The surrogate nipple technique in the rat provides a useful animal model of suckling in bottle-feeding circumstances: reply to Blass (2002).
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Aging↗
Biomedical subjects
N E Spear
Publications and source records attributed to N E Spear.
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↗
Nursing experiences with an alcohol-intoxicated rat dam counteract appetitive conditioned responses toward alcohol.
BACKGROUND: Infant rats detect small amounts of alcohol (175 mg%) that are present in maternal milk whenever the dam is moderately intoxicated with alcohol. Interaction with an alcohol-intoxicated mother during the first 2 weeks of life facilitates the preweanling's subsequent discrimination of alcohol's orosensory attributes and produces conditioned aversion to alcohol. The present study further analyzed the hedonic content of infantile alcohol memories established in the nursing context by testing the interaction between experiences with an alcohol-intoxicated dam and learning procedures aimed at establishing an appetitive conditioned response toward alcohol. METHODS: Experiment 1 was to determine appropriate parameters to establish a reliable conditioned preference for alcohol in 16-day-old infants. For conditioning, intraorally infused sucrose solution (appetitive reinforcer) was paired with alcohol's orosensory cues derived from an acute state of alcohol intoxication (3 g/kg). Two control groups included an unpaired condition and a group given sucrose after water intubation. Infants then were evaluated in an alcohol intake test. Relative to control animals, a reliable conditioned preference for alcohol was registered in paired pups. In experiment 2, these conditioning procedures were applied to infant rats which, before conditioning, suckled from dams subjected to a 2.5 g/kg alcohol dose (intragastric) or from water-treated females during postpartum days 3, 5, 7, 9, 11, and 13. RESULTS: Experiment 2 showed that maternal treatment significantly affected the establishment of conditioned preferences for alcohol. Whereas pups reared by control dams exhibited reliable appetitive conditioning to alcohol, infants raised by alcohol dams completely failed to develop appetitive conditioning. CONCLUSIONS: The present results suggest that alcohol-related memories generated via infantile interactions with an intoxicated dam counteract subsequent conditioning of alcohol ingestion. In conjunction with prior studies, it is concluded that alcohol-related nursing experiences are capable of promoting alcohol memories with a negative hedonic content.
Alcoholic Intoxication↗
Acute effects of ethanol on behavior of adolescent rats: role of social context.
BACKGROUND: First experiences with alcohol in humans occur predominantly in adolescence, and to a large extent the attractiveness of alcohol at this age is based on its ability to facilitate certain forms of social behavior (social facilitation). Adolescence is strongly marked by a focus on peer relationships, and the social nature of the situation plays an important role in responsiveness to alcohol. Peer-directed social activity of adolescent rats may be a valuable experimental model for the study of ethanol-induced changes in social behavior and assessment of the role of the social context in responsiveness to ethanol. METHOD: In the present study we used a modified dyad social interaction test to characterize acute effects of ethanol on different forms of social behavior (social investigation, contact behavior, and play) and social motivation (preference/avoidance of a peer) in adolescent rats. Ethanol effects on behavior directed toward a peer were compared with those induced by exposure to an inanimate novel object. RESULTS: In the social context, the effects of ethanol were dose-dependent and biphasic. Low doses of ethanol (0.25-0.75 g/kg) produced apparent social facilitation (increased social activity and enhanced social preference), whereas higher doses (3 and 4 g/kg) caused social inhibition (decreased social activity and avoidance of a peer). This pattern was not observed for a nonsocial stimulus: Although overall activity in the nonsocial context was suppressed by 2 and 3 g/kg of ethanol, 0.5 g/kg of ethanol did not activate overall activity directed to the inanimate object. CONCLUSIONS: These findings demonstrate that the social nature of the testing situation plays an important role in responsiveness to alcohol in adolescence, especially to its activating effects. The results suggest also that the study of ethanol effects on social behavior of adolescent rats may be an effective tool for the study of adolescent alcohol use and abuse.
Age Factors↗
Ethanol as a reinforcer in the newborn's first suckling experience.
