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Glucagon-like peptide-1 receptor (GLP-1R) agonists are common type 2 diabetes medications that have been repurposed for adult chronic weight management. Clinical trials suggest this class may also be beneficial for obesity in pediatric populations. Since several GLP-1R agonists cross the blood-brain barrier, it is important to understand how postnatal developmental exposure to GLP-1R agonists might affect brain structure and function in adulthood. Toward that end, we systemically treated male and female C57BL/6 mice with the GLP-1R agonist exendin-4 (0.5 mg/kg, twice daily) or saline from postnatal day 14 to 21, then allowed uninterrupted development to adulthood. Beginning at 7 weeks of age, we performed open field and marble burying tests to assess motor behavior and the spontaneous location recognition (SLR) task to assess hippocampal-dependent pattern separation and memory. Mice were sacrificed, and we counted ventral hippocampal mossy cells, as we have recently shown that most murine hippocampal neuronal GLP-1R is expressed in this cell population. We found that GLP-1R agonist treatment did not alter P14-P21 weight gain, but modestly reduced adult open field distance traveled and marble burying. Despite these motor changes, there was no effect on SLR memory performance or time spent investigating objects. Finally, we did not detect any changes in ventral mossy cell number using two different markers. These data suggest developmental exposure to GLP-1R agonists might have specific rather than global effects on behavior later in life and that extensive additional study is necessary to clarify how drug timing and dose affect distinct constellations of behavior in adulthood.

BackgroundThe anterior hippocampus of individuals with early psychosis or schizophrenia is hyperactive, as is the ventral hippocampus in rodent models for schizophrenia risk. Hyperactive ventral hippocampal projections to extrahippocampal brain regions contribute to schizophrenia symptoms, but less is known about the functional effects of hyperactive projections within the hippocampal formation long axis. We approached this question by testing whether hyperactivation of ventral dentate gyrus (DG) mossy cells (MCs), which densely project intrahippocampally to the dorsal DG, influences spatial memory, a cognition dependent on intact dorsal DG function.MethodsIn CD-1 mice, we targeted dorsal DG-projecting ventral DG MCs using an adeno-associated virus intersectional strategy. In vivo fiber photometry recording of ventral DG MCs was performed during exploratory behaviors. We targeted excitatory chemogenetic constructs to ventral DG MCs and tested whether their hyperactivation impaired encoding in a spatial memory task.ResultsVentral DG MCs were activated during behavior related to environmental information gathering (rearing) but not during non-exploratory motor behaviors. Ventral DG MCs made functional monosynaptic inputs to dorsal DG granule cells, with chemogenetic activation of ventral DG MCs leading to increased activity of dorsal DG granule cells. Finally, chemogenetic activation of ventral DG MCs during the encoding phase of an object location memory task impaired retrieval 24 hours later, without effects on locomotion or other exploratory behaviors.ConclusionsThese data suggest that localized hippocampal hyperactivity may have longitudinal intrahippocampal functional consequences, supporting study of longitudinal circuits as targets to mitigate cognitive deficits associated with schizophrenia.

Understanding the role of dentate gyrus (DG) mossy cells (MCs) in learning and memory has rapidly evolved due to increasingly precise methods for targeting MCs and for in vivo recording and activity manipulation in rodents. These studies have shown MCs are highly active in vivo, strongly remap to contextual manipulation, and that their inhibition or hyperactivation impairs pattern separation and location or context discrimination. What is not well understood is how MC activity is modulated by neurohormonal mechanisms, which might differentially control the participation of MCs in cognitive functions during discrete states, such as hunger or satiety. In this study, we demonstrate that glucagon-like peptide-1 (GLP-1), a neuropeptide produced in the gut and the brain that regulates food consumption and hippocampal-dependent mnemonic function, might regulate MC function through selective expression of its receptor, GLP-1R. RNA-seq demonstrated that most Glp1r in hippocampal principal neurons is expressed in MCs, and in situ hybridization revealed strong expression of Glp1r in hilar neurons. Glp1r-ires-Cre mice crossed with Ai14D reporter mice followed by co-labeling for the MC marker GluR2/3 revealed that almost all MCs in the ventral DG expressed Glp1r and that almost all Glp1r-expressing hilar neurons were MCs. However, only ~60% of dorsal DG MCs expressed Glp1r, and Glp1r was also expressed in small hilar neurons that were not MCs. Consistent with this expression pattern, peripheral administration of the GLP-1R agonist exendin-4 (5 μg/kg) increased cFos expression in ventral but not dorsal DG hilar neurons. Finally, whole-cell patch-clamp recordings from ventral MCs showed that bath application of exendin-4 (200 nM) depolarized MCs and increased action potential firing. Taken together, this study identifies a potential neurohormonal mechanism linking a critically important satiety signal with activity of MCs in the ventral DG that might have functional effects on learning and memory during distinct states.

