Kinetic Analysis of Miniature Synaptic Currents in Rat Substantia Gelatinosa Neurons |
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Authors: | I V Melnick |
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Institution: | 1. Bogomolets Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine
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Abstract: | Interneurons of the substantia gelatinosa (SG) form a complex synaptic network in the dorsal horn of the spinal cord. The properties of miniature excitatory and inhibitory
postsynaptic currents (mEPSCs and mIPSCs, respectively) were studied in spinal cord slices of 3- to 4-week-old rats. The reversal
potentials of the currents were close to 0 mV for excitatory and –70 mV for inhibitory events. Under recording conditions
close to physiological ones (holding potential –40 mV, temperature 32°C, low intracellular Cl–]), the mean rise times of these currents were, respectively, 1.0 and 1.8 msec. The decay of the currents was monoexponential
in the majority of occurrences (94 and 91.4%), with a time constant (τ) of 2.7 msec for mEPSCs and 7.2 msec for mIPSCs. A
part (8.6%) of mIPSCs had an additional slow component with τ = 30.1 msec. All mEPSCs were blocked by 10 mM CNQX, an antagonist
of the AMPA/kainate subtype of glutamate receptors. Monoexponential mIPSCs were blocked by 1 mM strychnine, an antagonist
of glycine receptors, while two-component mIPSCs required the additional presence of 10 mM bicuculline, a blocker of GABAA
receptors. Only two cells of 23 (~9%) demonstrated pure GABA-ergic mIPSCs (τ = 26.2 msec). It is concluded that, under physiological
conditions, AMPA/kainate but not NMDA receptors mediate excitatory synaptic transmission in SG neurons. Synaptic inhibition is mediated predominantly by glycine receptors, with mild fractions of IPSCs provided by GABA-ergic
transmission and GABA/glycine co-release. |
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Keywords: | |
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