Dopaminergic modulation of regional cerebral blood flow: An arterial spin labelling study of genetic and pharmacological manipulation of COMT activity

Dopamine has direct and complex vasoactive effects on cerebral circulation. Catechol-O-methyltransferase (COMT) regulates cortical dopamine, and its activity can be influenced both genetically and pharmacologically. COMT activity influences the functional connectivity of the PFC at rest, as well as its activity during task performance, determined using blood oxygen level-dependent (BOLD) fMRI. However, its effects on cerebral perfusion have been relatively unexplored. Here, 76 healthy males, homozygous for the functional COMT Val¹⁵⁸Met polymorphism, were administered either the COMT inhibitor tolcapone or placebo in a double-blind, randomised design. We then assessed regional cerebral blood flow at rest using pulsed arterial spin labelling. Perfusion was affected by both genotype and drug. COMT genotype affected frontal regions (Val¹⁵⁸ > Met¹⁵⁸), whilst tolcapone influenced parietal and temporal regions (placebo > tolcapone). There was no genotype by drug interaction. Our data demonstrate that lower COMT activity is associated with lower cerebral blood flow, although the regions affected differ between those affected by genotype compared with those altered by acute pharmacological inhibition. The results extend the evidence for dopaminergic modulation of cerebral blood flow. Our findings also highlight the importance of considering vascular effects in functional neuroimaging studies, and of exercising caution in ascribing group differences in BOLD signal solely to altered neuronal activity if information about regional perfusion is not available.

Biochemical and genetic predictors and correlates of response to lamotrigine and folic acid in bipolar depression: Analysis of the CEQUEL clinical trial

OBJECTIVES

CEQUEL (Comparative Evaluation of QUEtiapine plus Lamotrigine combination versus quetiapine monotherapy [and folic acid versus placebo] in bipolar depression) was a double-blind, randomized, placebo-controlled, parallel group, 2×2 factorial trial that examined the effect of adding lamotrigine and/or folic acid (FA) to quetiapine in bipolar depression. Lamotrigine improved depression, but its effectiveness was reduced by FA. We investigated the baseline predictors and correlates of clinical response, and the possible basis of the interaction.

METHODS

The main outcome was change in depressive symptoms at 12 weeks, measured using the Quick Inventory for Depressive Symptoms-self report version 16 (QIDS-SR16). We examined the relationship between symptoms and lamotrigine levels, and biochemical measures of one-carbon metabolism and functional polymorphisms in catechol-O-methyltransferase (COMT), methylene tetrahydrofolate reductase (MTHFR) and folate hydrolase 1 (FOLH1).

RESULTS

Lamotrigine levels were unaffected by FA and did not differ between those participants who achieved remission and those with persisting symptoms. When participants with subtherapeutic serum levels were excluded, there was a main effect of lamotrigine on the main outcome, although this remained limited to those randomized to FA placebo. None of the biochemical measures correlated with clinical outcome. The negative impact of FA on lamotrigine response was limited to COMT Met carriers. FOLH1 and MTHFR had no effect.

CONCLUSIONS

Our results clarify that FA's inhibition of lamotrigine's efficacy is not a pharmacokinetic effect, and that low serum lamotrigine levels contributed to lamotrigine's lack of a main effect at 12 weeks. We were unable to explain the lamotrigine-FA interaction, but our finding that it is modulated by the COMT genotype provides a starting point for follow-on neurobiological investigations. More broadly, our results highlight the value of including biochemical and genetic indices in randomized clinical trials.

A systematic review of calcium channel antagonists in bipolar disorder and some considerations for their future development

l-type calcium channel (LTCC) antagonists have been used in bipolar disorder for over 30 years, without becoming an established therapeutic approach. Interest in this class of drugs has been rekindled by the discovery that LTCC genes are part of the genetic aetiology of bipolar disorder and related phenotypes. We have therefore conducted a systematic review of LTCC antagonists in the treatment and prophylaxis of bipolar disorder. We identified 23 eligible studies, with six randomised, double-blind, controlled clinical trials, all of which investigated verapamil in acute mania, and finding no evidence that it is effective. Data for other LTCC antagonists (diltiazem, nimodipine, nifedipine, methyoxyverapamil and isradipine) and for other phases of the illness are limited to observational studies, and therefore no robust conclusions can be drawn. Given the increasingly strong evidence for calcium signalling dysfunction in bipolar disorder, the therapeutic candidacy of this class of drugs has become stronger, and hence we also discuss issues relevant to their future development and evaluation. In particular, we consider how genetic, molecular and pharmacological data can be used to improve the selectivity, efficacy and tolerability of LTCC antagonists. We suggest that a renewed focus on LTCCs as targets, and the development of 'brain-selective' LTCC ligands, could be one fruitful approach to innovative pharmacotherapy for bipolar disorder and related phenotypes.

Mood instability: significance, definition and measurement

Mood instability is common, and an important feature of several psychiatric disorders. We discuss the definition and measurement of mood instability, and review its prevalence, characteristics, neurobiological correlates and clinical implications. We suggest that mood instability has underappreciated transdiagnostic potential as an investigational and therapeutic target.

What causes aberrant salience in schizophrenia? A role for impaired short-term habituation and the GRIA1 (GluA1) AMPA receptor subunit

The GRIA1 locus, encoding the GluA1 (also known as GluRA or GluR1) AMPA glutamate receptor subunit, shows genome-wide association to schizophrenia. As well as extending the evidence that glutamatergic abnormalities have a key role in the disorder, this finding draws attention to the behavioural phenotype of Gria1 knockout mice. These mice show deficits in short-term habituation. Importantly, under some conditions the attention being paid to a recently presented neutral stimulus can actually increase rather than decrease (sensitization). We propose that this mouse phenotype represents a cause of aberrant salience and, in turn, that aberrant salience (and the resulting positive symptoms) in schizophrenia may arise, at least in part, from a glutamatergic genetic predisposition and a deficit in short-term habituation. This proposal links an established risk gene with a psychological process central to psychosis and is supported by findings of comparable deficits in short-term habituation in mice lacking the NMDAR receptor subunit Grin2a (which also shows association to schizophrenia). As aberrant salience is primarily a dopaminergic phenomenon, the model supports the view that the dopaminergic abnormalities can be downstream of a glutamatergic aetiology. Finally, we suggest that, as illustrated here, the real value of genetically modified mice is not as 'models of schizophrenia' but as experimental tools that can link genomic discoveries with psychological processes and help elucidate the underlying neural mechanisms.

