Neural mechanisms underlying bladder hyperactivity and incontinence.
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Adult↗
Biomedical subjects
W C de Groat
Publications and source records attributed to W C de Groat.
Differences in Fluorogold and wheat germ agglutinin-horseradish peroxidase labelling of bladder afferent neurons.
Rat urinary bladder afferent neurons were significantly smaller (34%) when labelled with Fluorogold (FG) than when labelled with wheat germ agglutinin-horseradish peroxidase (WGA-HRP). This study showed that this difference was due to an artifact of tissue processing (ethanol dehydration) and was not due to uptake and transport of the two tracers by two different subpopulations of bladder afferents.
Afferent Pathways↗
The effect of rhizotomy on NADPH diaphorase staining in the lumbar spinal cord of the rat.
In the L6-S1 spinal segments of the rat NADPH diaphorase fiber-like staining extending along the lateral edge of the dorsal horn to the sacral parasympathetic nucleus was eliminated 1-3 weeks following dorsal-ventral L6-S1 rhizotomy. However, other NADPH diaphorase staining in the dorsal horn was not affected by rhizotomy. Rhizotomy also doubled the number (5 versus 10 cells/section) of NADPH diaphorase positive neurons in the region of the sacral parasympathetic nucleus (SPN). These data indicate that NADPH diaphorase is present in primary afferent projections to the SPN and that NADPH diaphorase activity in SPN neurons can be enhanced by neuronal injury. The functional significance of the NADPH diaphorase histochemical stain remains to be determined; however, if NADPH diaphorase is nitric oxide synthase then this would suggest that NO has an important role in the neural pathways to the pelvic viscera.
Amino Acid Oxidoreductases↗
Localization of NADPH-diaphorase in pelvic afferent and efferent pathways of the rat.
The NADPH diaphorase histochemical reaction was used in combination with retrograde axonal transport of Fluorogold (FG) from the major pelvic ganglion (MPG) to determine if NADPH diaphorase is contained within afferent and preganglionic efferent pathways to pelvic visceral organs. In L6 and S1 dorsal root ganglia, 68.5% and 62.2%, respectively, of FG-labeled afferent neurons were NADPH-diaphorase positive. In the sacral parasympathetic nucleus (SPN) of the L6 and S1 spinal cord segments, 49.4% and 51.7%, respectively of FG labeled preganglionic efferent neurons were NADPH-diaphorase positive. NADPH-diaphorase-positive neurons were also observed in laminae I and II of the dorsal horn, around the central canal and in the dorsal commissure. In addition, fiber-like NADPH diaphorase staining was present in superficial dorsal horn, Lissauer's tract and the lateral edge of the dorsal horn extending into the region of the SPN. If NADPH diaphorase activity in neurons does indicate a physiological function of nitric oxide, then nitric oxide may have a role as a neuromodulator or neurotransmitter within visceral afferent and preganglionic efferent pathways to the pelvic viscera in the rat.
Afferent Pathways↗
Spinal pathways mediate coordinated bladder/urethral sphincter activity during reflex micturition in decerebrate and spinalized neonatal rats.
Coordination between the urinary bladder and the external urethral sphincter is necessary for normal voiding. However, it is uncertain whether the spinal cord or brainstem generates this coordination. Bladder and urethral sphincter activity were examined during reflex voiding induced by perineal stimulation or bladder distension in decerebrate non-spinalized and spinalized 15 to 26-day-old neonatal rats. Perineal stimulation induced voiding and coordinated bladder/sphincter activity in both types of rats, indicating that spinal pathways can generate coordinated voiding behavior. The discoordination observed during voiding induced by bladder distension in spinalized pups may be due to the loss of descending pathways or to the emergence of detrimental spinal reflexes.
Action Potentials↗
Localization of NADPH diaphorase in bladder afferent and postganglionic efferent neurons of the rat.
