The Effect of Spinal Cord Transection on VCS-induced Fos Expression and Modulation of that Fos Expression by Amniotic Fluid Ingestion
Hoey, Robert F.
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At delivery, numerous physiological, hormonal, behavioral, and sensory events are occurring at the same time. To date, each of these events has been tested individually for its influence in shortening the latency to the onset of maternal behavior. Each event has been shown to decrease the time it takes for a virgin female rat to behave maternally for the first time, but the individual effects are insufficient alone to produce a latency that is as short as that occurring during natural delivery. Therefore, the co-occurrence of these events constitutes an overlapping, redundant, system that converges at delivery to ensure immediate expression of caretaking behaviors. Previous research has shown that vaginal-cervical mechanical stimulation (VCS) interacts with amniotic fluid (and presumably Placental Opioid-Enhancing Factor [POEF]) ingestion to produce an increase in Fos expression in a nucleus crucial for maternal behavior, the medial preoptic area. VCS information reaches the brain through either the spinal or vagal pathways, or both. After spinal cord transection, residual responses to VCS (analgesia and pupil dilation) are still detectable, but it was not known how transection would influence Fos expression. The goals of the present experiments were: (a) to determine the pathway by which VCS afferent information reaches the brain to increase Fos expression and (b) to determine the possible interaction of VCS and amniotic fluid ingestion on VCS-induced Fos after spinal transection. Results show that spinal transection blocks VCS-induced Fos expression. This response is not changed by oral administration of amniotic fluid. Furthermore, in sham-surgery rats, amniotic fluid ingestion decreased Fos expression caused by VCS at high force (300g) but potentiated Fos expression at low force (75g).