Respones of trigeminal ganglion and brain stem neurones in the cat to mechanical and thermal stimulation of the face

Abstract

Microelectrode penetrations were made in the trigeminal ganglion and brain stem nuclei to characterize the responses of single neurones to mechanical and thermal stimulation of the hairy skin of the face of the unanaesthetized cat. The mechanoreceptive fields of primary neurones innervating the hairy skin of the face were associated with 3 hair follicle types. Receptive fields involving single vibrissae were the most common. Both slowly and rapidly adapting units innervated each follicle type and a preliminary survey of peripheral conduction velocity indicated that the neurones were associated with myelinated nerve fibres. The mechanical response properties of brain stem neurones in nuclei oralis and caudalis of the unanaesthetized cat were similar to those noted in previous investigations of decerebrate or anaesthetized animals. The receptive field areas of brain stem neurones were considerably larger than those of primary neurones. Moreover, receptive fields in the perioral region of the face were significantly smaller than receptive fields in posterior facial areas. Many of these mechanosensitive neurones were also responsive to thermal changes in their receptive field. There was no evidence of specific thermoreceptive units innervating facial hairy skin in either the trigeminal ganglion or brain stem nuclei of the unanaesthetized cat. This contrasts with previous findings of specific thermoreceptors in intraoral and peri-nasal regions. Most of the bimodal neurones showed marked sensitivity to even small temperature changes. The common response was an increased discharge to cooling and a depression of discharge on warming. A few units showed some sensitivity to constant temperatures. The response properties of bimodal neurones in nuclei oralis and caudalis could be completely accounted for by an input from primary neurones sensitive to mechanical as well as thermal stimulation.