BACKGROUND: Recent evidence suggests that human infants prefer alcohol-flavored milk when fed through a bottle. Animal models also indicate a surprising predisposition for neonatal and infant rats to voluntarily and willingly ingest ethanol. These findings suggest high susceptibility to the reinforcing properties of ethanol early in ontogeny. METHODS: A surrogate nipple technique-a highly effective tool for investigation of the reinforcing properties of different fluids-was applied in the present study. Tests of ethanol reinforcement were accomplished in terms of two basic paradigms of Pavlovian conditioning. In one paradigm, the conditioned stimulus (CS) was the surrogate nipple, and in the other, the CS was a novel odor. RESULTS: Newborn rats showed sustained attachment to the nipple providing 5% ethanol, and later reproduced this behavioral pattern toward the empty nipple (CS alone). Ingestion of ethanol yielding appetitive reinforcement was accompanied by detectable blood alcohol concentrations, with most in the range of 20-30 mg/dl. The reinforcing efficacy of ethanol was also confirmed in the classical olfactory conditioning paradigm: following pairing with intraoral ethanol infusions, the odor (CS) alone elicited sustained attachment to an empty nipple. Females showed better olfactory conditioning with low concentrations of ethanol, whereas males were effectively more conditioned to high concentrations. Although there were no reinforcing consequences of intraperitoneally injected ethanol [as an unconditioned stimulus (US)] when a neutral odor was the CS, when paired with ingestion of water from a nipple, the injection of ethanol had a reinforcing effect. CONCLUSIONS: The present series of experiments revealed ethanol reinforcement in the newborn rat. Two varieties of Pavlovian conditioning established that ethanol can serve as an effective US, and hence reinforcer, in such a way as to increase the approach and responsiveness toward stimuli paired with that US, indicating appetitive reinforcement.
Animals↗
Self-administration of ethanol and saccharin in newborn rats: effects on suckling plasticity.
Responsiveness to a surrogate nipple providing water, saccharin, 5% ethanol, or 10% ethanol was tested in newborn rats naive to suckling (3-5 hr old) on Postnatal Day (P) 0 and in older neonates with regular suckling experience on P1 or P2. At all ages, pups demonstrated greater nipple attachment for saccharin or 5% ethanol than for water. Intake of saccharin and 5% ethanol was high in newborns, far exceeding that of water. At P1 and P2, pups exhibited a preference for saccharin, but not for 5% ethanol. Preexposure to a nipple providing ethanol or saccharin (but not a nipple alone or fluids alone) increased subsequent responsiveness toward an empty surrogate nipple (no fluid), both 1 hr and 24 hr after preexposure. Although, during preexposure, pups responded most positively to the nipple providing saccharin, the longest time spent on an empty nipple was observed in pups preexposed to 10% ethanol.
Animals↗
Infant rats are more likely than adolescents to orient differentially to amodal (intensity-based) features of single-element and compound stimuli.
An infantile predisposition to process quantity, over quality, of stimulation has been suggested in theories of cognitive and perceptual development, as well as for understanding ontogenetic differences in learning. In the present study, responsivity to stimulus intensity was assessed in preweanling and periadolescent rats by using magnitude of cardiac orienting as an index of perceived stimulus intensity. In Experiment 1, cardiac orienting was measured to low- and high-intensity auditory and visual stimuli in 15-, 17-, and 30-day-old rats. The results demonstrated that younger rats are more predisposed to respond differentially to single-element stimuli on the basis of stimulus intensity. Experiments 2, 3, and 4 examined cardiac orienting in preweanlings to compound stimuli. In accordance with studies of ontogeny of learning, the results of these experiments indicated that preweanlings process compound stimuli on the basis of net intensity, but only if there had been no prior experience with the compound's elements.
Age Factors↗
Fetal associative learning mediated through maternal alcohol intoxication.
BACKGROUND: The aim of the present study was to analyze whether alcohol as an unconditioned stimulus is capable of supporting associative learning in near-term fetuses. METHODS: In experiment 1, we determined pharmacokinetic profiles of alcohol and of an aromatic substance (cineole) in amniotic fluid and maternal blood during late gestation. The results obtained through gas chromatographic analysis allowed a second experiment in which we explicitly paired peak levels of cineole with peak levels of alcohol in amniotic fluid and blood, by intragastrically administering cineole and ethanol to the dams during gestational days 17 through 20 (paired condition). Control groups were dams given cineole 4 hr before commencement of an acute state of alcohol intoxication (long-delay group) or were only exposed to water administrations (water control group). The progeny were evaluated during postnatal day 16 in terms of behavioral responsiveness to intraorally infused solutions (cineole or alcohol presented in milk vehicle, or milk alone). RESULTS: Mouthing responsiveness to cineole was strongly affected by the nature of prenatal treatments. Pups in the paired prenatal condition mouthed significantly less than did long-delay and water controls. Physical and behavioral measures allowed us to reject the possibility that these effects were due to teratogenic effects of alcohol during late gestation. CONCLUSIONS: These results indicate that before birth, rat fetuses are capable of acquiring associative memories supported by the unconditioned properties of alcohol. This associative memory can be expressed during infancy through a significant reduction in mouth movements in the presence of the specific orosensory cue explicitly paired with alcohol interoceptive effects in utero.
