Acute infusion of chemotactic or enkephalin-analog peptides into rat cerebral ventricles: scanning and transmission electron microscopy of leukocyte immigration in vivo.

Acute infusions of the formylated chemotactic peptide formyl-methionyl-leucyl-phenylalanine-lysine (FMLPL) or enkephalin analogue (Sandoz peptide) were made to the lateral cerebral ventricle of adult male rats to examine potential cellular responses within the central nervous system (CNS). Ependymal regions lining the third ventricle atop the hypothalamus were examined using scanning and transmission electron microscopy. The formylated peptide induced a significant, primarily neutrophilic cellular response in animals sacrificed 1 h after infusion. Cells were observed within and external to neuropil blood capillaries, suggestive of emigration from vasculature in response to the peptide. In contrast, the enkephalin analogue did not induce any leukocyte cellular response within the same time frame. Earlier studies have shown a monocyte/macrophage response in the same setting to the opioid peptides beta-endorphin, and to a lesser extent, methionine enkephalin. The present findings suggest that a formylated peptide is a potent stimulus for neutrophil migration within a CNS site, while opioid peptides may be variable with respect to effectiveness on cells of the immune system within the CNS, depending upon chemical configuration.