[Show abstract][Hide abstract] ABSTRACT: This study used the Frankenhaeuser-Huxley axonal model to analyze the effects of non-symmetric waveforms on conduction block of myelinated axons induced by high-frequency (10-300 kHz) biphasic electrical stimulation. The results predict a monotonic relationship between block threshold and stimulation frequency for symmetric waveform and a non-monotonic relationship for non-symmetric waveforms. The symmetric waveform causes conduction block by constantly activating both sodium and potassium channels at frequencies of 20-300 kHz, while the non-symmetric waveforms share the same blocking mechanism from 20 kHz up to the peak threshold frequency. At the frequencies above the peak threshold frequency the non-symmetric waveforms block axonal conduction by either hyperpolarizing the membrane (if the positive pulse is longer) or depolarizing the membrane (if the negative pulse is longer). This simulation study further increases our understanding of conduction block in myelinated axons induced by high-frequency biphasic electrical stimulation, and can guide future animal experiments as well as optimize stimulation parameters that might be used for electrically induced nerve block in clinical applications.
[Show abstract][Hide abstract] ABSTRACT: This study examined the role of β-adrenergic and opioid receptors in spinal reflex bladder activity and in the inhibition induced by pudendal nerve stimulation (PNS) or tibial nerve stimulation (TNS). Spinal reflex bladder contractions were induced by intravesical infusion of 0.25% acetic acid in α-chloralose anesthetized cats after an acute spinal cord transection (SCT) at the thoracic T9/T10 level. PNS or TNS at 5 Hz was applied to inhibit these spinal reflex contractions at 2 and 4 times the threshold intensity (T) for inducing anal or toe twitch respectively. During a cystrometrogram (CMG) PNS at 2T and 4T significantly (p<0.05) increased bladder capacity from 58.0±4.7% to 85.8±10.3% and 96.5±10.7% respectively of saline control capacity, while TNS failed to inhibit spinal reflex bladder contractions. After administering propranolol (3 mg/kg i.v., a β1/β2-adrenergic receptor antagonist), the effects of 2T and 4T PNS on bladder capacity were significantly (p<0.05) reduced to 64.5±9.5% and 64.7±7.3% respectively of the saline control capacity. However, the residual PNS inhibition (about 10% increase in capacity) was still statistically significant (p<0.05). Propranolol treatment also significantly (p=0.0019) increased the amplitude of bladder contraction, but did not change the control bladder capacity. Naloxone (1 mg/kg i.v., an opioid receptor antagonist) had no effect on either spinal reflex bladder contractions or PNS inhibition. At the end of experiments, hexamethonium (10 mg/kg i.v., a ganglionic blocker) significantly (p<0.05) reduced the amplitude of the reflex bladder contractions. This study indicates an important role of β1/β2-adrenergic receptors in pudendal inhibition and spinal reflex bladder activity.
[Show abstract][Hide abstract] ABSTRACT: The goal of this study was to determine if supraspinal pathways are necessary for inhibition of bladder reflex activity induced by activation of somatic afferents in the pudendal or tibial nerve. Cats anesthetized with α-chloralose were studied after acute spinal cord transection at the thoracic T9/T10 level. Dilute (0.25%) acetic acid (AA) was used to irritate bladder, activate nociceptive afferent C-fibers and trigger spinal reflex bladder contractions (amplitude 19.3±2.9 cmH2O). Hexamethonium (a ganglionic blocker, i.v.) significantly (p<0.01) reduced the amplitude of the reflex bladder contractions to 8.5±1.9 cmH2O. Injection of lidocaine (2%, 1-2 ml) into the sacral spinal cord or transection of the sacral spinal roots and spinal cord further reduced the contraction amplitude to 4.2±1.3 cmH2O. Pudendal nerve stimulation (PNS) at frequencies of 0.5-5 Hz and 40 Hz but not at 10-20 Hz inhibited the reflex bladder contractions, while tibial nerve stimulation (TNS) failed to inhibit the bladder contractions at all tested frequencies (0.5-40 Hz). These results indicate that PNS inhibition of nociceptive afferent C-fiber mediated spinal reflex bladder contractions can occur at the spinal level in the absence of supraspinal pathways, but TNS inhibition requires supraspinal pathways. In addition, this study shows for the first time that after acute spinal cord transection reflex bladder contractions can be triggered by activating the nociceptive bladder afferent C-fibers using AA irritation. Understanding the sites of action for PNS or TNS inhibition is important for clinical application of pudendal or tibial neuromodulation to treat bladder dysfunctions.
