Abstract
properties of colon specific DRG neurons. Results: We found that the visceromoter response to CRD in 6-to-8 week old female rats was significantly greater than that in age-matched male Sprague-Dawley rats (p<0.05 at 30, 40 and 50 mmHg). Patch clamp recordings showed significant differences between the colon-specific DRG neurons from female and male rats. The membrane input resistance in female DRG neurons was significantly lower than that in male DRG neurons (195±27 vs 424±54 Mohm, p<0.05); action potential duration and action potential threshold of DRG neurons were significantly greater in females than those in males (6.0±0.7 vs 3.6±0.5 msec, and -15.8±1.3 vs -22.3±1.4 mV, respectively, p<0.05). We obtained colon-specific DRG neurons 24-hours after daily treatment of male rats with i.m. progesterone (10mg/kg) for seven-days. Progesterone treatment significantly depolarized the resting membrane potential (-59±1 vs -51±1mV, p<0.05), increased input resistance (424±54 vs 872±88Mohm, p<0.05), decreased rheobase (0.42±0.05 vs 0.09±0.01 nA, p<0.05), increased action potential duration (3.6±0.5 vs 5.2±0.3msec, p<0.05) and decreased action potential threshold (-22.3±1.4 vs -26.6±1.0 mV, p<0.05). All these changes in the active and passivemembrane properties of DRGneurons indicate an increase in the excitability of DRG neurons. In support of this, we found that the visceromoter response to CRD was significantly greater in male rats 24-hours after 7-days of daily treatment with PG, when compared with baseline (p<0.05). However, the visceromoter response returned to normal range 7-days after the end of progesterone treatment. Conclusions: We conclude that the baseline visceromoter response to colorectal distension in female rats is greater than that in age-matched male rats. Daily treatment of male rats with exogenous PG sensitizes the DRG neurons and enhances the visceromoter response. The female sex hormone progesterone may be one of the factors that promote visceral hypersensitivity in females predisposing them to a higher incidence of visceral pain.
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