Chronic beta-adrenergic stimulation increases in mice the sensitivity to methysergide and the number of cerebral high affinity serotonin binding sites (5-HT-1).

Reserpine administration in mice causes, among other effects an akinesia which can be reversed by the serotonin agonist-antagonist methysergide. The effect of methysergide is potentiated by clenbuterol, a beta-adrenergic agonist, which itself causes hypomotility. Potentiation is weak after a single injection of clenbuterol, but becomes much stronger after repeated administration for 12 days. This treatment also causes a 50% increase in the number of high affinity 5-HT-1 binding sites in the brain. This increase would explain the increased potency of methysergide against reserpine-induced akinesia. These results show that: a beta-adrenergic drug, clenbuterol modulates the serotoninergic system; this modulation takes its importance after chronic treatment only; this interrelation may be important in depressive illness since it is observed on a test used in the screening of antidepressant drugs.