Nefopam reduces thermal hypersensitivity in acute and postoperative pain models in the rat.

The activity of nefopam, a centrally acting compound, not structurally related to other analgesics, was examined in acute and postoperative thermal pain models in the rat. Its antinociceptive potency was evaluated using heat noxious stimuli either in intact or in injured animals after skin and muscular incisions. In the hot plate and in the plantar tests, nefopam after acute administration by different routes exhibited a dose-dependent attenuation of the nociceptive responses at 10-30 mg x kg(-1) by intraperitoneal or subcutaneous administration, at 60 mg x kg(-1) by oral dosing, and from 3 mg x kg(-1) after intravenous injection. In the postoperative pain model, at 30 mg x kg(-1) nefopam augmented the endpoint to thermal threshold, 60 and 90 minutes after administration compared to the threshold recorded after the incision. In the same conditions, morphine and tramadol displayed antinociceptive activities. As the plantar test provides a good index of nociception in humans, these results point out the usefulness of nefopam for attenuating moderate to severe pain, and for postoperative analgesia. In conclusion, nefopam has shown potent properties to reduce thermal hypersensitivity after acute or postoperative pain in rats.

Functional modulation of gamma-aminobutyric acid(A) receptors by etifoxine and allopregnanolone in rodents.

We looked for an interaction between etifoxine and the neurosteroid allopregnanolone at central gamma-aminobutyric acid (GABA(A)) receptors. Etifoxine (2 microM) did not affect the affinity of allopregnanolone (IC(50)=108 nM) for its site in preparations of Sprague-Dawley rat cerebral cortex membranes, as determined by the inhibition of [(35)S] t-butylbicyclophosphorothionate binding, a specific ligand of the GABA(A) receptor chloride channel site. Etifoxine and allopregnanolone were anticonvulsants, blocking the clonic convulsions induced by bicuculline (an antagonist of the GABA(A) receptor) in CD1 mice. A combination of subactive doses of the two compounds showed additive anticonvulsant effects. These results suggest that etifoxine and allopregnanolone bind to distinct putative recognition sites at or near the chloride channel site. Functionally, their binding may have an additive effect by enhancing GABA(A) inhibitory transmission.