Role of spinal α1-adrenergic mechanisms in the control of lower urinary tract in the rat

The role of spinal α₁-adrenergic mechanisms in the control of urinary bladder function was examined in urethane (1.2 g/kg s.c.) anesthetized and decerebrate unanesthetized female Sprague–Dawley rats (250–320 g). Bladder activity was recorded via a transurethral catheter during continuous infusion (0.21 ml/min) cystometrograms or under isovolumetric conditions. All drugs were administered intrathecally at the L₆-S₁ segmental level of spinal cord. During cystometrograms, 3 or 30 nmol of phenylephrine (α₁-adrenergic agonist) did not alter bladder activity; whereas 300 nmol increased the intercontraction interval by 98% and pressure threshold for inducing micturition by 115%, but did not change bladder contraction amplitude. A large dose of phenylephrine (3000 nmol) completely blocked reflex voiding and induced overflow incontinence at a high baseline pressure (mean: 33 cmH₂O; range: 28–42 cmH₂O). Under isovolumetric conditions, 3–30 nmol of phenylephrine abolished bladder activity for 22–45 min; whereas smaller doses (0.003–0.3 nmol) were inactive. Doxazosin (50 nmol), an α₁-adrenergic antagonist, decreased intercontraction intervals but did not change bladder contraction amplitude during cystometrograms. Under isovolumetric conditions this dose of doxazosin increased bladder contraction frequency and decreased bladder contraction amplitude. Smaller doses (5 or 25 nmol) of doxazosin did not alter bladder activity. These studies suggest that two types of spinal α₁-adrenergic mechanisms are involved in reflex bladder activity: (1) inhibitory control of the frequency of voiding reflexes presumably by regulating afferent processing in the spinal cord and (2) facilitatory modulation of the descending limb of the micturition reflex pathway.     

Effect of capsaicin on micturition and associated reflexes in chronic spinal rats

The role of capsaicin-sensitive bladder afferents in micturition was studied in unanesthetized chronic spinal rats. Reflex voiding in response to tactile stimulation of the perigenital region appeared 5–9 days after spinal cord injury (SCI) whereas voiding induced by bladder distension occurred 2–3 weeks after SCI. The frequency and amplitude of reflex bladder contractions recorded under isovolumetric conditions were similar in chronic spinal and urethane-anesthetized CNS-intact rats. However, cystometrograms (CMGs) performed 6–8 weeks after SCI revealed that the chronic spinal rats had larger bladder capacities (1.86 ml) than CNS-intact rats (0.48 ml) and also exhibited multiple, small-amplitude, nonvoiding bladder contractions that were not detected in CNS-intact rats. Administration of capsaicin (50 mg/kg s.c.) acutely (onset 14–40 min) suppressed reflex bladder activity induced by bladder distension or by perigenital stimulation in chronic spinal animals. However, pretreatment of chronic spinal rats with capsaicin (125 mg/kg s.c.) 4 days before the experiment did not depress voiding reflexes or change bladder capacity but did eliminate the nonvoiding contractions. Inhibition of reflex bladder contractions by mechanical stimulation of rectoanal canal or the uterine cervix-vagina was not altered by pretreatment with capsaicin. These data indicate that capsaicin-sensitive bladder afferents are not essential for the initiation of reflex micturition in chronic spinal rats. However, these afferents do contribute to hyperactivity of the bladder during the filling phase of the CMG. Thus, capsaicin-sensitive bladder afferents should be evaluated as possible targets for the pharmacological treatment of bladder hyperreflexia in patients with SCI.     

Pharmacological modulation of the pontine micturition center.

