EXPRESSION OF ALPHA(2) ADRENOCEPTORS DURING RAT-BRAIN DEVELOPMENT .2.ALPHA(2C) MESSENGER-RNA EXPRESSION AND [H-3] RAUWOLSCINE BINDING

The distributions of alpha(2C) adrenoceptor messenger RNA and high-aff inity [H-3]rauwolscine binding sites were characterized in developing rat brain. Using in situ hybridization with S-35-labeled riboprobes di rected against the third intracellular loop, alpha(2C) messenger RNA e xpression appeared in an adult-like pattern during the first and secon d postnatal weeks, in the anterior olfactory nucleus, caudate-putamen, olfactory tubercles, islands of Calleja and hippocampus, following th e rime-course of maturation of these structures. Only in the cerebellu m was alpha(2C) messenger RNA transiently expressed during the critica l period of granule cell development. High-affinity [H-3]rauwolscine b inding sites were detected using receptor autoradiography and revealed a similar spatial and temporal time-course of appearance during rat b rain development. The highest numbers of binding sites were detected i n the olfactory tubercles and islands of Calleja, and moderate numbers in the anterior olfactory nucleus, caudate-putamen and hippocampus. L ike alpha(2C) messenger RNA expression, high-affinity [H-3]rauwolscine binding sites were transiently expressed in the cerebellum In some ar eas (e.g., the substantia nigra), [H-3]rauwolscine binding sites were detected even though alpha(C2) messenger RNA expression was absent. Th e strong spatial and temporal correspondence between messenger RNA exp ression and radioligand binding supports the conclusion that [H-3]rauw olscine selectively labels alpha(2C) adrenoceptors in the rat brain. T he developmental pattern which was observed is in marked contrast to t he early, transient expression of the at, adrenoceptor. Thus, the alph a(2A) and alpha(2C) receptor types may serve distinct functional roles in the developing brain. Copyright (C) 1996 IBRO.