American journal of physiology. Renal physiology 07/2014; 307(6). DOI:10.1152/ajprenal.00308.2014 · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of a non-symmetric waveform on nerve conduction block induced by high-frequency biphasic stimulation is investigated using a lumped circuit model of the unmyelinated axon based on Hodgkin-Huxley equations. The simulation results reveal that the block threshold monotonically increases with the stimulation frequency for the symmetric stimulation waveform. However, a non-monotonic relationship between block threshold and stimulation frequency is observed when the stimulation waveform is non-symmetric. Constant activation of potassium channels by the high-frequency stimulation results in the increase of block threshold with increasing frequency. The non-symmetric waveform with a positive pulse 0.4-0.8 μs longer than the negative pulse blocks axonal conduction by hyperpolarizing the membrane and causes a decrease in block threshold as the frequency increases above 12-16 kHz. On the other hand, the non-symmetric waveform with a negative pulse 0.4-0.8 μs longer than the positive pulse blocks axonal conduction by depolarizing the membrane and causes a decrease in block threshold as the frequency increases above 40-53 kHz. This simulation study is important for understanding the potential mechanisms underlying the nerve block observed in animal studies, and may also help to design new animal experiments to further improve the nerve block method for clinical applications.
[Show abstract][Hide abstract] ABSTRACT: This study is aimed at determining the effect of duloxetine (a serotonin-norepinephrine reuptake inhibitor) on pudendal inhibition of bladder overactivity. Cystometrograms were performed on 15 cats under α-chloralose anesthesia by infusing saline and then 0.25% acetic acid (AA) to induce bladder overactivity. To inhibit bladder overactivity, pudendal nerve stimulation (PNS) at 5 Hz was applied to the right pudendal nerve at 2 and 4 times the threshold (T) intensity for inducing anal twitch. Duloxetine (0.03-3 mg/kg) was administered intravenously to determine the effect on PNS inhibition. AA irritation significantly (p<0.01) reduced bladder capacity to 27.9±4.6% of saline control capacity. PNS alone at both 2T and 4T significantly (p<0.01) inhibited bladder overactivity and increased bladder capacity to 83.6±7.6% and 87.5±7.7% of saline control, respectively. Duloxetine at low doses (0.03-0.3 mg/kg) caused a significant reduction in PNS inhibition without changing bladder capacity. However, at high doses (1-3 mg/kg) duloxetine significantly increased bladder capacity but still failed to enhance PNS inhibition. WAY100635 (a 5-HT1A receptor antagonist, 0.5-1 mg/kg, i.v.) reversed the suppressive effect of duloxetine on PNS inhibition and significantly (p<0.05) increased the inhibitory effect of duloxetine on bladder overactivity but did not enhance the effect of PNS. These results indicate that activation of 5-HT1A auto-receptors on the serotonergic neurons in the raphe nucleus may suppress duloxetine and PNS inhibition, suggesting that the co-administration of a 5-HT1A antagonist drug might be useful in enhancing the efficacy of duloxetine alone and/or the additive effect of PNS-duloxetine combination for the treatment of overactive bladder symptoms.
Journal of Pharmacology and Experimental Therapeutics 03/2014; 349(3). DOI:10.1124/jpet.113.211557 · 3.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Picrotoxin, an antagonist for γ-aminobutyric acid receptor subtype A (GABAA), was used to investigate the role of GABAA receptors in nociceptive and non-nociceptive reflex bladder activities and pudendal inhibition of these activities in cats under α-chloralose anesthesia. Acetic acid (AA, 0.25%) was used to irritate the bladder and induce nociceptive bladder overactivity, while saline was used to distend the bladder and induce non-nociceptive bladder activity. To modulate the bladder reflex pudendal nerve stimulation (PNS) was applied at multiple threshold (T) intensities for inducing anal sphincter twitching. AA irritation significantly (p<0.01) reduced bladder capacity to 34.3±7.1% of the saline control capacity; while PNS at 2T and 4T significantly (p<0.01) increased AA bladder capacity to 84.0±7.8% and 93.2±15.0%, respectively, of the saline control. Picrotoxin (0.4 mg, i.t.) did not change AA bladder capacity but completely removed PNS inhibition of AA-induced bladder overactivity. Picrotoxin (i.v.) only increased AA bladder capacity at a high dose (0.3 mg/kg) but significantly (p<0.05) reduced 2T PNS inhibition at low doses (0.01-0.1 mg/kg). During saline cystometry, PNS significantly (p<0.01) increased bladder capacity to 147.0±7.6% at 2T and 172.7±8.9% at 4T of control capacity; and picrotoxin (0.4 mg, i.t. or 0.03-0.3 mg/kg, i.v.) also significantly (p<0.05) increased bladder capacity. However, picrotoxin treatment did not alter PNS inhibition during saline infusion. These results indicate that spinal GABAA receptors have different roles in controlling nociceptive and non-nociceptive reflex bladder activities and in PNS inhibition of these activities.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to determine the effect of tibial nerve stimulation (TNS) on the micturition reflex. Experiments were conducted in 24 rats under urethane anesthesia. A catheter was inserted into the bladder via the bladder dome for saline infusion. A cuff electrode was placed around right tibial nerve for stimulation. TNS (5 Hz, 0.2 msec pulse width) at 2-4 times the threshold (T) intensity for inducing a toe movement was applied either during slow (0.08 mL/min) infusion of the bladder or for 30 min with an empty bladder. TNS had no effect on the micturition reflex when it was applied during slow bladder infusion. However, the 30-min TNS applied with an empty bladder induced poststimulation inhibition and significantly (P < 0.05) increased the bladder capacity to about 140% of prestimulation level in a 50-min period following the termination of stimulation. The bladder compliance was also significantly (P < 0.05) increased after the 30-min TNS. These results suggest that different mechanisms might exist in acute- and post-TNS inhibition of micturition reflex. The animal model developed in this study will be very useful for further investigations of the neurotransmitter mechanisms underlying tibial neuromodulation of bladder function.
