Neonatal handling enhances contextual fear conditioning and alters corticosterone stress responses in young rats

Previous studies have indicated that neonatal handling influences development of hypothalamic-pituitary-adrenal (HPA) control of corticosterone. In addition, corticosterone influences memory consolidation processes in contextual fear conditioning. Therefore, neonatal handling may affect hippocampal-dependent memory processes present in contextual fear conditioning by influencing the development of HPA control of corticosterone. To investigate the effects of neonatal handling on early learning, rat pups were either handled (15-min removal from home cage) on the first 15 days after birth or left undisturbed in their home cage. Handled rats and nonhandled rats were fear conditioned at 18, 21, or 30 days of age and then tested at two time points--24 h following conditioning and at postnatal day 45. Subsequently, at approximately postnatal day 60, rats were exposed to restraint stress and corticosterone levels were assessed during restraint and recovery. Handled and nonhandled rats did not differ significantly in their freezing response immediately following footshock on the conditioning day. However, when tested for contextual fear conditioning at 24 h following conditioning and at postnatal day 45, handled rats showed more freezing behavior than nonhandled rats. When exposed to restraint stress, handled rats had a more rapid return of corticosterone to basal levels than nonhandled rats. These results indicate that neonatal handling enhances developmentally early memory processes involved in contextual fear conditioning and confirms previously reported effects of neonatal handling on HPA control of corticosterone.     

Adaptive significance of male parental care in a monogamous mammal

Paternal behaviour presumably evolved because male care of young was critical for offspring survival. We report field evidence indicating that paternal behaviour enhances offspring survival in a monogamous mammal, the biparental California mouse, Peromyscus californicus. Male removal resulted in lower offspring survival in father-absent than in father-present families. New males took up residence with widowed females, but usually after females had stopped lactating, suggesting that the importance of the father is not primarily protection against infanticidal intruders but rather direct care of young.     

Evolutionary pathway of child development

An evolutionary theory of socialization suggests that children from father-absent families will mature earlier, and form less-stable pair bonds, compared with those from father-present families. Using a sample of about 1,000 persons the recent study focuses on elements of father-absent children’s behavior that could be better explained by a Darwinian approach than by rival social science theories. As a result of their enhanced interest in male competition, father-absent boys were found to engage in rule-breaking behavior more intensively than father-present boys. Compared with father-present children, adolescents from widowed households (both boys and girls) showed a higher intensity of various kinds of noncompliant behavior, which can be linked to their earlier maturation. School attendance, age at marriage, and marital success proved to be influenced by the children’s early family experiences, governed by adapted evolutionary strategies. Father-absent daughters conceived more children than those whose fathers were present during their childhood. As evolutionary theory predicts, reproductive behavior of individuals from divorced households differed from that of individuals who grew up in widowed households. Finally, the strong correlation found between spontaneous abortion/stillbirths and family arrangement indicates that father absence has certain direct impacts on the neurohormonal processes of child development.     

Neonatal handling increases sensitivity to acute neurodegeneration in adult rats

Environmental stimuli during the perinatal period can result in persistent individual differences in neural viability and cognitive functions. Earlier studies have shown that brief daily maternal separation and/or handling of rat pups during the first weeks of life reduces stress reactivity during adulthood and attenuates neuronal loss and cognitive decline during aging. In the present study we examined whether neonatal handling also affects the sensitivity of the adult brain to an acute neurotoxic insult. Postnatally handled and nonhandled control rats were left undisturbed from weaning onwards until the age of 11 months. At this age, the animals were subjected to a neurotoxic challenge by unilateral infusion of 60 mM of the glutamate analogue N-methyl-D-aspartate (NMDA) into the nucleus basalis magnocellularis (NBM). The brains were collected to measure cholinergic cell and fiber loss. In the nonlesioned side of the brain, cholinergic cell number in the NBM and fiber density in the cortex were not different between postnatally handled and control rats. However, in the lesioned hemisphere handled animals exhibited a significantly higher loss of choline-acetyltransferase-immunoreactive and acetylcholinesterase-positive fibers in the somatosensory cortex. The present results provide evidence for an enhanced vulnerability of postnatally handled rats to acute neurodegeneration in contrast to the previously reported attenuation of spontaneous aging-related neurodegenerative processes.     

