Dystrophins in neurohypophysial lobe of normal and dehydrated rats: immunolocalization and biochemical characterization.

Dystrophin, utrophin and dystroglycan are present not only in muscle but also in brain. In muscle, they link the extracellular matrix to the cytoskeleton. Their function in brain is not understood. Here we show their presence in the hypothalamo-neurohypophysial system which secretes the neurohormones oxytocin and vasopressin. Using immunocytochemistry, we showed that dystrophins are present in the neurohypophysis of control rats. After water deprivation, immunoreactivity dramatically decreased and appeared in axonal swellings in the hypothalamic tract. Dystrophin immunostaining can be ascribed to dystrophin and/or utrophin as well as the DMD (Duchenne Muscular Dystrophy) gene short products Dp140 and Dp71 as revealed by Western immunoblots of synaptosomes isolated from neurohypophyses of control rats. In synaptosomes isolated from rats under water deprivation, the immunoreactivity entirely disappeared. Further biochemichal characterization of isolated neurosecretory granules (NSG) showed that Dp140 and Dp71 are enriched in the NSG stored in the swellings of the neurohypophysis whereas the NSG of the nerve endings are devoid of these proteins. In addition we observed that the presence of beta-dystroglycan and actin correlates with the presence of dystrophins. Our data favor a direct implication of the dystrophins and/or utrophin, dystroglycan and actin in the neurosecretory processes of the hypothalamo-neurohypophysial system.