Chlorpromazine, one of the phenothiazine derivatives, suppresses the avoidance response at doses which neither produce ataxia nor impair the performance of an escape response (Cook et al. ; MILLn~ et M., 1957 a; MAF~II). The avoidance response suppression is a property of most, if not all, phenothiazine derivatives (FE~,LOWS & COOK; InvI~; STONE; COOK & KELL~ER), and can be manifested during acquisition and extinction (ADEn & CLINK; MILLEn et al., 1957a MILLEn et al., , 1957b)), as well as maintenanee, of the response (COOK & W~ID~Eu VER~AVE et al.). The avoidance-suppressing property of the phenothiazine derivatives may be related to the drugs' action in relieving psychotic disorders, because a rank order relation has been demonstrated between the dose at which any one phenothiazine derivative suppresses the avoidance response and its rglative potency in psychotic relief (Cook & KELLn~ER). However, some nonataraetic compounds, including morphine and belladonna alkaloids such as atropine and scopolamine, also specifically suppress the avoidance response (MI~Lso~ et M. cited by BEROEn; MAFFII; PASKAL & VA~DnnWOLF). A more detailed discussion can be found in HEnz's review of drug-induced avoidance response suppression.
The three experiments reported here form part of a systematic search for the factors underlying the specific suppression of the avoidance response by chlorpromazine. Two separate conclusions have been reached to explain chlorpromazine-indueed avoidance response suppression. Some investigators (e.g., ADEn & CLI~K; MILL~n et al., 1957a; Ton~Es) have suggested that chlorpromazine reduces "fear" or "anxiety" the presence of which is believed necessary ~or the reinforcement of the avoidance response. The "fear reduction" suggestion has an intuitive plausibility to it because of the drug's therapeutic effect, but other investigators (e.g., KILLA~ & KILLA~; BnA~)LEY; Knu have concluded that ehlorpromazine produces an impairment of "sensory-arousal" functions, an impairment which could suppress the avoidance response by inhibiting