HISTAMINE-INDUCED SENSITIZATION OF THE HEAT RESPONSE OF CANINE VISCERAL POLYMODAL RECEPTORS

In elucidating the possible involvement of histamine (His) in hyperalg esia to heat, the effects of His on the heat response of testicular po lymodal receptors were studied in vitro in canine testis-spermatic ner ve preparations. His (100 and 1000 mu M) induced discharges >0.5 impul ses/s (high-responders) in about one third of units tested. His (great er than or equal to 10 mu M) facilitated the heat response irrespectiv e of whether His alone induced substantial excitation, and the magnitu de of facilitation at 100 mu M did not differ between high- and low-re sponders (His-induced discharges less than or equal to 0.5 impulses/s) . Conduction velocity of high-responders at 100 mu M (2.2 +/- 0.9 m/s, n = 5) was slower on average than that of low-responders (12.9 +/- 1. 6 m/s, n = 9). The sensitizing effect of His reported in this paper su ggests that His plays a role in hyperalgesia.