TY - JOUR
T1 - Analysis of quantal size of voltage responses to retinal stimulation in the accessory optic system
AU - Ariel, Michael
AU - Johny, Manu Ben
N1 - Funding Information:
We thank Tian Xing Fan for his help with the experimental recordings and Drs. Terrance Egan and Amy Harkins for their helpful comments on the manuscript. This work was supported by NSF IBN9974891.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/7/9
Y1 - 2007/7/9
N2 - In the intact vertebrate central nervous system, the quantal nature of synaptic transmission is difficult to measure because the postsynaptic sites may be distributed along a tortuous dendritic tree that cannot be readily clamped spatially to a uniform potential. Titrating the intact brain's extracellular concentration of calcium ions is also challenging because of its strong buffering mechanisms. In this study, using a whole brain with eye attached preparation, quantal neurotransmission was examined in the turtle brainstem in vitro, by recording from accessory optic system neurons that receive direct input from visually responsive retinal ganglion cells. Unitary EPSPs, evoked by microstimulation of a single ganglion cell, were measured during whole cell current-clamp recordings. In this preparation, the neurons exhibit direction-selectivity, despite the hypoxic conditions. Bath application of cadmium to reduce calcium influx also reduced evoked EPSP amplitudes to that of the spontaneous synaptic events. Statistical analyses indicated that these evoked response amplitudes could be well fitted to a Poisson distribution for most brainstem neurons. Therefore, the spontaneous miniature excitatory synaptic events of approximately 1 mV, as also observed during spike blockade of the retina [Kogo, N., Ariel, M., 1997. Membrane properties and monosynaptic retinal excitation of neurons in the turtle accessory optic system. Journal of Neurophysiology 78, 614-627], are likely responses to the neurotransmitter of single vesicles release by retinal axon terminals.
AB - In the intact vertebrate central nervous system, the quantal nature of synaptic transmission is difficult to measure because the postsynaptic sites may be distributed along a tortuous dendritic tree that cannot be readily clamped spatially to a uniform potential. Titrating the intact brain's extracellular concentration of calcium ions is also challenging because of its strong buffering mechanisms. In this study, using a whole brain with eye attached preparation, quantal neurotransmission was examined in the turtle brainstem in vitro, by recording from accessory optic system neurons that receive direct input from visually responsive retinal ganglion cells. Unitary EPSPs, evoked by microstimulation of a single ganglion cell, were measured during whole cell current-clamp recordings. In this preparation, the neurons exhibit direction-selectivity, despite the hypoxic conditions. Bath application of cadmium to reduce calcium influx also reduced evoked EPSP amplitudes to that of the spontaneous synaptic events. Statistical analyses indicated that these evoked response amplitudes could be well fitted to a Poisson distribution for most brainstem neurons. Therefore, the spontaneous miniature excitatory synaptic events of approximately 1 mV, as also observed during spike blockade of the retina [Kogo, N., Ariel, M., 1997. Membrane properties and monosynaptic retinal excitation of neurons in the turtle accessory optic system. Journal of Neurophysiology 78, 614-627], are likely responses to the neurotransmitter of single vesicles release by retinal axon terminals.
KW - Brainstem
KW - EPSP
KW - Electrophysiology
KW - Retinal afferents
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U2 - 10.1016/j.brainres.2007.04.067
DO - 10.1016/j.brainres.2007.04.067
M3 - Article
C2 - 17543898
AN - SCOPUS:34250683501
SN - 0006-8993
VL - 1157
SP - 41
EP - 55
JO - Brain research
JF - Brain research
IS - 1
ER -