EXPRESSION OF GLUTAMATE (AMPA TYPE) AND GAMMA-AMINOBUTYRIC-ACID (GABA)(A) RECEPTORS IN THE RAT CAUDAL TRIGEMINAL SPINAL NUCLEUS

The localization of GABA(A) receptor gamma 1 and gamma 2 subunits and the AMPA-type glutamate receptor subunits GluR1 and GluR2/3 were ident ified in the caudal trigeminal spinal tract nucleus (TNC) by immunohis tochemistry using specific antibodies. The receptor species on the pro jecting neurons to the thalamus in TNC were also examined. A retrograd e tracer, Fluoro-gold (FG), was injected into the thalamus, and the se ctions were simultaneously labeled with the antibodies. Injection of F G into the ventral posteromedial nucleus of the thalamus resulted in l abeling of scattered neurons contralaterally in the TNC, Most of the n eurons labeled by retrograde tracing also showed gamma 1- and gamma 2- like immunoreactivity, while many of the neurons containing FG lacked GluR1- and GluR2/3-like immuno-reactivity. These findings show that ne urons projecting to the thalamus from the TNC receive GABAergic input via GABA(A) receptors containing gamma 1 and gamma 2 subunits, while m any neurons expressing the AMPA-type receptor did not project to the t halamus.