Reduced hippocampal volume is a consistent finding in neuroimaging studies of individuals with schizophrenia. While these studies have the advantage of large-sample sizes, they are unable to quantify the cellular basis of structural or functional changes. In contrast, postmortem studies are well suited to explore subfield and cellular alterations, but low sample sizes and subject heterogeneity impede establishment of statistically significant differences. Here we use a meta-analytic approach to synthesize the extant literature of hippocampal subfield volume and cellular composition in schizophrenia patients and healthy control subjects. Following pre-registration (PROSPERO CRD42019138280), PubMed, Web of Science, and PsycINFO were searched using the term: (schizophrenia OR schizoaffective) AND (post-mortem OR postmortem) AND hippocampus. Subjects were adult men and women with schizophrenia or schizoaffective disorder or non-psychiatric control subjects, and key outcomes, stratified by hippocampal hemisphere and subfield, were volume, neuron number, neuron density, and neuron size. A random effects meta-analysis was performed. Thirty-two studies were included (413 patients, 415 controls). In patients, volume and neuron number were significantly reduced in multiple hippocampal subfields in left, but not right hippocampus, whereas neuron density was not significantly different in any hippocampal subfield. Neuron size, averaged bilaterally, was also significantly reduced in all calculated subfields. Heterogeneity was minimal to moderate, with rare evidence of publication bias. Meta-regression of age and illness duration did not explain heterogeneity of total hippocampal volume effect sizes. These results extend neuroimaging findings of smaller hippocampal volume in schizophrenia patients and further our understanding of regional and cellular neuropathology in schizophrenia.

With the advent of tools for recording and manipulating activity with high spatiotemporal resolution in defined neural circuits in behaving animals, behavioral neuroscience is now tasked with establishing field-wide standards for implementing and interpreting these powerful approaches. Theoretical frameworks for what constitute proof of fundamental neurobiological principles is an ongoing and frequently debated topic. On the other hand, standardizing interpretation of individual experimental findings to avoid spurious conclusions in practice has received less attention. Even within subfields, similar assays are often used to support widely disparate conclusions which in part has contributed to a slew of studies claiming highly specified functions for cell types and circuits which are often in direct disagreement with one another. In this opinion piece, we discuss common pitfalls in design and interpretation of approaches for recording or manipulating neural activity in animal models of motivated behavior. We emphasize the importance of integrating findings across multiple behavioral assays concomitant with tempered inference regarding specialized neuronal functions as a standardized starting point for parsing circuit control of behavior. Our aim is to stimulate an open and accessible discourse in the literature to address issues of continuity across behavioral neurosciences.

The prevalence of ASD remains relatively stable across the lifespan, necessitating a quantitative understanding of how intervention clinical research is applied across age groups. Here we report a systematic review of treatment studies between 2013 and 2017, enrolling 11,213 subjects with ASD in 218 studies. Individuals under 18 years old constituted the majority of studies (84%) and subjects (92%). Subjects under 18 years old were more likely to be enrolled in behavioral studies (OR (CI) = 1.34 (1.17–1.54)), and less likely to be enrolled in pharmacological (OR = 0.60 (0.52–0.69)) studies than subjects ≥ 18 years old. Identified disparities in both intervention modalities and outcome measures should serve to guide future research priorities.

Human genome-wide association studies (GWAS), transcriptome analyses of animal models, and candidate gene studies have advanced our understanding of the genetic architecture of aggressive behaviors. However, each of these methods presents unique limitations. To generate a more confident and comprehensive view of the complex genetics underlying aggression, we undertook an integrated, cross-species approach. We focused on human and rodent models to derive eight gene lists from three main categories of genetic evidence: two sets of genes identified in GWAS studies, four sets implicated by transcriptome-wide studies of rodent models and two sets of genes with causal evidence from Online Mendelian Inheritance in Man (OMIM) and knockout (KO) mice reports. These gene sets were evaluated for overlap and pathway enrichment to extract their similarities and differences. We identified enriched common pathways such as the G-protein coupled receptor (GPCR) signaling pathway, axon guidance, reelin signaling in neurons and ERK/MAPK signaling. Also, individual genes were ranked based on their cumulative weights to quantify their importance as risk factors for aggressive behavior, which resulted in 40 top-ranked and highly-interconnected genes. The results of our cross-species and integrated approach provide insights into the genetic etiology of aggression.

Neuropsychiatric disorders are frequently complicated by aggressive behaviors. For some individuals, existing behavioral and psychopharmacological treatments are ineffective or confer significant side effects, necessitating development of new ways to treat patients with severe aggression. Nicotinic acetylcholine receptors (nAChRs) are a large and diverse family of ligand-gated ion channels expressed throughout the brain that influence behaviors highly relevant for neuropsychiatric disorders, including attention, mood, and impulsivity. Nicotine and other drugs targeting nAChRs can reduce aggression in animal models of offensive, defensive, and predatory aggression, as well as in human laboratory studies. Human genetic studies have suggested a relationship between the CHRNA7 gene encoding the alpha-7 nAChR and aggressive behavior, although these effects are heterogeneous and strongly influenced by genetic background and environment. Here we review animal, human genetic, and clinical studies supporting a consistent role of nicotine and nAChR signaling in modulation of aggressive behaviors. We integrate findings from recent studies of aggression neuroscience, discuss the circuitry that may be involved in these effects of nAChRs, and identify multiple key questions that must be answered prior to safe and effective translation for human patients. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Nicotinic acetylcholine receptors (nAChRs), particularly the α7 nAChR, are implicated in the pathophysiology of both autism spectrum disorder (ASD) and aggressive behavior. We explored the feasibility, tolerability, and preliminary efficacy of targeting nAChRs using transdermal nicotine to reduce aggressive symptoms in adults with ASD. Eight subjects were randomized in a double-blind crossover trial of seven milligrams transdermal nicotine or placebo, each for one week. All participants tolerated nicotine treatment well. Five subjects contributed data to the primary outcome, Aberrant Behavior Checklist-Irritability (ABC-I) subscale change from baseline, which was improved by nicotine compared to placebo. Sleep ratings were also improved by nicotine and correlated with ABC-I improvement. These findings support further investigation of nAChR agonists for aggression and sleep in ASD.

