The Regulatory Effects Of Medial Prefrontal Cortex Corticotropin-Releasing Factor Neurons On Stress Response

Stress response is a highly conserved physiological process that promotes survival despite uncontrollable and often unpredictable changes in the environment.Hypothalamus and autonomic nervous systems were the final common pathways of physiological stress response.The medial prefrontal cortex could play in coordinating activity between the autonomic and hypothalamic-pituitary-adrenocortical(HPA)axis to regulate both emotional/reactive and executive functions in response to environmental stimuli.CRF(also referred to as corticotropin-releasing hormone-CRH)in hypothalamus is the major physiological activator of the HPA axis,and coordinates the neuroendocrine response to stress.The anatomical distribution of CRF in the brain suggests that CRF is expressed throughout the central nervous system(CNS)including in most limbic and cortical structures besides hypothalamus.CRF not only acts as a key neuroendocrine stress mediator,but is also able to regulate neuronal activity and emotional and cognitive components of the stress response in a neuromodulatory fashion.However,it is not yet known the regulation mechanism of CRF neurons in medial prefrontal cortex on stress response.The present studies applied morphological methods,whole-cell patch-clamp recordings and behavioral tests to explore the function and possible mechanism of CRF neural circuit in medial prefrontal cortex in response to stress.In the present study,we observed that cell bodies of CRF neurons were mainly distributed in layers 2 and 3(L2/3)of medial prefrontal cortex with a variety of morphological features by using CRF transgenic mice.Based on electrophysiological characteristics of current-evoked firing,CRF neurons could be divided into four categories.Acute restraint stress elevated the neural excitability of one type of regular-spiking CRF neurons in medial prefrontal cortex.By using CRF transgenic mice and immunofluorescent staining,we found that the percentage of the immediate early gene c-Fos positive/CRF positive neurons of CRF neurons in restraint mice was increased significantly.Under acute restraint stress,the rate of evoked action potential and rest membrane potential of pyramidal neurons in medial prefrontal cortex were increased,while the threshold current was decreased.CRFR1,but not CRFR2,antagonists NBI27914 depressed the neural excitability of pyramidal neurons in medial prefrontal cortex of stressed mice.While in normal physiological condition,NBI27914 had no effect on the neural excitability of pyramidal neurons in medial prefrontal cortex.Perfusion of 50 nM CRF could simulate the effect of acute restraint stress by enhancing the neural excitability of pyramidal neurons in medial prefrontal cortex.NBI27914 blocked the effect of perfusion of 50 nM CRF.Phosphorylation level of ERK kinases of neurons in medial prefrontal cortex was increased after CRF treatment.These results suggest that acute restraint stress elevates the level of CRF peptide released from CRF neurons in medial prefrontal cortex.The elevated CRF increases the neural excitability of pyramidal neurons through CRFR1 and the downstream ERK signaling pathway.In the following research,to investigate the behaviour function of CRF neurons in medial prefrontal cortex,we used virus delivery method to manipulate CRF neurons.We found that ablation of CRF neurons bilaterally in medial prefrontal cortex impaired social memory while had no effect on social affiliation and sociability.Ablation of CRF neurons bilaterally in medial prefrontal cortex enhanced anxiety-like and depression-like behaviours measured by elevated plus maze and forced swimming test and increased stress vulnerability during subthreshold social defeat stress.Acute inhibition of CRF neurons bilaterally in medial prefrontal cortex caused the same effects on anxiety-like and depression-like behaviours with ablation of CRF neurons bilaterally.Acute activation of CRF neurons bilaterally in medial prefrontal cortex decreased anxiety-like and depression-like behaviours measured by open field test,elevated plus maze and forced swimming test.Meanwhile,activation of CRF neurons bilaterally in medial prefrontal cortex during repeated social defeat stress could reversed the impaired sociability and decreased anxiety induced by social defeat stress.Altogether,these results indicate that CRF neurons in medial prefrontal cortex is a critical regulator of stress vulnerability and depression related behaviours.