Excitatory and inhibitory responses of the ongoing sympathetic discharge in single renal neurons to liminal stimulation of aortic C-fibres in the rabbit

Excitatory and inhibitory responses of sympathetic discharge were recorded in single renal postganglionic neurons of rabbits anaesthetized with urethane and chloralose. The animals were vagotomized and had transected aortic nerves. Responses were elicited by single volleys in the aortic C-fibres. Excitatory responses consisted in short-lasting increase in the rate of ongoing sympathetic discharge and were followed by inhibitory responses. Excitatory effects together with inhibitory responses were seen in 68% of units (19/28). Only excitatory effects appeared in 2 neurons (7.1%) and only inhibitory effects in 7 neurons (25%). In renal neurons exhibiting both effects, the excitatory responses appeared after latency of 172 +/- 8 ms (x +/- S.D.) and had duration of 64 +/- 11 ms. Inhibitory effects had latency o f 257 +/- 10 ms and their duration amounted to 265 +/- 22 ms. In more than half of recordings the excitatory responses were separated from the inhibitory effects by discharge lasting 33 +/- 4 ms. Significant correlations between latencies of excitatory and inhibitory responses and between duration of excitatory and latency of inhibitory responses suggest interaction between both effects. Increase in the number of afferent volleys (1 through 5) evoked relatively small changes in duration of the excitatory effect indicating that temporal facilitation is of minor importance in generating this response. Temporal facilitation was found to play an important role in determining duration of the inhibitory response. Comparison of effects of unilateral and bilateral stimulation of the aortic C-fibres showed larger occlusion of durations of the excitatory than inhibitory responses.     

Responses of motoneurons undergoing chromatolysis

The delayed and asynchronous firing of chromatolytic motoneurons in response to group I afferent volleys is shown to be evoked monosynaptically, there being an abnormally long and variable delay between onset of monosynaptic action and generation of impulse discharge. Intensity of monosynaptic excitatory action is reduced, and considerable variability in the form of successively evoked postsynaptic potentials is often observed. No evidence has been found for the development of excitatory group I polysynaptic pathways. Reduction in responsiveness of finer dendrites is indicated by the feeble "d" response evoked by an antidromic volley in a chromatolytic motor nucleus. Antidromic impulses appear to invade the cell bodies and coarse dendrites, but die out at points short of the normal extent of dendritic invasion. Vigorous firing of Renshaw cells can be elicited by antidromic volleys. Chromatolytic motoneurons appear to maintain reasonably normal resting membrane potentials, but are more susceptible to damage than are normal cells. Action potentials are large and usually overshoot the resting potential level. Post spike potentials are similar to those of normal cells except for a less prominent, or absent, early phase of depolarisation. In contrast with the reduced responsiveness of peripheral dendrites, there is a lowered threshold for antidromic and segmental reflex synaptic activation of the more central regions, probably the cell bodies and nearby coarse dendrites, of motoneurons undergoing chromatolysis.     

Early post-tetanic potentiation and low frequency depression of some group I reflex actions

Group I reflex functions, namely monosynaptic reflex transmission, facilitation of synergists, and direct and disynaptic inhibition, show early post-tetanic potentiation following conditioning with a brief, high frequency, tetanus. Of these reflex functions, monosynaptic transmission always shows low frequency depression. Direct inhibitory pathways, and therefore inhibitory junctions, are insensitive to low frequency depression. The fact that direct inhibition can be potentiated shows it to be sufficiently labile that a decrease in efficacy at inhibitory junctions during repetitive activity should be revealed. Disynaptic inhibition often shows low frequency depression. As it is likely that inhibitory junctions in the direct and disynaptic pathways are similar, the low frequency depression of disynaptic inhibition is probably due to the properties of the excitatory relay between afferent fibers and interneurons in that pathway. Facilitation between synergists is often more depressed when the conditioning and testing volleys are nearly simultaneous than when they are separated by 1 to 1.5 msec. This result indicates that an early and rapid phase of action, responsible for homonymous and heteronymous transmission, is more sensitive to low frequency depression than is residual facilitation. In general, reflex transmission is more sensitive than are other aspects of action by group I fibers to events concurrent with and following repetitive activation.     