Humans with 15q13.3 microdeletion syndrome (15q13.3DS) are typically hemizygous for CHRNA7, the gene coding for the α7 nicotinic acetylcholine receptor (nAChR), and manifest a variable neuropsychiatric phenotype that frequently includes persistent aggression. In mice, nAChR activation by nicotine is anti-aggressive, or 'serenic,' an effect which requires α7 nAChRs and is recapitulated by GTS-21, an α7 nAChR partial agonist. Pharmacotherapies potentiating α7 nAChR signaling have also been shown to reduce aggression in human 15q13.3DS. These findings identify the α7 nAChR as an important regulator of aggressive behavior, but the underlying neurobiological substrates remain to be determined. We therefore investigated the brain regions and potential neural circuits in which α7 nAChRs regulate aggressive behavior in male mice. As in 15q13.3DS, mice heterozygous for Chrna7 were significantly more aggressive compared to wild-type controls in the resident-intruder test. We subsequently examined the hippocampus, where α7 nAChRs are highly expressed, particularly in GABAergic interneurons. Resident-intruder interactions strongly activated granule cells in the dentate gyrus (DG). In contrast, GTS-21, which reduces aggression in mice, reduced DG granule cell activity during resident-intruder interactions. Short hairpin RNA knockdown of Chrna7 in the DG enhanced baseline aggression and eliminated the serenic effects of both nicotine and GTS-21 on attack latency. These data further implicate α7 nAChRs in regulation of aggression, and demonstrate that hippocampal α7 nAChR signaling is necessary and sufficient to limit aggression. These findings suggest that nAChR-mediated regulation of hippocampal excitatory-inhibitory balance could be a promising therapeutic intervention for aggression arising in certain forms of neuropsychiatric disease.

Cognitive dysfunction in schizophrenia (SCZ) and Alzheimer’s disease (AD) is a major driver of functional disability but is largely unresponsive to current therapeutics. Animal models of cognitive dysfunction relevant to both disorders suggest the α7 nicotinic acetylcholine receptor (nAChR) may be a promising drug development target, with multiple clinical trials subsequently testing this hypothesis in individuals with SCZ and AD. However, the translational value of rodent cognitive tasks for predicting the overall efficacy of this therapeutic target in clinical trials is unknown. To compare effect sizes between rodent and human studies, we searched PubMed and the Cochrane Library for all randomized, placebo-controlled trials of compounds with pharmacological activity at the α7 nAChR for treatment of cognitive dysfunction in SCZ and AD and identified 18 studies comprising 2670 subjects treated with eight different compounds acting as full or partial agonists. Cognitive outcomes were standardized, and random-effects meta-analyses revealed no statistically significant effects of α7 nAChR agonists on overall cognition or any of eight cognitive subdomains when all doses were included (Range of all cognitive outcomes: Cohen’s d = −0.077 to 0.12, negative favoring drug). In contrast, analysis of 29 rodent studies testing the same α7 agonists revealed large effect sizes in multiple commonly used preclinical behavioral tests of cognition (Range: d = −1.18 to −0.73). Our results suggest that targeting the α7 nAChR with agonists is not a robust treatment for cognitive dysfunction in SCZ or AD and necessitate a better understanding of the translational gap for therapeutics targeting the α7 nAChR.

Social avoidance is a common component of neuropsychiatric disorders that confers substantial functional impairment. An unbiased approach to identify brain regions and neuronal circuits that regulate social avoidance might enable development of novel therapeutics. However, most paradigms that alter social avoidance are irreversible and accompanied by multiple behavioral confounds. Here we report a straightforward behavioral paradigm in male mice enabling the reversible induction of social avoidance or approach with temporal control. C57BL/6J mice repeatedly participated in both negative and positive social experiences. Negative social experience was induced by brief social defeat by an aggressive male CD-1 mouse, while positive social experience was induced by exposure to a female mouse, each conducted daily for five days. Each social experience valence was conducted in a specific odorant context (i.e. negative experience in odorant A, positive experience in odorant B). Odorants were equally preferred pre-conditioning. However, after conditioning, mice sniffed positive experience-paired odorants more than negative experience-paired odorants. Furthermore, positive- or negative-conditioned odorant contexts increased or decreased, respectively, the approach behavior of conditioned mice toward conspecifics. Because individual mice undergo both positive and negative conditioning, this paradigm may be useful to examine neural representations of social approach or avoidance within the same subject.

A potent VEGF inhibitor with novel antibody architecture and antigen binding mode has been developed. The molecule, hereafter referred to as VEGF dual dAb (domain antibody), was evaluated in vitro for binding to VEGF and for potency in VEGF-driven models and compared with other anti-VEGF biologics that have been used in ocular anti-angiogenic therapeutic regimes. VEGF dual dAb is more potent than bevacizumab and ranibizumab for VEGF binding, inhibition of VEGF receptor binding assays (RBAs), and VEGF-driven in vitro models of angiogenesis and displays comparable inhibition to aflibercept (Eylea). VEGF dual dAb is dimeric, and each monomer contains two distinct anti-VEGF domain antibodies attached via linkers to a human IgG1 Fc domain. Mechanistically, the enhanced in vitro potency of VEGF dual dAb, in comparison to other anti-VEGF biologics, can be explained by increased binding stoichiometry. A consistent model of the target engagement has been built based on the x-ray complexes of each of the two isolated domain antibodies with the VEGF antigen.

