Cocaine-elicited imbalances in ventromedial prefrontal cortex Homer1 versus Homer2 expression: implications for relapse

Abstract

Withdrawal from a history of extended access to self-administered cocaine produces a time-dependent intensification of drug-seeking, which might relate to a cocaine-induced imbalance in the relative expression of constitutively expressed Homer1 versus Homer2 isoforms within the ventromedial aspect of the prefrontal cortex (vmPFC). Thus, we employed immunoblotting to examine the relation between cue-reinforced lever-pressing at 3 versus 30 days withdrawal from a 10-day history of extended access (6 hrs/day) to intravenous cocaine (0.25 mg/infusion) or saline (Sal6h) and the expression of Homer1b/c and Homer2a/b within the vmPFC versus the more dorsomedial aspect of this structure (dmPFC). Behavioral studies employed adeno-associated viral vectors (AAVs) to reverse cocaine-elicited changes in the relative expression of Homer1 vs. Homer2 isoforms and tested animals for cocaine prime-, and cue-induced responding following extinction training. Cocaine self-administration elevated both Homer1b/c and Homer2a/b levels within the vmPFC at 3 days withdrawal and the rise in Homer2a/b persisted for at least 30 days. dmPFC Homer levels did not change as a function of self-administration history. Reversing the relative increase in Homer2 versus Homer1 expression via Homer1c over-expression or Homer2b knock-down failed to influence cue-reinforced lever-pressing when animals were tested in a drug-free state, but both AAV treatments prevented cocaine-primed reinstatement of lever-pressing behavior. These data suggest that a cocaine-elicited imbalance in the relative expression of constitutively expressed Homer2 versus Homer1 within the vmPFC is necessary for the capacity of cocaine to reinstate drug-seeking behavior, posing drug-induced changes in vmPFC Homer expression as a molecular trigger contributing to drug-elicited relapse.

Homer2 within the nucleus accumbens core bidirectionally regulates alcohol intake by both P and Wistar rats

“…Their brains were removed and stored in PBS, until sectioning along the coronal plane on a vibratome at the level of the NAc (50 µm), according to the atlas of Paxinos and Watson (2006). Sections from AAV-cDNA infused rats were stained with an antibody against the hemagglutinin (HA) tag using a mouse anti-HA primary antibody (1:1000 dilution; Covance, San Diego, CA) using standard immunohistochemical techniques and examined for vector spread under a light microscope, while sections from AAV-GFP and AAV-shRNA infused rats were examined for GFP immunofluorescence under a fluorescent microscope (e.g., Cozzoli et al, 2009; 2012, 2014; Gould et al, 2015; Goulding et al, 2011; Szumlinski et al, 2004; 2006). Only rats whose injector cannulae were located within the boundaries of the NAcC and that exhibited neuronal transduction were included in the statistical analyses of the data.…”

“…Wistar rats were employed in this study as they are readily available from a commercial source, are similar to the foundation line for the P rats, as well as other selectively bred high-alcohol consuming rats (Bell, Rodd, Engleman, Toalston, & McBride, 2014), and do not require quarantine procedures. The immunoblotting procedures used to quantify AAV-mediated changes in Homer1/2 expression were identical to those used previously in mouse studies (e.g., Ary et al, 2013; Cozzoli et al, 2009; Goulding et al, 2011) and rats (Gould et al, 2015). In brief, at 8 weeks post-AAV infusion, animals were infused with 0.5 µL of black ink to locate the AAV infusion site.…”

“…The section was laid flat on an ice-chilled glass plate and an 18-gauge punch was employed to bilaterally dissect out the tissue stained by the ink. The tissue was then subjected to our standard homogenization and immunoblotting procedures (e.g., Ary et al, 2013; Cozzoli et al, 2009; Gould et al, 2015; Goulding et al, 2011), using rabbit anti-Homer2a/b (Cosmo Bio USA Inc., Carlsbad, CA; 1:1000 dilution) and anti-Homer1b/c (GeneTex Inc., Irvine, CA; 1:1000 dilution). Immunoreactive bands were detected by enhanced chemiluminescence (ECL Plus; GE Healthcare, Piscataway, NJ, USA).…”

Effects of Cocaine Sensitization on Drug Self-Administration, Mesocorticolimbic SAPAP Levels, and Prefrontal Ionotropic Glutamate Receptors

“…As evidence of this phenomena, 10-days of cocaine self-administration in rats causes a long term elevation in Homer1a/b in the ventral mPFC [144]. Cocaineprimed reinstatement can be extinguished in these animals by knockdown of Homer1a in the ventral mPFC, or increased expression of an isoform able to crosslink mGluRs, Homer1c [144]. Note also that increased stimulation concurrently increases Homer1a levels [145].…”

“…Lack of clustering of mGluR5 receptors, similar to NMDA receptors, would lower the efficiency of these receptors. As evidence of this phenomena, 10-days of cocaine self-administration in rats causes a long term elevation in Homer1a/b in the ventral mPFC [144]. Cocaineprimed reinstatement can be extinguished in these animals by knockdown of Homer1a in the ventral mPFC, or increased expression of an isoform able to crosslink mGluRs, Homer1c [144].…”