Zhiying Xiao

Role of spinal GABAA receptors in pudendal inhibition of nociceptive and nonnociceptive bladder reflexes in cats.

Picrotoxin, an antagonist for γ-aminobutyric acid receptor subtype A (GABAA), was used to investigate the role of GABAA receptors in nociceptive and nonnociceptive 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 nonnociceptive 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 it) did not change AA bladder capacity but completely removed PNS inhibition of AA-induced bladder overactivity. Picrotoxin (iv) 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 it or 0.03-0.3 mg/kg iv) 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 nonnociceptive reflex bladder activities and in PNS inhibition of these activities.

Somatic modulation of spinal reflex bladder activity mediated by nociceptive bladder afferent nerve fibers in cats

The goal of the present 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 was used to irritate the bladder, activate nociceptive afferent C-fibers, and trigger spinal reflex bladder contractions (amplitude: 19.3 ± 2.9 cmH2O). Hexamethonium (a ganglionic blocker, intravenously) 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 reflex bladder contractions, whereas tibial nerve stimulation (TNS) failed to inhibit 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 nociceptive bladder afferent C-fibers using acetic acid irritation. Understanding the sites of action for PNS or TNS inhibition is important for the clinical application of pudendal or tibial neuromodulation to treat bladder dysfunctions.

Role of the brain stem in tibial inhibition of the micturition reflex in cats.

This study examined the role of the brain stem in inhibition of bladder reflexes induced by tibial nerve stimulation (TNS) in α-chloralose-anesthetized decerebrate cats. Repeated cystometrograms (CMGs) were performed by infusing saline or 0.25% acetic acid (AA) to elicit normal or overactive bladder reflexes, respectively. TNS (5 or 30 Hz) at three times the threshold (3T) intensity for inducing toe movement was applied for 30 min between CMGs to induce post-TNS inhibition or applied during the CMGs to induce acute TNS inhibition. Inhibition was evident as an increase in bladder capacity without a change in amplitude of bladder contractions. TNS applied for 30 min between saline CMGs elicited prolonged (>2 h) poststimulation inhibition that significantly (P < 0.05) increased bladder capacity to 30-60% above control; however, TNS did not produce this effect during AA irritation. TNS applied during CMGs at 5 Hz but not 30 Hz significantly (P < 0.01) increased bladder capacity to 127.3 ± 6.1% of saline control or 187.6 ± 5.0% of AA control. During AA irritation, naloxone (an opioid receptor antagonist) administered intravenously (1 mg/kg) or directly to the surface of the rostral brain stem (300-900 μg) eliminated acute TNS inhibition and significantly (P < 0.05) reduced bladder capacity to 62.8 ± 22.6% (intravenously) or 47.6 ± 25.5% (brain stem application). Results of this and previous studies indicate 1) forebrain circuitry rostral to the pons is not essential for TNS inhibition; and 2) opioid receptors in the brain stem have a critical role in TNS inhibition of overactive bladder reflexes but are not involved in inhibition of normal bladder reflexes.

Propranolol, but not naloxone, enhances spinal reflex bladder activity and reduces pudendal inhibition in cats

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 iv, 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 contractions but did not change the control bladder capacity. Naloxone (1 mg/kg iv, 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 iv, 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.

Role of µ, κ, and δ Opioid Receptors in Tibial Inhibition of Bladder Overactivity in Cats

In α-chloralose anesthetized cats, we examined the role of opioid receptor (OR) subtypes (µ, κ, and δ) in tibial nerve stimulation (TNS)-induced inhibition of bladder overactivity elicited by intravesical infusion of 0.25% acetic acid (AA). The sensitivity of TNS inhibition to cumulative i.v. doses of selective OR antagonists (cyprodime for µ, nor-binaltorphimine for κ, or naltrindole for δ ORs) was tested. Naloxone (1 mg/kg, i.v., an antagonist for µ, κ, and δ ORs) was administered at the end of each experiment. AA caused bladder overactivity and significantly (P < 0.01) reduced bladder capacity to 21.1% ± 2.6% of the saline control. TNS at 2 or 4 times threshold (T) intensity for inducing toe movement significantly (P < 0.01) restored bladder capacity to 52.9% ± 3.6% or 57.4% ± 4.6% of control, respectively. Cyprodime (0.3–1.0 mg/kg) completely removed TNS inhibition without changing AA control capacity. Nor-binaltorphimine (3–10 mg/kg) also completely reversed TNS inhibition and significantly (P < 0.05) increased AA control capacity. Naltrindole (1–10 mg/kg) reduced (P < 0.05) TNS inhibition but significantly (P < 0.05) increased AA control capacity. Naloxone (1 mg/kg) had no effect in cyprodime pretreated cats, but it reversed the nor-binaltorphimine–induced increase in bladder capacity and eliminated the TNS inhibition remaining in naltrindole pretreated cats. These results indicate a major role of µ and κ ORs in TNS inhibition, whereas δ ORs play a minor role. Meanwhile, κ and δ ORs also have an excitatory role in irritation-induced bladder overactivity.

