Effects of thalamic sensory relay nucleus stimulation on trigeminal subnucleus caudalis neurons in the cat. Abnormal bursting hyperactivity after trigeminal rhizotomy.

Abstract

We studied in the cat the effects of thalamic sensory relay nucleus (TSRN) stimulation on abnormal hyperactivity following trigeminal rhizotomy within the contralateral trigeminal subnucleus caudalis, a trigeminal equivalent of the dorsal horn. The animals were subjected to unilateral retrogasserian rhizotomy 2-6 weeks prior to the experiments. Following the rhizotomy, abnormal bursting and continuous nonbursting hyperactivities were recorded from laminae IV-V of the trigeminal subnucleus caudalis on the rhizotomized side. Some of these neurons responded to peripheral stimuli applied to rostral cervical dermatomes in a manner resembling the nociceptive, wide dynamic range (WDR) neurons of the intact side. However, periaqueductal gray (PAG) stimulation inhibited the hyperactive neurons on the rhizotomized side less frequently than the WDR neurons on the intact side. In contrast to PAG stimulation, TSRN stimulation inhibited the hyperactive neurons on the rhizotomized side as frequently as the WDR neurons on the intact side. These results are apparently consistent with our clinical observation that neurogenic pain due to deafferentation can be relieved by TSRN stimulation but not by PAG stimulation. This in turn suggests that the pain relief obtained with TSRN stimulation may result at least in part from inhibition of the nociceptive activity or abnormal hyperactivity of dorsal horn neurons.