Autophosphorylation of αCaMKII affects social interactions in mice

Social Interaction Is Less Rewarding in Adult Female than in Male Mice

(1) Background: Positive social relationships are essential for mental and physical health. However, not all individuals experience social interaction as a rewarding activity. (2) Methods: Social interaction reward in mice can be assessed by social conditioned place preference (CPP). The aim of this study is to investigate sex-dependent differences in the neurological underpinnings underlying social versus non-social phenotypes, using adult male and female C57BL/6J mice. (3) Results: Adult female mice expressed significantly less social reward than males from the same strain. Accordingly, pairs of male mice spent more time interacting as compared to female pairs. Subsequently, we analyzed neuropeptides previously reported to be important regulators of social behavior such as oxytocin, vasopressin, and orexin, in addition to Ca2+/calmodulin-dependent protein kinase II (αCaMKII), shown to be involved in social reward. Levels of neuropeptides and αCaMKII were comparable between males and females in all investigated regions. Yet, a significant negative correlation was found between endogenous oxytocin expression and social reward in female pairs. (4) Conclusions: Sex differences in the prevalence of many mental health disorders might at least in part be due to sex differences in social reward. Therefore, more research is needed to unravel the candidate(s) underlying this behavioral difference.

Protein kinases in natural versus drug reward

Natural and drug rewards act on the same neural pathway, the mesolimbic dopaminergic system. In brain regions such as the nucleus accumbens and ventral tegmental area, drugs of abuse-induced stimulation of signaling pathways can lead to synaptic reshaping within this system. This is believed to be underlying the maladaptive alterations in behaviors associated with addiction. In this review, we discuss animal studies disclosing the implication of several protein kinases, namely protein kinase A (PKA), extracellular signal regulated kinase (ERK) mitogen-activated protein kinases (MAPK), p38 MAPK, and calcium/calmodulin-dependent kinase II (CaMKII), in reward-related brain regions in drug and natural reward. Furthermore, we refer to studies that helped pave the way toward a better understanding of the neurobiology underlying non-drug and drug reward through genetic deletion or brain region-specific pharmacological inhibition of these kinases. Whereas the role of kinases in drug reward has been extensively studied, their implication in natural reward, such as positive social interaction, is less investigated. Discovering molecular candidates, recruited specifically by drug versus natural rewards, can promote the identification of novel targets for the pharmacological treatment of addiction with less off-target effects and being effective when used combined with behavioral-based therapies.

The Anti-social Brain in Schizophrenia: A Role of CaMKII?

Current pharmacological therapy has limited effects on the cognitive impairments and negative symptoms associated with schizophrenia. Therefore, understanding the molecular underpinnings of this disorder is essential for the development of effective treatments. It appears that a reduction in calcium/calmodulin-dependent protein kinase II (α-CaMKII) activity is a common mechanism underlying the abnormal social behavior and cognitive deficits associated with schizophrenia. In addition, in a previous study social interaction with a partner of the same sex and weight increased the activity of α-CaMKII in rats. Here, we propose that boosting of CaMKII signaling, in a manner that counteracts this neuropsychiatric disease without disrupting the normal brain function, might ameliorate the abnormalities in social cognition and the negative symptoms of schizophrenia.

Rewarding Social Interaction in Rats Increases CaMKII in the Nucleus Accumbens

Calcium/calmodulin-dependent protein kinase II (CaMKII) is known to be involved in the sensitized locomotor responses and drug-seeking behavior to psychostimulants. However, little is known about the contribution of CaMKII signaling in the nucleus accumbens (NAc) in natural rewards such as social interaction. The present experiments explored the implication of CaMKII signaling in drug versus natural reward. In the NAc of rats expressing cocaine or social interaction conditioned place preference (CPP), αCaMKII activation was induced in those expressing social interaction but not cocaine CPP. In order to investigate the role of NAc CaMKII in the expression of reward-related learning of drug versus non-drug stimuli, we inhibited CaMKII through an infusion of KN-93, a CaMKII inhibitor, directly into the NAc shell or core, before the CPP test in a concurrent paradigm in which social interaction was made available in the compartment alternative to the one associated with cocaine during conditioning. Whereas vehicle infusions led to equal preference to both stimuli, inhibition of CaMKII by a KN-93 infusion before the CPP test in the shell but not the core of the NAc shifted the rats' preference toward the cocaine-associated compartment. Altogether, these results suggest that social interaction reward engages CaMKII in the NAc.

