPIs), 201 and 301. The synaptic outputs of these FPIs were similar in that both made monosynaptic connections with a different bilaterally homologous pair of motoneurons. Both also produced larger EPSPs and more vigorous spiking in contralateral members of the bilateral motoneuron pairs. A previous study demonstrated that interneurons 201 and 301 are the only postural interneurons yet identified that express motor programs indistinguishable from command neurons. Taken together, these results suggest that certain intersegmental interneurons share properties with command neurons and driver neurons, and that there may not be a sharp morphological or functional distinction between these two cell types.     

Relation between fast and slow elemental synaptic potentials in command neurons in Helix lucorum taurica L

In experiments on a semi-intact snail preparation and a preparation of the snail isolated CNS, after spikes (Sp) evoked in presynaptic neurones by depolarizing current, not only rapid (R) EPSPs emerged in the command neurones of the defensive reaction of closing the pneumostome, but they were also followed by slow (S) EPSPs lasting over 2 min. For each single synaptic contact, the R and S EPSP amplitudes were in a good linear correspondence. In different synapses no direct connection was observed between R EPSP and S EPSP. It is suggested that R and S EPSPs may set in as a result of the action of different substances on the command neurones. Functional significance of S EPSPs with different amplitudes in different command neurones may consist in a prolonged specific preparation of the neurones for the action of stimuli.     

Synaptic inputs to the omega neuron of the cricket Teleogryllus oceanicus: differences in EPSP waveforms evoke by low and high sound frequencies

EPSP waveforms were recorded from the omega neuron of Teleogryllus oceanicus for 5 kHz and ultrasonic sound stimuli. EPSPs in response to 5 kHz stimuli were smooth in shape and increased in amplitude with increasing stimulus intensity, while responses to ultrasound consisted of series' of large, discrete, unitary EPSPs, which increased in frequency with stimulus intensity.The hypothesis that a few, synaptically potent receptors might account for ultrasound sensitivity was tested by examining temporal coupling between ultrasound responses of the omega neuron and of another ultrasound-sensitive neuron, INT-1. INT-1 spikes were temporally correlated both to omega neuron spikes and to the large EPSPs recorded in the omega neuron. Coupling was not apparent for 5 kHz stimuli.The omega neuron encodes the intensity of 5 kHz and ultrasonic stimuli with similar resolution. Response latencies are markedly shorter for ultrasonic stimuli.These findings suggest that 5 kHz information is carried by a relatively large number of receptors, each of which has only a small effect on central neurons, while ultrasound information is carried by a few, synaptically potent, receptors.     

Amygdaloid or cortical facilitation of antidromic activity of trigeminal motoneurons in the rat

1. Electrical stimulation of the rat's contralateral central amygdaloid (CAm) nucleus or the contralateral frontal cortex markedly augmented the antidromic field potential evoked by stimulation of mylohyoid (Myl) nerve. 2. This facilitation was shown to be due to EPSPs of the mylohyoid-anterior digastric (Myl-Dig) motoneurons. 3. In a few motoneurons, cortical EPSPs had fixed short latencies following high-frequency double stimuli and this is believed to be due to a monosynaptic pathway. 4. The amygdaloid or cortically evoked EPSPs relieved IS-SD blockade in a few motoneurons and also facilitated antidromic discharge in others which did not show any IS or M spike response to the same subthreshold antidromic stimulation. The underlying mechanisms are discussed.     

The Enhancement of the N1 Wave Elicited by Sensory Stimuli Presented at Very Short Inter-Stimulus Intervals Is a General Feature across Sensory Systems

Background

A paradoxical enhancement of the magnitude of the N1 wave of the auditory event-related potential (ERP) has been described when auditory stimuli are presented at very short (<400 ms) inter-stimulus intervals (ISI). Here, we examined whether this enhancement is specific for the auditory system, or whether it also affects ERPs elicited by stimuli belonging to other sensory modalities.

Methodology and Principal Findings

We recorded ERPs elicited by auditory and somatosensory stimuli in 13 healthy subjects. For each sensory modality, 4800 stimuli were presented. Auditory stimuli consisted in brief tones presented binaurally, and somatosensory stimuli consisted in constant-current electrical pulses applied to the right median nerve. Stimuli were delivered continuously, and the ISI was varied randomly between 100 and 1000 ms. We found that the ISI had a similar effect on both auditory and somatosensory ERPs. In both sensory modalities, ISI had an opposite effect on the magnitude of the N1 and P2 waves: the magnitude of the auditory and the somatosensory N1 was significantly increased at ISI≤200 ms, while the magnitude of the auditory and the somatosensory P2 was significantly decreased at ISI≤200 ms.