Neonatal Handling Impairs Spatial Memory and Leads to Altered Nitric Oxide Production and DNA Breaks in A Sex Specific Manner

Early life events lead to behavioral and neurochemical changes in adulthood. The aim of this study is to verify the effects of neonatal handling on spatial memory, nitric oxide (NO) production, antioxidant enzymatic activities and DNA breaks in the hippocampus of male and female adult rats. Litters of rats were non-handled or handled (10 min/day, days 1–10 after birth). In adulthood they were subjected to a Morris water maze or used for biochemical evaluations. Female handled rats showed impairment in spatial learning. They also showed decreased NO production, while no effects were observed in these parameters in male rats. No effects were observed on the number of hippocampal NADPH diaphorase positive cells. In the Comet Assay, male handled rats showed increased DNA breaks index when compared to non-handled ones. We conclude that neonatal handling impairs learning performance in a sex-specific manner, what may be related to NO decreased levels.     

Interactions of partners in family pairs,care of the offspring,and the role of tactile stimulation in formation of parental behavior of the Mongolian gerbil (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>) under laboratory conditions

The interactions of sexual partners and care of the offspring in male and female Mongolian gerbils reared in biparental and uniparental family groups (without an adult male) were compared. In individuals reared in biparental family groups, sexual differences related to the manifestation of parental care were small and statistically insignificant. In individuals reared in uniparental groups, the interactions of sexual partners related to grooming changed; the duration in males decreased threefold, as compared to the norm; indices of parental behavior of females and, especially of males, related to tactile stimulation of pups (huddling with pups in the nest and duration of licking pups) also decreased. The importance of the parental contribution of males, especially of tactile stimulation, in the evolution of the family-group mode of life is discussed.     

An olfactory basis for maternal discrimination of sex of offspring in rats (rattus norvegicus)

Lactating Long-Evans rats (Rattus norvegicus) were presented with three-day-old male and female pups that were either untreated, coated with collodion in the anogenital region or on the neck, or perfumed; or with female pups odorized with either male or female pup urine. As measured by related t-tests of maternal anogenital licking, male and female pups were discriminated in the untreated condition, but not when masking stimuli were present. Female pups treated with male urine elicited more licking than female pups treated with female urine. Overall, maternal licking was decreased by olfactory masking agents and increased by pup urine. It was concluded that olfactory stimuli from pups both stimulate maternal licking and serve as a basis for discriminating male and female offspring.     

Neonatal handling of Amazon parrots alters the stress response and immune function

The influence of neonatal handling on behavior and immune function was assessed in Orange-winged Amazon parrots (Amazona amazonica). Chicks (n=11) were gently handled daily from 25 days of age until 38 days post-fledging, while control chicks (n=9) were not handled. At 10 days post-fledging ( approximately 66 days of age), chicks were given tests to evaluate tameness (e.g., willingness to perch on an offered finger). They were then restrained for 10 min, either by being held while perching (handled group) or, because they would not perch, by being restrained in a towel (nonhandled group). Serum corticosterone levels were measured and immune status was assessed by: the delayed-type hypersensitivity (DTH) response to phytohemagglutinin-P (PH-P) injection; the humoral response to a killed Newcastle disease virus (NDV) challenge; and heterophil:lymphocyte ratio (H:L). Handled chicks were tamer by all measures of tameness. DTH was greater in nonhandled chicks (P相似文献   

Do sires and juvenile male mice (C57BL/6) contribute to the rearing of the offspring?

