Internalization of intracerebrally administered porcine galanin (1-29) by a discrete nerve cell population in the hippocampus of the rat

In spite of numerous studies utilizing intraventricular administration of p orcine galanin (1-29), little is known about the spread and cellular distri bution of exogenous galanin following intraventricular administration. In t his study a discrete nerve cell body population with their dendrites became strongly galanin immunoreactive (IR) in the dorsal hippocampus following i ntraventricular porcine galanin (1.5 nmol/rat), Time course experiments sho wed that after time intervals of 10 and 20 min, but not at 60 min, scattere d small-to medium-sized galanin-IR nerve cell bodies and their dendrites we re present in all layers of the dorsal and ventral hippocampus. In double-i mmunolabeling experiments most of these nerve cells were identified as puta tive GABA interneurons costoring NPY-IR or somatostatin-IR in some cases. T wenty minutes after intraventricular injection of artificial cerebrospinal fluid (aCSF), only endogenous punctate and coarse galanin-IR terminals were found, but no galanin-IR cell bodies. Intrahippocampal injection of fluoro phore-labeled galanin resulted in the appearance of fluorescent nerve cell bodies with the same morphology and localization as in the above experiment s. Coadministration of the putative galanin antagonist M35 (0.5 nmol) and g alanin (1.5 nmol) resulted in a reduced number of galanin-IR nerve cell bod ies in the hippocampus of half of the rats. These findings support the exis tence of a population of putative hippocampal GABA interneurons with the ab ility to internalize and concentrate galanin and/or its fragments present i n the extracellular fluid, possibly mediated by galanin receptors. (C) 2000 Academic Press.