Abstract
Microinjections of various α 1-adrenoceptor agonists including phenylephrine and phenylpropanolamine into the paraventricular hypothalamic nucleus (PVN) suppress food intake in rats, suggesting that this receptor type might act in opposition to previously identified facilatory PVN α 2-adrenoceptors in the modulation of feeding. In the present experiments, we examine the effects on food and water intake of intra-PVN as well as systemic injection of cirazoline, a highly potent α 1-adrenoceptor agonist. In Experiment 1, intra-PVN microinjection of cirazoline (0, 3, 6, 12 and 24 nmol) suppressed food intake (ED 50 = 23.4 nmol) without significant effects on water intake. In Experiment 2, systemic injection of cirazoline (0, 0.05, 0.1, 0.2, 0.4 mg/kg) also markedly suppressed food intake (ED 50 = 0.05 mg/kg i.p.), with a less potent action on water intake (ED 50 = 0.22 mg/kg i.p.). The results of this study as well as our previous investigations strongly support the notion that α 1-adrenoceptors within rat PVN act to reliably suppress food intake.
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