Copulation and/or cohabitation with a pregnant female facilitate paternal behavior in male mice. However, their contribution to the rearing of the offspring is still not well understood. Our aims were to investigate the behavior of sires toward own or alien pups; the immediate consequences of the presence of fathers on the offspring and the behavior of the mother; and whether the exposure of juvenile males to newborn siblings, in an overlapping litters context, facilitates paternal behavior in C57BL/6 mice. We found that sires behaved paternally toward alien pups at both postpartum days 3 and 7; did not affect the behavior of the mother (e.g., licking and grooming, retrieval behavior, time in the nest, and crouching postures); and reduced the time offspring stayed alone in the nest. The exposure to newborn siblings did not promote paternal behavior in juvenile males. Therefore, sires are more paternal than usually described in the literature for laboratory mice, suggesting a facultative role in the rearing of the offspring. However, juvenile male mice, in contrast to juvenile females, could be adapted to leave the nest earlier without major contribution to the offspring.     

Low maternal licking/grooming stimulation increases pain sensitivity in male mouse offspring

Deprivation of maternal care has been associated with higher pain sensitivity in offspring. In the present study, we hypothesized that the maternal licking/grooming behavior was an important factor for the development of the pain regulatory system. To test this hypothesis, we used male F2 offspring of early-weaned (EW) F1 mother mice that exhibit lower frequency of licking/grooming behavior. The formalin test revealed that F2 offspring of EW F1 dams showed significantly higher pain behavior than F2 offspring of normally-weaned (NW) F1 dams. We found that the mRNA levels of transient receptor potential vanilloid 1 (TRPV1), a nociceptor, were higher in the lumbosacral dorsal root ganglion (DRG) of F2 offspring of EW F1 dams than those of F2 offspring of NW F1 dams, suggesting that the higher pain sensitivity may be attributed to low licking/grooming, which may result in developmental changes in nociceptive neurons. In the DRG, mRNA levels of Mas-related G-protein coupled receptor B4 (MrgprB4), a marker of sensory neurons that detect gentle stroking, was also up-regulated in the F2 offspring of EW F1 dams. Considering that gentle touch alleviates pain, Mrgprb4 up-regulation may reflect a compensatory change. The present findings indicate important implications of maternal licking/grooming behavior in the development of the pain regulatory system.     

Neonatal handling induces alteration in progesterone secretion after sexual behavior but not in angiotensin II receptor density in the medial amygdala: implications for reproductive success

Neonatal handling affects the hypothalamus-pituitary-gonadal axis in female rats. Indeed, postnatal handling induces anovulatory estrous cycles and decreases sexual receptiveness. On the other hand, Angiotensin II (Ang II) infused into the medial amygdala (MeA) reduces sexual behavior in male and female rats. Considering this, and that gonadal steroid secretion after copulatory behavior is important for reproductive success, the purpose of the present study was to investigate whether the reduction in sexual receptiveness in neonatally handled female rats is mediated by changes in Ang II receptor density in MeA. Moreover, gonadal steroid secretion after sexual behavior was analyzed. Two groups of female Wistar rats were studied: nonhandled (pups were left undisturbed) and handled (pups were handled for 1 min once a day during the first 10 days of life). Once they were 80-85 days old in the evening of the proestrus day, sexual receptiveness was recorded and after that the animals were killed by decapitation. Trunk blood samples were collected, and plasma estradiol and progesterone were measured by radioimmunoassay. The brains were removed for Ang II receptor autoradiography in MeA. The decreased lordosis quotient in the neonatally handled group was confirmed in the present study. Neonatal handling also reduced the progesterone concentration in the plasma, but did not change the estradiol and the density of Ang II receptors in MeA. The reduced progesterone could be due to the decreased lordosis frequency of handled females. However, this decreased sexual receptiveness is not mediated by changes in Ang II receptors in MeA.     

