Rare coding variants in ten genes confer substantial risk for schizophrenia.

Rare coding variation has historically provided the most direct connections between gene function and disease pathogenesis. By meta-analysing the whole exomes of 24,248 schizophrenia cases and 97,322 controls, we implicate ultra-rare coding variants (URVs) in 10 genes as conferring substantial risk for schizophrenia (odds ratios of 3-50, P < 2.14 × 10-6) and 32 genes at a false discovery rate of <5%. These genes have the greatest expression in central nervous system neurons and have diverse molecular functions that include the formation, structure and function of the synapse. The associations of the NMDA (N-methyl-D-aspartate) receptor subunit GRIN2A and AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptor subunit GRIA3 provide support for dysfunction of the glutamatergic system as a mechanistic hypothesis in the pathogenesis of schizophrenia. We observe an overlap of rare variant risk among schizophrenia, autism spectrum disorders1, epilepsy and severe neurodevelopmental disorders2, although different mutation types are implicated in some shared genes. Most genes described here, however, are not implicated in neurodevelopment. We demonstrate that genes prioritized from common variant analyses of schizophrenia are enriched in rare variant risk3, suggesting that common and rare genetic risk factors converge at least partially on the same underlying pathogenic biological processes. Even after excluding significantly associated genes, schizophrenia cases still carry a substantial excess of URVs, which indicates that more risk genes await discovery using this approach.

GWAS significance thresholds for deep phenotyping studies can depend upon minor allele frequencies and sample size.

An important issue affecting genome-wide association studies with deep phenotyping (multiple correlated phenotypes) is determining the suitable family-wise significance threshold. Straightforward family-wise correction (Bonferroni) of p < 0.05 for 4.3 million genotypes and 335 phenotypes would give a threshold of p < 3.46E-11. This would be too conservative because it assumes all tests are independent. The effective number of tests, both phenotypic and genotypic, must be adjusted for the correlations between them. Spectral decomposition of the phenotype matrix and LD-based correction of the number of tested SNPs are currently used to determine an effective number of tests. In this paper, we compare these calculated estimates with permutation-determined family-wise significance thresholds. Permutations are performed by shuffling individual IDs of the genotype vector for this dataset, to preserve correlation of phenotypes. Our results demonstrate that the permutation threshold is influenced by minor allele frequency (MAF) of the SNPs, and by the number of individuals tested. For the more common SNPs (MAF > 0.1), the permutation family-wise threshold was in close agreement with spectral decomposition methods. However, for less common SNPs (0.05 < MAF ≤ 0.1), the permutation threshold calculated over all SNPs was off by orders of magnitude. This applies to the number of individuals studied (here 777) but not to very much larger numbers. Based on these findings, we propose that the threshold to find a particular level of family-wise significance may need to be established using separate permutations of the actual data for several MAF bins.

International Medical Graduates in the United States Psychiatry Workforce.

OBJECTIVE: This study describes the supply, distribution, and characteristics of international medical graduate (IMG) psychiatrists who provide services in the USA. METHODS: Cross-sectional study design, using descriptive statistics based on combined data from the American Medical Association (2020 Physician Masterfile) and the Educational Commission for Foreign Medical Graduates. RESULTS: International medical graduates continue to make significant contributions to the US physician workforce. As a group, they represent 29% of active psychiatrists in the USA, compared to 23% in all other medical specialties. Many IMG psychiatrists were US citizens who obtained their medical degrees outside the USA or Canada, often in the Caribbean. In some states (i.e., Florida, New Jersey), over 40% of active psychiatrists are IMGs. Over 30% of IMG psychiatrists graduated from medical schools in India and Pakistan. CONCLUSIONS: This study provides an overview of the psychiatric workforce in the USA, quantifying the specific contribution of IMGs. Several factors, including immigration policies, continued expansion of US medical schools, and the number of available residency positions, could impact the flow of IMGs to the US. Longitudinal studies are needed to better understand the implications for workforce composition and distribution, and their potential impact on the care of psychiatric patients.

A Meta-Analysis of Brain-Derived Neurotrophic Factor Effects on Brain Volume in Schizophrenia: Genotype and Serum Levels.

