Perineuronal Nets in Syrian Hamsters: Anatomical Localization, Sex Differences, Diurnal Variation, and Response to Social Stress.

Purpose: Perineuronal nets (PNNs) are extracellular matrix proteoglycans surrounding neurons and glia. It has been suggested that PNNs are involved in the pathophysiology of multiple CNS illnesses, including stress-related neuropsychiatric disorders like schizophrenia, major depressive disorder, and anxiety disorders.

Method: Before examining the putative role of PNNs in stress-related responses, we described for the first time the anatomical distribution in Syrian hamsters (Mesocricetus auratus), an excellent model organism for studying social stress and circadian rhythms.

Identification of hippocampal area CA2 in hamster and vole brain.

Prairie voles (Microtus ochrogaster) and Syrian, or golden, hamsters (Mesocricetus auratus) are closely related to mice (Mus musculus) and are commonly used in studies of social behavior including social interaction, social memory, and aggression. Hippocampal area CA2 is known to play a key role in these behaviors in mice and responds to social stimuli in rats, but CA2 has yet to be characterized in hamsters or voles, which are also used in studies of social behaviors. Here, we used immunofluorescence to determine whether CA2 could be molecularly identified in tissue from voles and hamsters.

Identification of hippocampal area CA2 in hamster and vole brain.

Prairie voles () and Syrian, or golden, hamsters () are closely related to mice () and rats (, for example) and are commonly used in studies of social behavior including social interaction, social memory, and aggression. The CA2 region of the hippocampus is known to play a key role in social memory and aggression in mice and responds to social stimuli in rats, likely owing to its high expression of oxytocin and vasopressin 1b receptors. However, CA2 has yet to be identified and characterized in hamsters or voles.

Sex-dependent regulation of social avoidance by oxytocin signaling in the ventral tegmental area.

It has been hypothesized that oxytocin increases the salience of social stimuli, whether the valence is positive or negative, through its interactions with the ventral tegmental area (VTA). Indeed, oxytocin neurons project to the VTA and activate dopamine neurons that are necessary for social experiences with positive valence. Surprisingly, though, there has not been an investigation of the role of oxytocin in the VTA in mediating social experiences with negative valence (e.

Perineuronal net degradation rescues CA2 plasticity in a mouse model of Rett syndrome.

Perineuronal nets (PNNs), a specialized form of extracellular matrix, are abnormal in the brains of people with Rett syndrome (RTT). We previously reported that PNNs function to restrict synaptic plasticity in hippocampal area CA2, which is unusually resistant to long-term potentiation (LTP) and has been linked to social learning in mice. Here we report that PNNs appear elevated in area CA2 of the hippocampus of an individual with RTT and that PNNs develop precociously and remain elevated in area CA2 of a mouse model of RTT (Mecp2-null).

Novel role for mineralocorticoid receptors in control of a neuronal phenotype.

Mineralocorticoid receptors (MRs) in the brain play a role in learning and memory, neuronal differentiation, and regulation of the stress response. Within the hippocampus, the highest expression of MRs is in area CA2. CA2 pyramidal neurons have a distinct molecular makeup resulting in a plasticity-resistant phenotype, distinguishing them from neurons in CA1 and CA3.