Absence seizures occur in several types of human epilepsy and result from widespread, synchronous feedback between the cortex and thalamus that produces brief episodes of loss of consciousness. Genetic rodent models have been invaluable for investigating the pathophysiological basis of these seizures. Here, we identify tetratricopeptide-containing Rab8b-interacting protein (TRIP8b) knockout mice as a new model of absence epilepsy, featuring spontaneous spike-wave discharges on electroencephalography (EEG) that are the electrographic hallmark of absence seizures. TRIP8b is an auxiliary subunit of the hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels, which have previously been implicated in the pathogenesis of absence seizures. In contrast to mice lacking the pore-forming HCN channel subunit HCN2, TRIP8b knockout mice exhibited normal cardiac and motor function and a less severe seizure phenotype. Evaluating the circuit that underlies absence seizures, we found that TRIP8b knockout mice had significantly reduced HCN channel expression and function in thalamic-projecting cortical layer 5b neurons and thalamic relay neurons, but preserved function in inhibitory neurons of the reticular thalamic nucleus. Our results expand the known roles of TRIP8b and provide new insight into the region-specific functions of TRIP8b and HCN channels in constraining cortico-thalamo-cortical excitability.

Psychiatry residents' experiences in forensic psychiatry vary greatly across the country, and many psychiatry programs meet the Accreditation Council for Graduate Medical Education requirements for a forensic experience through general psychiatry rotations (e.g., on a consult-liaison service) or classroom-based activities. Forensic clinical experiences during psychiatry residency are important for preparing future general psychiatrists for practice with justice-involved patients, generating interest in forensic psychiatry, and easing the transition from "healer to evaluator" for future fellows. Unfortunately, residency programs interested in expanding their forensic training may face many challenges because of current regulatory frameworks, the nature of forensic practice, and competing demands within residency training programs. This article describes these challenges, and the experience of the authors at one institution with developing a novel forensic experience in a criminal justice diversion setting. The authors conclude with some practical considerations for educators interested in developing forensic experiences at their institutions.

Aggression remains a major cause of morbidity in patients with autism spectrum disorder (ASD). Current pharmacotherapy for aggression is not always effective and is often associated with morbidity. Nicotinic acetylcholinergic neurotransmission may play a prominent role in ASD pathophysiology based on human and animal studies, and preclinical studies show nicotine administration can reduce aggression-related behaviors. Transdermal nicotine has been used to treat agitation in neuropsychiatric conditions with cholinergic dysfunction. Here we report the use of transdermal nicotine as an adjunctive medication to treat aggression in a hospitalized adolescent with ASD. Nicotine patch was recurrently well tolerated, and reduced the need for emergency medication and restraint. These findings suggest further study of transdermal nicotine for aggression comorbid with ASD is warranted.

Aggression and irritability in children occur across a range of diagnoses, and are associated with both economic cost and negative psychosocial outcomes. Antipsychotics are frequently prescribed in these cases.A random effects meta-analysis of 14 random controlled trials was conducted. Overall effect sizes for antipsychotics for irritability and aggression were extracted. Subgroup analyses were conducted according to diagnostic indication, specific medication and degree of sedation. Meta-regression examined effects of antipsychotic dose.Overall, antipsychotics were effective in reducing aggression and irritability (SMD = 0.74, 95% confidence interval [CI] 0.57-0.92, z = 8.4, p 0.0001). In stratified subgroup analysis, individual antipsychotic agents did not differ in efficacy (χClinical data supports the efficacy of risperidone and aripiprazole for aggression and irritability across diagnoses, with insufficient data available for other agents. Available data does not support a difference in efficacy based on underlying diagnosis, choice of agent, or its degree of sedation.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are subthreshold activated voltage-gated ion channels. In the cortex, these channels are predominantly expressed in dendrites where they significantly modify dendritic intrinsic excitability as well synaptic potential shapes and integration. HCN channel trafficking to dendrites is regulated by the protein, TRIP8b. Additionally, altered TRIP8b expression may be one mechanism underlying seizure-induced dendritic HCN channel plasticity. HCN channels, though, are also located in certain mature cortical synaptic terminals, where they play a vital role in modulating synaptic transmission. In this study, using electrophysiological recordings as well as electron microscopy we show that presynaptic, but not dendritic, cortical HCN channel expression and function is comparable in adult TRIP8b-null mice and wild-type littermates. We further investigated whether presynaptic HCN channels undergo seizure-dependent plasticity. We found that, like dendritic channels, wild-type presynaptic HCN channel function was persistently decreased following induction of kainic acid-induced seizures. Since TRIP8b does not affect presynaptic HCN subunit trafficking, seizure-dependent plasticity of these cortical HCN channels is not conditional upon TRIP8b. Our results, thus, suggest that the molecular mechanisms underlying HCN subunit targeting, expression and plasticity in adult neurons is compartment selective, providing a means by which pre- and postsynaptic processes that are critically dependent upon HCN channel function may be distinctly influenced.

The dorsal and ventral regions of the hippocampus perform different functions. Whether the integrative properties of hippocampal cells reflect this heterogeneity is unknown. We focused on dendrites where most synaptic input integration takes place. We report enhanced backpropagation and theta resonance and decreased summation of synaptic inputs in ventral versus dorsal CA1 pyramidal cell distal dendrites. Transcriptional Kv4.2 down-regulation and post-transcriptional hyperpolarization-activated cyclic AMP-gated channel (HCN1/2) up-regulation may underlie these differences, respectively. Our results reveal differential dendritic integrative properties along the dorso-ventral axis, reflecting diverse computational needs.