Modulation of hippocampal dopamine metabolism and hippocampal-dependent cognitive function by catechol-O-methyltransferase inhibition

Catechol-O-methyltransferase (COMT) catabolises the catecholamine neurotransmitters and influences cognitive function. COMT modulates dopamine levels in the prefrontal cortex and its action in this region is generally invoked to explain its effects on cognition. However, its role in other brain regions important for cognitive function remains largely unexplored. Here, we investigated COMT's impact on dopamine metabolism in the hippocampus and hippocampal-dependent behaviour. We examined the acute effects of a centrally-acting COMT inhibitor, tolcapone (30 mg/kg i.p.), on dopamine metabolism in the rat dorsal hippocampus, assessed both in tissue homogenates and extracellularly, using in vivo microdialysis. Additionally, we investigated the effect of tolcapone on delayed-rewarded alternation and spatial novelty preference, behavioural tasks which are dependent on the dorsal hippocampus. Tolcapone significantly modulated dopamine metabolism in the dorsal hippocampus, as indexed by the depletion of extracellular homovanillic acid (HVA) and the accumulation of dihydroxyphenylacetic acid (DOPAC). Tolcapone also improved performance on the delayed-rewarded alternation and spatial novelty preference tasks, compared to vehicle-treated rats. Our findings suggest that COMT regulates dorsal hippocampal neurochemistry and modulates hippocampus-dependent behaviours. These findings support the therapeutic candidacy of COMT inhibition as a cognitive enhancer, and suggest that, in addition to the prefrontal cortex, the hippocampus might be a key region for mediating these effects.

The role of catechol-O-methyltransferase in reward processing and addiction

Catechol-O-methyltransferase (COMT) catabolises dopamine and is important for regulating dopamine levels in the prefrontal cortex. Consistent with its regulation of prefrontal cortex dopamine, COMT modulates working memory and executive function; however, its significance for other cognitive domains, and in other brain regions, remains relatively unexplored. One such example is reward processing, for which dopamine is a critical mediator, and in which the striatum and corticostriatal circuitry are implicated. Here, we discuss emerging data which links COMT to reward processing, review what is known of the underlying neural substrates, and consider whether COMT is a good therapeutic target for treating addiction. Although a limited number of studies have investigated COMT and reward processing, common findings are beginning to emerge. COMT appears to modulate cortical and striatal activation during both reward anticipation and delivery, and to impact on reward-related learning and its underlying neural circuitry. COMT has been studied as a candidate gene for numerous reward-related phenotypes and there is some preliminary evidence linking it with certain aspects of addiction. However, additional studies are required before these associations can be considered robust. It is premature to consider COMT a good therapeutic target for addiction, but this hypothesis should be revisited as further information emerges. In particular, it will be critical to reveal the precise neurobiological mechanisms underlying links between COMT and reward processing, and the extent to which these relate to the putative associations with addiction.

Human brain weight is correlated with expression of the 'housekeeping genes' beta-2-microglobulin (β2M) and TATA-binding protein (TBP)

AIMS

Many variables affect mRNA measurements in post mortem human brain tissue. Brain weight has not hitherto been considered to be such a factor. This study examined whether there is any relationship between brain weight and mRNA abundance.

METHODS

We investigated quantitative real-time RT-PCR data for five 'housekeeping genes' using the 104 adult brains of the Stanley Microarray Consortium series. Eleven data sets were analysed, from cerebellum, hippocampus, and anterior cingulate cortex. We used a specified sequence of correlations, partial correlations and multiple regression analyses.

RESULTS

Brain weight correlated with the 'raw' (i.e. non-normalized) data for two mRNAs, β2-microglobulin and TATA-binding protein, measured in cerebellum and hippocampus, respectively. In hippocampus, the geometric mean of three housekeeping gene transcripts also correlated with brain weight. The correlations were significant after adjusting for age, sex and other confounders, and the effect of brain weight was confirmed using multiple regression. No correlations with brain weight were seen in the anterior cingulate cortex, nor for the other mRNAs examined.

CONCLUSIONS

The findings were not anticipated; they need replication in another brain series, and a more systematic survey is indicated. In the interim, we suggest that quantitative gene expression studies in human brain should inspect for a potential influence of brain weight, especially as the affected transcripts are commonly used as reference genes for normalization purposes in studies of neurological and psychiatric disorders. The relationship of brain weight with β2-microglobulin mRNA may reflect the roles of major histocompatibility complex class I genes in synapse formation and plasticity.

Expression of D-serine and glycine transporters in the prefrontal cortex and cerebellum in schizophrenia

The NMDA receptor co-agonists D-serine and glycine are thought to contribute to glutamatergic dysfunction in schizophrenia. They are removed from the synapse by specific neuronal and glial transporters, the status of which is clearly relevant to theories of D-serine and glycine function in the disorder. D-serine is primarily transported by Asc-1, and glycine by GlyT1 but maybe also by SNAT2. As a first step to addressing this issue, we studied Asc-1, GlyT1 and SNAT2 expression in dorsolateral prefrontal cortex and cerebellum of 18 subjects with schizophrenia and 20 controls, using immunoblotting and in situ hybridization. Asc-1 protein and SNAT2 mRNA were decreased in schizophrenia in both regions. GlyT1 mRNA and protein, and Asc-1 mRNA, were not altered. Antipsychotic administration for 14 days did not alter expression of the genes in rat brain. Unchanged GlyT1 suggests that glycine transport is not markedly affected in schizophrenia, and therefore that increased synaptic removal is not the basis for the putative deficit in glycine modulation of NMDA receptors in the disorder. Lowered Asc-1 in schizophrenia implies that D-serine reuptake is reduced, perhaps as a response to decreased synaptic D-serine availability. However, this interpretation remains speculative. Further investigations will be valuable in the evaluation of these transporters as potential therapeutic targets in psychosis.

