Oral Presentation The International Congress of Neuroendocrinology 2014

Prefrontal Cortical Mechanisms of Chronic Stress Adaptation (#14)

Brent Myers 1 , Jessica McKlveen 1 , Joshua Azevedo 2 , Rachel Morano 1 , Mark Baccei 3 , Robert Thompson 2 , James P Herman 1
  1. Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, USA
  2. Department of Psychiatry, University of Michigan, Ann Arbor, MI, USA
  3. Department of Anesthesiology, University of Cincinnati, Cincinnati, OH, USA

Stress is a complex biological and psychological experience that engages multiple bodily systems to generate survival-promoting physiological and behavioral adaptations. Appropriate elaboration of stress responses is highly dependent on balance across excitatory and inhibitory circuits. The medial prefrontal cortex (mPFC) is particularly important for coordination of neuroendocrine, autonomic, and behavioral stress responses, largely through infralimbic (IL) projections to stress effector circuits in the amygdala, hypothalamus, and brainstem. Our studies used molecular (RNAseq), electrophysiological (single-cell patch clamp), anatomical (immunohistochemistry), and functional approaches (neuroendocrine profiling, behavioral testing) to assess the impact of chronic variable stress on IL function, focusing on the role of GABAergic neurotransmission. RNAseq data from ventral mPFC microdissections indicated that CVS causes expression changes in at least 39 mRNAs that can be directly linked to interneuron function, and suggest a stress-induced enhancement of GABAergic signaling. Electrophysiological studies were designed to test the CVS-GABA link, and revealed increases in inhibitory synaptic drive onto lL neurons, characterized by increased mIPSC frequency and increased ratio of mIPSC to mEPSC frequency. Anatomical studies indicate that CVS increases GABAergic innervation of IL pyramidal cells, suggesting that CVS increases inhibitory innervation of IL neurons. Notably, CVS significantly decreases glucocorticoid receptors (GR) specifically in IL GABAergic neurons, suggesting that loss of glucocorticoid signaling is linked to enhanced GABA-mediated inhibition. Consistent with this finding, viral vector knockdown of GR in the IL causes hypothalamo-pituitary-adrenocortical axis hyper-reactivity and enhances immobility in the forced swim test. Further, this stress hyper-reactivity can be mimicked with viral vector knockdown of glutamate packaging in the IL. Our results suggest that CVS causes a functional reduction in IL output that may be mediated by reduced GR signaling. The functional data suggest that IL GABAergic neurons play a critical role in appropriate neuroendocrine (as well as emotional) control in the face of chronic stress.