Mitsuru Takata

Excitatory and inhibitory postsynaptic potentials in cat hypoglossal motoneurons during swallowing

SummaryThe postsynaptic potentials produced in cat genioglossus and styloglossus motoneurons (GG- and SG-Mns) during swallowing were studied. During swallowing elicited by placing water on the dorsum of the tongue, the GG-muscle discharged for 80–210 ms (mean±S. D. 123±31 ms, N=59) and was abruptly suppressed, and the SG-muscle began discharging in synchrony with the GG-muscle and discharged for 200–360 ms (mean+ S. D. 247±36 ms, N=59). The GG and the SG-Mns were identified if unitary muscle activity followed the induced spike of the motoneuron one-for-one. During swallowing, excitatory postsynaptic potentials (EPSPs) were evoked in the SG-Mns regardless of the respiratory drive on the SG-Mns, and inhibitory postsynaptic potential (IPSP) or EPSP-IPSP was evoked on the GG-Mns regardless of the respiratory drive on the GG-Mns. By increasing the intracellular concentration of chloride ions, the IPSP elicited in the GG-Mn during swallowing was turned into a depolarizing potential. In immobilized cats, a depolarizing potential and a depolarizing-hyperpolarizing potential sequence was evoked successively on a tongue retractor motoneuron and a tongue protruder motoneuron by repetitive electrical stimulation of the superior laryngeal nerve.

The excitability of hypoglossal motoneurons undergoing chromatolysis

Abstract In chromatolysed hypoglossal motoneurons impulse transmission from the initial segment to the soma-dendritic membrane, the relationship of firing frequency to stimulating current, and the trajectory of antidromic responses were explored. In some axotomized motoneurons by the 7th post-operative day the initial segment component could not be separated from the soma-dendritic component. No significant changes were observed on inhibitory postsynaptic potentials produced by lingual nerve stimulation in comparison with normal motoneurons. The slope of the primary range showed a high gain in relation to stimulating current in axotomized motoneurons 14 days after axotomy. On the 28th post-operative day most axotomized motoneurons produced a large delayed depolarization following an antidromic spike. From these findings it is suggested that hypoglossal motoneurons undergoing chromatolysis have a high safety factor for impulse transmission from the initial segment component to the soma-dendritic component and a low threshold for the generation of a spike in the soma-dendritic membrane.

Two components of inhibitory postsynaptic potentials evoked in hypoglossal motoneurons by lingual nerve stimulation

Abstract The properties of inhibitory postsynaptic potentials (IPSPs) produced in hypoglossal motoneurons by lingual nerve stimulation were explored. In many motoneurons innervating protruder and retractor tongue muscles, IPSPs produced by lingual nerve stimulation were the composite of a short- and a long-lasting IPSP. The short-lasting IPSP was reversed to a depolarizing potential by displacing the membrane potential toward hyperpolarization and by increasing the intracellular concentration of chloride. However, no reversal of the long-lasting IPSP was obtained when the cell membrane was hyperpolarized. The short-lasting IPSP was blocked by the administration of strychnine, but the long-lasting IPSP was insensitive to strychnine and it was selectively blocked by the administration of picrotoxin. When the lingual nerve was stimulated by double shocks separated by about 70-ms intervals, it was found that the second shock produced only a short-lasting IPSP.

Food-induced firing patterns in motoneurons producing jaw movements inAplysia kurodai

