The Role of Arginine Vasopressin (AVP) during Birth Asphyxia

Abstract

During normal vaginal birth, a surge of the stress hormone arginine vasopressin (AVP) occurs in the periphery that helps the fetus to quickly adjust to extrauterine life. During complicated birth such as mild birth asphyxia, the resulting AVP levels are even higher. So far there is only indirect evidence for central AVP release in the brain during birth.

In this experiment, we aimed to study the effect of asphyxia on the number and thickness of visible vasopressinergic fibers in the region of neonatal dorsal raphe nucleus (DRN) in a rat model. We hypothesized that there will be more visible AVP fibres in the DRN after birth asphyxia compared to a control group. For this, male and female neonatal pups were exposed to asphyxia or room air when they were 11 days old. Fixed brain sections including the DRN were processed for double immunocytochemistry against Neurophysin2, a surrogate marker for AVP, and serotonin. The fiber fractional area (FFA) was analysed and compared between the groups.

We found that, in neonatal male pups, asphyxia treatment does not seem to increase FFA in DRN compared to controls. However, in females, we found a selective significant increase in medial ventral DRN subregion after asphyxia treatment, while FFA in caudal and rostral DRN remained similar in both treatment groups. This suggests that in males, asphyxia treatment does not lead to increased AVP release, whereas in females there might be a sub-region specific increase after asphyxia treatment. Another prominent finding was the sex difference of Neurophysin2 fiber innervation between neonatal males and females, where males seem to possess significantly higher rate of Neurophysin2 fibers than females.