title: Milk-induced, opioid-mediated antinociception in rats at the time of cesarean delivery.
abstract: Four experiments were conducted in rats within 2 hr of cesarean delivery to assess antinociception at birth and its possible opioid bases. Morphine antinociception was established in a dose-dependent fashion (0.0625-5.0 mg/kg bw). Analgesia was naloxone (1.0 mg/kg) reversible. In succeeding experiments, antinociception equivalent to that produced by 0.0625-0.125 mg/kg morphine injections was induced by a single 20-microliters bolus of milk (commercial half-and-half) that was delivered over 1-2 s to the middle of the tongue. This, too, was naloxone reversible. Milk-induced antinociception was maintained for at least 4 min. Finally, baseline latencies were progressively reduced during the first 2 hr after delivery to levels (8-10 s) that are typically obtained in older (10-day-old) rats. This decline was not opioid mediated because it was not affected by naloxone. Thus, at birth, delivering milk to the mouth in physiological volumes can exert opioid-mediated antinociceptive effects in rats born by cesarean delivery that had never suckled or experienced any other form of maternal contact.
authors.affiliation: Department of Psychology, Cornell University, Ithaca, New York 14853.
authors.forename: E M
authors.initials: EM
authors.lastname: Blass
authors.forename: A M
authors.initials: AM
authors.lastname: Jackson
authors.forename: W P
authors.initials: WP
authors.lastname: Smotherman
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001143:Arousal / Q000502:physiology*; D002585:Cesarean Section; D004723:Endorphins / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology*; D013391:Sucking Behavior / Q000502:physiology*; D013697:Thermosensing / Q000502:physiology
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid