Voltage Oscillations in Xenopus Spinal Cord Neurons: Developmental Onset and Dependence on Co-activation of NMDA and 5HT Receptors

The development of intrinsic, N-methyl-D-aspartate (NMDA) receptor-mediated voltage oscillations and their dependence on co-activation of 5-hydroxytryptamine (5HT) receptors was explored in motor neurons of late embryonic and early larval Xenopus laevis. Under tetrodotoxin, 100 μM NMDA elicited a membrane depolarization of around 20 mV, but did not lead to voltage oscillations. However, following the addition of 2–5 μM 5HT, oscillations were observed in 12% of embryonic and 70% of larval motor neurons. The voltage oscillations depended upon co-activation of NMDA and 5HT receptors since they were curtailed by selectively blocking NMDA receptors with D-2-amino-5-phosphonovaleric acid (APV) or by excluding Mg²⁺ from the experimental saline. 5HT applied in the absence of NMDA also failed to elicit oscillations. Oscillations could be induced by the non-selective 5HT_1a receptor agonist, 5-carboxamidotryptamine (5CT) and both 5HT- and 5CT-induced oscillations were abolished by pindobind-5HT₁, a selective 5HT_1a receptor antagonist. To test whether 5HT enables voltage oscillations by modulating the voltage-dependent block of NMDA channels by Mg²⁺, membrane conductance was monitored under tetrodotoxin. Although 5HT caused membrane hyperpolarization of 4–8 mV, there was little detectable change in conductance. NMDA application caused an approximate 20 mV depolarization and an ‘apparent’ decrease in conductance, presumably due to the conductance pulse bringing the membrane into a voltage region where Mg²⁺ blocks the NMDA ionophore. 5HT further decreased conductance, which we propose is due to its enhancement of the voltage-dependent Mg²⁺ block. When the membrane potential was depolarized by ～20 mV via depolarizing current injection (to mimic the NMDA-induced depolarization), 5HT increased rather than decreased membrane conductance. Furthermore, 5HT did not affect the increase in membrane conductance following NMDA applications in zero Mg²⁺ saline. The results suggest that intrinsic, NMDA receptor-mediated voltage oscillations develop in a brief period after hatching, and that they depend upon the co-activation of 5HT and NMDA receptors. The enabling function of 5HT may involve the facilitation of the voltage-dependent block of the NMDA ionophore by Mg²⁺ through activation of receptors with 5HT_1a-like pharmacology.     

Unmyelinated cutaneous afferent neurons activate two types of excitatory amino acid receptor in the spinal cord of Xenopus laevis embryos

The trunk and tail skin of Xenopus laevis embryos near the time of hatching is innervated by the mechanoreceptive free nerve endings of Rohon-Beard neurons, a homogeneous class of cutaneous primary afferent fibers. Rohon-Beard neurons have cell bodies and axons in the dorsal spinal cord, where they monosynaptically excite a population of dorsolaterally situated interneurons (Clarke and Roberts, 1984). EPSPs can be recorded in these dorsolateral interneurons following electrical stimulation of the unmyelinated neurites of Rohon-Beard neurons in the skin. The EPSPs are dual component, consisting of separate fast and slow potentials that are usually evoked synchronously and that closely resemble those described previously in Xenopus and lamprey motoneurons (Dale and Roberts, 1985; Dale and Grillner, 1986). The excitation of dorsolateral interneurons by Rohon-Beard neurons is reduced by the bath application of excitatory amino acid antagonists. Kynurenic acid suppresses both the fast and slow components of the EPSPs, while both (+/-)-2-amino-5-phosphonovaleric acid (APV) and 1 mM magnesium reduce the slow component but have little or no effect on the peak amplitude of the EPSPs. These data suggest that Rohon-Beard neurons release an excitatory amino acid neurotransmitter, which acts simultaneously at both N-methyl-D-aspartate (NMDA) and non-NMDA receptor types. This is the first direct demonstration of dual-component excitatory amino acid-mediated synaptic transmission from cutaneous primary afferent neurons in the vertebrate spinal cord. The bath application of the agonists NMDA, kainate, or quisqualate in salines containing 1 microM TTX depolarized the interneurons and reduced their input resistance, which suggests that the interneurons possess all 3 types of excitatory amino acid receptor. Kynurenic acid strongly inhibits responses to NMDA and kainate, but is relatively less effective against the larger responses of quisqualate in this system.     

