Noradrenergic alpha-1 and alpha-2 antagonists block L-dopa-induced air-stepping in neonatal rats.

Five-day-old rat pups suspended in air and administered L-3,4-dihydroxyphenylalanine (L-DOPA) engage in a highly stereotyped and coordinated locomotor behavior termed air-stepping. L-DOPA is a precursor for dopamine and noradrenaline and one or both of these neurotransmitters could play a role in L-DOPA-induced air-stepping. The role of noradrenaline was investigated by assessing the abilities of the alpha-1 noradrenergic receptor antagonist prazosin and the alpha-2 noradrenergic receptor antagonist idazoxan to block L-DOPA-induced air-stepping in 5-day-old rats. Both antagonists decreased the duration of air-stepping. In addition, prazosin altered the topography of air-stepping by interfering with coordination of the hindlimbs. The results suggest that alpha-1 and alpha-2 noradrenergic receptor subtypes are involved in L-DOPA-induced air-stepping.