title: Pharmacological characterization of central alpha-adrenoceptors which mediate clonidine-induced locomotor hypoactivity in the developing rat.
abstract: The present experiment was designed to pharmacologically characterize receptors which mediate the clonidine-induced locomotor change in the developing rat. A subcutaneous injection of clonidine (0.78 mumol/kg) produced locomotor hyperactivity in 7-day-old rats but hypoactivity in 20-day-old rats. Phenoxybenzamine (1.5 mumol/kg, 5.9 mumol/kg and 15 mumol/kg) decreased spontaneous activity in a dose-dependent manner but did not antagonize clonidine-induced hypoactivity in 20-day-old rats. By contrast, the significant reversal of the clonidine-induced hypoactivity by pretreatment with phentolamine (1.6 mumol/kg and 6.3 mumol/kg), yohimbine (1.3 mumol/kg and 5.1 mumol/kg) and piperoxan (7.4 mumol/kg) was observed at such doses when the blockers did not cause any hypoactivity by themselves. It is suggested that clonidine could induce locomotor hypoactivity by activating presynaptic (alpha 2-type) alpha-adrenoceptors in the CNS of 20-day-old rat.
mesh_terms: D000375:Aging; D000818:Animals; D002490:Central Nervous System / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D010646:Phentolamine / Q000494:pharmacology; D010883:Piperoxan / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D010883:Piperoxan; D003000:Clonidine; D010646:Phentolamine