Estrogen replacement in ovariectomized rats during acquisition delays the habit formation consistently observed in intact female rats with the same level of instrumental training
Bremer, Gillian P
Bremer, Gillian P
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Abstract
Sex differences in the neurobiological mechanisms of learning have become evident in the literature over the years. Estrogen, a potent sex hormone, has effects on brain structure and neurotransmitter release throughout the brain, including dopamine in the dorsal striatum. Previous findings in our lab have demonstrated a sex difference in habit formation such that female rats require less reinforcer exposures to develop a habitual behavior compared to males. To determine if estrogen plays a critical role in this effect in females, we ovariectomized female rats and replaced naturally cycling estrogen with a silastic tube that constantly released low non-biologically inactive 17beta-estradiol (E2), in order to maintain the presence of the estrogen receptor. During acquisition, one half of the females were given 2 sub-cutaneous injections of E2 at proestrous levels. Training was done to 160 reinforcer exposures, a level at which intact females reliably exhibit habitual responding. After reward devaluation, we found that both ovariectomized (OVX) low E2 and OVX + cycling E2 responded in a goal-directed manner. These results suggest that neither low constant estrogen, nor cycling high estrogen are producing the habitual behavior that is observed at this training level in intact females.
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2021-01-01
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Neuroscience