Journal of Neuroscience, Vol 14, 6289-6299, Copyright © 1994 by Society for Neuroscience
Immunolocalization of NMDA receptors in the central nervous system of weakly electric fish: functional implications for the modulation of a neuronal oscillator
JE Spiro, N Brose, SF Heinemann and W Heiligenberg
Department of Biology, University of California at San Diego, La Jolla 92093-0202.
Using a monoclonal antibody raised against the R1 subunit of the rat NMDA
receptor, we mapped the distribution of NMDA receptors in the brains of
three genera of electric fish. On Western blots, the antibody recognized a
glycoprotein of approximately 105 kDa throughout the CNS. On tissue
sections, it strongly labeled a number of neuronal somata and dendrites in
the medulla, with weaker immunoreactivity in the forebrain and across much
of the rest of the nervous system. At the ultrastructural level, reaction
product was localized, though not exclusively, to the postsynaptic region
of synapses. To study the role of NMDA receptors in a specific neural
circuit, we focused on the medullary pacemaker nucleus. Neurons in this
nucleus, which fire action potentials regularly and trigger each electric
organ discharge (EOD), receive glutamatergic input from identified premotor
areas. Activity in these areas can cause the pacemaker nucleus to produce
outputs with distinct temporal dynamics, which are observed in the behaving
animal as modulations of the EOD. The projection cells of the pacemaker
nucleus, the relay cells, were heavily labeled with the anti-NMDA R1
antibody in all genera studied. These results are consistent with the
previous finding that a particular EOD modulation mediated by the
connection from one premotor area of the brain to the relay cells is
blocked by application to the pacemaker nucleus of NMDA receptor blockers.
Our results complement ongoing efforts to study this nucleus and provide
additional evidence for the role of NMDA receptors in diverse neural
circuits.
