Prefrontal cortex is necessary for long-term social recognition memory in mice

A systematic review and meta-analysis of how social memory is studied

Social recognition is crucial for survival in social species, and necessary for group living, selective reproduction, pair bonding, and dominance hierarchies. Mice and rats are the most commonly used animal models in social memory research, however current paradigms do not account for the complex social dynamics they exhibit in the wild. To assess the range of social memories being studied, we conducted a systematic analysis of neuroscience articles testing the social memory of mice and rats published within the past two decades and analyzed their methods. Our results show that despite these rodent's rich social memory capabilities, the majority of social recognition papers explore short-term memories and short-term familiarity levels with minimal exposure between subject and familiar stimuli-a narrow type of social memory. We have identified several key areas currently understudied or underrepresented: kin relationships, mates, social ranks, sex variabilities, and the effects of aging. Additionally, reporting on social stimulus variables such as housing history, strain, and age, is limited, which may impede reproducibility. Overall, our data highlight large gaps in the diversity of social memories studied and the effects social variables have on social memory mechanisms.

Oxytocin receptors in the prefrontal cortex play important roles in short-term social recognition in mice

We examined the roles of oxytocin (OT) receptors in the prefrontal cortex (PFC) in short- and long-term social recognition and anxiety-related behaviors in mice. Mice injected with high or low doses of an OT receptor antagonist (OTA) or vehicle performed the social recognition test, the open-field test, and the light-dark transition test. In the social recognition test, with three daily trials over three consecutive days, control mice showed short-term recognition of a conspecific on all three days. In contrast, a high-dose injection of OTA impaired short-term social recognition on the second and third days, and it was impaired by a low-dose injection of OTA on the third day. These results suggested that OTA injection into the PFC dose-dependently inhibited short-term social recognition within each day. All three groups did not show any long-term social recognition across three days. OTA injection did not affect anxiety related behavior in the open-field and light-dark transition tests. Our findings demonstrated that OT receptors in the PFC played important roles in short-term social recognition.

Mind the gap: A systematic review and meta-analysis of how social memory is studied

Social recognition is crucial for survival in social species, and necessary for group living, selective reproduction, pair bonding, and dominance hierarchies. Mice and rats are the most commonly used animal models in social memory research, however current paradigms do not account for the complex social dynamics they exhibit in the wild. To assess the range of social memories being studied, we conducted a systematic analysis of neuroscience articles testing the social memory of mice and rats published within the past two decades and analyzed their methods. Our results show that despite these rodent's rich social memory capabilities, the majority of social recognition papers explore short-term memories and short-term familiarity levels with minimal exposure between subject and familiar stimuli - a narrow type of social memory. We have identified several key areas currently understudied or underrepresented: kin relationships, mates, social ranks, sex variabilities, and the effects of aging. Additionally, reporting on social stimulus variables such as housing history, strain, and age, is limited, which may impede reproducibility. Overall, our data highlight large gaps in the diversity of social memories studied and the effects social variables have on social memory mechanisms.

From rodents to humans: Rodent behavioral paradigms for social behavioral disorders

Social cognition guides social behavior. Subjects with proper social cognition should be able to: (1) have reasonable social motivation, (2) recognize other people and infer their intentions, and (3) weigh social hierarchies and other values. The choice of appropriate behavioral paradigms enables the use of rodents to study social behavior disorders in humans, thus enabling research to go deeper into neural mechanisms. This paper reviews commonly used rodent behavioral paradigms in studies of social behavior disorders. We focused specifically on sorting out ways to transfer the study of human social behavior to rodents through behavioral paradigms.

The role of the prefrontal cortex in social interactions of animal models and the implications for autism spectrum disorder

Social interaction is a complex behavior which requires the individual to integrate various internal processes, such as social motivation, social recognition, salience, reward, and emotional state, as well as external cues informing the individual of others' behavior, emotional state and social rank. This complex phenotype is susceptible to disruption in humans affected by neurodevelopmental and psychiatric disorders, including autism spectrum disorder (ASD). Multiple pieces of convergent evidence collected from studies of humans and rodents suggest that the prefrontal cortex (PFC) plays a pivotal role in social interactions, serving as a hub for motivation, affiliation, empathy, and social hierarchy. Indeed, disruption of the PFC circuitry results in social behavior deficits symptomatic of ASD. Here, we review this evidence and describe various ethologically relevant social behavior tasks which could be employed with rodent models to study the role of the PFC in social interactions. We also discuss the evidence linking the PFC to pathologies associated with ASD. Finally, we address specific questions regarding mechanisms employed by the PFC circuitry that may result in atypical social interactions in rodent models, which future studies should address.

