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PubMed1984

Transitions in the dehydration-induced inhibition of milk intake in suckling rats.

The effects of acute cellular or extracellular dehydration on milk intake via suckling were determined in rats 5, 10, 15, and 20 days of age. Milk was made available 10 times to each rat pup by the intravenous infusion of oxytocin to anesthetized test dams. Prior to 15 days of age, milk intake was not affected by either intracellular or extracellular dehydration. In rats 15 days and older, however, both forms of dehydration reduced milk intake at the nipple. Thus, dehydration starts to inhibit suckling behavior at the onset of weaning, when food and water are both taken directly from the environment by the developing animal.

Animals↗
PubMed1988

Sensory determinants of nipple-attachment behavior in 2-4-day-old kittens.

Fourteen kittens, 2-4 days of age, were studied on their anesthetized dams for nipple attachment behavior. In agreement with a previous report (Larson, M. A., & Stein, B. E., 1984, Dev. Psychobiol., 17: 423-436) we find that olfaction contributed rather little to nipple attachment in kittens. The major determinants appear to be tactile, centering in the mouth and trigeminal projection field. The behavior of kittens with temporary oral and/or trigeminal deafferentation is described in detail to provide some understanding of the contribution of each of those areas to nipple attachment in kittens.

Animals↗
PubMed2006

Dynorphin A (1-13) and responsiveness of the newborn rat to a surrogate nipple: immediate behavioral consequences and reinforcement effects in conditioning.

The role of endogenous opioid system in learning (Pavlovian conditioning) and reinforcement was studied in newborn rats by pairing central injection of dynorphin A (1-13), an endogenous ligand with high affinity for kappa opioid receptors, with a surrogate nipple. For conditioning, the nipple served as the conditioned stimulus and dynorphin as the unconditioned stimulus. Dynorphin was found to elicit an immediate unconditioned, dose-dependent increase in the neonatal responsiveness to a surrogate nipple providing water, an effect apparently mediated through the kappa opioid receptors. This immediate effect of dynorphin was evident in the context of suckling behavior but not in the context of adult-like drinking when water was delivered through an intra-oral cannula. One hour after injection, the unconditioned stimulatory effect of dynorphin had dissipated and no longer affected responsiveness to the nipple. However, pairing of centrally injected dynorphin and suckling on a nipple delivering water substantially enhanced responsiveness to a nipple 1h later. This suggested conditioning, and hence reinforcement, by the centrally injected dynorphin. The conditioned sustained nipple attachment was mediated through both kappa and micro opioid receptors. These experiments confirm a central role for the brain opioid systems in reinforcement of neonatal behavior on the nipple.

Animals↗
PubMed1987

Activity patterns within the genioglossus during suckling in domestic dogs and pigs: interspecific and intraspecific plasticity.

Suckling is universal among terrestrial mammals, but it is not clear whether mechanisms of suckling are the same in mammals of differing morphology or feeding ecology. An evaluation of the literature on tongue movements during suckling suggests that pigs and dogs may use the tongue differently, with humans being intermediate. Electromyographic (EMG) recordings of the middle and posterior portions of genioglossus of pigs and dogs were compared in order to (1) see whether neuromotor patterns for tongue movement during suckling can be recognized and (2) identify interspecific differences in neuromotor patterns if present. A single pattern of coordination was found in dogs, but results from pigs indicated plasticity, both within and between individuals. The literature on humans indicates that, as in pigs, suckling patterns may vary. In addition to the difference in variability, pigs and dogs differed in EMG burst duration and cycle length. The performance of suckling in pigs, dogs and humans, respectively, resembled the tongue movements used in drinking in each species. The greater plasticity of suckling behavior in pigs (and possibly humans) may be related to an ability to acquire milk under a variety of environmental conditions or to a generally variable feeding process characteristic of omnivorous mammals.

Animals↗
PubMed2002

Classical conditioning in the rat fetus: temporal characteristics and behavioral correlates of the conditioned response.

