Effect of local injection of cysteamine and cystamine on somatostatin and neuropeptide Y levels in the rat striatum.

Cysteamine and its dimeric form cystamine have been applied to the rat striatum by local injection. Both compounds resulted in a dose-dependent decrease of somatostatin levels. Maximal reduction of somatostatin (by about 50%) was obtained at a dose of 50 micrograms of cysteamine or cystamine after about 6 h. All three molecular weight forms of somatostatin--somatostatin-14, somatostatin-28, and the 13,000 molecular weight form of somatostatin--were reduced, as shown by size exclusion HPLC. Injection of radiolabeled cystamine revealed a fast conversion of the compound to cysteamine, suggesting it is active in the monomeric form. The levels of neuropeptide Y, which is colocalized with somatostatin in striatal neurons, failed to be changed by local or intraperitoneal injection of cysteamine, suggesting that this treatment does not affect vesicles of somatostatin/neuropeptide Y neurons.