The group II metabotropic glutamate receptor 3 (mGluR3, mGlu3, GRM3): expression, function and involvement in schizophrenia

Group II metabotropic glutamate receptors (mGluRs) comprise mGluR2 (mGlu2; encoded by GRM2) and mGluR3 (mGlu3; encoded by GRM3) and modulate glutamate neurotransmission and synaptic plasticity. Here we review the expression and function of mGluR3 and its involvement in schizophrenia. mGluR3 is expressed by glia and neurons in many brain regions and has a predominantly presynaptic distribution, consistent with its role as an inhibitory autoreceptor and heteroceptor. mGluR3 splice variants exist in human brain but are of unknown function. Differentiation of mGluR3 from mGluR2 has been problematic because of the lack of selective ligands and antibodies; the available data suggest particular roles for mGluR3 in long-term depression, in glial function and in neuroprotection. Some but not all studies find genetic association of GRM3 polymorphisms with psychosis, with the risk alleles also being associated with schizophrenia-related endophenotypes such as impaired cognition, cortical activation and glutamate markers. The dimeric form of mGluR3 may be reduced in the brain in schizophrenia. Finally, preclinical findings have made mGluR3 a putative therapeutic target, and now direct evidence for antipsychotic efficacy of a group II mGluR agonist has emerged from a randomised clinical trial in schizophrenia. Together these data implicate mGluR3 in aetiological, pathophysiological and pharmacotherapeutic aspects of the disorder.

The met(158) allele of catechol-O-methyltransferase (COMT) is associated with obsessive-compulsive disorder in men: case-control study and meta-analysis

Existing data suggest a genetic association between the met(158) allele of catechol-O-methyltransferase (COMT) and obsessive-compulsive disorder (OCD). However, the results are inconclusive and complicated by possible gender differences. We sought to resolve the question in two ways. First, we carried out a new case-control study in 87 adults with OCD and 327 healthy comparison subjects. The study replicated reports of an increased met(158) allele frequency in men with OCD (odds ratio (OR)=1.91, 95% confidence interval (CI) 1.07-3.40, P=0.026), with no effect in women (OR=1.13, 95% CI 0.74-1.72, P=0.56). Second, we performed a meta-analysis of all published case-control data (n=1908 subjects). This revealed an association of COMT met(158) with OCD (OR=1.23, 95% CI 1.06-1.42, P=0.005) and an interaction with gender (z=4.27, P<0.0001). The association between COMT met(158) and OCD was present in men (OR=1.88, 95% CI 1.45-2.44, P<0.001) but not in women (OR=0.98, 95% CI 0.78-1.22, P=0.83). We conclude that COMT may play a role in the genetic aetiology of OCD in men. The biological plausibility of the association is increased by the functionality of the val(158)met polymorphism in terms of its effect on COMT enzyme activity, and by the role of COMT in cortical dopamine signalling and information processing. The finding also extends the evidence for sexual dimorphism in COMT and in OCD.

Differential control of the scapulothoracic muscles in humans

The control of the scapulothoracic muscles trapezius (Tr) and serratus anterior (SA) has been examined in normal human subjects. Electromyographic recordings were made from the SA and Tr muscles (upper trapezius UTr, lower trapezius LTr) using surface electrodes placed bilaterally. Magnetic stimulation of the motor cortex and electrical stimulation of peripheral nerves were used to examine their descending and reflex control. The average optimal site of cortical stimulation was found to be the same for SA, UTr and LTr (an approximate centre of gravity of -0.6 cm, 3.7 cm where the centre of gravity is expressed as the mean anterio-posterior position, the mean medio-lateral position). Some asymmetry in the cortical representation of UTr was found in each individual tested. Magnetic stimulation evoked bilateral MEPs in Tr (latency contralateral (c) UTr 8.5 +/- 1.6 ms, ipsilateral (i) UTr 19.0 +/- 2.7 ms) but only contralateral responses were evoked in SA (11.2 +/- 2.6 ms). Electrical stimulation of the long thoracic nerve at two sites was used to examine homonymous and heteronymous reflexes of SA, while electrical stimulation of cervical nerve of C3/4 was used to examine the heteronymous reflexes of Tr. Ipsilateral SA H reflexes were evoked at a latency of 9.9 +/- 0.8 ms (proximal site) and 10.8 +/- 1.2 ms (distal site). No group I reflexes were evoked from SA to its contralateral homologue. No group I reflexes were evoked between Tr and SA. Finally, cross-correlation of activity from the Tr muscle pairs and the SA muscle pair revealed that the motoneurones of the Tr muscles share some common presynaptic input whereas there was no detectable common presynaptic input to the SA muscle pair. This study extends and consolidates knowledge regarding the neural control of trapezius and for the first time explores the neural control of SA. The study demonstrates a contrasting bilateral control of Tr and SA. These patterns of connections are discussed in relation to the contrasting bilateral functional roles of these muscles.

Differential control of the scapulothoracic muscles in humans

The control of the scapulothoracic muscles trapezius (Tr) and serratus anterior (SA) has been examined in normal human subjects. Electromyographic recordings were made from the SA and Tr muscles (upper trapezius UTr, lower trapezius LTr) using surface electrodes placed bilaterally. Magnetic stimulation of the motor cortex and electrical stimulation of peripheral nerves were used to examine their descending and reflex control. The average optimal site of cortical stimulation was found to be the same for SA, UTr and LTr (an approximate centre of gravity of -0.6 cm, 3.7 cm where the centre of gravity is expressed as the mean anterio-posterior position, the mean medio-lateral position). Some asymmetry in the cortical representation of UTr was found in each individual tested. Magnetic stimulation evoked bilateral MEPs in Tr (latency contralateral (c) UTr 8.5 +/- 1.6 ms, ipsilateral (i) UTr 19.0 +/- 2.7 ms) but only contralateral responses were evoked in SA (11.2 +/- 2.6 ms). Electrical stimulation of the long thoracic nerve at two sites was used to examine homonymous and heteronymous reflexes of SA, while electrical stimulation of cervical nerve of C3/4 was used to examine the heteronymous reflexes of Tr. Ipsilateral SA H reflexes were evoked at a latency of 9.9 +/- 0.8 ms (proximal site) and 10.8 +/- 1.2 ms (distal site). No group I reflexes were evoked from SA to its contralateral homologue. No group I reflexes were evoked between Tr and SA. Finally, cross-correlation of activity from the Tr muscle pairs and the SA muscle pair revealed that the motoneurones of the Tr muscles share some common presynaptic input whereas there was no detectable common presynaptic input to the SA muscle pair. This study extends and consolidates knowledge regarding the neural control of trapezius and for the first time explores the neural control of SA. The study demonstrates a contrasting bilateral control of Tr and SA. These patterns of connections are discussed in relation to the contrasting bilateral functional roles of these muscles.