Effects of neonatal handling on sympathoadrenal activity and body composition in adult male rats

Neonatal handling permanently alters the hypothalamic-pituitary-adrenal (HPA) response to stress. Because the sympathetic nervous system (SNS) and adrenal medulla also participate in stress responses, the impact of daily handling between birth and weaning on SNS and adrenal medullary function was examined in adult rats using techniques of [(3)H]norepinephrine ([(3)H]NE) turnover and urinary catecholamine excretion. Handled animals exhibited a 23% reduction in [(3)H]NE turnover in heart and a 53% decrease in spleen. [(3)H]NE turnover in brown adipose tissue, stomach, and kidney did not differ between handled and nonhandled animals. In contrast, urinary epinephrine (Epi) excretion was significantly greater in handled rats in response to a 3-day fast than in nonhandled animals. Although body weight, weight gain in response to dietary enrichment with sucrose or lard, or body fat content did not differ in handled and nonhandled animals, handled rats displayed heavier abdominal fat depots than nonhandled animals, implying a difference in body fat distribution. Neonatal handling thus leads to decreased sympathetic activity within specific subdivisions of the SNS and, by contrast, to increased adrenal medullary responsiveness.     

Individual variations in maternal care early in life correlate with later life decision-making and c-fos expression in prefrontal subregions of rats

Early life adversity affects hypothalamus-pituitary-adrenal axis activity, alters cognitive functioning and in humans is thought to increase the vulnerability to psychopathology--e.g. depression, anxiety and schizophrenia--later in life. Here we investigated whether subtle natural variations among individual rat pups in the amount of maternal care received, i.e. differences in the amount of licking and grooming (LG), correlate with anxiety and prefrontal cortex-dependent behavior in young adulthood. Therefore, we examined the correlation between LG received during the first postnatal week and later behavior in the elevated plus maze and in decision-making processes using a rodent version of the Iowa Gambling Task (rIGT). In our cohort of male and female animals a high degree of LG correlated with less anxiety in the elevated plus maze and more advantageous choices during the last 10 trials of the rIGT. In tissue collected 2 hrs after completion of the task, the correlation between LG and c-fos expression (a marker of neuronal activity) was established in structures important for IGT performance. Negative correlations existed between rIGT performance and c-fos expression in the lateral orbitofrontal cortex, prelimbic cortex, infralimbic cortex and insular cortex. The insular cortex correlations between c-fos expression and decision-making performance depended on LG background; this was also true for the lateral orbitofrontal cortex in female rats. Dendritic complexity of insular or infralimbic pyramidal neurons did not or weakly correlate with LG background. We conclude that natural variations in maternal care received by pups may significantly contribute to later-life decision-making and activity of underlying brain structures.     

Prenatal choline supplementation attenuates spatial learning deficits of offspring rats exposed to low-protein diet during fetal period

Prenatal intake of choline has been reported to lead to enhanced cognitive function in offspring, but little is known about the effects on spatial learning deficits. The present study examined the effects of prenatal choline supplementation on developmental low-protein exposure and its potential mechanisms. Pregnant female rats were fed either a normal or low-protein diet containing sufficient choline (1.1 g/kg choline chloride) or supplemented choline (5.0 g/kg choline chloride) until delivery. The Barnes maze test was performed at postnatal days 31–37. Choline and its metabolites, the synaptic structural parameters of the CA1 region in the brain of the newborn rat, were measured. The Barnes maze test demonstrated that prenatal low-protein pups had significantly greater error scale values, hole deviation scores, strategy scores and spatial search strategy and had lesser random search strategy values than normal protein pups (all P<.05). These alterations were significantly reversed by choline supplementation. Choline supplementation increased the brain levels of choline, betaine, phosphatidylethanolamine and phosphatidylcholine of newborns by 51.35% (P<.05), 33.33% (P<.001), 28.68% (P<.01) and 23.58% (P<.05), respectively, compared with the LPD group. Prenatal choline supplementation reversed the increased width of the synaptic cleft (P<.05) and decreased the curvature of the synaptic interface (P<.05) induced by a low-protein diet. Prenatal choline supplementation could attenuate the spatial learning deficits caused by prenatal protein malnutrition by increasing brain choline, betaine and phospholipids and by influencing the hippocampus structure.     

