Maternal care, infant fear memory retention, and the moderating role of variations in separation-induced ultrasonic vocalizations

Communal nesting shapes the sex-dependent glutamatergic response to early life stress in the rat prefrontal cortex

Introduction

Early social environment, either positive or negative, shapes the adult brain. Communal nesting (CN), a naturalistic setting in which 2-3 females keep their pups in a single nest sharing care-giving behavior, provides high level of peer interaction for pups. Early social isolation (ESI) from dam and siblings represents, instead, an adverse condition providing no peer interaction.

Methods

We investigated whether CN (enrichment setting) might influence the response to ESI (impoverishment setting) in terms of social behavior and glutamate system in the medial prefrontal cortex (mPFC) of adult and adolescent male and female rats.

Results

Pinning (a rewarding component of social play behavior) was significantly more pronounced in males than in females exposed to the combination of CN and ESI. CN sensitized the glutamate synapse in the mPFC of ESI-exposed male, but not female, rats. Accordingly, we observed (i) a potentiation of the glutamatergic neurotransmission in the mPFC of both adolescent and adult males, as shown by the recruitment of NMDA receptor subunits together with increased expression/activation of PSD95, SynCAM 1, Synapsin I and αCaMKII; (ii) a de-recruiting of NMDA receptors from active synaptic zones of same-age females, together with reduced expression/activation of the above-mentioned proteins, which might reduce the glutamate transmission. Whether similar sex-dependent glutamate homeostasis modulation occurs in other brain areas remains to be elucidated.

Discussion

CN and ESI interact to shape social behavior and mPFC glutamate synapse homeostasis in an age- and sex-dependent fashion, suggesting that early-life social environment may play a crucial role in regulating the risk to develop psychopathology.

Minimizing Variability in Developmental Fear Studies in Mice: Toward Improved Replicability in the Field

In rodents, the first weeks of postnatal life feature remarkable changes in fear memory acquisition, retention, extinction, and discrimination. Early development is also marked by profound changes in brain circuits underlying fear memory processing, with heightened sensitivity to environmental influences and stress, providing a powerful model to study the intersection between brain structure, function, and the impacts of stress. Nevertheless, difficulties related to breeding and housing young rodents, preweaning manipulations, and potential increased variability within that population pose considerable challenges to developmental fear research. Here we discuss several factors that may promote variability in studies examining fear conditioning in young rodents and provide recommendations to increase replicability. We focus primarily on experimental conditions, design, and analysis of rodent fear data, with an emphasis on mouse studies. The convergence of anatomical, synaptic, physiological, and behavioral changes during early life may increase variability, but careful practice and transparency in reporting may improve rigor and consensus in the field. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC.

Inheritance of wild and truncated DAT alleles from grand-parents: Opposite transgenerational consequences on the behavioral phenotype in adolescent DAT heterozygous rats

Dopamine plays important roles in implicit memory and motivation of behavior. Environmental inputs can produce transgenerational epigenetic changes. This concept also includes the uterus: experimentally, we sought to create hyper-dopaminergic uterine conditions through ineffective dopamine-transporter (DAT) protein, obtained by inserting a stop-codon into the SLC6A3 gene. By crossing WT-dam with KO-sire (or vice-versa), we obtained a 100% DAT-heterozygous (HET) offspring with known derivation of the wild allele: MAT rats are offspring of WT-female and KO-male; PAT rats are offspring of KO-female and WT-male. We reconstructed inheritance of alleles, by crossing PAT-male with MAT-female or vice-versa, obtaining GIX (PAT-male with MAT-female) and DIX (MAT-male with PAT-female) rats (such offspring present specular paths in allele inheritance from grandparents). We conducted three experiments: first, we assessed maternal behaviour (four epigenotypes: WT, MAT, PAT and WHZ=HET-pups fostered-to-a WT-dam); in the second, we analysed sleep-wake cycles of GIX and DIX epigenotypes with their WIT siblings as controls; in the third, we explored the impact of WT or MAT mother on WT or HET pups. MAT-dams (with GIX-pups) express excessive licking/grooming. However, in the mere presence of "sick" epigenotype, PAT-dams (with DIX-pups) and also WHZ (i.e., WT-dams but with HET-pups) expressed greater nest-building care towards the offspring, compared to "true-wild" litters (WT-dams with WT-pups). In Exp. 2 at adolescence, GIX epigenotype showed locomotor hyperactivity during late waking-phase, while DIX epigenotype exhibited pronounced hypoactivity compared to controls. In Exp. 3, we confirmed that HET adolescent pups receiving cares from a MAT-dam may develop additional hyperactivity when awake, but additional hypoactivity during rest-hours. Thus, behavioral changes observed in DAT-heterozygous offspring have opposite courses based on of DAT-allele inheritance from a grandparent through the sire or the dam. In conclusion, behavioural changes in the offspring have antithetic courses with respect to inheritance of DAT-allele via sperm or egg.

Infant ultrasonic vocalizations predict adolescent social behavior in rats: Effects of early life adversity

Early life adversity (ELA) increases risk for psychopathologies that often manifest during adolescence and involve disrupted social functioning. ELA affects development of the prefrontal cortex (PFC), which plays a role in social behavior. PFC oxytocin and vasopressin are important regulators of, first, mother-infant attachment, and, later, social behavior, and are implicated in psychiatric disorders. Here, we tested whether infant social communication is predictive of PFC development and adolescent social behavior. We used the limited bedding (LB) ELA model in rats during postnatal days (P)2-14, and measured isolation-induced ultrasonic vocalizations (USVs) at P10 to characterize differences in an early social response. Rats were tested for dyadic social interaction in adolescence (P34). Adolescent oxytocin receptor (Oxtr) and arginine-vasopressin receptor 1a mRNA were measured in the PFC. Relationships between infant USVs, adolescent behavior, and gene expression were assessed. LB-reared rats exhibited fewer USVs at P10. While social behaviors were not robustly affected by rearing, fewer total and complex-type infant USVs predicted fewer interactions in adolescence. LB increased Oxtr in both sexes but Oxtr was not directly predicted by USVs. Findings support the use of USVs as indicators of differential early life experience in rodents, toward further characterization of early factors associated with vulnerability.

Adults who are more anxious and were anxiously attached as children report later first memories

Here, we examined retrospective reports of adults' earliest autobiographical memory, the age of this report and whether the reported age was associated with exposure to early life adversity, current anxiety and childhood attachment. Across four studies, we found that reporting a later 'earliest' memory was associated with higher self-reported anxiety in both American (Studies 1, 2 and 4) and Australian (Study 3) samples. Furthermore, in Studies 2-4, we found that reporting a later earliest memory uniquely predicted anxiety when controlling for number of adverse childhood events (a risk factor for the development of anxiety). In Study 4, we established that this relation is partially mediated by childhood anxious attachment. Although we consistently demonstrated that later earliest memories were associated with current anxiety, we found little evidence for a relation between reported age at the time of earliest memory and childhood adversity. We also found no evidence of gender differences in the associations of interest. These results suggest that poorer memory of early childhood is associated with greater childhood anxious attachment and anxiety in adulthood. The implications of this work are discussed in terms of the adaptive nature of autobiographical memory and the development of a coherent life narrative.