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The present experiment was designed to investigate the dose–effect and time–effect functions of the κ−opioid receptor agonist [5α,7α,8β)-(−)-N-Methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl]benzeneacetamide] (U69,593) in intact and gonadectomized male and female rats as a function of hotplate temperature (45°C or 51°C). At 45°C baseline lick latencies were longer in female rats than in male rats. Lick latencies increased dose-dependently in all subjects except intact female rats. U69,593 increased lick latencies as a function of time since its administration in all subjects. At 51°C baseline lick latencies did not differ between groups and they increased dose-dependently in all subjects. The effectiveness of U69,593 decreased as a function of time since its administration, but not in castrated male rats. These observations suggest that gonadal hormones could play a role in modulating the behavioral effects of …