Excitatory and inhibitory inputs to single neurones in the solitary tract nucleus and adjacent reticular formation

Abstract

Summary Microelectrode recordings were made from single neurones located in the solitary tract nucleus and adjacent reticular formation of decerebrate or anaesthetized cats. Stimulation of various cranial nerves and cutaneous areas and the cerebral cortex was used to characterize the excitatory and inhibitory inputs to these brain stem regions. Most solitary tract units could be excited by stimulation of only the superior laryngeal nerve (SLN) or glossopharyngeal nerve (IX). In particular the laryngeal input was examined, and both primary afferent fibres and neurones in the nucleus could be activated with a short-latency to SLN stimulation. The neurones could be inhibited for as long as 700 msec by conditioning stimulation especially of SLN and IX and of the infraorbital nerve (IO). Other conditioning stimuli used were rarely effective. Neurones in the reticular formation ventral to the nucleus exhibited an excitatory input from SLN, IX, IO and sometimes other cranial nerves. However, some neurones could be excited only by IO stimulation. The latencies of the neurones to SLN stimulation were longer in general than those noted in solitary tract neurones. The neurones were subject to more widespread inhibitory influences than those in solitary tract neurones, and the responses of some could also be facilitated. On the basis of antidromic activation, many reticular formation neurones were found to project rostrally to the vicinity of the trigeminal motor nucleus. The excitatory and inhibitory influences acting on the solitary tract and reticular formation neurones are discussed in relation to their possible involvement in the perceptual and reflex activities with which the orofacial and pharyngeal-laryngeal areas are concerned.