Characterization and Function of Spinal Excitatory Interneurons with Commissural Projections in Xenopus laevis embryos

The multipolar somata of dorsolateral commissural (dlc) interneurons (Roberts and Clarke, 1982) lie in a superficial dorsolateral position in the spinal cord of Xenopus laevis embryos. By applying horseradish peroxidase to one-half of the 100 microm diameter spinal cord, these neurons have been backfilled. Their dendritic branching pattern, commissural axonal projection and distribution near the time of hatching is described. Using Lucifer yellow-filled microelectrodes a population of sensory interneurons with dlc morphology has been identified. They have multipolar somata in a dorsolateral superficial position, obliquely projecting dendrites and a ventral commissural axon. They receive presumed monosynaptic excitation in response to electrical stimulation of sensory neurites in the skin on the same side as the soma. During fictive swimming activity in curarized embryos the dlc interneurons are rhythmically inhibited in time with ventral root discharge on the same side. Dlc interneurons can fire multiple impulses and can turn on fictive swimming when stimulated by intracellular current injection. Skin stimulation is followed by excitatory postsynaptic potentials (EPSPs) in contralateral ventral rhythmic neurons. These EPSPs are reduced by the application of NMDA receptor antagonist. We conclude that dlc interneurons are excited by primary skin afferent Rohon - Beard neurons, carry sensory information across the spinal cord to excite neurons on the opposite side by release of an excitatory amino acid transmitter and participate in reflexes and in the initiation of swimming.     

Fatal meningoencephalitis due to Bacillus anthracis

Abstract: We report the first case of fatal anthrax meningoencephalitis in Hong Kong over the past 60 years. A 13 year-old boy presented with right lower quadrant pain, diarrhoea and progressive headache. Lumbar puncture yielded gram positive bacilli initially thought to be Bacillus cereus, a contaminant. He was treated with ampicillin and cefotaxime, but died 3 days after hospitalization. The organism isolated from blood and cerebrospinal fluid was later identified as Bacillus anthracis.     

A prospective study of methylenetetrahydrofolate reductase and methionine synthase gene polymorphisms, and risk of colorectal adenoma

We examined the relationship between a functional polymorphism (667C-- >T, ala-->val) of the methylenetetrahydrofolate reductase gene (MTHFR) and the risk of colorectal adenomas in the prospective Nurses' Health Study. Among 257 incident polyp cases and 713 controls, the MTHFR val/val polymorphism [relative risk (RR) = 1.35, 95% confidence interval (CI) 0.84-2.17] was not significantly associated with risk of adenomas. This lack of association was observed for both small (RR = 1.36, 95% CI 0.76-2.45) and large (RR = 1.32, 95% CI 0.66-2.66) adenomas. Furthermore, there was no significant interaction between this polymorphism and consumption of either folate, methionine or alcohol. We also examined the relationship of a newly identified polymorphism (asp919gly) of the methionine synthase gene (MS) with the risk of colorectal adenomas in the same population. The MS gly/gly polymorphism was also not significantly associated with risk of colorectal adenomas (RR = 0.66, 95% CI 0.26-1.70). These results, which need to be confirmed in other studies, suggest that the MTHFR val/val polymorphism, which has been previously inversely associated with risk of colorectal cancer, plays a role only in a late stage (adenoma-- >carcinoma) of colorectal tumorigenesis, and/or may protect against malignant transformation in the subset of benign adenomas, which may progress to malignancy.      

