85

Periaqueductal gray and tooth pulp afferent interaction on units in caudal medulla oblongata

T. Yokota and S. Hashimoto, Brain Res., 117 (1976) 508-512

The effects of electrical stimulation of the periaqueductal gray matter (PAG) was examined in trigeminal nucleus caudalis neurons activated by tooth pulp stimuli in anesthetized cats. PAG stimulation inhibited the responses of marginal rim units activated exclusively by tooth pulp stimuli. Neurons in nucleus reticularis dorsalis subjacent to the magnocellular layer were activated by tooth pulp and orofacial tactile stimuli and responses to both types of stimuli were inhibited by PAG stimulation. PAG and thalamic stimulation elicited antidromic responses in some cases. In nucleus reticularis ventralis, a possible caudal extension of nucleus reticularis gigantocellularis, neurons responded to tooth pulp, cornea1 and nasal tactile stimuli. Re- sponses to all stimuli were inhibited by PAG stimulation. Approximately one-half of the units were antidromically activated from the thalamus. PAG stimulation had no effect on mechanically evoked responses in magnocellular neurons. In summary, tooth pulp-evoked responses in 3 different locations of nucleus caudalis and nearby reticular formation were suppressed by PAG stimulation, supporting previous similar findings in trigeminal nucleus oralis and nucleus caudalis (Sessle et al., Canad. J. Physiol. Pharmacol., 54 (1976) 66-69).

Response of unmyelinated (C) polymodal nociceptors to thermal stimuli applied to monkey’s face

R.E. Beitel and R. Dubner, J. Neurophysiol., 39 (1976) 1160-1175

Responses of unmyelinated (C) polymodal nociceptors to thermal and mechanical stimuli were recorded in the trigeminal ganglion of anesthetized rhesus monkeys. Thermal thresholds ranged from 38 to 49°C and maximum discharge frequencies were in the noxious heat range (45-55°C). Applica- tion of near threshold temperatures typically sensitized or enhanced the response of units to subsequent applications of heat stimuli. In a correlative analysis, the latency and pattern of discharge of polymodal nociceptors were compared with the escape responses in two monkeys to 49 and 51°C nox- ious heat stimuli. The analysis revealed that the discharge of C polymodal nociceptors alone cannot account for fast escape responses of less than 3.0- 3.5 set, but may contribute to escape behavior occurring at longer latencies.

Inputs to trigeminal brain neurons from facial, oral, tooth pulp and pharyn- golaryngeal tissues. II. Role of trigeminal nucleus caudalis in modulating responses to innocuous and noxious stimuli

L.F. Greenwood and B.J. Sessle, Brain Res., 117 (1976) 227-238