AIM: The Val66Met single-nucleotide polymorphism (SNP) on the BDNF gene has established pleiotropic effects on schizophrenia incidence and morphologic alterations in the illness. The effects of brain-derived neurotrophic factor (BDNF) on brain volume measurements are however mixed seeming to be less established for most brain regions. The current meta-analytic review examined (1) the association of the Val66Met SNP and brain volume alterations in schizophrenia by comparing Met allele carriers to Val/Val homozygotes and (2) the association of serum BDNF with brain volume measurements. METHOD: Studies included in the meta-analyses were identified through an electronic search of PubMed and PsycInfo (via EBSCO) for English language publications from January 2000 through December 2017. Included studies had conducted a genotyping procedure of Val66Met or obtained assays of serum BDNF and obtained brain volume data in patients with psychotic disorders. Nonhuman studies were excluded. RESULTS: Study 1 which included 52 comparisons of Met carriers and Val/Val homozygotes found evidence of lower right and left hippocampal volumes among Met allele carriers with schizophrenia. Frontal measurements, while also lower among Met carriers, did not achieve statistical significance. Study 2 which included 7 examinations of the correlation between serum BDNF and brain volume found significant associations between serum BDNF levels and right and left hippocampal volume with lower BDNF corresponding to lower volumes. DISCUSSION: The meta-analyses provided evidence of associations between brain volume alterations in schizophrenia and variations on the Val66Met SNP and serum BDNF. Given the limited number of studies, it remains unclear if BDNF effects are global or regionally specific.

Neuroinflammation and Schizophrenia.

PURPOSE OF REVIEW: There are longstanding, intriguing findings of immune dysfunction in schizophrenia. These findings span peripheral immune markers, especially cytokine abnormalities. RECENT FINDINGS: This review describes recent genetic and immune marker studies and emergent treatment studies. Collectively, this provides a synthesis and current appraisal of the neuroimmune hypothesis of schizophrenia.

Adjunct Aripiprazole Reduces Prolactin and Prolactin-Related Adverse Effects in Premenopausal Women With Psychosis: Results From the DAAMSEL Clinical Trial.

PURPOSE/BACKGROUND: Prolactin-related adverse effects contribute to nonadherence and adverse health consequences, particularly in women with severe mental illness. Treating these adverse effects may improve treatment acceptability, adherence, and long-term outcomes. METHODS/PROCEDURES: Premenopausal women with a Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder were recruited for a randomized, double-blind, placebo-controlled 16-week trial of adjunct aripiprazole (5-15 mg/d). Participants had elevated prolactin (>24 ng/mL) and were experiencing galactorrhea, amenorrhea, oligomenorrhea, or sexual dysfunction on a prolactin-elevating antipsychotic. Participants were evaluated biweekly for prolactin elevation and galactorrhea and completed a menstrual diary review. Psychiatric symptoms and adverse effects were closely monitored. FINDINGS/RESULTS: Forty-six women were randomized (n = 25 aripiprazole, n = 21 placebo). Thirty-seven completed at least 8 weeks of the study (n = 20 [80%] aripiprazole and n = 17 [81%] placebo). Aripiprazole (mean dose, 11.7 ± 2.4 mg/d) was effective for lowering prolactin relative to placebo (P = 0.04). In addition, 45% (9/20) of the aripiprazole group had a normalized prolactin (<24 mg/mL) compared with 12% (2/17) of the placebo group (P = 0.028). Galactorrhea resolved in 77% (10/13) of the aripiprazole-treated participants compared with 33% (4/12) in the placebo group (P = 0.028). Normalization of sexual function (<16 on the Arizona Sexual Experience Scale) occurred in 50% on aripiprazole (7/14) versus 9% (1/11) on placebo (P = 0.030). No differences between groups in symptoms or adverse effects were noted. Overall, women rated a mean score of 4.6 ± 0.6 on a 5-point Likert scale for sexual function improvement, suggesting their particular satisfaction with improvement in this domain. IMPLICATIONS/CONCLUSIONS: Building upon prior studies, this rigorous evaluation confirms the utility of adjunctive aripiprazole as a strategy for improving prolactin and managing prolactin-related adverse effects in premenopausal women with psychosis.

Staphylococcus aureus Strain Newman D2C Contains Mutations in Major Regulatory Pathways That Cripple Its Pathogenesis.