Catechol-o-methyltransferase enzyme activity and protein expression in human prefrontal cortex across the postnatal lifespan

The prefrontal cortex (PFC) dopamine system, which is critical for modulating PFC function, undergoes remodeling until at least young adulthood in primates. Catechol-o-methyltransferase (COMT) alters extracellular dopamine levels in PFC, and its gene contains a functional polymorphism (Val(158)Met) that has been associated with variation in PFC function. We examined COMT enzyme activity and protein immunoreactivity in the PFC during human postnatal development. Protein was extracted from PFC of normal individuals from 6 age groups: neonates (1-4 months), infants (5-11 months), teens (14-18 years), young adults (20-24 years), adults (31-43 years), and aged individuals (68-86 years; n = 5-8 per group). There was a significant 2-fold increase in COMT enzyme activity from neonate to adulthood, paralleled by increases in COMT protein immunoreactivity. Furthermore, COMT protein immunoreactivity was related to Val(158)Met genotype, as has been previously demonstrated. The significant increase in COMT activity from neonate to adulthood complements previous findings of protracted postnatal changes in the PFC dopamine system and may reflect an increasing importance of COMT for PFC dopamine regulation during maturation.

Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia

We investigated the effect of acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (Howe Sound, BC, Canada) on primary productivity and chlorophyll a levels in the receiving waters of Howe Sound before, during, and after freshet from the Squamish River. Elevated concentrations of copper (integrated average through the water column >0.050 mgl(-1)) in nearshore waters indicated that under some conditions a small gyre near the mouth of Britannia Creek may have retained the AMD from Britannia Creek and from a 30-m deep water outfall close to shore. Regression and correlation analyses indicated that copper negatively affected primary productivity during April (pre-freshet) and November (post-freshet). Negative effects of copper on primary productivity were not supported statistically for July (freshet), possibly because of additional effects such as turbidity from the Squamish River. Depth-integrated average and surface chlorophyll a were correlated to copper concentrations in April. During this short study we demonstrated that copper concentrations from the AMD discharge can negatively affect both primary productivity and the standing stock of primary producers in Howe Sound.

Interstitial white matter neuron density in the dorsolateral prefrontal cortex and parahippocampal gyrus in schizophrenia

Alterations in the density or distribution of interstitial white matter neurons are taken as evidence in support of an early developmental component to schizophrenia. However, the existence and nature of interstitial white matter neuron changes in schizophrenia remain inconclusive. Recently, we reported that interstitial white matter neuron density is increased in the superficial white matter of the superior temporal gyrus in schizophrenia, but unchanged in deep white matter. This study extends our investigations to the dorsolateral prefrontal cortex and parahippocampal gyrus. Using the specific neuronal antibody NeuN, interstitial white matter neuron density was found to be increased in schizophrenia in the superficial white matter of the dorsolateral prefrontal cortex, with no significant changes elsewhere. As interstitial white matter neurons are presumed to be remnants of the embryonic cortical subplate, these findings provide additional evidence supportive of an early developmental abnormality in schizophrenia.

Comparison by PAM fluorometry of photosynthetic activity of nine marine phytoplankton grown under identical conditions

The photosynthetic activity of marine phytoplankton from five algal classes (Phaeodactylum tricornutum, Skeletonema costatum, Thalassiosira oceanica, Thalassiosira weissflogii, Dunaliella tertiolecta, Mantoniella squamata, Emiliania huxleyi, Pavlova lutheri and Heterosigma akashiwo) was investigated under identical growth conditions to determine interspecies differences. Primary photochemistry and electron transport capacity of individual species were examined by pulse amplitude-modulated (PAM) fluorescence. Although few differences were found in maximal photosystem II (PSII) photochemical efficiency between various species, large differences were noticed in their PSII-photosystem I (PSI) electron transport activity. We found that species such as T. oceanica and M. squamata have much lower photochemical activity than H. akashiwo. It appeared that processes involved in electron transport activity were more susceptible to change during algal evolution compared with the primary photochemical act close to PSII. Large variations in the nonphotochemical energy dissipation event among species were also observed. Light energy required to saturate photosynthesis was very different between species. We have shown that M. squamata and H. akashiwo required higher light energy (>1300 micromol m(-2) s(-1)) to saturate photosynthesis compared with S. costatum and E. huxleyi (ca 280 micromol m(-2) s(-1)). These differences were interpreted to be the result of variations in the size of light-harvesting complexes associated with PSII. These disparities in photosynthetic activity might modulate algal community structure in the natural environment where light energy is highly variable. Our results suggest that for an accurate evaluation of primary productivity from fluorescence measurements, it is essential to know the species composition of the algal community and the individual photosynthetic capacity related to the major phytoplankton species present in the natural phytoplankton assemblage.

