Differential influence of adult and juvenile conspecifics on feeding by weanling rats (Rattus norvegicus): A size-related explanation.

Weanling Sprague Dawley rat pups (Rattus norvegicus) selected between 2 safe palatable diets in concordance with the preferences of either an adult or a juvenile conspecific model (Experiment 1). Nevertheless, weanlings chose to feed more in the vicinity of an adult than in the vicinity of a juvenile, thus fulfilling the prediction of an adaptive feeding strategy (Experiment 2). The weanlings' bias for feeding in the vicinity of an adult was eliminated by increasing the magnitude of pup stimulus to 3 pups (Experiment 3). Thus, weanlings do not possess a specialization rendering them more sensitive to adults than to pups as models for diet selection. By responding to stimulus magnitude, weanlings are more likely to feed with adult conspecifics, choose foods used by them, and derive the benefits correlated with the adults' successful feeding habits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Another hamster paradox: more males carry pups and fewer kill and cannibalize young than do females

The response of virgin male and female golden hamsters to young was studied. In contrast to most species, males are more likely to carry pups than are females. All males carried pups, but approximately 50% of females cannibalized the young. The females that did not cannibalize the pups carried them with less hesitation and after shorter latencies than did the males. The response of females to young was not correlated with the aggressiveness displayed toward adult males during separate tests. Tests with gonadectomized females indicated that the maintenance of pup-killing behavior is not dependent on concurrent gonadal hormones. Progesterone injections did not significantly increase pup killing in males that had previously carried young. Speculations on the adaptive significance of the male and female hamster's response to pups are presented.     

Communal reproductive success in rats (Rattus norvegicus): Effects of group composition and prior social experience.

Compared the reproductive success and maternal behavior of sibling pairs of female Long-Evans rats (Rattus norvegicus) housed together from birth (familiar) to that of pairs of unrelated females housed apart during development (unfamiliar). Sires either remained in the colonies through weaning of their pups or were removed before parturition. Familiar animals reared more pups to weaning, were more likely to share in caring for pups, and were less likely to exhibit infanticide than were unfamiliar ones. The presence of males in cages with pups had no direct effect on the reproductive success of females, but female pairs housed with males spent less time than female pairs housed alone caring for pups together in a combined nest. Conflicting evidence for communal rearing in populations of wild rats may reflect differences in the genetic relatedness or early social experience of female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age differences in the response of California ground squirrels (Spermophilus beecheyi) to avian and mammalian predators.

The antipredator behavior of juvenile and adult California ground squirrels (Spermophilus beecheyi) was videotaped in Experiment 1 to measure the effects of age on assessment of a briefly presented live dog and a model red-tailed hawk (Buteo jamaicensis) in simulated flight. Adult squirrels treated the hawk as more dangerous than the dog, whereas juvenile squirrels showed less differentiation of the predator types. Juvenile squirrels also perceived the dog as a more immediate danger than adult squirrels did. For Experiment 2, the red-tailed hawk model was compared with models of a nonthreatening turkey vulture (Cathartes aura) and crow (Corvus brachyrhynchos). Neither age class differentiated the avian models; however, the adult squirrels treated these birds as more threatening than the juvenile squirrels did. Both studies suggest that learning may contribute to predator assessment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-mate or twin sibling: Effects on interactions between monkey mothers and infants.

Examined the effects of the twin sibling relationship upon interactions between mother and infant. 12 rhesus monkey infants were reared with a mother and nonsibling peers; 8 had an age-mate or twin sibling, while 4 control infants did not. The sibling pairs were formed by fostering newborns 2 to a mother; the control infants were fostered 1 to a mother. Findings indicate that the twin infants did not engage in as much interaction with their mothers throughout a 7-mo period of observation on a wide range of indexes, including such basic behaviors as a contact with the mother's ventrum and nipples. The mothers rearing twins spent less time cradling their infants and less frequently rejected them. There were a few additional differences, notably in the area of restrictive behavior, but it is concluded that the differences in maternal behavior were principally a reaction to the differences in infant behavior. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

μ Opioid receptors in the ventrolateral periaqueductal gray mediate stress-induced analgesia but not immobility in rat pups.

