Because infant rats learn about odors that elicit suckling, and because certain chemosensory cues that help elicit mating behavior in adults are similar to those that elicit suckling, an experiment was undertaken to assess the influence of suckling-associated odors experienced during infancy on adult sexual behavior. Rat pups lived with and suckled dams whose nipple and vaginal odors were altered with citral, a lemon scent. The rats were weaned and never exposed again, until testing, to citral or females. At about 100 days of age, the males were paired in mating tests with a normal sexually receptive female or with a sexually receptive female that had been treated perivaginally with citral immediately before testing. The males ejaculated readily when paired with citral-treated females but were slow to achieve ejaculation when paired with normal females. These findings implicate an infantile experience as a determinant of adult sexual behavior in a mammal.

In this study, the calming effects of sucrose in 1-3-day-olds was evaluated. Sucrose (0.5 ml, 14% weight/volume) reduced crying relative to water. Infants who received 0.2,0.6, or 1.0 ml of sucrose cried much less than infants who sucked a pacifier for 2,6,10, or 14 min. Sucrose infused through a pacifier reduced crying more effectively than did water through a pacifier. These differences support the idea of two separate functional calming systems in human newborns.

Hand-mouth coordination was studied in l-3-day-old human infants by delivering 0.2 ml of sterile 12% sucrose solution intraorally once every 2 min. Sucrose was extraordinarily calming and caused sustained hand-in-mouth contact. The calm state persisted well beyond sucrose termination. Handin-mouth behavior, however, stopped upon sucrose termination, demonstrating stimulus control over this integrated behavior. In subsequent studies we demonstrated that hand-in-mouth behavior was not attributable to calming per se. Moreover, hand activity could be prevented by placing a pacifier in the mouth. This demonstrates that the behavior was under intraoral somesthetic control and was not necessarily the expression of a motor pattern triggered by the sweet taste. These findings are interpreted within the contexts of sucrose (a) calming through an endogenous opioid system and (b) activating suckling-feeding mechanisms, causing the expression of integrated hand, mouth, and head motor patterns.In human development, hand-mouth contact is among the earliest cases of a sustained behavioral pattern that integrates two separate motor systems. Studies of human fetal activity have placed this phenomenon as early as 18 weeks menstrual age (Humphrey, 1968). The behavior remains prominent, appearing within the first hours after birth (Kravitz, Goldenberg, & Neyhus, 1978). According to Korner and her associates (Korner & Beason, 1972; Korner, Church, & Dontchos, 1968;Korner & Kraemer, 1972), it occurs up to 20% of the time in awake infants lying prone or on their sides.Hand-mouth integration changes developmentally, coming under the control of perceptual systems by 5 months of age when infants start to reach for (Hofsten, 1979(Hofsten, , 1982, then to grasp (Yonas & Granrud, 1985), and finally to bring objects to the mouth (Piaget, 1952;Rochat, 1985;Ruff, 1984; see Gibson & Spelke, 1983, for review). The transitional phases between the early behavior that is independent of eye-hand coordination and the later aspects that integrate reaching and grasping have not been identified or analyzed in any systematic fashion.The early expression of hand-mouth contact, its increased frequency during the pregrasping and prereaching months, its expansion during the period when all grasped objects are brought into the mouth, and its eventual contraction to actions supporting ingestive behavior reflect changing elements of control among integrated perceptual, motor, and affective systems. 963brought to-the mouth, could reveal some of the characteristics of perceptual and affective systems determining gustatory and haptic identification of objects, motivational systems concerning ingestive behaviors, and those concerned with affect. The eventual smoothing of hand-to-mouth actions and the ultimate ability to substitute one motor pattern for another (reflecting the initial position of the limb, its relationship with the body, and the characteristics of the grasped object) in the service of bringing an object to the mouth is of interest to students of mo...

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.

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