Cord B. Sengstake

Sexually dimorphic extinction of a conditioned taste aversion in rats

The existence of a sexual dimorphism in the extinction of conditioned taste aversions in both fluid-deprived and nondeprived rats was investigated. When nondeprived rats were poisoned with LiCl after consuming a sucrose solution, males extinguished the subsequent conditioned taste aversion more slowly than females. There was no difference in the rate of extinction of a LiCl-induced conditioned taste aversion in fluid-deprived rats. Using marihuana extract distillate as the toxin, it was shown that the dimorphism found in the nondeprived rats is not a toxin-specific effect, and does not appear to be due to the males being made more ill. Possible explanations for the appearance of the dimorphism and its relation to the deprivational state of the organism are discussed.

Sexually dimorphic acquisition of a conditioned taste aversion in rats: Effects of gonadectomy, testosterone replacement and water deprivation

Abstract Sexual dimorphism was found to exist with respect to the acquisition of a conditioned taste aversion. When 0.30 meq of LiCl was used as a toxin, the proportion of male rats in whom aversion developed was greater than the proportion of females. Gonadectomy had an unclear effect on the behavior of females. However, gonadectomized males had less of a tendency to acquire the aversion than did intact males. Testosterone replacement counteracted this effect. Water deprivation, which has been shown to feminize testosterone-dependent slow extinction of a conditioned taste aversion, reduced the proportion of males in whom aversion developed. Thus, sexual dimorphism in the acquisition of this behavior depends at least in part on the presence of testosterone.

Temporal aspects of the dependency of a dimorphic rate of extinction on testosterone.

Abstract Previous work has shown that rate of extinction of a conditioned taste aversion is affected by concurrent levels of testosterone in adult rats. In the present study, castrated male and female adult rates were given either oil or testosterone during acquisition of the conditioned taste aversion and then either oil or testosterone during extinction. The males and females that received testosterone during the extinction of the aversion showed the slower, masculine rate of extinction regardless of the type of injections they received during acquisition. Conversely, the animals that received oil during extinction showed the faster, feminine rate of extinction regardless of the type of injection during acquisition. In light of these findings, a number of alternative behavioral changes that could account for the effect of testosterone on the rate of extinction were evaluated.

Differential effects of fluid deprivation on the acquisition and extinction phases of a conditioned taste aversion

Previous work has shown that the rate of extinction of a conditioned taste aversion by a male (but not a female) rat is affected by the state of fluid deprivation. In the present study, adult male rats were either fluid deprived or nondeprived during acquisition of the conditioned taste aversion and then either fluid deprived or nondeprived during its extinction. The males that were fluid deprived during extinction showed a faster, female-like rate of extinction regardless of the deprivation state during acquisition. These results were related to previous work showing that the rate of extinction of a conditioned taste aversion is dependent on levels of testosterone.

Pseudo-castration effects of social isolation on extinction of a taste aversion

Abstract The effects of social isolation on the slow rate of extinction of a conditioned taste aversion exhibited by male rats were investigated. When the males were isolated for six weeks prior to poisoning, they showed a nontypical, rapid rate of extinction from the conditioned taste aversion. The isolation had no effect on the already rapid rate of extinction exhibited by the females. Behaviorally, the change in the rate of extinction in the male following social isolation is identical to the change in rate that occurs following castration of the male. It was therefore proposed that isolation increased the rate of extinction in the male by decreasing the availability of testosterone. This proposal was supported by the finding that socially isolated males had lower plasma testosterone levels than did non-isolated males.

The role of serum testosterone in the accelerated extinction of a conditioned taste aversion in fluid deprived male rats

Fluid deprivation decreases serum testosterone (T) levels and increases the rate of extinction of a conditioned taste aversion in Sprague-Dawley male rats. It has been suggested that the decreased serum levels may be the primary factor responsible for the accelerated extinction rates during fluid deprivation. To test the generality of this hypothesis, the effect of fluid deprivation on T levels and extinction rate was investigated in Fischer 344 male rats. Extinction rates were accelerated in Fischer 344 rats but T levels were not decreased. In a second study, the behavioral and hormonal responses of Fischer 344 and Sprague-Dawley males to fluid deprivation were compared. Extinction rates were increased in both strains of rat by fluid deprivation, but serum T levels were decreased in fluid-deprived Sprague-Dawley males and not Fischer 344 males. It was suggested that the accelerated extinction in fluid-deprived Sprague-Dawley males was primarily due to decreases in serum T levels, while the faster extinction in deprived Fisher 344 males could be accounted for by decreases in sensitivity to T.

Decreased testosterone levels and accelerated extinction of a conditioned taste aversion in fluid-deprived male rats

The hypothesis that fluid deprivation accelerates extinction of a conditioned taste aversion in male Sprague-Dawley-derived rats by reducing serum testosterone levels was tested. Serum testosterone levels were found to be lower in fluid-deprived males than in nondeprived males (Experiments 1 and 2). Exogenous testosterone treatment that results in high physiological levels of serum testosterone slowed the extinction of fluid-deprived gonadectomized males to rates comparable with those of nondeprived sham males (Experiment 3). It was noted, however, that testosterone treatment was less effective in slowing extinction in fluid-deprived gonadectomized males than in nondeprived gonadectomized males even though the serum testosterone levels were the same (Experiments 3 and 4). These results provide strong support for the original hypothesis, but they suggest that fluid deprivation also reduces sensitivity to testosterone.

Sensitivity of male, female, and androgenized female rats to testosterone during extinction of a conditioned taste aversion.

Experiment 1 tested the hypothesis that male and female rats differ in the amount of testosterone (T) required to prolong extinction of a conditioned taste aversion. Gonadectomized male and female rats were implanted with empty or 30-, 60-, or 120-mm T-filled capsules. The males had slower extinction rates than females when both were implanted with 30-mm and 60-mm capsules but not when implanted with 120-mm capsules. The dimorphic sensitivity was not due to differences in plasma T levels: the levels for males and females were not different. Experiment 2 tested the hypothesis that the presence of T during the perinatal period results in a greater sensitivity to T in adulthood. Females exposed to T during the perinatal period showed prolonged extinction when given a 30-mm T-filled capsule as an adult, whereas unexposed females did not. These results support the hypothesis that the amount of T required to activate the prolonged extinction in an adult depends on perinatal exposure to T.

Disruption of sexual behavior in socially isolated adult male rats

The effect of social isolation on adult male sexual behavior was investigated. Seven Sprague—Dawley-derived male rats were placed in individual cages when 63 days old. An additional seven remained in an all-male colony cage. When 258 days old, the sexual behavior of all 14 males was tested. The sexual behavior of the isolated rats was disrupted. In the first two tests none of the isolated males exhibited either intromission or ejaculation, whereas six out of the seven non-isolated males both intromitted and ejaculated. For most of the isolated males, the disruption was reversible; by test 15, five of the seven were performing indistinguishably from nonisolated males. These data indicate that social isolation of adult males disrupts sexual behavior.