The microbiome-gut-brain axis: implications for schizophrenia and antipsychotic induced weight gain

With the emergence of knowledge implicating the human gut microbiome in the development and regulation of several physiological systems, evidence has accumulated to suggest a role for the gut microbiome in psychiatric conditions and drug response. A complex relationship between the enteric nervous system, the gut microbiota and the central nervous system has been described which allows for the microbiota to influence and respond to a variety of behaviors and psychiatric conditions. Additionally, the use of pharmaceuticals may interact with and alter the microbiota to potentially contribute to adverse effects of the drug. The gut microbiota has been described in several psychiatric disorders including depression and anxiety, but only a few reports have discussed the role of the microbiome in schizophrenia. The following review examines the evidence surrounding the gut microbiota in behavior and psychiatric illness, the role of the microbiota in schizophrenia and the potential for antipsychotics to alter the gut microbiota and promote adverse metabolic events.

Norepinephrine transporter heterozygous knockout mice exhibit altered transport and behavior

The norepinephrine (NE) transporter (NET) regulates synaptic NE availability for noradrenergic signaling in the brain and sympathetic nervous system. Although genetic variation leading to a loss of NET expression has been implicated in psychiatric and cardiovascular disorders, complete NET deficiency has not been found in people, limiting the utility of NET knockout mice as a model for genetically driven NET dysfunction. Here, we investigate NET expression in NET heterozygous knockout male mice (NET(+/-) ), demonstrating that they display an approximately 50% reduction in NET protein levels. Surprisingly, these mice display no significant deficit in NET activity assessed in hippocampal and cortical synaptosomes. We found that this compensation in NET activity was due to enhanced activity of surface-resident transporters, as opposed to surface recruitment of NET protein or compensation through other transport mechanisms, including serotonin, dopamine or organic cation transporters. We hypothesize that loss of NET protein in the NET(+/-) mouse establishes an activated state of existing surface NET proteins. The NET(+/-) mice exhibit increased anxiety in the open field and light-dark box and display deficits in reversal learning in the Morris water maze. These data suggest that recovery of near basal activity in NET(+/-) mice appears to be insufficient to limit anxiety responses or support cognitive performance that might involve noradrenergic neurotransmission. The NET(+/-) mice represent a unique model to study the loss and resultant compensatory changes in NET that may be relevant to behavior and physiology in human NET deficiency disorders.

Multivariate permutation analysis associates multiple polymorphisms with subphenotypes of major depression

Unipolar major depressive disorder (MDD) is a prevalent, disabling condition with multiple genetic and environmental factors impacting disease risk. The diagnosis of MDD relies on a cumulative measure derived from multiple trait dimensions and alone is limited in elucidating MDD genetic determinants. We and others have proposed that MDD may be better dissected using paradigms that assess how specific genes associate with component features of MDD. This within-disease design requires both a well-phenotyped cohort and a robust statistical approach that retains power with multiple tests of genetic association. In the present study, common polymorphic variants of genes related to central monoaminergic and cholinergic pathways that previous studies align with functional change in vitro or depression associations in vivo were genotyped in 110 individuals with unipolar MDD. Subphenotypic characteristics were examined using responses to individual items assessed with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM IV), the 17-item Hamilton Rating Scale for Depression (HAM-D) and the NEO Five Factor Inventory. Multivariate Permutation Testing (MPT) was used to infer genotype-phenotype relationships underlying dimensional findings within clinical categories. MPT analyses show significant associations of the norepinephrine transporter (NET, SLC6A2) -182 T/C (rs2242446) with recurrent depression [odds ratio, OR = 4.15 (1.91-9.02)], NET -3081 A/T (rs28386840) with increase in appetite [OR = 3.58 (1.53-8.39)] and the presynaptic choline transporter (CHT, SLC5A7) Ile89Val (rs1013940) with HAM-D-17 total score {i.e. overall depression severity [OR = 2.74 (1.05-7.18)]}. These relationships illustrate an approach to the elucidation of gene influences on trait components of MDD and with replication, may help identify MDD subpopulations that can benefit from more targeted pharmacotherapy.

Monoamine transporter gene structure and polymorphisms in relation to psychiatric and other complex disorders

The norepinephrine, dopamine and serotonin transporters (NET, DAT and SERT, respectively), limit cellular signaling by recapturing released neurotransmitter, and serve as targets for antidepressants and drugs of abuse, emphasizing the integral role these molecules play in neurotransmission and pathology. This has compelled researchers to search for polymorphisms in monoamine (MA) transporter genes. Studies support linkage and association of MA transporter genetic variation in psychiatric and other complex disorders. Understanding the contribution of MA transporter polymorphisms to human behavior, disease susceptibility and response to pharmacotherapies will involve further progress in linkage and association that will be aided by both definition of highly selective phenotypes and utilization of a large number of polymorphic markers. The relationship of polymorphisms to alterations in transport capacity, likely a complex interaction, involving genetic background, disease state, and medication, will elucidate the means by which MA transporter genetic variability contributes to our individuality.

