Thermally evoked tail avoidance reflex: input-output relationships and their modulation.

Abstract

Latency to onset and magnitude (angular displacement) of thermally evoked tail avoidance reflexes (TETAR) to graded thermal stimuli were measured in pentobarbital-treated and untreated rats. The latency to onset was inversely and the magnitude was directly proportional to the thermal stimulus intensity. Pentobarbital prolonged the latency to onset of the TETAR to low by not high stimulus intensities. Activation of (-)-nicotine sensitive brainstem hyperalgesic processes shortened the latency and increased the magnitude of the TETAR. The hyperalgesic actions of (-)-nicotine were most demonstrable at lower thermal stimulus intensities. These studies suggest that the TETAR is graded in intensity as the stimulus intensity is increased and that the response evoked by different intensities of stimulus probably involve common neurophysiologic mechanisms.