GPER1 deficiency causes sex-specific dysregulation of hippocampal plasticity and cognitive function.

Estrogens regulate synaptic properties and influence hippocampus-related learning and memory via estrogen receptors, which include the G-protein-coupled estrogen receptor 1 (GPER1). Studying mice, in which the GPER1 gene is dysfunctional (GPER1-KO), we here provide evidence for sex-specific roles of GPER1 in these processes. GPER1-KO males showed reduced anxiety in the elevated plus maze, whereas the fear response ('freezing') was specifically increased in GPER1-KO females in a contextual fear conditioning paradigm. In the Morris water maze, spatial learning and memory consolidation was impaired by GPER1 deficiency in both sexes. Notably, in the females, spatial learning deficits and the fear response were more pronounced if mice were in a stage of the estrous cycle, in which E2 serum levels are high (proestrus) or rising (diestrus). On the physiological level, excitability at Schaffer collateral synapses in CA1 increased in GPER1-deficient males and in proestrus/diestrus ('E2 high') females, concordant with an increased hippocampal expression of the AMPA-receptor subunit GluA1 in GPER1-KO males and females as compared to wildtype males. Further changes included an augmented early long-term potentiation (E-LTP) maintenance specifically in GPER1-KO females and an increased hippocampal expression of spinophilin in metestrus/estrus ('E2 low') GPER1-KO females. Our findings suggest modulatory and sex-specific functions of GPER1 in the hippocampal network, which reduce rather than increase neuronal excitability. Dysregulation of these functions may underlie sex-specific cognitive deficits or mood disorders.

Neuronal Adenosine A1 Receptor is Critical for Olfactory Function but Unable to Attenuate Olfactory Dysfunction in Neuroinflammation.

Adenine nucleotides, such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), as well as the nucleoside adenosine are important modulators of neuronal function by engaging P1 and P2 purinergic receptors. In mitral cells, signaling of the G protein-coupled P1 receptor adenosine 1 receptor (A1R) affects the olfactory sensory pathway by regulating high voltage-activated calcium channels and two-pore domain potassium (K2P) channels. The inflammation of the central nervous system (CNS) impairs the olfactory function and gives rise to large amounts of extracellular ATP and adenosine, which act as pro-inflammatory and anti-inflammatory mediators, respectively. However, it is unclear whether neuronal A1R in the olfactory bulb modulates the sensory function and how this is impacted by inflammation. Here, we show that signaling via neuronal A1R is important for the physiological olfactory function, while it cannot counteract inflammation-induced hyperexcitability and olfactory deficit. Using neuron-specific A1R-deficient mice in patch-clamp recordings, we found that adenosine modulates spontaneous dendro-dendritic signaling in mitral and granule cells via A1R. Furthermore, neuronal A1R deficiency resulted in olfactory dysfunction in two separate olfactory tests. In mice with experimental autoimmune encephalomyelitis (EAE), we detected immune cell infiltration and microglia activation in the olfactory bulb as well as hyperexcitability of mitral cells and olfactory dysfunction. However, neuron-specific A1R activity was unable to attenuate glutamate excitotoxicity in the primary olfactory bulb neurons in vitro or EAE-induced olfactory dysfunction and disease severity in vivo. Together, we demonstrate that A1R modulates the dendro-dendritic inhibition (DDI) at the site of mitral and granule cells and impacts the processing of the olfactory sensory information, while A1R activity was unable to counteract inflammation-induced hyperexcitability.

Hyperfunction of the stress response system and novelty-induced hyperactivity correlate with enhanced cocaine-induced conditioned place preference in NCAM-deficient mice.

