Yoshihide Satoh

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.

Modulation of two types of jaw-opening reflex by stimulation of the red nucleus

The red nucleus (RN) is divided cytoarchitecturally into two parts, the parvicellular part (RPC) and the magnocellular part (RMC). The present study aims, first, to compare the effects of RN stimulation between low- and high-threshold afferents-evoked jaw opening reflexes (JORs), and secondly to compare the size of these effects in the RPC and RMC. Experiments were performed on rats anesthetized with urethane-chloralose. The JOR was evoked by electrical stimulation of the inferior alveolar nerve and was recorded as the electromyographic response of the anterior belly of the digastric muscle. The stimulus intensity was either 1.2 (low-threshold) or 4.0 (high-threshold) times that necessary to elicit the JOR. Conditioning electrical stimulation of the RN significantly facilitated the JOR evoked by the low-threshold afferents. On the other hand, conditioning electrical stimulation of the RN significantly suppressed the JOR evoked by the high-threshold afferents. Microinjection of monosodium glutamate into the RN also facilitated the JOR evoked by the low-threshold afferents, but suppressed that evoked by high-threshold afferents. Facilitation did not differ between the RMC and the RPC. Suppression by the RMC stimulation was significantly greater than that by the RPC stimulation. These results suggest that the RN has distinct functional roles in the control of the JOR.

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.

Facilitation of the jaw reflexes by stimulation of the red nucleus in the rat.

The effects of the red nucleus (RN) stimulation on the jaw-opening reflex (JOR) and the masseteric monosynaptic reflex (MMR) were studied in anesthetized rats. The JOR was evoked by electrical stimulation of the inferior alveolar nerve. The MMR was evoked by electrical stimulation of the mesencephalic trigeminal nucleus. The JOR and the MMR were recorded as electromyographic responses of the anterior belly of the digastric and the masseter muscles, respectively. The conditioning electrical stimulation of the RN facilitated both the JOR and the MMR bilaterally. The facilitatory effect on the JOR was much larger than that on the MMR. Additionally, microinjection of monosodium glutamate into the RN also elicited facilitation of the JOR and the MMR. The results suggest the RN plays an important role in reflex control of jaw movements.

Modulation of the masseteric monosynaptic reflex by stimulation of the vestibular nuclear complex in rats

The effect of stimulation of the vestibular nuclear complex (VN) on the masseteric monosynaptic reflex (MMR) was studied in anesthetized rats. The MMR was evoked by electrical stimulation of the mesencephalic trigeminal nucleus and was recorded, bilaterally, as the electromyographic responses of the masseter muscles. Conditioning electrical stimulation of the medial vestibular nucleus (MVN) facilitated the MMR bilaterally, as did microinjection of monosodium glutamate into the MVN. In contrast, conditioning electrical stimulation of the inferior vestibular nucleus (IVN) inhibited the MMR bilaterally. Microinjection of monosodium glutamate into the IVN also inhibited the MMR bilaterally. Conditioning electrical stimulation of the lateral and superior vestibular nuclei did not modulate the MMR. These results suggest that the MVN and the IVN are involved in modulation of the MMR and plays an important role in controlling jaw movements.

Modulation of the jaw-opening reflex by stimulation of the vestibular nuclear complex in rats

The effect of stimulation of the vestibular nuclear complex (VN) on the jaw-opening reflex (JOR) was studied in anesthetized rats. The JOR was evoked by electrical stimulation of the inferior alveolar nerve, and was recorded as the electromyographic responses of the anterior belly of the digastric muscle, bilaterally. Conditioning electrical stimulation of the medial (MVN), lateral (LVN) and superior (SVN) vestibular nuclei facilitated the JOR bilaterally. Microinjection of monosodium glutamate into the SVN, LVN and MVN also facilitated the JOR bilaterally. In contrast, conditioning electrical stimulation of the inferior vestibular nucleus (IVN) inhibited the JOR ipsilaterally. Microinjection of monosodium glutamate into the IVN also inhibited the JOR ipsilaterally. These results suggest that the VN is involved in modulation of the JOR and plays an important role in controlling the jaw movements.

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.

Ionotropic NMDA receptor evokes an excitatory response in superior salivatory nucleus neurons in anaesthetized rats

Extracellular recordings were taken from preganglionic superior salivatory nucleus (SSN) neurons projecting to submandibular and intra-lingual ganglia, in order to study the action of SSN neurons resulting from ionophoretic application of ionotropic NMDA receptor agonist in urethane-chloralose anaesthetized rats. Single SSN neurons were identified by their antidromic spike responses following stimulation of the chorda-lingual nerve (CLN), chorda tympani branches (CTBs) and the lingual nerve (LN). About one-third (33%, 10/30) of the identified SSN neurons were induced to fire by ionophoretic application of the NMDA receptor agonists used, dl-homocysteic acid (DLH) and N-methyl-D-aspartic acid (NMDA). More than half exhibited firing at high frequencies, often exceeding 40 Hz. About one-fifth (20%; 6/30) of the identified SSN neurons exhibited orthodromic spike responses to the combination of NMDA receptor agonist application and sensory nerve (CLN or LN) stimulus. These excitatory responses evoked by application of NMDA receptor agonist were attenuated (n = 4) by ionophoretic application of DL-2-amino-5-phosphonovaleric acid (AP5; NMDA receptor antagonist). About half (47%) of the neurons did not respond to any combination of NMDA receptor agonist and sensory nerve stimuli. No differences were observed between SSN neurons with B fibre axons and those with C fibre axons in response to ionophoresis of the NMDA receptor agonists. The NMDA-sensitive neurons, which exhibited high frequency firing, were predominantly found in the rostral part of the SSN. In summary, activation of ionotropic NMDA receptors exerts an excitatory effect on about half of the SSN neurons. These data support the view that NMDA receptors are involved in information processing and transmission on SSN neurons.

Suppression of the nociceptive jaw-opening reflex by stimulation of the red nucleus

We studied the effect of stimulation of the red nucleus (RN) on the jaw-opening reflex (JOR) in anesthetized rats. The JOR was evoked by electrical stimulation of the tooth pulp of a lower incisor, and was recorded as the electromyographic responses of the anterior belly of the digastric muscle, bilaterally. Conditioning electrical stimulation of the RN was found to suppress the JOR bilaterally. Microinjection of monosodium glutamate into the RN also suppressed the JOR bilaterally. The suppressive effect of the magnocellular part of the RN was significantly larger than that of the parvicellular part of the RN. These results imply that the RN is involved in control of the JOR evoked by noxious stimulus.