QUANTITATIVE AUTORADIOGRAPHIC MAPPING OF NEUROHYPOPHYSEAL HORMONE BINDING-SITES IN THE RAT FOREBRAIN AND PITUITARY-GLAND .2. COMPARATIVE-STUDY ON THE LONG-EVANS AND BRATTLEBORO STRAINS

The anatomical distribution and pharmacological characteristics of the different types of neurohypophysial hormone binding sites were compared in the forebrains and pituitary glands of Long-Evans rats and its mutant Brattleboro strain, genetically deficient in vasopressin. Quantitative autoradiography on sections incubated in the presence of 5 nM of either [3H]oxytocin or [3H]vasopressin revealed the presence of the same types of sites in the brains of both strains but nocticeable variations in their denstities were found in several areas. In the forebrain, oxytocin/vasopressin sites, which bind both peptides with similar high nanomolar affinities, had the same locations and densities in the ventral subiculum, in several nuclei of the amygdala, the bed nucleus of the stria terminalis and the olfactory tubercle. The density of such sites was, in contrast, lower in the ventromedial hypothalamic nucleus of the Brattleboro rat. Selective vasopressin sites which bind [3H]vasopressin with a nanomolar-range affinity and [3H]oxytocin with a much lower affinity showed more variations. They were not found in the Brattleboro rat thalamus but were highly concentrated in several thalamic nuclei in the Long-Evans rat. Conversely, their densities were higher in the dopaminergic 13 cell group of the zona incerta and the suprachiamatic nucleus of the Brattleboro rat. Their denstities were similar in the lateral septal nucleus and in the fundus striati of both strains. In the hypothalamo-neurohypophysial system, [3H]oxytocin and [3H]vasopressin binding occurred in the Long-Evans rat with characteristics different from those found in other brain areas. In the Brattleboro rat, no [3H]vasopressin binding and only low [3H]oxytocin binding, restricted to the magnocellar neclei, were found. While these results clearly demonstrate differences in the densitites and distribution of neurohypophysial hormone binding sites between the Brattleboro mutant and its strain of origin, whether or not these variations are directly related to the deficience of vasopressin the Brattleboro rat brain remains to be demonstrated.