NADPH diaphorase histochemistry was used in combination with axonal labelling techniques to determine if NADPH diaphorase is present in afferent and postganglionic efferent pathways to the urinary bladder of the rat. In the L6 and S1 dorsal root ganglia, 80.9 and 78.5%, respectively, of bladder afferent neurons labelled with fluorescent dyes were NADPH diaphorase positive. In the major pelvic ganglion (MPG), many non-labelled neurons and fibers were intensely stained for NADPH diaphorase. Intensely stained cells were clustered near the exit of the penile nerve although stained cells were also scattered throughout the ganglion. Only a small percentage (3.5%) of bladder postganglionic neurons in the MPG were NADPH diaphorase positive. Since NADPH diaphorase activity commonly reflects the presence of nitric oxide synthase, the present findings raise the possibility that nitric oxide may have a role as a neurotransmitter or neuromodulator in afferent pathways from the urinary bladder.
Amino Acid Oxidoreductases↗
Effects of LY274614, a competitive NMDA receptor antagonist, on the micturition reflex in the urethane-anaesthetized rat.
1. The effects of 3 competitive N-methyl-D-aspartate (NMDA) receptor antagonists, LY274614, LY233536 and LY235723, on the micturition reflex and external urethral sphincter EMG activity, were examined either under isovolumetric conditions or during continuous filling cystometry in urethane-anaesthetized (1.2 g kg-1, s.c.) rats. 2. Intravenous administration of LY274614 (3-30 mg kg-1) inhibited in a dose-dependent fashion both bladder and sphincter activity in the intact rats. In addition, the volume threshold for inducing micturition was increased and voided volume was decreased. 3. Intrathecal administration of LY274614 (0.06-30 micrograms) similarly inhibited bladder and sphincter activity during cystometry in intact rats. 4. In chronic spinal cord (T6-T8) transected rats LY274614 (0.1-30 mg kg-1, i.v.) did not alter bladder activity under isovolumetric conditions but decreased the amplitude of micturition contractions and sphincter EMG activity during cystometry at a dose of 10-30 mg kg-1. 5. The inhibitory effects of i.v. administration of LY274614, on bladder and sphincter activity induced by infusion of chemical irritant (0.1% acetic acid) or saline, were similar; except that a slightly larger dose was needed to inhibit sphincter activity during acetic acid infusion. 6. Peak amplitude of micturition contractions recovered to 50% of control 3 h following i.v. (30 mg kg-1) or i.t. (6 micrograms) administration of LY274614. 7. Two other chemically related NMDA antagonists, LY233536 and LY235723 produced similar but less potent effects than LY274614 when given i.v. 8. These data indicate that glutamatergic transmitter mechanisms at the level of the spinal cord are important in modulating bladder activity in the intact animal, but that these mechanisms do not contribute to bladder reflexes in the chronic spinal rat. These mechanisms may, however, contribute to sphincter activity in both intact or chronic spinal rats.
Acetates↗
Modulation of release of [3H]acetylcholine in the major pelvic ganglion of the rat.
Cholinergic modulation of [3H]acetylcholine release evoked by electrical stimulation was studied in the rat major pelvic ganglion, which was prelabeled with [3H]choline. Acetylcholine (ACh) release was independent of the frequency of stimulation; 0.3 Hz produced the same volley output as 10 Hz. Tetrodotoxin (1 microM) or omission of Ca2+ from the medium abolished ACh release. The M1 receptor agonist (4-hydroxy-2-butynyl)-1-trimethylammonium m-chlorocarbanilate chloride (McN-A 343, 50 microM) increased release (by 136%), whereas the M2 muscarinic agonist oxotremorine (1 microM) decreased ACh release (by 22%). The muscarinic antagonists, atropine (1 microM) or pirenzepine (M1 selective, 1 microM), did not change ACh release. However, pirenzepine (1 microM) blocked the facilitatory effect of McN-A 343, and atropine (1 microM) blocked the inhibitory effect of oxotremorine. The cholinesterase inhibitor physostigmine (1-5 microM), the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP, 10 microM), and the nicotinic antagonist D-tubocurarine (50 microM) did not change ACh release. 4-Aminopyridine, a K+ channel blocker, significantly increased the release (by 146%). Seven days after decentralization of the major pelvic ganglion, the evoked release of ACh was abolished. It is concluded that release of ACh occurs from the preganglionic nerve terminals rather than from the cholinergic cell bodies and is not modulated by actions of endogenous ACh on either muscarinic or nicotinic autoreceptors. These data confirm and extend previous electrophysiological findings indicating that synapses in the major pelvic ganglion have primarily a relay function.
Acetylcholine↗
Changes in bladder and external urethral sphincter function after spinal cord injury in the rat.