PSD-95 in CA1 Area Regulates Spatial Choice Depending on Age

Cognitive processes that require spatial information rely on synaptic plasticity in the dorsal CA1 area (dCA1) of the hippocampus. Since the function of the hippocampus is impaired in aged individuals, it remains unknown how aged animals make spatial choices. Here, we used IntelliCage to study behavioral processes that support spatial choices of aged female mice living in a group. As a proxy of training-induced synaptic plasticity, we analyzed the morphology of dendritic spines and the expression of a synaptic scaffold protein, PSD-95. We observed that spatial choice training in young adult mice induced correlated shrinkage of dendritic spines and downregulation of PSD-95 in dCA1. Moreover, long-term depletion of PSD-95 by shRNA in dCA1 limited correct choices to a reward corner, while reward preference was intact. In contrast, old mice used behavioral strategies characterized by an increased tendency for perseverative visits and social interactions. This strategy resulted in a robust preference for the reward corner during the spatial choice task. Moreover, training decreased the correlation between PSD-95 expression and the size of dendritic spines. Furthermore, PSD-95 depletion did not impair place choice or reward preference in old mice. Thus, our data indicate that while young mice require PSD-95-dependent synaptic plasticity in dCA1 to make correct spatial choices, old animals observe cage mates and stick to a preferred corner to seek the reward. This strategy is resistant to the depletion of PSD-95 in the CA1 area. Overall, our study demonstrates that aged mice combine alternative behavioral and molecular strategies to approach and consume rewards in a complex environment.SIGNIFICANCE STATEMENT It remains poorly understood how aging affects behavioral and molecular processes that support cognitive functions. It is, however, essential to understand these processes to develop therapeutic interventions that support successful cognitive aging. Our data indicate that while young mice require PSD-95-dependent synaptic plasticity in dCA1 to make correct spatial choices (i.e., choices that require spatial information), old animals observe cage mates and stick to a preferred corner to seek the reward. This strategy is resistant to the depletion of PSD-95 in the CA1 area. Overall, our study demonstrates that aged mice combine alternative behavioral and molecular strategies to approach and consume rewards in a complex environment. Second, the contribution of PSD-95-dependent synaptic functions in spatial choice changes with age.

Cognitive enhancer ST101 improves schizophrenia-like behaviors in neonatal ventral hippocampus-lesioned rats in association with improved CaMKII/PKC pathway

Atypical antipsychotics improve positive and negative symptoms but are not effective for treating cognitive impairments in patients with schizophrenia. We previously reported that cognitive impairments in neonatal ventral hippocampus (NVH)-lesioned rats show resistance to atypical antipsychotics risperidone and are associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) signaling in memory-related regions. The cognitive enhancer ST101 (spiro[imi-dazo[1,2-a]pyridine-3,2-indan]-2(3H)-one) stimulates CaMKII activity in the hippocampus and medial prefrontal cortex (mPFC). We thus tested ST101 on cognitive impairments in NVH-lesioned rats. Chronic ST101 administration (0.1 and/or 0.5 mg/kg, p.o.) significantly improved deficits in prepulse inhibition (PPI), social interaction, and cognitive function in NVH-lesioned rats. ST101 administration (0.5 mg/kg, p.o.) significantly restored the decreased CaMKII autophosphorylation (Thr-286) in the mPFC and hippocampal CA1 regions of NVH-lesioned rats when assessed by immunohistochemistry. Chronic ST101 administration (0.1 mg/kg, p.o.) improved the decline in phosphorylation levels of CaMKII (Thr-286), PKCα (Ser-657), α-amino-3-hydroxy-5-methyl-4-isoxazol- propionic acid (AMPA)-type glutamate receptor subunit 1 (GluA1: Ser-831), and N-methyl-d-aspartate (NMDA) receptor subunit 1 (GluN1: Ser-896) in the mPFC and hippocampal CA1 regions. Taken together, these results suggest that ST101 improves schizophrenia-like behaviors and cognitive impairment by enhancing CaMKII/PKCα signaling in the mPFC and hippocampus in NVH-lesioned rats.

Automated, Long-term Behavioral Assay for Cognitive Functions in Multiple Genetic Models of Alzheimer's Disease, Using IntelliCage

Multiple factors-such as aging and genes-are frequently associated with cognitive decline. Genetically modified mouse models of cognitive decline, such as Alzheimer's disease (AD), have become a promising tool to elucidate the underlying mechanisms and promote the therapeutic advances. An important step is the validation and characterization of expected behavioral abnormality in the models, in the case of AD, cognitive decline. The long-term behavioral investigations of laboratory animals to study the effect of aging demand substantial efforts from researchers. The IntelliCage system is a high-throughput and cost-effective test battery for mice that eliminates the need for daily human handling. Here, we describe how the system is utilized in the long-term phenotyping of a genetic Alzheimer's disease model, specifically focusing on the cognitive functions. The experiment employs repeated battery of tests that assess spatial learning and executive functions. This cost-effective age-dependent phenotyping allows us to identify the transient and/or permanent effects of genes on various cognitive aspects.