The objective of this investigation is to examine possible interactions between the BNST PACAP stress system and hormone levels during the estrous cycle of naturally cycling female rats. This is significant as behavioral consequences, analogous to anxiety disorders in humans, including increased startle, anxious behavior during open arm tests, and decreased feeding are associated with increased transcripts of PACAP and PAC1 within the BNST of animals undergoing a chronic variant stress paradigm (reviewed by Hammack & May, 2014). As females are at a greater risk to suffer from symptoms of PTSD than men (Veteran Affairs, 2017), studying females is of great importance to stress researchers. To study the interaction between estrous cycle and the BNST PACAP system, this research examines PACAP mRNA transcript levels as well as its associated PAC1 receptor mRNA transcript levels in non-overectomized female rats. PACAP and PAC1 transcript levels were determined at each of the four stages of the estrous cycle using qPCR technique. In rat models, estradiol treatment increased BNST PACAP transcription in females suggesting that PACAP and estradiol may have an interaction that explains the sexual dimorphism seen in human PTSD pathologies(Lezak et al., 2014; Ressler et al., 2011). Further investigation into natural hormone cycling in females may lead to clearer answers regarding the regulation of PACAP in the presence of estrogen hormones and why this previously mentioned sexual dimorphism occurs in stress-related disorders like PTSD