Spinal cord injury (SCI) in humans results in inappropriate contractions of the external urethral sphincter muscle (EUS) during micturition (bladder-sphincter dyssynergia), leading to urinary retention. The major goal of this study was to determine whether SCI in rats has similar detrimental effects on micturition. After chronic SCI, urethan-anesthetized rats had a significantly (15-fold) increased bladder capacity and impaired voiding (31-fold increase in residual volume) compared with control rats. Bladder contractions in SCI rats were accompanied by abnormal tonic EUS electromyographic activity, whereas the EUS electromyograms of control rats exhibited a burst pattern (4-8 Hz) during voiding. Suppression of EUS activity with neuromuscular blockade did not improve the fraction of urine voided in SCI rats and reduced the fraction voided in control rats. Therefore, both tonic activity and complete quiescence of the rat's EUS appear to be detrimental to voiding, suggesting that the normal bursting EUS activity facilitates bladder emptying. In summary, rats and humans exhibit similar micturition dysfunctions after SCI (e.g., bladder-sphincter dyssynergia and impaired voiding).
Animals↗
Effects of capsaicin on micturition and associated reflexes in rats.
The effect of capsaicin on micturition and associated reflexes was studied in urethan-anesthetized female rats. Capsaicin or vehicle solution were administered 4 days before the experiment in a dose of 125 mg/kg sc or during the experiment in a dose of 50-100 mg/kg sc. Activity of the urinary bladder was recorded by measuring intravesical pressure via a urethral catheter while slowly filling (0.052 ml/min) the bladder or when the bladder was distended beyond the micturition threshold and maintained at a constant volume. Pretreatment with capsaicin did not significantly change various parameters of urinary bladder function including micturition volume threshold or the amplitude, duration, and interval between reflex bladder contractions. However, capsaicin pretreatment significantly reduced (80% decrease) the arterial pressor responses accompanying reflex bladder contractions and reduced by approximately one-half the percentage of animals in which bladder activity was inhibited by stimulation of the uterine cervix. A large dose of capsaicin (50 mg/kg sc) elicited an acute block of bladder activity that persisted for 8-15 h. This effect is attributable to an action on myelinated afferent or efferent components of the micturition reflex pathway. It is concluded that capsaicin-sensitive afferents are not essential for the performance of micturition in the rat. However, these afferents are involved in cervicovesical reflex mechanisms that modulate bladder activity and in vascular reflexes triggered by isometric bladder contractions.
Animals↗
Induction of c-fos expression in spinal neurons by nociceptive and nonnociceptive stimulation of LUT.
Expression of c-fos gene in spinal neurons was detected with an immunocytochemical technique to study the spinal processing of nociceptive and nonnociceptive input from the lower urinary tract (LUT) of the urethan-anesthetized rat. Two preparations were used to activate afferent pathways in the LUT: 1) the urinary bladder was exposed through an abdominal incision, and saline or 1% acetic acid solution was infused directly into the bladder lumen and expelled through the urethra; and 2) the bladder was catheterized through the urethra, and the urethral outlet was ligated to allow distension and reflex contractions to occur under isovolumetric conditions. The first preparation mimicked the physiological changes occurring during normal voiding, whereas the second preparation generated high (presumably nociceptive) pressures when the bladder contracted against a closed outlet. The results indicate that distension-induced voiding increased c-fos expression largely in the region of the sacral parasympathetic nucleus (52% of the total number of cells/L6 section) and the dorsal commissure (25% of the total number of cells), whereas nociceptive stimuli markedly increased the number of c-fos-positive cells in the dorsal commissure (3.5 x increase above the number induced by distension, representing 50% of the total number of cells/L6 section). Bladder contractions against a closed outlet elicited a distribution of c-fos-positive cells similar to that induced by chemical irritation. Drugs that suppressed bladder reflexes did not reduce c-fos induced by distension, indicating that voiding reflexes do not contribute to c-fos expression.
Afferent Pathways↗
Anatomy and physiology of the lower urinary tract.
