Undergraduate Honors Theses

Thesis Defended

Spring 2017

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Psychology & Neuroscience

First Advisor

Dr. Steven Maier

Second Advisor

Dr. Heidi Day

Third Advisor

Dr. Alison Vigers

Abstract

Prolonged exposure to uncontrollable aversive stimuli has been shown to elicit a range of behavioral alterations in rats that are representative of an anxiety-like phenotype. One of the common anxiety-like behaviors is a reduction in juvenile social interaction following stress exposure, mediated by the sensitized release of serotonin from the dorsal raphe nucleus onto the basolateral amygdala. Serotonin production and regulation has been shown to be under circadian control, therefore we sought out to examine whether diurnal variations in stressor susceptibility exist. Rats were exposed to a series of inescapable tail-shocks during either their active or inactive phase, then juvenile social interaction behavior was assessed revealing that the expected reduction in juvenile social interaction following stress did not occur in animals stressed during their active phase. mRNA expression of tryptophan hydroxylase (TPH2), the rate-limiting enzyme in serotonin production, and expression of the serotonin inhibitory autoreceptor (5-HT1AR) gene peaked during the inactive phase. Corticosterone concentrations following stress did not differ based on time of day, however stress during the inactive phase relative to the active phase resulted in significantly greater activation of serotonergic neurons in the middle-dorsal raphe nucleus, but the same level of generalized activation of the basolateral amygdala. While these results indicate that an inescapable stress-induced anxiety-like behavior is time of day dependent, they do not supply a clear mechanism for the diurnal variation in stress susceptibility. Additional experiments are needed to assess cell-type specific activation within the basolateral amygdala and diurnal variations in other dimensions of the learned helplessness paradigm.

Share

COinS