The
anticonvulsant or proconvulsant properties of
ligands at
metabotropic glutamate receptors (mGluRs) were examined in a chemoconvulsant model using
pentylenetetrazole (PTZ). Mice received mGluR
ligands by intracerebroventricular (i.c.v.) infusion prior to a
subcutaneous injection of PTZ and the latency to onset of tonic convulsions was recorded. The group I mGluR antagonist
1-aminoindan-1,5-dicarboxylic acid (AIDA) dose-dependently antagonised PTZ-induced
seizures with a mean ED50 value of 465 nmol. In contrast, the selective group I mGluR agonist, (S)-3,5-dihydroxyphenylglycine [(S)-
DHPG], was proconvulsive and decreased the PTZ-induced seizure latency (ED50=60 nmol i.c.v.). A selective agonist of group II mGluRs, (1S,3S)-1-aminocyclopentane dicarboxylic
acid [(1S,3S)-ACPD], was proconvulsive but did not affect PTZ-induced seizure latency. Moreover, the proconvulsant effect of (IS,3S)-ACPD was not blocked by the
mGluR2 antagonist,
alpha-methylserine-O-phosphate monophenyl ester but was blocked by AIDA suggesting the involvement of group I mGluRs. (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine (
PCCG-IV), which is a potent
mGluR2 antagonist and a group III mGluR agonist at higher doses, increased the PTZ-induced seizure latency (ED50=51 nmol) and this effect was fully reversed by the group III mGluR antagonist, (S)-2-amino-2-methyl-4-phosphonobutanoic
acid (
MAP4). Similarly, the group III mGluR agonist 1-amino-3-(phosphonomethylene)cyclobutanecarboxylate (cyclobutylene-AP5) increased the PTZ-induced seizure latency (ED50=12 nmol) in a MAP4-sensitive manner. Collectively, these data suggest that mGluR
ligands modulate PTZ-induced seizure activity in mice by either antagonizing group I mGluRs or activating group III mGluRs.