Identification and Distribution of Neuroleptic Binding Sites in the Rat Spinal Cord

Abstract

Identification of neuroleptic receptor sites in the rat spinal cord could be achieved by binding [3H]haloperidol to membranes taken from the different horns. The use of pooled frozen microdiscs punched from these different spinal cord areas allowed the detection of saturable stereospecific binding, as defined in the presence of (+)- and (-)-butaclamol. Comparison of the binding constants with those obtained in the corpus striatum resulted in similar Kd and Hill''s slopes. Maximal binding capacity was quite different, being the greatest in the whole striatum (157 .+-. 8 f[femto]mol/mg protein) followed by the dorsal horn (56 .+-. 3 fmol/mg protein) and the lateral (34 .+-. 5 fmol/mg protein) and ventral horns (31 .+-. 2 fmol/mg protein). The displacement of the labeled ligand by different dopaminergic and nondopaminergic drugs at various concentrations gave similar results in the whole striatum and the spinal cord; a dopaminergic innervation of spinal cord evidently exists indicating that dopaminergic receptor sites are distributed through the different spinal horns, with a maximal density in the dorsal horn as for dopamine levels. No detectable stereospecific binding could be obtained from the surrounding spinal white matter, even at high tissue concentrations. Owing to poor sensitivity of the binding technique, no stereospecific neuroleptic binding could be demonstrated in the whole spinal cord, even at very high tissue concentration, but it could be detected in spinal cord tissue sampled from restricted areas of dense dopaminergic innervation.