Rat pups become immobile and analgesic when exposed to an adult male rat. The aim of this study was to determine whether these reactions are under the control of endogenous opioids and to determine the role of the midbrain periaqueductal gray (PAG), which mediates stress-induced immobility and analgesia in adult animals. In Experiment 1, 14-day-old rats were injected systemically with the general opioid receptor antagonist naltrexone (1 mg/kg), which blocked male-induced analgesia to thermal stimulation but did not affect immobility. In Experiment 2, the selective μ opioid receptor antagonist {d}-Phe-Cys-Tyr-{d}-Trp-Orn-Thr-Pen-Thr-NH? (CTOP; 50 or 100 ng/200 nl) was microinjected into the ventrolateral and lateral PAG. CTOP suppressed male-induced analgesia when injected into the ventrolateral PAG. Male-induced immobility was not affected by CTOP. Male proximity therefore seems to induce analgesia in rat pups by releasing endogenous opioids that bind to μ opioid receptors in the ventrolateral PAG. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother's milk and adult presence: Two factors determining initial dietary selection by weanling rats.

Reports 3 experiments with (a) 10 female hooded rats and their litters (reduced to 6 pups/litter); (b) 1 male and 4 female wild rats (Rattus norvegicus) and 2 litters (6 pups/litter) born to colony members; and (c) 6 litters of wild and 4 litters of hooded rat pups. Results indicate that adult Ss were capable of influencing their pups' choice of diet during weaning in 2 ways: (a) cues transmitted from a mother to her pups during the nursing period were sufficient to determine the dietary preference of the young at weaning, and (b) the presence of adult Ss at a feeding site was sufficient to determine the choice of feeding site by the pups independent of cues transmitted during the nursing period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ingestion of a novel flavor before exposure to pups injected with lithium chloride produces a taste aversion in mother rats (Rattus norvegicus).

A series of experiments investigated the ability of Sprague-Dawley mother rats to learn aversions to novel flavors ingested prior to the illness of their pups. In Exp I, 24 mothers learned to avoid a novel flavored solution ingested prior to the illness of their nursing litters. Exp II was designed to investigate the extent to which any adult rat is capable of such learning: 16 nonlactating multiparous females learned aversions to novel flavors ingested prior to exposure to pups injected with LiCl, whereas 16 nonlactating nulliparous females and 16 males did not learn these aversions. Several possible reasons for differences in this learning ability are discussed. In Exps III and IV, the nature of the UCS for these aversions was investigated. Visual, auditory, and taste cues associated with the lithium-injected pups did not mediate the aversions. Evidence suggests that olfactory characteristics of the lithium-injected pups mediated the flavor aversions in the present experiments. These olfactory cues did not appear to be general stress signals but instead were likely specific cues for gastrointestinal discomfort. Results are discussed in terms of classical conditioning and also of their adaptive significance for both mother and offspring. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term effects of prenatal indomethacin administration on the pulmonary circulation in rats

Mechanical properties of the adult pulmonary vasculature are affected by perinatal experience of hypoxic pulmonary hypertension. In the present study, we followed the long-term effects of perinatal pulmonary hypertension induced by means other than hypoxia in rats. Daily injections of indomethacin (1 mg.kg-1 body weight (BW)) were given to the parturient rats. Their newborn pups had significantly increased number of muscularized peripheral pulmonary vessels. Pulmonary hypertension, however, did not persist to adulthood (mean pulmonary arterial pressure (Ppa) was 17.2 +/- 1.3 torr in the experimental group and 16.4 +/- 0.8 torr in controls). Pulmonary hypertension induced in adult rats by exposure to chronic hypoxia or by acute hypoxic challenges was similar in indomethacin-treated and control rats. Normoxic perfusion pressure/flow (P/Q) plots in isolated lungs were less steep in indomethacin-treated than in control rats. Acute hypoxia increased the slope of P/Q plots in indomethacin treated rats but not in controls. The described changes in the pulmonary vasculature induced by indomethacin are similar to those found previously in adult rats born in hypoxia. We conclude that perinatal pulmonary hypertension permanently modifies the pulmonary vasculature.     

Age-mate or twin sibling: Effects on monkey age-mate interactions during infancy.

