Ken'Ichi Ishizuka

Reflex responses of single salivatory neurons to stimulation of trigeminal sensory branches in the cat.

Responses of 71 single salivatory neurons, identified by antidromic spikes evoked by stimulation of the chorda tympani, were tested to stimulation of the ipsilateral infraorbital (IO), inferior alveolar (IA) and lingual nerves (LN) in the cat. Fifty-one neurons responded with spike potentials to stimulation of one or more of these nerves (responsive type, R), while the remaining 20 neurons did not respond to stimulation of any of them (non-responsive type, NR). Thirty-three R neurons were activated by stimulation of all of the 3 trigeminal afferent branches, while 12 neurons responded with spikes to stimulation of only one branch, usually of LN. Reflex spike responses appeared with a latency of 5.6-14.6 ms to LN stimulation, 6.4-15.7 ms to IO stimulation and 6.0-26.0 ms to IA stimulation. Impulses of both A beta and A delta afferent fibres of the trigeminal nerve were found to be effective for activation of salivatory neurons.

Responses of inferior salivatory neurons to stimulation of trigeminal sensory branches.

A total of 84 single inferior salivatory neurons was identified by antidromic stimulation of the tympanic nerve. Their responsiveness was tested to stimulation of the ipsilateral infraorbital, lingual, and inferior alveolar nerves in urethane-chloralose-anesthetized cats. The conduction velocities of preganglionic fibers of inferior salivatory neurons ranged from 2.2 to 9.1 m/s, and 54% of those neurons responded with spikes to stimulation of at least one of the infraorbital, lingual, or inferior alveolar nerves (responsive type neurons). The latencies of spike responses to stimulation of the trigeminal sensory branches ranged from 4.0 to 21.0 ms, which were shorter than those of superior salivatory neurons. Impulses of both A-beta and A-delta afferent fibers of the trigeminal nerve were found to be effective for activation of inferior salivatory neurons. The convergence of excitatory inputs from more than one sensory nerve was found in most of the responsive type neurons (73%).

Changes in cortically induced rhythmic jaw movements after lesioning of the red nucleus in rats

We study whether the red nucleus (RN) lesion can modify rhythmic jaw movements. Rhythmic jaw movements were induced by repetitive electrical stimulation of the two cortical masticatory areas (area A: the orofacial motor cortex; area P: the insular cortex). Lesions made by applied electric current in the RN were found to influence the rhythmic jaw movements induced by stimulation of A-area. The distance between the maximum and minimum jaw-opening positions was less after the lesions were induced. The duration of rhythmic jaw movements was shorter after lesioning. In contrast, lesions of the RN did not influence rhythmic jaw movements induced by stimulation of the P-area. Next, kainic acid (0.2 microl, lesion group) or phosphate-buffered saline (0.2 microl, control group) was injected into the left RN. Three days after injection, rhythmic jaw movements were induced by repetitive electrical stimulation of the A-area. The distance between the maximum and minimum jaw-opening positions in the lesion group was smaller than in the control group. The rhythmic jaw movements of the lesion group had shorter duration than the control group. These results suggest that the RN is involved in the modification of jaw movements induced by stimulation of the A-area.

Antidromic responses and reflex activity of single salivatory neurons in the cat.

Abstract Single salivatory neurons of the brain stem of the urethane-chloralose anesthetized cat were identified by their antidromic responses to stimulation of the chorda tympani. The antidromically identified neurons were recorded in the lateral reticular formation of the brain stem between the spinal trigeminal nucleus and the vestibular complex. As suggested by previous anatomic work, the salivatory neurons appear to be diffusely distributed within the region. The identified neurons responded synaptically to stimulation of the lingual nerve, but this reflex activity was not mediated by an input from the taste fibers.

Modulation of cortically induced rhythmical jaw movements by stimulation of the red nucleus in the rat.

We study whether stimulation of the red nucleus (RN) can modulate rhythmical jaw movements in rats anesthetized by urethane. Rhythmical jaw movements were induced by repetitive electrical stimulation of the two cortical masticatory areas (area A: the orofacial motor cortex; area P: the insular cortex). Stimuli applied to the RN did influence rhythmical jaw movements induced by stimulation of the A-area. Stimuli applied in the jaw-closing phase increased the amplitude of the jaw-closing movement. Stimuli applied in the jaw-opening phase disturbed the rhythm of jaw movements and induced a small jaw-closing movement. Stimuli applied to the RN did not influence rhythmical jaw movements induced by stimulation of the P-area. These results indicate that the RN is involved in the modulation of rhythmical jaw movements induced by stimulation of the A-area.

Convergence of excitatory inputs from the chorda tympani, glossopharyngeal, and vagus nerves onto inferior salivatory nucleus neurons in the cat

Superior salivatory nucleus (SSN) neurons were identified by antidromic spike responses to stimulation of the chorda tympani nerve, and were tested to stimulation of the ipsilateral chorda tympani, glossopharyngeal, vagus and lingual nerves in urethane-chloralose anesthetized cats. In 48 SSN neurons identified, 33 (69%) responded with spikes to stimulation of at least one of these nerves, and 24 (50%) were excited with inputs from more than one stimulated nerve. The mean latencies of the reflex responses to stimulation of the chorda tympani, glossopharyngeal, vagus or lingual nerve were 13.2, 18.9, 24.6 or 11.4 ms, respectively.

