Integrated regulation of PKA by fast and slow neurotransmission in the nucleus accumbens controls plasticity and stress responses.

Cortical glutamate and midbrain dopamine neurotransmission converge to mediate striatum-dependent behaviors, while maladaptations in striatal circuitry contribute to mental disorders. However, the crosstalk between glutamate and dopamine signaling has not been entirely elucidated. Here we uncover a molecular mechanism by which glutamatergic and dopaminergic signaling integrate to regulate cAMP-dependent protein kinase (PKA) via phosphorylation of the PKA regulatory subunit, RIIß. Using a combination of biochemical, pharmacological, neurophysiological, and behavioral approaches, we find that glutamate-dependent reduction in cyclin-dependent kinase 5 (Cdk5)-dependent RIIß phosphorylation alters the PKA holoenzyme autoinhibitory state to increase PKA signaling in response to dopamine. Furthermore, we show that disruption of RIIß phosphorylation by Cdk5 enhances cortico-ventral striatal synaptic plasticity. In addition, we demonstrate that acute and chronic stress in rats inversely modulate RIIß phosphorylation and ventral striatal infusion of a small interfering peptide that selectively targets RIIß regulation by Cdk5 improves behavioral response to stress. We propose this new signaling mechanism integrating ventral striatal glutamate and dopamine neurotransmission is important to brain function, may contribute to neuropsychiatric conditions, and serves as a possible target for the development of novel therapeutics for stress-related disorders.

Autoimmune encephalitis: proposed recommendations for symptomatic and long-term management.

The objective of this paper is to evaluate available evidence for each step in autoimmune encephalitis management and provide expert opinion when evidence is lacking. The paper approaches autoimmune encephalitis as a broad category rather than focusing on individual antibody syndromes. Core authors from the Autoimmune Encephalitis Alliance Clinicians Network reviewed literature and developed the first draft. Where evidence was lacking or controversial, an electronic survey was distributed to all members to solicit individual responses. Sixty-eight members from 17 countries answered the survey. The most popular bridging therapy was oral prednisone taper chosen by 38% of responders while rituximab was the most popular maintenance therapy chosen by 46%. Most responders considered maintenance immunosuppression after a second relapse in patients with neuronal surface antibodies (70%) or seronegative autoimmune encephalitis (61%) as opposed to those with onconeuronal antibodies (29%). Most responders opted to cancer screening for 4 years in patients with neuronal surface antibodies (49%) or limbic encephalitis (46%) as opposed to non-limbic seronegative autoimmune encephalitis (36%). Detailed survey results are presented in the manuscript and a summary of the diagnostic and therapeutic recommendations is presented at the conclusion.

Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management.

The objective of this paper is to evaluate available evidence for each step in autoimmune encephalitis management and provide expert opinion when evidence is lacking. The paper approaches autoimmune encephalitis as a broad category rather than focusing on individual antibody syndromes. Core authors from the Autoimmune Encephalitis Alliance Clinicians Network reviewed literature and developed the first draft. Where evidence was lacking or controversial, an electronic survey was distributed to all members to solicit individual responses. Sixty-eight members from 17 countries answered the survey. Corticosteroids alone or combined with other agents (intravenous IG or plasmapheresis) were selected as a first-line therapy by 84% of responders for patients with a general presentation, 74% for patients presenting with faciobrachial dystonic seizures, 63% for NMDAR-IgG encephalitis and 48.5% for classical paraneoplastic encephalitis. Half the responders indicated they would add a second-line agent only if there was no response to more than one first-line agent, 32% indicated adding a second-line agent if there was no response to one first-line agent, while only 15% indicated using a second-line agent in all patients. As for the preferred second-line agent, 80% of responders chose rituximab while only 10% chose cyclophosphamide in a clinical scenario with unknown antibodies. Detailed survey results are presented in the manuscript and a summary of the diagnostic and therapeutic recommendations is presented at the conclusion.

Biological and Psychological Factors Determining Neuropsychiatric Outcomes in COVID-19.