Conclusion and Significance

The observation that both the auditory and the somatosensory N1 are enhanced at short ISIs indicates that this phenomenon reflects a physiological property that is common across sensory systems, rather than, as previously suggested, unique for the auditory system. Two of the hypotheses most frequently put forward to explain this observation, namely (i) the decreased contribution of inhibitory postsynaptic potentials to the recorded scalp ERPs and (ii) the decreased contribution of ‘latent inhibition’, are discussed. Because neither of these two hypotheses can satisfactorily account for the concomitant reduction of the auditory and the somatosensory P2, we propose a third, novel hypothesis, consisting in the modulation of a single neural component contributing to both the N1 and the P2 waves.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

Synaptic potentials of digastric-muscle motoneurons

We studied the antidromic and synaptic potentials evoked from 32 digastric-muscle motoneurons by stimulation of the motor nerve to this muscle, different branches of the trigeminal nerve, and the mesencephalic trigeminal nucleus. Antidromic potentials appeared after 1.1 msec and lasted about 2.0 msec. Stimulation of the infraorbital, lingual, and inferior alveolar nerves led to development of excitatory postsynaptic potentials (EPSP) and action potentials in the motoneurons. The antidromically and synaptically evoked action potentials of the digastric-nerve motoneurons were characterized by weak after-effects. We were able to record EPSP and action potentials in two of the motoneurons investigated in response to stimulation of the mesencephalic trigeminal nucleus, the latent period being 1.3 msec. This indicates the existence of a polysynaptic connection between the mesencephalic-nucleus neurons and the digastric-muscle motoneurons. Eight digastric-muscle motoneurons exhibited inhibitory postsynaptic potentials (IPSP), which were evoked by activation of the afferent fibers of the antagonistic muscle (m. masseter). The data obtained indicate the presence of reciprocal relationships between the motoneurons of the antagonistic muscles that participate in the act of mastication.A. A. Bogomol'ts Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 52–57, January–February, 1971.     

齿状回突触后电位和群峰电位的负相关现象

考察大鼠静卧状态下,相同强度刺激信号作用于前穿质通道时,海马齿状回颗粒细胞诱发电场电位的兴奋性突触后电位EPSP和群峰电位PS之间的一种负相关变化关系,即EPSP斜率减小时,PS幅值增加。采用同时记录齿状回诱发电位和大脑皮层ECoG电位的方法,分析诱发电位各成份和ECoG功率谱密度之间的关系,可见ECoG出现低频高幅慢波时,与ECoG出现高频低幅快波时比较,齿状回诱发响应的PS幅值较大,而EPSP斜率较小。这可能是因为：中脑网状结构上行激励系统通过丘脑－皮层回路使ECoG去同步化（出现低幅快波ECoG）时,同时也通过另一途径,即隔－海马连接,激活了作用于齿状回颗粒细胞胞体的抑制性神经通路,使得颗粒细胞兴奋性降低,从而使反应动作电位总和的PS幅值减小。在麻醉剂乌拉坦作用下,EPSP和PS的负相关变化减小或消失。这种负相关现象对于研究海马的生理功能具有重要的意义。     

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.     

Postsynaptic excitation and in hibition in neurons of the turtle general cortex in response to moving stimuli

Responses of the general cortex to moving stimuli were studied in turtles. The evoked potential, the synaptic nature of its individual components, and the mechanisms of their generation were analyzed. The evoked potential had a negative-positive sequence. The negative part consisted of a slow negative wave on which fast negative complexes were superposed. These components reflected EPSPs of afferent nature generated on dendrites of the principal neurons. The first fast negative complex was followed by a rhythmic discharge superposed on the slow negative and positve waves. The negative waves of the rhythmic discharge were shown to reflect EPSPs and the positive waves IPSPs, probably generated on dendrites of cortical neurons. The rhythmic EPSP — IPSPs are evidently generated by a feedback mechanism, whereas the positive wave reflects dendritic IPSPs of the principal neurons.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 249–256, May–June, 1977.     

Functional characteristics of the input-output correlation in the frog vestibular nuclei

Field and intracellular potentials were recorded in the vestibular nuclear complex of the frog perfused brain following stimulation of the anterior branch of the ipsilateral vestibular nerve and spinal cord. Mono- and polysynaptic EPSPs with orthodromic APs were recorded from vestibular neurones following vestibular nerve stimulation. Antidromic activation of neurones sending their axons to the labyrinth was also recorded. Antidromic APs of vestibulo-spinal neurones evoked with mean latency of 1.43 and 2.19 ms to stimulation of cervical and lumbar cords, respectively, were revealed.     

Factors that control the efficacy of group Ia synapses in alpha-motoneurons

1.) This review considers factors that produce systematic variations in the amplitude of monosynaptic group Ia EPSPs in triceps surae alpha-motoneurons belonging to different motor unit types. 2.) Anatomical studies using horseradish peroxidase to label functionally-identified group Ia afferents and motoneurons postsynaptic to them, and combined anatomicalelectro-physiological studies of type-identified alpha-motoneurons, have constrained some of the factors that produce variations in peak Ia EPSP amplitude in different cells. 3.) Computer modeling studies based on these experimental data, together with other evidence in the literature, suggest that the major factor that produces systematic variation in Ia EPSP amplitudes in type FF, FR, and S motoneurons is a corresponding variation in the density of active group Ia synapses. 4.) Although EPSP amplitudes are also affected by the relative conductance of the somatic membrane, as reflected in the dendritic-to-somatic conductance ratio, it is possible that at least some of this influence is an artifact produced by microelectrode penetration.