Evaluation of functional GABA(B) receptors in dental pulp

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter that is elevated in inflamed human dental pulp. Because GABA agonists are antihyperalgesic in other tissue, it is possible that GABA agonists have similar effects in dental pulp assuming that this tissue contains GABA receptors. We tested the hypothesis that dental pulp contains functional GABA(B) receptors using a GTPgamma35S binding assay. This is a functional assay because GTPgamma35S will be bound to cell membranes only when activation of metabotropic receptors has lead to binding and activation of their associated G(alpha)-proteins via release of GDP and binding of the GTPgamma35S. Baclofen, a GABA(B) agonist, evoked GTPgamma35S binding in both human and bovine dental pulp. This was mediated by the GABA(B) receptor because it was blocked by the selective antagonist phaclofen in both tissues. The presence of GABA and its receptor, GABA(B), suggests that this system may be relevant in the production or management of endodontic pain.