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Alterations in the gastrocnemius muscle of undernourished suckling rats.

Protein-energy undernutrition (PEU) during both the gestational and suckling periods causes a reduction in muscle fiber cross-section and a delay in fiber type differentiation. Such changes are not found when PEU occurs after the suckling period. To elucidate the consequences of PEU on muscle during the suckling period, we undernourished (UND) newborn rats by reducing their food intake, including a 6-hour fast every day, and doubling the number of pups suckled by the nursing rat. At day 24 of life, the gastrocnemius muscle showed a discrete reduction in lipids in the fibers of 5 control rats, and in 15 UND rats (P < 0.001). The type 2a and 2b fibers of the UND rats showed a smaller cross-sectional area than control rats (P < 0.05). The distribution frequency histogram for the muscle fibers was skewed to the left in the undernourished rats, and this was significant for type 2a and 2b fibers. PEU during the suckling period may thus induce a delay in muscle fiber maturation but does not produce significant structural alterations.

Adenosine Triphosphatases↗

Prenatal alcohol exposure: recent work on behavioral dysfunctions in pre-weanling rats.

This article reviews recent data collected in our laboratory examining the behavioral effects of prenatal alcohol exposure in pre-weanling rats. The behavioral alterations which are discussed include suckling dysfunctions, overactivity, and early learning deficits. Similar behavioral dysfunctions have also been reported in children exposed to alcohol during prenatal development. These similarities are discussed as well as possible insights that might be gained from animal models of fetal alcohol effects.

Animals↗

The early feeding skills assessment for preterm infants.

Preterm infants develop the skills necessary to begin oral feeding as their health stabilizes and as they reach a postconceptional age that supports coordination of breathing and swallowing with oral-motor functioning. The time from initiation of oral feeding to full oral feedings (with adequate intake for growth and maintenance of physiologic stability) can vary from days to months for the preterm infant. The approach to feeding the infant during this transition period must be developmentally supportive and tailored to meet the needs of the individual. To accomplish this, caregivers--notably nurses and parents--need to communicate about the specific skills that the infant has gained, about skills that are emerging, and about skills that the infant has not yet developed. The Early Feeding Skills (EFS) Assessment is a checklist for assessing infant readiness for and tolerance of feeding and for profiling the infant's developmental stage regarding specific feeding skills: the abilities to remain engaged in feeding, organize oral-motor functioning, coordinate swallowing with breathing, and maintain physiologic stability. This article introduces the EFS.

Age Factors↗

Olfactory aversive conditioning in the newborn (3-hr-old) rat impairs later suckling for water and milk.

An olfactory conditioning paradigm tested whether newborn rats can acquire a conditioned aversion to olfactory events associated with their first postnatal meal 3-5 hr after birth. Exposure to lemon odor (conditioned stimulus [CS]) paired with intraoral infusions of 0.1% quinine (unconditioned stimulus) resulted in explicit conditioning. Responsiveness to a surrogate nipple providing water in the presence of the CS was significantly lower than the 3 control conditions. The conditioning dramatically suppressed responsiveness to a surrogate nipple providing milk, which normally is expressed voraciously in terms of sustained nipple attachment and milk intake. These findings suggest that as early as 3-5 hr after birth newborn rats are capable of aversive conditioning to odors in the context of suckling behavior.

Animals↗

The first suckling episode in the rat: the role of endogenous activity at mu and kappa opioid receptors.

The present study examined the role of endogenous activity at mu and kappa opioid receptors in attachment to and ingestion of milk from a surrogate nipple in cesarean-delivered newborn rats prior to regular suckling experience. Selective opioid antagonist drugs were injected into the cisterna magna (IC administration) or lateral ventricles (ICV administration). Blockade of endogenous activity at mu opioid receptors by IC administration of the selective antagonist CTOP reduced attachment time and markedly increased disengagements from the nipple. CTOP also increased the intensity of suckling measured as milk intake per min attached to the nipple, when milk was available from the nipple in a free-access regime, and enhanced intake when milk was infused through an intraoral cannula aside from the suckling context. The ICV administration of the selective kappa antagonist nor-BNI considerably increased latency to grasp the surrogate nipple, while time on the nipple and milk intake were decreased. The presented data suggest that populations of mu and kappa receptor-containing neurons, differentiable by the route of antagonist administration, play an important role in initiation and maintenance of suckling behavior in the newborn rat during its first encounter with the nipple and milk. The kappa opioid system is predominantly involved in the initiation of the newborn's behavior directed toward the nipple providing milk. The role of the mu opioid system seems more complicated: it transforms initial oral grasp responses into sustained attachment to the nipple and maintains the intake of milk at a certain physiological level.

Animals↗

Prenatal and postnatal determinants of the 1st suckling episode in albino rats.

Conditions under which an odor could elicit the 1st nipple attachment in albino rats were investigated. In Experiment I rats exposed prenatally and immediately after birth to citral, a lemon scent, suckled the washed nipples of an anesthetized, parturient dam when the nipples had been scented with citral. Moreover, these rats did not suckle the normal, unwashed nipples of these dams. In Experiment II rats were exposed to citral either (a) in utero, (b) immediately after birth, (c) both pre- and postnatally, or (d) not at all. Only rats in Group (c) attached to washed, citral-scented nipples and did not suckle the normal unwashed nipples that elicited suckling in control rats. These findings suggest that prenatal and postnatal events can determine which olfactory stimuli elicit the newborn rat's 1st nipple attachment.

