A probable role for norepinephrine in feeding after hypothalamic injection of morphine

When morphine is instilled directly into the ventromedial hypothalamus of rats there is a latent period followed by a prolonged bout of feeding. This enhanced activity may be mediated by the release of norepinephrine; for morphine-induced feeding was depressed by the alpha-adrenergic receptor blocker phentolamine. Several neurotransmitter agonists and antagonists failed to duplicate this action: propranolol, serotonin, methysergide, apomorphine and haloperidol were ineffective in modifying ingestion elicited after morphine. Unlike apomorphine, dopamine augmented morphine's feeding effect. This difference may exist because dopamine acts as a precursor for norepinephrine formation in local ventromedial hypothalamic neurons.