Effects of Duloxetine and WAY100635 on Pudendal Inhibition of Bladder Overactivity in Cats

This study was 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 two and four 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 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide; 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 autoreceptors on the serotonergic neurons in the raphe nucleus may suppress duloxetine and PNS inhibition, suggesting that the coadministration 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.

Role of glycine in nociceptive and non-nociceptive bladder reflexes and pudendal afferent inhibition of these reflexes in cats.

This study examined the role of glycinergic transmission in nociceptive and non‐nociceptive bladder reflexes and in inhibition of these reflexes by pudendal nerve stimulation (PNS).

Role of spinal metabotropic glutamate receptor 5 in pudendal inhibition of the nociceptive bladder reflex in cats

This study examined the role of spinal metabotropic glutamate receptor 5 (mGluR5) in the nociceptive C-fiber afferent-mediated spinal bladder reflex and in the inhibtion of this reflex by pudendal nerve stimulation (PNS). In α-chloralose-anesthetized cats after spinal cord transection at the T9/T10 level, intravesical infusion of 0.25% acetic acid irritated the bladder, activated nociceptive C-fiber afferents, and induced spinal reflex bladder contractions of low amplitude (<50 cmH2O) and short duration (<20 s) at a smaller bladder capacity ∼80% of saline control capacity. PNS significantly (P < 0.01) increased bladder capacity from 85.5 ± 10.1 to 137.3 ± 14.1 or 148.2 ± 11.2% at 2T or 4T stimulation, respectively, where T is the threshold intensity for PNS to induce anal twitch. MTEP {3-[(2-methyl-4-thiazolyl)ethynyl]pyridine; 3 mg/kg iv, a selective mGluR5 antagonist} completely removed the PNS inhibition and significantly (P < 0.05) increased bladder capacity from 71.8 ± 9.9 to 94.0 ± 13.9% of saline control, but it did not change the bladder contraction amplitude. After propranolol (3 mg/kg iv, a β1/β2-adrenergic receptor antagonist) treatment, PNS inhibition remained but MTEP significantly (P < 0.05) reduced the bladder contraction amplitude from 18.6 ± 2.1 to 6.6 ± 1.2 cmH2O and eliminated PNS inhibition. At the end of experiments, hexamethonium (10 mg/kg iv, a ganglionic blocker) significantly (P < 0.05) reduced the bladder contraction amplitude from 20.9 ± 3.2 to 8.1 ± 1.5 cmH2O on average demonstrating that spinal reflexes were responsible for a major component of the contractions. This study shows that spinal mGluR5 plays an important role in the nociceptive C-fiber afferent-mediated spinal bladder reflex and in pudendal inhibition of this spinal reflex.

MP12-07 THE ROLE OF GLYCINE IN PUDENDAL NERVE STIMULATION AND BLADDER OVERACTIVITY

INTRODUCTION AND OBJECTIVES: Recent fMRI studies revealed supraspinal networks in response to bladder filling involved in perception and processing of bladder distension. However significance of supraspinal network activity and network localizations varied largely due to the different filling protocols. Therefore, our aim was to standardize filling paradigms using a MR-synchronized pump system for accurate timing and filling volume. METHODS: 31 right-handed healthy subjects, 16 women and 15 men, mean age 34 years (range 19e54) with no history of urinary urgency and/or urinary incontinence were included, were prospectively investigated using a 3 Tesla Phillips scanner. After catheterization, bladder was pre-filled until a persistent desire to void was perceived by each subject. The scan paradigm comprised automated, repetitive bladder filling of 100 mL body warm saline over 15sec by using a MRcompatible pump system, i.e. block design study. Neuroimaging data was analyzed with SPM8. Blood-oxygenation-level dependent signal analysis during bladder filling was compared to rest, i.e. pre-filled bladder. Second-level random effects group analysis was corrected for gender, age and total intracranial volume and was performed to account for between-subject variability, i.e. within-group results at P1⁄40.05 familywise error rate (FWE). RESULTS: 3 subjects, 2 women and 1 man, were excluded from further analysis due to excessive head motions. Within-group results from the remaining 28 subjects revealed activation in the following brain regions: bilateral insula, left inferior parietal lobe (BA40) and right frontal inferior operculum (BA44). CONCLUSIONS: Automated, repetitive bladder filling of body warm saline elicited robust brain activity on a high significance level in specific areas known to be involved in supraspinal lower urinary tract control.