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The dopamine D1 receptor agonist SKF 38393 suppresses detrusor hyperreflexia in the monkey with parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)
NeuropharmacologyVol. 32, No. 4, pp. 315-321, 1993 Printed in Great Britain.All rights reserved
0028-3908/93 $6.00+ 0.00 Copyright © 1993 PergamonPress Ltd
THE DOPAMINE Di RECEPTOR AGONIST SKF 38393 SUPPRESSES D E T R U S O R HYPERREFLEXIA IN THE MONKEY WITH PARKINSONISM I N D U C E D BY 1-METHYL-4-PHENYL- 1,2,3,6-TETRAHYDROPYRIDINE (MPTP) N. YOSHIMURA,1 E. MIZUTA,2 S. KUNO,2. M. SASA3 and O. YOSHIDAl ~Department of Urology, Faculty of Medicine, Kyoto University, Kyoto 606, Japan, 2Department of Neurology, Center for Neurological Diseases, Utano National Hospital, Ukyo-ku, Kyoto 616, Japan and 3Department of Pharmacology, Faculty of Medicine, Hiroshima University, Hiroshima 734, Japan
(Accepted 13 January 1993) Sununary--A pharmacological study using monkeys, in which parkinsonism was induced by l-methyl-4phenyl-l,2,3,6-tetrahydropyridine (MPTP), was undertaken to elucidate the mechanism underlying urinary bladder dysfunctions in Parkinson's disease. Under ketamine anesthesia, cystometrograms showed that, in MPTP-treated monkeys, a contraction of the urinary bladder was induced with smaller bladder volume than that in normal monkeys. In MPTP-treated monkeys, subcutaneously injected SKF 38393, a dopamine D~ receptor agonist, significantly increased the bladder volume and pressure thresholds for inducing the micturition reflex without affecting those in normal monkeys. In contrast, subcutaneous injections of quinpirole, a dopamine D2 receptor agonist, and apomorphine, a dopamine D t and D2 receptor agonist, slightly, but significantly reduced the volume threshold of the bladder for the micturition reflex in both normal and MPTP-treated groups. These results indicate that, in parkinsonism, the degeneration of dopaminergic neurons in the substantia nigra leads to the detrusor hyperreflexia, probably due to a failure of activation of dopamine D~ receptors.
Key words--parkinsonism, MPTP, monkeys, detrusor hyperreflexia, dopamine D~ receptor.
Idiopathic parkinsonism is known to be a disorder primarily caused by degeneration of dopaminergic neurons originating in the substantia nigra (Bernheimer, Birkmayer and Hornyckiewicz, 1973). It has been clinically documented that patients with Parkinson's disease often exhibit lower urinary tract dysfunctions such as urinary urgency or incontinence, and that the most commonly observed urodynamic manifestation is detrusor hyperreflexia (Pavlakis, Siroky, Goldstein and Krane, 1983; Berger, Blaivas, DeLaRocha and Salinas, 1987). The underlying mechanism for inducing detrusor hyperactivity in parkinsonism remains unclear, although it has been reported that the basal ganglia including substantia nigra has an inhibitory effect on the micturition reflex in the cat (Lewin, Dillard and Porter, 1967; Yoshimura, Sasa, Yoshida and Takaori, 1992). It has been well documented that repeated intravenous injections of a neurotoxin, 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP), induce irreversible degeneration of dopamine-containing cells in the substantia nigra in the primate, thereby producing typical and stable parkinsonian symptoms (Burns, Chiueh, Markey, Ebert, Jacobitz and Kopin, 1983). In addition, the urinary bladder function was *To whom correspondence should be addressed.
found to be hyperreflexic after MPTP treatment in marmosets (Albanese, Jenner, Marsden and Stephenson, 1988). Therefore, the present study was undertaken to elucidate the underlying mechanism for dysfunctions of the urinary bladder in parkinsonism using MPTP-induced parkinsonian monkeys.