Several studies in humans and rodents suggest an association between impulsivity and activity of the stress response on the one hand and addiction vulnerability on the other. The neural cell adhesion molecule (NCAM) has been related to several neuropsychiatric disorders in humans. Constitutively NCAM-deficient (-/-) mice display enhanced novelty-induced behavior and hyperfunction of the hypothalamic-pituitary-adrenal axis. Here we hypothesize that NCAM deficiency causes an altered response to cocaine. Cocaine-induced behaviors of NCAM-/- mice and wild-type (+/+) littermates were analyzed in the conditioned place preference (CPP) test. c-fos mRNA levels were investigated by quantitative polymerase chain reaction (qPCR) to measure neural activation after exposure to the cocaine-associated context. NCAM-/- mice showed an elevated cocaine-induced sensitization, enhanced CPP, impaired extinction, and potentiated cocaine-induced hyperlocomotion and CPP after extinction. NCAM-/- showed no potentiated CPP as compared with NCAM+/+ littermates when a natural rewarding stimulus (ie, an unfamiliar female) was used, suggesting that the behavioral alterations of NCAM-/- mice observed in the CPP test are specific to the effects of cocaine. Activation of the prefrontal cortex and nucleus accumbens induced by the cocaine-associated context was enhanced in NCAM-/- compared with NCAM+/+ mice. Finally, cocaine-induced behavior correlated positively with novelty-induced behavior and plasma corticosterone levels in NCAM-/- mice and negatively with NCAM mRNA levels in the hippocampus and nucleus accumbens in wild-type mice. Our findings indicate that NCAM deficiency affects cocaine-induced CPP in mice and support the view that hyperfunction of the stress response system and reactivity to novelty predict the behavioral responses to cocaine.

Physiological relevance of the neuronal isoform of inositol-1,4,5-trisphosphate 3-kinases in mice.

Inositol-1,4,5-trisphosphate 3-kinase-A (ITPKA) is the neuronal isoform of ITPKs and exhibits both actin bundling and InsP3kinase activity. In addition to neurons, ITPKA is ectopically expressed in tumor cells, where its oncogenic activity increases tumor cell malignancy. In order to analyze the physiological relevance of ITPKA, here we performed a broad phenotypic screening of itpka deficient mice. Our data show that among the neurobehavioral tests analyzed, itpka deficient mice reacted faster to a hotplate, prepulse inhibition was impaired and the accelerating rotarod test showed decreased latency of itpka deficient mice to fall. These data indicate that ITPKA is involved in the regulation of nociceptive pathways, sensorimotor gating and motor learning. Analysis of extracerebral functions in control and itpka deficient mice revealed significantly reduced glucose, lactate, and triglyceride plasma concentrations in itpka deficient mice. Based on this finding, expression of ITPKA was analyzed in extracerebral tissues and the highest level was found in the small intestine. However, functional studies on CaCo-2 control and ITPKA depleted cells showed that glucose, as well as triglyceride uptake, were not significantly different between the cell lines. Altogether, these data show that ITPKA exhibits distinct functions in the central nervous system and reveal an involvement of ITPKA in energy metabolism.

Treatment during a vulnerable developmental period rescues a genetic epilepsy.

The nervous system is vulnerable to perturbations during specific developmental periods. Insults during such susceptible time windows can have long-term consequences, including the development of neurological diseases such as epilepsy. Here we report that a pharmacological intervention timed during a vulnerable neonatal period of cortical development prevents pathology in a genetic epilepsy model. By using mice with dysfunctional Kv7 voltage-gated K(+) channels, which are mutated in human neonatal epilepsy syndromes, we demonstrate the safety and efficacy of the sodium-potassium-chloride cotransporter NKCC1 antagonist bumetanide, which was administered during the first two postnatal weeks. In Kv7 current-deficient mice, which normally display epilepsy, hyperactivity and stereotypies as adults, transient bumetanide treatment normalized neonatal in vivo cortical network and hippocampal neuronal activity, prevented structural damage in the hippocampus and restored wild-type adult behavioral phenotypes. Furthermore, bumetanide treatment did not adversely affect control mice. These results suggest that in individuals with disease susceptibility, timing prophylactically safe interventions to specific windows during development may prevent or arrest disease progression.

Susceptibility to the long-term anxiogenic effects of an acute stressor is mediated by the activation of the glucocorticoid receptors.

The specificity of the response of an organism is an important variable influencing stress-related parameters and psychopathological states. We have shown that trait anxiety in C57BL/6 mice, determined by their emergence latencies in the free choice open field test, positively correlates with the long-term behavioral and neuroendocrinological changes induced by a stressor. Here, we show that this interindividual variability is caused by a different reactivity of the hypothalamus-pituitary-adrenal (HPA) axis upon exposure to a stressor. Mice with high trait anxiety (long emergence latency, LEL) display a more pronounced stress-induced activation of the HPA axis than mice with low trait anxiety (short emergence latency, SEL). Moreover, stress-induced activation of tyrosine hydroxylase and corticotropin-releasing hormone occurred in LEL but not SEL mice. In search of the molecular mechanisms underlying these differences, we found that under non-stressed conditions mRNA and protein levels of the glucocorticoid receptor in the hippocampus were higher in LEL mice compared to SEL mice. Also, systemic injection of the glucocorticoid receptor antagonist RU486 decreased the stress-induced activation of the HPA axis and the long-term anxiogenic effects of stress observed in LEL mice. Finally, the rewarding properties of cocaine were enhanced in LEL mice compared to SEL mice, suggesting a causal link between trait anxiety, stress activity and the behavioral responses to drugs of addiction.

