Bladder contractions and micturition in fetal sheep: their relation to behavioral states

Abstract

Fetal bladder contractions, indicative of micturition (voiding), and behavioral states were monitored in unanesthetized fetal sheep in utero during the last third of gestation. Fetal voids began during low-voltage electrocortical activity (LV ECoG) at a greater frequency (91.4 +/- 1.0%) than expected (57.2%) and began during high-voltage electrocortical activity (HV ECoG) with a lower frequency (8.7 +/- 1.0%) than expected (42.8%). Fetal voids began significantly sooner after the onset of LV ECoG (5.84 +/- 0.13 min) than after the onset of HV ECoG (10.88 +/- 0.04 min). Electroocular and nuchal muscle activities were associated with 96.2 and 66.0% of the voids, respectively, but there was no significant association between fetal voiding and swallowing episodes. Abolition of spontaneous voiding, by urine drainage (24 h), caused no significant differences, relative to a 24-h control period, in the duration or number of episodes of LV or HV ECoG or percentage of time spent in these states. Also, induction of voiding by infusing saline into the bladder did not significantly alter the time to the next change of ECoG state. However, the mean time to the next void and the mean volume of saline infused into the bladder to induce voiding tended to be less during LV ECoG than HV ECoG, although not significantly less. Our data show that most spontaneous voids in the fetus begin during LV ECoG, suggesting that voiding is regulated by descending information from the brain. Furthermore, these experiments demonstrate that fetal bladder contractions and voiding, either spontaneous or induced, do not influence the normal cycling of fetal ECoG states.