PURPOSE OF REVIEW: We present biological and psychological factors implicated in psychiatric manifestations of SARS-CoV-2, as well as its neuroinvasive capability and immune pathophysiology. RECENT FINDINGS: Preexisting mental illness leads to worse clinical outcomes in COVID-19. The presence of the virus was reported in the cerebrospinal fluid (CSF) and brain tissue post-mortem. Most common psychiatric manifestations include delirium, mood disorders, anxiety disorders, and posttraumatic stress disorder. "Long-COVID" non-syndromal presentations include "brain-fogginess," autonomic instability, fatigue, and insomnia. SARS-CoV-2 infection can trigger prior vulnerabilities based on the priming of microglia and other cells, induced or perpetuated by aging and mental and physical illnesses. COVID-19 could further induce priming of neuroimmunological substrates leading to exacerbated immune response and autoimmunity targeting structures in the central nervous system (CNS), in response to minor immune activating environmental exposures, including stress, minor infections, allergens, pollutants, and traumatic brain injury.

Local Protein Translation and RNA Processing of Synaptic Proteins in Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a heritable neurodevelopmental condition associated with impairments in social interaction, communication and repetitive behaviors. While the underlying disease mechanisms remain to be fully elucidated, dysfunction of neuronal plasticity and local translation control have emerged as key points of interest. Translation of mRNAs for critical synaptic proteins are negatively regulated by Fragile X mental retardation protein (FMRP), which is lost in the most common single-gene disorder associated with ASD. Numerous studies have shown that mRNA transport, RNA metabolism, and translation of synaptic proteins are important for neuronal health, synaptic plasticity, and learning and memory. Accordingly, dysfunction of these mechanisms may contribute to the abnormal brain function observed in individuals with autism spectrum disorder (ASD). In this review, we summarize recent studies about local translation and mRNA processing of synaptic proteins and discuss how perturbations of these processes may be related to the pathophysiology of ASD.

Anti-NMDAR Encephalitis: A Multidisciplinary Approach to Identification of the Disorder and Management of Psychiatric Symptoms.

BACKGROUND: The novelty of anti-NMDA receptor encephalitis, for which somatic treatments have only recently been developed, has led to a lack of information on assessment and treatment of its variable behavioral manifestations. METHOD: In this article, we discuss 4 challenging cases of anti-NMDAR encephalitis, focusing on the importance of a multidisciplinary approach to identification and management of the disorder and the necessity of close collaboration in the acute hospital setting for management of the behavioral symptoms. CONCLUSION: The cases we discuss highlight some of the medication and nonpharmacologic treatment strategies that may facilitate management of psychiatric symptoms, both while the medical workup is ongoing and after the diagnosis has been confirmed.

Regulation of ERK Kinase by MEK1 Kinase Inhibition in the Brain.

Metabotropic (slow) and ionotropic (fast) neurotransmission are integrated by intracellular signal transduction mechanisms involving protein phosphorylation/dephosphorylation to achieve experience-dependent alterations in brain circuitry. ERK is an important effector of both slow and fast forms of neurotransmission and has been implicated in normal brain function and CNS diseases. Here we characterize phosphorylation of the ERK-activating protein kinase MEK1 by Cdk5, ERK, and Cdk1 in vitro in intact mouse brain tissue and in the context of an animal behavioral paradigm of stress. Cdk5 only phosphorylates Thr-292, whereas ERK and Cdk1 phosphorylate both Thr-292 and Thr-286 MEK1. These sites interact in a kinase-specific manner and inhibit the ability of MEK1 to activate ERK. Thr-292 and Thr-286 MEK1 are phosphorylated in most mouse brain regions to stoichiometries of ~5% or less. Phosphorylation of Thr-292 MEK1 is regulated by cAMP-dependent signaling in mouse striatum in a manner consistent with negative feedback inhibition in response to ERK activation. Protein phosphatase 1 and 2A contribute to the maintenance of the basal phosphorylation state of both Thr-292 and Thr-286 MEK1 and that of ERK. Activation of the NMDA class of ionotropic glutamate receptors reduces inhibitory MEK1 phosphorylation, whereas forced swim, a paradigm of acute stress, attenuates Thr-292 MEK1 phosphorylation. Together, the data indicate that these inhibitory MEK1 sites phosphorylated by Cdk5 and ERK1 serve as mechanistic points of convergence for the regulation of ERK signaling by both slow and fast neurotransmission.

