DISTRIBUTION OF PROSAPOSIN-LIKE IMMUNOREACTIVITY IN RAT-BRAIN

Prosaposin is the precursor for saposins A, B, C, and D, which are sma ll lysosomal proteins required for the hydrolysis of sphingolipids by specific lysosomal hydrolases. With a monospecific anti-saposin C anti body, which cross-reacts with prosaposin but not with saposin A, B, or D, the present immunoblot experiments showed that the rat brain expre sses an unprocessed approximately 72 kDa protein (possibly prosaposin) and little saposin C. Regional analysis demonstrated that prosaposin is abundant in the brainstem, hypothalamus, cerebellum, striatum, and hippocampus, and less abundant in the cerebral cortex. Consistent with this finding, prosaposin-like immunoreactive neurons and fibers as re vealed by immunohistochemistry were observed frequently in subcortical regions. The medial septum, diagonal bands, basal nucleus of Meynert, ventral striatum, medial habenular nucleus, and motor nuclei of crani al nerve had significant numbers of immunoreactive neurons. There were also nerve fibers with prosaposin-like immunoreactivity in several pr ojection fields of the above nuclei. Other brain areas that contained prosaposin-like immunoreactive neurons and/or processes were: several brain nuclei (nucleus caudate putamen, globus pallidus, substantia nig ra, red nucleus) constituting the so-called extrapyramidal system, ret icular thalamic nucleus, entopeduncular nucleus, mammillary nuclei, au ditory relay nuclei, cerebellum, sensory cranial nerve nuclei, and the reticular formation. The distribution pattern of prosaposin is appare ntly different from that of other neuroactive substances so far examin ed, and thus prosaposin may be involved in novel central events. (C) 1 993 Wiley-Liss, Inc.