Monosynaptic reflex response of spinal motoneurons to graded afferent stimulation

Monosynaptic reflex response of spinal motoneurons to graded afferent volleys has been studied in natural populations and in a representative sample of individual motoneurons. By analysis of input-response relations certain of the requirements for initiation of reflex discharge have been defined. Initation of motoneuron discharge by monosynaptic afferent excitatory volleys results from the development of transmitter potentiality among members of a pool. Transmitter potentiality is considered to have the following characteristics: 1. It is a function of the number of active excitatory synaptic knobs, the degree to which such knobs are aggregated on the motoneuron soma, and the intensity of action per knob. 2. It has an appreciable spatial decrement and rapid temporal decay. 3. While transmitter potentiality has considerable dependence on number of active excitatory knobs, proximity of such knobs is an important variable. Total activation of a discrete zone does not appear to be necessary for initiation of discharge. In addition to initiation of discharge, volleys in monosynaptic afferent excitatory fibers facilitate response otherwise engendered. Such facilitation depends upon the production of an increment in transmitter potentiality. Facilitator potentiality has the following characteristics: 1. It depends principally on number of active excitatory synaptic knobs and intensity of action per knob. 2. Facilitatory action may result from synchronous activity in knobs interspersed among aggregations of knobs otherwise activated, thus fulfilling spatial requirements for transmitter potentiality. Alternatively a residual facilitation may result from a generalized action. 3. Residual facilitation has a slow temporal decay in comparison with transmitter potentiality.     

Inhibitory effects of beta-alanine on the vagal efferent and afferent excitatory responses of the stomach to stimulation of vagal trunk in cats.

The effects of beta-alanine on the electrically evoked vagal efferent (hexamethonium-sensitive initial excitatory response) and afferent (hexamethonium-resistant delayed excitatory response) responses of the cat stomach were studied. beta-alanine (30 to 300 micrograms/kg, i.v.) dose-dependently inhibited both the efferent and afferent response. The IC50 values of beta-alanine on the efferent and afferent response were 296 +/- 65 micrograms/kg and 128 +/- 35 microgram/kg, respectively. Maximal inhibitory effects of beta-alanine (300 micrograms/kg, i.v.) appeared about 1 hr after the injection. Glycine and taurine (100 to 10,000 micrograms/kg) did not affect these responses. Treatment with hexamethonium (10 mg/kg, i.v.) prevented the efferent response, but augmented the afferent response. The treatment with hexamethonium abolished the inhibitory effect of beta-alanine on the afferent response. Both picrotoxin (100 and 500 micrograms/kg, i.v.) and bicuculline (2000 micrograms/kg, i.v.) antagonized the inhibitory effects of beta-alanine on the vagal efferent and afferent responses of the stomach. The present experiments clearly demonstrated that beta-alanine inhibited both the vagal efferent and afferent excitatory responses of stomach to electrical stimulation of vagal trunk in cats.     

Discharge frequency and excitability of human firing motoneurone

The excitability of firing motoneurones activated by voluntary contraction of the flexor carpi ulnaris or tibialis anterior was tested by single excitatory Ia afferent volleys. In order to estimate the stimulation effects, the peri-stimulus time histograms of single motoneurones were plotted, and the firing indices were calculated. It was shown that the firing-frequency effect was absent within the range of 4-14 imp/s during testing by low-intensity excitatory volley. At higher intensity of afferent volley, the excitability increased at a low firing rate. It is suggested that the characteristics of the interspike-interval excitability trajectories underlie these relations. These findings made it possible to explicate some conflicting literature data which were usually reported without taking the afferent volley intensity effect into account. The mechanisms controlling the firing motoneurone excitability and possible trajectories of interspike-interval membrane potential in human motoneurones are discussed.     

