Effects of sex hormones on associative learning in spontaneously hypertensive rats

Abstract

Pavlovian conditioning of a visual stimulus paired with food was examined in spontaneously hypertensive rats (SHR), which are a commonly used model for Attention-Deficit/Hyperactivity Disorder (ADHD), and in Wistar rats (normoactive control). In gonadally intact rats of both strains, males spent more time in the food cup following onset of the light than did females, indicating a stronger association of the conditioned stimulus (CS) with reward. Gonadectomy carried out in adulthood affected conditioning differently in the two strains. In Wistar rats, gonadectomy had no effect on conditioned responding in females, but reduced conditioned responding in males, effectively eliminating the sex difference in behavior. This result suggests that circulating androgens in male Wistar rats normally aid conditioning in this task. In contrast, gonadectomy enhanced conditioning in both sexes in the SHR rats, indicating that androgens and/or estrogens impair conditioned associations in this strain. These data indicate that gonadal steroids can influence conditioning in rats and that the valence of steroid action on this behavior is strain-dependent. To the extent that SHR serves as a model of ADHD in humans, the influence of steroids on associative learning may play a role in the expression of ADHD-like behaviors.

Figure 1

Amount of time spent inside the food cup during presentation of the visual CS in male and female intact and gonadectomized Wistar (A) and SHR rats (B). Gonadectomy enhanced conditioning in SHR rats but not in Wistar rats. Data are mean ± S.E.M.

Figure 2

Amount of time spent inside the food cup prior to CS onset (A, pre-CS behavior) and after the CS was turned off and food was delivered (B, post-CS responding). Data are means across all 10 session ± S.E.M.

Figure 3

Distance traveled in the open field apparatus by male and female intact and gonadectomized Wistar (A) and SHR rats (B). Female rats exhibited more locomotor activity than males rats. In addition, Wistar rats traveled a longer distance than SHR rats. Data are mean ± S.E.M.