Since estradiol attenuates cannabinoid-induced increases in energy intake, energy expenditure and transmission at proopiomelanocortin (POMC) synapses in the hypothalamic arcuate nucleus (ARC), we tested the hypothesis that neuronal nitric oxide synthase (nNOS) plays an integral role. To this end, whole animal experiments were carried out in gonadectomized female guinea pigs. Estradiol benzoate (EB; 10 µg; s.c.) decreased incremental food intake as well as O2 consumption, CO2 production and metabolic heat production as early as 2 hours post administration. This was associated with increased phosphorylation of nNOS, as evidenced by an elevated (pnNOS)/nNOS ratio in the ARC. Administration of the cannabinoidreceptor agonist WIN 55,212-2 (3μg; i.c.v.)) into the third ventricle evoked hyperphagia as early as 1 hour post administration, which was blocked by EB and restored by the non-selective NOS inhibitor L-NAME (100μg; i.c.v.) when the latter was combined with the steroid. Whole-cell patch clamp recordings showed that 17β-estradiol (E2; 100nM) rapidly diminished cannabinoid-induced decreases in mEPSC frequency, which was mimicked by pre-treatment with the NOS substrate L-arginine (30μM) and abrogated by L-NAME (300μM). Furthermore, E2 antagonized endocannabinoid-mediated depolarization-induced suppression of excitation, which was nullified by the nNOS-selective inhibitor NPLA (10μM). These effects occurred in a sizable number of identified POMC neurons. Taken together, the estradiol-induced decrease in energy intake is mediated by a decrease in cannabinoid sensitivity within the ARC feeding circuitry through the activation of nNOS. These findings provide compelling evidence for the need to develop rational, gender-specific therapies to help treat metabolic disorders like cachexia and obesity.
Copyright © 2014, Journal of Neurophysiology.