Ovarian Hormone Modulation of Learning Strategy Preferences: A Role for Hippocampal Disinhibition

High levels of circulating ovarian hormones are related to use of the hippocampus-sensitive place learning strategy whereas low hormone levels are related to use of the striatum-sensitive response strategy. Other studies demonstrate that estrogen suppresses hippocampal GABAergic function and that progesterone's agonistic actions at GABAA receptors may enhance hippocampal inhibition. It is possible that the balance between estrogen-induced disinhibition and progesterone-induced inhibition contribute to the estrous cycle-related strategy differences. In this work, hippocampal GABA was pharmacologically suppressed and enhanced to evaluate the contribution of inhibition to strategy preferences across the estrous cycle. Intrahippocampal infusions of the GABA A antagonist bicuculline failed to shift strategy use from response to place in estrous rats (Chapter 2), while intrahippocampal infusions of the GABAA agonist muscimol caused proestrous rats to shift from a place to a response strategy preference (Chapter 3). To evaluate the independent role of estrogen in the muscimol-induced response strategy preference at proestrus, strategy preferences in ovariectomized rats treated with oil, estrogen or estrogen+progesterone were measured. Estrogen treatment induced a place strategy bias, which was reversed by progesterone (Chapter 4, Experiment 1). Furthermore, muscimol treatment produced shifts to response in rats treated with estradiol only, suggesting the presence of progesterone is not necessary to observe muscimol's effects (Chapter 4, Experiment 2). These experiments provide evidence for the emerging theory that ovarian hormones work, at least in part, through hippocampal activity to modulate learning strategies. Further, these studies use a unique approach to the study of cognitive neural systems, a field dominated by studies using pharmacological manipulations in male rats. In contrast, these studies demonstrate how ovarian hormones change the balance of neural systems such that changes in learning strategies are observed.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Neuroscience

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• McElroy, Molly

Contributors dc:contributor

• Korol, Donna L.

• Biology, Neuroscience

Language dc:language

eng

Identifier

(MiAaPQ)AAI3269974

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/82514