Static and dynamic properties of synaptic transmission at the cyto- neural junction of frog labyrinth posterior canal

The properties of synaptic transmission have been studied at the cyto-neural junction of the frog labyrinth posterior canal by examining excitatory postsynaptic potential (EPSP) activity recorded intraaxonally from the afferent nerve after abolishing spike firing by tetrodotoxin. The waveform, amplitude, and rate of occurrence of the EPSPs have been evaluated by means of a procedure of fluctuation analysis devised to continuously monitor these parameters, at rest as well as during stimulation of the semicircular canal by sinusoidal rotation at 0.1 Hz, with peak accelerations ranging from 8 to 87 deg.s-2. Responses to excitatory and inhibitory accelerations were quantified in terms of maximum and minimum EPSP rates, respectively, as well as total numbers of EPSPs occurring during the excitatory and inhibitory half cycles. Excitatory responses were systematically larger than inhibitory ones (asymmetry). Excitatory responses were linearly related either to peak acceleration or to its logarithm, and the same occurred for inhibitory responses. In all units examined, the asymmetry of the response yielded nonlinear two-sided input-output intensity functions. Silencing of EPSPs during inhibition (rectification) was never observed. Comparison of activity during the first cycle of rotation with the average response over several cycles indicated that variable degrees of adaptation (up to 48%) characterize the excitatory response, whereas no consistent adaptation was observed in the inhibitory response. All fibers appeared to give responses nearly in phase with angular velocity, at 0.1 Hz, although the peak rates generally anticipated by a few degrees the peak angular velocity. From the data presented it appears that asymmetry, adaptation, and at least part of the phase lead in afferent nerve response are of presynaptic origin, whereas rectification and possible further phase lead arise at the encoder. To confirm these conclusions a simultaneous though limited study of spike firing and EPSP activity has been attempted in a few fibers.     

Inhibitory Contribution to Suprathreshold Corticostriatal Responses: An Experimental and Modeling Study

Neostriatal neurons may undergo events of spontaneous synchronization as those observed in recurrent networks of excitatory neurons, even when cortical afferents are transected. It is necessary to explain these events because the neostriatum is a recurrent network of inhibitory neurons. Synchronization of neuronal activity may be caused by plateau-like depolarizations. Plateau-like orthodromic depolarizations that resemble up-states in medium spiny neostriatal neurons (MSNs) may be induced by a single corticostriatal suprathreshold stimulus. Slow synaptic depolarizations may last hundreds of milliseconds, decay slower than the monosynaptic glutamatergic synaptic potentials that induce them, and sustain repetitive firing. Because inhibitory inputs impinging onto MSNs have a reversal potential above the resting membrane potential but below the threshold for firing, they conform a type of “shunting inhibition”. This work asks if shunting GABAergic inputs onto MSNs arrive asynchronously enough as to help in sustaining the plateau-like corticostriatal response after a single cortical stimulus. This may help to begin explaining autonomous processing in the striatal micro-circuitry in the presence of a tonic excitatory drive and independently of spatio-temporally organized inputs. It is shown here that besides synaptic currents from AMPA/KA- and NMDA-receptors, as well as L-type intrinsic Ca²⁺- currents, inhibitory synapses help in maintaining the slow depolarization, although they accomplish the role of depressing firing at the beginning of the response. We then used a NEURON model of spiny cells to show that inhibitory synapses arriving asynchronously on the dendrites can help to simulate a plateau potential similar to that observed experimentally. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Afferent sensillar inputs to the Retzius cell of the leech Hirudo medicinalis

Water-wave and photic stimulation of the sensilla elicits synaptic potentials identical to those elicited by electrical stimulation of the segmental roots. Mechanical stimulation elicits a localized IPSP and a generalized EPSP in the RCs and an IPSP in the AE motoneurons. Photic stimulation gives rise to a generalized EPSP in the RCs alone. The impulse discharges elicited in the afferent fibers by the two kinds of stimuli is transmitted along the cord both anteriorly and posteriorly to the stimulated segment. This implies that the afferent impulses excite a pool of intersegmental neurons in each ganglion, which distribute their discharges to the adjacent ganglia. The evidence for occlusion between cordal and photically elicited volleys indicates that it shares with the sensillar input a common pool of interneurons. The possible functional significance of the inhibitory and excitatory inputs is discussed.     

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.     

