Cultured cerebellar cells as an in vitro model of excitatory amino acid receptor function

Primary cultures of neurons from 8-day-old rat pups were grown for 10 days in vitro in antibiotic-free media and then analysed for changes in cyclic guanosine monophosphate (cGMP) in response to several excitatory amino acid (EAA) agonists or related antagonists. Kainic acid (KA), N-methyl-D-aspartic acid (NMDA) and quisqualic acid (QA) produced dose- and calcium-dependent increases in cGMP with KA producing the largest and QA the least increase in this cyclic nucleotide. The increase induced by NMDA was additive with both KA and QA; however, KA and QA were not additive with each other. In fact, QA completely antagonized the effects of KA and to a much greater degree than did the EAA antagonists, glutamylaminomethylsulfonic acid (GAMS) or cis-2,3-piperidine dicarboxylic acid (PDA). 2-Amino-7-phosphonoheptanoic acid completely prevented the NMDA-induced elevations of cGMP yet had little effect on either the KA- or QA-induced elevations of this parameter. GAMS and PDA, on the other hand, were more effective in blocking the effects of KA and QA than of NMDA. These data show that cGMP levels in cerebellar granule cells provide an excellent model for studying the subtypes of EAA receptors.