Comparative study of the distribution of calmodulin kinase II and calcineurin in the mouse brain

Chlorogenic Acids, Acting via Calcineurin, Are the Main Compounds in Centella asiatica Extracts That Mediate Resilience to Chronic Stress in Drosophila melanogaster

Common symptoms of depressive disorders include anhedonia, sleep problems, and reduced physical activity. Drugs used to treat depression mostly aim to increase serotonin signaling but these can have unwanted side effects. Depression has also been treated by traditional medicine using plants like Centella asiatica (CA) and this has been found to be well tolerated. However, very few controlled studies have addressed CA's protective role in depression, nor have the active compounds or mechanisms that mediate this function been identified. To address this issue, we used Drosophila melanogaster to investigate whether CA can improve depression-associated symptoms like anhedonia and decreased climbing activity. We found that a water extract of CA provides resilience to stress induced phenotypes and that this effect is primarily due to mono-caffeoylquinic acids found in CA. Furthermore, we describe that the protective function of CA is due to a synergy between chlorogenic acid and one of its isomers also present in CA. However, increasing the concentration of chlorogenic acid can overcome the requirement for the second isomer. Lastly, we found that chlorogenic acid acts via calcineurin, a multifunctional phosphatase that can regulate synaptic transmission and plasticity and is also involved in neuronal maintenance.

Prolactin Action Is Necessary for Parental Behavior in Male Mice

Parental care is critical for successful reproduction in mammals. Recent work has implicated the hormone prolactin in regulating male parental behavior, similar to its established role in females. Male laboratory mice show a mating-induced suppression of infanticide (normally observed in virgins) and onset of paternal behavior 2 weeks after mating. Using this model, we sought to investigate how prolactin acts in the forebrain to regulate paternal behavior. First, using c-fos immunoreactivity in prolactin receptor (Prlr) Prlr-IRES-Cre-tdtomato reporter mouse sires, we show that the circuitry activated during paternal interactions contains prolactin-responsive neurons in multiple sites, including the medial preoptic nucleus, bed nucleus of the stria terminalis, and medial amygdala. Next, we deleted Prlr from three prominent cell types found in these regions: glutamatergic, GABAergic, and CaMKIIα. Prlr deletion from CaMKIIα, but not glutamatergic or GABAergic cells, had a profound effect on paternal behavior as none of these KO males completed the pup-retrieval task. Prolactin was increased during mating, but not in response to pups, suggesting that the mating-induced secretion of prolactin is important for establishing the switch from infanticidal to paternal behavior. Pharmacological blockade of prolactin secretion at mating, however, had no effect on paternal behavior. In contrast, suppressing prolactin secretion at the time of pup exposure resulted in failure to retrieve pups, with exogenous prolactin administration rescuing this behavior. Together, our data show that paternal behavior in sires is dependent on basal levels of circulating prolactin acting at the time of interaction with pups, mediated through Prlr on CaMKIIα-expressing neurons.SIGNIFICANCE STATEMENT Parental care is critical for offspring survival. Compared with maternal care, however, the neurobiology of paternal care is less well understood. Here we show that the hormone prolactin, which is most well known for its female-specific role in lactation, has a role in the male brain to promote paternal behavior. In the absence of prolactin signaling specifically during interactions with pups, father mice fail to show normal retrieval behavior of pups. These data demonstrate that prolactin has a similar action in both males and females to promote parental care.

Coexpression of calcineurin A and B subunits in various subcellular and synaptic compartments of cerebellar neurons and glia with particular abundance at parallel fiber-Purkinje cell synapses

Calcineurin (CN) is a Ca²⁺/calmodulin-dependent serine/threonine protein phosphatase consisting of catalytic CNA and regulatory CNB subunits, and links activity-dependent Ca²⁺ signals to various neural functions. Here we studied CN expression in the mouse brain by producing subunit-specific probes and antibodies. Of five CN subunits. CNAα, CNAβ, and CNB1 mRNAs were predominantly expressed over the brain from early embryonic to adult stage, and all were high in the telencephalon and cerebellum. Protein localization was examined in the cerebellum by immunofluorescence with cellular and terminal markers and by preembedding silver-enhanced immunogold microscopy. CNB1 and CNAβ were co-distributed in subcellular and synaptic elements of various cerebellar neurons and glia, whereas CNAα was exclusive in granule cell elements, including parallel fiber terminals. The present study thus discloses that CNB1 subunit well coexists with one or two CNA subunits in various cerebellar compartments. Moreover, high CN contents are provided to parallel fiber-Purkinje cell synapses, i.e., CNAα, CNAβ, and CNB1 in their presynaptic side and CNAβ and CNB1 in their postsynaptic side. These findings will be the anatomical basis, at least partly, for the known regulatory roles of postsynaptic CNs in long-term depression and presynaptic CNs in transmitter release function.

Serine/Threonine Phosphatases in LTP: Two B or Not to Be the Protein Synthesis Blocker-Induced Impairment of Early Phase

Dephosphorylation of target proteins at serine/threonine residues is one of the most crucial mechanisms regulating their activity and, consequently, the cellular functions. The role of phosphatases in synaptic plasticity, especially in long-term depression or depotentiation, has been reported. We studied serine/threonine phosphatase activity during the protein synthesis blocker (PSB)-induced impairment of long-term potentiation (LTP). Established protein phosphatase 2B (PP2B, calcineurin) inhibitor cyclosporin A prevented the LTP early phase (E-LTP) decline produced by pretreatment of hippocampal slices with cycloheximide or anisomycin. For the first time, we directly measured serine/threonine phosphatase activity during E-LTP, and its significant increase in PSB-treated slices was demonstrated. Nitric oxide (NO) donor SNAP also heightened phosphatase activity in the same manner as PSB, and simultaneous application of anisomycin + SNAP had no synergistic effect. Direct measurement of the NO production in hippocampal slices by the NO-specific fluorescent probe DAF-FM revealed that PSBs strongly stimulate the NO concentration in all studied brain areas: CA1, CA3, and dentate gyrus (DG). Cyclosporin A fully abolished the PSB-induced NO production in the hippocampus, suggesting a close relationship between nNOS and PP2B activity. Surprisingly, cyclosporin A alone impaired short-term plasticity in CA1 by decreasing paired-pulse facilitation, which suggests bi-directionality of the influences of PP2B in the hippocampus. In conclusion, we proposed a minimal model of signaling events that occur during LTP induction in normal conditions and the PSB-treated slices.

Procedures for Culturing and Genetically Manipulating Murine Hippocampal Postnatal Neurons

Neuronal hippocampal cultures are simple and valuable models for studying neuronal function. While embryonic cultures are widely used for different applications, mouse postnatal cultures are still challenging, lack reproducibility and/or exhibit inappropriate neuronal activity. Yet, postnatal cultures have major advantages such as allowing genotyping of pups before culture and reducing the number of experimental animals. Herein we describe a simple and fast protocol for culturing and genetically manipulating hippocampal neurons from P0 to P3 mice. This protocol provides reproducible cultures exhibiting a consistent neuronal development, normal excitatory over inhibitory neuronal ratio and a physiological neuronal activity. We also describe simple and efficient procedures for genetic manipulation of neurons using transfection reagent or lentiviral particles. Overall, this method provides a detailed and validated protocol allowing to explore cellular mechanisms and neuronal activity in postnatal hippocampal neurons in culture.