Alcoholic Intoxication↗
The infant rat learns about alcohol through interaction with an intoxicated mother.
BACKGROUND: Infant rats detect the presence of alcohol in milk when the dam suffers a moderate state of alcohol intoxication. The present study examined when rat pups begin to show behavioral changes indicative of the interaction with an intoxicated dam. The study also attempted to determine if infantile experiences involving a moderately intoxicated dam result in alcohol-derived memories with a particular hedonic content. METHODS: Infant rats were allowed to interact during postnatal days (PDs) 3, 5, 7, 9, 11 and 13 with alcohol-intoxicated (EtOH dose: 2.5 g/kg) or alcohol-free dams. After the interaction took place, some pups were tested in terms of ultrasonic vocalizations (USVs) and motor reactivity when isolated and placed on each of two distinctive tactile surfaces (sandpaper or soft fabric) presented in a counterbalanced order, and the second of which was always paired with ambient ethanol odor. At PD 14 pups were evaluated in terms of the preference for texture (sandpaper versus soft fabric) and odor (alcohol versus clove) as well as alcohol ingestion. RESULTS: Very early in life (PD 3) USVs and overall activity were significantly higher in pups that had previously interacted with an intoxicated dam than in those exposed to an alcohol-free dam. Although this difference was not apparent during the following days, it was clear that a specific memory of alcohol's chemosensory cues was formed. Pups interacting with intoxicated dams followed by pairing of ethanol odor and an arousing texture (sandpaper), later avoided this texture in the preference test; pups that interacted with alcohol-free dams did not show this effect. The former animals also exhibited less consumption of alcohol than preweanlings never exposed to alcohol in the context of nursing. CONCLUSIONS: In conjunction with prior studies these results indicate that very early in ontogeny the infant processes the presence of ethanol, and perhaps its effect on its mother, within the nursing context. Under the present experimental circumstances infants appear to acquire alcohol-related information that comprises an aversive hedonic component.
Alcoholic Intoxication↗
Rapid and robust olfactory conditioning with milk before suckling experience: promotion of nipple attachment in the newborn rat.
An olfactory conditioning paradigm tested the hypothesis that newborn rats are able to learn about events associated with their first experience with milk as early as 3-5 hr after birth. Exposure to lemon odor (conditioned stimulus, [CS]) paired with intraoral milk infusions (unconditioned stimulus, [US]) resulted in strong conditioning: In the presence of the CS, sustained attachment occurred to an empty nipple as if it provided milk, whereas pups in control conditions showed little attachment. A single CS-US pairing was sufficient for strong conditioning, which was evident with a trace interval as long as 60 s. Conditioning was robust enough to promote attachment to a nipple providing saline, which is aversive to the newborn rat, and comparably strong conditioning occurred with sucrose or saccharin as the US. These findings suggest that olfactory conditioning has the potential to modify suckling behavior.
Animals↗
Acute effects of ethanol and the first suckling episode in the newborn rat.
BACKGROUND: In humans, early postnatal experience with alcohol is far from rare and includes exposure to alcohol through breast milk or through the bottle to attain sedative effects (Croce, 1987). Exposure to alcohol though mother's milk alters the infant's suckling behavior. However, acute effects of alcohol on suckling behavior using animal models remain to be investigated. METHODS: The present study was designed to examine the effects of neonatal alcohol exposure on attachment to a surrogate nipple and ingestion of milk in rat pups, naive both to suckling and to maternal care. Cesarean-delivered rat pups were pre-exposed to four dosages of ethanol (0, 1, 2, and 3 g/kg intragastrically) and tested 30 min after ethanol administration. RESULTS: Suckling behavior was impaired only in pups exposed to a dosage of 3 g/kg of ethanol. Pups in this group demonstrated longer latency to attach followed by less efficient suckling--the pups maintained contact with the nipple but showed decreased ingestion of milk from it. Pups treated with 1 g/kg of ethanol showed the greatest suckling efficiency, ingesting far more milk per minute attached to the surrogate nipple than pups in all other groups. At the same time, nonevoked motor activity was significantly suppressed by all three dosages of ethanol. Blood alcohol levels showed a linear relationship with dose at 30 min postintubation. CONCLUSIONS: These findings suggest a dissociation between acute ethanol effects on suckling and overall motor activity, with suckling apparently less sensitive to suppressive and more sensitive to activating effects of ethanol.