Substance use is a major risk factor for various forms of violence, yet how cigarette smoking influences violence outcomes is incompletely understood. We investigated associations between cigarette smoking and three types of violence in a large, nationally representative, community-based sample.Adult subjects participating in both Wave 1 (2001-2002; N = 43 093) and Wave 2 (2004-2005; N = 34 653) of the National Epidemiological Survey on Alcohol and Related Conditions (NESARC) were stratified by daily cigarette smoking status at Wave 1, and individuals with unchanged smoking status between waves were analyzed (nonsmokers [consisting of never and former daily smokers]: N = 22 529; daily smokers: N = 7442). We created composites of other- and self-directed violence and victimization occurring between Waves 1 and 2, and performed logistic regression models, controlling for psychiatric diagnoses, alcohol and substance use, and relevant demographic covariates.Daily smokers at Wave 1 were 2.1 (95% CI: 1.5-3.0), 2.5 (2.1-2.9), and 1.7 (1.5-2.1) times more likely than nonsmokers to report self-directed violence, other-directed violence, or victimization between Waves 1 and 2, respectively. Former daily smokers were significantly less likely to report other-directed violence than individuals who were never daily smokers.Daily cigarette smoking is temporally associated with multiple forms of violence compared to never and former cigarette smokers, even when common covariates associated with violence are controlled. Smoking status should be carefully controlled for in studies designed to identify risk factors for violence, and may be a useful component of violence risk assessment.The findings suggest that cigarette smoking status should be carefully and systematically controlled for in studies of violence risk factors. The findings also support further investigation of the utility of cigarette smoking status for violence risk assessment, and whether smoking cessation strategies mitigate violence risk.

Ion channel trafficking and gating are often influenced by interactions with auxiliary subunits. Tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b) is an auxiliary subunit for neuronal hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. TRIP8b interacts directly with two distinct sites of HCN channel pore-forming subunits to control channel trafficking and gating. Here we use mutagenesis combined with electrophysiological studies to define and distinguish the functional importance of the HCN/TRIP8b interaction sites. Interaction with the last three amino acids of the HCN1 C terminus governed the effect of TRIP8b on channel trafficking, whereas TRIP8b interaction with the HCN1 cyclic nucleotide binding domain (CNBD) affected trafficking and gating. Biochemical studies revealed that direct interaction between TRIP8b and the HCN1 CNBD was disrupted by cAMP and that TRIP8b binding to the CNBD required an arginine residue also necessary for cAMP binding. In accord, increasing cAMP levels in cells antagonized the up-regulation of HCN1 channels mediated by a TRIP8b construct binding the CNBD exclusively. These data illustrate the distinct roles of the two TRIP8b-HCN interaction domains and suggest that TRIP8b and cAMP may directly compete for binding the HCN CNBD to control HCN channel gating, kinetics, and trafficking.

Parkinson's disease is a common neurodegenerative disorder characterized by a profound motor disability that is traceable to the emergence of synchronous, rhythmic spiking in neurons of the external segment of the globus pallidus (GPe). The origins of this pathophysiology are poorly defined for the generation of pacemaking. After the induction of a parkinsonian state in mice, there was a progressive decline in autonomous GPe pacemaking, which normally serves to desynchronize activity. The loss was attributable to the downregulation of an ion channel that is essential in pacemaking, the hyperpolarization and cyclic nucleotide-gated (HCN) channel. Viral delivery of HCN2 subunits restored pacemaking and reduced burst spiking in GPe neurons. However, the motor disability induced by dopamine (DA) depletion was not reversed, suggesting that the loss of pacemaking was a consequence, rather than a cause, of key network pathophysiology, a conclusion that is consistent with the ability of L-type channel antagonists to attenuate silencing after DA depletion.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) form the molecular basis for the hyperpolarization-activated current, Ih and modulation of h channels contributes to changes in cellular properties critical for normal functions in the mammalian brain and heart. Numerous mechanisms underlie h channel modulation during both physiological and pathological conditions, leading to distinct changes in gating, kinetics, surface expression, channel conductance or subunit composition of h channels. Here we provide a focused review examining contemporary mechanisms of h channel regulation, with an emphasis on recent findings regarding interacting proteins such as TRIP8b. This review is intended to serve as a comprehensive resource for physiologists to provide potential molecular mechanisms underlying functionally important changes in Ih in different biological models, as well as for molecular biologists to delineate the predicted h channel changes associated with complex regulatory mechanisms in both normal function and in disease states.