This study examined the temporal characteristics and behavioral correlates of the conditioned response (CR) following classical conditioning of the embryonic Day 20 (E20 rat fetus). The conditioning procedure involved pairing of an artificial nipple (the CS) with an infusion of milk (the US) to establish classical conditioning. The test for classical conditioning involved measurement of a stimulus-evoked facial wiping response in a classical conditioning test. Experiment 1 compared the effectiveness of one- and three-trial procedures to establish classical conditioning. Experiment 2, 3, and 4 described the time course for the CR following one- and three-trial conditioning procedures. Experiments 3b and 4b describe the behavioral responses to (a) presentation of the CS at the time of conditioning, (b) infusion of the milk US at the time of conditioning, and (c) reexposure to the CS before the test for classical conditioning. Experiments 5 and 6 exposed the fetus to manipulations that either increased or decreased stretching (a behavior found to be associated with the CR). The results are discussed in terms of the temporal characteristics and behavioral correlates of conditioned and unconditioned responses and their mediation by activity in endogenous mu and kappa opioid systems.

Animals↗
PubMed1992

Dimethyl disulfide mimics the effects of milk on fetal behavior and responsiveness to cutaneous stimuli.

This study examined the behavioral responses of near-term rat fetuses to a range of chemosensory fluids that resemble constituents of milk or are present in the context of suckling immediately after birth. Milk and dimethyl disulfide (DMDS), a constituent of pup saliva that promotes postnatal nipple attachment, were effective in altering fetal motor activity (increased mouthing and rearlimb movements after infusion), and producing changes in fetal responsiveness to perioral cutaneous stimulation (reduced incidence of facial wiping). The behavioral effects of DMDS were reversed by naloxone and the kappa receptor antagonist nor-binaltorphimine diHCl, suggesting kappa opioid involvement in these behavioral changes. The existence of prenatal responsiveness to DMDS suggests that this substance may function as a semiochemical during the neonatal period.

Animals↗
PubMed2000

Milk delivery schedules and stomach preloading alter patterns of suckling behavior by newborn rats on a surrogate nipple.

Newborn rat pups tested before suckling experience attached to and ingested milk from the surrogate nipple. Time attached to the nipple and amount of milk ingested depended on the schedule of milk infusion through the nipple. More frequent milk infusions resulted in more frequent disengagements from the nipple during the test, less time attached to the nipple, and less body weight gain. The initial patterns of attachment behavior--continuous or intermittent--were reproduced later when rats were tested on the surrogate nipple. Preloading of the stomach with milk effectively altered both attachment and ingestion from the nipple, whereas preloading with the same amount of water had no effect on suckling behavior. The data suggest that newborn rats flexibly adjust their attachment behavior to peculiarities of milk delivery through the surrogate nipple and reproduce the initial attachment pattern when reexposed to the surrogate nipple.

Animals↗
PubMed1994

Combined effects of caffeine and malnutrition during pregnancy on suckling behavior in newborn rats.

Six groups of pregnant dams were fed a 20%, 12%, and 6% protein diet with and without caffeine (2 mg/100 g b.wt.), starting on day 7 of gestation. At day 18 of gestation, randomly selected dams of each group were used to record prenatal fetal behavior. The remaining dams were continuously fed their respective diets until the birth of their pups. Upon delivery, newborn pups from the dams fed a 20%, 12%, or 6% protein diet with caffeine were placed with foster dams that the dietary regimen during gestation was a 20%, 12%, or 6% protein diet, respectively. Dams fed a noncaffeine diet, along with their newborns, were fed their respective diets until day 15. Suckling behavior tests for newborns were conducted on days 2, 8, and 15. On day 15, both nondeprived and deprived newborn rats were studied. Caffeine in combination with a malnourished diet has different effects on general activity in prenatal stages compared to postnatal stages. Our findings support the view that prenatal exposure to caffeine may produce greater effects because: a) caffeine and its metabolites pass freely into the embryo and attain a concentration slightly lower than in the maternal plasma; and b) caffeine may be poorly metabolized during pregnancy, causing an accumulation in the fetal tissues. Prenatal caffeine at the dosage we have used in combination with malnutrition may produce lasting metabolic alterations in the nervous system related to the emergence of suckling behavior and general motor activity.

Animals↗
PubMed1982

Dehydration inhibits suckling behavior in weanling rats.

The relation between dehydration and suckling behavior was determined in weanling rats 14, 20, and 23 days of age. After 15 days of age, intracellular and extracellular dehydration sharply reduced both the number of rats that suckled and the amount of milk consumed. Rehydration returned both behaviors to control levels. Thus, during the weaning period, the internal determinants of suckling are not homologous with those of drinking but are more homologous with those governing feeding.

