Deak, T. | Search bioRxiv

bioRxiv2022

Prenatal alcohol exposure alters axon formation and Robo/Slit guidance cue expression in the internal capsule at E15.5

We previously showed the prenatal alcohol exposure (PAE) induced precocious growth of E15.5 internal capsule axons. We set out to further delineate which axon tracts were affected and a potential mechanism for this phenomenon. Pregnant Swiss Webster mice were exposed to saline or 20% ethanol via subcutaneous injection from embryonic days (E) 7.5 until E14.5. E15.5 embryos were captured via C-section and brains were either fixed for immunostaining or flash frozen for tissue punches. To identify internal capsule axons we performed immunohistochemistry using L1 antibody to visualize all internal capsule axons and NetrinG1 antibody to identify thalamocortical axons specifically. mRNA was extracted from tissue punches to visualize Slit1, Robo1, Slit2, and Robo2 gene expression levels via real time RT PCR. We found that L1-expressing axons exhibited increased axon crossing in females with the opposite effect in males and no difference in Netrin-G1-expressing axons. We also found PAE increased Robo1 mRNA. Taken together, our results indicate that PAE elicits specific effects on axon trajectories, potentially via the Slit/Robo guidance family of repellents and receptors. These findings add to the growing body of evidence demonstrating alcohol disruptions of axon growth and guidance during embryonic development that may contribute to connectivity errors that characterize Fetal Alcohol Spectrum Disorders.

neuroscience↗

bioRxiv2019

Adolescent forced swim stress increases social anxiety-like behaviors and alters the dynorphin/kappa opioid receptor system in the basolateral amygdala of males

Adolescence is a developmental period marked by robust neural alterations and heightened vulnerability to stress, a factor that is highly associated with increased risk for emotional processing deficits, such as anxiety. Stress-induced upregulation of the dynorphin/kappa opioid receptor (DYN/KOR) system is thought to, in part, underlie the negative affect associated with stress. The basolateral amygdala (BLA) is a key structure involved in anxiety, and neuromodulatory systems, such as the DYN/KOR system, can 1) regulate BLA neural activity in an age-dependent manner in stress-naive animals and 2) underlie stress-induced anxiety in adults. However, the role of the DYN/KOR system in modulating stress-induced anxiety in adolescents is unknown. To test this, we examined the impact of an acute, 2-day forced swim stress (FSS - 10 min each day) on adolescent (~postnatal day (P) 35) and adult Sprague-Dawley rats (~P70), followed by behavioral, molecular and electrophysiological assessment 24 hours following FSS. Adolescent males, but not adult males or females of either age, demonstrated social anxiety-like behavioral alterations indexed via significantly reduced social investigation and preference when tested 24 hours following FSS. Conversely, adult males exhibited increased social preference. While there were no FSS-induced changes in expression of genes related to the DYN/KOR system in the BLA, these behavioral alterations were associated with a robust switch in BLA KOR function. Specifically, while the KOR agonist, U69593, significantly increased GABA transmission in the BLA of non-stressed adolescent males, U69593 significantly inhibited BLA GABA transmission in stressed adolescent males, consistent with the observed anxiogenic phenotype in stressed adolescent males. This is the first study to demonstrate a KOR-dependent mechanism that may contribute to stress-induced social anxiety in adolescent males. Importantly, these findings provide evidence for potential KOR-dependent mechanisms that may contribute to pathophysiological interactions with subsequent stress challenges.

neuroscience↗