Properties Of Miniature Glutamatergic Epscs In Neurons of the Locomotor Regions of the Developing Zebrafish. Declan W. Ali, Robert R. Buss, and Pierre Drapeau. Centre for Research in Neuroscience, Montreal General Hospital Research Institute, and Departments of Neurology & Neurosurgery and of Biology, McGill University, Montreal, Quebec, Canada.
APStracts 6:0475N, 1999.
As a first step in understanding the development of synaptic activation in the locomotor network of the zebrafish, we examined the properties of spontaneous, glutamatergic miniature excitatory postsynaptic currents (mEPSCs). Whole-cell patch clamp recordings were obtained from visually identified hindbrain reticulospinal neurons and spinal motoneurons of curarized zebrafish one to five days post-fertilization (larvae hatch after the second day of embryogenesis).
In the presence of tetrodotoxin (TTX) and blockers of inhibitory receptors (strychnine and picrotoxin), we detected fast glutamatergic mEPSCs that were blocked by the AMPA/kainate receptor-selective antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). At positive voltages or in the absence of Mg2+, a second, slower component of the mEPSCs was revealed which the NMDA receptor-selective antagonist DL-2-amino-5-phosphonovalerate (AP-5) abolished. In the presence of both CNQX and AP-5 all mEPSCs were eliminated. The NMDA component of reticulospinal mEPSCs had a large single channel conductance estimated to be 48 pS. Larval AMPA/kainate and NMDA components of the mEPSCs decayed with biexponential time courses that changed little during development. At all stages examined, approximately one half of synapses had only NMDA responses (lacking AMPA/kainate receptors) while the remainder of the synapses were composed of a mixture of AMPA/kainate and NMDA receptors. There was an overall increase in the frequency and amplitude of mEPSCs with an NMDA component in reticulospinal (but not motoneurons) during development. These results indicate that glutamate is a prominent excitatory transmitter in the locomotor regions of the developing zebrafish and that it activates either NMDA receptors alone at functionally silent synapses or together with AMPA/kainate receptors.
Received 6 July 1999; accepted in final form 9 September 1999.
APS Manuscript Number J543-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999