Animals↗
PubMed1991

Maternal diet alters the sensory qualities of human milk and the nursling's behavior.

Although the majority of human infants are breast-fed for the first few months of life, there is a paucity of information regarding the sensory qualities of human milk and how these qualities are affected by maternal diet. The present study investigated the effects of garlic ingestion by the mother on the odor of her breast milk and the suckling behavior of her infant. Evaluation of the milk samples by a sensory panel revealed garlic ingestion significantly and consistently increased the perceived intensity of the milk odor; this increase in odor intensity was not apparent 1 hour after ingestion, peaked in strength 2 hours after ingestion, and decreased thereafter. That the nursling detected these changes in mother's milk is suggested by the finding that infants were attached to the breast for longer periods of time and sucked more when the milk smelled like garlic. There was a tendency for infants to ingest more milk as well; the lack of a significant effect may be due to the inherent limitations on the total amount of milk available to the infant.

Adult↗
PubMed1981

Ontogeny of amphetamine anorexia in rats: a behavioral analysis.

These experiments were conducted to ascertain the effects of amphetamine on the behaviors associated with feeding in weanling and preweanling rats. The first two experiments produced the following results. (a) In 5-day-old pups, amphetamine increased speed of approach to an anesthetized dam but had no effect on other food-related behaviors, such as latency to attach to the nipple, time spent with the mother, duration of suckling, or weight gain. (b) At 15 days of age, amphetamine increased speed of approach to the dam but did not affect time spent in contact with the dam. However, it produced marked weight loss (relative to the weight of controls), slowed or reduced frequency of attachment to the nipple, and decreased time spent nursing. (c) AT 25 days of age, amphetamine disrupted all aspects of the feeding process except initial approach to the dam. Weight gain, time spent in contact with the dam, time spent nursing, and time attached to the nipple were all reduced by the drug. In Experiments 3 and 4, milk was delivered to pups 5, 15, and 25 days of age through tongue cannulas, which allowed ingestion without suckling. Under these circumstances amphetamine produced clear-cut weight loss (anorexia) in pups of all three ages. This developmental analysis shows that the feeding process consists of a complex and changing sequence of behavioral events which ae differentially affected by amphetamine at each age studied. Early in development the anorectic effects of amphetamine are overridden by the strong suckling response which is not disrupted by the drug.

Aging↗
PubMed2001

The Krox-20 null mutation differentially affects the development of masticatory muscles.

The Krox-20 null mutation results in a loss of rhombomeres 3 and 5, which give rise to neurons that are essential to oral motor behaviors. Thus, the Krox-20 null mutant is an excellent model to investigate the development of oral motor circuitry. Our morphological examination of embryonic and neonatal Krox-20 null mutants revealed that a significant reduction of anterior digastric and mylohyoid muscles, the primary jaw openers, occurs between embryonic days 15 and 19. There are no gross morphological alterations in other masticatory muscles. These findings demonstrate that Krox-20 expression is critical for the normal development of the primary jaw opener musculature and they help explain previous studies documenting a reduction in jaw opening in Krox-20 null mutants. Since jaw opening is the power stroke of suckling behavior, our data help explain the reduction of colostrum/milk ingestion in Krox-20 null mutant neonates.

Animals↗
PubMed1999

The effect of early handling is dependent upon the state of the rabbit (Oryctolagus cuniculus) pups around nursing.

We investigated the behavior toward humans in 4-week-old pups and adult rabbits handled daily at different times around the nursing visits during their 1st week of life. The timing of handling significantly influenced its efficiency in altering the subsequent behavior of rabbits. Animals handled around nursing readily approached a human hand when tested at weaning. Other pups, handled either 6, 12, or 18 hr after nursing, avoided the human hand. Our results show that there is a narrow sensitive period for successful stimulation, because only those rabbits that were handled within the interval starting 15 min before and ending 30 min after nursing became tame. The effect of early handling proved to be long-lasting because nonhandled rabbits tested as adults were afraid of humans and showed behavioral elements of avoidance, while the handled ones behaved fearlessly in the open field. The effect of handling proved to be specific toward humans because both handled and nonhandled animals showed avoidance toward a stuffed fox.

Adult↗
PubMed1985

Gustatory determinants of suckling in albino rats 5-20 days of age.

