1¢46 2"-eny|)-barbituric acid (3M2B, which differs from amylobarbitone only in having a terminal double bond in the 5-C substitution) and picrotoxin (a convulsant antagonist of GABA at the receptor ionophore complex, Johnston et al., 1984). The results are heterogeneous and paradoxical, with picrotoxin the only drug to give a uniform result (analgcsia). They are summarised in the Table. Test Pain ratio ~ Test Pain ratio = 1. Pentobarbitone 3. Amylobarbitone footflick 0.82 footflick 1.57 * tailfliek 1.28 * tailflick 1.39 * formalin 1.04 formalin 0.77 * constriction 1.59 * constriction 4.90 * Picrotoxin 4. 3M2B footflick 0.59 * footflick 0.75 tailfl~ 0.65 * tailflick 0.66 * formalin 0.16 * formalin 0.73 * constriction 0.22 * constriction 0.13 * # The ratio is of the index of pain sensitivity in saline treated animals/drug treated animals. A ratio of 1.0 is unchanged by the treatment. A value greater than 1.0 indicates (after the band of statistical error has h)T~,ralgesia, while a value significantly less than 1.0 indicates analgesia. * indicates a difference from 1.0 with a significance level of at least P < 0.05. indicates that nociception been taken into account) There is no obvious pattern in these results, either with a particular drug or in the acute cf the chronic tests. These disparities imply that different pathways must subserve the different nociceptive test, s, while some but not all involve classic GABA A receptors. Rderenees Carmody, JJ., Jamieson, D.D. and dePoort~re, R.Y., 1986. Naunyn. Schmied. Arch. Pharmacol. 334, 193. Andrews, P.R., Jones, G.P. and Lodge, D: 1979. Eurcp. J. Pharmacol. 55, 115. Johnston, G.A.R., AHan, R.D. and Skerritt, J.H, 1984, GABA Receptors, in: Handbook of Neuroscience (2nd edition), ed Lajtha, A. (l~enurn Press, New York), p. 213. P.we.325 ] Evaluation oF ~ analgesic effect o| fluvoxamine on experimental acute and chronic pain • ,.6-" Mic6, J.A., Casas. J., G..,errez, M., G6mez-Cama, M.C., Valverde, O., Aracama, J.R., Elorza, J. and Gibert-Rahola, J. Unidad de Neuropsicofarmac-ologi~ Dpto. Neurociencias, Universidadde Cddiz, Spain Considerable evidence exits to implicate a role for the neurotransmitter serotonin (5HT) in the modulation of the nociceptive transmission (MESSING and LYTLE, 1977). Activation of the descending serotoninergic bulbospinal system produces inhibition of behavioral and dorsal horn neuronal response to noxious stimuli. For instance, increasing postsynaptic 5HT receptor activity by administration of selective 5HT inhibitors may induce antinocicep- tion in mice, rats and humans. However, variable effects of 5 HT uptake inhibitors have been reported. Antinocicep- tion as well as no effect in the hot plate and tail frick tests have been demonstrated in mice and rats. Moreover, in mice, some selective 5HT uptake inhibitors produced hyperalgesia in the formal in test. Antidepressants with 5HT inhibiting properties have been used ~n the treatment of chronic pain (WALSH 1983). On the other hand, sex differences in the sensitivity of mice to ~:erctonin agonists have been reported, females are more susceptible than males (CARLSSON and CARLSSON 1988) The following experiments were undertaken to characterize the effects of