Prone position in covid-19: Can we tackle rising dead space?

Little is known about the impact of proning on oxygenation and ventilatory efficiency on patients with severe Covid-19. In this retrospective observational study we calculated Pa/FiO2 ratio (P/F) as a marker of oxygenation and dead space fraction (Vd/Vt) to assess ventilation. 12 patients who were proned twice or more were included. There was a significant improvement in P/F ratio when prone (110.18 ± 28.11) compared to supine (88.95 ± 19.34) (p < 0.01). There was no improvement in Vd/Vt on proning (p > 0.05). Vd/Vt as a function of time displayed a positive linear correlation in those who did not survive (n = 9) (Rs = 0.48, p < 0.01) but no observed correlation in those who survived (n = 3) (Rs = 0.002, p = 0.97). Our findings indicate that prone position in patients with Covid-19 has little effect on dead space fraction but does improve oxygenation. Rise in dead space with time appears to be a prognostic factor for death in patients with severe Covid- 19.

An assessment of animal welfare impacts in wild Norway rat (Rattus norvegicus) management

Norway rats (Rattus norvegicus) are considered one of the most significant vertebrate pests globally, because of their impacts on human and animal health. There are legal and moral obligations to minimise the impacts of wildlife management on animal welfare, yet there are few data on the relative welfare impacts of rat trapping and baiting methods used in the UK with which to inform management decisions. Two stakeholder workshops were facilitated to assess the relative welfare impacts of six lethal rat management methods using a welfare assessment model. Fifteen stakeholders including experts in wildlife management, rodent management, rodent biology, animal welfare science, and veterinary science and medicine, participated. The greatest welfare impacts were associated with three baiting methods, anticoagulants, cholecalciferol and non-toxic cellulose baits (severe to extreme impact for days), and with capture on a glue trap (extreme for hours) with concussive killing (mild to moderate for seconds to minutes); these methods should be considered last resorts from a welfare perspective. Lower impacts were associated with cage trapping (moderate to severe for hours) with concussive killing (moderate for minutes). The impact of snap trapping was highly variable (no impact to extreme for seconds to minutes). Snap traps should be regulated and tested to identify those that cause rapid unconsciousness; such traps might represent the most welfare-friendly option assessed for killing rats. Our results can be used to integrate consideration of rat welfare alongside other factors, including cost, efficacy, safety, non-target animal welfare and public acceptability when selecting management methods. We also highlight ways of reducing welfare impacts and areas where more data are needed.

Ebselen has lithium-like effects on central 5-HT2A receptor function

BACKGROUND AND PURPOSE

Lithium's antidepressant action may be mediated by inhibition of inositol monophosphatase (IMPase), a key enzyme in G_q -protein coupled receptor signalling. Recently, the antioxidant agent ebselen was identified as an IMPase inhibitor. Here, we investigated both ebselen and lithium in models of the 5-HT_2A receptor, a G_q -protein coupled receptor involved in lithium's actions.

EXPERIMENTAL APPROACH

5-HT_2A receptor function was assessed in mice by measuring the behavioural (head-twitches, ear scratches) and molecular (cortical immediate early gene [IEG] mRNA; Arc, c-fos, Egr2) responses to 5-HT_2A receptor agonists. Ebselen and lithium were administered either acutely or repeatedly prior to assessment of 5-HT_2A receptor function. Because lithium and 5-HT_2A receptor antagonists augment the action of selective serotonin reuptake inhibitors (SSRIs), ebselen was tested for this activity by co-administration with the SSRI citalopram in microdialysis (extracellular 5-HT) experiments.

KEY RESULTS

Acute and repeated administration of ebselen inhibited behavioural and IEG responses to the 5-HT_2A receptor agonist DOI. Repeated lithium also inhibited DOI-evoked behavioural and IEG responses. In comparison, a selective IMPase inhibitor (L-690330) attenuated the behavioural response to DOI whereas glycogen synthase kinase inhibitor (AR-A014418) did not. Finally, ebselen enhanced the increase in extracellular 5-HT induced by citalopram, and also increased regional brain 5-HT synthesis.

CONCLUSIONS AND IMPLICATIONS

Our data demonstrated lithium-mimetic effects of ebselen in different experimental models of 5-HT_2A receptor function, probably mediated by IMPase inhibition. This evidence of lithium-like neuropharmacological effects of ebselen adds further support for the clinical testing of ebselen in mood disorders, including as an antidepressant augmenting agent.

Cardiopulmonary exercise testing (CPET) in the United Kingdom-a national survey of the structure, conduct, interpretation and funding

Background

Cardiopulmonary exercise testing (CPET) is an exercise stress test with concomitant expired gas analysis that provides an objective, non-invasive measure of functional capacity under stress. CPET-derived variables predict postoperative morbidity and mortality after major abdominal and thoracic surgery. Two previous surveys have reported increasing utilisation of CPET preoperatively in England. We aimed to evaluate current CPET practice in the UK, to identify who performs CPET, how it is performed, how the data generated are used and the funding models.

Methods

All anaesthetic departments in trusts with adult elective surgery in the UK were contacted by telephone to obtain contacts for their pre-assessment and CPET service leads. An online survey was sent to all leads between November 2016 and March 2017.

Results

The response rate to the online survey was 73.1% (144/197) with 68.1% (98/144) reporting an established clinical service and 3.5% (5/144) setting up a service. Approximately 30,000 tests are performed a year with 93.0% (80/86) using cycle ergometry. Colorectal surgical patients are the most frequently tested (89.5%, 77/86). The majority of tests are performed and interpreted by anaesthetists. There is variability in the methods of interpretation and reporting of CPET and limited external validation of results.

Conclusions

This survey has identified the continued expansion of perioperative CPET services in the UK which have doubled since 2011. The vast majority of CPET tests are performed and reported by anaesthetists. It has highlighted variation in practice and a lack of standardised reporting implying a need for practice guidelines and standardised training to ensure high-quality data to inform perioperative decision making.

