Degree

Doctor of Philosophy (PhD)

Department

Biology

Document Type

Dissertation

Abstract

Oxytocin is a neurohypophyseal hormone that plays a crucial role in regulating mother-infant bonding and maternal behavior. Oxytocin modulates sex-specific parental behaviors by binding to the oxytocin receptor (OXTR)-expressing neurons in the brain. This study investigates the sexually dimorphic OXTR neurons in the anteroventral periventricular nucleus (AVPV) to understand how oxytocin modulates behavior in females. Specifically, we explored the behavioral roles, neural projections, and intrinsic electrophysiological characteristics of these neurons in the female mice. Using immunohistochemistry revealed that the number of OXTR-expressing neurons was enhanced in postpartum females compared with virgin females, suggesting that these neurons are involved in female-specific behavior, such as maternal behavior. Moreover, our study showed that a subset of the OXTR neurons in the AVPV are immunoreactive to tyrosine hydroxylase (TH+), an enzyme essential for dopamine synthesis. Therefore, this subset of OXTR-expressing neurons is likely dopaminergic, and their function may drive maternal motivation. In postpartum females, using DREADD coupled to the inhibitory G-protein (Gi), inactivated AVPV-OXTR neurons. This neuronal inactivation impaired maternal behavior, specifically pup retrieval and building nest. Since behavior is a direct result of neuronal activity, we extend our study further to characterize AVPV-OXTR neurons. Whole-cell patch clamp recordings revealed heterogeneity in the electrophysiological properties of AVPV-OXTR neurons. TH+ OXTR neurons displayed a pacemaker-like intrinsic rhythmic short bursting activity, whereas TH- OXTR neurons displayed either no firing at all, irregular firing, or a phasic firing. Moreover, some TH- OXTR neurons could switch back and forth among these firing patterns. The differences in the firing patterns between these two populations were likely derived from the difference in their expression of spike afterpotentials. TH+ OXTR neurons showed more depolarizing afterpotential (DAP) than after-hyperpolarization (AHP), while TH- OXTR neurons exhibited more AHP than DAP. Results from immunohistochemistry of patched neurons revealed TH- OXTR neurons showing more dendritic arborization than TH+ neurons. Altogether, this study will contribute to an enhanced understanding of oxytocin related neuronal mechanisms underlying sex-specific parenting behavior, potentially paving the way for developing new therapeutic approaches for sex-specific psychiatric disorders such as postpartum depression (PPD).

Date

7-16-2025

Committee Chair

Dr. Ryoichi Teruyama

DOI

10.31390/gradschool_dissertations.6889

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