Previous studies have indicated that an area of the rostral pontine tegmentum known as the 'pontine micturition center' (PMC) plays an essential role in the regulation of lower urinary tract function. The present pharmacologic experiments were conducted on either decerebrate unanesthetized or chloralose anesthetized cats to identify the location of the PMC and to examine the neurotransmitter mechanisms controlling micturition. Microinjections of excitatory and inhibitory amino acids were made at stereotaxic coordinates P1 to P3, L2 to L3, H0 to H-4 where electrical stimulation with trains of pulses (2-30 V, 80-120 Hz and 50-300 ms train duration) elicited short latency (less than 2 s) bladder contractions or voiding. Injections of L-glutamate (L-GLUT) (20-130 nmol) or DL-homocysteic acid (DLH) (20-100 nmol) into the region of the locus coeruleus or parabrachial nucleus elicited voiding as well as an increase in the frequency or amplitude of isovolumetric bladder contractions. In some anesthetized animals, L-GLUT and DLH also had mixed excitatory-inhibitory or pure inhibitory effects. Injections of muscimol (9-70 nmol) depressed rhythmic bladder activity, increased the bladder volume for inducing micturition or completely abolished the voiding induced by bladder filling. The inhibitory effects of muscimol were reversed by microinjections of bicuculline methiodide (BCMI) (3-22 nmol). Injections of BCMI (1-1.5 nmol) into untreated cats stimulated bladder activity and lowered the bladder volume for inducing micturition. It is concluded that: (1) neurons in the rostral pons are an essential component of the micturition reflex pathway, (2) several populations of neurons located in the region of the locus coeruleus complex and parabrachial nucleus contribute to the functions of the PMC, and (3) PMC neurons are under a tonic GABAergic inhibitory control which regulates the micturition threshold and in turn regulates bladder capacity.     

Inhibitory effect of intrathecal glycine on the micturition reflex in normal and spinal cord injury rats

We examined the influence of lumbosacral glycinergic neurons on the spinobulbospinal and spinal micturition reflexes. Female rats were divided into intact rats, rats with acute injury to the lower thoracic spinal cord (SCI), and rats with chronic SCI. Under urethane anesthesia, isovolumetric cystometry was performed in each group before and after intrathecal (IT) injection of glycine or strychnine into the lumbosacral cord level. The glutamate and glycine levels of the lumbosacral cord were measured after injection of glycine or strychnine in intact and chronic SCI rats. Expression of strychnine-sensitive glycine receptor alpha-1 (GlyR alpha1) mRNA in the lumbosacral cord was also assessed in both rats. In chronic SCI rats, the interval and amplitude of bladder contractions were shorter and smaller when compared with intact rats. IT glycine (0.1-100 microg) prolonged the interval and decreased the amplitude of bladder contractions in both intact rats and chronic SCI rats. IT strychnine (0.01-10 microg) elevated the baseline pressure in intact rats and induced bladder contraction in acute SCI rats. On amino acid analysis, IT glycine (0.01-100 microg) decreased the glutamate level of the lumbosacral cord in intact rats, but not in chronic SCI rats. The glycine level of the lumbosacral cord was 54% lower in chronic SCI rats when compared with intact rats, while the GlyR alpha1 mRNA level did not change after SCI. These results suggest that glycinergic neurons may have an important inhibitory effect on the spinobulbospinal and spinal micturition reflexes at the level of the lumbosacral cord.     

Suppression of the micturition reflex in urethane-anesthetized rats by intracerebroventricular injection of WAY100635, a 5-HT(1A) receptor antagonist

The influence of supraspinal 5-HT_1A receptors on reflex bladder activity was evaluated in anesthetized rats by studying the effects of intracerebroventricular (i.c.v.) administration of WAY100635 (1–100 μg), a selective 5-HT_1A receptor antagonist. The drug dose-dependently decreased the frequency and/or amplitude of isovolumetric reflex bladder contractions. Low doses (1–10 μg) increased the interval between contractions but only slightly reduced the amplitude of the contractions. However, 100 μg of WAY100635 elicited an initial complete block of bladder reflexes followed by a recovery period lasting 10–15 min during which the frequency of reflex contractions was normal but the amplitude was markedly suppressed by 70–80%. Mesulergine (0.1 mg/kg, i.v.), a 5-HT_2C antagonist, which transiently eliminated bladder activity in some rats (five of 11), blocked the inhibitory effect of WAY100635 (10 or 100 μg, i.c.v.) in only two of six rats. Our data coupled with the results of previous studies suggest that spinal and supraspinal 5-HT_1A receptors are involved in multiple inhibitory mechanisms controlling the spinobulbospinal micturition reflex pathway. The regulation of the frequency of bladder reflexes is presumably mediated by a suppression of afferent input to the micturition switching circuitry in the pons, whereas the regulation of bladder contraction amplitude may be related to an inhibition of the output from the pons to the parasympathetic nucleus in the spinal cord.     