Decreased expression of vesicular glutamate transporter 1 and complexin II mRNAs in schizophrenia: further evidence for a synaptic pathology affecting glutamate neurons

Synaptic protein gene expression is altered in schizophrenia. In the hippocampal formation there may be particular involvement of glutamatergic neurons and their synapses, but overall the profile remains unclear. In this in situ hybridization histochemistry (ISHH) study, we examined four informative synaptic protein transcripts: vesicular glutamate transporter (VGLUT) 1, VGLUT2, complexin I, and complexin II, in dorsolateral prefrontal cortex (DPFC), superior temporal cortex (STC), and hippocampal formation, in 13 subjects with schizophrenia and 18 controls. In these areas, VGLUT1 and complexin II are expressed primarily by excitatory neurons, whereas complexin I is mainly expressed by inhibitory neurons. In schizophrenia, VGLUT1 mRNA was decreased in hippocampal formation and DPFC, complexin II mRNA was reduced in DPFC and STC, and complexin I mRNA decreased in STC. Hippocampal VGLUT1 mRNA declined with age selectively in the schizophrenia group. VGLUT2 mRNA was not quantifiable due to its low level. The data provide additional evidence for a synaptic pathology in schizophrenia, in terms of a reduced expression of three synaptic protein genes. In the hippocampus, the loss of VGLUT1 mRNA supports data indicating that glutamatergic presynaptic deficits are prominent, whereas the pattern of results in temporal and frontal cortex suggests broadly similar changes may affect inhibitory and excitatory neurons. The impairment of synaptic transmission implied by the synaptic protein reductions may contribute to the dysfunction of cortical neural circuits that characterises the disorder.

Schizophrenia genes, gene expression, and neuropathology: on the matter of their convergence

This review critically summarizes the neuropathology and genetics of schizophrenia, the relationship between them, and speculates on their functional convergence. The morphological correlates of schizophrenia are subtle, and range from a slight reduction in brain size to localized alterations in the morphology and molecular composition of specific neuronal, synaptic, and glial populations in the hippocampus, dorsolateral prefrontal cortex, and dorsal thalamus. These findings have fostered the view of schizophrenia as a disorder of connectivity and of the synapse. Although attractive, such concepts are vague, and differentiating primary events from epiphenomena has been difficult. A way forward is provided by the recent identification of several putative susceptibility genes (including neuregulin, dysbindin, COMT, DISC1, RGS4, GRM3, and G72). We discuss the evidence for these and other genes, along with what is known of their expression profiles and biological roles in brain and how these may be altered in schizophrenia. The evidence for several of the genes is now strong. However, for none, with the likely exception of COMT, has a causative allele or the mechanism by which it predisposes to schizophrenia been identified. Nevertheless, we speculate that the genes may all converge functionally upon schizophrenia risk via an influence upon synaptic plasticity and the development and stabilization of cortical microcircuitry. NMDA receptor-mediated glutamate transmission may be especially implicated, though there are also direct and indirect links to dopamine and GABA signalling. Hence, there is a correspondence between the putative roles of the genes at the molecular and synaptic levels and the existing understanding of the disorder at the neural systems level. Characterization of a core molecular pathway and a 'genetic cytoarchitecture' would be a profound advance in understanding schizophrenia, and may have equally significant therapeutic implications.

Functional modulation of shoulder girdle stability

We have previously reported that electrical stimulation of the ulnar nerve at group I strength evokes reflex excitation of the trapezius muscle in normal human subjects. In the present study this reflex has been evoked while subjects were performing a number of different tasks. When subjects performed a task involving a high degree of manual dexterity, the reflex was larger. On the other hand, when subjects performed a task that can be achieved with virtually no movement of the hand or wrist musculature, the reflex does not appear to show any task dependency. These results support the view that in delicate tasks of the hand, such compensatory reflexes are more important than in basic mechanisms such as lifting an object. The functional consequences of these findings and their significance in relation to the possibility that these task-related reflex gain changes produce intention tremor is discussed.

Catechol-o-methyltransferase inhibition improves set-shifting performance and elevates stimulated dopamine release in the rat prefrontal cortex

The Val158Met polymorphism of the human catechol-O-methyltransferase (COMT) gene affects activity of the enzyme and influences performance and efficiency of the prefrontal cortex (PFC); however, although catecholaminergic neurotransmission is implicated, the underlying mechanisms remain elusive because studies of the role of COMT in PFC function are sparse. This study investigated the effect of tolcapone, a brain-penetrant COMT inhibitor, on a rat model of attentional set shifting, which is dependent on catecholamines and the medial PFC (mPFC). Additionally, we investigated the effect of tolcapone on extracellular catecholamines in the mPFC using microdialysis in awake rats. Tolcapone significantly and specifically improved extradimensional (ED) set shifting. Tolcapone did not affect basal extracellular catecholamines, but significantly potentiated the increase in extracellular dopamine (DA) elicited by either local administration of the depolarizing agent potassium chloride or systemic administration of the antipsychotic agent clozapine. Although extracellular norepinephrine (NE) was also elevated by local depolarization and clozapine, the increase was not enhanced by tolcapone. We conclude that COMT activity specifically affects ED set shifting and is a significant modulator of mPFC DA but not NE under conditions of increased catecholaminergic transmission. These data suggest that the links between COMT activity and PFC function can be modeled in rats and may be specifically mediated by DA. The interaction between clozapine and tolcapone may have implications for the treatment of schizophrenia.

Stretch reflexes in human abdominal muscles

Homonymous and heteronymous reflex connections of the abdominal muscles were investigated by the application of a tap to the muscle belly and observation of surface electromyographic responses. Reflex responses of the following abdominal muscles were investigated both ipsilateral and contralateral to the tap: rectus abdominis (RA), external oblique (EO) and internal oblique (IO). Reflexes were evoked in each of the homonymous muscles with latencies and estimated conduction velocities compatible with being evoked by Ia muscle afferents and having a monosynaptic component. Short latency heteronymous excitatory reflex connections were also observed in muscles on both ipsilateral and contralateral sides in response to the same stimulus. The latencies of the crossed responses were only marginally longer than responses evoked in the respective ipsilateral muscle. Moreover, the reflexes evoked in the IO muscle from ipsilateral and contralateral IO muscle afferents were of comparable amplitude, as were those reflexes evoked in ipsilateral and contralateral EO and RA muscles when tapping IO. These similarities in the reflex characteristics on the ipsilateral and contralateral sides suggest that abdominal muscle afferents activate similar pathways to muscles on both sides of the body. It follows that if the homonymous stretch reflex of abdominal muscles have a monosynaptic component, then a similar monosynaptic pathway activates synergistic motoneurones, not only ipsilaterally but also contralaterally.

