Adrenergic modulation of the hypothalamic cholinergic mechanism in the control of emotional-defensive behavior in the cat.

Effects of drugs influencing the activity of the hypothalamic noradrenergic system on the carbachol-induced emotional-defensive response were investigated. Intrahypothalamic injections of noradrenalin, amphetamine and reserpine did not produce any changes in cats' behavior. Injections of carbachol into the same hypothalamic loci, following the injections of noradrenalin, amphetamine or reserpine evoked all the characteristic symptoms of emotional-defensive behavior. However, a strong decrease in the number of growls and the duration of growling was observed when reserpine injections preceded the injections of carbachol into the same hypothalamic areas. Adrenergic alpha and beta agonists (methoxamine and isoprenaline) as well as antagonists (phentolamine and oxprenolol) when injected alone had no influence on the cats' behavior. Their effect on vocal responses evoked by subsequent injections of carbachol was not statistically significant. Results show that emotional-defensive behavior cannot be triggered by an activation of the hypothalamic noradrenergic system. However, emotional defensive behavior induced by cholinergic stimulation of the hypothalamus may be modified by changes in the activity of the hypothalamic noradrenergic system.