Autoimmune encephalitis and its relation to infection.

Encephalitis, an inflammatory condition of the brain that results in substantial morbidity and mortality, has numerous causes. Over the past decade, it has become increasingly recognized that autoimmune conditions contribute significantly to the spectrum of encephalitis causes. Clinical suspicion and early diagnosis of autoimmune etiologies are of particular importance due to the need for early institution of immune suppressive therapies to improve outcome. Emerging clinical observations suggest that the most commonly recognized cause of antibody-mediated autoimmune encephalitis, anti-N-methyl-D-aspartate (NMDA) receptor encephalitis, may in some cases be triggered by herpes virus infection. Other conditions such as Rasmussen's encephalitis (RE) and febrile infection-related epilepsy syndrome (FIRES) have also been posited to be autoimmune conditions triggered by infectious agents. This review focuses on emerging concepts in central nervous system autoimmunity and addresses clinical and mechanistic findings linking autoimmune encephalitis and infections. Particular consideration will be given to anti-NMDA receptor encephalitis and its relation to herpes simplex encephalitis.

Regulation of NMDA Receptor Signaling at Single Synapses by Human Anti-NMDA Receptor Antibodies.

The NMDA receptor (NMDAR) subunit GluN1 is critical for receptor function and plays a pivotal role in synaptic plasticity. Mounting evidence has shown that pathogenic autoantibody targeting of the GluN1 subunit of NMDARs, as in anti-NMDAR encephalitis, leads to altered NMDAR trafficking and synaptic localization. However, the underlying signaling pathways affected by antibodies targeting the NMDAR remain to be fully delineated. It remains unclear whether patient antibodies influence synaptic transmission via direct effects on NMDAR channel function. Here, we show using short-term incubation that GluN1 antibodies derived from patients with anti-NMDAR encephalitis label synapses in mature hippocampal primary neuron culture. Miniature spontaneous calcium transients (mSCaTs) mediated via NMDARs at synaptic spines are not altered in pathogenic GluN1 antibody exposed conditions. Unexpectedly, spine-based and cell-based analyses yielded distinct results. In addition, we show that calcium does not accumulate in neuronal spines following brief exposure to pathogenic GluN1 antibodies. Together, these findings show that pathogenic antibodies targeting NMDARs, under these specific conditions, do not alter synaptic calcium influx following neurotransmitter release. This represents a novel investigation of the molecular effects of anti-NMDAR antibodies associated with autoimmune encephalitis.

Role of responsive neurostimulation and immunotherapy in refractory epilepsy due to autoimmune encephalitis: A case report.

Autoimmune encephalitis (AE) frequently presents with seizures in the acute setting. Seizures are often refractory to anti-seizure medications (ASM) but have been shown to be responsive to immunomodulatory therapies. A subset of patients with AE continues to have refractory epilepsy, recently named "autoimmune-associated epilepsy (AAE)," for years after the acute AE presentation. Optimal treatment for AAE has not been determined. Furthermore, the efficacy of neuromodulation and immunotherapy has not been well established in AAE. Here, we report a patient with probable autoantibody negative AE who initially presented with new onset refractory status epilepticus (NORSE). After his acute presentation, he continued to have frequent seizures that were refractory to four ASMs at therapeutic doses. A responsive neurostimulation (RNS®, NeuroPace) system was implanted for diagnostic and therapeutic purposes, with minimal change in seizure frequency. Due to continued frequent seizures despite ASMs and neurostimulation, he underwent a trial of immunotherapy consisting of high-dose intravenous (IV) corticosteroids and intravenous immunoglobulin (IVIG). Despite the addition of immunotherapy to his treatment regimen, the patient experienced no significant clinical or electrographic change in seizure frequency. This case does not support the use of immunotherapy for treatment of AAE and illustrates the need for consensus guidelines in the management of patients with AAE. Further, the use of electrocorticography (ECoG) data provided an objective surrogate measure of seizure frequency; this may support the role for early neuromodulation in the management of AAE.