Neuregulin-1 (NRG-1) mRNA and protein in the adult human brain

Neuregulin-1 (NRG-1) plays important roles in the development and plasticity of the brain, and it has recently been identified as a susceptibility gene for schizophrenia. Though there are rodent data, little is known about its distribution in the human brain. The aim of this study was to ascertain the localization of NRG-1 and its mRNA in multiple regions of the normal adult human brain. We investigated NRG-1 mRNA in 11 subjects using in situ hybridization and northern analysis, and NRG-1 protein in six subjects using immunohistochemistry and Western blotting. NRG-1 mRNA was present as bands of approximately 2, 3 and 6 kb. It was clearly detected in the prefrontal cortex (middle laminae), hippocampal formation (except CA1), cerebellum, oculomotor nucleus, superior colliculus, red nucleus and substantia nigra pars compacta. At the cellular level, NRG1 mRNA was abundant in hippocampal and cortical pyramidal neurons and some interneurons, and in cerebellar Purkinje cells and Golgi cells. NRG-1 protein was detected as bands of approximately 140, 110, 95 and 60 kD. Immunohistochemistry revealed NRG-1 in many cell populations, consistent with the mRNA data, being prominent in pyramidal neurons, Purkinje cells, several brainstem nuclei, and white matter neurons. Moderate NRG-1 immunoreactivity was also observed in cerebellar and dentate gyrus granule cells, and some glia. Within neurons, NRG-1 staining was primarily somatodendritic; in the cell body staining was granular, with clustering close to the plasma and nuclear membranes. There was also labeling of some fiber tracts, and local areas of neuropil (e.g. in the dentate nucleus) suggestive of a pre-synaptic location of NRG-1. The data show a widespread expression of NRG-1 in the adult human brain, including, but not limited to, brain areas and cell populations implicated in schizophrenia. Using these normative data, future studies can ascertain whether the role of NRG-1 in the disease is mediated, or accompanied, via alterations in its expression.

Interstitial white matter neurons express less reelin and are abnormally distributed in schizophrenia: towards an integration of molecular and morphologic aspects of the neurodevelopmental hypothesis

Two main pieces of neurobiological evidence are adduced to support an early neurodevelopmental component to schizophrenia. Firstly, an abnormal distribution of neurons, especially interstitial white matter neurons (IWMNs). Secondly, decreased expression of reelin, a key developmental signalling molecule. Although influential, neither result is wholly established, and a possible link between them has not been examined. We addressed both issues, in superior temporal cortex, in 12 subjects with schizophrenia and 14 controls. The distribution and density of IWMNs, immunostained with the neuronal marker NeuN, was increased in the superficial white matter in schizophrenia (+16%; P=0.03). IWMN density in deep white matter was unaffected. Using in situ hybridization, reelin mRNA was found to be expressed by many IWMNs, layer I neurons, and scattered interneurons. Superficial IWMNs (P=0.008) and layer I neurons (P=0.036) both expressed less reelin mRNA per cell in schizophrenia, with a trend for deep IWMNs (P=0.055). In conclusion, we replicated findings of increased IWMN density, and of decreased reelin expression, in schizophrenia. The loss of reelin reflects, at least partly, its decreased expression by IWMNs. These findings together support neurodevelopmental theories of the disorder, and indicate a link between reelin and IWMNs in this process, consistent with evidence from the heterozygous reeler mutant mouse. The alterations may contribute to the aberrant synaptic connectivity seen in schizophrenia. However, the functional implications of the abnormalities, as well as the mechanisms involved, remain to be fully elucidated.

Deliberate self-harm is associated with allelic variation in the tryptophan hydroxylase gene (TPH A779C), but not with polymorphisms in five other serotonergic genes

BACKGROUND

There is a heritable component to suicidal behaviour, encouraging the search for the associated risk alleles. Given the putative role of the 5-HT (5-hydroxytryptamine; serotonin) system in suicidal behaviour, serotonergic genes are leading candidates. In particular, several studies have reported an association with variants in the tryptophan hydroxylase (TPH) gene.

METHOD

We studied six serotonergic gene polymorphisms in a well-characterized sample of 129 deliberate self-harm subjects and 329 comparison subjects. The polymorphisms were TPH (A779C), 5-HT transporter (5-HTT, LPR S/L), monoamine oxidase A (MAOA G941T), 5-HT1B receptor (HTR1B G861C), 5-HT2A receptor (HTR2A T102C), and 5-HT2C receptor (HTR2C Cys23Ser). Genotyping was done using polymerase chain reaction (PCR)-based assays. The primary analyses compared allele and genotype frequencies between cases and controls. There were a limited number of planned secondary analyses within the deliberate self-harm group.

RESULTS

The TPH A779 allele was more common in deliberate self-harm subjects than in controls (OR 1.38, 95% CI 1.02-1.88; P = 0.03). None of the other polymorphisms was associated with deliberate self-harm. Within the deliberate self-harm group there were no associations with impulsivity, suicide risk, lifetime history of depression, or family history of deliberate self-harm.

CONCLUSIONS

Our data extend the evidence that allelic variation in the TPH gene is a risk factor for deliberate self-harm. No evidence was found to implicate the other polymorphisms.

A postmortem study of the mediodorsal nucleus of the thalamus in schizophrenia

Four studies have reported that the mediodorsal nucleus of the thalamus (MD) is smaller and contains fewer neurons in schizophrenia. The MD is a key node in a circuit proposed to be dysfunctional in the disorder. However, one study did not find a MD volume loss in schizophrenia, and all the studies to date are relatively small. Given the importance of establishing unequivocally the presence of MD pathology, we have carried out a study of the volume and number of neurons in the left and right MD in 21 patients with schizophrenia and 27 healthy comparison subjects. We also measured the size of MD neurons, and estimated total thalamic volume. We found no difference in the volume of the MD, the number of MD neurons, or the size of MD neurons in either hemisphere in schizophrenia. Neither was total thalamic volume altered. There are no obvious methodological or clinical factors to explain our failure to replicate the finding of MD involvement in schizophrenia. Hence our negative observations, in the largest sample yet investigated, cast doubt on the robustness and/or the generalisability of MD neuropathology in schizophrenia.

