[Effects of capsaicin on spontaneous unit discharges in medial thalamic single neurons of cats (author's transl)].

The effect of capsaicin was studied in gallamine triethiodide immobilized adult cats. Single neurons were recorded from the medial thalamus with a stainless steel microelectrode. Out of 21 neurons recorded in this experiment, 10 were responsive to both nociceptive (pinch) and non-nociceptive (hair bending and/or tapping) stimuli. Six neurons were responsive to only non-nociceptive stimuli and 5 were not responsive to these stimuli. Out of 10 neurons responding to both nociceptive and non-nociceptive stimuli, 9 were responsive to both bradykinin (3 microgram) and capsaicin (3 microgram). Out of 6 neurons responding to only non-nociceptive stimuli, 5 were not responsive to either bradykinin and capsaicin. All neurons responding to bradykinin were also responsive to capsaicin. The latency for bradykinin and capsaicin was 7.64 +/- 1.12 sec and 0.97 +/- 0.07 sec, respectively. The increased in firing frequency produced by capsaicin was depressed by morphine. However, these depressant effects of morphine on single unit activity were antagonized by naloxone.