[Show abstract][Hide abstract] ABSTRACT: The study aims to determine the functionality of a wireless-controlled implantable stimulator designed for stimulation and block of the pudendal nerve.
In five cats under α-chloralose anesthesia, the stimulator was implanted underneath the skin on the left side in the lower back along the sacral spine. Two tripolar cuff electrodes were implanted bilaterally on the pudendal nerves in addition to one bipolar cuff electrode that was implanted on the left side central to the tripolar cuff electrode. The stimulator provided high-frequency (5-20 kHz) biphasic stimulation waveforms to the two tripolar electrodes and low-frequency (1-100 Hz) rectangular pulses to the bipolar electrode. Bladder and urethral pressures were measured to determine the effects of pudendal nerve stimulation (PNS) or block.
The maximal (70-100 cmH2 O) urethral pressure generated by 20-Hz PNS applied via the bipolar electrode was completely eliminated by the pudendal nerve block induced by the high-frequency stimulation (6-15 kHz, 6-10 V) applied via the two tripolar electrodes. In a partially filled bladder, 20-30 Hz PNS (2-8 V, 0.2 ms) but not 5 Hz stimulation applied via the bipolar electrode elicited a large sustained bladder contraction (45.9 ± 13.4 to 52.0 ± 22 cmH2 O). During cystometry, the 5 Hz PNS significantly (p < 0.05) increased bladder capacity to 176.5 ± 27.1% of control capacity.
The wireless-controlled implantable stimulator successfully generated the required waveforms for stimulation and block of pudendal nerve, which will be useful for restoring bladder functions after spinal cord injury.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study is to determine whether duloxetine (a serotonin-norepinephrine reuptake inhibitor) combined with transcutaneous foot stimulation or WAY100635 (a 5HT1A antagonist) can enhance inhibition of bladder overactivity in cats. Cystometrograms were performed on 8 cats under α-chloralose anesthesia by infusing saline and then 0.25% acetic acid (AA) to induce bladder overactivity. To inhibit bladder overactivity, foot stimulation (5 Hz) was applied via transcutaneous pad electrodes to the right hind foot at 2 and 4 times the threshold (T) intensity for inducing a toe twitch. Duloxetine (0.003-3 mg/kg) was administered intravenously to determine the effect of combination treatment. After the 3 mg/kg dose of duloxetine, WAY100635 (0.5 mg/kg) was given intravenously. AA irritation significantly (P<0.0001) reduced bladder capacity to 42.7±7.4% of saline control capacity. Foot stimulation alone at both 2T and 4T significantly (P<0.0001) inhibited bladder overactivity and increased bladder capacity to 66.7±6.3% and 85.7±6.5% of saline control, respectively. Duloxetine alone dose-dependently inhibited bladder overactivity and completely restored bladder capacity to saline control (109±15.5%) at 3 mg/kg. Although duloxetine combined with foot stimulation did not further enhance the inhibition, WAY100635 (0.5 mg/kg) given after 3 mg/kg duloxetine further increased (P=0.008) bladder capacity to 162.2±22.5% of saline control. Although duloxetine and foot stimulation independently inhibited bladder overactivity, combined treatment did not enhance the inhibition. Duloxetine combined with WAY100635, however, synergistically enhanced bladder inhibition, indicating a potential novel treatment for overactive bladder if duloxetine is combined with a 5HT1A receptor antagonist drug.
[Show abstract][Hide abstract] ABSTRACT: To determine if electrical stimulation of somatic afferent nerves in the foot can delay bladder filling sensations and increase bladder capacity in healthy humans without overactive bladder (OAB).
