A method for stimulation of cyclic AMP levels in vivo by intracerebral injection in the rat olfactory tubercle.

A method is described for stimulation of cAMP levels in brain by direct injection of dopamine (DA) and other neuroactive substances. Intracerebral microinjection was preceded by intraperitoneal injection of 3-isobutyl-1-methylxanthine (IBMX) to inhibit cyclic nucleotide phosphodiesterase. In vivo adenylate cyclase and phosphodiesterase activities were terminated by focused microwave radiation and the injected tissue assayed for protein and cAMP content. Increases in cAMP levels in response to injections of DA were both time- and dose-dependent. Animals receiving only vehicle or sham injections into the olfactory tubercle had basal cAMP levels of 5 pmol/mg protein. Up to five-fold increases above basal (25 pmol cAMP/mg protein) were observed for DA. With the injection of other neuroactive substances, values ranging from 160 pmol cAMP/mg protein for norepinephrine (NE), to 15 pmol cAMP/mg protein for gamma-amino butyric acid (GABA) were observed. The present study demonstrates that neuroactive substances can stimulate cAMP production in vivo when injected directly into brain tissue.