Staphylococcus aureus is a major human pathogen that imposes a great burden on the health care system. In the development of antistaphylococcal modalities intended to reduce the burden of staphylococcal disease, it is imperative to select appropriate models of S. aureus strains when assessing the efficacy of novel agents. Here, using whole-genome sequencing, we reveal that the commonly used strain Newman D2C from the American Type Culture Collection (ATCC) contains mutations that render the strain essentially avirulent. Importantly, Newman D2C is often inaccurately referred to as simply "Newman" in many publications, leading investigators to believe it is the well-described pathogenic strain Newman. This study reveals that Newman D2C carries a stop mutation in the open reading frame of the virulence gene regulator, agrA In addition, Newman D2C carries a single-nucleotide polymorphism (SNP) in the global virulence regulator gene saeR that results in loss of protein function. This loss of function is highlighted by complementation studies, where the saeR allele from Newman D2C is incapable of restoring functionality to an saeR-null mutant. Additional functional assessment was achieved through the use of biochemical assays for protein secretion, ex vivo intoxications of human immune cells, and in vivo infections. Altogether, our study highlights the importance of judiciously screening for genetic changes in model S. aureus strains when assessing pathogenesis or the efficacy of novel agents. Moreover, we have identified a novel SNP in the virulence regulator gene saeR that directly affects the ability of the protein product to activate S. aureus virulence pathways.IMPORTANCEStaphylococcus aureus is a human pathogen that imposes an enormous burden on health care systems worldwide. This bacterium is capable of evoking a multitude of disease states that can range from self-limiting skin infections to life-threatening bacteremia. To combat these infections, numerous investigations are under way to develop therapeutics capable of thwarting the deadly effects of the bacterium. To generate successful treatments, it is of paramount importance that investigators use suitable models for examining the efficacy of the drugs under study. Here, we demonstrate that a strain of S. aureus commonly used for drug efficacy studies is severely mutated and displays markedly reduced pathogenicity. As such, the organism is an inappropriate model for disease studies.

Transcriptome in vivo analysis (TIVA) of spatially defined single cells in live tissue.

Transcriptome profiling of single cells resident in their natural microenvironment depends upon RNA capture methods that are both noninvasive and spatially precise. We engineered a transcriptome in vivo analysis (TIVA) tag, which upon photoactivation enables mRNA capture from single cells in live tissue. Using the TIVA tag in combination with RNA sequencing (RNA-seq), we analyzed transcriptome variance among single neurons in culture and in mouse and human tissue in vivo. Our data showed that the tissue microenvironment shapes the transcriptomic landscape of individual cells. The TIVA methodology is, to our knowledge, the first noninvasive approach for capturing mRNA from live single cells in their natural microenvironment.

Combination Antipsychotic Therapies: An Analysis From a Longitudinal Pragmatic Trial.

BACKGROUND: Combination antipsychotics (CAs) are prescribed in schizophrenia despite limited evidence of efficacy. To explore the effect of switching from CA to monotherapy, we performed an exploratory analysis of the PROACTIVE (Preventing Relapse in Schizophrenia: Oral Antipsychotics Compared with Injectables: Evaluating Efficacy) study data, in which 305 patients with schizophrenia and schizoaffective disorder were followed for 30 months after randomization to long-acting injectable (LAI) risperidone or second-generation oral antipsychotic (OA). METHODS: Patients who entered the PROACTIVE study on CA (n = 50), LAI (n = 20), or OA (n = 206) were compared in terms of time to relapse and clinical measures. FINDINGS: The OA group had significantly fewer hospitalizations than the CA group (P = 0.009) at baseline. In the CA group, 68% patients relapsed versus 53% in the LAI, and 52% in the OA groups. Although there was no significant difference in the relapse rate among groups on χ test (χ = 3.85, P = 0.146), the log-rank test showed a significant difference among the groups in time to first relapse (χ = 6.81, P = 0.033), with significantly longer time to relapse in the OA group (mean, 562.8 days) than in the CA group (mean, 409.5; P = 0.011). The LAI group's mean time to first relapse (594 days) was not significantly different from the other groups. However, after adjusting for number of hospitalizations, group was no longer significant (hazard ratio, 1.541; P = 0.052). IMPLICATIONS: Based on our exploratory analysis, taking antipsychotic combinations predicts earlier relapse and calls for additional treatment guidance in schizophrenia.

Electronic cigarette use in patients with schizophrenia: Prevalence and attitudes.