SERT and uncertainty: serotonin transporter expression influences information processing biases for ambiguous aversive cues in mice

The long allele variant of the serotonin transporter (SERT, 5-HTT) gene-linked polymorphic region (5-HTTLPR) is associated with higher levels of 5-HTT expression and reduced risk of developing affective disorders. However, little is known about the mechanisms underlying this protective effect. One hypothesis is that 5-HTT expression influences aversive information processing, with reduced negative cognitive bias present in those with higher 5-HTT expression. Here we investigated this hypothesis using genetically-modified mice and a novel aversive learning paradigm. Mice with high levels of 5-HTT expression (5-HTT over-expressing, 5-HTTOE mice) and wild-type mice were trained to discriminate between three distinct auditory cues: one cue predicted footshock on all trials (CS+); a second cue predicted the absence of footshock (CS−); and a third cue predicted footshock on 20% of trials (CS20%), and was therefore ambiguous. Wild-type mice exhibited equivalently high levels of fear to the CS+ and CS20% and minimal fear to the CS−. In contrast, 5-HTTOE mice exhibited high levels of fear to the CS+ but minimal fear to the CS− and the CS20%. This selective reduction in fear to ambiguous aversive cues suggests that increased 5-HTT expression reduces negative cognitive bias for stimuli with uncertain outcomes.

Welfare aspects of vertebrate pest control and culling: ranking control techniques for humaneness

The management of vertebrate pests depends on the use of traps, pesticides, repellents and other methods, each of which can cause varying levels of pain and other negative experiences to animals. Vertebrate pest control is essential for managing the impacts of unwanted or over-abundant animals on human and animal health, ecological balance and economic interests. As the need for this management is unlikely to diminish over time, a framework has been developed for assessing the humaneness of each technique by considering their negative impacts on animal welfare so that these can be included in decision-making about the selection of techniques for a specific control operation. This information can also support evidence-based regulations directed at managing such animal welfare impacts. In this paper, the authors discuss this assessment framework, briefly review two assessments conducted using the framework and discuss ways in which Competent Authorities and others can use it and other means to improve animal welfare in vertebrate pest management.

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.

46XY girls: the importance of careful newborn examination

STUDY OBJECTIVE

To understand the timing and factors affecting diagnosis of phenotypically female 46XY children.

DESIGN, SETTING, AND PARTICIPANTS

We studied all phenotypically female 46XY children who attended our multidisciplinary disorders of sexual differentiation (DSD) clinic in Nottingham England in a 3-year period since its inception. Case notes from a prospectively maintained database were reviewed and data were analyzed on the age at presentation, family history, findings on genital examination, and underlying endocrine abnormality.

RESULTS

Eleven children were studied, all of whom were being raised as girls. The median age of presentation was 18 months (range birth-15 years). Although the newborn examination detected the possibility of DSD in only 3 cases; 10 of 11 children had at least one significant abnormality in their external genitalia at presentation.

CONCLUSION

Careful neonatal genital examination can identify children with DSD. However, not all children with these conditions are identified early. Early diagnosis, when possible, is important, as it has the potential to make the management of this difficult condition more straightforward.

GluN1 hypomorph mice exhibit wide-ranging behavioral alterations

The psychotomimetic effects of N-methyl-d-aspartate receptor (NMDA) antagonists such as ketamine and phencyclidine suggest a role for reduced NMDA receptor-mediated neurotransmission in schizophrenia. GluN1 ‘hypomorph’ (GluN1^hypo) mice exhibit reduced NMDA receptor expression and have been suggested as a mouse model of schizophrenia. However, NMDA receptors are ubiquitous and are implicated in many physiological and pathological processes. The GluN1^hypo mice have a global reduction of NMDA receptors and the consequences of such a global manipulation are likely to be wide-ranging. We therefore assessed GluN1^hypo mice on a battery of behavioral tests, including tests of naturalistic behaviors, anxiety and cognition. GluN1^hypo mice exhibited impairments on all tests of cognition that we employed, as well as reduced engagement in naturalistic behaviors, including nesting and burrowing. Behavioral deficits were present in both spatial and non-spatial domains, and included deficits on both short- and long-term memory tasks. Results from anxiety tests did not give a clear overall picture. This may be the result of confounds such as the profound hyperactivity seen in GluN1^hypo mice, although hyperactivity cannot account for all of the results obtained. When viewed against this background of far-reaching behavioral abnormalities, the specificity of any one behavioral deficit is inevitably called into question. Indeed, the present data from GluN1^hypo mice are indicative of a global impairment rather than any specific disease. The deficits seen go beyond what one would expect from a mouse model of schizophrenia, thus questioning their utility as a selective model of this disease.

Spike-timing relationship of neurochemically-identified dorsal raphe neurons during cortical slow oscillations

The firing activity of dorsal raphe neurons is related to arousal state. However, it is unclear how this firing activity is precisely related to cortical activity, in particular oscillations occurring during sleep rhythms. Here we conducted single-cell extracellular recordings and juxtacellular labelling while monitoring electrocorticogram (ECoG) activity in urethane anaesthetised rats, to relate activity in neurochemically identified groups of neurons to cortical slow-wave activity (SWA). We observed that electrophysiological heterogeneity in dorsal raphe neurons revealed different neurochemical groups of DRN neurons and was mirrored by significant differences in the phase and strength of coupling to the cortical slow oscillations. Spike firing relationship of clock-like neurons, identified as 5-HT (5-hydroxytryptamine) or serotonin neurons, was higher during the inactive component of the oscillations. In contrast, half of the identified bursting 5-HT neurons did not exhibit strong cortical entrainment; those that did fired most during the inactive component of the SWA. Two groups of putatively non-5-HT neurons (irregular slow-firing and fast-firing) exhibited significant coherence and fired most during the active component of the SWA. These findings indicate that within the DRN electrophysiologically and neurochemically discrete neuronal groups exhibit distinct relations to cortical activity.

High-frequency stimulation of the subthalamic nucleus inhibits the firing of juxtacellular labelled 5-HT-containing neurones

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) is an established neurosurgical therapy for movement disability in advanced Parkinson's disease (PD), but some patients experience psychiatric side-effects like depression. In a previous electrophysiological study, we observed that HFS of the STN inhibited a population of neurones in the rat dorsal raphe nucleus (DRN), with firing properties characteristic of 5-HT neurones. The present study extended these findings to a second population of neurones, and combined extracellular recording with juxtacellular-labelling to investigate the chemical identity of the neurones affected by HFS. Bilateral HFS (130 Hz, 100-200 μA, 5 min) of the STN inhibited (26.0±2.9%) the firing of 37/74 DRN neurones displaying a slow, regular firing pattern. Slower firing neurones were more strongly inhibited than those firing faster. Importantly, 10 inhibited DRN neurones were juxtacellular-labelled with neurobiotin, and all neurones contained 5-HT as shown by post-mortem 5-HT immunocytochemistry. A minority of slow firing DRN neurones (18/74) were activated by STN HFS (37.9±8.3%) which was not observed previously. Of these neurones, three were juxtacellular-labelled and one was 5-HT immunopositive. Also a small number of DRN neurones (19/74) did not respond to HFS, four of which were juxtacellular-labelled and all contained 5-HT. These data show that individual chemically-identified 5-HT-containing neurones in the DRN were modulated by STN HFS, and that the majority were inhibited but some were activated and some failed to respond. These data extend previous findings of modulation of the 5-HT system by STN HFS but suggest a destabilisation of the 5-HT system rather than simple inhibition as indicated previously. Although the mechanism is not yet known, such changes may contribute to the psychiatric side-effects of STN stimulation in some PD patients.

