Mood regulatory actions of nucleus accumbens deep brain stimulation

The mood regulatory mechanisms of deep brain stimulation (DBS) therapy are yet to be fully understood. DBS is shown to have antidepressant actions in severe, treatment-resistant depression (TRD). Interestingly, DBS of mesoaccumbens neurologic targets, including the nucleus accumbens (NAc), have also been shown to induce mania in vulnerable individuals. The nucleus accumbens (NAc) is a critical node in the mesocorticolimbic system and plays a major role in mediating antidepressant behavioral responses in the forced swim test (FST), a preclinical screen for antidepressant efficacy. This study investigates the antidepressant effects of NAc DBS in an established animal model of TRD. Wistar rats were divided into 4 groups: TRD-DBS (n = 9), TRD-Sham (n = 8), TRD (n = 10), and Control (n = 10). Bilateral stimulating electrodes were implanted into the NAc of TRD-Sham and TRD-DBS animals. Antidepressant-resistance and depression behaviors were induced through adrenocorticotropic-hormone (ACTH-(1–24); 100 lg/day; 2nd and 3rd weeks) administration and concurrent social isolation (all 3 weeks) respectively. DBS was administered throughout the 2nd week of ACTH treatment via a back mounted rodent DBS system. 24-hour locomotor activity counts were obtained using infrared detectors and weekly sucrose preference tests were performed throughout the 3 week protocol. Open field and FST were completed at the end of the 3 weeks. Brains were then removed and stored at 80°C. NAc tissue levels of brain-derived and glialderived neurotrophic factors (BDNF and GDNF, respectively) were quantified using western blot. Results demonstrate significant increases in locomotor activity for TRD-DBS animals (DBS-Vs-Sham: p = 0.0248). Lowered immobility was observed during FST for TRD-DBS animals (DBS-Vs-Sham: p = 0.0188). ACTHinduced BDNF expression increased in the outer region substructure NAc-shell (p = 0.0487) and decreased in the inner region substructure NAc-core (p = 0.0275) compared to controls. These data support antidepressant actions of NAc DBS in TRD. Local changes in neurotrophic factors may contribute to these mechanisms. Importantly, observed increases in locomotor activity over the 3 weeks highlight the potential for mesoaccumbens DBS to impact behaviors such as locomotor activity which may contribute to risk for induction of mania. Preliminary analysis of concurrent effects of daily dopamine reuptake inhibitor GBR12909 (16 mg/kg) administration coupled with NAc DBS demonstrates dopamine-mediated augmentation of these mania-like behaviors.