BEHAVIORAL AND NEURAL BIOLOGY 30, 80--89 (1980) Sex Affects the Initial Strength but not the Extinction of Poison-Based Taste Aversions in Deer Mice (Peromyscus maniculatus bairdi) ROBERT J. ROBBINS 1"~ Department of Zoology, Michigan State University, East Lansing, Michigan, 48824 An examination of the effect of sex upon taste-aversion learning in deer mice (Peromyscus maniculatus bairdi) found that (a) sex has no apparent effect upon either the acquisition or the extinction of a LiCl-induced aversion to sucrose solution if the animals are tested while fluid deprived, but that (b) if the animals are tested under nondeprived conditions, males exhibit a greater initial aversion than females but both sexes seem to extinguish their aversions at similar rates. These findings differ from those previously reported for laboratory rats, in which it has been found that sex affects the extinction but not the acquisition of poison- induced taste aversions. It was suggested that either (a) sex interacts with taste- aversion learning via different mechanisms in deer mice and in rats, or (b) the apparent differences in extinction rates reported for rats might conceivably reflect differences in initial aversion strength which were undetected due to the use of high doses of toxin. Much work has shown that animals can form strong taste aversions following a single flavor/illness pairing (see extensive bibliography in Riley & Clarke, 1977), and recent work has reported sex-related differ- ences in this phenomenon. In 1976, Chambers and Sengstake found (using 2-hr, single-bottle tests on nondeprived animals) that male Sprague- Dawley-derived rats extinguished LiC1- and delta-9-THC-induced aver- sions toward sucrose solution much more slowly than did similarly treated females. Since then, castration, hormone-supplement, and hormone- antagonist studies have reported that this difference is testosterone mediated, that it is an activational rather than an organizational effect of testosterone, that it is the result of the androgenic rather than the es- trogenic properties of testosterone, and that it depends upon the concur- rent presence of testosterone during extinction but not during acquisition (Chambers & Sengstake, 1978, 1979; Earley & Leonard, 1978). I Thanks must go to Kevin Murphy and to Joyce Luteyn for their assistance in the taking of data. John A. King and Stephen C. Bromley provided a critical reading of the manuscript. This paper represents an expansion of a brief presentation at the 1979 Annual Meeting of the Psychonomic Society held in Phoenix, Ariz. 2 To whom requests for reprints should be sent. 80 0163-1047/80/090080-10502.00/0 Copyright © 1980by AcademxcPress, Inc. All rights of reproduction in any form reserved