When administered to rats in a cold environment, 3,4-methylenedioxymethamphetamine reduces brown adipose tissue thermogenesis and increases tail blood flow: effects of pretreatment with 5-HT1A and dopamine D2 antagonists

When given in a warm environment MDMA (3,4-methylenedioxymethamphetamine, ecstasy) causes hyperthermia by increasing interscapular brown adipose tissue (iBAT) heat production and decreasing heat loss via cutaneous vasoconstriction. When given in a cold environment, however, MDMA causes hypothermia by an unknown mechanism. This paper addresses these mechanisms and in addition examines whether antagonists at 5-HT(1A) and D(2) receptors reduce the hypothermic action of MDMA. Male Sprague-Dawley rats instrumented with a Doppler probe for measuring tail blood flow, and probes for measuring core and iBAT temperatures, were placed in a temperature-controlled chamber. The chamber temperature was reduced to 10 degrees C and vehicle (0.5 ml Ringer), the 5-HT(1A) antagonist WAY 100635 (0.5 mg/kg), the D(2) antagonist spiperone (20 mug/kg), or the combination of Way 100635 and spiperone were injected s.c. Thirty minutes later the antagonists were injected again along with MDMA (10 mg/kg) or vehicle. MDMA reduced core body temperature by preventing cold-elicited iBAT thermogenesis and by transiently reversing cold-elicited cutaneous vasoconstriction. Pretreatment with WAY 100635 prevented MDMA induced increases in tail blood flow, and briefly attenuated MDMA's effects on iBAT and core temperature. While spiperone alone failed to affect any of the parameters, the combination of spiperone and WAY 100635 decreased MDMA-mediated hypothermia by attenuating both the effects on tail blood flow and iBAT thermogenesis. MDMA's prevention of cold-induced iBAT thermogenesis appears to have a central origin as it rapidly reverses cold-induced increases in iBAT sympathetic nerve discharge in anesthetized rats. Our results demonstrate that MDMA in a cold environment reduces core body temperature by inhibiting iBAT thermogenesis and tail artery vasoconstriction and suggest that mechanisms by which this occurs include the activation of 5-HT1A and dopamine D2 receptors.     

Consequences of exposure to peri-articular injections of micro- and nano-particulate cobalt–chromium alloy

Metal hip replacements generate both metal particles and ions. The biological effects of peri-articular exposure to nanometre and micron sized cobalt chrome (CoCr) wear particles were investigated in a mouse model. Mice received injections of two clinically relevant doses of nanoparticles (32 nm), one of micron sized (2.9 μm) CoCr particles or vehicle alone into the right knee joint at 0, 6, 12 and 18 weeks. Mice were analysed for genotoxic and immunological effects 1, 4 and 40 weeks post exposure. Nanoparticles but not micron particles progressively corroded at the injection site. Micron sized particles were physically removed. No increase of Co or Cr was seen in peripheral blood between 1 and 40 weeks post exposure to particles. No significant inflammatory changes were observed in the knee tissues including ALVAL or necrosis. DNA damage was increased in bone marrow at one and forty weeks and in cells isolated from frontal cortex at 40 weeks after injection with nanoparticles. Mice exposed to the micron sized, but not nanoparticles became immunologically sensitized to Cr(III), Cr (VI) and Ni(II) over the 40 week period as determined by lymphocyte transformation and ELISpot (IFN-γ and IL-2) assays. The data indicated that the response to the micron sized particles was Th1 driven, indicative of type IV hypersensitivity. This study adds to understanding of the potential adverse biological reactions to metal wear products.     

Origin of serotonin innervation of the arcuate and ventromedial hypothalamic region

Combined fluorescence serotonin immunohistochemistry and retrograde transport labelling with Fast blue and Fluoro-gold were used to identify serotonin-immunoreactive neurons in the midbrain and pons which project to the region of the arcuate and ventrome-dial hypothalamic nuclei. Approximately 90% of doubly labelled neurons were located in the 3 major mesencephalic serotonin-containing cell groups: dorsal raphe (38%), median raphe (21%) and medial lemniscus group (29%). Within these groups, there were numerous non-retrogradely labelled serotonin-immunoreactive neurons as well as numerous non-serotonin-immunoreactive retrogradely labelled neurons. No doubly labelled neurons were observed caudal to raphe pontis although non-serotonin-immunoreactive neurons were retrogradely labelled in the more caudal raphe nuclei.     

