Immunocytochemically-stained vasopressin binding sites in rat brain. Ventricular application of vasopressin/Accurel in the Brattleboro rat.

An immunocytochemical procedure was developed to localize binding sites for vasopressin (VP) in the brain of Brattleboro (di/di) rats after 2 weeks of continuous ventricular administration of the peptide. Accurel-polypropylene tubing loaded with 0.15, 1.5 or 15 micrograms vasopressin was implanted into the lateral ventricle. Subsequently, bound VP was detected immunocytochemically in 2 distinct patterns: in perineuronal structures and dots between cells, in the lateral septum (dorsorostral part), striatum, cingulate cortex, granular cells of the dentate gyrus of the hippocampus, pyramidal cells of CA1 and CA3 hippocampal areas and around cerebellar Purkinje cells. The high dose (15 micrograms) loaded implants revealed the most intense staining; in the cytoplasm of neuronal cell bodies in the lateral and medial septum, striatum, cingulate cortex, bed nucleus of the stria terminalis, organum vasculosum of the laminae terminalis and locus coeruleus. The most intense staining in cell bodies was observed in brains which had low-loaded implants (0.15-1.5 microgram). A variety of controls, proved that no aspecific uptake was involved in the present procedure. The distribution of VP binding sites was only partly coincident with known sites of VP fiber innervation, and largely agrees with data obtained by autoradiographic techniques for [3H]VP binding. The present immunocytochemical technique gave a higher resolution than the currently used autoradiographic techniques. The differences in pattern and intensity of staining due to increasing the dosage rate of the in vivo vasopressin treatment, might mean that the current procedure retains preferentially either low or high affinity populations of binding sites depending on the implanted dose.