The effect of electrical stimulation in the hypothalamus on the monosynaptic jaw closing and the disynaptic jaw opening reflexes in the cat

Abstract

The effects of electrical stimulation in the hypothalamus on the monosynaptic jaw closing and the disynaptic jaw opening reflexes were investigated in cats anaesthetized with chloralose. The hypothalamic electrodes were located by observation of behavioural attack responses in the unanaesthetized animal and by means of Horsley-Clarke coordinates. The locations were verified in histological serial sections. Hypothalamic conditioning with trains of 3--10 pulses, 0.5 ms duration, 0.5 mA, 500 Hz, evoked a strong facilitation of the jaw closing reflex and a facilitation followed by an inhibition of the jaw opening reflex. These effects differed from those elicited from the cerebral cortex. The hypothalamic effects had a longer latency (11--13 ms) and required a longer train of conditioning stimuli than was the case with those evoked from the cortex. Bilateral ablation of the sensorimotor cerebral cortex or lesion of the pyramids at the lower pontine level diminished but did not abolish the hypothalamic effects. They did, however, disappear after lesions including the ventral midbrain tegmentum. The stimulus positions eliciting the largest hypothalamic effects on the jaw reflexes were located in a region extending medio-laterally from the perifornical area to the entrance of the ansa lenticularis in the lateral hypothalamus. Rostro-caudally the location was found at the level of the ventromedial hypothalamic nucleus and the anterior hypothalamus just rostral to this nucleus. The region corresponds to those parts of the hypothalamus from which agonistic and feeding responses have been evoked. It is suggested that the observed hypothalamotrigeminal mechanism may exercise a tonic influence on the trigeminal motoneurones, thereby controlling the set point of the biting force. The implications of this hypothesis on the etiology of bruxism and the myofascial pain dysfunction are discussed.

Neurobiological Mechanisms Involved in Sleep Bruxism

“…In rabbits, stimulation of the hypothalamic 'defense attack area' facilitates the jaw-closing muscle reflex, which indicates that the trigeminal sensorimotor system is activated in aggressive behavior (Landgren and Olsson, 1977). In rats, projections from the central amygdaloid nuclei to the contralateral trigeminal motor nuclei, the parabrachial area, the supratrigeminal area, and the pontine reticular formation (Takeuchi et al, 1988) and, in monkeys, from the magnocellular divisions of basal nuclei of the amygdala and the CMA (Hatanaka et al, 2000) also support the interaction among reactive behavior (e.g., aggressive), trigeminal sensorimotor functions, and autonomic activities.…”

Projections of the Midlateral Posterior Hypothalamic Area Influencing Cardiorespiratory Function in Rats

“…His studies sug gested that the region not only supports intrinsic rhythmicity of respiration but also affects the HeringBreuer reflex, chemoreceptor response and degree of inspiratory effort against airway obstruction. The area of the posterior hypothalamus stimulating respi ration in anesthetized animals also overlaps the area shown to elicit stimulus-bound oral behaviors and vo calization in unanesthetized animals [Nakao, 1958;Flynn, 1967;Cox and Valenstein, 1969;Landgren and Olsson, 1980], so its connections with upper air way motoneurons may have an important overall influence on cotrol of ventilation.…”

Forebrain projections to brainstem nuclei involved in the control of mandibular movements in rats

“…Previous studies have suggested that only primates possess forebrain premotor neurons that project directly to the Mo5 (15, 25). With regard to the subcortical control of jaw movements, electrophysiological studies in rats have demonstrated that stimulation of the LHA, of the amygdala, and of a ‘small area of the ventromedial portion of the internal capsule’ induce firing of Mo5 motoneurons (20, 30, 31). In addition, it has recently been shown that there are fibers and varicosities within the Mo5 that are immunoreactive to orexin, a neuropeptide produced only in the LHA (32).…”

“…The LHA is related to the control of a variety of functions, including emotional responses such as aggressive attack and defense (42). Electrical stimulation of the LHA in anesthetized cats has been shown to produce increases in heart rate and to facilitate the jaw‐closing reflex (30), as well as to activate the masseter muscle (31).…”