Sociability development in mice with cell-specific deletion of the NMDA receptor NR1 subunit gene

Social affiliative behavior is an important component of everyday life in many species and is likely to be disrupted in disabling ways in various neurodevelopmental and neuropsychiatric disorders. Therefore, determining the mechanisms involved in these processes is crucial. A link between N-methyl-d-aspartate (NMDA) receptor function and social behaviors has been clearly established. The cell types in which NMDA receptors are critical for social affiliative behavior, however, remain unclear. Here, we use mice carrying a conditional allele of the NMDA R1 subunit to address this question. Mice bearing a floxed NMDAR1 (NR1) allele were crossed with transgenic calcium/calmodulin-dependent kinase IIα (CaMKIIα)-Cre mice or parvalbumin (PV)-Cre mice targeting postnatal excitatory forebrain or PV-expressing interneurons, respectively, and assessed using the three-chambered Social Approach Test. We found that deletion of NR1 in PV-positive interneurons had no effect on social sniffing, but deletion of NR1 in glutamatergic pyramidal cells resulted in a significant increase in social approach behavior, regardless of age or sex. Therefore, forebrain excitatory neurons expressing NR1 play an important role in regulating social affiliative behavior.

Calcineurin signaling as a target for the treatment of alcohol abuse and neuroinflammatory disorders

Converging lines of evidence point to a significant role of neuroinflammation in a host of psychiatric conditions, including alcohol use disorder, TBI, and PTSD. A complex interaction of both peripheral and central signaling underlies processes involved in neuroinflammation. Calcineurin is a molecule that sits at the nexus of these processes and has been clearly linked to a number of psychiatric disorders including alcohol use disorder (AUD). Like its role in regulating peripheral immune cells, calcineurin (CN) plays an integral role in processes regulating neuroimmune function and neuroinflammatory processes. Targeting CN or elements of its signaling pathways at critical points may aid in the functional recovery from neuroinflammatory related disorders. In this review we will highlight the role of neuroinflammation and calcineurin signaling in AUD, TBI and stress-induced disorders and discuss recent findings demonstrating a therapeutic effect of immunosuppressant-induced calcineurin inhibition in a pre-clinical model of binge alcohol drinking.

A Friend or Foe: Calcineurin across the Gamut of Neurological Disorders

The serine/threonine phosphatase calcineurin (CaN) is a unique but confounding calcium/calmodulin-mediated enzyme. CaN has shown to play essential roles from regulating calcium homeostasis to being an intricate part of learning and memory formation. Neurological disorders, despite differing in their etiology, share similar pathological outcomes, such as mitochondrial dysfunction and apoptotic signaling brought about by excitotoxic elements. CaN, being deeply integrated in vital neuronal functions, may be implicated in various neurological disorders. Understanding the enzyme and its physiological niche in the nervous system is vital in uncovering its roles in the spectrum of brain disorders. By reviewing the crosstalk in different neurological pathologies, a possible grasp of CaN's complex signaling may lead to forming better neurotherapy. This Outlook attempts to explore the various neuronal functions of CaN and investigate its pervasive role through the gamut of neurological disorders.

Central Administration of Cyclosporine A Decreases Ethanol Drinking

Aims

Abstinence among alcohol dependent liver graft recipients is remarkably high. The routine use of anti-immune agents in these patients led to rodent studies showing that immunosuppressants acting through inhibition of calcineurin (CLN) are highly effective in decreasing alcohol consumption. It remained unclear, however, whether the decreased alcohol consumption in rodent models is mediated through peripheral suppression of immune response or centrally through direct inhibition of cyclophilin-CLN in the brain. We tested the hypothesis that direct brain inhibition of CLN with intracerebroventricular (ICV) injections of the immunosuppressant cyclosporine A (CsA) is sufficient to decrease ethanol consumption in a rodent model of binge-like drinking.

Methods

Male C57BL/6NHsd mice were put through a modified 'drinking in the dark' (DID) paradigm. Effects of both peripheral (IP) and central (ICV) injections of CsA on ethanol consumption were assessed.

Results

Here, as in earlier work, IP CsA administration significantly decreased alcohol consumption. Supporting our hypothesis, central administration of CsA was sufficient to decrease alcohol consumption in a dose-dependent manner. There was no significant effect of CsA on water or sucrose consumption.

Conclusions

These results clearly implicate a CLN-mediated mechanism in brain in the inhibitory effects of CsA on ethanol consumption and provide novel targets for investigation of treatment for Alcohol Use Disorders (AUD). These results also add to the growing body of literature implicating neuroimmune mechanisms in the etiology, pathophysiology and behaviors driving AUD.

Short Summary

The unusually high abstinence rate and routine use of immunosuppressants in AUD liver graft recipients led us to rodent studies showing that immunosuppressants acting through inhibition of calcineurin (CLN) are highly effective in decreasing drinking. Here we demonstrate that this effect is mediated by brain rather than peripheral immune mechanisms.

Prominent increased calcineurin immunoreactivity in the superior temporal gyrus in schizophrenia: A postmortem study

Many neuroimaging studies have demonstrated structural changes in the superior temporal gyrus (STG) in patients with schizophrenia. Several postmortem studies have reported on the pathogenesis of schizophrenia, but few reports have investigated alterations in molecules in the STG. In addition, several studies have suggested that calcineurin (CaN) inadequacy may be a risk factor for schizophrenia, but no reports about CaN expression in the STG in schizophrenia have been published. We compared the density of CaN-immunoreactive (CaN-IR) neurons in the STG from 11 patients with schizophrenia with that of 11 sex- and age-matched controls. We used immunohistochemical analysis with rabbit polyclonal antibodies against human CaN. In the STG, the density of CaN-IR neurons in layers II - VI in the group with schizophrenia was significantly higher than that in the control group. Our results confirmed pathological changes in the STG in patients with schizophrenia, suggesting that alterations in the CaN pathway play a role in the pathogenesis of schizophrenia.

CaMKII as a target for arrhythmia suppression

Calcium/calmodulin-dependent protein kinase II (CaMKII) has emerged as key enzyme in many cardiac pathologies, especially heart failure (HF), myocardial infarction and cardiomyopathies, thus leading to contractile dysfunction and malignant arrhythmias. While many pathways leading to CaMKII activation have been elucidated in recent years, hardly any clinically viable compounds affecting CaMKII activity have progressed from basic in vitro science to in vivo studies. This review focuses on recent advances in anti-arrhythmic strategies involving CaMKII. Specifically, both inhibition of CaMKII itself to prevent arrhythmias, as well as anti-arrhythmic approaches affecting CaMKII activity via alterations in signaling cascades upstream and downstream of CaMKII will be discussed.