The role of capsaicin-sensitive afferent fibers in the lower urinary tract dysfunction induced by chronic spinal cord injury in rats

The role of capsaicin-sensitive afferents in neurogenic voiding dysfunction was studied in chronic spinal cord injured rats (SCI). Cystometry and external urethral sphincter (EUS) electromyography were performed on 2 consecutive days after induction of urethane anesthesia in SCI rats 6-8 weeks after spinal cord injury. SCI rats exhibited voiding abnormalities including: non-voiding contractions (NVCs) before micturition, increased volume threshold (VT) for initiating voiding, increased amplitude and duration of voiding contractions, decreased voiding efficiency, increased residual urine, and changes in the pattern of the EUS-EMG. In SCI rats, the EUS electromyogram (EUS-EMG) consisted of more prominent tonic activity, shorter periods of bursting activity, and a reduction in the ratio of silent to active periods during bursting. These changes were more prominent during deeper levels of anesthesia on day 1. Capsaicin (125 mg/kg, s.c., 4 days before urodynamic examination) reduced VT and the number of NVCs, decreased the amplitude and duration of voiding contractions, partially normalized the pattern of EUS-EMG activity, and improved the voiding efficiency on day 1 after induction of anesthesia but not on day 2. Capsaicin treatment increased the percentage of animals (from 55% to 80%) that voided on day 1. The results indicate that capsaicin-sensitive C-fiber bladder afferents are not essential for reflex micturition in SCI rats. However, these afferents do contribute to overactivity of the bladder and detrusor sphincter dyssynergia in deeply anesthetized SCI rats.     

Plasticity in reflex pathways to the lower urinary tract following spinal cord injury

The lower urinary tract has two main functions, storage and periodic expulsion of urine, that are regulated by a complex neural control system in the brain and lumbosacral spinal cord. This neural system coordinates the activity of two functional units in the lower urinary tract: (1) a reservoir (the urinary bladder) and (2) an outlet (consisting of bladder neck, urethra and striated muscles of the external urethra sphincter). During urine storage the outlet is closed and the bladder is quiescent to maintain a low intravesical pressure. During micturition the outlet relaxes and the bladder contracts to promote efficient release of urine. This reciprocal relationship between bladder and outlet is generated by reflex circuits some of which are under voluntary control. Experimental studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through a coordination center (the pontine micturition center) located in the rostral brainstem. This reflex pathway is in turn modulated by higher centers in the cerebral cortex that are involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary control of voiding as well as the normal reflex pathways that coordinate bladder and sphincter function. Following spinal cord injury the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. However the bladder does not empty efficiently because coordination between the bladder and urethral outlet is lost. Studies in animals indicate that dysfunction of the lower urinary tract after spinal cord injury is dependent in part on plasticity of bladder afferent pathways as well as reorganization of synaptic connections in the spinal cord. Reflex plasticity is associated with changes in the properties of ion channels and electrical excitability of afferent neurons and appears to be mediated in part by neurotrophic factors released in the spinal cord and/or the peripheral target organs.     

Pudendal-to-bladder reflex in chronic spinal-cord-injured cats

The effects of pudendal nerve stimulation on reflex bladder activity were investigated in cats with chronic spinal cord injury (6-12 months) under alpha-chloralose anesthesia. Electrical stimulation of the pudendal nerve on one side at different frequencies and intensities induced either inhibitory or excitatory effects on bladder activity. The inhibitory effect peaked at a stimulation frequency of 3 Hz and gradually decreased at lower or higher frequencies. The inhibitory effect could occur at stimulation intensities between 0.3 and 1 V (pulse width 0.1 ms) and increased at intensities up to 10 V. Stimulation of the central end of transected pudendal nerve also inhibited bladder activity, indicating that afferent axons in pudendal nerve are involved. Nerve transections also showed that both hypogastric and pelvic nerves might be involved in the inhibitory pudendal-to-bladder spinal reflex. Pudendal nerve stimulation at 20 Hz and at the same intensities (1-10 V) elicited a bladder excitatory response. Although this excitatory effect could not sustain a long lasting bladder contraction at small bladder volumes, it did induce continuous rhythmic bladder contractions at large bladder volumes. This study indicated the possibility of developing a neuroprosthetic device based on pudendal nerve electrical stimulation to restore micturition function after spinal cord injury.     