The axonal chemorepellant semaphorin 3A is increased in the cerebellum in schizophrenia and may contribute to its synaptic pathology

The neuropathological features of schizophrenia are suggestive of a developmentally induced impairment of synaptic connectivity. Semaphorin 3A (sema3A) might contribute to this process because it is a secreted chemorepellant which regulates axonal guidance. We have investigated sema3A in the cerebellum (an area in which expression persists in adulthood), and measured its abundance in 16 patients with schizophrenia and 16 controls. In adults, sema3A was predominantly localized to the inner part of the molecular layer neuropil, whereas infants and rats showed greater labelling of Purkinje cell bodies. Sema3A was increased in schizophrenia, as shown by enzyme-linked immunosorbent assay (+28%; P<0.05) and immunohistochemistry (+45%; P<0.01). We also measured reelin mRNA, since reelin is involved in related developmental processes and is decreased in other brain regions in schizophrenia. Reelin mRNA showed a trend reduction in the subjects with schizophrenia (-26%; P=0.07) and, notably, was negatively correlated with sema3A. Sema3A also correlated negatively with synaptophysin and complexin II mRNAs. The results show that sema3A is elevated in schizophrenia, and is associated with downregulation of genes involved in synaptic formation and maintenance. In this respect, sema3A appears to contribute to the synaptic pathology of schizophrenia, perhaps via ongoing effects of persistent sema3A elevation on synaptic plasticity. The findings are consistent with an early neurodevelopmental origin for the disorder, and the reciprocal changes in sema3A and reelin may be indicative of a pathogenic mechanism that affects the balance between trophic and inhibitory factors regulating synaptogenesis.

Reflex connections from forearm and hand afferents to shoulder girdle muscles in humans

Using surface electromyographic recordings from the trapezius and serratus anterior muscles and percutaneous electrical stimulation of the median, ulnar and radial nerves, the reflex connections from forearm and hand afferents to these shoulder girdle muscles have been investigated in normal human subjects. Stimulation of the median, ulnar and radial nerves at the shoulder, elbow and wrist evoked late, excitatory reflexes in the upper and lower parts of trapezius and in serratus anterior. These reflexes are not evoked by stimulation of cutaneous afferents alone, since there was no response to stimulation of the distal cutaneous branches of these three nerves. Measurements of the conduction velocity of afferents of the median, ulnar and radial nerve evoking these reflexes gave a mean conduction velocity of approximately 50 m/s. The lowest stimulus intensities at which these reflexes could be evoked were found to be 0.3 times motor threshold (MT). By taking into account the reflex latency, the length of the conduction path and that the reflex was mediated by low threshold, fast conducting afferents, it is proposed that group I muscle afferents from the forearm or hand evoke a supraspinal reflex to trapezius and serratus anterior. It appears that the functional significance of these reflexes is to aid in the stability of the shoulder girdle.

Does tape facilitate or inhibit the lower fibres of trapezius?

The application of tape to the skin overlying the lower fibres of trapezius is generally thought to facilitate this muscle. However, this facilitation has not been thoroughly investigated. In this study, the effect of tape upon trapezius motoneurone pool excitability was assessed using the trapezius H reflex. The amplitude of the H reflex was measured across four conditions: before tape application, with Endura Fix tape, with the addition of Endura Sports tape and finally with the tape removed. Instead of the expected facilitation of lower trapezius, this tape inhibited lower trapezius activity. On average, the application of Endura Fix tape inhibited trapezius by 4%. The application of Endura Sports tape overlaying the Endura Fix tape inhibited trapezius on average by 22%. This inhibition did not last once the tape was removed. This suggests that any change in shoulder girdle symptoms or movement, which occurs with the application of this particular tape, is not explicable on the basis of the facilitation of the lower fibres of trapezius.

An RT-PCR study of 5-HT(6) and 5-HT(7) receptor mRNAs in the hippocampal formation and prefrontal cortex in schizophrenia

5-Hydroxytryptamine (5-HT; serotonin) 5-HT(6) receptors (5-HT(6)R) and 5-HT(7) receptors (5-HT(7)R) have been implicated in schizophrenia and as targets of atypical antipsychotic drugs. We have studied the expression of these receptors in the hippocampal formation and dorsolateral prefrontal cortex (DLPFC) of 17 subjects with schizophrenia and 17 controls using reverse transcription-polymerase chain reaction (RT-PCR) with cyclophilin co-amplification. In schizophrenia, 5-HT(6)R mRNA was decreased in the hippocampal formation, and 5-HT(7)R mRNA was decreased in the dorsolateral prefrontal cortex. The mRNAs were unchanged in rats treated for 2 weeks with haloperidol, chlorpromazine, risperidone, olanzapine or clozapine. Regional decreases in 5-HT(6)R and 5-HT(7)R expression in schizophrenia may contribute to the overall serotonergic alterations which occur in the disorder, in part through their interactions with other neurotransmitter systems including glutamate and acetylcholine.

Bromocriptine use is associated with decreased smoking rates

Dopaminergic transmission in the central nervous system is thought to underlie addictive behaviours, including smoking. One effective smoking cessation drug, bupropion, enhances dopaminergic transmission; conversely, antipsychotic drugs, which are dopamine antagonists, are associated with increased smoking. Thus we hypothesized that subfertile women treated with the potent dopamine agonist bromocriptine might smoke less as a consequence of their treatment. Among 4,608 subfertile women those conceiving on bromocriptine were half as likely to smoke as those taking other drugs or those conceiving without medication (p < 0.0001). This observation supports the role of dopamine in nicotine addiction, and suggests that bromocriptine-like drugs could be used effectively by pregnant women to aid cessation.

Improvement of the sediment ecosystem following diversion of an intertidal sewage outfall at the Fraser river estuary, Canada, with emphasis on Corophium salmonis (Amphipoda)

Primary treated sewage effluent from the city of Vancouver, Canada was deposited directly onto the intertidal ecosystem of Sturgeon bank, Fraser river estuary between 1962 and 1988. In response to the degraded sediment conditions an azoic zone developed near the discharge outfall. Effluent discharges into the intertidal zone were almost completely stopped in 1988 with the construction of a submerged outfall. Our studies, conducted between 1994 and 1996, showed considerable improvement in the environment of the mudflat ecosystem, including increased dissolved oxygen, decreased sediment chlorophyll, decreased organic material in the sediment, reduced heavy metals in surficial sediment and increased grain size. The amphipod Corophium salmonis, important in the food web for juvenile salmon and other fish species, recolonized the previously azoic location. At reference stations, C. salmonis density was similar to that observed in previous surveys two decades earlier. Our data strongly suggest that improvement or sediment conditions near the former sewage outfall was a major factor enabling colonization by C. salmonis.