The Effects of Insulin-Induced Hypoglycaemia on Tyrosine Hydroxylase Phosphorylation in Rat Brain and Adrenal Gland

In this study we investigated the effects of insulin-induced hypoglycaemia on tyrosine hydroxylase (TH) protein and TH phosphorylation in the adrenal gland, C1 cell group, locus coeruleus (LC) and midbrain dopaminergic cell groups that are thought to play a role in response to hypoglycaemia and compared the effects of different concentrations of insulin in rats. Insulin (1 and 10 U/kg) treatment caused similar reductions in blood glucose concentration (from 7.5-9 to 2-3 mmol/L); however, plasma adrenaline concentration was increased 20-30 fold in response to 10 U/kg insulin and only 14 fold following 1 U/kg. Time course studies (at 10 U/kg insulin) revealed that in the adrenal gland, Ser31 phosphorylation was increased between 30 and 90 min (4-5 fold), implying that TH was activated to increase catecholamine synthesis in adrenal medulla to replenish the stores. In the brain, Ser19 phosphorylation was limited to certain dopaminergic groups in the midbrain, while Ser31 phosphorylation was increased in most catecholaminergic regions at 60 min (1.3-2 fold), suggesting that Ser31 phosphorylation may be an important mechanism to maintain catecholamine synthesis in the brain. Comparing the effects of 1 and 10 U/kg insulin revealed that Ser31 phosphorylation was increased to similar extent in the adrenal gland and C1 cell group in response to both doses whereas Ser31 and Ser19 phosphorylation were only increased in response to 1 U/kg insulin in LC and in response to 10 U/kg insulin in most midbrain regions. Thus, the adrenal gland and some catecholaminergic brain regions become activated in response to insulin administration and brain catecholamines may be important for initiation of physiological defences against insulin-induced hypoglycaemia.

Camk2a-Cre-mediated conditional deletion of chromatin remodeler Brg1 causes perinatal hydrocephalus

Mammalian SWI/SNF-like BAF chromatin remodeling complexes are essential for many aspects of neural development. Mutations in the genes encoding the core subunit Brg1/SmarcA4 or other complex components cause neurodevelopmental diseases and are associated with autism. Congenital hydrocephalus is a serious brain disorder often experienced by these patients. We report a role of Brg1 in the pathogenesis of hydrocephalus disorder. We discovered an unexpected early activity of mouse Camk2a-Cre transgene, which mediates Brg1 deletion in a subset of forebrain neurons beginning in the late embryonic stage. Brg1 deletion in these neurons led to severe congenital hydrocephalus with enlargement of the lateral ventricles and attenuation of the cerebral cortex. The Brg1-deficient mice had significantly smaller subcommissural organs and narrower Sylvian aqueducts than mice that express normal levels of Brg1. Effects were non-cell autonomous and may be responsible for the development of the congenital hydrocephalus phenotype. Our study provides evidence indicating that abnormalities in Brg1 function result in defects associated with neurodevelopmental disorders and autism.

Role of CA2+/calmodulin on ethanol neurobehavioral effects

RATIONALE

The cAMP-dependent protein kinase A (PKA) signaling transduction pathway has been shown to play an important role in the modulation of several ethanol-induced behaviors. Different studies have demonstrated intracellular calcium (Ca(2+))-dependent activation of the PKA cascade after ethanol administration. Thus, the cAMP cascade mediator Ca(2+)-dependent calmodulin (CaM) has been strongly implicated in the central effects of ethanol.

OBJECTIVES

In this study, we assessed the role of the CaM inhibitor W7 on ethanol-induced stimulation, ethanol intake, and ethanol-induced activation of PKA.

METHODS

Swiss mice were pretreated with W7 (0-10 mg/kg) 30 min before ethanol (0-3.75 g/kg) administration. Immediately, animals were placed during 20 min in an open-field chamber. Ethanol (10 %, v/v) intake in 2 h was assessed using a limited access paradigm. Experiments with caffeine (0-15 mg/kg), cocaine (0-4 mg/kg), and saccharine (0.1 %, w/v) were designed to compare their results to those obtained with ethanol. Western blot was assayed 45 min after ethanol administration.

RESULTS

Results showed that pretreatment with W7, reduced selectively in a dose-dependent fashion ethanol-induced locomotor stimulation and ethanol intake. The ethanol-induced activation of PKA was also prevented by W7 administration.

CONCLUSIONS

These results demonstrate that CaM inhibition resulted in a selective reduction of ethanol-stimulating effects and ethanol intake. The PKA activation induced by ethanol was blocked after the CaM blockade with W7. These results provide further evidence of the key role of cellular Ca(2+)-dependent pathways on the central effects of ethanol.

Targeted deletion of the gene encoding the La autoantigen (Sjögren's syndrome antigen B) in B cells or the frontal brain causes extensive tissue loss

La antigen (Sjögren's syndrome antigen B) is a phosphoprotein associated with nascent precursor tRNAs and other RNAs, and it is targeted by autoantibodies in patients with Sjögren's syndrome, systemic lupus erythematosus, and neonatal lupus. Increased levels of La are associated with leukemias and other cancers, and various viruses usurp La to promote their replication. Yeast cells (Saccharomyces cerevisiae and Schizosaccharomyces pombe) genetically depleted of La grow and proliferate, whereas deletion from mice causes early embryonic lethality, raising the question of whether La is required by mammalian cells generally or only to surpass a developmental stage. We developed a conditional La allele and used it in mice that express Cre recombinase in either B cell progenitors or the forebrain. B cell Mb1(Cre) La-deleted mice produce no B cells. Consistent with αCamKII Cre, which induces deletion in hippocampal CA1 cells in the third postnatal week and later throughout the neocortex, brains develop normally in La-deleted mice until ∼5 weeks and then lose a large amount of forebrain cells and mass, with evidence of altered pre-tRNA processing. The data indicate that La is required not only in proliferating cells but also in nondividing postmitotic cells. Thus, La is essential in different cell types and required for normal development of various tissue types.

Neural functions of calcineurin in synaptic plasticity and memory

Major brain functions depend on neuronal processes that favor the plasticity of neuronal circuits while at the same time maintaining their stability. The mechanisms that regulate brain plasticity are complex and engage multiple cascades of molecular components that modulate synaptic efficacy. Protein kinases (PKs) and phosphatases (PPs) are among the most important of these components that act as positive and negative regulators of neuronal signaling and plasticity, respectively. In these cascades, the PP protein phosphatase 2B or calcineurin (CaN) is of particular interest because it is the only Ca(2+)-activated PP in the brain and a major regulator of key proteins essential for synaptic transmission and neuronal excitability. This review describes the primary properties of CaN and illustrates its functions and modes of action by focusing on several representative targets, in particular glutamate receptors, striatal enriched protein phosphatase (STEP), and neuromodulin (GAP43), and their functional significance for synaptic plasticity and memory.

Increased ratio of calcineurin immunoreactive neurons in the caudate nucleus of patients with schizophrenia

Calcineurin (CaN) has been investigated extensively in numerous biochemical, behavioral, and genetic studies in schizophrenia because its function is closely related to dopamine-glutamate signal transduction, which is thought to be associated with pathophysiological changes in schizophrenia. Although evidence has suggested that dysfunction of CaN may be a risk factor for schizophrenia, there have been few reports focusing on the expression of CaN mRNA and CaN protein levels in the brains of schizophrenic patients. In addition, findings on CaN expression in postmortem brains from patients with schizophrenia have been inconsistent. Here, we conducted immunohistochemical examinations of several regions in postmortem brains, including the dorsolateral prefrontal cortex (DLPFC), hippocampus, caudate nucleus, and putamen, using specific antibodies, and compared the results from the brains of nine schizophrenic subjects to nine age- and sex-matched control subjects. There was no significant difference in the ratio of CaN immunoreactive (IR) neurons between schizophrenia and control groups in the DLPFC or hippocampus, and a significantly increased ratio of CaN-IR neurons was seen in the caudate nucleus in the brains from schizophrenia patients. As the striatum contains most of the brain dopamine, the results of the present study have critical implications and suggest that alterations in CaN signaling in the caudate contribute to the pathogenesis of schizophrenia. This is the first report of caudate CaN abnormalities in schizophrenia.

