Somatostatin (SRIF) receptors are expressed in the external granule cell layer of the rat cerebellum during early postnatal life. The aim of the present study was to investigate the distribution and biochemical characteristics of SRIF binding sites in the cerebellum of homozygous (vasopressin deficient) Brattleboro rats, which exhibit a selective impairment of their granule cell layer. This study has been conducted in 13-day-old rats by means of membrane-binding assay and autoradiography using [125I-Tyr0,DTrp8]S14 as a radioligand. In the cerebellum of homozygous Brattleboro rats, Scatchard plot analysis revealed the existence of a single class of SRIF receptors with similar Kd values as in Long-Evans or heterozygous Brattleboro rats (180-200 pM). Conversely, a marked reduction of the concentration of SRIF binding sites was observed in Brattleboro rats as compared to heterozygous or Long-Evans rats. In homozygous Brattleboro rats, autoradiographic studies revealed that the concentration of SRIF receptors was reduced in all lobules of the cerebellum as compared to Long-Evans. In addition, the magnitude of the decrease of receptor concentration was greater than the loss of granule cells observed in the homozygous Brattleboro rat. These results indicate that the expression of SRIF receptors by immature granule cells of the cerebellum is markedly reduced in Brattleboro rats. Whether the impairment of SRIF receptors in diabetes insipidus rats can directly be ascribed to vasopressin deficiency remains to be determined.