Posterior intralaminar region in rat: Neuronal responses to noxious and nonnoxious cutaneous stimuli

Abstract

We recorded from 125 neurons affected by noxious and nonnoxious cutaneous stimuli in the thalamic posterior intralaminar region (PIR) in rats anesthetized with a mixture of 2 3 N 2O - 1 3 O 2 and 0.5% halothane. Twenty-seven neurons were exclusively excited by a nonoxious brisk tap sharply applied on any part of the body. Ninety-eight neurons were affected by noxious stimuli, 25 being inhibited and 73 activated. In addition, 34 98 were also excited by tapping. Noxious stimuli were efficacious whatever their location on the body surface. The different kinds of cells seemed to be intermingled in the PIR; however, “tap” and “noxious activated” neurons were less numerous in the rostrodorsal than in the other sectors. Neurons excited by noxious cutaneous stimuli were also tested with intense transcutaneous electrical stimulation. They exhibited an easily reproducible bursting response whose latency (20 to 40 ms) was consistent with an Aδ fiber input. Fifteen noxious activated neurons were tested with graded noxious heat. Response thresholds were high (48.9 ± 1.37°C); no unit was observed which encoded stimulus temperature by frequency of discharge, moreover, there was a great variability of responses to an identical stimulus. All these data indicate that PIR neuronal responses to noxious stimuli largely differ from those of the ventrobasal complex of the thalamus and play an eventual role in nociception processes.