12 rhesus monkey infants were reared with a mother and nonsibling peers; 8 had an age-mate or twin sibling, while 4 control infants did not. The twin sibling relationship was produced experimentally by pairing infants at birth and fostering them 2 to a mother; the control infants were also paired but fostered 1 to a mother. Positive affiliation with the paired rearing partner began earlier in the twin group and continued at higher levels throughout a 7-mo period of observation. The twins also engaged in more positive affiliation with age-mates other than the rearing partner, while the control infants more frequently engaged in solitary activities and displayed more aggressive and submissive behavior. It is concluded that the age-mate sibling had a beneficial effect upon early social development. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context dependency of conditioned aversions to water and sweet tastes.

Three experiments exposed rats (Rattus norvegicus) to a discriminative conditioning procedure whereby a specific fluid was followed by lithium in one environment but not in another. This produced context-specific aversion to water, as detected by 2-bottle tests in Experiment 1, and a context-dependent saccharin aversion, which was unaffected by context extinction, in Experiment 2. Experiment 3 found that sucrose preexposure increased contextual control over the aversion established by sucrose-lithium pairings but had no effect on the target context. By contrast, target context exposure during conditioning reduced aversion to this context but did not affect contextual control of the sucrose aversion. In conclusion, depending on the conditioning procedures, contextual control of a taste aversion can be independent of the context's Pavlovian properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother rats interact differently with male amd female offspring.

60 lactating Long-Evans rats were observed to interact differently with male and female pups during the 1st 18 days postpartum. Differences were related to the gender composition of the home litter (GHL), to the sex of a single introduced pup, and to the sex of individual pups within the litter. Major differences were the greater time spent in licking the anogenital region of own male pups and the greater stimulation of anogenital licking by male foster pups, an effect that did not interact with GHL or age of pup. GHL interacted with day of testing to affect nest building and time spent near pups. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postnatal maternal separation during the stress hyporesponsive period enhances the adrenocortical response to novelty in adult rats by affecting feedback regulation in the CA1 hippocampal field

The aim of the present experiment was to study the effects of early postnatal maternal separation on behavioural and adrenocortical responses to novelty in rats tested as adults. Sprague-Dawley rat pups were exposed to daily maternal separation (5 h/day) from postnatal day 2 to 6, during the stress hyporesponsive period. Since this procedure requires physical contact with the animals, a first control group of daily handled pups was introduced. A second control group, consisting of pups never handled or separated from the mother, was also considered. At postnatal day 45, the rats were tested in a two-compartment exploratory apparatus: the maternally separated and the non-handled rats, whose behavioural performance did not differ, showed higher emotional behaviour when compared with the handled rats (P < 0.05), suggesting that the handling procedure but not maternal separation improved the capacity to cope with novelty. Corticosterone plasma levels were found to be higher in the maternally separated rats than in the other two groups (P < 0.05), either at resting conditions or at 30 min after novelty exposure (P < 0.05). Levels of nuclear glucocorticoid receptor immunoreactivity in the CA1 hippocampal field were shown to be regulated by novelty exposure, as expected, in both the handled and the non-handled rats but not in the maternally separated rats. In conclusion, repeated maternal separation periods of 5 h/day during the first week of life produced long-lasting effects on the hippocampal regulation of the hypothalamic-pituitary-adrenocortical axis, which appear to be associated with increased responsiveness to stress stimuli in adulthood.     

Requirement for Brn-3b in early differentiation of postmitotic retinal ganglion cell precursors

Postnatal development of the spinal cord serotonergic (5-HT) system and of swimming movements were studied in newborn Sprague-Dawley rats, in which the serotonin level in the central nervous system was lowered in the prenatal period. For this purpose, para-chlorophenylalanine (PCPA) (300 mg/kg) was administered intraperitoneally to pregnant mother rats on day 8 of gestation, followed by a daily injection of PCPA (80 mg/kg) from day 9 of gestation to delivery. The postnatal development of the 5-HT system in the spinal cord of the pups (PCPA-treated pups) born from the PCPA-administered mothers was markedly delayed during the period between PND 1 and PND 10 in comparison to that in the control pups born from healthy mothers. Postnatally, the control pups developed their swimming movements regularly through three distinct phases: forelimb dominant, forelimb and hindlimb well coordinated, hindlimb dominant. In contrast, in the PCPA-treated pups, swimming movements were disorganized during the period in which the development of 5-HT system was delayed. However, between PND 17 and 22 in which the 5-HT system developed to that extent observed in the control pups, the pups eventually developed swimming movements as observed in the control pups. These results suggest that the disorganized developmental process of swimming movements in the PCPA-treated pups is due to the possible failure in the prenatal and postnatal development of the 5-HT system and its target system in the brain stem and the spinal cord.     

