Fig. 3. (A ) A typical response to uterine cervical distension in a single fiber from a 21-day-pregnant rat. (B ) Net nerve activity (elicited activity during distension minus activity in the absence of stimulation) during uterine cervical distension increases progressively during pregnancy. Values are mean ± SE of 51 nonpregnant, 49 pregnant day 17, and 51 pregnant day 21 units. * P < 0.05 compared with nonpregnant. # P < 0.05 compared with day 17 pregnant.