Effects of MK-801 and CNQX, glutamate receptor antagonists, on bladder activity in neonatal rats

This study was undertaken to examine the role of N-methyl-d-aspartate (NMDA) and -amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamatergic receptors in the regulation of urinary bladder activity in the neonatal rat. Experiments were conducted using an in vitro spinal cord-bladder (SB) preparation from 1- to 5-day-old rats or awake neonatal rats 6 and 7 days old. SB preparations were isolated under hypothermic anesthesia. Isovolumetric bladder contractions occurred spontaneously, were induced by electrical stimulation (ES) of the bladder wall or were evoked reflexly by perineal tactile stimulation (PS). MK-801 (3–30 μM), an NMDA receptor antagonist, enhanced the amplitude of spontaneous, ES- and PS-evoked contractions. Removal of the spinal cord after MK-801 abolished PS-evoked reflex contractions but did not change the amplitude of spontaneous and ES-evoked contractions. Removal of the spinal cord in the absence of MK-801 increased the amplitude of spontaneous and ES-evoked contractions, indicating that the bladder is subject to a tonic inhibitory control originating in the spinal cord. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 3–30 μM), an AMPA receptor antagonist, decreased the amplitude of PS-evoked contractions and the frequency of spontaneous contractions in the SB preparation. Removal of the spinal cord after CNQX enhanced the amplitude of spontaneous and ES-evoked contractions but abolished PS-evoked contractions. The frequency of spontaneous contractions which decreased after CNQX increased to near control levels after removal of the spinal cord. In awake neonatal rats, intraperitoneal injection of MK-801 (3 mg/kg) induced spontaneous micturition. A large dose of CNQX (30 mg/kg) decreased PS-evoked micturition volume. These results suggest that NMDA glutamatergic receptors are involved in a lumbosacral spinal inhibitory mechanism controlling bladder activity; whereas AMPA glutamatergic receptors are involved in the perineal-to-bladder reflex pathway in neonatal rats.     

Restoration of micturition using microelectric current in experimentally induced spastic urinary bladder in rabbits

The 29 rabbits used in this study were divided into three groups, A (A1 and A2), B, and C. In subgroup A1, 4 animals were used in order to verify whether the contact of an electrode to the sacral nerves results in some abnormality of voiding reflex. In subgroups A1 and A2 (4 animals each) we further studied the micturition function using three parameters: (i) urinary bladder fluoroscopy and radiography, (ii) cystomanometry, and (iii) electromyography of the pelvic floor muscles (external sphinter). In group B (9 rabbits) spastic paraplegia and micturition disturbances resulted from spinal cord compression that was induced by inserting a balloon catheter into the T11-T12 intervertebral foramen. In this group the parameters studied revealed a spastic urinary bladder in all animals. Finally, the 12 animals of group C were rendered paraplegic as described in group B, and microelectrodes were placed over the sacral nerves as in subgroup A1. By applying a specific sequence of sacral nerve stimulation we succeeded in satisfactory urinary bladder emptying as confirmed by the micturition parameters studied: The urinary bladder pressure decreased from 65 +/- 3 to 28 +/- 3 mm Hg. The pelvic floor muscle amplitude was lowered from 130 +/- 7 to 20 +/- 3 microV, and finally the radiological bladder size also decreased from 38 cm2 before voiding to 18 +/- 3 cm2 after voiding. These results indicate that microelectric current stimulation of the sacral nerves, when applied under a specific sequence, could rather satisfactorily restore micturition disturbances, at least in this experimental animal.     