Analysis of naturally occurring mutations that cause seizures in rodents has advanced understanding of the molecular mechanisms underlying epilepsy. Abnormalities of Ih and h channel expression have been found in many animal models of absence epilepsy. We characterized a novel spontaneous mutant mouse, apathetic (ap/ap), and identified the ap mutation as a 4 base pair insertion within the coding region of Hcn2, the gene encoding the h channel subunit 2 (HCN2). We demonstrated that Hcn2ap mRNA is reduced by 90% compared to wild type, and the predicted truncated HCN2ap protein is absent from the brain tissue of mice carrying the ap allele. ap/ap mice exhibited ataxia, generalized spike–wave absence seizures, and rare generalized tonic–clonic seizures. ap/+ mice had a normal gait, occasional absence seizures and an increased severity of chemoconvulsant-induced seizures. These findings help elucidate basic mechanisms of absence epilepsy and suggest HCN2 may be a target for therapeutic intervention.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) are the molecular basis for the current,Ih, which contributes crucially to intrinsic neuronal excitability. The subcellular localization and biophysical properties of h channels govern their function, but the mechanisms controlling these characteristics, and especially the potential role of auxiliary subunits or other binding proteins, remain unclear. We focused on TRIP8b, an h channel-interacting protein that colocalizes with HCN1 in cortical and hippocampal pyramidal neuron dendrites, and found that it exists in multiple alternative splice variants with distinct effects on h channel trafficking and function. The developmentally regulated splice variants of TRIP8b all shared dual, C terminus-located interaction sites with HCN1. When coexpressed with HCN1 in heterologous cells individual TRIP8b isoforms similarly modulated gating ofIh, causing a hyperpolarizing shift in voltage dependence of channel activation, but differentially upregulated or downregulatedIhcurrent density and HCN1 surface expression. In hippocampal neurons, coexpression of TRIP8b isoforms with HCN1 produced isoform-specific changes of HCN1 localization. Interestingly, the TRIP8b isoforms most abundant in the brain are those predicted to enhance h channel surface expression. Indeed, shRNA knockdown of TRIP8b in hippocampal neurons significantly reduced nativeIh. Thus, although TRIP8b exists in multiple splice isoforms, our data suggest that the predominant role of this protein in brain is to promote h channel surface expression and enhanceIh. BecauseIhexpression is altered in models of several diseases, including temporal lobe epilepsy, TRIP8b may play a role in both normal neuronal function and in aberrant neuronal excitability associated with neurological disease.

Aggression is frequently comorbid with neuropsychiatric conditions and is a predictor of worse outcomes, yet current pharmacotherapies are insufficient and have debilitating side effects, precluding broad use. Multiple models of aggression across species suggest that the nicotinic acetylcholine receptor (nAChR) agonist nicotine has anti-aggressive (serenic) properties. Here we demonstrate dose-dependent serenic effects of acute nicotine administration in three distinct mouse strains: C57BL/6, BALB/c, and CD1. While acute nicotine administration (0.25 mg/kg) modestly reduced solitary homecage locomotion, this could not account for nicotine’s serenic effects since social encounters eliminated the hypolocomotor effect, and nicotine did not alter social interaction times. Pretreatment with the homomeric (α7 subunit) nAChR antagonist methyllycaconitine (5 mg/kg), but not the heteromeric (β2 or β4 subunit-containing) nAChR antagonist dihydro-β-erythroidine (DHβE, 3 mg/kg), blocked the serenic effects of nicotine. By contrast, pretreatment with DHβE blocked the effect of acute nicotine administration on locomotion, uncoupling nicotine’s serenic and hypolocomotor effects. Finally, the α7 nAChR partial agonist GTS-21 reduced aggression in C57BL/6 mice. These results support the idea that acute nicotine administration has serenic effects and provide evidence for specificity of this effect distinct from effects on locomotion. Furthermore, pharmacological studies suggest that activation of α7 nAChRs underlies the serenic effects of nicotine. Further studies of nAChRs could enhance understanding of the neurobiology of aggression and may lead to the development of novel, more specific treatments for pathological aggression.

To the Editors: Delusional infestation is defined by fixed, false beliefs of infestation with parasites or inanimate objects. Patients typically present to clinicians in primary care and dermatology rather than to mental health practitioners.1 To our knowledge, this is the first reported case of delusional infestation associated with “black mold.” Further, it is a rare case with systemic involvement and of fungus-related delusional infestation. Case report. Mr A, a divorced 54-year-old homeless white man, was transferred to our hospital’s medicine service for videoelectroencephalography (vEEG) after experiencing seizures at another hospital. He reported taking more than 20 mg of lorazepam daily, explaining that lorazepam treated the “neurotoxic” effects of a “black mold infection” he acquired over 1 year ago, and his lorazepam supply had run out 2 days prior to presentation. He attributed numerous somatic symptoms to the black mold, or Stachybotrys chartarum, infection including tinnitus, fatigue, and headaches. Mr A was a limited historian and declined to identify collateral sources but alluded to multiple inpatient psychiatric and substance admissions. Pertinent medical history was limited to a head injury as an adolescent. Mental status examination revealed an unkempt, agitated man with forceful speech, intense and labile affect, and obsessive thoughts with moderate paranoia. His thoughts were perseverative and overinclusive but generally linear and goal-directed. He denied hallucinations or suicidal or homicidal ideation. No seizure activity was seen on the vEEG, and a comprehensive physical, laboratory, and neuroimaging workup did not reveal evidence of fungal infection or another cause for his reported symptoms. Neuroleptics and mood stabilizers were recommended for psychosis and mood elevation but were persistently refused. A slow lorazepam taper was accompanied by episodes of rhythmic shaking and agitation at doses below 8 mg daily. Repeated EEGs during these episodes were unrevealing, substantiating a diagnosis of nonepileptic seizures. Mr A was dissatisfied with the taper and ultimately discharged against medical advice after undergoing a risk assessment and capacity evaluation. He refused treatment referral. Delusional infestation principally involves the skin, and almost all reported cases with fungus include dermatologic manifestations. We conducted a literature search using MEDLINE, EMBASE, and PsycINFO using terms related to delusions (psychosis, psychotic, delusion*, delusory, Ekbom*, parasitophobi*, and Morgellon*) with those related to fungus/black mold (mold*, fungus, fungal, mycotoxi*, and Stachybotrys).2–6 Table 1 provides a summary of the cases found. Table 1 Previously Reported Cases of Delusional Parasitosis or Infestation With Fungal Etiology This is a rare report of delusional infestation with systemic symptoms and, to our knowledge, the first reported case of black mold delusional infestation. Whereas a controversial study suggests that mycotoxins may cause vague neurologic illness,7 our patient’s limited mold exposure more than 1 year prior to presentation with persistent symptoms is inconsistent with even that report. Severe benzodiazepine use disorder was evident. A clear understanding of Mr A’s psychosis was hindered by lack of collateral history. No secondary cause was identified, so our differential diagnosis included schizophrenia, schizoaffective disorder, bipolar disorder, or obsessive-compulsive disorder with absent insight.3 Conversion disorder, factitious disorder, and malingering were also considered given the vEEG results. Detailed discussion of managing delusional infestation has been reviewed elsewhere.8–10 Management should include medical workup to rule out secondary causes. First-line treatment for primary delusional infestation includes antipsychotic medication. Both first-generation10 and second-generation9 agents have been used successfully. Attention should be given to common comorbid disorders such as depression and anxiety.11 Mental health referral is recommended. Patients with delusional infestation suffer substantially from psychosocial dysfunction and are at increased risk for harm from hazardous treatments, as exemplified by our patient using high-dose benzodiazepines. As with this case, most patients with delusional infestation present to nonpsychiatric physicians, thus an understanding of diagnosis, workup, and treatment approaches is critical to limit unwarranted medical intervention and promote functional recovery.