NR2B-deficient mice are more sensitive to the locomotor stimulant and depressant effects of ethanol

The NR2B subunit of N-methyl d-aspartate glutamate receptors influences pharmacological properties and confers greater sensitivity to the modulatory effects of ethanol. This study examined behavioral responses to acute ethanol in a conditional knockout mouse model that allowed for a delayed genetic deletion of the NR2B subunit to avoid mouse lethality. Mice lacking the NR2B gene (knockout) were produced by mating NR2B[f/f] mice with CAMKIIa-driven tTA transgenic mice and the tetO-CRE transgenic mice. Adult male and female offspring representing each of the resultant genotypes (knockout, CAM, CRE and wildtype mice) were tested for open-field locomotor activity following acute low- and high-dose ethanol challenge as well as loss of righting reflex. Findings indicate that male and female mice lacking the NR2B subunit exhibited greater overall activity in comparison to other genotypes during the baseline locomotor activity test. NR2B knockout mice exhibited an exaggerated stimulant response to 1.5 g/kg (i.p.) and an exaggerated depressant response to 3.0 g/kg (i.p.) ethanol challenge. In addition, NR2B knockout mice slept longer following a high dose of ethanol (4.0 g/kg, i.p.). To evaluate pharmacokinetics, clearance rates of ethanol (1.5, 4.0 g/kg, i.p.) were measured and showed that female NR2B knockouts had a faster rate of metabolism only at the higher ethanol dose. Western blot analyses confirmed significant reduction in NR2B expression in the forebrain of knockout mice. Collectively, these data indicate that the NR2B subunit of the N-methyl d-aspartate glutamate receptor is involved in regulating low-dose stimulant effects of ethanol and the depressant/hypnotic effects of ethanol.

Psychostimulant Drugs and Neuroplasticity

Drugs of abuse induce plastic changes in the brain that seem to underlie addictive phenomena. These plastic changes can be structural (morphological) or synaptic (biochemical), and most of them take place in the mesolimbic and mesostriatal circuits. Several addiction-related changes in brain circuits (hypofrontality, sensitization, tolerance) as well as the outcome of treatment have been visualized in addicts to psychostimulants using neuroimaging techniques. Repeated exposure to psychostimulants induces morphological changes such as increase in the number of dendritic spines, changes in the morphology of dendritic spines, and altered cellular coupling through new gap junctions. Repeated exposure to psychostimulants also induces various synaptic adaptations, many of them related to sensitization and neuroplastic processes, that include up- or down-regulation of D1, D2 and D3 dopamine receptors, changes in subunits of G proteins, increased adenylyl cyclase activity, cyclic AMP and protein kinase A in the nucleus accumbens, increased tyrosine hydroxylase enzyme activity, increased calmodulin and activated CaMKII in the ventral tegmental area, and increased deltaFosB, c-Fos and AP-1 binding proteins. Most of these changes are transient, suggesting that more lasting plastic brain adaptations should take place. In this context, protein synthesis inhibitors block the development of sensitization to cocaine, indicating that rearrangement of neural networks must develop for the long-lasting plasticity required for addiction to occur. Self-administration studies indicate the importance of glutamate neurotransmission in neuroplastic changes underlying transition from use to abuse. Finally, plastic changes in the addicted brain are enhanced and aggravated by neuroinflammation and neurotrophic disbalance after repeated psychostimulants.

Modeling the impact of mitochondrial DNA damage in forebrain neurons and beyond

We have generated an inducible transgenic mouse model, which expresses a mutated version of UNG1 (mutUNG1) that removes thymine, in addition to uracil from mitochondrial DNA. The abasic-sites (AP-sites) generated by removal of thymine or uracil are a threat to genomic integrity, and are particularly harmful in mitochondria due to inhibition of mitochondrial DNA polymerase. MutUNG1, accompanied by a luciferase reporter-gene, is controlled by the Tet-on system. Transgene expression is spatially regulated by the forebrain specific CaMKIIα-promoter, and temporally by the addition of doxycycline. Mice harboring this transgene develop compromised mitochondrial dynamics, neurodegeneration and impaired behavior.

Zebrafish calcium/calmodulin-dependent protein kinase II (cam-kii) inhibitors: expression patterns and their roles in zebrafish brain development

Calcium/calmodulin-dependent protein kinase II (CaM-KII) plays a critical role in neuronal functions. In this report, we demonstrate the expression patterns, functional analysis, and development role of the two zebrafish CaM-KII inhibitors, cam-kiin1 and cam-kiin2. Both of these genes were detected in the 5-somite stage and are persistently expressed thereafter. The RNA transcripts of cam-kiin1 were prominently expressed in the forebrain and hindbrain regions, especially in the telencephalon, while cam-kiin2 was detected in the anterior brain region and neurons of the hindbrain. Through GST-pull down, co-immunoprecipitation, and kinase assay, cam-kii inhibitors can bind to and reduce cam-kiiα activity. However, no overt alternation of brain marker such as ngn1, otx2, and pax2.1 was observed in morphants received each one or combined MO. Our results suggest that the two cam-kii inhibitors exhibited distinct expression pattern and may play a minor role in zebrafish brain development.

Genetic and pharmacological inhibition of calcineurin corrects the BDNF transport defect in Huntington's disease

Background

Huntington's disease (HD) is an inherited neurogenerative disease caused by an abnormal expansion of glutamine repeats in the huntingtin protein. There is currently no treatment to prevent the neurodegeneration caused by this devastating disorder. Huntingtin has been shown to be a positive regulator of vesicular transport, particularly for neurotrophins such as brain-derived neurotrophic factor (BDNF). This function is lost in patients with HD, resulting in a decrease in neurotrophic support and subsequent neuronal death. One promising line of treatment is therefore the restoration of huntingtin function in BDNF transport.

Results

The phosphorylation of huntingtin at serine 421 (S421) restores its function in axonal transport. We therefore investigated whether inhibition of calcineurin, the bona fide huntingtin S421 phosphatase, restored the transport defects observed in HD. We found that pharmacological inhibition of calcineurin by FK506 led to sustained phosphorylation of mutant huntingtin at S421. FK506 restored BDNF transport in two complementary models: rat primary neuronal cultures expressing mutant huntingtin and mouse cortical neurons from Hdh^Q111/Q111 HD knock-in mice. This effect was the result of specific calcineurin inhibition, as calcineurin silencing restored both anterograde and retrograde transport in neurons from Hdh^Q111/Q111 mice. We also observed a specific increase in calcineurin activity in the brain of Hdh^Q111/Q111 mice potentially accounting for the selective loss of huntingtin phosphorylation and contributing to neuronal cell death in HD.

Conclusion

Our results validate calcineurin as a target for the treatment of HD and provide the first demonstration of the restoration of huntingtin function by an FDA-approved compound.

Neural activity regulates synaptic properties and dendritic structure in vivo through calcineurin/NFAT signaling

The calcium-regulated protein phosphatase Calcineurin (CaN) participates in synaptic plasticity and the regulation of transcription factors, including Nuclear Factor of Activated T cells (NFAT). To understand how CaN contributes to neuronal circuit development, whole-cell mEPSC recordings and multiphoton imaging were performed in the visual system of living Xenopus laevis tadpoles electroporated to express either a CaN phosphatase inhibitor or N-VIVIT, a nuclear localization sequence-tagged VIVIT peptide that blocks the binding of CaN to select substrates including NFAT. Both strategies increased mEPSC frequency and dendritic arbor complexity in tectal neurons over 3 days. Expression of either of two constitutively active Xenopus NFATs (CA-NFATs) restored normal synaptic properties in neurons expressing N-VIVIT. However, the morphological phenotype was only rescued by a CA-NFAT bearing an intact regulatory domain, implying that transcriptional control of morphological and electrophysiological properties of neurons is mediated by distinct NFAT interactions.