Neuropathological studies of synaptic connectivity in the hippocampal formation in schizophrenia

Cytoarchitectural changes in the hippocampal formation have been prominent among the various neuropathological abnormalities reported in schizophrenia. Replicated positive findings include decreased neuronal size and alterations in presynaptic and dendritic markers. These findings, in the absence of neurodegenerative changes, suggest that there are alterations in the neural circuitry in schizophrenia. These may represent the anatomical correlate of the aberrant functional connectivity described in neuroimaging studies, which in turn contributes to the psychotic and cognitive symptomatology of the disorder. The identity of the affected hippocampal circuits remains unclear; there is evidence for both glutamatergic and GABAergic involvement, and perhaps for a gradient of pathology in which changes are most apparent in CA4 and the subiculum, and least in CA1. The data, their interpretation, and their limitations are discussed, with particular emphasis upon molecular and immunological studies of synaptic protein gene expression.

In vitro evidence that 5-hydroxytryptamine increases efflux of glial glutamate via 5-HT(2A) receptor activation

Recent studies have established the presence of 5-hydroxytryptamine (5-HT)(2A) receptors on glial cells in culture and in the brain in situ. Here we used cultured C6 glioma cells to investigate the possibility that 5-HT(2A) receptors on glia regulate glutamate release from the cell. The efflux of endogenous glutamate from cultured C6 glioma cells was increased by addition of 5-HT in a concentration-dependent manner (maximal effect +200%). The efflux of serine and aspartate was not altered. The effect of 5-HT was mimicked by both the nonselective 5-HT receptor agonist quipazine and the selective 5-HT(2) receptor agonist 4-iodo-2,5-dimethoxyamphetamine (DOI; both 0.01-100 microM). The 5-HT(2A) receptor antagonists ketanserin (1 microM) and spiperone (1 microM) inhibited the glutamate response to 5-HT, quipazine, and DOI, whereas the effect of 5-HT was not inhibited by the 5-HT(2B/C) receptor antagonist SB200646 (1 microM). The effect of 5-HT on glutamate was specific in that it was reduced in low-calcium medium but was not prevented by furosemide (5 mM), which prevents cell swelling-induced glutamate release. Finally, the glutamate uptake inhibitor 2,4,trans-pyrollidine dicarboxylic acid (50 microM) did not block the 5-HT-induced efflux of glutamate, making involvement of glutamate transport unlikely. In conclusion, 5-HT stimulates the efflux of glutamate from C6 glioma cells following 5-HT(2A) receptor activation and involves a calcium-dependent mechanism.

The bilateral reflex control of the trapezius muscle in humans

Abstract. Electromyographic recordings were made from the trapezius muscle in 18 healthy subjects using surface electrodes placed bilaterally. A mechanical tap applied to the insertion of the lower fibres of trapezius evoked a reflex at 11.9 +/- 1.4 ms (mean plus minus SD) in the ipsilateral trapezius muscle. In addition and surprisingly, short latency, facilitatory reflexes were also seen on the contralateral side at a latency of 14.3 +/- 1.7 ms. Electrical stimulation of the afferent nerve to trapezius, the cervical nerve of C3/4, also evoked short latency, facilitatory reflexes from both the ipsilateral and contralateral muscles. Since this nerve carries the Ia fibres from trapezius, this reflex would appear to be the equivalent of the H reflex seen in the soleus muscle. The latency of this reflex was 10.9 +/- 1.4 ms ipsilaterally and 11.9 +/- 1.5 ms contralaterally, the difference being only 1.0 +/- 0.7 ms. Voluntary activity of the ipsilateral trapezius increased the amplitude of both mechanically and electrically evoked ipsilateral and crossed reflexes, and vibration of the ipsilateral trapezius decreased the amplitude of both reflexes. These results together suggest that the earliest parts of both ipsilateral and crossed reflexes are monosynaptic in origin. If the crossed reflex is, in part, due to a common Ia presynaptic input, correlation of bilateral trapezius activity should produce a peak in the cross-correlogram. Indeed, cross-correlation of the bilateral trapezius activity during elevation of the arms produced a short duration peak. Moreover, this was significantly larger when compared to that constructed from activity of the upper and lower fibres of trapezius from one side. These results imply that muscle spindle afferents from the ipsilateral trapezius monosynaptically activate motoneurones contralaterally.

A CUB-serine protease in the olfactory organ of the spiny lobster Panulirus argus

csp, a gene encoding a protein with high sequence identity to trypsinlike serine protease and CUB domains, was identified from a cDNA library from the olfactory organ (antennular lateral flagellum) of the spiny lobster Panulirus argus. The full-length cDNA sequence of csp is 1801 bp, encoding a protein of 50.25 kD, with three domains: signal peptide, trypsinlike serine protease, and CUB (named for a class of compounds including Complement subcomponents Clr/Cls, Uegf, and Bone morphogenic protein-1). RT-PCR, Northern blots, and immunoblots showed that csp is predominantly expressed in the lateral flagellum and eyestalk. Immunocytochemistry showed that Csp is present in olfactory (aesthetasc) sensilla around auxiliary cells (glia that surround the inner dendrites of olfactory receptor neurons, ORNs) and ORN outer dendrites. We propose that Csp is expressed and secreted by auxiliary cells, associates with ORN cell membranes or extracellular matrix via the CUB domain, and has trypsinlike activity. In the eyestalk, Csp is associated with cells surrounding axons between neuropils of the eyestalk ganglia. Possible functions in the olfactory organ and eyestalk are discussed. To our knowledge, this is the first report from any olfactory system of a gene encoding a protein with serine protease and CUB domains.