BACKGROUND: Smoking is highly prevalent in patients with schizophrenia. Electronic cigarettes (e-cigarettes) are becoming increasingly popular among smokers. Surveys indicate overall favorable attitudes toward the use of e-cigarettes to reduce or quit smoking, relieve withdrawal symptoms, and with respect to perceived health risks; however, less is known about their use in patients with schizophrenia. In the present study, we investigated the prevalence of and attitudes toward e-cigarettes in patients with schizophrenia. METHODS: Sixty inpatients and outpatients age 18 to 70 with schizophrenia completed a brief survey on e-cigarette use. RESULTS: Thirty-seven percent of participants reported having tried e-cigarettes, 24% of never-users were considering use, and 7% were current users. Thirty-four percent of surveyed patients believed that the health effects of e-cigarettes were less harmful than regular cigarettes. Health benefits (39%), cutting down (37%), and quitting smoking (37%) were the most frequently cited potential advantages, whereas cost (33%) was the most common potential disadvantage of e-cigarettes. Participants who were ever-users reported that regular cigarettes were significantly more helpful with reducing symptoms such as depression/anxiety, impaired concentration, and paranoia, than e-cigarettes (P < .05 for each). CONCLUSIONS: These preliminary findings should be investigated in larger samples, but suggest that e-cigarettes have, at best, modest relevance to smoking cessation in patients with schizophrenia.

Prioritizing Harm.

In this study, we examined if a self-report of trait spite, the Spitefulness Scale, retains the same associations with dark personality traits in individuals with severe mental illness. We also examine if reports on the Spitefulness Scale are correlated with observed spiteful behavior in a game developed to offer opportunities for spite. One hundred twenty individuals clinically diagnosed with psychotic spectrum disorders and receiving inpatient treatment at a state hospital participated in this study and completed measures of personality. The Spitefulness Scale retained its associations with measures of dark personality traits in individuals with psychosis. Spitefulness Scale scores were also related to a performance measure of spite and spite was evidenced by a significant proportion of participants across measures (20.8%-26.7%). These data suggest the presence of spite as it is understood in the general population in a significant subset of individuals with psychosis. Spite could be considered an independent personality trait and part of the family of dark personality traits.

Paternal age effect: Replication in schizophrenia with intriguing dissociation between bipolar with and without psychosis.

Advanced paternal age (APA) is a risk factor for schizophrenia (Sz) and bipolar disorder (BP). Putative mechanisms include heritable genetic factors, de novo mutations, and epigenetic mechanisms. Few studies have explored phenotypic features associated with APA. The Genomic Psychiatry Cohort established a clinically characterized repository of genomic samples from subjects with a Sz-BP diagnosis or unaffected controls, 12,975 with parental age information. We estimated relative risk ratios for Sz, schizoaffective depressed and bipolar types (SA-D, SA-B), and BP with and without history of psychotic features (PF) relative to the control group, comparing each paternal age group to the reference group 20-24 years. All tests were two-sided with adjustment for multiple comparisons. Subjects with fathers age 45+ had significantly higher risk for all diagnoses except for BP w/o PF. APA also bore no significant relation to family psychiatric history. In conclusion, we replicated APA as a risk factor for Sz. To our knowledge, this is the first published report of APA in a BP sample stratified by psychosis history, extending this association only in BP w/PF. This suggests that phenotypic expression of the APA effect in Sz-BP spectrum is psychosis, per se, rather than other aspects of these complex disorders. The lack of a significant relationship between paternal age and familial disease patterns suggests that underlying mechanisms of the paternal age effect may involve a complex interaction of heritable and non-heritable factors. The authors discuss implications and testable hypotheses, starting with a focus on genetic mechanisms and endophenotypic expressions of dopaminergic function. © 2015 Wiley Periodicals, Inc.

Traumatic brain injury and bipolar psychosis in the Genomic Psychiatry Cohort.

Approximately three million individuals in the United States sustain traumatic brain injury (TBI) every year, with documented impact on a range of neurological and psychiatric disturbances including mania, depression, and psychosis. Identification of subsets of individuals that may demonstrate increased propensity for posttraumatic symptoms and who may share genetic vulnerabilities for gene-environment interactions can enhance efforts to understand, predict, and prevent these phenomena. A sample of 11,489 cases from the Genomic Psychiatry Cohort (GPC), a NIMH-managed data repository for the investigation of schizophrenia and bipolar disorder, was used for this study. Cases were excluded if TBI was deemed causal to their mental illness. A k-means clustering algorithm was used to probe differences between schizophrenia and bipolar disorder associated with variables including onset age, hallucinations, delusions, head injury, and TBI. Cases were separated into an optimum number of seven clusters, with two clusters including all cases with brain injury. Bipolar disorder with psychosis and TBI were significantly correlated in one cluster in which 72% of cases were male and 99.2% sustained head injury. This cluster also carried the longest average period of unconsciousness. This study demonstrates an association of TBI with psychosis in a subset of bipolar cases, suggesting that traumatic stressors may have the ability to impact gene expression in a vulnerable population, and/or there is a heightened occurrence of TBI in individuals with underlying psychosis. Further studies should more closely examine the interplay between genetic variation in bipolar disorder and susceptibility to psychosis following TBI. © 2015 Wiley Periodicals, Inc.