Taste reactivity in suckling rat pups was assessed. Five-day-old rats in Experiment I were equipped with tongue cannulae seated 2 mm rostral, 0-3 mm caudal, or 4-6 mm caudal to the intermolar eminence. Either water, 1.4 X 10(-3) QHC1, .50M NH4Cl, or .43M NaCl was delivered in one of three fashions during suckling: (1) continuous: fluid was continuously available from a reservoir connected to the cannula, and could be obtained by exerting suction; (2) discrete: same procedure as above, save that fluid was available for only 30 sec every 3 min of the 30-min test; (3) pulsatile: here, .05 ml fluid was delivered by infusion pump 8-10 sec every 3 min, provided the pups were attached to a nipple. Based on intake, time and behavioral measures, we conclude behavioral reactivity exists especially to NH4Cl and NaCl. As to quinine, Day 5 pups were responsive only when QHCl was delivered in the continuous mode. In Experiment II, rats 10, 15, and 20 days of age received the above solutions by infusions with the cannulae located in one of the three positions. Quinine reactivity developed sequentially in an anterior to posterior direction. NH4Cl disrupted behavior in 5-, 10-, and especially 20-day-old rats. Remarkably, Day 15 rats were not behaviorally reactive to NH4Cl. Sodium chloride, especially in the anterior and middle positions, was treated as an aversive solution during suckling throughout development. Based on existing electrophysiological data, the last finding was unexpected.

Ammonium Chloride↗
PubMed1980

Teratogenic effects of alcohol in humans and laboratory animals.

The teratogenicity of alcohol has been demonstrated in humans through clinical studies, behavioral studies, and epidemiologic studies, and in animals through controlled laboratory experiments. In humans exposed to alcohol during gestation the effects can range from fetal alcohol syndrome in some offspring of chronic alcoholic women to reduced average birth weight in offspring of women reporting an average consumption of two to three drinks or more per day. The behavioral effects of such exposure may range from mental retardation in children with fetal alcohol syndrome to milder developmental and behavioral effects in infants born to social drinkers. In animals, exposure to alcohol in utero may result in death, malformation, and growth deficiency as well as behavioral and developmental abnormalities. The mechanisms of impairment and related risk factors are yet to be elucidated.

Abnormalities, Drug-Induced↗
PubMed1984

Development of suckling controls in the rat: independence from thyroxine.

Until 2 weeks of age, rat pups attach to the nipples of their dam with the same avidity regardless of whether they are fed or fasted. During the 3rd postnatal week, some mode of control of suckling appears such that fasted pups attach much more rapidly than fed pups. In this study we have investigated the effects of hyper- and hypothyroidism on the maturation of suckling controls. Surprisingly, the results indicate that this aspect of behavioral development is independent of the thyroxine status of the pup. We conclude that the maturation of suckling controls is not cued by the developmental rise of serum thyroxine that occurs during the 2nd postnatal week.

Animals↗
PubMed1984

The effect of exteroceptive pup stimuli on the responsiveness of prolactin release mechanisms to suckling stimuli in the lactating rat.

In the lactating rat, the neural stimulus of suckling not only acutely releases PRL but also maintains the responsiveness of PRL regulatory mechanisms to subsequent nursing stimuli. Beginning near midlactation exteroceptive pup stimuli (ECS) can acutely release PRL. We have examined the capacity of this signal also to maintain the responsiveness of PRL release mechanisms to subsequent suckling stimuli. On day 14 postpartum lactating rats were either isolated from their young or exposed to ECS (without suckling) for approximately 24 h. When both groups were later nursed, plasma PRL of mothers earlier exposed to ECS rose significantly higher than that of subjects previously isolated from their young. Suckling produced a significant depletion in pituitary PRL and GH concentrations of ECS-exposed mothers; it did not produce a similar depletion in the pituitaries of the previously isolated group. When the pups were returned for suckling, ECS-exposed mothers began to nurse their pups substantially faster than did females of the isolated group. During the 6 h after nursing, the mammary glands of ECS-exposed mothers secreted milk at twice the rate of mammary glands of the isolated females. We conclude that ECS can maintain the capacity of neuroendocrine mechanisms to respond to galactopoetic hormone-releasing stimuli (consequently enhancing milk secretion) and support the maternal behavior pattern necessary for suckling to occur. As a result, ECS may become an important factor during later stages of lactation, compensating for the decline in suckling stimuli known to occur at that time.

Animals↗