Separation of opioid from nonopioid mediation of affect in neonatal rats: Nonopioid mechanisms mediate maternal contact influences.

Abstract

A causal distinction is established in infant Norway rats between opioid- and nonopioid-mediated determinants of behavior. Contact influences are shown to be mediated by nonopioid pathways, whereas gustatory influences are shown to be opioid mediated. Specifically, naltrexone (0.5 and 1.0 mg/kg) did not at all diminish quieting exerted by contact with an anesthetized dam but completely reversed the quieting effects of morphine in isolated rats. Naloxone (5 mg/kg) did not affect the latencies with which nondeprived or 8-hr deprived rats 9, 12, 15, and 18 days of age attached to the nipples of anesthetized dams, nor did naloxone (5 and 10 mg/kg) cause any systematic change in nipple attachment in 10- and 18-day-old rats that had been deprived of their dam for either 0, 8, or 24 hr. In a 3rd experiment, naloxone (5 mg/kg) did not significantly reduce milk intake by 9-, 12-, 15-, or 18-day-old rats from the nipple when milk letdown was induced by oxytocin. Moreover, naloxone (5 and 10 mg/kg) did not reduce milk intake in Day-10 rats that, while suckling, received milk via a cannula placed in the posterior portion of the tongue at the level of the intermolar eminence or in rats that obtained milk directly from their awake mother. In contrast, milk intake was significantly reduced by naltrexone (0.25-1.0 mg/kg) in Day-10 rats that obtained milk (a) by licking it off a saturated substrate or (b) through an indwelling cannula located in the anterior portion of the lower jaw. (Milk delivered at this placement is thought to engage feeding systems by its taste and texture.) In a final set of experiments in Day-10 rats, intake of milk delivered via anterior jaw cannulae was reduced by naloxone (5 and 10 mg/kg) in rats that were either isolated, in contact with an anesthetized dam, or attached to her nipples. On the basis of resistance to naloxone and naltrexone administration, these experiments demonstrate that behavioral influences of the tactile (and possibly olfactory) qualities of the mother are not mediated by opioid systems. Implications for understanding the means through which mothers can influence their young and the infantile mediators of these maternal influences are discussed.

Acquisition and expression of a socially mediated separation response

“…A number of neurotransmitter systems are known to be capable of regulating isolation-induced USV by rat pups including GABA [51,81,86,119], opioid [4,20,57], serotonergic [53,117], cholinergic [13], corticotrophin-releasing hormone [34,50], vasopressinergic [114], and dopaminergic [27,58,59]. In most cases, it has not yet been determined whether the effects of exogenous administration of neuroactive ligands truly demonstrate roles for endogenous processes.…”

Examining the role of endogenous opioids in learned odor–stroke associations in infant rats

“…Neurochemical systems involved in mediating the neonate's response to touch include cholecystokinin (Weller & Feldman, 2003), opioids (Panksepp, Herman, Vilberg, Bishop & DeEskinazi, 1980), oxytocin (Insel, 1997;Nelson & Panksepp, 1996), and serotonin (McLean et al, 1993), although norepinephrine (NE, Sullivan & Wilson, 1994) has a particularly prominent role in mediating learned odor-stroke associations in rat neonates. It is well known that the calming (attenuation of stress) and analgesic effects of mother-infant interaction is mediated through endogenous opioids (Blass, Fillion, Weller, & Brunson, 1990;Gray, Watt, & Blass, 2000;Weller & Feldman, 2003); however, their role in learned odor-touch associations has not been examined. The goal of this research was to examine the role of opioids in the associative learning and memory of an odor preference following odor-stroke conditioning in neonatal rats.…”

Social Motivation in Recently Weaned Rats Is Modified by Opiates

“…That does not exclude, evidently, that the urge to suckle is the cause of increased motivation to be close to the mother. It seems, however, that only nutritional aspects of suckling arc opioid-dependent whereas tactile and olfactory qualities of the mother are mediated by oth er systems [39,40]. It is exactly these latter qualities that would be important as unconditioned rewards in the present experimental situation.…”

“…In the other, morphine and naloxone failed to affect learning in a T maze where access to the home cage was the reward [38]. This is not surprising because the consequences of tactile contact with the mother are not opioid-dependent [39,40], and such con tact could have been the major reward in the procedure employed.…”