Parental age effects on odor sensitivity in healthy subjects and schizophrenia patients.

A schizophrenia phenotype for paternal and maternal age effects on illness risk could benefit etiological research. As odor sensitivity is associated with variability in symptoms and cognition in schizophrenia, we examined if it was related to parental ages in patients and healthy controls. We tested Leukocyte Telomere Length (LTL) as an explanatory factor, as LTL is associated with paternal age and schizophrenia risk. Seventy-five DSM-IV patients and 46 controls were assessed for detection of PEA, WAIS-III for cognition, and LTL, assessed by qPCR. In healthy controls, but not schizophrenia patients, decreasing sensitivity was monotonically related to advancing parental ages, particularly in sons. The relationships between parental aging and odor sensitivity differed significantly for patients and controls (Fisher's R to Z: χ(2) = 6.95, P = 0.009). The groups also differed in the association of odor sensitivity with cognition; lesser sensitivity robustly predicted cognitive impairments in patients (<0.001), but these were unassociated in controls. LTL was unrelated to odor sensitivity and did not explain the association of lesser sensitivity with cognitive deficits.Parental aging predicted less sensitive detection in healthy subjects but not in schizophrenia patients. In patients, decreased odor sensitivity strongly predicted cognitive deficits, whereas more sensitive acuity was associated with older parents. These data support separate risk pathways for schizophrenia. A parental age-related pathway may produce psychosis without impairing cognition and odor sensitivity. Diminished odor sensitivity may furthermore be useful as a biomarker for research and treatment studies in schizophrenia. © 2015 Wiley Periodicals, Inc.

Serotonergic neuron regulation informed by in vivo single-cell transcriptomics.

Despite the recognized importance of the dorsal raphe (DR) serotonergic (5-HT) nuclei in the pathophysiology of depression and anxiety, the molecular components/putative drug targets expressed by these neurons are poorly characterized. Utilizing the promoter of an ETS domain transcription factor that is a stable marker of 5-HT neurons (Pet-1) to drive 5-HT neuronal expression of YFP, we identified 5-HT neurons in live acute slices. We isolated RNA from single 5-HT neurons in the ventromedial and lateral wings of the DR and performed single-cell RNA-Seq analysis identifying >500 G-protein coupled receptors (GPCRs) including receptors for classical transmitters, lipid signals, and peptides as well as dozens of orphan-GPCRs. Using these data to inform our selection of receptors to assess, we found that oxytocin and lysophosphatidic acid 1 receptors are translated and active in costimulating, with the α1-adrenergic receptor, the firing of DR 5-HT neurons, while the effects of histamine are inhibitory and exerted at H3 histamine receptors. The inhibitory histamine response provides evidence for tonic in vivo histamine inhibition of 5-HT neurons. This study illustrates that unbiased single-cell transcriptomics coupled with functional analyses provides novel insights into how neurons and neuronal systems are regulated.

Total and differential white blood cell counts, high-sensitivity C-reactive protein, and cardiovascular risk in non-affective psychoses.

Schizophrenia is associated with increased cardiovascular disease morbidity and mortality. Schizophrenia is also associated with immune and inflammatory abnormalities, including aberrant blood levels of lymphocytes, cytokines and high-sensitivity C-reactive protein (hsCRP). The purpose of this study is to investigate the relationship between total and differential white blood cell (WBC) counts, hsCRP, and indices of cardiovascular disease risk in patients with schizophrenia and related non-affective psychoses. 108 inpatients and outpatients age 18-70 with non-affective psychoses and 44 controls participated in this cross-sectional study. Subjects had a fasting blood draw between 8 and 9am for glucose, lipids, total and differential WBC counts, and hsCRP. Vital signs and medical history were obtained. Patients with non-affective psychosis had significantly higher hsCRP levels than controls (p=0.04). In linear regression analyses, lymphocyte and monocyte counts were a significant predictor of the total-to-HDL cholesterol ratio in subjects with non-affective psychosis (p⩽0.02 for each). In binary logistic regression analyses, total WBC count was a significant predictor of an elevated 10-year estimated risk of myocardial infarction and cardiovascular disease in subjects with non-affective psychosis (p⩽0.03 for each). Associations between total and differential WBC counts and cardiovascular disease risk indices were stronger in males than females with non-affective psychosis. Our findings provide further evidence that measurement of total and differential WBC counts may be germane to the clinical care of patients with schizophrenia and related disorders, and support an association between inflammation and cardiovascular disease risk in these patients.