Summary1.In semi-intact preparations we have demonstrated that the jaw-opening phase covered not only the radula-protraction phase (O-1 phase) but also the earlier time of the radula-retraction phase (O–2 phase) during a cycle of rhythmic movements of the buccal mass induced by application of seaweed extract.2.In the buccal ganglion we identified one jawopening motoneuron (JO1) producing jaw movements during the O-2 phase and three jaw-closing motoneurons (JC1, JC2 and JC3) by recording intracellular junction potentials, and they were all excitatory motoneurons.3.During the initial latency of the rhythmic response induced by food application, the membrane potential of jaw-opening and -closing motoneurons was firstly depolarized or hyperpolarized, respectively. In addition, electrical stimulation of cerebral-buccal connective or peripheral nerves mainly produced excitatory or inhibitory post-synaptic potentials (EPSP or IPSP) in jaw-opening or-closing motoneurons, respectively.4.During the food-induced response, the membrane potential of jaw-opening and -closing motoneurons underwent synchronous depolarization. The JO1 always started firing before the JC1, whilst both motoneurons terminated firing simultaneously. The slope of the rising phase of the membrane depolarization in the JO1 was always steeper than that in the JC1, suggesting that the phase shift in the initiation of their firing is caused by additional inputs from some premotor neurons. Immediately after cessation of their firing the synchronous IPSPs were seen in them, suggesting that the bursts of spikes in both neurons are terminated by common inhibitory inputs from some premotor neurons.

Synaptic efficacy of inhibitory synapses in hypoglossal motoneurons after transection of the hypoglossal nerves

In cat hypoglossal motoneurons after axotomy the synaptic efficacy of inhibitory synapses made by the lingual nerve afferent fibers was studied. The amplitude of the short- and the long-lasting inhibitory postsynaptic potential produced in tongue protruder motoneurons 24 days after axotomy by stimulation of the lingual nerve was significantly reduced in size as compared with the control on the unoperated side. In most protruder motoneurons 40 days after axotomy a large excitatory postsynaptic potential and a spike was produced by stimulation of either the ipsilateral or the contralateral lingual nerve. We have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was more prominent than that for the long-lasting inhibitory potential in the motoneuron 24 days after axotomy. After the cut axons of protruder motoneurons were re-united to tongue muscles, we have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was less prominent than that in axotomized protruder motoneurons.

Two types of inhibitory postsynaptic potentials in the hypoglossal motoneurons

!. Introduction 2. Stereotyped series of postsynaptic potentials in hypoglossal motoneurons 2.1. Short-lasting IPSP 2.2. Effect of strychnine on the short-lasting IPSP 2.3. Long-lasting IPSP 2.4. Effect of picrotoxin on the long-lasting IPSP 2.5. Membrane potential dependence of the long-duration hyperpolarizing potential 2.6. Membrane potential dependence of the EPSP 2.7. Localization of excitatory and inhibitory synapses 3. Two components of IPSPs in hypoglossal motoneurons 3.1. Lingually induced PSPs in tongue protruder and retractor motoneurons 3.2. Separation of two components of IPSPs by strychnine administration 3.3. Separation of two components of IPSPs by double shocks 4. Percentage magnitude of the Sand the L-IPSP in hypoglossal motoneurons 4.1. S% and L% in lingually induced IPSPs 4.2. S% and L% in inferior alveolar-induced IPSPs 5. Axotomized hypoglossal motoneurons 5.1. Firing of axotomized motoneurons 5.2. Lingually induced PSPs in axotomized motoneurons 5.3. Cortically induced PSPs in axotomized motoneurons 5.4. Disjunction of presynaptic contacts on axotomized motoneurons 6. Physiological characteristics on reinnervating and nonreinnervating hypoglossal motoneurons 6.1. Synaptic potentials in reinnervating and nonreinnervating motoneurons 6.2. Repetitive firing on reinnervating and nonreinnervating motoneurons 6.3. Recovery of the firing behaviors and synaptic efficacy in motoneurons 7. Percentage magnitude of the Sand the L-IPSP in reinnervating and nonreinnervating hypoglossal motoneurons 7.1. S% and L% in reinnervating motoneurons 7.2. S% and L% in nonreinnervating motoneurons 7.3. S% and L% in motoneurons after the self-union operation 7.4. Maintenance and rearrangements of synaptic contacts Acknowledgements References 385 386 386 387 388 388 389 389 39O 391 391 392 392 394 394 394 396 396 397 397 399 399 399 400 401

The properties of excitatory postsynaptic potentials evoked in trigeminal motoneurons by trigeminal nerve stimulation

Abstract Membrane potential dependence of excitatory postsynaptic potentials (EPSPs) produced in masseteric motoneurons by stimulation of either the infraorbital or the lingual nerve was explored in cats. No reversal of infraorbitally and lingually induced EPSPs was obtained even when the membrane was depolarized with large depolarizing currents.