罗格列酮单用或者与阿伐他汀联合使用对于2型糖尿病患者心血管疾病的非传统标志物的作用

背景和目的:罗格列酮与阿伐他汀联合疗法已经被证实对于2型糖尿病患者的血糖控制以及脂质水平都有益处。本试验将通过检测罗格列酮与阿伐他汀联合疗法对于2型糖尿病患者的生物标记水平的作用来研究该联合疗法对血管炎的作用。方法:30例患有2型糖尿病和高脂血症的患者被纳入治疗。对这些患者给予罗格列酮单一疗法4mg/d,持续3个月,然后在接下来的3个月中给予这些患者阿伐他汀10mg/d作为联合疗法。在研究开始时,罗格列酮单一疗法之后以及罗格列酮与阿伐他汀联合治疗之后测量炎性生物标记物,包括高敏C-反应蛋白(hs-CRP)、基质金属蛋白酶9(MMP…     

Electrical coupling synchronises spinal motoneuron activity during swimming in hatchling Xenopus tadpoles

The role of electrical coupling between neurons in the swimming rhythm generator of Xenopus embryos has been studied using pharmacological blockade of gap junctions. A conspicuous effect of 18β-glycyrrhetinic acid (18β-GA) and carbenoxolone, which have been shown to block electrical coupling in this preparation, was to increase the duration of ventral root bursts throughout the spinal cord during swimming. The left-right coordination, the swimming frequency and the duration of swimming episodes were not affected by concentrations of 18β-GA which significantly increased burst durations. However, the longitudinal coupling was affected such that 18β-GA led to a significant correlation between rostrocaudal delays and cycle periods, which is usually only present in older larval animals. Patch clamp recordings from spinal motoneurons tested whether gap junction blockers affect the spike timing and/or firing pattern of motoneurons during fictive swimming. In the presence of 18β-GA motoneurons continued to fire a single, but broader action potential in each cycle of swimming, and the timing of their spikes relative to the ventral root burst became more variable. 18β-GA had no detectable effect on the resting membrane potential of motoneurons, but led to a significant increase in input resistance, consistent with the block of gap junctions. This effect did not result in increased firing during swimming, despite the fact that multiple spikes can occur in response to current injection. Applications of 18β-GA at larval stage 42 had no discernible effect on locomotion. The results, which suggest that electrical coupling primarily functions to synchronize activity in synergistic motoneurons during embryo swimming, are discussed in the context of motor system development.     

Fluorescence in situ hybridization mapping of translocations and deletions involving the short arm of human chromosome 12 in malignant hematologic diseases

Translocations and deletions of the short arm of chromosome 12 [t(12p) and del(12p)] are common recurring abnormalities in a broad spectrum of hematologic malignant diseases. We studied 20 patients and one cell line whose cells contained 12p13 translocations and/or 12p deletions using fluorescence in situ hybridization (FISH) with phage, plasmid, and cosmid probes that we previously mapped and ordered on 12p12-13. FISH analysis showed that the 12p13 translocation breakpoints were clustered between two cosmids, D12S133 and D12S142, in 11 of 12 patients and in one cell line. FISH analysis of 11 patients with deletions demonstrated that the deletions were interstitial rather than terminal and that the distal part of 12p12, including the GDI-D4 gene and D12S54 marker, was deleted in all 11 patients. Moreover, FISH analysis showed that cells from 3 of these patients contained both a del(12p) and a 12p13 translocation and that the affected regions of these rearrangements appeared to overlap. We identified three yeast artificial chromosome (YAC) clones that span all the 12p13 translocation breakpoints mapped between D12S133 and D12S142. They have inserts of human DNA between 1.39 and 1.67 Mb. Because the region between D12S133 and D12S142 also represents the telomeric border of the smallest commonly deleted region of 12p, we also studied patients with a del(12p) using these YACs. The smallest YAC, 964c10, was deleted in 8 of 9 patients studied. In the other patient, the YAC labeled the del(12p) chromosome more weakly than the normal chromosome 12, suggesting that a part of the YAC was deleted. Thus, most 12p13 translocation breakpoints were clustered within the sequences contained in the 1.39 Mb YAC and this YAC appears to include the telomeric border of the smallest commonly deleted region. Whether the same gene is involved in both the translocations and deletions is presently unknown.