Evaluation of agonists and antagonists acting at Group I metabotropic glutamate receptors in the thalamus in vivo

Recordings were made from single neurones in the ventrobasal thalamus of an aesthetised rats in order to evaluate the properties of several agonists an d antagonists of Group I mGlu receptors. The selective mGlu1 receptor antag onist LY367385 was found to reduce excitatory responses to iontophoreticall y applied ACPD and DHPG whereas the mGlu5 agonist CHPG was resistant to ant agonism. The antagonists LY367366 and LY393053 reduced responses to all thr ee agonists, but without reducing responses to NMDA or AMPA. Although AIDA was also found to reduce mGlu agonist-evoked responses, this antagonist als o produced significant reductions in responses to NMDA and AMPA. These data suggest that there are functional mGlu1 and mGlu5 receptors in the thalamu s. Furthermore, LY367385 is a useful tool for investigating mGlu1 functions whereas LY367366 and LY393053 have a broader spectrum of action. The usefu lness of AIDA as an antagonist in physiological experiments would appear to be limited by its effects against NMDA and AMPA. (C) 1999 Elsevier Science Ltd. All rights reserved.