Neural mechanism generating firing patterns in jaw motoneurons during the food-induced response in Aplysia kurodai

Summary1.In each right and left buccal ganglia of Aplysia kurodai, we identified 4 premotor neurons impinging on the ipsilateral jaw-closing and -opening motoneurons. Three of them (MA1 neurons) had features of multifunctional neurons. Current-induced spikes in the MA1 neurons produced excitatory junction potentials (EJPs) in the buccal muscle fibers. In addition, tactile stimulation of the buccal muscle surface produced a train of spikes in the MA1 neurons without synaptic input. The other neuron (MA2) had only a premotor function.2.The MA1 and MA2 neurons had similar synaptic effects on the jaw-closing and -opening motoneurons. Current-induced spikes in the premotor neurons gave rise to monosynaptic inhibitory postsynaptic potentials (IPSPs) in the ipsilateral jaw-closing motoneurons. Simultaneously, spikes in one of the MA1 neurons and the MA2 also gave rise to monosynaptic excitatory postsynaptic potentials (EPSPs) in the ipsilateral jaw-opening motoneuron.3.The IPSPs and the EPSPs induced by spikes in the premotor neurons were reversibly blocked by d-tubocurarine and hexamethonium, respectively, suggesting that the MA1 and MA2 neurons are cholinergic.4.When depolarizing and hyperpolarizing current pulses were passed into one premotor neuron, attenuated but similar potential changes were produced in another randomly selected premotor neuron in the same ganglion, suggesting that they are electrotonically coupled

Food-induced firing patterns in motoneurons innervating the pharynx ofAplysia kurodai

Summary1.InAplysia kurodai buccal ganglia, a pair of motoneurons (pharynx bursting or PB neurons), innervating the ipsilateral posterior pharynx muscles (Px) were identified by recording excitatory junction potentials (EJP) in the muscle fiber.2.Seaweed extract applied to the lips in semi-intact preparations, induced rhythmic bursts of spikes in the PB neuron, out of phase with retractor muscle activity (response-I). Rhythmic bursts in the PB neuron were maintained even after cessation of retractor muscle activity (response-II). In both cases pharynx movements followed the bursts in the PB neuron.3.During response-II, rhythmic changes of internal pressure in the pharynx followed the bursting activities of the PB neuron inducing sequential movements of the pharynx and esophagus.4.The rhythmic change of membrane potential in the PB neuron and rhythmic pharynx movements during response-II were completely abolished by steady hyperpolarization of the PB neuron. In addition, rhythmic bursts of spikes were produced in the PB neuron by steady depolarization. Membrane properties of the PB neuron, in isolated preparations, were consistent with other endogenous bursting neurons, suggesting that rhythmic activity during response-II is an intrinsic property of the neuron.5.Ipsilaterally, synchronous burst activities in the anterior and posterior Px were recorded during response-II. Rhythmic bursts generated in the PB neuron by steady depolarization, were synchronized with muscle potentials recorded in the ipsilateral anterior Px, suggesting that the PB neuron also induces the movement of the ipsilateral anterior Px.

Inhibitory postsynaptic potentials evoked in hypoglossal motoneurons by lingual nerve stimulation

Abstract The percent magnitude of a short- and a long-lasting inhibitory postsynaptic potential (IPSP) produced in tongue retractor and protruder motoneurons by lingual nerve stimulation was studied in cats. In the retractor motoneurons, stimulation of the ipsilateral lingual nerve produced primarily the short-lasting IPSP, and the neurons had received synaptic input primarily from the afferent fibers in the contralateral lingual nerve generating the long-lasting IPSP. In the protruder motoneurons, in contrast, there was no pronounced difference in the IPSP patterns evoked by stimulation of the ipsilateral and contralateral lingual nerve.