Transgenic Analyses of Homer2 Function Within Nucleus Accumbens Subregions in the Regulation of Methamphetamine Reward and Reinforcement in Mice

Problems associated with the abuse of amphetamine-type stimulants, including methamphetamine (MA), pose serious health and socioeconomic issues world-wide. While it is well-established that MA's psychopharmacological effects involve interactions with monoamine neurotransmission, accumulating evidence from animal models implicates dysregulated glutamate in MA addiction vulnerability and use disorder. Recently, we discovered an association between genetic vulnerability to MA-taking and increased expression of the glutamate receptor scaffolding protein Homer2 within both the shell and core subregions of the nucleus accumbens (NAC) and demonstrated a necessary role for Homer2 within the shell subregion in MA reward and reinforcement in mice. This report extends our earlier work by interrogating the functional relevance of Homer2 within the NAC core for the conditioned rewarding and reinforcing properties of MA. C57BL/6J mice with a virus-mediated knockdown of Homer2b expression within the NAC core were first tested for the development and expression of a MA-induced conditioned place-preference/CPP (four pairings of 2 mg/kg MA) and then were trained to self-administer oral MA under operant-conditioning procedures (5-80 mg/L). Homer2b knockdown in the NAC core augmented a MA-CPP and shifted the dose-response function for MA-reinforced responding, above control levels. To determine whether Homer2b within NAC subregions played an active role in regulating MA reward and reinforcement, we characterized the MA phenotype of constitutive Homer2 knockout (KO) mice and then assayed the effects of virus-mediated overexpression of Homer2b within the NAC shell and core of wild-type and KO mice. In line with the results of NAC core knockdown, Homer2 deletion potentiated MA-induced CPP, MA-reinforced responding and intake, as well as both cue- and MA-primed reinstatement of MA-seeking following extinction. However, there was no effect of Homer2b overexpression within the NAC core or the shell on the KO phenotype. These data provide new evidence indicating a globally suppressive role for Homer2 in MA-seeking and MA-taking but argue against specific NAC subregions as the neural loci through which Homer2 actively regulates MA addiction-related behaviors.

Who is HOT and who is LOT? Detailed characterization of prescription opioid-induced changes in behavior between 129P3/J and 129S1/SvlmJ mouse substrains

Genetic factors are theorized to contribute to the substantial inter-individual variability in opioid abuse/addiction. To advance the behavioral genetics of prescription opioid abuse, our prior work identified the 129S1/SvlmJ (S1) and related 129P3/J (P3) mouse substrains, respectively, as low and high opioid-taking. Herein, we related our prior results to measures of sucrose reward/reinforcement, basal anxiety, opioid-induced place-conditioning, locomotor activity and Straub tail reaction, as well as behavioral and physiological signs of withdrawal. Substrains were also re-examined for higher-dose oxycodone and fentanyl intake under limited-access drinking procedures. S1 mice failed to acquire sucrose self-administration under various operant-conditioning procedures and exhibited lower sucrose intake in the home-cage. However, sucrose intake under limited-access procedures escalated in both substrains with repeated sucrose experience. S1 mice exhibited less spontaneous locomotor activity, as well as less opioid-induced locomotor activity and Straub tail reaction, than P3 mice and failed to exhibit an oxycodone-induced place-preference. The lack of conditioned behavior by S1 mice was unrelated to behavioral signs of withdrawal-induced negative affect or dependence severity, but might reflect high levels of basal anxiety-like behavior. Intriguingly, S1 and P3 mice initially exhibited equivalent oxycodone and fentanyl consumption in the home-cage; however opioid intake escalated only in P3 mice with repeated opioid experience. No sex differences were observed for any of our measures. These data provide additional evidence for robust differences in opioid addiction-related behaviors between P3 and S1 substrains and suggest that anxiety, learning, and/or motivational impairments might confound interpretation of operant- and place-conditioning studies employing the S1 substrain.

Medial Patellofemoral Ligament Reconstruction in a Revision Setting: Anchor and Interference Screw Fixation

Recurrent patellar instability is a common pathology and typically affects younger and more active patients. To prevent complete lateral dislocation of the patella, several osseous and soft-tissue procedures have been previously described, including reconstruction of the medial patellofemoral ligament (MPFL), which has been identified as the primary medial stabilizer of the patella. Several techniques have been reported for reconstruction of the MPFL, sometimes in conjunction with other procedures, with the majority showing success in the treatment and resolution of patellar instability. However, MPFL reconstruction is not free of complications, with previous reports of recurrence of medial patellar instability and patellar fracture after surgery. The objective of this Technical Note is to describe our preferred technique, comprising anchor as well as interference screw fixation, for reconstruction of the MPFL in a primary or revision setting.