Acute increases in forebrain blood flow during alerting responses in conscious rabbits

We have previously shown that alerting responses (documented by appearance of theta rhythm in the hippocampal EEG) are associated with a characteristically timed acute vasoconstriction in the ear artery bed of the conscious rabbit. We have now determined what happens to forebrain blood flow (Doppler probe chronically implanted around the internal carotid artery) during similar alerting responses in conscious rabbits, comparing forebrain flow to simultaneously measured ear flow. During an alerting response, forebrain flow increased by 31±8% of baseline (n=6, P<0.01), with the increase commencing within 1 s of the stimulus, at approximately the same time as the decrease in ear flow. Arterial pressure increased from 77±3 to 81±3 mmHg (P<0.01), so that internal carotid conductance increased from 0.17±0.02 to 0.20±0.02 kHz/mmHg (P<0.01). During a 1 h continuous recording period in the laboratory there was a negative correlation between forebrain and skin flow, with the Pearson coefficient in individual rabbits ranging from −0.18 to −0.62 (n=6, all correlations P<0.01). During this period, forebrain blood flow was just as variable, from second to second, as distal aortic flow, but not as variable as ear blood flow. Our study thus demonstrates that alerting responses in rabbits are associated with rapid increases in cerebral vascular conductance. We believe that this is the first demonstration of this phenomenon in the conscious experimental animal.     

5-hydroxytryptamine(2A) receptors regulate sympathetic nerves constricting the cutaneous vascular bed in rabbits and rats

Hyperthermia induced by 3,4-methylenedioxymethamphetamine (MDMA) is partially due to sympathetically-mediated cutaneous vasoconstriction that impairs normal heat dissipation. MDMA acts by releasing monoamines, including 5-hydroxytryptamine (5-HT), but receptor mechanisms underlying MDMA-elicited hyperthermia and cutaneous vasoconstriction are not known. The specific 5-HT2A agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) is a potent hallucinogen that also causes marked hyperthermia, suggesting the possibility that DOI, via stimulation of 5-HT2A receptors, might also cause sympathetically mediated cutaneous vasoconstriction. We tested this hypothesis in conscious unrestrained rabbits and rats.Blood flow was assessed by chronically implanted Doppler ultrasonic flow probes. Body temperature was measured by i.p. telemetric probes. We compared effects of DOI on cutaneous blood flow (ear pinna in rabbits, tail in rats) with effects on mesenteric blood flow and arterial pressure.Hyperthermia induced by DOI (5-100 microgram/kg i.v. in rabbits and 100 microgram/kg s.c. in rats) was preceded and accompanied by markedly reduced blood flow to the cutaneous bed, with no change in flow to the mesenteric bed. In rabbits, DOI (5 microgram/kg i.v.) did not affect arterial pressure or heart rate. DOI (100 microgram/kg i.v.) caused a moderate rise in arterial pressure. In rabbits, the 5-HT2A receptor antagonists ketanserin (0.3 mg/kg i.v.) and AC90179 (0.5 mg/kg i.v.) reversed the ear pinna vasoconstriction induced by DOI (5 microgram/kg i.v.). In rats, ketanserin (3 mg/kg s.c.) reversed tail vasoconstriction and hyperthermia induced by DOI (100 microgram/kg s.c.). In rabbits, the cutaneous vasoconstricting effect of DOI (5 microgram/kg i.v.) was substantially abolished in the ipsilateral ear pinna after interruption of preganglionic sympathetic nerve activity by unilateral section of the cervical sympathetic trunk.Thus hyperthermia evoked by direct stimulation of 5-HT2A receptors is associated with marked sympathetically mediated vasoconstriction, selective for the cutaneous bed. Impairment of the ability to dissipate heat following drug-induced stimulation of 5-HT2A receptors is likely to contribute to hyperthermia induced by MDMA and by hallucinogenic drugs such as LSD.     