Synaptic effects elicited in the Retzius cells of the leech Hirudo medicinalis by stimulation of the segmental roots

Electrical stimulation of the segmental roots of each ganglion of Hirudo medicinalis, elicits in both Retzius' cells inhibitory and excitatory effects. The IPSP and EPSP are chemical in nature, being dependent on the membrane potential, and suppressed by high Mg++. Selective inactivation of one RC shows that the responses of the contralateral RC are not due to electrotonic coupling between the two cells, but to synaptic actions impinging upon the membrane of both RCs. The two synaptic potentials appear to be mediated by two set of fibres with a different threshold to electrical stimulation. Their actions on the RCs appear to be polysynaptic on the basis of central latency. Simultaneous stimulation of two roots shows evidence for occlusion for IPSP and summation for EPSP, confirming the polysynaptic nature of the effects. The possible functional significance of the inhibitory and excitatory pathways, is discussed.     

Diphasic synaptic potentials and prolonged poststimulus hyperpolarization in Helix pomatia neurons

Synaptic activity of neurons giving diphasic excitatory-inhibitory potentials in response to orthodromic stimulation was recorded intracellularly. In response to stimulation of nerves by a single short pulse these neurons developed only the excitatory component of the diphasic potential, but with a longer stimulus a prolonged inhibitory phase, partly suppressing the initial excitatory component, was added. The excitatory phase appeared only when the resting potential reached a certain level. In their response to repetitive stimulation, neurons with a diphasic potential are divided into habituating and nonhabituating. The diphasic potential can also arise in response to application of acetylcholine to the soma of these neurons. It is postulated that this potential reflects the response of different receptors of the postsynaptic membrane to the same mediator. Prolonged poststimulus hyperpolarization can be obtained after repetitive orthodromic or direct stimulation of some neurons. However, as analysis of the results showed, poststimulus hyperpolarization is endogenous in origin and differs in its mechanisms from the diphasic potential.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 193–200, March–April, 1973.     

A computer model of generation of the motor cortex neuron processes seen in the course of execution of instrumental movement

A computer model of neuronal processes in the motor cortex column is presented. The model is consisted of two pyramidal cell layers with two groups of inhibitory interneurons, selectively controlling pyramidal cell soma and dendrite, in each. Active Na, Ca and K conductances are included in the model of a single neuron. Horizontal excitatory connections between pyramidal cells in the upper layer are largely of NMDA-receptor type, that in the lower layer--of non-NMDA-type. All inhibitory synapses are of GABA(A)-type. The model reproduces the main phenomenon observed in the motor cortex during the execution of conditioned movements. Consequent to an early excitation the upper layer pyramidal cells generate a late NMDA-dependent reflexive response to afferent conditional stimulation, which as in a real case is diminished by GABA(A)-type synaptic inhibition and afferent stimulus strength increase. The characteristic inverse relation between the late response manifestation and the stimulus strength observed in the real cortex can be reproduced in the model only if NMDA-glutamate receptors were preferentially localized in the terminals of pyramidal cell backward collaterals, not in the terminals of the afferent fibers on pyramidal neurons. The intended component of motor cortex neuronal activity is generated in NMDA-independent manner by the pyramidal cells of lower layer. The slow time coarse of intended component as compared with short duration of AMPA epsp's is due to a consecutive relay-race--like activation of pyramidal neurons with different dendrit-to-soma ratio.     

Effects of barbiturates on the inhibitory action of GABA on excitatory response of the stomach to stimulation of vagal afferent fibers in cat

Effects of barbiturates on the inhibitory action of GABA to the hexamethonium-resistant excitatory response of the stomach to stimulation of the vagal afferent fibers were studied in cats. Inhibition of the hexamethonium-resistant excitatory response by GABA were compared under alpha-chloralose, alpha-chloralose-phenobarbital (PhB), and alpha-chloralose-pentobarbital (PB)-anesthesia in cats. The ID50 of GABA on the hexamethonium-resistant excitatory response was not significantly affected by PhB, but reduced by PB. Both picrotoxin and bicuculline antagonized the effects of GABA. The present experiments demonstrated that PB potentiated the inhibitory effect of GABA on the hexamethonium-resistant excitatory response of the stomach, and suggested that the potentiation by PB may be due to activation of GABA-receptor-ionophore complex.     

