Mating induces pupillary dilatation in female rats: Role of pelvic nerve

In the present study, we demonstrate that natural or artificial vaginal stimulation exerts a powerful effect on autonomic activity, as measured by pupillary diameter. Pupillary diameter was recorded approximately 3-5 sec after copulatory mounts, intromissions, ejaculations or experimenter delivered stimulation. The pupil was magnified 43X and its diameter was measured directly from a calibrated video screen. Mating tests were performed on 13 female rats which received at least one complete ejaculatory series. Compared to the premount (baseline) value (1.01 mm), mean pupillary diameters were significantly greater during (a) mounts without intromissions (1.20 mm; 20% increase), (b) mounts with intromissions (1.34 mm; 33% increase), or (c) ejaculation (1.49 mm; 48% increase). Mean pupillary diameter during the post-ejaculatory interval (0.95 mm; 6% decrease) did not differ significantly from the premount baseline. Since the mean pupillary diameter at the last intromission before ejaculation was significantly larger (by 18%) than the diameter at the first intromission, repeated intromissions may generate a gradually increasing net sympathetic response reaching a peak at ejaculation. In order to identify the adequate stimuli for increasing pupillary diameter, we applied external genital stimulation (flank-perineal palpation), internal genital stimulation (probing the vaginal cervix with a glass rod), or both combined. Vaginal stimulation alone produced near-maximal pupillary dilatation; external genital stimulation was less effective, and combined internal and external genital stimulation was more effective. Thus, vaginal afferent activity is an adequate stimulus to produce pupillary dilatation. Furthermore, bilateral pelvic neurectomy markedly attenuated the effect of vaginal stimulation on dilating the pupil. Since pupillary diameter is at least partly a function of autonomic tone, this "bioassay" indicates that genital stimulation may produce a net sympathetic activating effect.