Dissociation in the effects of stress and D1 receptors activation on basolateral amygdalar LTP in juvenile and adult animals

Differential role of NMDA receptors in hippocampal-dependent spatial memory and plasticity in juvenile male and female rats

Early life, or juvenility, stands out as the most pivotal phase in neurodevelopment due to its profound impact over the long-term cognition. During this period, significant changes are made in the brain's connections both within and between different areas, particularly in tandem with the development of more intricate behaviors. The hippocampus is among the brain regions that undergo significant postnatal remodeling, including dendritic arborization, synaptogenesis, the formation of complex spines and neuron proliferation. Given the crucial role of the hippocampus in spatial memory processing, it has been observed that spatial memory abilities continue to develop as the hippocampus matures, particularly before puberty. The N-methyl-d-aspartate (NMDA) type of glutamate receptor channel is crucial for the induction of activity-dependent synaptic plasticity and spatial memory formation in both rodents and humans. Although extensive evidence shows the role of NMDA receptors (NMDAr) in spatial memory and synaptic plasticity, the studies addressing the role of NMDAr in spatial memory of juveniles are sparse and mostly limited to adult males. In the present study, we, therefore, aimed to investigate the effects of systemic NMDAr blockade by the MK-801 on spatial memory (novel object location memory, OLM) and hippocampal plasticity in the form of long-term potentiation (LTP) of both male and female juvenile rats. Our results show the sex-dimorphic role of NMDAr in spatial memory and plasticity during juvenility, as systemic NMDAr blockade impairs the OLM and LTP in juvenile males without an effect on juvenile females. Taken together, our results demonstrate that spatial memory and hippocampal plasticity are NMDAr-dependent in juvenile males and NMDAr-independent in juvenile females. These sex-specific differences in the mechanisms of spatial memory and plasticity may imply gender-specific treatment for spatial memory disorders even in children.

Early life stress impairs VTA coordination of BLA network and behavioral states

Motivated behaviors, such as social interactions, are governed by the interplay between mesocorticolimbic structures, such as the ventral tegmental area (VTA), basolateral amygdala (BLA), and medial prefrontal cortex (mPFC). Adverse childhood experiences and early life stress (ELS) can impact these networks and behaviors, which is associated with increased risk for psychiatric illnesses. While it is known that the VTA projects to both the BLA and mPFC, the influence of these inputs on local network activity which govern behavioral states - and whether ELS impacts VTA-mediated network communication - remains unknown. Our study demonstrates that VTA inputs influence BLA oscillations and mPFC activity, and that ELS weakens the ability of the VTA to coordinate BLA network states, likely due to ELS-induced impairments in dopamine signaling between the VTA and BLA. Consequently, ELS mice exhibit increased social avoidance, which can be recapitulated in control mice by inhibiting VTA-BLA communication. These data suggest that ELS impacts social reward via the VTA-BLA dopamine network.

Sex-dimorphic role of prefrontal oxytocin receptors in social-induced facilitation of extinction in juvenile rats

We previously reported that in the adult animal extinction in pairs resulted in enhanced extinction, showing that social presence can reduce previously acquired fear responses. Based on our findings that juvenile and adult animals differ in the mechanisms of extinction, here we address whether the social presence of a conspecific affects extinction in juvenile animals similarly to adults. We further address whether such presence has a different impact on juvenile males and females. To that end, we examined in our established experimental setting whether conditioned male and female animals extinguish contextual fear memory better while in pairs. Taking advantage of the role of oxytocin (OT) in the mediation of extinction memory and social interaction, we also study the effect of antagonizing the OT receptors (OTR) either systemically or in the prefrontal cortex on social interaction-induced effects of fear extinction. The results show that social presence accelerates extinction in males and females as compared to the single condition. Yet, we show differential and opposing effects of an OTR antagonist in both sexes. Whereas in females, the systemic application of an OTR antagonist is associated with impaired extinction, it is associated with enhanced extinction in males. In contrast, prefrontal OT is not engaged in extinction in juvenile males, while is it is critical in females. Previously reported differences in the levels of prefrontal OT between males and females might explain the differences in OT action. These results suggest that even during the juvenile period, critical mechanisms are differently involved in the regulation of fear in males and females.

Prefrontal Oxytocin is Involved in Impairments in Prefrontal Plasticity and Social Memory Following Acute Exposure to High Fat Diet in Juvenile Animals

Juvenility represents a critical developmental phase during which exposure to a high fat diet (HFD) can severely modify cognitive and emotional functioning. The purpose of this study was to address how short and acute exposure to a HFD during juvenility affects social memory recognition and prefrontal long-term potentiation (LTP). As LTP and social memory depend on the neuromodulator oxytocin (OXY) and due to its role in metabolism, we also examined the effects of OXY in mediating HFD-induced alterations in social memory and LTP. Our results show that short exposure to a HFD during juvenility impairs social preference memory and prefrontal LTP. Interestingly, whereas systemic injections of OXY reversed the impairments in HFD-fed animals and impaired LTP and memory in control animals; prefrontal injections of the OXY agonist TGOT reversed the effects in HFD animals without affecting control animals. Exposure to HFD was associated with a reduction in the levels of OXY in the prefrontal compared to control animals. Interestingly, the restoration of social memory by TGOT in HFD animals was also associated with normalization of OXY in the prefrontal. These results point to a role that prefrontal OXY has in mediating the effects of HFD on memory and plasticity.