Children reared in a reverse isolation environment: effects on cognitive and emotional development

Neonatal paternal deprivation impairs social recognition and alters levels of oxytocin and estrogen receptor α mRNA expression in the MeA and NAcc, and serum oxytocin in mandarin voles

Paternal care is necessary for the healthy development of social behavior in monogamous rodents and social recognition underpins social behavior in these animals. The effects of paternal care on the development of social recognition and underlying neuroendocrine mechanisms, especially the involvement of oxytocin and estrogen pathways, remain poorly understood. We investigated the effects of paternal deprivation (PD: father was removed from neonatal pups and mother alone raised the offspring) on social recognition in mandarin voles (Microtus mandarinus), a socially monogamous rodent. Paternal deprivation was found to inhibit the development of social recognition in female and male offspring according to a habituation-dishabituation paradigm. Paternal deprivation resulted in increased inactivity and reduced investigation during new encounters with other animals. Paternal deprivation reduced oxytocin receptor (OTR) and estrogen receptor α (ERα) mRNA expression in the medial amygdala and nucleus accumbens. Paternal deprivation reduced serum oxytocin (OT) concentration in females, but had no effect on males. Our results provide substantial evidence that paternal deprivation inhibits the development of social recognition in female and male mandarin voles and alters social behavior later in life. This is possibly the result of altered expression of central OTR and ERα and serum OT levels caused by paternal deprivation.

Maternal care influences hippocampal N-methyl-D-aspartate receptor function and dynamic regulation by corticosterone in adulthood

BACKGROUND

Variations in maternal care in the rat associate with robust differences in hippocampal development and synaptic plasticity in the offspring. Maternal care also influences pituitary-adrenal stress responses and corticosterone (CORT) regulation of hippocampal plasticity. N-methyl-D-aspartate receptors (NMDAR) regulate synaptic plasticity, and NMDAR function is modulated by stress and CORT. We hypothesized that altered NMDAR function underlies the interaction of maternal and stress effects on hippocampal synaptic plasticity.

METHODS

We used electrophysiology and western blot to examine NMDAR synaptic function/expression and NMDAR-dependent long-term potentiation (LTP) in adult offspring of mothers that varied in the frequency of pup licking/grooming (LG) (i.e., High or Low LG).

RESULTS

Basal NMDAR synaptic function was enhanced in the hippocampal dentate gyrus (DG) of adult Low LG offspring. Synaptic expression of NMDAR but not α-amino-3-hydroxy-methyl-4-isoxazole propionic acid receptors was also increased. Stress level CORT (100 nmol/L) rapidly (< 20 min) and robustly increased NMDAR function in High LG offspring, eliminating the maternal effect. Corticosterone did not affect NMDAR function in Low LG offspring. Bovine serum albumin-conjugated CORT reproduced the CORT effect in High LG offspring, implicating a membrane-bound corticosteroid receptor. NMDAR hyperfunction might impair synaptic plasticity. Partial NMDAR antagonism by low concentration DL-2-Amino-5-phosphonopentanoic acid rescued a basal LTP deficit in Low LG offspring and inhibited LTP in High LG offspring.

CONCLUSIONS

Low LG offspring exhibit basally elevated NMDAR function coupled with insensitivity to CORT modulation indicative of a chronic alteration of NMDAR function. Elevated NMDAR function in the hippocampus might underlie impaired LTP in Low LG offspring.

Effect of neonatal handling and paternal care on offspring cognitive development in the monogamous California mouse (Peromyscus californicus)

In the laboratory rat and mouse, neonatal handling enhances hippocampal-dependent learning in adulthood, an effect mediated by changes in maternal behavior toward the handled young. In the present study, we examined the interaction between neonatal handling and biparental care during the early postnatal period and its effect on cognitive function in adult California mice (Peromyscus californicus). We characterized the parental behavior of handled and nonhandled father-present and father-absent families over the first 15 days of life. We then assessed cognitive performance of male and female offspring in the Barnes maze and object recognition test after they were 60 days of age. We found that the amount of licking and grooming received by pups was decreased in father-absent families. By postnatal days 12-15, licking and grooming in handled, father-absent families were equivalent to that of nonhandled, father-present families. Handling enhanced novel object recognition in father-present male mice with no effect in females. In the nonhandled group, the presence of the father had no effect on object recognition learning in male or female mice. Handling also enhanced spatial learning in the Barnes maze. In nonhandled families, the presence of the father appeared to have no effect on spatial learning in the male offspring. Interestingly, spatial learning in nonhandled, father-absent, female offspring was similar to that of handled animals. The average amount of licking and grooming received by pups was negatively correlated with the average number of errors made on the first day of reversal training in the Barnes maze. These data support previous findings that neonatal handling facilitates learning and memory in adulthood, suggest that under certain environmental conditions, there is a sex difference in the response of pups to paternal care, and further demonstrate the importance of active parental investment for offspring cognitive development.

Partial reversal of the effect of maternal care on cognitive function through environmental enrichment

Maternal care influences hippocampal development in the rat. The offspring of mothers that exhibit increased levels of pup licking/grooming and arched-back nursing (High LG-ABN mothers) show increased hippocampal N-methyl-D-aspartate (NMDA) receptor binding and enhanced hippocampal-dependent spatial learning. In these studies we examined whether environmental enrichment from days 22-70 of life might reverse the effects of low maternal care. Environmental enrichment eliminated the differences between the offspring of High and Low LG-ABN mothers in both Morris water maze learning and object recognition. However, enrichment did not reverse the effect of maternal care on long-term potentiation in the dentate gyrus or on hippocampal NMDA receptor binding. In contrast, peripubertal enrichment did reverse the effects of maternal care on hippocampal alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor binding. These findings provide evidence for the reversal of the effects of reduced maternal investment in early life on cognitive function in adulthood. Such effects might involve compensatory changes associated with peripubertal enrichment.