FUNCTIONAL SUPERSENSITIVITY OF ALPHA-1-ADRENERGIC SYSTEM IN SPINAL VENTRAL HORN IS DUE TO ABSENCE OF AN UPTAKE SYSTEM AND NOT TO POSTSYNAPTIC CHANGE

The excitatory effects of adrenoceptor agonists on ventral horn cells were compared using an extracellular recording technique in spinal cord slices isolated from non-treated and 6-hydroxydopamine (6-OHDA)-treated rats (intracisternally 14 days previously). In spinal cord slices isolated from 6-OHDA-treated rats, the concentration-response curves for the alpha-1-adrenoceptor-mediated facilitatory effects produced by noradrenaline and phenylephrine but not those produced by methoxamine and isoproterenol were shifted to the left. 6-OHDA pretreatment decreased the level and uptake of noradrenaline and increased the number of [H-3]prazosin binding sites in the spinal cord. These results suggest that in 6-OHDA-induced denervation, functional supersensitivity of the alpha-1-adrenergic system in the spinal ventral horn is due to absence of an uptake system, and not to postsynaptic change.