The professional experiences of peer specialists in the Georgia Mental Health Consumer Network.

There has been an increase in the number of peer-led services within the mental health care system. There however remains little information about the experiences of peers serving in such helping roles. This study explored the professional experiences of peer specialists including the basic roles, benefits, and potential challenges of the peer specialist role. Peer specialists (N = 84) completed a battery of surveys and questionnaires. Qualitative analysis of participants' responses indicated that peer specialists face difficulties such as poor compensation, limited employment opportunities, work stress, emotional stress in helping others, and maintaining personal wellness. Quantitative analyses revealed that recovery attitudes may confer clinical and psychosocial benefits for peer specialists and employment may contribute to hope, empowerment, social engagement, and competence. Peer specialists would benefit from resources and supports aimed at their continued training and supervision. Fostering the vocational advancement of peer specialists could potentially enhance their experiential recovery and community functioning.

The Use of Simulation to Teach Suicide Risk Assessment to Health Profession Trainees-Rationale, Methodology, and a Proof of Concept Demonstration with a Virtual Patient.

OBJECTIVE: There is increasing use of educational technologies in medical and surgical specialties. Described herein is the development and application of an interactive virtual patient (VP) to teach suicide risk assessment to health profession trainees. We studied the effect of the following: (1) an interaction with a bipolar VP who attempts suicide or (2) completion of a video-teaching module on interviewing a bipolar patient, on medical students' proficiency in assessing suicide risk in standardized patients. We hypothesized that students who interact with a bipolar VP will be at least as likely to assess suicide risk, as their peers who completed a video module. METHODS: In a randomized, controlled study, we compared the frequency with which second-year students at the Medical College of Georgia asked suicide risk and bipolar symptoms questions by VP/video group. RESULTS: We recruited 67 students. The VP group inquired more frequently than the video group in 4 of 5 suicide risk areas and 11 of 14 other bipolar symptomatology areas. There were minimal to small effect sizes in favor of the VP technology. The students preferred the video over the VP as an educational tool (p = 0.007). CONCLUSIONS: Our study provides proof of concept that both VP and video module approaches are feasible for teaching students to assess suicide risk, and we present evidence about the role of active learning to improve communication skills. Depending on the learning context, interviewing a VP or observation of a videotaped interview can enhance the students' suicide risk assessment proficiency in an interview with a standardized patient. An interactive VP is a plausible modality to deliver basic concepts of suicide risk assessment to medical students, can facilitate individual preferences by providing easy access and portability, and has potential generalizability to other aspects of psychiatric training.

Divergence of RNA localization between rat and mouse neurons reveals the potential for rapid brain evolution.

BACKGROUND: Neurons display a highly polarized architecture. Their ability to modify their features under intracellular and extracellular stimuli, known as synaptic plasticity, is a key component of the neurochemical basis of learning and memory. A key feature of synaptic plasticity involves the delivery of mRNAs to distinct sub-cellular domains where they are locally translated. Regulatory coordination of these spatio-temporal events is critical for synaptogenesis and synaptic plasticity as defects in these processes can lead to neurological diseases. In this work, using microdissected dendrites from primary cultures of hippocampal neurons of two mouse strains (C57BL/6 and Balb/c) and one rat strain (Sprague-Dawley), we investigate via microarrays, subcellular localization of mRNAs in dendrites of neurons to assay the evolutionary differences in subcellular dendritic transcripts localization. RESULTS: Our microarray analysis highlighted significantly greater evolutionary diversification of RNA localization in the dendritic transcriptomes (81% gene identity difference among the top 5% highly expressed genes) compared to the transcriptomes of 11 different central nervous system (CNS) and non-CNS tissues (average of 44% gene identity difference among the top 5% highly expressed genes). Differentially localized genes include many genes involved in CNS function. CONCLUSIONS: Species differences in sub-cellular localization may reflect non-functional neutral drift. However, the functional categories of mRNA showing differential localization suggest that at least part of the divergence may reflect activity-dependent functional differences of neurons, mediated by species-specific RNA subcellular localization mechanisms.