Cdk5 is essential for adult hippocampal neurogenesis.

The molecular factors regulating adult neurogenesis must be understood to harness the therapeutic potential of neuronal stem cells. Although cyclin-dependent kinase 5 (Cdk5) plays a critical role in embryonic corticogenesis, its function in adult neurogenesis is unknown. Here, we assessed the role of Cdk5 in the generation of dentate gyrus (DG) granule cell neurons in adult mice. Cre recombinase-mediated conditional knockout (KO) of Cdk5 from stem cells and their progeny in the DG subgranular zone (SGZ) prevented maturation of new neurons. In addition, selective KO of Cdk5 from mature neurons throughout the hippocampus reduced the number of immature neurons. Furthermore, Cdk5 gene deletion specifically from DG granule neurons via viral-mediated gene transfer also resulted in fewer immature neurons. In each case, the total number of proliferating cells was unaffected, indicating that Cdk5 is necessary for progression of adult-generated neurons to maturity. This role for Cdk5 in neurogenesis was activating-cofactor specific, as p35 KO but not p39 KO mice also had fewer immature neurons. Thus, Cdk5 has an essential role in the survival, but not proliferation, of adult-generated hippocampal neurons through both cell-intrinsic and cell-extrinsic mechanisms.

Cyclin-dependent kinase 5 governs learning and synaptic plasticity via control of NMDAR degradation.

Learning is accompanied by modulation of postsynaptic signal transduction pathways in neurons. Although the neuronal protein kinase cyclin-dependent kinase 5 (Cdk5) has been implicated in cognitive disorders, its role in learning has been obscured by the perinatal lethality of constitutive knockout mice. Here we report that conditional knockout of Cdk5 in the adult mouse brain improved performance in spatial learning tasks and enhanced hippocampal long-term potentiation and NMDA receptor (NMDAR)-mediated excitatory postsynaptic currents. Enhanced synaptic plasticity in Cdk5 knockout mice was attributed to reduced NR2B degradation, which caused elevations in total, surface and synaptic NR2B subunit levels and current through NR2B-containing NMDARs. Cdk5 facilitated the degradation of NR2B by directly interacting with both it and its protease, calpain. These findings reveal a previously unknown mechanism by which Cdk5 facilitates calpain-mediated proteolysis of NR2B and may control synaptic plasticity and learning.

Properties of Individual Hippocampal Synapses Influencing NMDA-Receptor Activation by Spontaneous Neurotransmission.

NMDA receptor (NMDAR) activation is critical for maintenance and modification of synapse strength. Specifically, NMDAR activation by spontaneous glutamate release has been shown to mediate some forms of synaptic plasticity as well as synaptic development. Interestingly, there is evidence that within individual synapses each release mode may be segregated such that postsynaptically there are distinct pools of responsive receptors. To examine potential regulators of NMDAR activation because of spontaneous glutamate release in cultured hippocampal neurons, we used GCaMP6f imaging at single synapses in concert with confocal and super-resolution imaging. Using these single-spine approaches, we found that Ca2+ entry activated by spontaneous release tends to be carried by GluN2B-NMDARs. Additionally, the amount of NMDAR activation varies greatly both between synapses and within synapses, and is unrelated to spine and synapse size, but does correlate loosely with synapse distance from the soma. Despite the critical role of spontaneous activation of NMDARs in maintaining synaptic function, their activation seems to be controlled factors other than synapse size or synapse distance from the soma. It is most likely that NMDAR activation by spontaneous release influenced variability in subsynaptic receptor position, release site position, vesicle content, and channel properties. Therefore, spontaneous activation of NMDARs appears to be regulated distinctly from other receptor types, notably AMPARs, within individual synapses.

