Opioid mediation of amniotic fluid effects on chemosensory responsiveness in the neonatal rat.
The present study investigated if oral exposure to milk or amniotic fluid (AF) alters responsiveness to sensory stimulation in the neonatal rat, and whether these effects are mediated by the opioid system. Facial wiping evoked by intraoral lemon infusion was used as a measure of sensory responsiveness. Pups were tested in a supine posture, because they showed more paw-face strokes during facial wiping than pups tested prone (Experiment 1). Moreover, pups orally exposed to milk (Experiment 2) or AF (Experiment 3) showed a diminished wiping response to lemon compared to controls exposed to water. Blockade of opioid receptors with the nonselective antagonist naltrexone (Experiment 4) or the kappa antagonist nor-binaltorphimine (Experiment 5) reinstated higher levels of facial wiping after AF exposure. These findings confirm developmental continuity between fetal and neonatal behavioral responses to AF and the ability of AF to induce activity at kappa receptors of the endogenous opioid system.
Department of Psychology, University of Iowa, Iowa City, IA, USA.
Valerie
V
Méndez-Gallardo
Scott R
SR
Robinson
D000284:Administration, Oral; D000653:Amniotic Fluid; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D001522:Behavior, Animal / Q000187:drug effects*; D005260:Female; D008297:Male; D008892:Milk; D009043:Motor Activity / Q000187:drug effects*; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000037:antagonists & inhibitors / Q000187:drug effects*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects*; D013268:Stimulation, Chemical
D009292:Narcotic Antagonists; D018847:Opioid Peptides; D011957:Receptors, Opioid; C051844:norbinaltorphimine; D009271:Naltrexone