Related Experiment Video
Updated: Aug 31, 2026
Hyponeophagia: A Measure of Anxiety in the Mouse
Published on: May 17, 2011
Metergoline potentiates natural feeding and antagonizes the anorectic action of medical hypothalamic
1Clarke Institute of Psychiatry, University of Toronto, ON, Canada.
Abstract:
Medial hypothalamic injections of 5-hydroxytryptamine (5-HT) or its agonists have been reported to inhibit feeding elicited by norepinephrine (NE), suggesting that these two transmitter systems interact antagonistically in the control of ingestive behavior. The present study was designed to directly test the hypothesis that 5-HT inhibits adrenergic feeding, specifically at the onset of the rat's nocturnal eating cycle. Free-feeding animals were injected with 5-HT (5-20 nmol) immediately before NE (20 nmol) and food intake was measured 1.5 h postinjection. In separate groups of rats, the serotonergic antagonist metergoline (MET) (2.5-20nmol) was injected into the paraventricular nucleus (PVN) immediately before 5-HT, or before combined injections of 5-HT and NE. The feeding-stimulant action of MET alone, injected IP (0.25-2 mg/kg) or centrally (2.5-40 nmol), was also examined. Results indicated that administration of 5-HT into the PVN suppressed dark onset feeding and dose-dependently blocked NE-stimulated eating. Pretreatment with MET attenuated the inhibitory action of 5-HT on feeding, and reversed the serotonergic blockade of the adrenergic eating response. Further, systemically injected MET significantly increased dark onset feeding, whereas PVN injections failed to alter food intake reliably. These findings provide the first direct evidence that serotonergic and adrenergic systems within the PVN interact in a competitive manner to modulate the natural high rates of feeding displayed by rats during the early dark period. Although MET effectively blocked the anorectic effect of 5-HT, the feeding-stimulant action of this compound alone does not appear to be mediated within the PVN.
Related Concept Videos
01:23Drugs Acting on Autonomic Ganglia: Stimulants
Ganglionic stimulants activate NM nicotinic receptors in autonomic ganglia, falling into two categories: nicotine mimetics [e.g., lobeline, dimethylpiperazine, tetramethylammonium] and muscarinic receptor agonists [e.g., muscarine, methacholine]. The first category's action is rapid and blocked by nicotinic receptor antagonists, while the second category's action is delayed and blocked by atropine-like agents. Nicotine, an alkaloid, affects the heart rate by stimulating sympathetic or...
01:25Adrenergic Agonists: Indirect-Acting Agents
One mechanism involves depleting stored catecholamines by displacing them from synaptic vesicles. These agents, known as "displacers," are transported into vesicles at the expense of noradrenaline. Examples include amphetamine and tyramine, which lack a catechol moiety, resulting in prolonged action, improved oral bioavailability, and...
01:28Adrenergic Agonists: Mixed-Action Agents
Ephedrine and pseudoephedrine lack a catecholamine group, making them less susceptible to degradation by metabolic enzymes. They have increased oral bioavailability and lipophilicity, resulting in a longer duration of action. Their response is reduced by...
01:17Sedatives and Hypnotics Drugs: Miscellaneous Agents
Melatonin congeners like ramelteon (Rozerem) and tasimelteon (Hetlioz) selectively bind to melatonin receptors (MT1 and MT2) and thus mimic the actions of melatonin, a hormone that regulates sleep-wake cycles. Tasimelteon is primarily used for non-24-hour sleep-wake disorder, common in blind patients. They are also used to treat conditions like insomnia...
01:28Drugs Affecting GI Tract Motility: Dopamine Receptor Antagonists
01:23Drugs Affecting GI Tract Motility: Serotonin Receptor Agonists