Shigellosis in Bay of Bengal Islands,India: clinical and seasonal patterns,surveillance of antibiotic susceptibility patterns,and molecular characterization of multidrug-resistant Shigella strains isolated during a 6-year period from 2006 to 2011

This study aims to determine the clinical features and seasonal patterns associated with shigellosis, the antimicrobial resistance frequencies of the isolates obtained during the period 2006–2012 for 22 antibiotics, and the molecular characterization of multidrug-resistant strains isolated from endemic cases of shigellosis in the remote islands of India, with special reference to fluoroquinolone and third-generation cephalosporins resistance. During the period from January 2006 to December 2011, stool samples were obtained and processed to isolate Shigella spp. The isolates were evaluated with respect to their antibiotic resistance pattern and various multidrug resistance determinants, including resistance genes, quinolone resistance determinants, and extended-spectrum β-lactamase (ESBL) production. Morbidity for shigellosis was found to be 9.3 % among children in these islands. Cases of shigellosis occurred mainly during the rainy seasons and were found to be higher in the age group 2–5 years. A wide spectrum of resistance was observed among the Shigella strains, and more than 50 % of the isolates were multidrug-resistant. The development of multidrug-resistant strains was found to be associated with various drug-resistant genes, multiple mutations in the quinolone resistance-determining region (QRDR), and the presence of plasmid-mediated quinolone-resistant determinants and efflux pump mediators. This report represents the first presentation of the results of long-term surveillance and molecular characterization concerning antimicrobial resistances in clinical Shigella strains in these islands. Information gathered as part of the investigations will be instrumental in identifying emerging antimicrobial resistance, for developing treatment guidelines appropriate for that community, and to provide baseline data with which to compare outbreak strains in the future.     

The Subarachnoid Hemorrhage International Trialists (SAHIT) Repository: Advancing Clinical Research in Subarachnoid Hemorrhage

Researchers and other stakeholders continue to express concern about the failure of randomized clinical trials (RCT) in subarachnoid hemorrhage (SAH) to show efficacy of new treatments. Pooled data may be particularly useful to generate hypotheses about causes of poor outcomes and reasons for failure of RCT in SAH, and strategies to improve them. Investigators conducting SAH research collaborated to share data with the intent to develop a large repository of pooled individual patient data for exploratory analysis and testing of new hypotheses relevant to improved trial design and analysis in SAH. This repository currently contains information on 11,443 SAH patients from 14 clinical databases, of which 9 are datasets of recent RCTs and 5 are datasets of prospective observational studies and hospital registries. Most patients were managed in the last 15 years. Data validation and quality checks have been conducted and are satisfactory. Data is available on demographic, clinical, neuroimaging, and laboratory results and various outcome measures. We have compiled the largest known dataset of patients with SAH. The SAHIT repository may be an important resource for advancing clinical research in SAH and will benefit from contributions of additional datasets.     

Raphe region mediates changes in cutaneous vascular tone elicited by stimulation of amygdala and hypothalamus in rabbits

Raphe pallidus/parapyramidal neurons control cutaneous vasoconstriction induced by noxious stimuli. To determine whether they mediate forebrain-induced cutaneous vasoconstriction, we assessed changes in ear pinna blood flow elicited by electrical stimulation of amygdala and hypothalamus before and after injection of muscimol into the raphe/parapyramidal region. We compared ear flow with simultaneously recorded mesenteric flow. Experiments were performed in rabbits anesthetized with urethane (1.25-1.5 g/kg), paralysed and mechanically ventilated. Amygdala stimulation reduced skin conductance from 0.32+/-0.06 to 0.10+/-0.02 cm/s per mmHg (P<0.05, n=9), without effect on mesenteric conductance. Hypothalamic stimulation caused vasoconstriction in both cutaneous and mesenteric beds (conductances fell from 0.27+/-0.05 to 0.05+/-0.02 cm/s per mmHg and from 0.27+/-0.06 to 0.14+/-0.04 cm/s per mmHg (P<0.05, n=9), respectively). Muscimol microinjection (5 nmol in 100 nl) to raphe/parapyramidal region eliminated amygdala- and hypothalamus-induced skin vasoconstriction (pre-stimulus conductance 0.42+/-0.13 and 0.41+/-0.11 cm/s per mmHg, post-stimulus 0.41+/-0.12 and 0.39+/-0.10 cm/s per mmHg, respectively), but not hypothalamically-induced mesenteric vasoconstriction (pre-stimulus 0.29+/-0.06, post-stimulus 0.16+/-0.03 cm/s per mmHg, P<0.05, n=8). The latter was strongly attenuated by bilateral injection of muscimol to the rostral ventrolateral medulla. Data suggest that descending hypothalamo-spinal and amygdala-spinal pathways constricting the cutaneous vascular bed relay in the raphe/parapyramidal area. A relay in the rostral ventrolateral medulla contributes substantially to mesenteric vasoconstriction elicited from the hypothalamus.