Intrahypothalamic injections of norepinephrine facilitate feline affective aggression via α2-adrenoceptors

Abstract

The purpose of this study was to investigate the effects of noradrenergic agents infused into the anterior hypothalamus on feline affective defense responses elicited by electrical stimulation of the ventromedial hypothalamus. Anterior hypothalamic sites which are known to receive inputs from both the ventromedial hypothalamus and ascending noradrenergic pathways were selected for pharmacological analysis. Intracerebral infusions of NE (1.2–2.4 nmol) into the anterior hypothalamus significantly reduced the threshold current required to elicit the hissing component of affective defense via electrical stimulation of the ventromedial hypothalamus. Maximal threshold reductions (17 ± 3%to20 ± 3%) were observed 30 min following infusion. Anterior hypothalamic infusions of clonidine facilitated feline affective defense by reducing hissing current thresholds by 18 ± 4%. Clonidine-induced changes in response thresholds parallel those obtained with NE. Both NE-induced and clonidine-induced reductions in current thresholds were reversible by pre- and post-treatment of the anterior hypothalamic sites with yohimbine. These results demonstrate that the reductions in response thresholds are mediated by post-synaptic α₂-adrenoceptors located within the anterior hypothalamus. Thus the noradrenergic system may play an important role in the regulation of affective aggressive behavior.