Novel strategy to selectively label excitatory and inhibitory neurons in the cerebral cortex of mice

Revealing the connections of neuronal systems is critical for understanding how they function. The vast majority of neurons in all cortical areas consist of excitatory cells whose activity is controlled by inhibitory cells. Distribution and projection patterns of inhibitory and excitatory cells are key information to understand the organization of the nervous system. To investigate axonal projections, we developed a method to uniquely distinguish excitatory axons from inhibitory ones in the cortex using transgenic mice expressing Cre recombinase in the Ca2+/calmodulin-dependent protein kinase IIalpha-containing neurons. These animals were injected by an adenoviral vector engineered so that it directs red fluorescent protein expression in non-Cre-expressing cells, and green fluorescent protein in Cre-positive neurons. We demonstrated in vitro and in vivo that GFP-expressing neurons are GABA-immunonegative (excitatory), while the RFP-expressing cells are either GABAergic neurons or glial cells. One week after the viral vector injection RFP and GFP signals overlapped in a subset of cells but after 1 month, the two signals showed total segregation. Six months post-inoculation, GFP-labelling was clearly visible in axons but RFP remained only in somata and proximal dendrites. This technique can thus be used to differentiate excitatory axonal projections from inhibitory ones, and represent a unique tool in neuronal circuit analysis.

Role for D-serine within the ventral tegmental area in the development of cocaine's sensitization

Repeated exposure to cocaine results in motor sensitization that, in the ventral tegmental area (VTA), is associated to enhanced glutamate release, which in turn leads to enhanced calcium levels in dopaminergic neurons. Calcium influx activates calcium-calmodulin-dependent protein kinases such as CaMKII. D-Serine could participate on these effects, and the objective was to discern the role of VTA D-serine after a sensitizing regimen of cocaine (10 mg/kg daily), and to discern consequent expression changes in CaMKII and its activated form. For this purpose, D-serine, sodium benzoate (inhibitor of D-amino acid oxidase, the degradating enzyme of D-serine), and 7-chlorokynurenate (inhibitor of the glycine site of NMDA receptors) were injected into the VTA (in either the induction or expression phase of sensitization), and activation state of CaMKII was assessed through blotting. The findings indicated that intra-VTA administration of D-serine (5 mM) and sodium benzoate (100 and 200 microg/microl) during the induction phase (not expression) reliably augmented the expression of behavioral sensitization to cocaine, providing evidence that D-serine in the VTA participates in the initiation of motor sensitization to this psychostimulant drug. Intra-VTA infusions of D-serine, sodium benzoate and 7-chlorokynurenate did not elicit a motor effect of their own. Confirming the important role of NMDA receptors and their activation at the glycine site, the employment of 7-chlorokynurenate (2 and 5 microg/microl) led to blocking of the development of sensitization to cocaine. CaMKII within the VTA was found to participate in D-serine's effects because this kinase, that is activated after repeated cocaine, was further activated after co-treatment with D-serine or sodium benzoate. Besides CaMKII activity was otherwise reduced by 7-chlorokynurenate.

Differential expression of members of the RCAN family of calcineurin regulators suggests selective functions for these proteins in the brain

RCANs, also called Down Syndrome Critical Region-1 (DSCR1)-like proteins, Modulatory Calcineurin Interacting Proteins (MCIPs) or calcipressins, are regulators of calcineurin, a Ca(2+)-dependent protein phosphatase involved in several neuronal functions. Despite the potential importance of the RCAN proteins in brain physiology, very little is known about their relative abundance and distribution patterns in the central nervous system. In this study we report the expression and distribution of RCAN mRNA transcripts and proteins in the mouse brain. RT-PCR and Western blot analysis showed that all Rcan mRNAs (Rcan1-1, Rcan1-2, Rcan2-1, Rcan2-3 and Rcan3) and their corresponding protein products (RCAN1-L, RCAN1-S, RCAN2-L, RCAN2-S and RCAN3) are present in every adult mouse brain region examined. All protein isoforms are also expressed in these same brain regions at early postnatal stages. Within regions, RCAN1-L, RCAN1-S, RCAN2-L and RCAN3 are differentially expressed depending on the region and developmental stage, whereas RCAN2-S is distributed homogeneously. Detailed immunohistochemical analysis revealed significant differences in the cellular and subcellular distributions of RCAN proteins. In the adult, RCAN1 was mainly expressed in the neuropil throughout the brain. Although at lower levels, RCAN3 was also detected throughout the neuropil. In contrast, RCAN2 was highly expressed in scattered neurons, in both the nucleus and the cytoplasm. Interestingly, RCAN2 is the only member of the RCAN family that was detected in glial cells. Finally, the expression patterns of RCANs at early postnatal stages differed from those of the adult, in different brain areas, in both their distributions and relative abundance, suggesting that the expression of these proteins could be regulated during neuronal differentiation. The nonoverlapping expression patterns of the RCAN proteins shown here highlight the existence of different physiological scenarios and therefore suggest different RCAN functional activities in the brain, depending on the cellular context and developmental stage.

Calcineurin (protein phosphatase 2B) is involved in the mechanisms of action of antidepressants

Calcineurin (PP2B) is a Ca(2+)-dependent protein phosphatase enriched in the brain that takes part in intracellular signaling pathways regulating synaptic plasticity and neuronal functions. Calcineurin-dependent pathways are important for complex brain functions such as learning and memory. More recently, they have been suggested to play a role in the processing of emotional information. The aim of this study was to investigate whether calcineurin may be involved in the effect of antidepressants. We first found that chronic antidepressant treatment in mice leads to an increase of calcineurin levels in the hippocampus. We then studied the behavioral and molecular responses to fluoxetine of mice with a genetic overactivation of calcineurin in the hippocampus (constitutively-activated calcineurin transgenic mouse line #98, CN98 mice). We observed that CN98 mice are more sensitive to the behavioral effect of fluoxetine and desipramine tested in the tail suspension test. Moreover, the basal expression of growth factor brain-derived neurotrophic factor and subunit 1 of AMPA glutamate receptor, GluR1, both of which are modified after chronic antidepressant administration, are altered in the hippocampus of CN98 mice. These results suggest that calcineurin-dependent dephosphorylation plays an important role in the mechanisms of action of antidepressants, providing a new starting point for developing improved therapeutic treatments for depression.

An endogenous inhibitor of calcium/calmodulin-dependent kinase II is up-regulated during consolidation of fear memory

CaMKIINalpha and CaMKIINbeta are endogenous inhibitors of the abundant synaptic protein, calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII exerts a prominent function in memory formation and the endogenous inhibitors might be important regulators of CaMKII activity during this process. Here we investigated whether or not CaMKIINalpha and CaMKIINbeta gene expressions are regulated in the mouse hippocampus and amygdala after background contextual fear conditioning. Quantitative real-time PCR revealed that the hippocampal expression of CaMKIINalpha mRNA was up-regulated 30 and 60 min after conditioning. In contrast, CaMKIINbeta mRNA expression did not change. The up-regulation of CaMKIINalpha expression was specific for the fear memory because the context alone and a shock control did not induce any variation of transcription level. Quantification of in situ hybridization signals showed that CaMKIINalpha expression increased in hippocampal area CA1, in the dentate gyrus (DG) and in the lateral amygdala (LA) 30 min after training. Our findings show an up-regulation in the expression of the endogenous inhibitor gene CaMKIINalpha during consolidation of fear memory. The early onset and the amplitude of the up-regulation are similar to those of immediate-early genes. Taken together, our results suggest that the CaMKIINalpha inhibitor has a physiological role in controlling CaMKII activity from an early stage of memory consolidation.

