[³H]Clonidine binding to two α-adrenergic sites in rat CNS: Differential effects of 6-hydroxydopamine

[³H]Clonidine binds to two rat CNS α-receptor sites, with K_D values of 0.5 nM and 3.0 nM. These sites can be examined in isolation from each other. α-Agonists are more potent at the high affinity site, while the converse is true for α-antagonists. The regional distribution in rat CNS for high affinity and low affinity [³H]clonidine binding is different. In the cerebral cortex, 6-hydroxydopamine (6-OHDA) treatment doubles the number of high affinity sites, but does not affect the number of low affinity sites. Throughout the brain, 6-OHDA treatment increases high affinity binding much more than low affinity binding, except in the pons and medulla, where 6-OHDA did not change high affinity [³H]clonidine binding.