Principles of Sacral Nerve Stimulation (SNS) for the Treatment of Bladder and Urethral Sphincter Dysfunctions

Objectives. Sacral nerve stimulation (SNS) (Medtronic, Inc., Minneapolis, MN) is an exciting new treatment for refractory voiding disorders including urinary incontinence, retention, and voiding dysfunction. It is known that both voiding and continence reflex mechanisms are organized in the sacral spinal cord and that pathologic conditions can alter the balance between these two opposing mechanisms. Methods. The background and surgical technique of SNS will be presented. This will be followed by a discussion of hypotheses on how SNS works. Results. The beneficial effects of SNS are most reasonably attributed to activation of somatic afferent axons in the sacral spinal roots. This evoked afferent activity in turn modulates sensory processing and micturition reflex pathways in the spinal cord. Hyperactive voiding can be suppressed by direct inhibition of bladder preganglionic neurons as well as inhibition of interneuroneal transmission in the afferent limb of the micturition reflex. On the other hand, voiding in patients with urinary retention can be facilitated by inhibition of reflex pathways to the urethral outlet (guarding reflexes). Conclusions. SNS, a nonablative, minimally invasive technique for urologists, holds great promise for a large number of patients who suffer debilitating and refractory urinary symptoms.     

Somatovesical and vesicovesical excitatory reflexes in urethane-anaesthetized rats

The effect of spinal cord transection on excitatory somato- and vesicovesical micturition reflexes have been investigated in urethane-anaesthetized rats. In adult rats, 3 distinct types of excitatory reflexes to the bladder may be observed: a somatovesical reflex organized at spinal level and two vesicovesical reflexes organized at spinal and supraspinal level, respectively. In agreement with results of lesion experiments (Neurosci. Lett., 8 (1978) 27-33), bladder voiding is abolished following spinal cord transection although both somato- and vesicovesical reflexes may be demonstrated in acute spinal rats. Occurrence of the spinal vesicovesical reflex during the collecting phase of the cystometrogram appears to be inhibited by a supraspinal inhibitory pathway.     

Serotonergic modulation of spinal ascending activity and sacral reflex activity evoked by pelvic nerve stimulation in cats

Serotonin (5-HT) may be inhibitory to micturition at a spinal level. A potential mechanism of action for serotonergic inhibition of bladder function is a depression of the ascending limb of the supraspinal reflex mediating micturition. Ascending activity evoked by pelvic nerve stimulation was recorded in the thoracic spinal cord of anesthetized cats. For comparison, spinal reflex activity evoked by pelvic nerve stimulation was recorded on the pudendal nerve. The effects of intrathecal administration of serotonergic agents were examined to determine whether spinal and supraspinal responses to bladder afferent activation were modulated by 5-HT. Methysergide (60 nmol), a non-selective serotonergic antagonist, increased ascending activity by 61±7% and depressed spinal reflex activity by 38±6%. Zatosetron (10 nmol), a 5-HT₃ antagonist had a similar effect on both activities (increased by 93±24% and decreased by 77±7%, respectively). The effect on ascending activity of blocking 5-HT₃ receptors was also confirmed with ICS 205930 and MDL 72222. 2-Methyl-5-HT (800 nmol), a 5-HT₃ agonist, depressed ascending activity to 46±9% of control, but enhanced spinal reflex activity by 73±92%. These results demonstrate that stimulation of 5-HT₃ and methysergide-sensitive 5-HT receptors can inhibit ascending activity and facilitate spinal reflex activity elicited by activation of bladder afferents. It is suggested that descending serotonergic pathways may participate in the spinal coordination of urinary continence.     

Urine retention due to intra-spinal cord injection of colchicine in rats: improved recovery of bladder function by monosialoganglioside GM1 and nerve growth factor administration.

Intra-spinal cord injection of a low dose of colchicine (2 micrograms/rat) at the lumbar level affects the micturition reflex leading to voiding suppression, bladder hypertrophy and overflow incontinence which lasts about four weeks. The administration of nerve growth factor and monosialoganglioside GM1 normalizes urine output within 3 days and improves recovery of the bladder contraction tested by a cystometric analysis.     

