Properties of intraoral mechanoreceptors represented in the mesencephalic nucleus of the fifth nerve in the cat.

1. The activity of neurones in the mesencephalic nucleus of the fifth nerve that respond to forces applied to the teeth were recorded using extracellular microelectrodes; the properties of these neurones have been studied. 2. Electrophysiological evidence consistent with the view that primary afferent intraoral mechanoreceptor fibres have their cell bodies in the trigeminal mesencephalic nucleus is presented. 3. Two groups of intraoral mechanoreceptor neurones were found. The first group, the periodontal mechanoreceptor neurones, which have been described by previous workers, responded to electrical stimulation of the ipsilateral superior or inferior dental nerves and to forces applied to single teeth in the ipsilateral maxilla or mandible respectively. The response characteristics of the mesencephalic periodontal mechanoreceptor neurones differed in two respects from those observed in peripheral nerve studies by previous workers: (a) there were no spontaneously active neurones, and (b) there were no neurones that responded for over 10 sec to a sustained application of a suprathreshold mechanical stimulus to the teeth. The second group, not described before, responded to electrical stimulation of the ipsilateral palatine nerve, and responded to forces applied to all the teeth in the maxillary arch, both contralateral and ipsilateral as well as to forces applied to the nose and hard palate. The site of these receptors is unknown. They have been termed 'Type P' intraoral mechanoreceptors. 4. The recording sites of both the periodontal and Type P mechanoreceptor neurones were all situated in the caudal part of the mesencephalic nucleus of the fifth nerve.