Shared changes in gene expression in frontal cortex of four genetically modified mouse models of depression

This study aimed to identify whether genetic manipulation of four systems implicated in the pathogenesis of depression converge on shared molecular processes underpinning depression-like behaviour in mice. Altered 5HT function was modelled using the 5-HT transporter knock out mouse, impaired glucocorticoid receptor (GR) function using an antisense-induced knock down mouse, disrupted glutamate function using a heterozygous KO of the vesicular glutamate transporter 1 gene, and impaired cannabinoid signalling using the cannabinoid 1 receptor KO mouse. All 4 four genetically modified mice were previously shown to show exaggerated helpless behaviour compared to wild-type controls and variable degrees of anxiety and anhedonic behaviour. mRNA was extracted from frontal cortex and hybridised to Illumina microarrays. Combined contrast analysis was used to identify genes showing different patterns of up- and down-regulation across the 4 models. 1823 genes were differentially regulated. They were over-represented in gene ontology categories of metabolism, protein handling and synapse. In each model compared to wild-type mice of the same genetic background, a number of genes showed increased expression changes of >10%, other genes showed decreases in each model. Most of the genes showed mixed effects. Several previous array findings were replicated. The results point to cellular stress and changes in post-synaptic remodelling as final common mechanisms of depression and resilience.

Further pharmacological characterization of 5-HT(2C) receptor agonist-induced inhibition of 5-HT neuronal activity in the dorsal raphe nucleus in vivo

BACKGROUND AND PURPOSE

Recent experiments using non-selective 5-hydroxytryptamine (5-HT)(2C) receptor agonists including WAY 161503 suggested that midbrain 5-HT neurones are under the inhibitory control of 5-HT(2C) receptors, acting via neighbouring gamma-aminobutyric acid (GABA) neurones. The present study extended this pharmacological characterization by comparing the actions of WAY 161503 with the 5-HT(2C) receptor agonists, Ro 60-0275 and 1-(3-chlorophenyl) piperazine (mCPP), as well as the non-selective 5-HT agonist lysergic acid diethylamide (LSD) and the 5-HT releasing agent 3,4-methylenedioxymethamphetamine (MDMA).

EXPERIMENTAL APPROACH

5-HT neuronal activity was measured in the dorsal raphe nucleus (DRN) using extracellular recordings in anaesthetized rats. The activity of DRN GABA neurones was assessed using double-label immunohistochemical measurements of Fos and glutamate decarboxylase (GAD).

KEY RESULTS

Ro 60-0175, like WAY 161503, inhibited 5-HT neurone firing, and the 5-HT(2C) antagonist SB 242084 reversed this effect. mCPP also inhibited 5-HT neurone firing ( approximately 60% neurones) in a SB 242084-reversible manner. LSD inhibited 5-HT neurone firing; however, this effect was not altered by either SB 242084 or the 5-HT(2A/C) receptor antagonist ritanserin but was reversed by the 5-HT(1A) receptor antagonist WAY 100635. Similarly, MDMA inhibited 5-HT neurone firing in a manner reversible by WAY 100635, but not SB 242084 or ritanserin. Finally, both Ro 60-0275 and mCPP, like WAY 161503, increased Fos expression in GAD-positive DRN neurones.

CONCLUSIONS AND IMPLICATIONS

These data strengthen the hypothesis that midbrain 5-HT neurones are under the inhibitory control of 5-HT(2C) receptors, and suggest that the 5-HT(2C) agonists Ro 60-0175, mCPP and WAY 161503, but not LSD or MDMA, are useful probes of the mechanism(s) involved.

Establishment of a clinically correlated human pericardial fluid bank: evaluation of intrapericardial diagnostic potential

The development of a clinically correlated human pericardial fluid bank and database is described. A unique feature of this registry is the availability of a large number of pericardial fluid samples for testing with respect to multiple factors and for correlation with angiographic findings and clinical syndromes expressed by the patients. The collection of data at the present time comprises frozen pericardial fluid samples obtained from patients who have undergone cardiac surgery; and historical, clinical, and laboratory data obtained from the patient records. Nearly 400 samples have been stored and analyzed thus far, with sample entry continuing. This registry is designed to evaluate the local factors that play a role in mediating or reflecting myocardial or coronary responses. Pathophysiologic processes of particular interest include restenosis, plaque ruptures, and angiogenesis. Study of the pericardial fluid bank should lead to enhanced understanding of molecular mechanisms, as well as to the explanation for the reasons underlying interpatient variability in these processes. It is further anticipated that this information might provide a foundation for the diagnostic use of pericardial fluid to individualize therapies targeting angiogenesis or plaque physiology.

Evidence that increased 5-HT release evokes region-specific effects on blood-oxygenation level-dependent functional magnetic resonance imaging responses in the rat brain

This study aimed to determine the potential of in vivo functional magnetic resonance imaging (fMRI) methods as a non-invasive means of detecting effects of increased 5-HT release in brain. Changes in blood-oxygenation level-dependent (BOLD) contrast induced by administration of the 5-HT-releasing agent, fenfluramine, were measured in selected brain regions of halothane-anesthetized rats. Initial immunohistochemical measurements of the marker of neural activation, Fos, confirmed that in halothane-anesthetized rats fenfluramine (10 mg/kg i.v.) evoked cellular responses in cortical regions which were attenuated by pre-treatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (300 mg/kg i.p. once daily for 2 days). Fenfluramine-induced Fos was demonstrated in numerous glutamatergic pyramidal neurons (Fos/excitatory amino acid carrier 1 (EAAC1) co-labeled), but also a small number of GABA interneurons (Fos/glutamic acid decarboxylase (GAD)(67) colabeled). Fenfluramine (10 mg/kg i.v.) evoked changes in BOLD signal intensity in a number of cortical and sub-cortical regions with the greatest effects being observed in the nucleus accumbens (-13.0%+/-2.7%), prefrontal cortex (-10.1%+/-3.2%) and motor cortex (+2.3%+/-1.0%). Pre-treatment with p-chlorophenylalanine, significantly attenuated the response to fenfluramine (10 mg/kg i.v.) in all regions with the exception of the motor cortex which showed a trend. These experiments demonstrate that increased 5-HT release evokes region-specific changes in the BOLD signal in rats, and that this effect is attenuated in almost all regions by 5-HT depletion. These findings support the use of fMRI imaging methods as a non-invasive tool to study 5-HT function in animal models, with the potential for extension to clinical studies.