Bladder emptying by intermittent electrical stimulation of the pudendal nerve

Persons with a suprasacral spinal cord injury cannot empty their bladder voluntarily. Bladder emptying can be restored by intermittent electrical stimulation of the sacral nerve roots (SR) to cause bladder contraction. However, this therapy requires sensory nerve transection to prevent dyssynergic contraction of the external urethral sphincter (EUS). Stimulation of the compound pudendal nerve trunk (PN) activates spinal micturition circuitry, leading to a reflex bladder contraction without a reflex EUS contraction. The present study determined if PN stimulation could produce bladder emptying without nerve transection in cats anesthetized with alpha-chloralose. With all nerves intact, intermittent PN stimulation emptied the bladder (64 +/- 14% of initial volume, n = 37 across six cats) more effectively than either distention-evoked micturition (40 +/- 19%, p < 0.001, n = 27 across six cats) or bilateral intermittent SR stimulation (25 +/- 23%, p < 0.005, n = 4 across two cats). After bilateral transection of the nerves innervating the urethral sphincter, intermittent SR stimulation voided 79 +/- 17% (n = 12 across three cats), comparable to clinical results obtained with SR stimulation. Voiding via intermittent PN stimulation did not increase after neurotomy (p > 0.10), indicating that PN stimulation was not limited by bladder-sphincter dyssynergia. Intermittent PN stimulation holds promise for restoring bladder emptying following spinal injury without requiring nerve transection.     

Bladder and urethral sphincter responses evoked by microstimulation of S2 sacral spinal cord in spinal cord intact and chronic spinal cord injured cats

Urinary bladder and urethral sphincter responses evoked by bladder distention, ventral root stimulation, or microstimulation of S2 segment of the sacral spinal cord were investigated under alpha-chloralose anesthesia in cats with an intact spinal cord and in chronic spinal cord injured (SCI) cats 6-8 weeks after spinal cord transection at T9-T10 spinal segment. Both SCI and normal cats exhibited large amplitude reflex bladder contractions when the bladder was fully distended. SCI cats also exhibited hyperreflexic bladder contractions during filling and detrusor-sphincter dyssynergia during voiding, neither was observed in normal cats. Electrical stimulation of the ventral roots revealed that the S2 sacral spinal cord was the most effective segment for evoking large amplitude bladder contractions or voiding in both types of cats. Microstimulation with a stimulus intensity of 100 microA and duration of 30-60 s via a single microelectrode in the S2 lateral ventral horn or ventral funiculus evoked large amplitude bladder contractions with small urethral contractions in both normal and SCI cats. However, this stimulation evoked incomplete voiding due to either co-activation of the urethral sphincter or detrusor-sphincter dyssynergia. Stimulation in the S2 dorsal horn evoked large amplitude sphincter responses. The effectiveness of spinal cord microstimulation with a single electrode to induce prominent bladder and urethral sphincter responses in SCI animals demonstrates the potential for using microstimulation techniques to modulate lower urinary tract function in patients with neurogenic voiding dysfunctions.     

Leuprolide acetate induces structural and functional recovery of injured spinal cord in rats

Gonadotropin-releasing hormone (GnRH) and its synthetic analog leuprolide acetate, a GnRH agonist, have neurotrophic properties. This study was designed to determine whether administration of leuprolide acetate can improve locomotor behavior, gait, micturition reflex, spinal cord morphology and the amount of microglia in the lesion epicenter after spinal cord injury in rats. Rats with spinal cord compression injury were administered leuprolide acetate or saline solution for 5 weeks. At the 5^th week, leuprolide acetate-treated rats showed locomotor activity recovery by 38%, had improvement in kinematic gait and exhibited voiding reflex recovery by 60%, as compared with the 1^st week. By contrast, saline solution-treated rats showed locomotor activity recovery only by 7%, but voiding reflex did not recover. More importantly, leuprolide acetate treatment reduced microglial immunological reaction and induced a trend towards greater area of white and gray matter in the spinal cord. Therefore, leuprolide acetate has great potential to repair spinal cord injury.     

