Acute injections of opiate peptides into the rat cerebral ventricle: a macrophage-like cellular response.

Opiate peptides (beta-endorphin, alpha-endorphin or met-enkephalin) were administered to the lateral cerebral ventricle of adult male rats via single injection into implanted cannulas. Scanning EM of the third ventricle above the median eminence of animals sacrificed approximately one hour after peptide injection revealed numerous free cells above the ependyma. Beta-endorphin induced a significantly greater cellular response than other peptides or control injections. Transmission EM demonstrated that the cells had morphologic characteristics of macrophages. Opiate peptides in cerebrospinal fluid may act as "chemotactic" factors to induce the migration of macrophage-like supraependymal cells.