Stereotaxic surgery for implantation of guide cannulas for microinjection into the dorsomedial hypothalamus in young rats.

Stereotaxic surgery to implant guide cannulas into the rodent brain is a frequently used technique to deliver drugs to targeted brain regions in awake, freely moving animals. There are limited reports, however, of central injections in young animals, and no information on cannula implantation for drug administration into the dorsomedial hypothalamus (DMH) in young rats. Our protocol describes a simple and successful method for implanting guide cannulas in the brains of young, male Sprague-Dawley rats and outlines newly developed stereotaxic coordinates to accurately target the dorsomedial hypothalamus. •Stereotaxic surgical procedure for guide cannula implantation in the DMH in young rats.•Development of stereotaxic coordinates of the DMH in young rats.•Microinjection of drugs into the young rat brain.

2-arachidonylglycerol interacts with nitric oxide in the dorsomedial hypothalamus to increase food intake and body weight in young male rats.

The dorsomedial nucleus of the hypothalamus (DMH) is an important appetite regulatory center in the brain. In young rats, neural communication in the DMH is modulated by two interacting signals: endocannabinoids (eCBs) and nitric oxide (NO), both of which are known to modulate appetite. It remains unknown, however, whether eCBs and NO interact in the DMH to regulate food intake and body weight in young rats. We developed stereotaxic coordinates for the DMH in young, male Sprague-Dawley rats and conducted surgeries to implant bilateral guide cannulas for microinjection of vehicle, eCBs [2-arachidonylglycerol (2-AG) or anandamide]; NO (via the precursor l-arginine), or a combination of the two, with and without prior subcutaneous injections of drugs to block cannabinoid receptors or NO synthesis. Food intake and body weight of animals were measured two hours following the injection and brains were subsequently removed and sliced to verify placement of the cannulas relative to the DMH. Here we show that 2-AG, when administered in combination with l-arginine, significantly increased food intake and body weight, an effect that required type I cannabinoid receptors and NO synthesis. 2-AG and l-arginine had no effect on food intake or body weight when administered into the DMH independently. Anandamide also failed to affect these parameters when administered alone or with l-arginine. Together, these data suggest that 2-AG and NO interact in the DMH to increase food intake in young male rats and provide insight into a possible mechanism by which 2-AG increases appetite.