Animals↗
Social behavior and social motivation in adolescent rats: role of housing conditions and partner's activity.
The present study investigated 1) the effects of individual and grouped housing on social investigation, social contact behavior, and play behavior in adolescent rats tested with low socially active (grouped) and high socially active (isolated) play partners; and 2) the effects of long-term (8 days) and short-term (24 h) isolation on social behavioral manifestations and social motivation in terms of preference or avoidance of play partners. Social isolation of adolescent rats activated play behavior and social behaviors different from play, but play was predominantly affected under the conditions of this study. Long-term isolation was more effective than short-term, and resulted in greater manifestation of play and social preference. Adolescent rats were able to modify their social behaviors in response to social activity of the play partner: in isolated animals exposed to low socially active group-housed partners, play behavior was transformed into social activities unrelated to play; exposure of group-housed adolescents to high socially active previously isolated partners resulted in an increase of play behavior. Testing that allowed avoidance of social contacts revealed a dissociation between manifestations of play behavior and social motivation: group-housed play partners of isolated animals showed elevated levels of play behavior but a tendency to avoid their isolated pairmates.
Aging↗
Changes in progressive ratio responding for intravenous cocaine throughout the reproductive process in female rats.
Operant responding on a progressive ratio (PR) schedule for intravenous cocaine as well as sucrose reinforcement was examined in female rats throughout the reproductive process. Self-administration sessions began before mating, and continued throughout pregnancy and until lactational Day 8; following parturition, litters were present with dams during operant sessions. Physiological changes associated with the reproductive process dramatically altered PR responding for cocaine, while PR responding for sucrose was relatively stable throughout pregnancy and lactation. Female animals exhibited the highest number of responses/session for cocaine during estrus and the 1st trimester of pregnancy and the lowest responding near parturition, with levels only partially recovering during lactation. Dams self-administering cocaine exhibited notably different patterns of maternal behavior in the operant chambers than dams responding for sucrose. Thus, cocaine's reinforcing efficacy may be influenced by (a) the changing physiological profile associated with the reproductive process and (b) competition from the reinforcing properties of offspring during lactation.
Animals↗
A new model of ethanol self-administration in newborn rats: gender effects on ethanol ingestion through a surrogate nipple.
BACKGROUND: Ethanol intake in the context of suckling may have distinct and potentially long-lasting consequences for further responsiveness to and acceptance of ethanol, compared to other, more indirect and less natural ways of ethanol exposure early in ontogeny. METHOD: Our findings presented in this paper show that a surrogate nipple technique can be used for the study of early ethanol intake in cesarean-derived rat pups tested before any suckling experience. RESULTS: Neonatal rats attached to and voluntary ingested ethanol through the surrogate nipple as early as 4 hr after birth. Moderate concentrations of ethanol (2% and 5%, v/v) promoted substantial initial suckling behavior, including sustained attachment to the nipple. Higher concentrations (10% and 15%) were not effective in sustaining suckling. Females responded less positively to 10% ethanol than did males. High concentrations of ethanol were less effective in eliciting suckling behavior, probably due to the aversiveness of ethanol odor. However, when ethanol was presented in solution with milk, newborn pups attached to the nipple and ingested even 15% ethanol. Contamination of milk with 15% ethanol was more aversive for females than for males. Newborn rat pups demonstrated similar patterns of nipple attachment and ingestive behavior for 5% ethanol and milk. Initial experience with milk in the context of suckling did not prevent further voluntary ethanol ingestion from the same nipple; furthermore, initial exposure to 5% ethanol did not impair subsequent responsiveness to milk. CONCLUSIONS: Gender differences in responsiveness or sensitivity to ethanol can be detected in rat pups as early as a few hours after birth. The results suggest a leftward shift in the dose-response curve for females compared with males, indicating that female neonates are more sensitive or more responsive than males to ethanol. The similarity of suckling behaviors produced by moderate concentrations of ethanol and milk suggests a certain unity in their reinforcing mechanisms in the context of the first suckling episode.
