Social Motivation in Recently Weaned Rats Is Modified by Opiates

Abstract

An open field choice test was used to determine whether maternal deprivation enhanced the motivation to stay close to the mother. Pups could choose between the dam, 3 sisters and 3 unknown animals of the same age. In addition, an empty enclosure identical to those that contained the stimulus animals were present as a nonsocial choice. Rats that were separated from their mother at 20 days of age and tested about 13 h later were compared to animals that had stayed with the mother until just before the test. It was found that maternal separation increased the time spent close to the mother and reduced that spent close to strangers or an empty enclosure. In fact, weaned animals spent far more time close to the mother than they spent close to any other available choice. Moreover, the mean duration of visits to the mother was much increased during the latter half of the 60-min test. These data were interpreted as showing that the mother had rewarding properties, and that maternal deprivation increased her reward value. In further experiments, the role of opioids for this increase in reward value was evaluated. Morphine enhanced the time spent close to the mother, but only in animals that had been subjected to maternal deprivation for about 13 h. Naloxone had the opposite effect. These data show that the mother''s reward value is altered when the activity of opioid systems is modified. It is suggested that the mother acquires rewarding properties because of association with nutritive suckling-induced opioid release.

Individual Differences and Social Influences on the Neurobehavioral Pharmacology of Abused Drugs

“…When separated from the dam, rat pups exhibit increased distress calling, and on return they exhibit increased approach to the dam; these behaviors are decreased and increased, respectively, by m-opioid agonists and antagonists (Carden et al, 1991;Agmo et al, 1997). m-Opiate receptor knock-out mice fail to display preference for mother-associated cues or vocalizations in response to separation from their mothers (Moles et al, 2004).…”

Sex-dependent differences in the effect of early weaning on the chosen hormones secretion in sheep during the postnatal transition to puberty – Preliminary results

“…Feeding appears to regulate an adrenal sensitivity whereas tactile stimuli inhibit activation of centrally-controlled components of the hypothalamo-pituitary-adrenal (HPA) system in the developing mammal (Suchecki et al 1993, McCormick et al 1998. It was previously suggested, that the mother has rewarding properties for her young, associated with nutritive suckling, and maternal deprivation increases reward value of mother for the pup (Agmo et al 1997). In female lambs maternally-deprived at 12 weeks (late weaning), the increase in CRH release from the nerve terminals in the median eminence to the pituitary portal circulation is followed by the increase in the storage of ACTH manifested by hypertrophy and hyperplasia of corticotropic cells (Wańkowska et al 2006).…”

Impact neurobiologique de la séparation mère/nouveau-né chez le rongeur

“…Des données de la littérature montrent que le système opioïdergique est, chez le rongeur comme chez le singe, très impliqué dans la mise en place des relations entre la mère et le petit [20,21]. Les opioïdes entraînent ainsi des effets renforçateurs positifs (ils favorisent un comportement d'approche ou de consommation) dès le plus jeune âge: l'allaitement induit une libération d'opioïdes chez le nouveauné, ce qui lui permettrait de considérer la tétée comme ayant des propriétés de récompense et favoriserait les associations entre la mère, la tétée et l'état de récompense [22]. La cholé-cystokinine (CCK), quant à elle, coordonne la digestion, le métabolisme et la croissance de l'enfant en déve-loppement, et semble égale-ment participer aux aspects non nutritifs des relations entre l'enfant en développe-ment et sa mère [23].…”