Corticotropin-releasing factor, vasopressin and receptor systems in depression and anxiety

Affective disorders tend to be chronic and life-threatening diseases: suicide is estimated to be the cause of death in 10-15% of individuals with major depressive disorders. Major depression is one of the most prevalent and costly brain diseases with up to 20% of the worldwide population suffering from moderate to severe forms of the disease. Only 50% of individuals with depression show full remission in response to currently available antidepressant drug therapies which are based on serendipitous discoveries made in the 1950s. Previously underestimated, other severe depression-associated deleterious health-related effects have increasingly been recognized. Epidemiological studies have provided substantial evidence that patients with depression have a 2-4-fold increased risk both of developing cardiovascular disease and of mortality after experiencing a myocardial infarction. The majority of patients suffering from affective disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have increasingly been translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) and vasopressin (AVP) system elements. The cumulative evidence makes a strong case implicating dysfunction of these systems in the etiology and pathogenesis of depression and pathological anxiety. Translation of these advances into novel therapeutic strategies has already been started.

Differential expression of calcineurin A subunit mRNA isoforms during rat hippocampal and cerebellar development

Calcineurin (protein phosphatase 2B) is a calcium-dependent serine-threonine phosphatase. It has diverse roles and is centrally involved in synaptic plasticity. The catalytic A subunit of calcineurin has three isoforms, alpha, beta and gamma. Their expression and ontogeny in the brain has not been systematically investigated; such data become important with a report that PPP3CC, the gene encoding calcineurin Agamma, is a susceptibility gene for schizophrenia, and the finding that its expression is decreased in the disorder. We used in situ hybridization histochemistry to measure the relative transcript abundance of calcineurin Agamma and the other catalytic isoforms, Aalpha and Abeta, during development of the Sprague-Dawley rat hippocampus and cerebellum. All three isoforms are present in both regions at all time points [embryonic day 19 (E19) to postnatal day 42 (P42)] and undergo developmental regulation, but differ in their ontogenic profile. Calcineurin Aalpha and Abeta mRNAs increased from E19 through to adulthood, whereas Agamma mRNA was most highly expressed during early developmental stages. Calcineurin Aalpha and Abeta mRNAs positively correlated with synaptophysin mRNA (a synaptic marker), whilst Agamma mRNA was either unrelated to, or negatively correlated, with this transcript. These data confirm that all three calcineurin A subunits are expressed in the rodent brain, and indicate that calcineurin Agamma may have different roles than Aalpha and Abeta. The data also suggest a potential importance of calcineurin Agamma in neurodevelopment, and in the genetically influenced neurodevelopmental disturbance that is thought to underlie schizophrenia.

Inducible neuronal expression of transgenic TGF-β1in vivo: dissection of short-term and long-term effects

Various chronic neurological diseases are associated with increased expression of transforming growth factor-beta1 (TGF-beta1) in the brain. TGF-beta1 has both neuroprotective and neurodegenerative functions, depending on conditions such as duration and the local and temporal pattern of its expression. Previous transgenic approaches did not enable control for these dynamic aspects. To overcome these limitations, we established a transgenic mouse model with inducible neuron-specific expression of TGF-beta1 based on the tetracycline-regulated gene expression system. TGF-beta1 expression was restricted to the brain where it was particularly pronounced in the neocortex, hippocampus and striatum. Transgene expression was highly sensitive to the presence of doxycycline and completely silenced within 6 days after doxycycline application. After long-term expression, perivascular thioflavin-positive depositions, formed by amyloid fibrils, developed. These depositions persisted even after prolonged silencing of the transgene, indicating an irreversible process. Similarly, strong perivascular apolipoprotein E (ApoE) depositions were found after TGF-beta1 expression and these remained despite TGF-beta1 removal. These in vivo observations suggests that the continuous presence of TGF-beta1 as initial trigger is not necessary for the persistence and development of chronic lesions. Neuroprotective effects were observed after short-term expression of TGF-beta1. Death of striatal neurons induced by 3-nitropropionic acid was markedly reduced after induced TGF-beta1 expression.

Decreased hippocampal expression of the susceptibility gene PPP3CC and other calcineurin subunits in schizophrenia

BACKGROUND

Calcineurin (CaN) is a phosphatase involved in synaptic plasticity. A haplotype of the PPP3CC gene, which encodes the gamma isoform of the catalytic subunit (CaN A), has been associated with schizophrenia. However, the distribution of CaN A gamma is not established, nor whether its expression changes in schizophrenia.

METHODS

CaN A expression was analyzed in the hippocampal formation of 13 patients with schizophrenia and 12 controls. All three isoforms were examined, using in situ hybridization histochemistry, RT-PCR, and laser-assisted microdissection. CaN A protein was assessed using ELISA and immunohistochemistry. CaN A mRNAs were also measured in rats treated with haloperidol or chlorpromazine.

RESULTS

CaN was prominent in excitatory neurons. CaN A alpha and A beta isoforms were abundant in all subfields, but CaN A gamma was not reliably detected in CA1. CaN A protein, and all three mRNAs, were decreased in schizophrenia. The mRNA reductions were present in all subfields measured, except CA1. CaN A mRNAs were unaltered in the antipsychotic-treated rats.

CONCLUSIONS

Decreased CaN expression extends the evidence for aberrant hippocampal synaptic plasticity in schizophrenia, which particularly affects glutamatergic transmission, and which leaves CA1 relatively unaffected. Reduced expression of PPP3CC may underlie its genetic involvement in the disorder.

Listening to mutant mice: a spotlight on the role of CRF/CRF receptor systems in affective disorders

Genetically engineered mice were originally generated to delineate the role of a specific gene product in behavioral or neuroendocrine phenotypes, rather than to produce classic animal models of depression. To learn more about the neurobiological mechanisms underlying a clinical condition such as depression, it has proven worthwhile to investigate changes in behaviors characteristic of depressed humans, such as anxiety, regardless of whether or not these alterations may also occur in other disorders besides depression. The majority of patients with mood and anxiety disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have been increasingly translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) system elements (e.g. CRF and CRF-related peptides, their receptors, binding protein). Studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of these systems in the pathogenesis of depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies for depression.

Inducible and neuron-specific gene expression in the adult mouse brain with the rtTA2S-M2 system

To achieve inducible and reversible gene expression in the adult mouse brain, we exploited an improved version of the tetracycline-controlled transactivator-based system (rtTA2(S)-M2, rtTA2 hereafter) and combined it with the forebrain-specific CaMKIIalpha promoter. Several independent lines of transgenic mice carrying the CaMKIIalpha promoter-rtTA2 gene were generated and examined for anatomical profile, doxycycline (dox)-dependence, time course, and reversibility of gene expression using several lacZ reporter lines. In two independent rtTA2-expressing lines, dox-treatment in the diet induced lacZ reporter expression in neurons of several forebrain structures including cortex, striatum, hippocampus, amygdala, and olfactory bulb. Gene expression was dose-dependent and was fully reversible. Further, a similar pattern of expression was obtained in three independent reporter lines, indicating the consistency of gene expression. Transgene expression could also be activated in the developing brain (P0) by dox-treatment of gestating females. These new rtTA2-expressing mice allowing inducible and reversible gene expression in the adult or developing forebrain represent useful models for future genetic studies of brain functions.

