Pulsed magnetic field induced ''analgesia'' in the land snail, Cepaea nemoralis, and the effects of mu, delta, and kappa opioid receptor agonists/antagonists

A brief exposure to a pulsed magnetic field (Cnp: patent pending) had significant antinociceptive or ''analgesic'' effects in the land snail, Cepnea nemoralis, as evidenced by an increase in the latency of response to a warmed (40 degrees C) surface. This analgesia was in part opioid mediated being significantly reduced, but not eliminated: by the prototypic opiate antagonist, naloxone; the mu (mu) opioid receptor directed antagonists, naloxazine or beta-funaltrexamine, and the delta (delta) opioid receptor directed antagonists, naltrindole-5'-isothiocyanate or ICI 174,864. However the Cnp induced analgesia was unaffected by the kappa (kappa) opioid receptor directed antagonist, nor-binaltorphimine. The delta(1) and delta(2) opioid receptor directed agonists, (DPDPE, [D-Pen(2),D-Pen(5)]enkephalin), (deltorphin, [D-Ala(2),Glu(4)]), respectively, also had significant differential analgesic effects, supporting a functional delta opioid receptor mediated enkephalinergic mechanism in Cepaea. These results suggest that this specific pulsed magnetic field (Cnp) elicits significant analgesic effects through mechanisms that, in part, involve delta and, to a lesser extent, mu opioid receptors. (C) 1997 Elsevier Science Inc.