Stress-induced C-fos expression in the rat locus coeruleus is dependent on neurokinin 1 receptor activation

These experiments examined the role of substance P-selective neurokinin 1 receptors in the restraint-induced activation of the rat locus coeruleus. Immunohistochemistry revealed high levels of neurokinin 1 receptor expression in the plasma membrane of tyrosine hydroxylase-positive locus coeruleus neurons. The selective neurokinin 1 receptor antagonists, RP 67580 (5 nmol) and L-760,735 (3.4 nmol), were administered intracerebroventricularly prior to restraint stress, and c-fos protein was measured as an index of locus coeruleus activation. Both antagonists attenuated the restraint-induced increase in locus coeruleus c-fos expression, whereas their inactive enantiomers were ineffective. These results suggest that neurokinin 1 receptors may mediate activation of locus coeruleus neurons during stress. Neurokinin 1 receptor antagonists may prove to be novel therapeutic compounds in the treatment of anxiety and depression.

Analysis of tyrosine hydroxylase gene transcription using an intron specific probe

The nuclear run-on assay is the most commonly used technique to determine transcription rates of specific genes such as tyrosine hydroxylase. Its application to studies in the nervous system is problematic, however, as a result of limitations in sensitivity and the loss of anatomical integrity. We observed that the relative levels of tyrosine hydroxylase intron 2-containing RNA using a ribonuclease protection assay in the adrenal medulla changed in response to pharmacological treatments consistently with changes shown by the nuclear run-on assay. Our results indicate that measures of tyrosine hydroxylase primary transcript levels offer an alternative to the nuclear run-on assay and validate the application of intron-specific in situ hybridization as a means of assessing the relative transcriptional activity of the tyrosine hydroxylase gene. Similar quantitative results were obtained using intron-specific in situ hybridization with oligonucleotide probes specific for rat tyrosine hydroxylase intron 2. Furthermore, we observed that intron-specific in situ hybridization could be used to measure tyrosine hydroxylase transcription rates in the locus coeruleus, providing resolution at the level of single neurons. Thus, measuring the levels of tyrosine hydroxylase intron 2 provides a sensitive measure of tyrosine hydroxylase transcription rate that can be applied to the study of brain catecholaminergic neurons.

Tachykinin NK1 receptor antagonists enhance stress-induced c-fos in rat locus coeruleus

These experiments tested the hypothesis that substance P neurotransmission at tachykinin NK1 receptors in the locus coeruleus is involved in stress-induced activation of the locus coeruleus, using c-fos as an index of activation. Selective tachykinin NK1 receptor antagonists administered systemically did not result in substantial locus coeruleus c-fos expression. Restraint stress resulted in a large number of locus coeruleus c-fos expressing cells. Administration of two selective tachykinin NK1 receptor antagonists prior to restraint resulted in an increase in the number of locus coeruleus c-fos expressing cells, compared to restraint alone. These results suggest that the enhanced c-fos expression observed in response to tachykinin NK1 receptor antagonists combined with stress, could be due to the blockade of tachykinin NK1 receptor-mediated activity at sites other than the locus coeruleus, resulting in an overall activation of the locus coeruleus.

Microvascular techniques in limb-sparing surgery

Microvascular techniques allowing free tissue transfer have expanded the indications for limb salvage in tumor patients. Preoperative planning should predict the type of deficit anticipated. Specific techniques for soft tissue, skeletal, neurovascular, and composite tissue transfer are discussed. While demanding, the use of living autogenous tissue gives the potential for biologic adaptivity and life-long durability.

Determination of benzyl alcohol and its metabolite in plasma by reversed-phase high-performance liquid chromatography

A study undertaken following recent reports of deaths in neonatal children associated with the use of benzyl alcohol resulted in the development of a stability-indicating high-performance liquid chromatographic assay of benzyl alcohol in plasma using benzocaine as internal standard. Thawed plasma samples were diluted and subjected to solid-phase extraction using Extrelut and eluted with ethyl acetate. The evaporated eluate was reconstituted with mobile phase and chromatographed on a C18 column with water-acetonitrile-glacial acetic acid as mobile phase and detection at 254 nm. Baseline separation was achieved within 12 min for benzyl alcohol, benzaldehyde, benzoic acid, hippuric acid and benzocaine. Peak-height ratios were linear over 80-640 ng of benzyl alcohol injected (r = 0.998) and over 10-80 ng of benzoic acid injected (r = 0.999). Benzaldehyde and hippuric acid were not quantitated because these compounds were not detectable in actual dog plasma. Validation studies by spiking dog plasma with benzyl alcohol and benzoic acid gave overall percent recoveries (+/- relative standard deviation, n = 4) of 98.3 +/- 3.0 and 101.4 +/- 7.6%, respectively. The method was applied to the assay of actual plasma samples. Since benzyl alcohol is very susceptible to oxidation to benzaldehyde and benzoic acid, its purity in bulk liquid samples can be determined by this method.