Maternal Exercise during Pregnancy Increases BDNF Levels and Cell Numbers in the Hippocampal Formation but Not in the Cerebral Cortex of Adult Rat Offspring

Clinical evidence has shown that physical exercise during pregnancy may alter brain development and improve cognitive function of offspring. However, the mechanisms through which maternal exercise might promote such effects are not well understood. The present study examined levels of brain-derived neurotrophic factor (BDNF) and absolute cell numbers in the hippocampal formation and cerebral cortex of rat pups born from mothers exercised during pregnancy. Additionally, we evaluated the cognitive abilities of adult offspring in different behavioral paradigms (exploratory activity and habituation in open field tests, spatial memory in a water maze test, and aversive memory in a step-down inhibitory avoidance task). Results showed that maternal exercise during pregnancy increased BDNF levels and absolute numbers of neuronal and non-neuronal cells in the hippocampal formation of offspring. No differences in BDNF levels or cell numbers were detected in the cerebral cortex. It was also observed that offspring from exercised mothers exhibited better cognitive performance in nonassociative (habituation) and associative (spatial learning) mnemonic tasks than did offspring from sedentary mothers. Our findings indicate that maternal exercise during pregnancy enhances offspring cognitive function (habituation behavior and spatial learning) and increases BDNF levels and cell numbers in the hippocampal formation of offspring.     

Disruption of Parenting Behaviors in California Mice,a Monogamous Rodent Species,by Endocrine Disrupting Chemicals

The nature and extent of care received by an infant can affect social, emotional and cognitive development, features that endure into adulthood. Here we employed the monogamous, California mouse (Peromyscus californicus), a species, like the human, where both parents invest in offspring care, to determine whether early exposure to endocrine disrupting chemicals (EDC: bisphenol A, BPA; ethinyl estradiol, EE) of one or both parents altered their behaviors towards their pups. Females exposed to either compound spent less time nursing, grooming and being associated with their pups than controls, although there was little consequence on their weight gain. Care of pups by males was less affected by exposure to BPA and EE, but control, non-exposed females appeared able to “sense” a male partner previously exposed to either compound and, as a consequence, reduced their own parental investment in offspring from such pairings. The data emphasize the potential vulnerability of pups born to parents that had been exposed during their own early development to EDC, and that effects on the male, although subtle, also have consequences on overall parental care due to lack of full acceptance of the male by the female partner.     

An n-3 fatty acid deficient diet affects mouse spatial learning in the Barnes circular maze

Deficiency in n-3 fatty acids has been accomplished through the use of an artificial rearing method in which ICR mouse pups were hand fed a deficient diet starting from the 2nd day of life. There was a 51% loss of total brain DHA in mice with an n-3 fatty acid-deficient diet relative to those with a diet sufficient in n-3 fatty acids. n-3 fatty acid adequate and deficient mice did not differ in terms of locomotor activity in the open field test or in anxiety-related behavior in the elevated plus maze. The n-3 fatty acid-deficient mice demonstrated impaired learning in the reference-memory version of the Barnes circular maze as they spent more time and made more errors in search of an escape tunnel. No difference in performance between all dietary groups in the cued and working memory version of the Barnes maze was observed. This indicated that motivational, motor and sensory factors did not contribute to the reference memory impairment.     