The co-morbidity between smoking and mood disorders is striking. Preclinical and clinical studies of nicotinic effects on mood, anxiety, aggression, and related behaviors, such as irritability and agitation, suggest that smokers may use the nicotine in tobacco products as an attempt to self-medicate symptoms of affective disorders. The role of nicotinic acetylcholine receptors (nAChRs) in circuits regulating mood and anxiety is beginning to be elucidated in animal models, but the mechanisms underlying the effects of nicotine on aggression-related behavioral states (ARBS) are still not understood. Clinical trials of nicotine or nicotinic medications for neurological and psychiatric disorders have often found effects of nicotinic medications on ARBS, but few trials have studied these outcomes systematically. Similarly, the increase in ARBS resulting from smoking cessation can be resolved by nicotinic agents, but the effects of nicotinic medications on these types of mental states and behaviors in non-smokers are less well understood. Here we review the literature on the role of nAChRs in regulating mood and anxiety, and subsequently on the closely related construct of ARBS. We suggest avenues for future study to identify how nAChRs and nicotinic agents may play a role in these clinically important areas. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

A stereoselective synthetic approach to (2S,3R)-N-(1′,1′-dimethyl-2′,3′-epoxypropyl)-3-hydroxytryptophan an amino acid contained in cyclomarin A was accomplished. The synthesis is based on a diastereoselective addition of an indole Grignard into a chiral serine aldehyde equivalent.

Hyperpolarization-activated cyclic nucleotide-gated nonselective cation channels (HCN or h-channels) are important regulators of neuronal physiology contributing to passive membrane properties, such as resting membrane potential and input resistance ( RN), and to intrinsic oscillatory activity and synaptic integration. The correct membrane targeting of h-channels is regulated in part by the auxiliary h-channel protein TRIP8b. The genetic deletion of TRIP8b results in a loss of functional h-channels, which affects the postsynaptic integrative properties of neurons. We investigated the impact of TRIP8b deletion on long-term potentiation (LTP) at the two major excitatory inputs to CA1 pyramidal neurons: Schaffer collateral (SC) and perforant path (PP). We found that SC LTP was not significantly different between neurons from wild-type and TRIP8b-knockout mice. There was, however, significantly more short-term potentiation in knockout neurons. We also found that the persistent increase in h-current ( Ih) that normally occurs after LTP induction was absent in knockout neurons. The lack of Ih plasticity was not restricted to activity-dependent induction, because the depletion of intracellular calcium stores also failed to produce the expected increase in Ih. Interestingly, pairing of SC and PP inputs resulted in a form of LTP in knockout neurons that did not occur in wild-type neurons. These results suggest that the physiological impact of TRIP8b deletion is not restricted to the integrative properties of neurons but also includes both synaptic and intrinsic plasticity.

Nicotinic acetylcholine receptors (nAChRs) are a critical component of the cholinergic system of neurotransmission in the brain that modulates important physiological processes such as reward, cognition, and mood. Abnormalities in this system are accordingly implicated in multiple psychiatric illnesses, including addiction, schizophrenia, and mood disorders. There is significantly increased tobacco use, and therefore nicotine intake, in patient populations, and pharmacological agents that act on various nicotinic receptor subtypes ameliorate clinical features of these disorders. Better understanding of the molecular mechanisms underlying cholinergic dysfunction in psychiatric disease will permit more targeted design of novel therapeutic agents. The objective of this review is to describe the multiple cellular pathways through which chronic nicotine exposure regulates nAChR expression, and to juxtapose these mechanisms with evidence for altered expression of high-affinity nAChRs in human psychiatric illness. Here, we summarize multiple studies from pre-clinical animal models to human in vivo imaging and post-mortem experiments demonstrating changes in nAChR regulation and expression in psychiatric illness. We conclude that a mechanistic explanation of nAChR abnormalities in psychiatric illness will arise from a fuller understanding of normal nAChR trafficking, along with the detailed study of human tissue, perhaps using novel biotechnological advances, such as induced pluripotent stem cells.

