The effects of p-chlorophenylalanine, a serotonin depletor, on avoidance acquisition, pain sensitivity and related behavior in the rat.

Abstract

p-Chlorophenylalanine, a potent depletor of brain serotonin, produces faster acquisition of a conditioned (active) avoidance response if a low intensity of current is used. This faster acquisition appears to be primarily, and perhaps solely, a result of the drug's action in increasing animals' sensitivity to pain (electric shock). The data suggest that the alteration in pain sensitivity was a result of serotonin depletion in the central nervous system. The compound also resulted in decreased “emotional reactivity” (as measured by a conditioned emotional stimulus) and some decreased spontaneous motor activity. It is possible that the reduced emotional reactivity produced by p-ClPhe could have also contributed to a faster acquisition of the avoidance response. The drug did not affect learning ability as measured by acquisition of a position habit in a simple T-maze (water reinforcement). The decreased “emotional reactivity” and decreased spontaneous motor activity should not be confused with a picture of sedation or tranquilization. p-ClPhe treated animals generally appear quite normal in terms of gross behavior, and might even be somewhat more “irritable” when handled (Koe and Weissman, 1966b) possibly because of an increased sensitivity to touch as well as pain.