Characterization on Responsiveness of Excitatory Synaptic Transmissions to α1-Adrenoceptor Blockers in Substantia Gelatinosa Neurons Isolated From Lumbo-Sacral Level in Rat Spinal Cords

Abstract

Purpose The aim of this study was to characterize the responsiveness of miniature excitatory postsynaptic currents (mEPSCs) to α1-adrenoceptor blockers in substantia gelatinosa (SG) neurons from the spinal cord to develop an explanation for the efficacy of α1-adrenoceptor blockers in micturition dysfunction. Methods Male adult Sprague-Dawley rats were used. Blind whole-cell patch-clamp recordings were performed using SG neurons in spinal cord slices. Naftopidil (100μM), tamsulosin (100μM), or silodosin (30μM), α1-adrenoceptor blockers, was perfused. The frequency of mEPSCs was recorded in an SG neuron to which the 3 blockers were applied sequentially with wash-out periods. Individual frequencies in a pair before naftopidil and tamsulosin perfusion were plotted as baseline, and the correlation between them was confirmed by Spearman correlation coefficient; linear regression was then performed. The same procedure was performed before naftopidil and silodosin perfusion. Frequencies of pairs after naftopidil and tamsulosin perfusion and after naftopidil and silodosin perfusion were similarly analyzed. The ratios of the frequencies after treatment to before were then calculated. Results After the treatments, Spearman ρ and the slope were decreased to 0.682 from 0.899 at baseline and 0.469 from 1.004 at baseline, respectively, in the tamsulosin group relative to the naftopidil group. In the silodosin group, Spearman ρ and the slope were also decreased to 0.659 from 0.889 at baseline and 0.305 from 0.989 at baseline, respectively, relative to the naftopidil group. Naftopidil significantly increased the ratio of the frequency of mEPSCs compared to tamsulosin and silodosin (P=0.015 and P=0.004, respectively). Conclusions There was a difference in responsiveness in the frequency of mEPSCs to α1-adrenoceptor blockers, with the response to naftopidil being the greatest among the α1-adrenoceptor blockers. These data are helpful to understand the action mechanisms of α1-adrenoceptor blockers for male lower urinary tract symptoms in clinical usage.

Effect of Alpha 1-Adrnoceptor Antagonists on Postsynaptic Sensitivity in Substantia Gelatinosa Neurons From Lumbosacral Spinal Cord in Rats Using Slice Patch-Clamp Technique for mEPSC

“…The methods for obtaining slices of the adult rat spinal cord and for blind patch-clamp recordings from SG neurons have been described in detail elsewhere [ 17 , 19 ]. Briefly, adult male SpragueDawley rats (6–8 weeks old) were deeply anesthetized with urethane (1.2 g/kg, intraperitoneally), and a lumbosacral laminectomy then was performed.…”

“…1). Cell recordings were obtained in voltage-clamp mode at holding potentials of -70 mV to record EPSCs [17,19].…”

“…All drugs were applied by sequential perfusion in a single cell with washout periods via a three-way stopcock without changes in the perfusion rate or temperature. The application schedule was as described previously [17].…”

“…Analyses of frequency and amplitude distributions of mEPSCs permit determination of the loci of experimental manipulation (i.e., presynaptic and/or postsynaptic) [ 16 ]. The effects of naftopidil, tamsulosin, and silodosin on the frequency of excitatory synaptic currents at synaptic terminal sites in the spinal cord have been determined [ 17 ], and an explanation for the diversity of efficacy in treatment of storage symptoms by α1-adrenoceptor antagonists is being developed. Naftopidil inhibits the amplitudes of EPSCs evoked by dorsal root stimulation and increases the frequencies of mEPSCs [ 18 ].…”

Differential Effects of Alpha 1-Adrenoceptor Antagonists on the Postsynaptic Sensitivity: Using Slice Patch-Clamp Technique for Inhibitory Postsynaptic Current in Substantia Gelatinosa Neurons From Lumbosacral Spinal Cord in Rats

“…All drugs were applied by sequential perfusion in individual cells with washout periods via a three-way stopcock without changes in the perfusion rate or temperature. The application schedule was described previously [22].…”