High‐and Low‐Affinity States of Striatal D2 Receptors Are Not Affected by 6‐Hydroxydopamine or Chronic Haloperidol Treatment

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Abstract
Specific D2 binding in rat striatum was characterized and then the effects of chronic disruption of dopaminergic activity on antagonist and agonist binding to these sites were studied. D2 receptors were defined as those sites capable of binding [3H]spiperone in the presence of cinanserin, a 5-HT2 [5-hydroxytryptamine] antagonist, but not in the presence of (+)-butaclamol, a D2 and 5-HT2 blocker. Saturation, competition and kinetic analyses suggested that D2 receptors are a homogeneous population exhibiting more complex interactions with agonists than antagonists. Antagonist binding was monophasic and guanine nucleotide-insensitive whereas agonist binding was biphasic and guanine nucleotide-sensitive. D2 receptor density was elevated by > 40% following dopamine depletion by 6-hydroxydopamine or chronic receptor blockade by haloperidol. However neither treatment altered the affinities or magnitudes of the high- and low-affinity components associated with agonist binding to the D2 receptor.