Calcineurin in memory and bidirectional plasticity

The molecular mechanisms of learning and memory, and the underlying bidirectional changes in synaptic plasticity that sustain them largely implicate protein kinases and phosphatases. Specifically, Ca(2+)-dependent kinases and phosphatases actively control neuronal processing by forming a tightly regulated balance in which they oppose each other. In this balance, calcineurin (PP2B) is a critical protein phosphatase whose main function is to negatively modulate learning, memory, and plasticity. It acts by dephosphorylating numerous substrates in different neuronal compartments. This review outlines some of CN neuronal targets and their implication in synaptic functions, and describes the role of CN in the acquisition, storage, retrieval, and extinction of memory, as well as in bidirectional plasticity.

Suppressing calcium/calmodulin-dependent protein kinase II activity in the ventral tegmental area enhances the acute behavioural response to cocaine but attenuates the initiation of cocaine-induced behavioural sensitization in rats

In the present experiments we administered an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist (CNQX), N-methyl-D-aspartate (NMDA) receptor antagonist (AP-5), or l-type calcium channel blocker (diltiazem) directly into the ventral tegmental area (VTA) before each of four daily systemic cocaine injections in order to assess their influence on the initiation phase of behavioural sensitization. Results indicated that pretreatment with CNQX or AP-5 impaired the initiation of cocaine-induced behavioural sensitization. Intra-VTA administration of diltiazem significantly increased the behavioural activation induced by an acute cocaine injection, but impaired the development of cocaine-induced behavioural sensitization. Because AMPA and NMDA receptors, as well as l-type calcium channels are calcium permeable, we also investigated the role of the calcium-activated second messenger calcium/calmodulin-dependent protein kinase II (CaM-KII). Similar to the results obtained with diltiazem, administration of the CaM-KII inhibitor KN-93 into the VTA enhanced the acute behavioural response to cocaine but prevented the augmentation of cocaine-induced behavioural hyperactivity following repeated injections. Consistent with this finding, the behavioural hyperactivity produced by cocaine was markedly enhanced among homozygous alpha-CaM-KII knockout mice but the initiation of behavioural sensitization to cocaine was attenuated relative to wild-type mice. Separate experiments performed in rats demonstrated an increase in total protein levels of CaM-KII in the VTA 24 h after the last of seven daily injections of cocaine. Taken together, these results indicate that blocking l-type calcium channels or impairing CaM-KII activity in the VTA augments the acute behavioural hyperactivity induced by cocaine. The present findings also suggest that increased calcium influx through AMPA receptors, NMDA receptors and l-type calcium channels on dopaminergic neurons in the VTA contributes significantly to the initiation of behavioural sensitization by amplifying calcium signalling through CaM-KII.

Fkbp8: novel isoforms, genomic organization, and characterization of a forebrain promoter in transgenic mice

The immunophilin homolog FKBP8 has been implicated in the regulation of apoptosis. Here we show that the 38-kDa form of FKBP8 (FKBP38) derives from a truncated ORF. The extended FKBP8 ORFs are 46 and 44 kDa in mouse and 45 kDa in human. Although the genomic organization of mouse and human FKBP8 is evolutionarily conserved, additional first exons are encoded by the murine locus. A 4.4-kb murine Fkbp8 gene fragment, containing a GC-rich potential promoter, directed expression of a LacZ reporter gene to forebrain neurons in transgenic mice. Expression of the transgene was observed in CA1 pyramidal neurons of the hippocampus in transgenic mice from three lines. One transgenic founder mouse exhibited widespread forebrain expression of the LacZ transgene that resembles the pattern for the endogenous Fkbp8 gene. Thus promoter/enhancer elements for forebrain expression are located around the first exons of the mouse Fkbp8 gene.

Limbic corticotropin-releasing hormone receptor 1 mediates anxiety-related behavior and hormonal adaptation to stress

Corticotropin-releasing hormone (CRH) is centrally involved in coordinating responses to a variety of stress-associated stimuli. Recent clinical data implicate CRH in the pathophysiology of human affective disorders. To differentiate the CNS pathways involving CRH and CRH receptor 1 (Crhr1) that modulate behavior from those that regulate neuroendocrine function, we generated a conditional knockout mouse line (Crhr1(loxP/loxP)Camk2a-cre) in which Crhr1 function is inactivated postnatally in anterior forebrain and limbic brain structures, but not in the pituitary. This leaves the hypothalamic-pituitary-adrenocortical (HPA) system intact. Crhr1(loxP/loxP)Camk2a-cre mutants showed reduced anxiety, and the basal activity of their HPA system was normal. In contrast to Crhr1 null mutants, conditional mutants were hypersensitive to stress corticotropin and corticosterone levels remained significantly elevated after stress. Our data clearly show that limbic Crhr1 modulates anxiety-related behavior and that this effect is independent of HPA system function. Furthermore, we provide evidence for a new role of limbic Crhr1 in neuroendocrine adaptation to stress.

Evidence for functionally distinct synaptic NMDA receptors in ventromedial versus dorsolateral striatum

N-methyl-D-aspartate receptors (NMDARs) are comprised of different subunits. NR2 subunits confer different pharmacological and biophysical properties to NMDARs. Although NR2B subunit expression is uniform throughout striatum, NR2A subunit expression is greater laterally. Pharmacologically isolated NMDAR-mediated excitatory postsynaptic currents (NMDAR-EPSCs) were elicited using minimal local stimulation and recorded in the whole cell configuration to test the hypothesis that biophysical and pharmacological properties of NMDAR-EPSCs of striatal neurons would vary as a function of their location in adult rat striatum. We observed that the decay-time kinetics of NMDAR-EPSCs are significantly slower in neurons of ventromedial versus dorsolateral striatum. Whereas ifenprodil did not differentially affect NMDAR-EPSCs in these regions, application of either glycine or D-serine increased the peak current of NMDAR-EPSCs selectively in dorsolateral striatum. These data provide evidence for functionally distinct NMDARs in the same neuron type in the same brain region of the adult rodent brain. These data thus suggest that the nature of synaptic processing of excitatory input is different in the ventromedial and dorsolateral striatum of the adult rodent brain, regions differentially involved in limbic versus sensorimotor processes, respectively.

A CamKIIalpha iCre BAC allows brain-specific gene inactivation

We describe the generation of transgenic mouse lines expressing the Cre recombinase enzyme in brain under control of the CamKIIalpha gene present in a BAC expression vector. The CamKIIalpha BAC transgene gave a faithful expression pattern resembling the pattern of the endogenous CamKIIalpha gene. Specifically, high levels of CamKIIalpha Cre were detected in hippocampus, cortex, and amygdala, and lower levels were detected in striatum, thalamus, and hypothalamus. As expected, no expression was detected in the cerebellum or outside of the brain. The expression level of the BAC CamKIIalpha driven Cre was shown to be copy number dependent. To test the activity of the Cre recombinase, the transgenic mice were crossed with mice harbouring the CREB (cAMP response element binding protein) allele with the 10th exon flanked by two loxP sites, and recombination was monitored by the disappearance of the CREB protein. Finally, evaluation of the developmental postnatal expression of the CamKIIalpha Cre BAC revealed the expression of the Cre recombinase as early as P3.