Maternal entrainment of the developing circadian system in the Siberian hamster (Phodopus sungorus)

The aim of these studies was to investigate maternal entrainment of developing circadian locomotor activity rhythms in the Siberian hamster. In Experiment 1, mothers were transferred from a 16:8 LD cycle into constant dim red light (DD) from the day of parturition, and wheel-running activity of the mother and pups was individually monitored from the time of weaning. The phases of the individual pups' rhythms were found to be synchronized both to the phase of the mother and to the phase of lights off (ZT 12) of the photo cycle that the mother was exposed to until the day of parturition. To investigate whether this synchrony might reflect direct effects of light acting upon the fetal circadian system in late gestation, the experiment was repeated but with mothers placed into DD early in pregnancy (< or = day 7 of gestation). The results were similar to the first study, suggesting that the mother rather than the photo cycle during the latter part of gestation entrains the developing circadian system. The third experiment investigated whether this entrainment occurred during the postnatal period. Breeding pairs were maintained on alternative light-dark cycles, LD and DL, that were 12 h out of phase. Litters born to mothers on one light-dark cycle were exchanged on the day of birth with foster mothers from the reversed light-dark cycle, then raised in DD. Control litters exchanged between mothers from the same light-dark cycle had similar litter synchrony as shown by nonfostered litters of Experiment 1. However, pups cross-fostered with mothers on reversed LD cycles showed a very different distribution of pup phases. Pups were not synchronized to their natural mother but to their foster mother. Moreover, pups were more scattered over the 24-h period and were found to be significantly synchronized to the phase of the reversed LD cycle. These results demonstrate the occurrence of postnatal entrainment in the Siberian hamster. The increased scatter produced by the cross-fostering paradigm results from some litters being completely entrained to the phase of the foster mother, some with an intermediate distribution between the phase of the natural and foster mothers, and a minority being associated with the phase of the natural mother. These results suggest that Siberian hamster pups are initially synchronized either prenatally or at birth but that the mother continues to provide entrainment signals during the postnatal period.     

A comparison between systolic aortic root pressure and finger blood pressure

Isolation of the rat pup from the nest and dam for one hour per day from PN 2-9 is a useful paradigm for producing stress in the neonate. These previously isolated rats respond to an amphetamine challenge with alterations in activity at the juvenile stage or as adults. Furthermore, when dopamine release is measured in the nucleus accumbens, juveniles release 3 times more dopamine after amphetamine than do controls. This study describes changes in behavior and brain dopamine systems at PN 10. Experiment 1 determined an appropriate amphetamine dose that could be used for behavioral activation at PN 10. Experiment 2 produced significant evidence of enhanced behavioral activation after the isolation paradigm and indicated that brain regions innervated by the mesolimbic dopamine system, septum, and hypothalamus display increased dopamine turnover and that the nigrostriatal pathway is less active. Likewise, in Experiment 3, in vivo microdialysis of the nucleus accumbens indicated that previously isolated pups respond to an amphetamine challenge with a several-fold increase in dopamine release over a 4-hour session.     

Selective retrieving by maternal and nonmaternal female rats.

