Use of conditioned taste aversion as a conflict model: effects of anxiolytic drugs

Abstract

Moderate taste aversions were induced by pairing the initial consumption of 0.25% sodium saccharin (SACC) with either 25 mg/kg i.p. l-5-hydroxytryptophan or 30 mg/kg i.p. LiCl. The expression of these moderate conditioned SACC aversions was antagonized by pretreatments (i.p. or p.o.) with benzodiazepine and non-benzodiazepine anxiolytic drugs (lorazepam, diazepam, chlordiazepoxide, oxazepam, phenobarbital, meprobamate, and chlormezanone). Chlordiazepoxide produced less or no antagonism of the expression of stronger SACC aversions induced by 50 or 75 mg/kg l-5-hydroxytryptophan or by 60 or 90 mg/kg LiCl. Nonanxiolytic drugs, including dipsogenic compounds that increased the water intake of hydrated rats (2 M NaCl i.p.; isoproterenol HCl s.c.; and histamine diphosphate s.c.), and even additional 24 hr of fluid deprivation did not antagonize the expression of moderate conditioned taste aversions, indicating that anxiolytic drugs have a very selective effect and that they do not appear to act through homeostatic drinking mechanisms. An essential feature of the taste aversion conflict model is that thirsty rats encounter only SACC. When water was conspicuously available in addition to SACC in two-bottle tests, neither chlordiazepoxide nor phenobarbital antagonized the expression of conditioned taste aversion. Thus, anxiolytic drugs do not produce amnesia for the conditioned aversion, but attenuate the ability of conditioned SACC aversion to suppress SACC consumption in one-bottle tests. The antagonism of the expression of conditioned taste aversion measured with a one-bottle testing method offers a simple, sensitive, and selective screen for anxiolytic drugs. A possible mechanism by which anxiolytics increase both suppressed as well as unsuppressed fluid consumption is discussed.