Evidence that genetic variation in 5-HT transporter expression is linked to changes in 5-HT2A receptor function

Variability in expression of the 5-HT transporter (5-HTT) gene in the human population has been associated with a range of behavioural phenotypes. The underlying mechanisms are unclear but may involve changes in 5-HT receptor levels and/or signalling. The present study used a novel 5-HTT overexpressing transgenic mouse to test the hypothesis that variability in 5-HTT expression may alter 5-HT(2A) receptor function. In wildtype mice, the 5-HT(2) receptor agonist DOI increased regional brain mRNA expression of two immediate early genes (c-fos and Arc), and induced head twitches, and both effects were abolished by pre-treatment with the 5-HT(2A) receptor antagonist MDL 100907. In 5-HTT overexpressing mice, DOI induced a greater increase in both c-fos and Arc mRNA expression in cortical brain regions, and more head twitches, compared to wildtype mice. Autoradiographic and in situ hybridisation experiments showed that 5-HT(2A) receptor binding sites and 5-HT(2A) receptor mRNA did not differ between transgenic and wildtype mice. Finally, the transgenic mice had lower regional brain 5-HT levels compared to wildtype mice. This depletion of 5-HT may underpin the increase in 5-HT(2A) receptor function because in wildtype mice 5-HT depletion using the 5-HT synthesis inhibitor, p-chlorophenylalanine, enhanced the head twitch response to DOI. These data demonstrate that elevated 5-HTT expression is accompanied by increased 5-HT(2A) receptor function, an effect possibly mediated by decreased availability of synaptic 5-HT. Variation in levels of 5-HTT expression may therefore be a source of variability in 5-HT(2A) receptor function, which may be an important modifier of 5-HTT-linked phenotypes.

In vivo evidence that 5-HT(2C) receptors inhibit 5-HT neuronal activity via a GABAergic mechanism

BACKGROUND AND PURPOSE

Recent evidence suggests that 5-HT(2C) receptor activation may inhibit midbrain 5-HT neurones by activating neighbouring GABA neurones. This hypothesis was tested using the putative selective 5-HT(2C) receptor agonist, WAY 161503.

EXPERIMENTAL APPROACH

The effect of WAY 161503 on 5-HT cell firing in the dorsal raphe nucleus (DRN) was investigated in anaesthetised rats using single unit extracellular recordings. The effect of WAY 161503 on DRN GABA neurones was investigated using double label immunohistochemical measurements of Fos, glutamate decarboxylase (GAD) and 5-HT(2C) receptors. Finally, drug occupancy at 5-HT(2A) receptors was investigated using rat positron emission tomography and ex vivo binding studies with the 5-HT(2A) receptor radioligand [(11)C]MDL 100907.

KEY RESULTS

WAY 161503 caused a dose-related inhibition of 5-HT cell firing which was reversed by the 5-HT(2) receptor antagonist ritanserin and the 5-HT(2C) receptor antagonist SB 242084 but not by the 5-HT(1A) receptor antagonist WAY 100635. SB 242084 pretreatment also prevented the response to WAY 161503. The blocking effects of SB 242084 likely involved 5-HT(2C) receptors because the drug did not demonstrate 5-HT(2A) receptor occupancy in vivo or ex vivo. The inhibition of 5-HT cell firing induced by WAY 161503 was partially reversed by the GABA(A) receptor antagonist picrotoxin. Also, WAY 161503 increased Fos expression in GAD positive DRN neurones and DRN GAD positive neurones expressed 5-HT(2C) receptor immunoreactivity.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that WAY 161503 inhibits 5-HT cell firing in the DRN in vivo, and support a mechanism involving 5-HT(2C) receptor-mediated activation of DRN GABA neurones.

Differential involvement of serotonin and dopamine systems in cost-benefit decisions about delay or effort

RATIONALE

Although tasks assessing the role of dopamine in effort-reward decisions are similar to those concerned with the role of serotonin in impulsive choice in that both require analysis of the costs and benefits of possible actions, they have never been directly compared.

OBJECTIVES

This study investigated the involvement of serotonin and dopamine in two cost-benefit paradigms, one in which the cost was delay and the other in which it was physical effort.

METHODS

Sixteen rats were trained on a T-maze task in which they chose between high and low reward arms. In one version, the high reward arm was obstructed by a barrier, in the other, delivery of the high reward was delayed by 15 s. Serotonin and dopamine function were manipulated using systemic pCPA and haloperidol injections, respectively.

RESULTS

Haloperidol-treated rats were less inclined either to exert more effort or to countenance a delay for a higher reward. pCPA had no effect on the performance of the rats on the effortful task, but significantly increased the rats' preference for an immediate but smaller reward. All animals (drug treated and controls) chose the high reward arm on the majority of trials when the delay or effort costs were matched in both high and low reward arms.

CONCLUSION

A dissociation was found between the neurotransmitter systems involved in different types of cost-benefit decision making. While dopaminergic systems were required for decisions about both effort and delay, serotonergic systems were only needed for the latter.

Confounding effects of anesthesia on functional activation in rodent brain: a study of halothane and α-chloralose anesthesia

Functional magnetic resonance imaging (fMRI) in animal models provides a platform for more extensive investigation of drug effects and underlying physiological mechanisms than is possible in humans. However, it is usually necessary for the animal to be anesthetized. In this study, we have used a rat model of direct cortical stimulation to investigate the effects of anesthesia in rodent fMRI. Specifically, we have sought to answer two questions (i) what is the relationship between baseline neuronal activity and the BOLD response to stimulation under halothane anesthesia? And (ii) how does the BOLD response change after transferring from halothane to the commonly used anesthetic alpha-chloralose? In the first set of experiments, we found no significant differences in the amplitude of the BOLD response at the different halothane doses studied, despite electroencephalography (EEG) recordings indicating a dose-dependent reduction in baseline neuronal activity with increasing halothane levels. In the second set of experiments, a reduction in the spatial extent of the BOLD response was apparent immediately after transfer from halothane to alpha-chloralose anesthesia, although no change in the peak signal change was evident. However, several hours after transfer to alpha-chloralose, a significant increase in both the spatial extent and peak height of the BOLD response was observed, as well as an increased sensitivity to secondary cortical and subcortical activation. These findings suggest that, although alpha-chloralose anesthesia is associated with a greater BOLD response for a fixed stimulus relative to halothane, there is substantial variation in the extent and magnitude of the response over time that could introduce considerable variability in studies using this anesthetic.