NRXN1 depletion in the medial prefrontal cortex induces anxiety-like behaviors and abnormal social phenotypes along with impaired neurite outgrowth in rat

BACKGROUND

Neurodevelopmental disorders (NDDs) are a group of disorders induced by abnormal brain developmental processes. The prefrontal cortex (PFC) plays an essential role in executive function, and its role in NDDs has been reported. NDDs are associated with high-risk gene mutations and share partially overlapping genetic abnormalities.

METHODS

Neurexins (NRXNs) are related to autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). NRXN1, an essential susceptibility gene for NDDs, has been reported to be associated with NDDs. However, little is known about its key role in NDDs.

RESULTS

NRXN1 downregulation in the medial PFC induced anxiety-like behaviors and abnormal social phenotypes with impaired neurite outgrowth in Sh-NRXN1 in prefrontal neurons. Moreover, tandem mass tag (TMT)-based proteomic analysis of rat brain samples showed that NRXN1 downregulation led to significant proteome alterations, including pathways related to the extracellular matrix, cell membrane, and morphologic change. Furthermore, full-automatic immunoblotting analysis verified the differently expressed proteins related to cell morphology and membrane structure.

CONCLUSIONS

Our results confirmed the association of NRXN1 with abnormal behaviors in NDDs and provided richer insights into specific prefrontal knockdown in adolescence, potentially expanding the NRXN1 interactome and contributing to human health.

Low-Dose Lithium Supplementation Influences GSK3β Activity in a Brain Region Specific Manner in C57BL6 Male Mice

BACKGROUND

Lithium, a commonly used treatment for bipolar disorder, has been shown to have neuroprotective effects for other conditions including Alzheimer's disease via the inhibition of the enzyme glycogen synthase kinase-3 (GSK3). However, dose-dependent adverse effects of lithium are well-documented, highlighting the need to determine if low doses of lithium can reliably reduce GSK3 activity.

OBJECTIVE

The purpose of this study was to evaluate the effects of a low-dose lithium supplementation on GSK3 activity in the brain of an early, diet-induced Alzheimer's disease model.

METHODS

Male C57BL/6J mice were divided into either a 6-week or 12-week study. In the 6-week study, mice were fed a chow diet or a chow diet with lithium-supplemented drinking water (10 mg/kg/day) for 6 weeks. Alternatively, in the 12-week study, mice were fed a chow diet, a high-fat diet (HFD), or a HFD with lithium-supplemented drinking water for 12 weeks. Prefrontal cortex and hippocampal tissues were collected for analysis.

RESULTS

Results demonstrated reduced GSK3 activity in the prefrontal cortex as early as 6 weeks of lithium supplementation, in the absence of inhibitory phosphorylation changes. Further, lithium supplementation in an obese model reduced prefrontal cortex GSK3 activity as well as improved insulin sensitivity.

CONCLUSION

Collectively, these data provide evidence for low-dose lithium supplementation to inhibit GSK3 activity in the brain. Moreover, these results indicate that GSK3 activity can be inhibited despite any changes in phosphorylation. These findings contribute to an overall greater understanding of low-dose lithium's ability to influence GSK3 activity in the brain and its potential as an Alzheimer's disease prophylactic.

The prelimbic cortex but not the anterior cingulate cortex plays an important role in social recognition and social investigation in mice

The prefrontal cortex (PFC) has been implicated in social cognitive functions and emotional behaviors in rodents. Each subregion (prelimbic cortex, PL; infralimbic cortex; and anterior cingulate cortex, ACC) of the PFC appears to play a different role in social and emotional behaviors. However, previous investigations have produced inconsistent data, and few previous studies directly compared the roles of the PFC subregions using the same experimental paradigm. Accordingly, in the present study, we examined the role of the PL and the ACC in short-term social recognition, social investigation, and anxiety-related behaviors in C57BL/6J mice. We subjected mice with a lesioned PL or ACC, as well as those in a sham control group, to tests of social recognition and social novelty where juvenile and adult male mice were used as social stimuli. In the social recognition test, the PL-lesioned mice exhibited habituation but not dishabituation regardless of whether they encountered juvenile or adult mice. In a subsequent social novelty test, they spent less time engaged in social investigation compared with the control mice when adult mice were used as social stimuli. These results suggest that PL lesions impaired both social recognition and social investigation. In contrast, ACC-lesioned mice did not exhibit impaired short-term social recognition or social investigation regardless of the social stimulus. Furthermore, PL lesions and ACC lesions did not affect anxiety-related behavior in the open field test or light-dark transition test. Our findings demonstrate that the PL but not the ACC plays an important role in social recognition and social investigation.