Responses of neurons in cat primary somatosensory cortex to repetitive stimulation of vibrissae

Extra- and intracellular responses of neurons in the primary somatosensory cortex to repetitive mechanical stimulation of the vibrissae at different frequencies were studied in unanesthetized curarized adult cats. Unlike responses to electrical stimulation of the combined afferent input (the infraorbital nerve) spike discharges of neurons in response to vibrissal stimulation can reproduce rather higher frequencies of stimulation and their initial character changes more often in the course of the repetitive series. Most cortical neurons were characterized by limitation of the area of their peripheral receptive fields with an increase in the frequency of adequate repetitive stimulation. A group of cortical neurons was distinguished by its ability to respond to high-frequency stimulation and to generate burst discharges. Comparison of the frequency characteristics of spike responses of these cells and of inhibitory synaptic action in other cortical neurons led to the conclusion that this group of cells thus distinguished may be inhibitory cortical neurons. The role of interaction between excitatory and inhibitory processes arising in cortical neurons during repetitive stimulation of different areas of their receptive fields is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 164–171, March–April, 1982.     

Dynamic encoding of natural luminance sequences by LGN bursts

In the lateral geniculate nucleus (LGN) of the thalamus, visual stimulation produces two distinct types of responses known as tonic and burst. Due to the dynamics of the T-type Ca ²⁺ channels involved in burst generation, the type of response evoked by a particular stimulus depends on the resting membrane potential, which is controlled by a network of modulatory connections from other brain areas. In this study, we use simulated responses to natural scene movies to describe how modulatory and stimulus-driven changes in LGN membrane potential interact to determine the luminance sequences that trigger burst responses. We find that at low resting potentials, when the T channels are de-inactivated and bursts are relatively frequent, an excitatory stimulus transient alone is sufficient to evoke a burst. However, to evoke a burst at high resting potentials, when the T channels are inactivated and bursts are relatively rare, prolonged inhibitory stimulation followed by an excitatory transient is required. We also observe evidence of these effects in vivo, where analysis of experimental recordings demonstrates that the luminance sequences that trigger bursts can vary dramatically with the overall burst percentage of the response. To characterize the functional consequences of the effects of resting potential on burst generation, we simulate LGN responses to different luminance sequences at a range of resting potentials with and without a mechanism for generating bursts. Using analysis based on signal detection theory, we show that bursts enhance detection of specific luminance sequences, ranging from the onset of excitatory sequences at low resting potentials to the offset of inhibitory sequences at high resting potentials. These results suggest a dynamic role for burst responses during visual processing that may change according to behavioral state.     

Electrical stimulation of glossopharyngeal nerve and oesophageal EMG response in the pigeon

The effects of the efferent glossopharyngeal nerve stimulation, on EMG activity of the pigeon cervical oesophagus, were studied. In control animals, stimulation caused a biphasic response characterized by an intra-stimulus excitatory component followed by a post-stimulus inhibitory one. The EMG response to glossopharyngeal stimulation appeared simultaneously throughout the cervical oesophagus. A bell-shaped mechanical wave was detected relating to the electrical excitatory component. Atropine administration antagonized the excitatory component, while the inhibitory one persisted. It occurs intra-stimulus, and its duration is increased, compared to control ones. A reduction in the oesophageal resting pressure was observed relating to the electrical inhibitory component. Hexamethonium caused complete disappearance of any EMG response to glossopharyngeal stimulation, as well as suppression of mechanical responses. The comparison between the EMG responses to swallow and to efferent glossopharyngeal stimulation suggests that in pigeon cervical oesophagus: primary peristalsis is central in origin; a dual system of glossopharyngeal fibres, excitatory and inhibitory, carries the central control for oesophageal motility; these excitatory and inhibitory fibres supply the oesophageal muscle via intramural neurons; the synaptic arrangement of the inhibitory pathway is more complex than the excitatory one.     

