Mild Traumatic Brain Injury (TBI) Alters Endocannabinoids in the Amygdala of Female Alcohol Drinking Rats

Abstract

Traumatic brain injury (TBI) is a growing national health concern; nearly 2.5 million Americans sustain a TBI each year, and this number has increased since 2000 by nearly 60%. Most TBIs are ‘mild TBIs (mTBI)’, which predispose individuals to develop detrimental symptoms like cognitive impairment, anxiety, depression, and increased propensity for addictive behaviors.Alcohol is a known risk factor for incurring TBI, and our labs have demonstrated deleterious effects of alcohol on TBI outcomes and recovery. The amygdala is an important neural structure implicated in emergence of negative affective states and addiction. Mild TBI and alcohol each alter amygdala function and endocannabinoid (eCB) signaling, providing a potential neurobiological mechanism for post‐TBI psychiatric sequelae that are exacerbated by post‐TBI alcohol drinking.This study's aims were 1) to determine the effect of mTBI and operant alcohol self‐administration on endocannabinoid system protein expression in the central (CeA) and basolateral amygdala (BLA) of female rats and 2) to determine mTBI and operant alcohol self‐administration on endocannabinoid levels in the BLA. We hypothesized that mTBI would increase degradative eCB enzyme monoacylglycerol lipase (MAGL) expression and decrease endocannabinoid signaling in amygdaloid sub‐nuclei in alcohol drinking animals. Adult female Wistar rats were trained to self‐administer alcohol using an operant task. Following stabilization of alcohol responding, all rats underwent a 5‐mm left lateral craniotomy. Three days later, mild‐to‐moderate TBI (25ms, 28–32 PSI) or sham injury was delivered via lateral fluid percussion over the sensorimotor cortex. Operant alcohol self‐administration was measured every two days post‐injury, and animals were sacrificed 1 hour, 5 days, or 11 days post‐TBI. Following sacrifice, brains were excised, CeA and BLA were bilaterally dissected, and micropunches were used for either Western blot analysis of eCB protein expression (eCB synthetic and degradative enzymes and cannabinoid receptors) or quantification of endocannabinoid (i.e., 2‐arachidonyl glycerol [2‐AG], anandamide) levels via liquid chromatography and mass spectroscopy.Western blot analysis revealed downregulation of the synthetic 2‐AG enzyme, diacylglycerol lipase alpha, in BLA of female alcohol drinking mTBI rats 11 d post injury. Alcohol self‐administration decreased 2‐AG degradative enzyme, MAGL, expression in the BLA 11 d post injury. No changes in endocannabinoid protein expression were observed in alcohol‐naïve rats.Collectively, our results suggest that mTBI may decrease basolateral amygdalar 2‐AG synthesis in alcohol drinking rats, and these alterations may represent a mechanism by which mTBI increases alcohol drinking.Support or Funding InformationAA026468‐01A1 (ZFS), AA007577 (PEM), and AA023305 (NWG)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.