The prolonged imipramine or electroconvulsive shock treatment induced a decrease in ibotenate stimulated increase in cyclic AMP accumulation as well as it inhibited the synergistic interaction between ibotenate and noradrenaline; the glutamate-mediated inhibition of forskolin-stimulated cyclic AMP accumulation was not modified. Our results indicate that certain subtypes of metabotropic glutamate receptor are differently modified by prolonged antidepressant treatment.