The lower urinary tract has two main functions: storage and periodic elimination of urine. These functions are regulated by a complex neural control system located in the brain and spinal cord. This control system performs like a simple switching circuit to maintain a reciprocal relation between the reservoir (bladder) and outlet (urethra and urethral sphincter) components of the urinary tract. Spinal cord injury disrupts voluntary control and the normal reflex pathways that coordinate bladder and sphincter function. Studies in animals indicate that recovery of bladder function after spinal injury is dependent on the reorganization of reflex pathways in both the peripheral and the central nervous system. Part of this reorganization may be influenced by neural-target organ interactions that are mediated by neurotrophic factors released by the peripheral organs.
Animals↗
Effects of MK-801 on the micturition reflex in the rat--possible sites of action.
The i.v. administration of MK-801 (dizocilpine), a noncompetitive N-methyl-D-aspartate receptor antagonist, depresses reflex bladder contractions in the rat, suggesting that glutamatergic transmission may have an important role in the micturition reflex pathway. The site of action of MK-801 was analyzed in the present experiments by studying the effects of the drug in the following urethane-anesthetized preparations: 1) intact rats, 2) decerebrate rats, 3) chronic spinal rats with transection at the T6-T8 segment and 4) intact rats in which the drug was administered via an intrathecal (i.t.) catheter at the L6-S1 spinal cord segments. Reflex bladder activity was monitored by measuring intravesical pressure under isovolumetric conditions and during a cystometrogram where the bladder outlet was open and voiding occurred. MK-801 (0.001-3 mg/kg i.v.) administered to the intact rats produced a dose-dependent suppression of the amplitude of reflex bladder contractions recorded during a cystometrogram. The ED50 and dose to produce maximal inhibition were 0.36 mg/kg and 3 mg/kg i.v., respectively. Doses of 0.3 to 1 mg/kg i.v. doubled the volume threshold for inducing micturition and decreased by 80% the voided volume in the intact rats. In decerebrate rats, reflex bladder contractions were also inhibited by MK-801 (ED50 = 0.055 mg/kg i.v.); however, in chronic spinal animals, even large doses of MK-801 (3-30 mg/kg i.v.) did not inhibit reflex bladder activity. MK-801 (6-78 micrograms) administered i.t. in the intact rats produced a dose-dependent suppression of the amplitude of reflex bladder contractions (ED50 = 13 micrograms). These results suggest that the inhibition of micturition reflex by MK-801 is mediated at least in part by an action on the lumbosacral spinal cord and is dependent on an intact pathway between the brain and spinal cord.
Animals↗
Intravesical capsaicin for neurogenic bladder dysfunction.
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Administration, Intravesical↗
The effect of glutamate antagonists on c-fos expression induced in spinal neurons by irritation of the lower urinary tract.
Chemical irritation of the lower urinary tract (LUT) of the rat increases the expression of c-fos in neurons in the dorsal horn, dorsal commissure and intermediolateral region of the spinal cord. The role of glutamatergic synapses in this response was examined using two glutamate receptor antagonists, MK-801 (an NMDA antagonist) and CNQX (an AMPA antagonist). In rats with an intact spinal cord, MK-801 (3.5 mg/kg, i.v.) administered 15 min before bladder irritation decreased (50-60%) the number of c-fos-positive cells in all regions of the cord. A smaller dose of MK-801 (0.8 mg/kg, i.v.) was ineffective. In spinal transected rats (4-7 days prior to the experiment) MK-801 (3.5 mg/kg, i.v.) decreased c-fos expression only in the medial dorsal horn. CNQX (1.2 mg/kg, i.v.) was ineffective in both preparations. These results indicate that activation of NMDA receptors at glutamate synapses in the central nervous system may play a role in the processing of nociceptive input from the LUT and may also be involved in reflex pathways mediating micturition.
6-Cyano-7-nitroquinoxaline-2,3-dione↗
Evidence for inhibitory nicotinic and facilitatory muscarinic receptors in cholinergic nerve terminals of the rat urinary bladder.