Behavior and binding: correlations between alpha 1-adrenergic stimulation of acoustic startle and alpha 1-adrenoceptor occupancy and number in rat lumbar spinal cord

The relationship between alterations in alpha 1-adrenoceptors and behavioral effects of alpha 1-adrenergic agonists were investigated in a localized region of the rat central nervous system. Direct infusion of the alpha 1-adrenergic agonists, D-amphetamine or phenylephrine. into the subarachnoid space of the lumbar cord (intrathecal administration) increased the amplitude of the acoustic startle reflex, The magnitude of this behavioral facilitation correlated highly with the degree of alpha 1-adrenoceptor occupation measured by [3H]prazosin binding in lumbar spinal tissue. Using an in vitro estimate of receptor occupation, maximal potentiation of startle occurred following approximately 30% occupation of the receptors, using either D-amphetamine or phenylephrine. Intrathecal administration of 6-OHDA produced a 95% decrease in spinal norepinephrine and markedly enhanced the behavioral response to intrathecal phenylephrine as well as the number of alpha 1-adrenoceptors. The correlation between the time course of the behavioral and binding changes was 0.99. No change in receptor affinity (KD) or receptor occupation by phenylephrine was found after 6-OHDA. The data indicate that receptor binding parameters do have predictive value for behavior, especially if localized regions of the nervous system, critical to the behavior, are analyzed.     

Effect of bilateral hypogastric nerve transection on voiding dysfunction in rats with spinal cord injury

We determined if bilateral section of the hypogastric nerves (HGN), which provide the major sympathetic input to the urinary bladder neck/proximal urethra, could improve voiding by reducing urethral resistance in conscious, female spinal-cord-injured (SCI) rats 2-3 weeks after T(7-9) transection of the spinal cord. Cystometry was performed in animals with HGN intact and with HGN sectioned bilaterally 1-2 h before the experiment. Residual volume (RV), volume threshold for inducing micturition (VT), maximal voiding pressure, and bladder compliance were significantly lower (71, 35, 33, and 31%, respectively) in SCI rats with sectioned HGN than in rats with intact HGN, whereas voided volume (VV), pressure threshold for micturition, and bladder contraction duration (BCD) in the two groups were similar. Voiding efficiency (VE) in the HGN-sectioned group was 36% greater than that in the HGN-intact group. Antagonists for AMPA and NMDA glutamatergic receptors (LY215490 and MK-801, respectively) were administered to rats with sectioned HGN, to determine if activity in the HGN contributes to the previously reported inhibitory effects of these drugs, on voiding function after SCI. MK-801 (3 mg/kg iv) significantly reduced VV (75%) and VE (85%) and increased RV (8-fold), VT (87%), and bladder compliance (60%), whereas LY215490 (10 mg/kg iv) significantly increased VT and BCD by 15 and 19%, respectively. It is concluded that bilateral section of HGN reduces voiding dysfunction in the SCI rat but does not alter the effects of AMPA and/or NMDA glutamatergic receptor antagonists on the micturition reflex in the SCI rat. Thus the effects of these drugs are not dependent on changes in activity of sympathetic axons in the HGN.     

Effect of KW-7158, a putative afferent nerve inhibitor,on bladder and vesico-vascular reflexes in rats

The effects of KW-7158, a putative afferent nerve inhibitor, on reflex bladder activity and vesico-vascular reflexes were evaluated in urethane anesthetized SD rats with normal and xylene-irritated bladders. The bladder was filled with saline until the appearance of large amplitude spontaneous bladder contractions (LA-BC). Vesico-vascular reflexes were measured as increases in systolic arterial blood pressure during LA-BC or when the bladder was distended by a range of pressures. In normal rats, KW-7158 (10 and 100 microg/kg, i.v.) did not alter the amplitude or volume threshold for inducing LA-BC but increased the intercontraction interval. After xylene-irritation, which decreased volume threshold and intercontraction interval and induced small amplitude bladder contractions, KW-7158 increased volume threshold (65%) and intercontraction interval (150%) and decreased the number of small amplitude bladder contractions. Vesico-vascular reflexes induced during LA-BC or by bladder distension were suppressed (19.4-100%) by KW-7158. The effect of KW-7158 to depress vesico-vascular reflexes as well as xylene-induced bladder hyperactivity without altering the amplitude of contractions is consistent with the view that the drug affects reflex bladder activity at least in part by depressing afferent pathways.