Acyclic Monoterpenes↗

Behavioral effects of neonatal cocaine exposure using a rodent model.

This study examined the effects of neonatal cocaine exposure on behavior using a rodent model. Rat pups were implanted with intragastric cannulas on postnatal day (PND) 4 and artificially reared (AR) from PND 4-10. The AR groups included two cocaine doses (20 mg/kg per day and 60 mg/kg per day) and an AR control. A sham surgery control group was also included that was reared naturally by its dam. Offspring from these neonatal treatment groups were examined for suckling performance (PND 13), passive avoidance learning (PND 23-24), activity (PND 18-21), or spontaneous alternation (PND 21). Neonatal cocaine exposure had no effect on suckling measures or passive avoidance learning. Activity was increased in the 60 mg/kg per day cocaine group relative to controls. In addition, spontaneous alternation was delayed in the 20 mg/kg per day cocaine-exposed females relative to all other groups. These data suggest that neonatal cocaine exposure may alter performance on some relatively simple tasks. More work is clearly warranted to look at the effects of neonatal cocaine exposure on more complex behaviors.

Animals↗

Newborn rats' first suckling experience: taste differentiation and suckling plasticity.

The present study examined responsiveness of newborn rats to a surrogate nipple providing fluids with basic tastes (sweet, sour, bitter and salty) and assessed the effects of this first gustatory experience on subsequent responding to the nipple itself (empty nipple) or the nipple providing water. Responsiveness (attachment to and ingestion from a surrogate nipple providing saccharin, saline, quinine or ammonium chloride) was compared with that toward a nipple providing water. Compared to water, saline and quinine significantly reduced attachment to and ingestion from the nipple, while saccharin and milk significantly increased attachment behavior. Ammonium chloride increased attachment but not ingestive behavior. Suckling experience with saline, quinine and ammonium chloride attenuated both attachment and ingestive behaviors when subjects were tested 1 h later with an empty surrogate nipple or a nipple providing water. Experience with saccharin and milk (but not water) increased both measures. The data suggest that in newborn rats, as early as a few hours after birth, mechanisms of gustatory detection have control over suckling behavior. Initial experience with the tastants available from the nipple in the first suckling episode may alter further responsiveness to the nipple itself, mediated perhaps by mechanisms of appetitive and aversive conditioning.

Ammonium Chloride↗

Sensitization of ingestive responding in preweanling rats: time course and specificity.

Two experiments measured the response-enhancing effects of oral stimulation in young rats with no feeding experience. In Experiment 1, pups were implanted with oral cannulas and deprived for 0, 6, or 24 hr. In nondeprived rats, sucrose exposure transiently sensitized oral responding to subsequent stimuli for several minutes. Among 24-hr-deprived rats, baseline oral responding had increased to where sucrose exposure was no longer sensitizing. Unlike oral responding, sensitization of activity by sucrose exposure increased with deprivation. Sensitization was also evident in the microstructure of responses to infusions. In Experiment 2, the specificity of sensitization was examined by varying stimulus palatability. Sucrose exposure sensitized oral responding to both sucrose and quinine-adulterated sucrose, but quinine-adulterated sucrose was not sensitizing. The results suggest that in inexperienced rats, oral stimulation initiates changes in responding that may mimic the endogenous sequelae of deprivation, perhaps representing early substrates for learned controls of intake.

Animals↗

Behavioral and physiological consequences of suckling in rat and human newborns.

Suckling, in addition to yielding milk, water and calories, exerts profound behavioral effects on newborn rats and humans. In particular, suckling induces feelings of calm, reduces heart rate and metabolic rate, causes infants to bring their hands to their mouths and elevates the pain threshold. These changes are mediated by opioid and non-opioid systems, each having its own separate behavioral and neurological characteristics. The implications of suckling-induced changes for long-term motivational and cognitive change are discussed.

Adaptation, Psychological↗

Feeding readiness in preterm infants: the relationship between preterm behavioral state and feeding readiness behaviors and efficiency during transition from gavage to oral feeding.

PURPOSE: The purpose of this secondary analysis was to assess whether alert behavioral states were associated with an increased number of feeding readiness behaviors (FRBs) and whether the number of FRBs were associated with subsequent feeding efficiency in healthy premature infants born between 29 to 35 weeks gestation. STUDY DESIGN AND METHODS: The data were collected as part of a larger study designed to compare the frequency of FRBs and feeding efficiency between control and experimental groups. Data from 21 stable premature infants were included in this secondary analysis. Infants were videotaped immediately prior to each of the first three oral feedings, from which infant behavioral state (IBS) and FRBs were assessed. Feeding efficiency was determined by calculating the ratio of feeding intake to feeding duration. RESULTS: IBS was not a significant predictor of the number of FRBs. The number of FRBs was predictive of feeding efficiency (p <.05). Group assignment was a marginally significant predictor of feeding efficiency (p < .10). Infant sex (p < .05), birthweight (p < .01), gestational age at birth (p <.01), and gestational age at entry (p < .05) were identified as significant predictors of the number of FRBs. Group assignment was marginally significant (p < .10). CLINICAL IMPLICATIONS: Feeding efficiency may be predicted by the increased number of FRBs immediately prior to feeding. An infant's attributes (sex, birth-weight, and gestational age) may relate to feeding efficiency and should be assessed when instituting oral feeding. Assessment of FRBs can be easily incorporated into routine clinical practice.

Attention↗