Neural cell adhesion molecule ablation in mice causes hippocampal dysplasia and loss of septal cholinergic neurons.

The neural cell adhesion molecule (NCAM) is implicated in nervous system development and plasticity. In humans, abnormal NCAM expression has been linked to the pathogenesis of neuropsychiatric and neurodegenerative disorders accompanied by cognitive dysfunctions. Impaired cognition is also observed in NCAM-deficient (NCAM(-/-) ) mice. Considering the importance of the septal cholinergic nuclei and the hippocampus for cognition, we performed quantitative morphological analyses of these areas in young and adult (2 and 13 months old, respectively) NCAM(-/-) mice and wild-type (NCAM(+/+) ) littermates. In young mice, we found lower numbers of septal cholinergic neurons in NCAM(-/-) than in NCAM(+/+) mice. Despite deficient numbers of neurons, total lengths of cholinergic axons and choline acetyltransferase protein levels in the hippocampus of NCAM(-/-) mice were normal. The hippocampus of NCAM(-/-) mice was atrophic, notably in the CA3 subfield and the dentate gyrus (DG). The atrophy appeared to have different primary causes in the two subfields: loss of pyramidal cells in CA3 and reduced branching and volume of granule cell dendrites in the DG. The frequency of dendritic spines on dentate granule cells in NCAM(-/-) mice was normal. Numbers of parvalbumin-positive (PV(+) ) interneurons were reduced in NCAM(-/-) mice in proportion to subfield volume loss, and the ratios of principal cells to PV(+) interneurons were similar to those of NCAM(+/+) mice. None of the observed abnormalities was exaggerated or alleviated in adult NCAM(-/-) mice. Our observations indicate that NCAM ablation causes structural abnormalities in the hippocampus and the forebrain cholinergic system in adult mice, which may contribute to impaired cognition in NCAM(-/-) mice.

Expression of the snoRNA host gene gas5 in the hippocampus is upregulated by age and psychogenic stress and correlates with reduced novelty-induced behavior in C57BL/6 mice.

The growth arrest specific 5 (gas5) is a noncoding protein gene that hosts small nucleolar RNAs. Based on the observation that gas5 RNA level in the brain is highest in the hippocampus and remarkably enhanced in aged mice, we tested the hypothesis that gas5 is involved in functions controlled by the hippocampus and known to be affected by age, such as spatial learning and novelty-induced behaviors. We show that aged (22-month-old) C57BL/6 male mice have spatial-learning impairments, reduced novelty-induced exploration, and enhanced gas5 RNA levels in the hippocampus compared to young (3-month-old) mice. At both ages, levels of gas5 RNA in the hippocampus negatively correlated with novelty-induced exploration in the open field and elevated-plus maze tests. No correlations were found between gas5 RNA levels in the hippocampus and performance in the water maze test. The expression of gas5 RNA in the rest of the brain did not correlate with any behavioral parameter analyzed. Because variations in novelty-induced behaviors could be caused by stressfull experiences, we analyzed whether gas5 RNA levels in the hippocampus are regulated by acute stressors. We found that gas5 RNA levels in the hippocampus were upregulated by 50% 24 h after a psychogenic stressor (60-min olfactory contact with a rat) but were unchanged after exposure to an unfamiliar environment or after acquisition of new spatial information in a one-trial learning task. The present results suggest that strong psychogenic stressors upregulate gas5 RNA in the hippocampus, which in turn affects novelty-induced responses controlled by this region. We hypothesize that long-life exposure to stressors causes an age-dependent increase in hippocampal gas5 RNA levels, which could be responsible for age-related reduced novelty-induced behaviors, thus suggesting a new mechanism by which ageing and stress affect hippocampal function.