Inhibitory processes of hippocampal CA1 pyramidal neurons following kindling-induced epilepsy in the rat

To determine the alterations in cellular function which may contribute to the chronic predisposition of neuronal tissue to epileptiform activity, the membrane properties and inhibitory processes of hippocampal CA1 pyramidal cells were investigated using in vitro slices prepared from commissural-kindled rats. No changes were observed in resting membrane potential, input resistance, spike amplitude, and membrane time constant of "kindled" CA1 pyramidal neurons when compared with controls. There were also no differences between control and kindled preparations in the amplitude of recurrent inhibitory postsynaptic potentials (IPSP) and in the duration of inhibition produced by either alvear (Alv) or stratum radiatum (SR) stimulation. Irrespective of group, repetitive stimulation of the Alv reduced the amplitude of the recurrent IPSP but failed to induce seizurelike activity. On the other hand, repetitive stimulation of SR frequently produced a neuronal burst discharge even though the duration and to some extent the amplitude of orthodromic inhibition was increased. On the basis of these data, it may be suggested that chronic changes in CA1 pyramidal cell membrane properties and transient reductions of inhibitory processes do not underlie the enhanced sensitivity of these neurons to seizure activity associated with kindling.     

Effect of motor stimulation and stretching on afferent activity of the neuromuscular spindle isolated from the frog]

The arrangement of muscle spindles in m. ext. long. dig. IV has been examined by microdissection. It is confirmed that spindle systems generally appear to consist of individual receptors. Stimulation effects of fast motor fibres (conduction velocities greater than 12 m/sec) on the spindles of the same muscle were studied. Receptors were isolated with their nerves and the appropriate spinal roots, the latter ones were used for stimulating efferent fibres and recording sensory discharges. Single shocks to the ventral root filaments caused afferent responses ranging from a single action potential to a train of impulses. During repetitive stimulation (train of stimuli at frequency of 10 to 150/sec) a marked increase in afferent activity was found. Afferent activity could be driven by the frequency of stimuli ("driving") and the stimulus/action potentials ratio varied from 1:1 to 1:3 or more. The rate of sensory discharge depended on the frequency of stimuli: the maximum effect, was attained at 30 to 50 stimuli/sec and, in the most responsive receptors, up to 80 stimuli/sec. Slight increases of the initial lengths of the receptors caused facilitation of sensory responses to motor stimulation. Moreover, impairing effects, which appear during sustained or high-frequency stimulation, possibly related to fatigue in intrafusal neuromuscular transmission, could be relieved by increasing the initial length. The repetitive stimulation of fast fusimotor fibres increased both dynamic and static responses and also raised the afferent activity after a period of stretching, when usually a depression occurs; these effects varied according to the preparation, its initial tension and the frequency of stimulation. The main feature of the examined motor fibres, when stimulated, is the constant excitatory action on muscle spindle static response. Results are discussed. It is suggested that the different characteristics of intrafusal muscle fibres, the receptor initial tension and the frequency of motor units discharges, may together affect muscle spindles static or dynamic performance.     

Radular mechanosensory neuron in the buccal ganglia of the terrestrial slug,Incilaria fruhstorferi

A radular mechanosensory neuron, RM, was identified in the buccal ganglia of Incilaria fruhstorferi. Fine neurites ramified bilaterally in the buccal ganglia, and main neurites entered the subradular epithelium via buccal nerve 3 (n3). When the radula was distorted by bending, RM produced an afferent spike which was preceded by an axonic spike recorded at n3. The response of RM to radular distortion was observed even in the absence of Ca²⁺, which drastically suppressed chemical synaptic interactions. Therefore, RM was concluded to be a primary radular mechanoreceptor.During rhythmic buccal motor activity induced by food or electrical stimulation of the cerebrobuccal connective, RM received excitatory input during the radular retraction phase. In the isolated buccal ganglia connected to the radula via n3s, the afferent spike, which had been evoked by electrical stimulation of the subradular epithelium, was broadened with the phasic excitatory input. Since the afferent spike was also broadened by current injection into the soma, depolarization due to the phasic input may have produced the spike broadening.Spike broadening was also observed during repetitive firing evoked by current injection. The amplitude of the excitatory postsynaptic potential in a follower neuron increased depending on the spike broadening of RM.Abbreviations CBC cerebrobuccal connective - EPSP excitatory postsynaptic potential - n1,n3 buccal nerves 1 and 3 - RBMA rhythmic buccal motor activity - RM radular mechanosensory neuron - SMT supramedian radular tensor neuron