title: Effect of amniotic-fluid ingestion on vaginal-cervical-stimulation-induced Fos expression in female rats during estrus.
abstract: Placental Opioid-Enhancing Factor (POEF) is a substance found in amniotic fluid (AF) that, when ingested, potentiates opioid-mediated, but not non-opioid-mediated, hypoalgesia. Vaginal-cervical stimulation (VCS) produces a stimulus-bound, partially opioid-mediated hypoalgesia that previous research has shown to be potentiated by AF ingestion. To understand the mechanism of opioid enhancement by POEF we investigated the pattern of neural activation after a bout of VCS that produced hypoalgesia, with and without co-administration of AF. Specifically, virgin Long-Evans rats showing vaginal estrus were handled briefly (control) or received VCS (75g pressure, 1 min), in a pattern that approximated early parturition rather than copulation, using a spring-loaded glass-rod probe. Rats were given an orogastric infusion (0.25 ml) of either AF or 0.9% saline resulting in four groups (VCS or handling; AF or saline). Rats were perfused 90 min after treatment and tissue was processed by immunohistochemistry for Fos. The number of Fos-immunoreactive cells was counted in structures previously shown to express Fos in response to VCS (the medial preoptic area, MPOA; the ventrolateral portion of the ventromedial hypothalamic nucleus, vlVMH; the arcuate nucleus, ARC). We found that this pattern of VCS did not produce a significant increase in Fos expression in the MPOA and vlVMH unless it was paired with AF. VCS produced a significant increase in Fos in the ARC. The interaction of AF and VCS on Fos expression in the MPOA suggests that POEF may enhance vaginal-cervical sensory input at parturition to facilitate sensitization of the MPOA, and presumably facilitate maternal-behavior onset.
authors.affiliation: Behavioral Neuroscience Program, Department of Psychology, University at Buffalo, Buffalo, NY 14260, USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hoey
authors.forename: Seth W
authors.initials: SW
authors.lastname: Hurley
authors.forename: Derek
authors.initials: D
authors.lastname: Daniels
authors.forename: Mark B
authors.initials: MB
authors.lastname: Kristal
mesh_terms: D000653:Amniotic Fluid; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002584:Cervix Uteri / Q000294:innervation; D004435:Eating; D004971:Estrus; D005260:Female; D007150:Immunohistochemistry; D008425:Maternal Behavior / Q000502:physiology*; D010146:Pain / Q000378:metabolism; D017288:Pain Threshold / Q000502:physiology; D010812:Physical Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D020318:Rats, Long-Evans; D014621:Vagina / Q000294:innervation
chemical_list: D016760:Proto-Oncogene Proteins c-fos