Ion channels operate in intact tissues as part of large macromolecular complexes that can include cytoskeletal proteins, scaffolding proteins, signaling molecules, and a litany of other molecules. The proteins that make up these complexes can influence the trafficking, localization, and biophysical properties of the channel. TRIP8b (tetratricopetide repeat-containing Rab8b-interacting protein) is a recently discovered accessory subunit of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that contributes to the substantial dendritic localization of HCN channels in many types of neurons. TRIP8b interacts with the carboxyl-terminal region of HCN channels and regulates their cell-surface expression level and cyclic nucleotide dependence. Here we examine the molecular determinants of TRIP8b binding to HCN2 channels. Using a single-molecule fluorescence bleaching method, we found that TRIP8b and HCN2 form an obligate 4:4 complex in intact channels. Fluorescence-detection size-exclusion chromatography and fluorescence anisotropy allowed us to confirm that two different domains in the carboxyl-terminal portion of TRIP8b—the tetratricopepide repeat region and the TRIP8b conserved region—interact with two different regions of the HCN carboxyl-terminal region: the carboxyl-terminal three amino acids (SNL) and the cyclic nucleotide-binding domain, respectively. And finally, using X-ray crystallography, we determined the atomic structure of the tetratricopepide region of TRIP8b in complex with a peptide of the carboxy-terminus of HCN2. Together, these experiments begin to uncover the mechanism for TRIP8b binding and regulation of HCN channels.

The dorsoventral and developmental gradients of entorhinal layer II cell grid properties correlate with their resonance properties and with their hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channel current characteristics. We investigated whether such correlation existed in rat hippocampal CA1 pyramidal cells, where place fields also show spatial and temporal gradients. Resonance was absent during the first postnatal week, and emerged during the second week. Resonance was stronger in dorsal than ventral cells, in accord with HCN current properties. Resonance responded to cAMP in ventral but not in dorsal cells. The dorsoventral distribution of HCN1 and HCN2 subunits and of the auxiliary protein tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b) could account for these differences between dorsal and ventral cells. The analogous distribution of the intrinsic properties of entorhinal stellate and hippocampal cells suggests the existence of general rules of organization among structures that process complementary features of the environment.

The functions of HCN channels in neurons depend critically on their subcellular localization, requiring fine-tuned machinery that regulates subcellular channel trafficking. Here we provide evidence that regulatory mechanisms governing axonal HCN channel trafficking involve association of the channels with specific isoforms of the auxiliary subunit TRIP8b. In the medial perforant path, which normally contains HCN1 channels in axon terminals in immature but not in adult rodents, we found axonal HCN1 significantly increased in adult mice lacking TRIP8b (TRIP8b(-/-)). Interestingly, adult mice harboring a mutation that results in expression of only the two most abundant TRIP8b isoforms (TRIP8b[1b/2](-/-)) exhibited an HCN1 expression pattern similar to wildtype mice, suggesting that presence of one or both of these isoforms (TRIP8b(1a), TRIP8b(1a-4)) prevents HCN1 from being transported to medial perforant path axons in adult mice. Concordantly, expression analyses demonstrated a strong increase of expression of both TRIP8b isoforms in rat entorhinal cortex with age. However, when overexpressed in cultured entorhinal neurons of rats, TRIP8b(1a), but not TRIP8b(1a-4), altered substantially the subcellular distribution of HCN1 by promoting somatodendritic and reducing axonal expression of the channels. Taken together, we conclude that TRIP8b isoforms are important regulators of HCN1 trafficking in entorhinal neurons and that the alternatively-spliced isoform TRIP8b(1a) could be responsible for the age-dependent redistribution of HCN channels out of perforant path axon terminals.

Output properties of neurons are greatly shaped by voltage-gated ion channels, whose biophysical properties and localization within axodendritic compartments serve to significantly transform the original input. The hyperpolarization-activated current,Ih, is mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and plays a fundamental role in influencing neuronal excitability by regulating both membrane potential and input resistance. In neurons such as cortical and hippocampal pyramidal neurons, the subcellular localization of HCN channels plays a critical functional role, yet mechanisms controlling HCN channel trafficking are not fully understood. Because ion channel function and localization are often influenced by interacting proteins, we generated a knock-out mouse lacking the HCN channel auxiliary subunit, tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b). Eliminating expression of TRIP8b dramatically reducedIhexpression in hippocampal pyramidal neurons. Loss ofIh-dependent membrane voltage properties was attributable to reduction of HCN channels on the neuronal surface, and there was a striking disruption of the normal expression pattern of HCN channels in pyramidal neuron dendrites. In heterologous cells and neurons, absence of TRIP8b increased HCN subunit targeting to and degradation by lysosomes. Mice lacking TRIP8b demonstrated motor learning deficits and enhanced resistance to multiple tasks of behavioral despair with high predictive validity for antidepressant efficacy. We observed similar resistance to behavioral despair in distinct mutant mice lacking HCN1 or HCN2. These data demonstrate that interaction with the auxiliary subunit TRIP8b is a major mechanism underlying proper expression of HCN channels andIhin vivo, and suggest that targetingIhmay provide a novel approach to treatment of depression.