Cerebellar long-term depression: characterization, signal transduction, and functional roles

Cerebellar Purkinje cells exhibit a unique type of synaptic plasticity, namely, long-term depression (LTD). When two inputs to a Purkinje cell, one from a climbing fiber and the other from a set of granule cell axons, are repeatedly associated, the input efficacy of the granule cell axons in exciting the Purkinje cell is persistently depressed. Section I of this review briefly describes the history of research around LTD, and section II specifies physiological characteristics of LTD. Sections III and IV then review the massive data accumulated during the past two decades, which have revealed complex networks of signal transduction underlying LTD. Section III deals with a variety of first messengers, receptors, ion channels, transporters, G proteins, and phospholipases. Section IV covers second messengers, protein kinases, phosphatases and other elements, eventually leading to inactivation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolone-propionate-selective glutamate receptors that mediate granule cell-to-Purkinje cell transmission. Section V defines roles of LTD in the light of the microcomplex concept of the cerebellum as functionally eliminating those synaptic connections associated with errors during repeated exercises, while preserving other connections leading to the successful execution of movements. Section VI examines the validity of this microcomplex concept based on the data collected from recent numerous studies of various forms of motor learning in ocular reflexes, eye-blink conditioning, posture, locomotion, and hand/arm movements. Section VII emphasizes the importance of integrating studies on LTD and learning and raises future possibilities of extending cerebellar research to reveal memory mechanisms of implicit learning in general.

A significant increase in both basal and maximal calcineurin activity in the rat pilocarpine model of status epilepticus

This study focused on the effects of status epilepticus on the activity of calcineurin, a neuronally enriched, calcium-dependent phosphatase. Calcineurin is an important modulator of many neuronal processes, including learning and memory, induction of apoptosis, receptor function and neuronal excitability. Therefore, a status epilepticus-induced alteration of the activity of this important phosphatase would have significant physiological implications. Status epilepticus was induced by pilocarpine injection and allowed to continue for 60 min. Brain region homogenates were then assayed for calcineurin activity by dephosphorylation of p-nitrophenol phosphate. A significant status epilepticus-dependent increase in both basal and Mn(2+)-dependent calcineurin activity was observed in homogenates isolated from the cortex and hippocampus, but not the cerebellum. This increase was resistant to 150 nM okadaic acid, but sensitive to 50 microM okadaic acid. The increase in basal activity was also resistant to 100 microM sodium orthovanadate. Both maximal dephosphorylation rate and substrate affinity were increased following status epilepticus. However, the increase in calcineurin activity was not found to be due to an increase in calcineurin enzyme levels. Finally, increase in calcineurin activity was found to be NMDA-receptor activation dependent. The data demonstrate that status epilepticus resulted in a significant increase in both basal and maximal calcineurin activity.

Calcium/calmodulin-dependent protein kinase II inhibitor protein: localization of isoforms in rat brain

A second isoform of Ca2+/calmodulin-dependent-kinase II inhibitor protein (CaM-KIIN) has been identified using the yeast two-hybrid screen. The 1.8kb message encodes a 78 residue CaM-KIINalpha that is 65% identical in its putative open-reading frame and 95% identical in its inhibitory domain to the previously characterized CaM-KIINbeta. CaM-KIINalpha exhibits inhibitory properties towards recombinant mouse CaM-kinase IIalpha indistinguishable from CaM-KIINbeta. The 27 amino acid inhibitory peptide (CaM-KIINtide) derived from CaM-KIIN has the ability to inhibit brain CaM-kinase II activity from multiple organisms including rat, Drosophila and goldfish. Northern analysis of various rat tissues indicates that CaM-KIINalpha is specific to brain whereas CaM-KIINbeta message is also present in testis. In situ hybridization shows a general distribution of both isoforms in rat brain with stronger localization of CaM-KIINbeta in cerebellum and hindbrain and CaM-KIINalpha in frontal cortex, hippocampus and inferior colliculus. An antibody that recognizes both isoforms shows a distribution of CaM-KIIN in rat brain that correlates with immunoreactivity of CaM-kinase II. In cultured mature hippocampal neurons, CaM-KIIN is present in cell bodies and dendrites but, unlike CaM-kinase II, does not display punctate staining at synapses. These results suggest a localized function for CaM-KIIN in inhibiting specialized pools of CaM-kinase II.

Expression of ZAKI-4 messenger ribonucleic acid in the brain during rat development and the effect of hypothyroidism

We identified ZAKI-4 (also designated as DSCR1L1) as a thyroid hormone responsive gene in cultured human skin fibroblasts. Recently it has been reported that ZAKI-4 belongs to an evolutionary conserved family of proteins that function as calcineurin inhibitor. In human, ZAKI-4 and calcineurin are highly expressed in brain, where thyroid hormones play essential roles in the development during fetal and neonatal periods. In the present study, we examined the temporal and spatial expression patterns of ZAKI-4 messenger RNA (mRNA) in control and hypothyroid rat brains. Northern blot analysis revealed that ZAKI-4 mRNA was detected in both cerebral cortex and cerebellum as early as embryonic day (E)18. In the cerebral cortex, the expression level gradually increased with age, reaching a plateau at postnatal day (P)7 and remained constant thereafter until P30. A similar pattern of increase with age was also observed in hypothyroid rats; however, the magnitude of the increase was significantly reduced. In control rats, the fold increase in ZAKI-4 mRNA level from E18 to P17 was 10.8; whereas in hypothyroid rats, it was 7.4. In cerebellum the expression level did not change with age or by thyroid status. In situ hybridization revealed that ZAKI-4 mRNA is widely expressed in neurons throughout the brain. It is noteworthy that the expression in the neurons of layer VI of the cerebral cortex was more evident in control rats than that in hypothyroid rats from P17 to P30. Though not influenced by hypothyroidism, there were several regions of the brain in which ZAKI-4 mRNA was strongly expressed. These regions were the mitral cell layer of the olfactory bulb, the substantia nigra, and the hippocampus, where calcineurin is also abundantly expressed. Therefore, it may be hypothesized that ZAKI-4 plays an important role in the development and function of the brain by modulating calcineurin function; and decrease in ZAKI-4 mRNA expression in the specific brain areas may explain, in some parts, the mechanism of abnormal brain development by hypothyroidism.

Dscr1, a novel endogenous inhibitor of calcineurin signaling, is expressed in the primitive ventricle of the heart and during neurogenesis

We have demonstrated that DSCR1 acts as a negative regulator of calcineurin-mediated signaling and that its transcript is overexpressed in the Down syndrome (DS) fetal brain. To evaluate the possible involvement of DSCR1 in DS, we have cloned the mouse gene and analyzed its expression pattern in the central nervous system (CNS). Early expression of Dscr1 is detected mainly in the heart tube and in the CNS in rhombomere 4 and the pretectum. From embryonic day 14.5 onwards, Dscr1 is widely distributed in the CNS but becomes more restricted as the brain matures. We confirmed its neuronal expression pattern in the adult, preferentially in Purkinje and pyramidal cells, by double labeling with glial fibrillary acidic protein. We also show that although Dscr1 is present in trisomy in the Ts65Dn mouse, the adult brain expression pattern is not significantly altered. This expression pattern indicated that Dscr1 is a developmentally regulated gene involved in neurogenesis and cardiogenesis and suggests that it may contribute to the alterations observed in these organ systems in DS patients.