447. Behavioral and prefrontal cortical molecular effects of sodium butyrate in mice exposed to a model of post-traumatic stress disorder

Abstract

Abstract Background Exposure to intense stressors can induce the development of neuropsychiatric disorders, notably post-traumatic stress disorder (PTSD). In PTSD, impairment in fear extinction memory is a key factor, and activation of the endocannabinoid system, particularly CB1 receptors, facilitates the extinction of these memories in animal models and humans. There is also evidence that epigenetic mechanisms are involved in PTSD. Stress activates histone deacetylase enzymes (HDACs), and alterations in histone acetylation, resulting from increased activity of these enzymes, can modulate the expression of endocannabinoid system mediators. HDAC enzymes can be pharmacologically modulated, such as by sodium butyrate (NaB). Aims & Objectives To test whether NaB administered during repeated social defeat stress (RSDS) prevents persistent behavioral alterations in contextual fear memory and extinction, anxiety-like behavior, and social avoidance, and to investigate associated changes in HDAC and endocannabinoid-system (ECS) proteins in the prefrontal cortex (PFC). Method Mice received NaB (25, 50, or 100 mg/kg, i.p.) or vehicle 30 min before each RSDS session (6 days, 2 h/day). The open field test (OFT) and social avoidance test (SAT) were conducted 24 h after RSDS. A contextual fear conditioning protocol (CFC) was performed 7 days later. Overall emotionality and the proportion of emotionally affected animals were quantified using a Z-score derived from behavioral measures. For molecular analyses, PFC tissue was fractionated into cytoplasmic and nuclear compartments, and protein expression of HDAC1/2/3/4, CB1/CB2, TRPV1, NAPE-PLD, and FAAH was quantified by Western Blotting. Results RSDS induced hypolocomotion in the OFT and impaired fear extinction in the CFC. RSDS also increased overall emotionality and the proportion of emotionally affected animals compared with naïve controls. NaB at 25 and 50 mg/kg potentiated RSDS-induced hypolocomotion in the OFT. Moreover, NaB at 50 mg/kg attenuated the RSDS-related extinction impairment in the CFC and reduced emotionality and the proportion of emotionally affected animals. In non-stressed animals, NaB (50 mg/kg) produced an anxiolytic-like effect in the OFT without affecting locomotion, and did not alter SAT or CFC measures. At the molecular level, RSDS increased HDAC3 and CB2 protein expression in the cytoplasmic fraction of the PFC. NaB reduced HDAC1 expression independently of RSDS and decreased CB2 expression in an RSDS-dependent manner. No significant changes were detected for HDAC2, HDAC4, CB1, TRPV1, NAPE-PLD, or FAAH in either subcellular fraction. Discussion & Conclusions NaB administered during stress produced dose-dependent behavioral effects, including attenuation of stress-related fear extinction impairment at 50 mg/kg, alongside potentiation of RSDS-associated hypolocomotion at 25–50 mg/kg. RSDS selectively altered cytoplasmic HDAC3 and CB2 in the PFC levels and NaB modulated HDAC1 and normalized CB2. These findings highlight HDAC-sensitive processes engaged during stress and nominate cytoplasmic HDAC and CB2 associated pathways as candidates for mediating NaB’s effects on extinction.