Effects of H1-receptor antagonists on responding punished by histamine injection or electric shock presentation in...

Squirrel monkeys were trained to press a key under a two-component schedule of food presentation. In the presence of either green or red stimulus lights, the 30th response produced a food pellet (fixed-ratio schedule). During the red stimulus lights (punishment component), the first response of each fixed ratio produced either an IV injection of histamine (100.0 micrograms/kg/inj) or a brief electric shock (3.0 mA). Responding was selectively suppressed in either punishment component. Presession IM administration of chlorpheniramine (0.1 and 0.3 mg/kg), diphenhydramine (1.0 and 3.0 mg/kg), or pyrilamine (0.1 and 0.3 mg/kg) increased rates of responding punished by histamine but not those punished by electric shock. Presession administration of promethazine (0.1-3.0 mg/kg) or tripelennamine (0.1 and 0.3 mg/kg) also increased rates of responding punished by histamine in all subjects and response rates punished by electric shock in one of three subjects. Chlordiazepoxide (3.0-56.0 mg/kg) increased rates of responding punished by either histamine or electric shock. These results suggest that the punishing effects of histamine injection are mediated by H1 receptors and that H1-receptor antagonists increase rates of responding suppressed by punishment only under limited conditions including those in which histamine is the punishing stimulus.