Cdk5 modulates cocaine reward, motivation, and striatal neuron excitability.

Cyclin-dependent kinase 5 (Cdk5) regulates dopamine neurotransmission and has been suggested to serve as a homeostatic target of chronic psychostimulant exposure. To study the role of Cdk5 in the modulation of the cellular and behavioral effects of psychoactive drugs of abuse, we developed Cre/loxP conditional knock-out systems that allow temporal and spatial control of Cdk5 expression in the adult brain. Here, we report the generation of Cdk5 conditional knock-out (cKO) mice using the alphaCaMKII promoter-driven Cre transgenic line (CaMKII-Cre). In this model system, loss of Cdk5 in the adult forebrain increased the psychomotor-activating effects of cocaine. Additionally, these CaMKII-Cre Cdk5 cKO mice show enhanced incentive motivation for food as assessed by instrumental responding on a progressive ratio schedule of reinforcement. Behavioral changes were accompanied by increased excitability of medium spiny neurons in the nucleus accumbens (NAc) in Cdk5 cKO mice. To study NAc-specific effects of Cdk5, another model system was used in which recombinant adeno-associated viruses expressing Cre recombinase caused restricted loss of Cdk5 in NAc neurons. Targeted knock-out of Cdk5 in the NAc facilitated cocaine-induced locomotor sensitization and conditioned place preference for cocaine. These results suggest that Cdk5 acts as a negative regulator of neuronal excitability in the NAc and that Cdk5 may govern the behavioral effects of cocaine and motivation for reinforcement.

A dedicated lumbar puncture clinic: performance and short-term patient outcomes.

The purpose of the study was to evaluate patient outcomes, including success rates, factors associated with unsuccessful procedures and frequency of post-lumbar puncture headaches (PLPH), at a dedicated academic outpatient lumbar puncture (LP) clinic. All patients referred to our LP clinic between June 1, 2014 and May 31, 2015 were included in this consecutive observational series. We collected information about patient characteristics, operational parameters of the procedure, and complications. We also recorded rates of participation in biomedical research involving use of cerebrospinal fluid. Univariate analysis used Student's t test and Fisher's exact test. Logistic regression was used to determine independent risk factors associated with unsuccessful LP and PLPH. The mean age of patients referred to our LP clinic was 46 ± 17 years. Of the 307 referrals, 281 patients (92%) started the procedure, with successful acquisition of CSF in 267 (95%). Factors contributing to unsuccessful procedures included higher body mass index [odds ratio (OR) 1.8], older age (OR 1.9), and female sex (OR 10.3). The rate of PLPH was 5.7%. Younger age (OR 0.5), female sex (OR 6.9), high mean arterial pressure (OR 2.2), and a traumatic LP (OR 10.0) were identified as risk factors for PLPH. Notably, 202 patients (72%) consented to biomedical research. A standardized approach to outpatient LP demonstrates high procedural success rate, low PLPH rate, and high participation in biomedical research. Awareness of a group of patients at higher risk for complications including procedure failure or PLPH provides guidance for decision-making regarding referral to the outpatient LP clinic.

Phase I/II multicenter ketogenic diet study for adult superrefractory status epilepticus.

OBJECTIVE: To investigate the feasibility, safety, and efficacy of a ketogenic diet (KD) for superrefractory status epilepticus (SRSE) in adults. METHODS: We performed a prospective multicenter study of patients 18 to 80 years of age with SRSE treated with a KD treatment algorithm. The primary outcome measure was significant urine and serum ketone body production as a biomarker of feasibility. Secondary measures included resolution of SRSE, disposition at discharge, KD-related side effects, and long-term outcomes. RESULTS: Twenty-four adults were screened for participation at 5 medical centers, and 15 were enrolled and treated with a classic KD via gastrostomy tube for SRSE. Median age was 47 years (interquartile range [IQR] 30 years), and 5 (33%) were male. Median number of antiseizure drugs used before KD was 8 (IQR 7), and median duration of SRSE before KD initiation was 10 days (IQR 7 days). KD treatment delays resulted from intravenous propofol use, ileus, and initial care received at a nonparticipating center. All patients achieved ketosis in a median of 2 days (IQR 1 day) on KD. Fourteen patients completed KD treatment, and SRSE resolved in 11 (79%; 73% of all patients enrolled). Side effects included metabolic acidosis, hyperlipidemia, constipation, hypoglycemia, hyponatremia, and weight loss. Five patients (33%) ultimately died. CONCLUSIONS: KD is feasible in adults with SRSE and may be safe and effective. Comparative safety and efficacy must be established with randomized placebo-controlled trials. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that in adults with SRSE, a KD is effective in inducing ketosis.

