Group I mGluRs increase locomotor network excitability in Xenopus tadpoles via presynaptic inhibition of glycinergic neurotransmission

The group I metabotropic glutamate receptor agonist (S)-3,5-dihyroxyphenylglycine (DHPG) increases the frequency of rhythmic swimming activity in Xenopus tadpoles. This study explores the possibility that group I receptor modulation occurs in part via depression of inhibitory synaptic transmission. Applications of the glycine receptor antagonist strychnine occluded the effects of DHPG, providing preliminary evidence that group I receptors affect motor network output by reducing glycinergic transmission. This evidence was supported further by intracellular and whole-cell patch-clamp recordings from presumed motorneurons. DHPG applications produced two prominent effects: (i) during swimming activity, glycinergic mid-cycle IPSPs were reduced in amplitude; and (ii) during quiescent periods, the frequency of spontaneous miniature IPSPs was also reduced. No change in membrane potential or input resistance following group I receptor activation was detected. The reduction in fast synaptic inhibition provides a plausible explanation for the increased excitability of the locomotor network, although other contributory mechanisms activated in parallel by group I receptors cannot be discounted. Aspects of this work have been published previously in abstract form [R. J. Chapman &amp; K. T. Sillar (2003) SFN Abstracts 277.8].</p

Combined imaging and chemical sensing of L-glutamate release from the foregut plexus of the Lepidopteran, Manduca sexta

A new combined imaging and chemical detection sensor for the measurement of localized L-glutamate release at the insect neuromuscular junction (NMJ) is presented. The sensor is comprised of an L-glutamate-sensitive fluorescent gel, spin-coated onto the tip of an optical imaging fiber. The gel is composed of L-glutamate oxidase (GLOD); a pH-sensitive fluorescent dye, SNAFL; and poly(acrylamide-co-N-acryloxysuccinimide) (PAN). NH3 is liberated from the interaction of L-glutamate with GLOD, which reversibly reduces the emitted fluorescence signal from SNAFL. This sensor has a spatial resolution of 3-4 μm, and an L-glutamate detection limit of between 10 and 100 μM. L-glutamate release and re-uptake from the foregut plexus of Manduca sexta was detected by the sensor in the presence of the L-glutamate re-uptake blocker dihydrokainate, and the post-synaptic L-glutamate receptor antagonist CNQX.</p

Muscarinic acetylcholine and proctolin receptors in the foregut of the locust Schistocerca gregaria:Role of inositol phosphates, protein kinase C and calcium in second messenger effects

Acetylcholine (ACh) induced dose-dependent contraction of the locust (Schistocerca gregaria) foregut was antagonised by 4-DAMP (1,1-dimethyl-4- diphenylacetoxypiperidinium; 10 nM-10 μM) and Li+ (50- 100 mM). The inhibition by Li+, of ACh-induced gut contraction suggests that this muscarinic ACh receptor is linked to phosphatidylinositol second messenger systems. ACh (1 μM and 0.5 mM) stimulated concentration-dependent production of [3H]-inositol phosphates, including [3H]-inositol trisphosphate, from foregut homogenates incubated in Tris buffer containing [3H]-myo-inositol. Pre-incubation of homogenates with Li+ (50 mM) or atropine (10 μM) reduced ACh-stimulated inositol phosphate production by 95%. The contractile effects of ACh, 1-oleoyl-2-sn-glycerol (OAG) and phorbol 12,13-dibutyrate (PDBu), but not those of proctolin, on the foregut, were reduced by the protein kinase C (PKC) inhibitor H7 (10 nM-10 μM) and the L-type Ca2+ channel blocker verapamil (1 μM-0.1 mM). In comparison, the contractile effects of proctolin, but not those of ACh, OAG and PDBu, were potentiated by H7 (10 nM- 10 μM) and attenuated by the inositol 1,4,5-trisphosphate (IP3) receptor blocker decavanadate (10 μM-0.5 mM) and ryanodine (1 μM-0.1 mM), an inhibitor of intracellular Ca2+ release. Decavanadate and ryanodine had no effect on ACh-induced tissue contraction. Proctolin-induced contraction was unaffected by the presence of verapamil at concentrations as high as 1 mM but was abolished by 10 mM Co2+ . These data suggest, that in the locust foregut, stimulation of ACh receptors causes activation of PKC, thereby promoting Ca2+ entry via the opening of L-type Ca2+ channels. However, the function of IP3 produced following activation of tissue muscarinic receptors is unclear. In contrast, activation of proctolin receptors causes verapamil-insensitive entry of extracellular Ca2+ as well as the generation of IP3 which causes release of Ca2+ from intracellular stores to bring about an increase in gut contractility.</p

Classification of compression bandages: Practical aspects

BACKGROUND Compression bandages appear to be simple medical devices. However, there is a lack of agreement over their classification and confusion over the use of important terms such as elastic, inelastic, and stiffness. OBJECTIVES The objectives were to propose terms to describe both simple and complex compression bandage systems and to offer classification based on in vivo measurements of subbandage pressure and stiffness. METHODS A consensus meeting of experts including members from medical professions and from companies producing compression products discussed a proposal that was sent out beforehand and agreed on by the authors after correction. RESULTSPressure, layers, components, and elastic properties (P-LA-C-E) are the important characteristics of compression bandages. Based on simple in vivo measurements, pressure ranges and elastic properties of different bandage systems can be described. Descriptions of composite bandages should also report the number of layers of bandage material applied to the leg and the components that have been used to create the final bandage system. CONCLUSION Future descriptions of compression bandages should include the subbandage pressure range measured in the medial gaiter area, the number of layers, and a specification of the bandage components and of the elastic property (stiffness) of the final bandage