Alcohol Drinking↗
Stimulus intensity modulates associative and nonassociative responding in preweanling rats.
The purpose of the present study was to determine whether preweanling rats respond differentially to the intensity and energy source of a stimulus. Previous studies have suggested that infants process compound stimuli based on net stimulus intensity regardless of the energy source of the compound's elements, but more direct tests have been needed of the infant's response to the stimulus attributes of intensity and energy source. This response was tested for auditory and visual stimuli that had been equated (Experiment 1) in terms of perceived intensity (low and high). Intensity level and energy source of the stimuli were varied independently within nonassociative (Experiment 2) and associative (Experiment 3) procedures. The overall results indicate that stimuli of a low-perceived intensity were processed in terms of their intensity, whereas high-intensity stimuli were processed on the basis of energy source. These results are relevant to contemporary issues of cognitive development in humans and animals.
Acoustic Stimulation↗
Effects of preweanling ethanol odor exposure on ethanol preference.
Preweaning exposure to a foreign odor has been shown to alter later responding to that odor. Early experience with ethanol odor may alter not only responding to ethanol odor, but also intake of ethanol solutions. The present study tested the effects of exposure to ethanol odor prior to weaning on ethanol odor preference and ethanol consumption. Sprague-Dawley-derived rats were exposed to the odor of 100% ethanol from postnatal day 1 to 22 in the home cage. An odor preference test was conducted on postnatal day 14 and a two-bottle ethanol intake test was conducted after weaning. In both odor preference and intake tests, animals previously exposed to ethanol odor exhibited a greater preference for ethanol than controls. The results demonstrate that early experience with the odor of ethanol can increase ingestion of ethanol later in life.
Alcohol Drinking↗
Behavioral detection of low concentrations of ethanol in milk in the preweanling rat.
Previous animal models testing infantile reactivity to ethanol (EtOH) in maternal milk used EtOH doses that vastly exceeded levels actually encountered in a mildly or moderately intoxicated dam. The present study assessed whether 12- and 16-day-old rats are capable of detecting EtOH in milk at levels actually recorded in an intoxicated dam. Experiment 1 determined representative levels of EtOH in maternal milk as a function of maternal intragastric administration of EtOH (0.5-3.0 g/kg). Experiment 2A assessed generalization of conditioned taste aversions accrued with a high level of EtOH (6%) in either water or milk vehicles towards lower, more representative EtOH levels obtained from Experiment 1. With body weight gain as the dependent measure, conditioned aversions to milk were evident with the milk vehicle, but there was no detection of EtOH at any level at either age. Detection of the high level of EtOH (6%) in milk, however, was observed by 16 day olds within an habituation paradigm (Exp. 2b) via cardiac and behavioral (locomotion, mouthing) indexes. In Experiment 3 application of Experiment 2's more sensitive, behavioral index to assess generalization of the conditioned taste aversions revealed detection of a lower, more representative concentration of EtOH (175 mg%) in milk in 16-day-old rats. Overall the results show that the unweaned rat is capable of detecting very low concentrations of EtOH in milk and can modify their behavior accordingly. The expression of this capability is not, however, homogeneous across different response indexes. In conjunction with prior research it is clear that the infant rat's perception of EtOH in milk, including the very low levels of EtOH found in maternal milk during mild or moderate intoxication, is a relevant experience for generating new responses towards EtOH.
Animals↗
A sensory-enhanced context facilitates learning and multiple measures of unconditioned stimulus processing in the preweanling rat.
This study tested the hypothesis that increased processing or efficacy of the unconditioned stimulus (US) contributes to the facilitation of trace conditioning that occurs when preweanling rats are conditioned in a novel sensory-rich context. Experiment 1 extended previous findings (D. L. McKinzie & N. E. Spear, 1995) of facilitated acoustic trace conditioning in the 17-day-old rat in a sensory-enhanced versus a home odor context. In the enhanced or more familiar context, Experiment 2 tested rats of this age for degree of spontaneous locomotor activity and ultrasonic vocalizations, activity and ultrasounding in response to shock, and the acoustic startle reflex. The enhanced context resulted in a greater overall activity response to shock, increased ultrasounding to discrete shocks, and a sensitized latency to startle. The results suggest that enhanced US processing in a sensory-rich context is a likely contributor to its facilitative effect on infant learning.
Animals↗