ALPHA(2B) ADRENOCEPTOR MESSENGER-RNA EXPRESSION DURING RAT-BRAIN DEVELOPMENT

The expression of alpha(2B) adrenoceptor mRNA in developing and adult rat brain was examined, using in situ hybridization with S-35-labeled riboprobes. Tn the adult we have detected more widespread expression t han previously reported, with moderate to strong hybridization signals in the fundus striati, olfactory tubercles, septum, thalamus and Purk inje cells of the cerebellum. In addition, there was low expression in the endopiriform nucleus, claustrum, cortex, caudate-putamen and spin al trigeminal nucleus of the brain stem. During embryonic development, there was intense, transient mRNA expression in the developing vascul ar plexus and vasculature which disappeared by birth. In most brain ar eas which exhibit mRNA expression in the adult, expression started dur ing late embryonic development: with the exception of the thalamus, wh ere expression was differentially regulated in sensory and non-sensory thalamic nuclei starting at the end of the first postnatal week, Tn a ddition, there was transiently upregulated expression in the caudate-p utamen and cerebellar Purkinje cells during late embryonic and early p ostnatal development, respectively. This transient expression correlat es with thr time of neuronal migration and differentiation in these st ructures and complements the developmental expression of alpha(2A) and alpha(2C) adrenoceptors. These results suggest that alpha(2B) adrenoc eptors may play a role in angiogenesis and in mediating neurotrophic f unctions of norepinephrine in some brain areas.