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.

Evaluation of the effect of chronic antidepressant treatment on neurokinin-1 receptor expression in the rat brain

Clinically effective antidepressants are thought to exert their therapeutic effects by facilitating central monoamine neurotransmission. However, recent data showing that neurokinin-1 receptor (NK1R) antagonists have antidepressant properties in both animal and clinical studies raise the possibility that classical antidepressants may also influence NK1R expression in the brain. To test this hypothesis, rats were treated with desipramine, paroxetine, venlafaxine, tranylcypromine or vehicle for 14-42 days. NK1R binding sites and mRNA were determined in a wide variety of brain areas using in situ hybridization and quantitative receptor autoradiography. In all areas examined, the abundance of NK1R binding sites was unchanged after 14 days of treatment. None of the treatments altered the number of NK1R binding sites following 42 days treatment with the exception that an increase was found in the locus coeruleus with tranylcypromine. Taken together, we report that repeated treatment with antidepressants of different classes does not cause significant changes in NK1R expression.

Glutamate receptor activation is involved in 5-HT2 agonist-induced Arc gene expression in the rat cortex

Brain 5-HT regulates the expression of gene transcription factor as well as novel effector immediate early genes (IEGs). The 5-HT regulation of the gene transcription factor IEG, c-fos, involves activation of 5-HT2A and ionotropic glutamate receptors. Here, we investigate whether these receptors are also involved in the regulation of the effector IEG, Arc. In rats, the 5-HT2 agonist DOI induced a marked increase in expression of Arc mRNA in a variety of cortical regions. This effect was blocked by the selective 5-HT2A receptor antagonist, MDL 100,907, but not the 5-HT(2B/2C) receptor antagonist, SB206553. The AMPA receptor antagonist GYKI 52466 also attenuated DOI-induced Arc mRNA expression, as did the NMDA receptor antagonist MK801 in some regions. Immunofluorescence studies showed that DOI increased Arc-immunoreactivity in cortical cells that expressed AMPA and NMDA receptor subunits but not the 5-HT2A receptor. Finally, DOI-induced Arc-immunoreactivity in cortical cells was extensively co-localised with c-fos-immunoreactivity. These results suggest that, as with c-fos expression, ionotropic glutamate receptors (AMPA and NMDA) are involved in 5-HT2A receptor-induced Arc expression. This finding, together with evidence of extensive Arc and c-fos co-localisation, suggests that 5-HT2A receptor activation may induce the expression of both effector and transcription factor IEGs via common molecular and cellular substrates.

Neurochemical and anatomical identification of fast- and slow-firing neurones in the rat dorsal raphe nucleus using juxtacellular labelling methods in vivo

GABA neurones in the dorsal raphe nucleus (DRN) influence ascending 5-hydroxytryptamine (5-HT) neurones but are not physiologically or anatomically characterised. Here, in vivo juxtacellular labelling methods in urethane-anaesthetised rats were used to establish the neurochemical and morphological identity of a fast-firing population of DRN neurones, which recent data suggest may be GABAergic. Slow-firing, putative 5-HT DRN neurones were also identified for the first time using this approach. Fast-firing, DRN neurones were successfully labelled with neurobiotin (n=10) and the majority (n=8/10) were immunoreactive for the GABA synthetic enzyme glutamic acid decarboxylase. These neurones were located in the DRN (mainly lateral regions), and consistently fired spikes with short width (1.1+/-0.1 ms) and high frequency (12.1+/-2.0 Hz). In most cases spike trains were regular but displayed low frequency oscillations (1-2 Hz). These neurones were morphologically heterogeneous but commonly had branching axons with varicosities and dendrites that extended across DRN subregions and the midline. Slow-firing DRN neurones were also successfully labelled with neurobiotin (n=24). These neurones comprised a population of neurones immunopositive for 5-HT and/or tryptophan hydroxylase (n=12) that fired broad spikes (2.2+/-0.2 ms) with high regularity and low frequency (1.7+/-0.2 Hz). However, a slow-firing, less regular population of neurones immunonegative for 5-HT/tryptophan hydroxylase (n=12) was also apparent. In summary, this study chemically identifies fast- and slow-firing neurones in the DRN and establishes for the first time that fast-firing DRN neurones are GABAergic. The electrophysiological and morphological properties of these neurones suggest a novel function involving co-ordination between GABA and 5-HT neurones dispersed across DRN subregions.

Gene expression array profile of human osteosarcoma

The aims of this pilot study were to determine whether needle and open biopsies from osteosarcoma (OS) provide sufficient quality of mRNA for cDNA array analyses to gain insights into the expression profile of OS. A total of 22 samples collected from OS were used for array analyses. A primary cell culture was also established from one of the OS biopsies. Total RNA was extracted and probes were generated for cDNA arrays. cDNA probes were made for all the 22 samples. Two of these samples were needle core bone biopsies. Statistical analysis confirmed the reliability of array data obtained in 16 of the 22 samples. Known genes involved in bone metabolism and osteosarcoma were identified as highly expressed, and the putative new marker Ezrin was also identified. Confirmatory immunohistochemical staining using the Ezrin antibody was performed in a selection of samples.

Power of exclusion for parentage verification and probability of match for identity in American kennel club breeds using 17 canine microsatellite markers

DNA analysis of microsatellite markers has become a common tool for verifying parentage in breed registries and identifying individual animals that are linked to a database or owner. Panels of markers have been developed in canines, but their utility across and within a wide range of breeds has not been reported. The American Kennel Club (AKC) authorized a study to determine the power to exclude non-parents and identify individuals using DNA genotypes of 17 microsatellite markers in two panels. Cheek swab samples were voluntarily collected at Parent Breed Club National Specialty dog shows and 9561 samples representing 108 breeds were collected, averaging 88.5 dogs per breed. The primary panel of 10 markers exceeded 99% power of exclusion for canine parentage verification of 61% of the breeds. In combination with the secondary panel of seven markers, 100% of the tested breeds exceeded 99% power of exclusion. The minimum probability match rate of the first panel was 3.6 x 10(-5) averaged across breeds, and with the addition of the second panel, the probability match rate was 3.2 x 10(-8); thus the probability of another random, unrelated dog with the same genotype is very low. The results of this analysis indicated that, on average, the primary panel meets the AKC's needs for routine parentage testing, but that a combination of 10-15 genetic markers from the two panels could yield a universal canine panel with enhanced processing efficiency, reliability and informativeness.