Conducted an investigation to learn whether nonpregnant female rats made maternal by exposure to pups would act more like nonmaternal females than lactating mothers. Ss were 32 nulliparous females of the Charles River CD strain and an additional number of females that provided pups for inducing maternal behavior in virgins and in testing all Ss in pup vs toy tests. The behavior toward a pup and a toy was studied in 1 group of nonmaternal virgins, 2 groups of maternal virgins, and 1 group of lactating mothers, during 7 daily 5-min tests. Measures of the frequency and duration of retrieving-related behavior and analysis of behavioral sequences in relation to the pup or toy showed that pup-induced maternal virgins more closely resemble the lactating mothers than nonmaternal virgins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phosphatidylcholine synthesis and pulmonary oxygen toxicity

That organisms cannot remember events occurring during infancy may be the result of common forgetting processes exacerbated by the organism's increase in size during development or a unique process such as insufficient neurological development at the time of the early experience. To establish the uniqueness of infantile forgetting, size change was made irrelevant by exposing infant rats to "off-baseline" Pavlovian fear conditioning and assessing the effect of an apparatus-free conditioned stimulus upon independently established bar pressing. In Experiment 1, bar pressing by rats exposed to Pavlovian contingencies when 20-22 days old was substantially suppressed by the conditioned stimulus both 1 and 42 days after conditioning. In Experiment 2, pups conditioned when 17-19 and 20-22 days old again showed excellent retention, whereas pups conditioned when 11-13 and 14-16 days old showed total forgetting 42 days later. In Experiment 3, pups conditioned when 14-16 days old remembered well after 5 days, less well 10 days later, and not at all after 20 days. These findings suggest that size change may contribute to the forgetting of events occurring late in development, but that neurological immaturity may underly the forgetting of earlier events.     

Ontogeny of preference for nutritive over nonnutritive suckling in albino rats.

Investigated nutritive vs nonnutritive suckling in 48 10–21 day old Sprague-Dawley rat pups in a spatial discrimination task. Ss preferred nutritive to nonnutritive suckling on their anesthetized mother at l7 and 21 days of age, but no preference was apparent in 10- and 12-day-old Ss. Rearing in isolation from the mother during Days 11–26 did not impair the development of preference for nutritive suckling in 16 17-day-old Ss. Thus, the appetitive component of suckling of infant rats, like the consummatory component, appears to come under the direct control of nutritional factors at the start of the weaning period. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of cross-fostering on neonatal sodium balance and adult blood pressure in the spontaneously hypertensive rat

1. The aim of the present study was to compare electrolyte handling in naturally reared neonatal spontaneously hypertensive rats (SHR) with those reared by a Wistar-Kyoto (WKY) rat foster mother (denoted SHRX), as cross-fostering SHR pups to a WKY rat dam lowers adult blood pressure in the SHR. 2. The electrolyte content of WKY rat and SHR dams' milk was determined and electrolyte intake and urinary excretion rates were calculated in both naturally reared and cross-fostered WKY rat and SHR pups. 3. The milk sodium concentration fell in both strains (WKY rat: 31.8 +/- 2.0 to 15.2 +/- 1.2 mmol/L; SHR 31.9 +/- 2.5 to 18.2 +/- 1.6 mmol/L; P < 0.001), as did potassium (P < 0.001), over lactation, but there were no differences between strains. Calcium and magnesium concentrations increased (P < 0.001), although SHR dam's milk contained less calcium (P < 0.001) than that of WKY rat dams during the third week of lactation. 4. Spontaneously hypertensive rat pups ingested less milk (P < 0.05) than WKY rat pups; therefore, their cumulative sodium intake over postnatal days 4-15 was significantly lower than that of WKY rat pups (WKY rat vs SHR: 84.4 +/- 3.6 vs 59.7 +/- 2.6 mumol/g bodyweight, respectively; P < 0.05) and fostered SHRX pups (77.7 +/- 7.0 mumol/g bodyweight; P < 0.05). Potassium and magnesium intakes were comparable between SHR, WKY rat and SHRX pups, but SHR pups ingested significantly less calcium than either WKY rat pups (136.1 +/- 6.4 vs 200.1 +/- 9.5 mumol/g bodyweight, respectively; P < 0.05) or SHRX pups (200.0 +/- 18.0 mumol/g bodyweight; P < 0.05). 5. These data show that the neonatal SHR experiences a period of sodium deficiency during the developmental stage when cross-fostering is effective in lowering blood pressure. This is consistent with the reported up-regulation of the renin-angiotensin system observed in SHR at this time and may have a long-term influence on blood pressure.