Associations among within-litter differences in early mothering received and later emotional behaviors,mothering, and cortical tryptophan hydroxylase-2 expression in female laboratory rats

This article is part of a Special Issue “Parental Care”. The effects of differential maternal care received on offspring phenotype in rodents has been extensively studied between litters, but the consequences of differential mothering within litters on offspring neurobehavioral development have been rarely examined. We here investigated how variability in maternal care received among female rat siblings (measured four times daily on postnatal days 4, 6, 8, and 10) relates to the siblings' later emotional and maternal behaviors. As previously reported, we found that some female pups received up to three times more maternal licking bouts compared to their sisters; this difference was positively correlated with the pups' body weights. The number of maternal licking bouts that females received was negatively correlated with their later neophobic behaviors in an open field during periadolescence, but positively correlated with their anxiety-related behavior in an elevated plus maze during adulthood. Licking received was also positively correlated with females' later likelihood to retrieve pups in a maternal sensitization paradigm. In addition, females' neophobia during adolescence and anxiety-related behavior during adulthood predicted some aspects of both postpartum and sensitized maternal responsiveness. Medial prefrontal cortex expression of tryptophan hydroxylase-2 (TPH2; enzyme necessary for serotonin synthesis) was negatively associated with early maternal licking received. Interestingly, cortical TPH2 was positively associated with the maternal responsiveness of sensitized virgins but negatively associated with it in postpartum females. These results indicate that within-litter differences in maternal care received is an often neglected, but important, contributor to individual differences in offspring socioemotional behaviors as well as to the cortical serotonin neurochemistry that may influence these behaviors.     

Reducing Mouse Anxiety during Handling: Effect of Experience with Handling Tunnels

Handling stress is a well-recognised source of variation in animal studies that can also compromise the welfare of research animals. To reduce background variation and maximise welfare, methods that minimise handling stress should be developed and used wherever possible. Recent evidence has shown that handling mice by a familiar tunnel that is present in their home cage can minimise anxiety compared with standard tail handling. As yet, it is unclear whether a tunnel is required in each home cage to improve response to handling. We investigated the influence of prior experience with home tunnels among two common strains of laboratory mice: ICR(CD-1) and C57BL/6. We compared willingness to approach the handler and anxiety in an elevated plus maze test among mice picked up by the tail, by a home cage tunnel or by an external tunnel shared between cages. Willingness to interact with the handler was much greater for mice handled by a tunnel, even when this was unfamiliar, compared to mice picked up by the tail. Once habituated to handling, C57BL/6 mice were most interactive towards a familiar home tunnel, whereas the ICR strain showed strong interaction with all tunnel handling regardless of any experience of a home cage tunnel. Mice handled by a home cage or external tunnel showed less anxiety in an elevated plus maze than those picked up by the tail. This study shows that using a tunnel for routine handling reduces anxiety among mice compared to tail handling regardless of prior familiarity with tunnels. However, as home cage tunnels can further improve response to handling in some mice, we recommend that mice are handled with a tunnel provided in their home cage where possible as a simple practical method to minimise handling stress.     

Spatial learning and memory in male mice with altered growth hormone action

Growth hormone (GH) has a significant influence on cognitive performance in humans and other mammals. To understand the influence of altered GH action on cognition, we assessed spatial learning and memory using a Barnes maze (BM) comparing twelve-month old, male, bovine GH (bGH) and GH receptor antagonist (GHA) transgenic mice and their corresponding wild type (WT) littermates. During the acquisition training period in the BM, bGH mice showed increased latency, traveled longer path lengths and made more errors to reach the target than WT mice, indicating significantly poorer learning. Short-term memory (STM) and long-term memory (LTM) trials showed significantly suppressed memory retention in bGH mice when compared to the WT group. Conversely, GHA mice showed significantly better learning parameters (latency, path length and errors) and increased use of an efficient search strategy than WT mice. Our study indicates a negative impact of GH excess and a beneficial effect of the inhibition of GH action on spatial learning and memory and, therefore, cognitive performance in male mice. Further research to elucidate GH's role in brain function will facilitate identifying therapeutic applications of GH or GHA for neuropathological and neurodegenerative conditions.