Multi-source inputs converge on the superior salivatory nucleus neurons in anaesthetized rats

Activation of parasympathetic nerves innervating salivary glands evokes not only salivation but also vascular responses. These parasympathetic nerves may have cardiac and/or respiratory-related activity as well as the cardiovascular sympathetic nerves that control vascular bed of salivary glands. Therefore, we investigated whether preganglionic superior salivatory nucleus (SSN) neurons projecting to the submandibular and intra-lingual ganglia exhibit pulse-related and/or respiratory-related activity, and whether they can be excited by electrical stimulation of the lingual nerve. 25% of SSN neurons were found to have pulse-related and tracheal pressure-related activities, implying that they receive cardiac and respiratory inputs. 44% of neurons exhibited only pulse-related activity, whereas 31% of the neurons had neither pulse-related nor tracheal pressure-related activity. Neurons with pulse and tracheal pressure-related activities, and those only with pulse-related activity, had B and C fibre range axons. 53% of SSN neurons received both cardiac and lingual nerve inputs. 16% of neurons recorded were found to receive only cardiac inputs, and 26% only lingual nerve inputs; whereas 5% received neither cardiac nor lingual nerve inputs. We conclude that the inputs from diverse sources converge on the SSN neurons, and they can cooperate to modulate SSN neuronal activity.

Role of the parvicellular reticular formation in facilitating the jaw-opening reflex in rats by stimulation of the red nucleus.

In a previous study, we have shown that electrical and chemical stimulation of the red nucleus (RN) facilitates the jaw-opening reflex (JOR). The RN sends projection fibers bilaterally, with contralateral dominance, to the part of the parvicellular reticular formation (RFp) containing premotor neurons projecting to the trigeminal motor nucleus. This implies that RN-induced facilitation of the JOR might be mediated via last-order neurons in the RFp. Here, we address this issue by investigating whether microinjection of lidocaine or l-glutamate into the RFp affects RN-induced modulation of the JOR. Experiments were performed on rats anesthetized with urethane-chloralose. The JOR was evoked by electrical stimulation of the inferior alveolar (IA) nerve and was recorded as an electromyographic response from the anterior belly of the digastric muscle. Conditioning stimulation was delivered unilaterally to the RN 12 ms before the IA test stimulation. We found that local injections of 2% lidocaine (0.5 microl) into the RFp, contralateral to the RN, significantly (P < 0.05) reduce RN-induced facilitation of the JOR, whereas corresponding injections of 0.1 mM l-glutamate (0.5 microl) significantly (P < 0.05) increase it. These results suggest that the facilitatory effect of RN stimulation on the JOR is mediated partly by a relay in the RFp.

Non-NMDA and NMDA receptor agonists induced excitation and their differential effect in activation of superior salivatory nucleus neurons in anaesthetized rats

We investigated the effects of the ionophoretic application of ionotropic non-NMDA receptor agonist (AMPA) and NMDA receptor agonist (NMDA) on extracellularly recorded and antidromically identified superior salivatory nucleus (SSN) neurons. A great majority (93%) of SSN neurons was induced to fire by ionophoretic application of AMPA, and they were classified into high firing rate (more than 6 spikes/s), and low firing rate (less than 3 spikes/s) neurons. No clear differences were found between high firing rate and low firing rate neurons according their fibre type and histological locations. Of the SSN neurons that excited by AMPA, 22% (4/18) and 50% (5/9) of the neurons also were induced to fire following ionophoretic application of the NMDA receptor agonist NMDA in different concentrations, 20 mM and 100 mM, respectively. In neurons that induced firing by AMPA and by NMDA, AMPA-evoked firings were induced by the lower intensities of applied current and had higher mean firing rates than NMDA-evoked firing. Neurons that were induced firing by AMPA and by NMDA had B fibre and C fibre axons as well as those that induced firing only by AMPA. Neurons that were fired only by AMPA were found in whole SSN area, whereas neurons that were induced firing by AMPA and by NMDA were mainly found in intermediate SSN area. In conclusion, activation of ionotoropic non-NMDA receptor has a greater excitatory effect on the SSN neurons than that of ionotropic of NMDA receptor. Our data support the view that non-NMDA receptor plays a major role, whereas NMDA receptor plays a minor role, in the activation of SSN neurons.

Effect of orofacial motor cortex stimulation on neuronal activity in the red nucleus

We studied modulation of the activities of the red nucleus (RN) neurons under to electrical stimulation of the orofacial motor cortex (OfM) in urethane-anesthetized rats. Of 57 neurons studied, 30 (53%) neurons modulated the firing patterns. The firing patterns of the RN neurons were classified into four types: an excitation (E) type (n=4), a long inhibition (LI) type (n=4), a short inhibition (SI) type (n=22), and a no-effect type (n=27). These modulated neurons were intermingled in the dorso-ventral part of the RN. Our results suggest that the RN neurons receive excitatory or inhibitory inputs from the OfM.