Biomedical subjects

Keith J Todd

Publications and source records attributed to Keith J Todd.

4 recordsLinked to original sources

PubMed2006

Purinergic modulation of synaptic signalling at the neuromuscular junction.

Purines have physiologically important functions throughout the nervous system. In both the central (CNS) and peripheral nervous systems (PNS), purines in the form of adenosine triphosphate and adenosine can play a number of roles in neuronal activation and inhibition. In addition, purines are known to be important for glial cell signaling in both the CNS and PNS. In the PNS, the neuromuscular junction (NMJ) is an excellent model for studying simple synaptic interactions. It is well suited to investigations of neuron-glia interactions because synaptic properties are well defined and perisynaptic Schwann cells (PSCs), glial cells at the NMJ, dynamically interact with the pre- and postsynaptic elements. At the NMJ, purines are critical for presynaptic modulation but also for neuron-glia interactions. Purines signal to PSCs through metabotropic and ionotropic receptors and activation of these receptors can have both modulatory and activating functions. This review will discuss recent developments in our understanding of purinergic modulation of the NMJ with an emphasis on the involvement of purines in neuron-glia interactions at this synapse.

Adenosine Triphosphate↗

PubMed2006

Glial cells in synaptic plasticity.

Plasticity of synaptic transmission is believed to be the cellular basis for learning and memory, and depends upon different pre- and post-synaptic neuronal mechanisms. Recently, however, an increasing number of studies have implicated a third element in plasticity; the perisynaptic glial cell. Originally glial cells were thought to be important for metabolic maintenance and support of the nervous system. However, work in the past decade has clearly demonstrated active involvement of glia in stability and overall nervous system function as well as synaptic plasticity. Through specific modulation of glial cell function, a wide variety of roles for glia in synaptic plasticity have been uncovered. Furthermore, interesting circumstantial evidence suggests a glial involvement in multiple other types of plasticity. We will discuss recent advances in neuron-glial interactions that take place during synaptic plasticity and explore different plasticity phenomena in which glial cells may be involved.

Animals↗

PubMed2006

Neuron-glia interactions at the neuromuscular synapse.

The contribution of glial cells in the regulation of the transfer of information in CNS and PNS is now increasingly recognized. Perisynaptic Schwann cells (PSCs), glial cells at the neuromuscular junction (NMJ), have proven to be an exceptionally important model for studying these roles. PSCs surround nerve terminals at the NMJ and are activated by transmitter release in a frequency-dependent manner. All of these receptors, except one type, are coupled to G proteins and can be regrouped into two categories: activators and modulators of PSCs. In the former category are muscarinic (unknown subtype) and purinergic receptors (P2X and P2Y). In the latter category are adenosine (A1), Substance P (NK-1) and CGRP receptors. All receptors coupled to G proteins induce the release of Ca2+ from internal stores. In return for this activation, PSCs modulate synaptic activity and short-term plasticity. In this review, we will focus on the role of purines in the induction of glial cell activity and their possible involvement in the modulation of synaptic transmission as a result of the synaptic-induced glial activity.

Acetylcholine↗

PubMed2004

Activation of ionotropic glutamate receptors on peripheral axons of primary motoneurons mediates transmitter release at the zebrafish NMJ.

The development and function of the vertebrate neuromuscular junction (NMJ) is continually being redefined. Previous studies have indicated that glutamate may play a role in the development or function of the NMJ by associating with presynaptic receptors. We have used larval zebrafish (Danio rerio) to investigate the presence of presynaptic ionotropic glutamate receptors (iGluRs) at the NMJ in vivo. In whole-mount zebrafish larvae, antibody staining directed to NR2A subunits colocalized with specific staining of motoneuron axon tracts. Whole cell voltage-clamp recordings of miniature endplate currents (mEPCs) from axial white muscle were performed during application of iGluR agonists and antagonists. Local perfusion of the NMJ with iGluR agonists resulted in significant increases in the frequency of spontaneous acetylcholine (ACh) release. These increases were blocked by the N-methyl-d-aspartate (NMDA) receptor antagonist d-(-)-2-amino-5-phosphonopentanoic acid (50 microM) and by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione (50 microM). Further pharmacological investigation revealed no effect of the kainate receptor-specific antagonist (2S,4R)-4-methylglutamate (10 microM) on kainate-induced rises in the frequency of spontaneous ACh release. However, these were blocked with the AMPA receptor-specific antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (50 microM). Application of glutamate (1 mM) in the presence of the glutamate uptake inhibitor d-threo-beta-benzyloxyaspartate(200 microM) resulted in a significant increase in the frequency of mEPCs. These results suggest the presence of AMPA and NMDA receptors in association with motoneuron axons of larval zebrafish.

Acetylcholine↗