METHODS
Eight adult male cynomolgus monkeys (Macaca fascicularis) weighing 4.2-5.8 kg were used. Four animals were treated with three consecutive injections of MPTP hydrochloride (0.3 mg/kg, i.v.; Aldrich) at an interval of 3 or 4 days, followed by several injections of the same dose of MPTP at 7 days intervals, with the cumulative dose of MPTP ranging between 26 and 34mg. These 4 monkeys were confirmed to develop persistent parkinsonian symptoms such as mild to severe degree of postural tremor and poverty of movements, which continued more than 20 months after the last MPTP injection. Further details of MPTP treatment were described previously (Kuno, Mizuta, Nishida and Takechi, 1992). Four other monkeys, which received no injections of MPTP, were used as normal controls. Under ketamine anesthesia (initial dose of 10mg/kg, i.m., and supplemental doses of each 5 mg/kg, i.m., when 315
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316
Table 1. Parameters of cystometrogramsin normal and MPTP-treatedmonkeys Volume Pressure Maximumintravesical Animal number threshold(ml) threshold(cm H20) pressure(cm H20) Normal monkey No. I 85 7 41 No. 2 141 7 36 No. 3 94 5 36 No. 4 68 6 51 Mean + SEM 97.0 + 15.6 6.3 + 0.5 41.0 ± 3.5 MPTP-treated monkey No. 1 22 9 No. 2 55 7 No. 3 34 8 No. 4 36 6 Mean + SEM 36.8 + 6.8* 7.5 + 0.6 *P < 0.05; compared with normal monkeys(unpaired t-test). required), a cystometrogram was obtained with a 6 Fr. dual lumen catheter inserted into the bladder transurethrally. The changes of the intravesical pressure induced by continuous infusion of physiological saline into the urinary bladder at a rate of 6 ml/min were recorded using a pressure transducer (Nihon Kohden, TP-200T) connected to an amplifier (Nihon Kohden, AP-600G) on a pen recorder (Rikadenki Kogyo, R-031). In order to compare changes among cystometrograms, three parameters including volume and pressure thresholds of the bladder for inducing reflex bladder contractions, and the maximum intravesical pressure during bladder contractions were measured on each cystometrogram. Cystometrograms examining the effect of dopaminergic drugs were carried out 20, 50 a n d 90 min after each drug injection, and were also obtained 120 and 150min after the drug application when the effect of the drug had continued in the last cystometrogram. Drugs used were as follows; apomorphine (Sigma), a nonspecific dopamine receptor agonist, SKF 38393 (Research Biochemicals Inc.), a dopamine Dl receptor agonist, and quinpirole (Eli-Lilly), a dopamine D 2 receptor agonist. Each dose of all these drugs was subcutaneously injected after dissolved with physiological saline. Statistical significance (P <0.05) was determined using Student's t-test for paired or unpaired values. RESULTS
Control Prior to the drug application, three consecutive cystometrograms in each animal were obtained at an interval of 15 min, and found to be fairly consistent. Table 1 shows the three parameters including volume and pressure thresholds, and maximum intravesical pressure for the bladder contraction in the first cystometrogram of each animal. In normal monkeys,
38 29 32 36 33.8 + 2.0
a contraction of the urinary bladder with a maximum intravesical pressure of 41.0+3.5 cmH20 (mean _ SEM, n = 4) was induced with the volume and pressure thresholds of 9 7 . 0 _ 1 5 . 6 m l and 6.3 4- 0.5 cm H20, respectively [Fig. I(A) and Table 1]. In contrast, in MPTP-treated monkeys, a bladder contraction was elicited with a significantly (P < 0.05) smaller volume threshold of 36.8 + 6.8 ml (n = 4) than that in normal monkeys, although the pressure threshold and maximum intravesical pressure did not differ between two groups [Fig. I(B) and Table 1].
SKF 38393 In normal animals, subcutaneous injections of SKF 38393 at doses of 5 and 10 mg/kg did not alter the three parameters in cystometrogram [Figs I(A), 2 and 3]. However, in MPTP-treated monkeys, subcutaneously injected SKF 38393 significantly increased the volume and pressure thresholds for the micturition reflex without affecting the maximum intravesical pressure during bladder contractions [Fig. I(B)]. The percent volume threshold was elevated to 153.4-t- 14.3 (P <0.05)and 170.2 4- 12.0% (P <0.01) of the predrug value 20 min after the injection of SKF 38393 at doses of 5 and 10 mg/kg, respectively (Fig. 2). In MPTP-treated monkeys, SKF 38393 at doses of 5 and 10 mg/kg also significantly (P <0.05) increased respectively the pressure threshold to 132.6 _ 7.9 and 199.6 4- 17.6% of the value before the drug application (Fig. 3). The inhibitory effect of SKF 38393 on the micturition reflex in the MPTPtreated group was observed 20 min after the injection, and maintained for 50 and 90 min at doses of 5 and 10 mg/kg, respectively.
Quinpirole and apomorphine In contrast with an inhibitory effect of SKF 38393 on the micturition reflex in MPTP-treated animals,
Fig. 1. (A) Cystometrograms in a normal monkey. 1: Control; 2, 3 and 4:20 min after subcutaneous injections of SKF 38393 (I0 mg/kg), quinpirole (1 mg/kg) and apomorphine (0.5 mg/kg), respectively. (B) Cystometrograms in a MPTP-treated monkey. 1: Control; 2-6:20 min after subcutaneous injections of dopamine receptor agonists; 2: SKF 38393 (5mg/kg); 3: SKF 38393 (10mg/kg); 4: quinpirole (0.2 mg/kg); 5: quinpirole (1 mg/kg); 6: apomorphine (0.5 mg/kg). The threshold volume for inducing the bladder contraction was indicated by an arrow in each trace.
