Antagonism by propranolol of isolation-induced aggression in mice: Correlation with 5-hydroxytryptamine receptor blockade

The effects of β-adrenoceptor antagonists, (±)-propranolol, pindolol, metroprolol, atenolol and (+)-propranolol, and of 5-HT receptor antagonists, methysergide and cyproheptidine, were studied on the aggressive behaviour induced in male mice by prolonged isolation. A close correlation was found between the dose of drug required to antagonize 5-HTP-induced head twitches in mice and that which prevented fighting in previously isolated mice. Metroprolol, atenolol and (+) -propranolol were inactive in both tests, while the other agents all reduced aggressive behaviour in doses of 0.5-4 mg/kg. In a dose of 10 mg/kg, 5-HTP increased aggressive behaviour in isolated mice. It is suggested that fighting behaviour is associated with an increased activation of 5-HTP pathways in the C.N.S. β-Adrenoceptor antagonists prevent this behaviour because of their blockade of 5-HT receptors rather than those of nor-adrenaline.