Glutamate receptor 5/6/7-like and glutamate transporter-1-like immunoreactivity in the leech central nervous system

Previous physiological and pharmacological evidence has suggested a neurotr ansmitter role for the excitatory amino acid glutamate in the leech central nervous system (CNS). In the present study, we sought to localize glutamat e receptor (GluR) subunits (GluR 5/6/7, GluR 2/3 and N-methyl-D-aspartate r eceptor 1 [NMDAR 1]) and a glutamate transporter subtype [GLT-1] within the leech CNS using mono- and polyclonal antibodies. In whole-mounted tissue, small cells of the outer capsule and putative microglia labeled with both G luR 5/6/7 and GluR 2/3 but not NMDAR 1 subunit antisera. In general, GluR 5 /6/7-like immunofluorescence was both more intense and more widespread than GluR 2/3-like immunolabeling. Cryostat-sectioned tissue revealed extensive GluR 5/6/7-like immunoreactivity throughout the neuropil as well as labeli ng within a few neuronal somata. GLT-1-like immunoreactivity localized to t he inner capsule, which is the interface between neuronal somata and the ne uropil and is deeply invested by processes of neuropil glia. These results complement previous physiological and pharmacological findings indicating t hat the leech CNS possesses the cellular machinery to respond to glutamate and to transport glutamate from extracellular spaces. Together, they provid e further evidence for glutamate's role as a neurotransmitter within the le ech CNS. (C) 1999 Wiley-Liss, Inc.