Cholinergic prejunctional modulatory receptors on parasympathetic nerves in the rat urinary bladder were studied by measuring 3H-acetylcholine (ACh) release in muscle strips from the bladder body. Electrical field stimulation markedly increased 3H-ACh overflow in strips preloaded with 3H-choline. Oxotremorine (1 microM), an M2 receptor agonist and DMPP (10 microM) a nicotinic (N) receptor agonist decreased the release of ACh (50% and 55% respectively); whereas McN-A 343 (50 microM) an M1 receptor agonist increased the release (33%), indicating the presence of three types of modulatory receptors. The anticholinesterase agent, physostigmine in concentrations of 1, 5 and 25 microM and neostigmine (5 microM) increased ACh release (44-710%). However a low concentration of physostigmine (0.05 microM) decreased release. Pirenzepine, an M1 muscarinic antagonist or atropine blocked the increased ACh release in physostigmine-treated strips, but in normal strips pirenzepine did not change release and atropine increased release. McN-A 343 or prolonged application (15 min) of DMPP increased ACh release (376% and 391% respectively) in physostigmine-treated strips. The response to McN-A 343 was blocked by pirenzepine. d-Tubocurarine (DTC), a nicotinic receptor blocker, enhanced ACh release in the presence of physostigmine but proved to be ineffective in normal preparations. These findings suggest that all three cholinergic receptors (M1 facilitatory, N inhibitory and M2 inhibitory) are activated by endogenous ACh in physostigmine treated preparations whereas only M2-inhibitory receptors are activated in normal preparations. It will be important in future studies to determine whether M1 and M2 mechanisms can also be activated under more physiological conditions in the bladder and whether they are present at other cholinergic synapses.
Acetylcholine↗
Modulation of the spinobulbospinal micturition reflex pathway in cats.
Micturition, which is mediated by a spinobulbospinal reflex pathway, can be modulated by various spinal and supraspinal mechanisms. This study examined modulation of the micturition reflex in decerebrate unanesthetized cats. Electrical stimulation of the pontine micturition center (PMC) elicited two types of bladder responses: small-amplitude short-duration responses due to direct activation of the bulbospinal pathway (PS-direct contractions) and large-amplitude long-duration reflex responses induced by PS-direct contractions but maintained by afferent feedback (PS-reflex contractions). Rectal and vaginal-cervical stimulation inhibited the PS-direct contractions, indicating inhibition of the descending or efferent limb of the micturition pathway. Stimulation of the central end of a transected S2 ventral root elicited recurrent inhibition of PS-reflex contractions but not of PS-direct contractions, indicating that recurrent inhibition does not directly affect the descending pathway. Continuous electrical stimulation (20 Hz) of the PMC decreased (53 +/- 21%) bladder capacity, presumably by affecting transmission in the pons or ascending input to the pons. Thus the micturition reflex could be modulated at several sites: the pons, the ascending or descending pathways, or spinal interneuronal sites.
Afferent Pathways↗
Increased c-fos expression in spinal neurons after irritation of the lower urinary tract in the rat.
This study utilized neuronal c-fos expression to examine the spinal pathways involved in processing nociceptive and non-nociceptive afferent input from the lower urinary tract (LUT) of the urethane-anesthetized rat. C-fos protein was detected immunocytochemically in only a small number of cells (< 2 cells/L6 section) in control animals. However, chemical irritation with 1% acetic acid or mechanical stimulation of the LUT markedly increased the number of c-fos-positive neurons (56-180 cells/L6 section) in four regions of the caudal lumbosacral (L6-S1) spinal cord: medial dorsal horn (MDH), lateral dorsal horn, dorsal commissure (DCM), and sacral parasympathetic nucleus (SPN). Only small numbers of c-fos-positive cells were detected in rostral lumbar segments, a region that is thought to receive nociceptive input from the LUT via afferent pathways in sympathetic nerves. The distribution of c-fos-positive cells in the L6 spinal cord varied according to the stimulus (i.e., urethral catheter, bladder distension, or chemical irritation). Distension of the urinary bladder increased the number of c-fos-positive cells mainly in DCM and SPN regions of the cord. In contrast, irritation of the LUT increased c-fos expression largely in DCM and MDH areas. Spinal cord transection (T8 level) did not alter the c-fos expression induced by a catheter or chemical irritation, indicating that gene expression was mediated by spinal pathways. Denervation experiments showed that c-fos expression was induced by activation of afferent pathways in the pelvic and pudendal nerves. These results suggest that neurons in several regions of the spinal cord are involved in processing afferent input from different parts of the LUT. Neurons in the DCM appear to have an important role since they respond to both nociceptive and non-nociceptive inputs and to visceral (pelvic nerve) and somatic (pudendal nerve) afferent pathways. Thus, these neurons may be involved in the mechanisms of visceral-somatic referred pain.
Afferent Pathways↗