Behavioral Effects of Bromocriptine

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in head twitch and yawning responses in rats induced by bromocriptine (BC). Rats administered BC (1-10mg/kg, i. p.) initially evoked head twitch and subsequently yawning. The head twitches evoked by BC (2.5mg/kg, i. p.) were not affected by pretreatment with a low dose of haloperidol (0.02mg/kg, i. p.) and sulpiride (20mg/kg, i. p.), but were inhibited by high dose of haloperidol (1mg/kg, i. p.), naloxone (2mg/kg, i. p.), physostigmine (0.2mg/kg, i. p.) and scopolamine (0.5mg/kg, i. p.). The head twitch response was potentiated by methysergide (10mg/kg, i. p.) and cyproheptadine (5mg/kg, i. p.). BC-induced yawning was not affected by naloxone (2mg/kg, i. p.) but was inhibited by low and high doses of haloperidol (0.02 and 1mg/kg, i. p.), sulpiride (20mg/kg, i. p.), methysergide (10mg/kg, i. p.), cyproheptadine (5mg/kg, i. p.) and scopolamine (0.5mg/kg, i. p.). The present results suggest that the BC-induced twitch response is associated with the dopaminergic activation and serotonergic inhibition and increased activity of the opioid system, and that yawning may involve stimulation of presynaptic dopamine receptors and subsequent cholinergic activation.