Association of Autoimmune Encephalitis With Combined Immune Checkpoint Inhibitor Treatment for Metastatic Cancer.

IMPORTANCE: Paraneoplastic encephalitides usually precede a diagnosis of cancer and are often refractory to immunosuppressive therapy. Conversely, autoimmune encephalitides are reversible conditions that can occur in the presence or absence of cancer. OBJECTIVE: To report the induction of autoimmune encephalitis in 2 patients after treatment of metastatic cancer with a combination of the immune checkpoint inhibitors nivolumab and ipilimumab. DESIGN, SETTING, AND PARTICIPANTS: A retrospective case study was conducted of the clinical and management course of 2 patients with progressive, treatment-refractory metastatic cancer who were treated with a single dose each (concomitantly) of the immune checkpoint inhibitors nivolumab, 1 mg/kg, and ipilimumab, 3 mg/kg. EXPOSURES: Nivolumab and ipilimumab. MAIN OUTCOMES AND MEASURES: The clinical response to immunosuppressive therapy in suspected autoimmune encephalitis in the setting of immune checkpoint inhibitor use. RESULTS: Autoantibody testing confirmed identification of anti-N-methyl-D-aspartate receptor antibodies in the cerebrospinal fluid of 1 patient. Withdrawal of immune checkpoint inhibitors and initiation of immunosuppressive therapy, consisting of intravenous methylprednisolone sodium succinate equivalent to 1000 mg of methylprednisolone for 5 days, 0.4 mg/kg/d of intravenous immunoglobulin for 5 days, and 2 doses of rituximab, 1000 mg, in 1 patient and oral prednisone, 60 mg/d, in the other patient, resulted in improved neurologic symptoms. CONCLUSIONS AND RELEVANCE: Immune checkpoint inhibition may favor the development of immune responses against neuronal antigens, leading to autoimmune encephalitis. Early recognition and treatment of autoimmune encephalitis in patients receiving immune checkpoint blockade therapy will likely be essential for maximizing clinical recovery and minimizing the effect of drug-related toxic effects. The mechanisms by which immune checkpoint inhibition may contribute to autoimmune encephalitis require further study.

The role of ventral striatal cAMP signaling in stress-induced behaviors.

The cAMP and cAMP-dependent protein kinase A (PKA) signaling cascade is a ubiquitous pathway acting downstream of multiple neuromodulators. We found that the phosphorylation of phosphodiesterase-4 (PDE4) by cyclin-dependent protein kinase 5 (Cdk5) facilitated cAMP degradation and homeostasis of cAMP/PKA signaling. In mice, loss of Cdk5 throughout the forebrain elevated cAMP levels and increased PKA activity in striatal neurons, and altered behavioral responses to acute or chronic stressors. Ventral striatum- or D1 dopamine receptor-specific conditional knockout of Cdk5, or ventral striatum infusion of a small interfering peptide that selectively targeted the regulation of PDE4 by Cdk5, produced analogous effects on stress-induced behavioral responses. Together, our results demonstrate that altering cAMP signaling in medium spiny neurons of the ventral striatum can effectively modulate stress-induced behavioral states. We propose that targeting the Cdk5 regulation of PDE4 could be a new therapeutic approach for clinical conditions associated with stress, such as depression.