4/13/2016 C:\DOCS\MSS\PIECH.HTM http://cogprints.org/68/1/piech.htm 1/7 Pergamon Physiology & Behavior. Vol. 57, No. 2, pp. 209212, 1995 Copyright © 1995 Elsevier Science Ltd 00319384(94)002754 Ingestion of Amniotic Fluid by Postpartum Rats Enhances Morphine Antinociception Without Liability to Maternal Behavior J. A. TARAPACKI, M. PIECH AND M. B. KRISTAL 1 Behavioral Neuroscience Program, Department of Psychology, State University of New York at Buffalo, Buffalo, NY 142604110 email: KRISTAL @ acsu.buffalo.edu Received 1 April 1993 TARAPACKI, J. A., M. PIECH AND M.B. KRISTAL. Ingestion of amniotic fluid by postpartum rats enhances morphine anti nociception without liability to maternal behavior. PHYSIOL BEHAV 57(2) 209212. 1995.  Ingestion of amniotic fluid or placenta by rats has been shown to enhance opioidmediated analgesia induced by morphine injection, foot shock, vaginal/cervical stimulation, or late pregnancy. The present study was designed to determine whether this mechanism might be a means of providing greater analgesia during the periparturitional period without contributing to the disruption of maternal behavior (measured primarily as retrieval) that can result from excessive opioid levels. Postpartum primiparous rats, injected with either 2 or 3 mg/kg morphine sulfate or vehicle and given orogastric infusions of either amniotic fluid or saline, were tested for maternal behavior. Pain threshold (determined by tailflick latency test) in rats injected with 2 mg/kg morphine and infused with amniotic fluid was elevated to a level that did not differ significantly from that of a separate group of rats injected with 3 mg/kg morphine and infused with saline. This enhanced analgesia was not, however, accompanied by the significant disruption of maternal behavior found among the rats receiving the higher morphine dose. Parturition Maternal behavior Opioids Analgesia Morphine Placentophagia Pain POEF Tailflick test Amniotic fluid AMONG most nonaquatic placental mammals, placentophagia, the ingestion of birth membranes and fluids, is typical during delivery (16,17). One of the effects of this behavior is the enhancement of opioidmediated analgesia (16). By itself, the ingestion of placenta or amniotic fluid does not produce analgesia (20,23), nor does it appear to enhance nonopioidmediated analgesia (19). It does, however, enhance analgesia produced by injection of morphine (1,6,18 20,22,23,31), foot shock (22), vaginal/cervical stimulation (1,7,23), and late pregnancy (21). The relevance of this phenomenon to normal parturition is supported by findings that opioid levels (8,9,12,14,26,27,34) and pain thresholds (2,10,11) are elevated during pregnancy and show peaks at or near delivery. One question that this strategy of potentiating the analgesic effect of the opioids available at parturition raises is whether it offers some advantage over increased opioid production or release. The possibility has been suggested (16) that it may be a way of providing the benefit of greater analgesia with less risk of the disruption of maternal behavior that a number of studies (4,13,15,24,25,29) have shown to be a consequence of excessive levels of opioids. Those studies used retrieval and grouping of pups as a combined index of the quality of maternal behavior. The choice of these criteria is supported by the observation that the test rats exhibiting these components of maternal behavior, especially retrieval, also exhibit most if not all the other components of maternal behavior (e.g., crouching over pups in a nursing posture;