L-2-amino-4-phosphonobutyrate (L-AP4) is an agonist at the type IV metabotropic glutamate receptor which is negatively coupled to adenylate cyclase.

Glutamate and L-AP4 inhibited forskolin-stimulated cyclic AMP (cAMP) production in baby hamster kidney (BHK) cells transfected with the type IV metabotropic receptor (mGluR4). In situ hybridization revealed a high level of mRNA for the mGluR4 in the entorhinal cortex, but not in the dentate gyrus. These data demonstrate that mGluR4 receptors are negatively coupled to the cAMP cascade, and suggest that the mGluR4 receptor may be the previously described presynaptic L-AP4 receptor.