Antidepressant drug treatment induces Arc gene expression in the rat brain

The mechanism underlying the therapeutic effect of antidepressants is not known but neuroadaptive processes akin to long-term potentiation have been postulated. Arc (Activity-regulated, cytoskeletal-associated protein) is an effector immediate early gene implicated in LTP and other forms of neuroplasticity. Recent data show that Arc expression is regulated by brain 5-hydroxytryptamine neurones, a target of many antidepressants. Here in situ hybridisation and immunohistochemistry were used to examine whether Arc expression in rat brain is altered by antidepressant drug treatment. Repeated administration of the monoamine reuptake inhibitors paroxetine, venlafaxine or desipramine induced region-specific increases in Arc mRNA. These increases were greatest in regions of the cortex (frontal and parietal cortex) and hippocampus (CA1 layer) and absent in the caudate putamen. Repeated treatment with the monoamine oxidase inhibitor, tranylcypromine, increased Arc mRNA in a similar fashion to the monoamine reuptake inhibitors. The antidepressant drugs also increased the number of Arc-immunoreactive cells in the parietal cortex. Acute antidepressant injection, and repeated administration of the antipsychotic drug chlorpromazine, produced either limited or no changes in Arc mRNA. The data suggest that chronic treatment with antidepressant drugs induces Arc gene expression in specific regions across the rat forebrain. Up-regulation of Arc expression may be part of the process by which antidepressant drugs achieve long-term changes in synaptic function in the brain.

GABA transmission in the ventral pallidum is not involved in the control of latent inhibition in the rat

Latent inhibition describes a process of learning to ignore stimuli of no consequence, and is disrupted in acute, positive-symptomatic schizophrenia. Understanding the neural basis of latent inhibition in animals may help to elucidate the neural dysfunction underlying positive schizophrenic symptoms in man. Evidence suggests a crucial role for dopamine transmission in the nucleus accumbens in the control of latent inhibition. The present studies investigated the role of the GABA-ergic efferent from the nucleus accumbens to the ventral pallidum in latent inhibition. The GABA(A) agonist muscimol (4.56 ng/microl), and antagonist picrotoxin (0.2 microg/microl), were infused into the ventral pallidum, and effects on latent inhibition were assessed using a conditioned suppression procedure. Neither drug produced specific effects on latent inhibition when given alone and, in the case of muscimol, failed to reverse the disruption of latent inhibition induced by systemic amphetamine. In addition to significant non-specific drug effects, a positive control experiment revealed that intra-pallidal picrotoxin significantly enhanced locomotion, suggesting that our manipulations of ventral pallidal GABA function were behaviourally effective. We conclude that modulating ventral pallidal GABA transmission does not affect latent inhibition. The implications of this finding for theories of the neural circuitry mediating latent inhibition and for understanding the functional role of ventral pallidal GABA transmission are discussed.

Evidence that central 5-HT2A and 5-HT2B/C receptors regulate 5-HT cell firing in the dorsal raphe nucleus of the anaesthetised rat

1. Systemic administration of phenethylamine-derived, 5-hydroxytryptamine(2) (5-HT(2)) receptor agonists inhibits the firing of midbrain 5-HT neurones, but the 5-HT receptors involved are poorly defined, and the contribution of peripheral mechanisms is uncertain. This study addresses these issues using extracellular recordings of 5-HT neurones in the dorsal raphe nucleus of anaesthetised rats. 2. The 5-HT(2) receptor agonists DOI ((+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride) and DOB ((+/-)-2,5-dimethoxy-4-bromoamphetamine hydrobromide), caused a dose-related (10-100 micro g kg(-1) i.v.) inhibition of 5-HT neuronal activity, with the highest dose reducing firing rates by >80%. 3. Pretreatment with the 5-HT(2) receptor antagonist ritanserin (1 mg kg(-1) i.v.) completely blocked the action of DOI. The 5-HT(2A) receptor antagonist MDL 100,907 (0.2 mg kg(-1) i.v.) blocked the action of both DOI and DOB. In comparison, the 5-HT(2B/C) receptor antagonist SB 206553 (0.5 mg kg(-1) i.v.) caused a small, but statistically significant, shift to the right in the dose response to DOI and DOB. 4. Pretreatment with the peripherally acting 5-HT(2) receptor antagonist BW 501C67 (0.1 mg kg(-1) i.v.) had no effect on the DOI-induced inhibition of 5-HT cell firing, but completely blocked the DOI-induced rise in mean arterial blood pressure. 5. These data indicate that the inhibition of 5-HT cell firing induced by systemic administration of DOI and DOB is mediated predominantly by the 5-HT(2A) receptor-subtype, but that 5-HT(2B/C) receptors also play a minor role. Moreover, central and not peripheral mechanisms are involved. Given evidence that 5-HT(2) receptors are not located on 5-HT neurones, postsynaptic 5-HT feedback mechanisms are implicated.

Fat distribution is altered in HIV-infected men without clinical evidence of the HIV lipodystrophy syndrome

OBJECTIVE

To determine if fat distribution is altered in HIV-infected men without clinical evidence of lipodystrophy.

METHODS

In a cross-sectional design, 14 protease inhibitor (PI)-treated men with lipodystrophy and 12 PI-treated and five PI-naive men without clinical evidence of lipodystrophy underwent body composition and fat distribution analysis by dual-energy X-ray absorptiometry and computed tomography. Their fat distribution was compared to 43 uninfected male controls matched for age and BMI.

RESULTS

The percent of body fat in the trunk of men with HIV lipodystrophy was significantly greater compared to both HIV-infected and healthy controls. The percentage of body fat in the extremities was significantly lower in men with HIV lipodystrophy compared to both HIV-infected and healthy controls. HIV-infected men without clinical evidence of lipodystrophy also had a significantly greater percentage of total body fat in the trunk and a significantly lower percent of body fat in the extremities compared to healthy controls. Among the HIV-infected men, age was an independent predictor of truncal and extremity adiposity.

CONCLUSION

This study suggests that a continuum of change is present in the adipose organ of HIV-infected men on antiretroviral therapy. Physical examination alone can miss significant changes in body fat distribution in HIV-infected patients.

