Immunohistochemical localization of NMDA- and AMPA-type glutamate receptorsubunits in the basal ganglia of red-eared turtles

Corticostriatal and thalamostriatal projection systems have been shown to u tilize glutamate as a neurotransmitter in mammals and birds. Although corti costriatal and thalamostriatal projection systems have been demonstrated in turtles, it is uncertain whether they too use glutamate as their neurotran smitter, Immunohistochemical localization of glutamate and of NMDA- and AMP A-type ionotropic glutamate receptor subunits (NMDAR2A/B, GluR1, GluR2/3, a nd GluR4) were used to address this issue. Numerous medium-sized neurons th at were rich in NMDAR2A/B and GluR2/3 were observed in the striatal part of the basal ganglia of red-eared turtles. Smaller numbers of medium-sized ne urons and some large neurons rich in the GluR1 and GluR4 subunits were also observed in the striatum. The striatal neuropil was notably rich in GluR1, GluR2/3 and NMDAR2A/B subunits. The pallidal region was specifically rich in large neurons possessing GluR4 subunits. Consistent with the glutamate r eceptors on striatal and pallidal neurons, sources of input to the striatum and pallidum in turtle such as the dorsomedial and dorsolateral thalamic n uclei (which appear to correspond to intralaminar thalamic nuclei), telence phalic pallial cell groups, and the apparent subthalamic nucleus homologue were rich in glutamatergic neurons. The results show that the thalamostriat al, corticostriatal and subthalamo-pallidal projection systems of turtles a re glutamatergic and that similar basal ganglia cell types in turtles and m ammals have largely similar glutamate receptor characteristics. Copyright ( C) 2000 S. Karger AG, Basel.