Eight subjects underwent 90 minutes of foot stimulation using skin surface electrodes connected to a transcutaneous electrical nerve stimulator. The electrodes were attached to the bottom of the foot. Subjects completed a 3-day voiding diary during which foot stimulation was applied on the second day. Stimulation parameters included a pulse frequency of 5 Hz, a rectangular waveform pulse width of 0.2 ms, and an intensity of 2-6 times the minimal stimulation current necessary to induce a toe twitch. The stimulation intensity was set by each subject to a maximal level without causing any discomfort. The subjects were provided 500-1000 mL of water to drink during stimulation.
The average volume per void was 350±22 mL during the 24 hour period prior to foot stimulation, and this voided volume increased to 547±52 mL (p<0.01) for up to 5 hours after the stimulation. The average voided volume returned to 363±21 mL within 36 hours after stimulation. There were no adverse events.
Foot stimulation can delay bladder filling sensations and significantly increase bladder capacities in healthy humans without OAB. Although the study group was small, our results support moving forward with clinical trials of foot neuromodulation in OAB patients.
The Journal of urology 10/2013; 191(4). DOI:10.1016/j.juro.2013.10.024 · 3.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The role of the 5-HT3 receptors in pudendal neuromodulation of bladder activity and its interaction with opioid receptors were investigated in anesthetized cats. The bladder was distended with either saline to induce normal bladder activity or with 0.25% acetic acid (AA) to induce bladder overactivity. Pudendal afferent nerves were activated by 5 Hz stimulation at multiples of the threshold (T) intensity for inducing anal twitching. AA irritation significantly reduced bladder capacity to 16.5±3.3% of saline control capacity, while pudendal nerve stimulation (PNS) at 1.5-2T and 3-4T restored the capacity to 82.0±12% (P=0.0001) and 98.6±15% (P<0.0001), respectively. Cumulative doses (1-3mg/kg, i.v.) of ondansetron, a 5-HT3 receptor antagonist, eliminated low intensity (1.5-2T) PNS inhibition and reduced high intensity (3-4T) PNS inhibition of bladder overactivity. During saline distention, PNS at 1.5-2T and 3-4T significantly increased bladder capacity to 173.2±26.4% (P=0.036) and 193.2±22.5% (P=0.008), respectively, of saline control capacity, but ondansetron (0.003-3mg/kg, i.v.) did not alter PNS inhibition. Ondansetron (0.1-3 mg/kg) also significantly (P<0.05) increased control bladder capacity (50-200%) during either AA irritation or saline distention. In both conditions the effect of low and high intensity PNS were not significantly different. After ondansetron (3 mg/kg) treatment, naloxone (1 mg/kg, i.v.) significantly (P<0.05) decreased control bladder capacity (40-70%) during either AA irritation or saline distention, but failed to affect PNS inhibition. This study revealed that activation of 5-HT3 receptors has a role in PNS inhibition of bladder overactivity. It also indicated that 5-HT3 receptor antagonists might be useful for treating overactive bladder symptoms.
[Show abstract][Hide abstract] ABSTRACT: The role of 5-HT2 and opioid receptors in pudendal inhibition of bladder activity induced by intravesical infusion of saline or 0.25% acetic acid (AA) was investigated in anesthetized cats using methysergide (a 5-HT2 receptor antagonist) and naloxone (an opioid receptor antagonist). AA irritated the bladder and significantly (P<0.0001) reduced bladder capacity to 27.0±7.4% of saline control capacity. Pudendal nerve stimulation (PNS) at multiples of the threshold (T) intensity for inducing anal sphincter twitching restored bladder capacity to 60.1± 8.0% at 1-2T (P<0.0001) and 92.2±14.1% at 3-4T (P=0.001) of the saline control capacity. Methysergide (0.03-1 mg/kg, i.v.) suppressed low intensity (1-2T) PNS inhibition but not high intensity (3-4T) inhibition, and also significantly (P<0.05) increased control bladder capacity at the dosage of 0.3-1 mg/kg. During saline infusion without AA irritation, PNS significantly increased bladder capacity to 150.8±9.9% at 1-2T (P<0.01) and 180.4±16.6% at 3-4T (P<0.01) of the saline control capacity. Methysergide (0.1-1 mg/kg) significantly (P<0.05) increased saline control bladder capacity and suppressed PNS inhibition at the dosage of 0.03-1 mg/kg. After methysergide treatment (1 mg/kg), naloxone significantly (P<0.05) reduced control bladder capacity during AA infusion but had no effect during saline infusion. Naloxone also had no influence on PNS inhibition. These results suggest that 5-HT2 receptors play a role in PNS inhibition of reflex bladder activity and interact with opioid receptors in micturition reflex pathway. Understanding neurotransmitter mechanisms underlying pudendal neuromodulation is important for the development of new treatments for bladder disorders.