Effect of different 5-HT1A receptor antagonists in combination with paroxetine on expression of the immediate-early gene Arc in rat brain

Selective 5-HT(1A) receptor antagonists enhance the effect of selective serotonin reuptake inhibitors (SSRIs) on presynaptic 5-HT function, and have potential as antidepressant augmentation therapies. The present study tested the effect of different selective 5-HT(1A) receptor antagonists (WAY 100635, NAD-299, p-MPPI and LY 426965) in combination with a SSRI (paroxetine), on postsynaptic 5-HT function measured by increased expression of the immediate early gene, Arc. Paroxetine (5 mg/kg s.c.) combined with WAY 100635 (0.3 mg/kg s.c.) increased Arc mRNA in frontal, parietal and piriform cortices, and caudate putamen. Paroxetine (5 mg/kg s.c.) plus NAD-299 (1 or 5 mg/kg s.c.) had a similar effect. None of these drugs increased Arc mRNA when administered alone. Paroxetine (5 mg/kg s.c.) plus p-MPPI (8.5 mg/kg s.c.) also increased Arc mRNA but p-MPPI itself elevated Arc mRNA in many regions. Whilst LY 426965 (3 or 10 mg/kg s.c.) had no effect alone, when combined with paroxetine (5 mg/kg s.c.), the drug increased Arc mRNA in caudate putamen but not cortical regions.In conclusion, this study demonstrates that four 5-HT(1A) receptor antagonists augment the effect of an SSRI on Arc mRNA expression, which is suggestive of increased postsynaptic 5-HT function. However, the data reveal certain differences in the 5-HT(1A) receptor antagonists not recognised in models of presynaptic 5-HT function.

GABA and mood disorders

A γ-aminobutyric acid (GABA)-ergic theory of mood disorders was proposed by Emrich and colleagues (1980) following observations of the efficacy of the GABAergic anticonvulsant, valproate, in the treatment of mania. Since then, increasing biochemical and pharmacological evidence from animal and human studies has supported the hypothesis that mood disorders are associated with abnormalities in brain GABA function.

Electrophysiological evidence for convergence of inputs from the medial prefrontal cortex and lateral habenula on single neurons in the dorsal raphe nucleus

Neuronal projections to the dorsal raphe nucleus (DRN) from the medial prefrontal cortex (mPFC) and lateral habenula nucleus (LHb) provide the two key routes by which information processed by mood regulatory, cortico-limbic-striatal circuits input into the 5-HT system. These two projections may converge as it appears that both activate local GABAergic neurons to inhibit 5-HT neurons in the DRN. Here we have tested this hypothesis by measuring the effect of stimulation of the mPFC and LHb on the activity of 5-HT and non-5-HT, putative gamma-amino butyric acid (GABA) neurons in the DRN using extracellular recordings in anaesthetized rats. A total of 119 5-HT neurons (regular, slow firing, broad spike width) and 21 non-5-HT, putative GABA neurons (fast-firing, narrow spike width) were tested. Electrical stimulation of the mPFC or LHb caused a poststimulus inhibition (30 ms latency) of 101/119 5-HT neurons, of which 61 (60%) were inhibited by both the mPFC and LHb. Electrical stimulation of the mPFC or LHb also caused a short latency (12-20 ms) poststimulus facilitation of 10/21 non-5-HT neurons, of which 5 (50%) were activated by both the mPFC and LHb. These data indicate that a significant number of 5-HT neurons and non-5-HT neurons in the DRN are influenced by both the mPFC and LHb. Moreover, the data are compatible with the hypothesis and that there is a convergence of mPFC and LHb inputs on local circuit GABAergic neurons in the DRN which in turn inhibit the activity of 5-HT neurons.

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.

Evidence for a role of GABA interneurones in the cortical modulation of midbrain 5-hydroxytryptamine neurones

Recent electrophysiological studies demonstrate that the ventral medial prefrontal cortex has a powerful inhibitory influence on 5-hydroxytryptamine (5-HT) neurones in the dorsal raphe nucleus. Here we utilised a combination of anatomical and electrophysiological methods to characterise the cellular substrate underlying this effect.Anterograde tracing (Phaseolus vulgaris leucoagglutinin) using electron microscopy demonstrated a pathway from the ventral medial prefrontal cortex that makes neuronal contacts throughout the dorsal raphe nucleus. These contacts were predominantly asymmetrical synapses adjoining GABA immunoreactive dendrites and spines. In vivo extracellular recordings were made in the dorsal raphe nucleus of the anaesthetised rat from a subpopulation of non-5-HT neurones. These neurones were fast-firing, irregular and with short spike width, properties strongly reminiscent of immunochemically identified GABA interneurones in other brain regions. Recordings of classical 5-HT neurones were also included. Electrical stimulation of the ventral medial prefrontal cortex elicited a rapid onset (16 ms latency), orthodromic excitation of the non-5-HT neurones (13/25 neurones). This stimulation also caused a pronounced inhibition of most 5-HT neurones tested, with a longer latency (30 ms), and this was partially blocked by locally applied bicuculline. These data provide the first evidence that the ventral medial prefrontal cortex influences the activity of large numbers of raphe 5-HT neurones by targeting a local network of GABA neurones. This circuitry predicts that physiological and pathological changes in the ventral medial prefrontal cortex will impact on significant parts of the forebrain 5-HT system.

Technical constraints in the development of reduced-fat bakery products

The present study was funded by the Ministry of Agriculture, Fisheries and Food, its aim being to identify the technical barriers to the development of reduced-fat alternatives for bakery products. Using National Food Survey (Ministry of Agriculture, Fisheries and Food, 1998) statistics on dietary consumption within the home, biscuits, cakes and pastries were identified as contributing significant amounts of fat to the population's dietary intake. Face-to-face interviews were conducted with contacts in the technical community of the baking industry, who were usually working in technical and new-product development functions. A discussion guide was developed to cover the main lines of enquiry. The companies selected were ingredient suppliers (eight), manufacturers (twelve) and retailers (four) and so represented each step of the food supply chain. In brief, results showed that current labelling rules were too stringent, and constrained development of reduced-fat bakery products. Products with lower fat levels are harder to make due to altered handling and processing properties. Their quality is usually poorer than standard products, particularly for flavour, texture and mouthfeel. The perception of freshness is reduced and product shelf-life may consequently be shorter. For the product developer, there are relatively few ingredients that can be used in place of fat, and knowledge of how they work is limited, which inhibits product development. There is no identifiable source of technical knowledge in this field. Consumers perceive reduced-fat bakery products to be of lower quality and are generally unwilling to pay higher prices than for standard products.

Antidopaminergic effects of dietary tyrosine depletion in healthy subjects and patients with manic illness

BACKGROUND

In rats, amino acid mixtures lacking tyrosine and its precursor phenylalanine decrease the release of dopamine produced by the psychostimulant drug amphetamine. Amphetamine has been proposed as a model for clinical mania.

AIMS

To assess whether dietary tyrosine depletion attenuates the psychostimulant effects of methamphetamine in healthy volunteers and diminishes the severity of mania in acutely ill patients.

METHOD

Sixteen healthy volunteers received a tyrosine-free amino acid mixture and a control mixture in a double-blind crossover design 4 h before methamphetamine (0.15 mg/kg). Twenty in-patients meeting DSM-IV criteria for mania were allocated blindly and randomly to receive either the tyrosine-free mixture or the control mixture.

RESULTS

The tyrosine-free mixture lowered both subjective and objective measures of the psychostimulant effects of methamphetamine. Ratings of mania were lower in the patients who received the tyrosine-free mixture. CONCLUSIONS; Decreased tyrosine availability to the brain attenuates pathological increases in dopamine neurotransmission following methamphetamine administration and putatively in mania.

Olanzapine activates the rat locus coeruleus: in vivo electrophysiology and c-Fos immunoreactivity

BACKGROUND

Activation of central noradrenergic pathways by atypical antipsychotics has been hypothesized to play a role in their efficacy in treating the negative symptoms and cognitive impairment of schizophrenia. Because acute administration of the atypical antipsychotic olanzapine has been shown to increase extracellular levels of norepinephrine in the medial prefrontal cortex, we examined the effects of olanzapine on the noradrenergic cells of the locus coeruleus (LC).

METHODS

The effects of olanzapine (0.25-16 mg kg(-1), IV) on the firing rates and patterns of LC neurons were determined by extracellular, single-unit recordings in chloral hydrate-anaesthetized rats. The effects of olanzapine and clozapine on c-Fos expression in the LC, nucleus subcoeruleus part alpha (SubCA), and nucleus A5 (A5) were studied by immunohistochemistry.

RESULTS

Olanzapine increased LC cell firing rates, de-regularized firing, and induced burst firing. Induction of c-Fos expression in the LC by olanzapine and clozapine was confirmed and was also found in the SubCA, but not in A5.

CONCLUSIONS

Acute administration of olanzapine activates the noradrenergic neurons of the rat LC. This increased activity of LC neurons may play an important role in the efficacy of olanzapine and clozapine in treating both the negative symptoms and cognitive impairment observed in schizophrenic patients.

Cross infection control measures and the treatment of patients at risk of Creutzfeldt Jakob disease in UK general dental practice

AIMS

To determine the suitability of key infection control measures currently employed in UK dental practice for delivery of dental care to patients at risk of prion diseases.

MATERIALS AND METHODS

SUBJECTS

Five hundred dental surgeons currently registered with the General Dental Council of the UK.

DATA COLLECTION

Structured postal questionnaire.

ANALYSIS

Frequencies, cross-tabulations and chi-squared analysis.

RESULTS

The valid response rate to the questionnaire was 69%. 33% of practices had no policy on general disinfection and sterilisation procedures. Only 10 of the 327 responding practices (3%) possessed a vacuum autoclave. 49% of dentists reported using the BDA medical history form but less than 25% asked the specific questions recommended by the BDA to identify patients at risk of iatrogenic or familial CJD. However, 63% of practitioners would refer such patients, if identified, to a secondary care facility. Of the 107 practitioners who were prepared to provide dental treatment, 75 (70%) would do so using routine infection control procedures.

CONCLUSIONS

Most of the dental practices surveyed were not actively seeking to identify patients at risk of prion diseases. In many cases, recommended procedures for providing safe dental care for such patients were not in place.

Tyrosine depletion attenuates the behavioural stimulant effects of amphetamine and cocaine in rats

Neurochemical studies show that a tyrosine-free amino acid mixture depletes brain tyrosine and decreases dopamine synthesis and release. Here, we tested whether such a mixture would reduce the behavioural effects of amphetamine and other psychostimulants. A tyrosine-free amino acid mixture decreased the behavioural activation induced by both D-amphetamine (2 mg/kg s.c.) and cocaine (2 mg/kg s.c.). In contrast, the activation induced by the dopamine agonist, apomorphine (0.75 and 5 mg/kg s.c.), or the 5-hydroxytryptamine releasing agent, p-chloroamphetamine (2 mg/kg s.c.) was not altered. These findings provide behavioural evidence that tyrosine-free amino acid mixtures reduce presynaptic dopamine function in the brain.

Different tonic regulation of neuronal activity in the rat dorsal raphe and medial prefrontal cortex via 5-HT(1A) receptors

It has been established that 5-HT(1A) receptors are expressed both presynaptically as autoreceptors by 5-HT containing neurones, and postsynaptically by a variety of other neurones. Activation of either somatodendritic 5-HT(1A) autoreceptors or postsynaptic 5-HT(1A) receptors induces hyperpolarisation and inhibition of action potential discharge of the neurones, but it is unclear whether 5-HT(1A) receptors are under a general tonic influence by 5-HT. In the present study, using single unit recordings from both anesthetized and non-anesthetized rats, we show that the activity of neurones in the medial prefrontal cortex is not altered by systemic administration of the selective 5-HT(1A) receptor antagonist, WAY 100635. In contrast, WAY 100635 increased the firing rate of 5-HT neurones in the dorsal raphe nucleus. Our findings indicate a tonic activation of presynaptic somatodendritic but not postsynaptic cortical 5-HT(1A) receptors.

Electroconvulsive shock increases tachykinin NK(1) receptors, but not the encoding mRNA, in rat cortex

Recent studies have suggested that the substance P (tachykinin NK(1)) receptor may be a pharmacological target for the treatment of mood disorders. Here, the effects of electroconvulsive shock on tachykinin NK(1) receptor gene expression in the rat brain was investigated. Rats received either a single electroconvulsive shock or five shocks on alternate days. Quantitative autoradiography with [(125)I]Bolton Hunter-substance P, and in situ hybridisation histochemistry, were used to measure tachykinin NK(1) receptor-binding site densities and mRNA abundance, respectively. Densities of tachykinin NK(1) receptor-binding sites were significantly increased in the cerebral cortex following repeated electroconvulsive shock compared to sham treated animals. Densities remained unchanged in the hippocampus, striatum and amygdala. Neither single nor repeated electroconvulsive shock altered tachykinin NK(1) receptor mRNA in the brain regions examined. Hence, repeated electroconvulsive shock increases tachykinin NK(1) receptors in the rat brain in a regionally specific way. Upregulation of receptor-binding sites without a change in mRNA indicates that translational or post-translational mechanisms underlie this process.