Detrusor hypcrreflcxia in parkinsonism
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subcutaneous injections of quinpirole and apomorphine produced facilitatory effects on the micturition reflex in both normal and MPTP-treated groups (Fig. 1). In normal monkeys, subcutaneously injected quinpirole at a dose of l mg/kg significantly (P <0.05) reduced the volume threshold for the micturition reflex to 82.7 ___2.7% of the value obtained before the drug application (Fig. 2). When apomorphine at a dose of 0.5 mg/kg was subcutaneously injected, the volume threshold again decreased to 80.9 + 3.9% (P <0.05) of the predrug value (Fig. 2). In MPTP-treated monkeys, the relative volume threshold was significantly (P<0.05) reduced to 77.0 + 6.9 and 75.7 + 6.5% of the predrug value by subcutaneous injections of quinpirole (1 mg/kg) and apomorphine (0.5 mg/kg), respectively (Fig. 2). The quinpirole- and apomorphine-induced reductions of the volume threshold for the micturition reflex occurred 20 min after the drug application, and lasted for 90min in both normal and MPTP-treated monkeys. Neither quinpirole nor apomorphine had any effect on the pressure threshold and maximum intravesical pressure in the two groups of animals (Fig. 3). DISCUSSION In the present study, the micturition reflex was evoked with much smaller bladder volume in MPTP-
treated monkeys than in untreated animals, indicating hyperreflexia of the detrusor function in MPTP-induced parkinsonism. These findings are similar to those observed in marmosets by Albanese et al. (1988). Idiopathic parkinsonism is known to be caused by the degeneration of dopamine-containing cells of pars compacta of the substantia nigra (Bernheimer et al., 1973). A neurotoxin, MPTP, has been demonstrated to selectively destroy dopaminergic cell bodies in the melanin-containing substantia nigra of primates, resulting in the development of the typical parkinsonian symptoms, which are identical to those seen in humans with parkinsonism (Burns et al., 1983; D'Amato, Lipman and Snyder, 1986). Clinical urodynamic studies have also shown that the detrusor hyperreflexia is most commonly observed in patients with Parkinson's disease (Pavlakis et al., 1983; Berger et al., 1987). Therefore, it is likely that a loss of dopaminergic neurons in the substantia nigra is related to the detrusor hyperreflexia in parkinsonism. In addition, the postmortem study in patients with Parkinson's disease revealed the degeneration of noradrenergic and serotonergic, but not dopaminergic, pathways in the lumber spinal cord (Scatton, Dennis, L'Heureux, Monfort, Duyckaerts and Javoy-Agid, 1986). Since the spinal noradrenergic and serotonergic systems reportedly play important roles in modulation of the detrusor function (de Groat, Booth and Yoshimura, 1992), the changes in such spinal
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Fig. 2. Effects of dopamine receptor agonists on the volume threshold for inducing reflex bladder contractions in normal (n = 4) and MPTP-treated (n = 4) monkeys. The responses are expressed as percent (mean 4- SEM) of control volume threshold prior to the drug application. Statistical significances using paired t-test are determined by comparisons between respective controls (100%) in normal and MPTP-treated groups, and the values after drug application in each group. *P < 0.05, **P < 0.01.
Detrusor hyperreflexia in parkinsonism
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Fig. 3. Effects of dopamine receptor agonists on the pressure threshold for inducing reflex bladder contractions in normal (n = 4) and MPTP-treated (n = 4) monkeys. The responses are expressed as percent (mean +_SEM) of control pressure threshold prior to the drug application. Statistical significances using paired t-test are determined by comparisons between respective controls (100%) in normal and MPTP-treated groups, and the values after drug application in each group. *P < 0.05. neuronal pathways might also be involved in the detrusor dysfunction observed in parkinsonism. The major finding in this study was that the reduction in the bladder volume threshold for the micturition reflex in MPTP-induced parkinsonian monkeys is antagonized by subcutaneously injected S K F 38393, a dopamine D~ receptor agonist, in a dose-dependent manner. These results suggest that the detrusor hyperreftexia in parkinsonism results from a failure of activation of dopamine D~ receptors due to the degeneration of dopaminergic neurons in the substantia nigra. However, S K F 38393 had no effects on the cystometrogram in normal monkeys. The marked effect of SKF 38393 in MPTP-treated animals might be explained by receptor supersensitivity following the denervation of dopaminergic neurons. In the rat with unilateral legions by 6-hydroxydopamine of the nigrostriatal pathway, SKF 38393 has been shown to induce contralateral rotational behavior due to supersensitive striatal dopamine D I receptors on the lesion side (Arnt and Hyttel, 1984). Rinne, Rinne, Laakso, L6nnberg and Rinne (1985) also found that dopamine D l receptor binding sites increased in the striatum, especially in the putamen, of patients with Parkinson's disease, although dopamine D~ receptors were reportedly less susceptible than D2 receptors to changes after dopaminergic denervation (Graham, Clarke, Boyce, Sambrook, Crossman and Woodruff, 1990). These
observations are consistent with our assumption that SKF 38393 increases the bladder volume threshold for the micturition reflex in MPTP-treated monkeys because of supersensitive dopamine DI receptors. Since all drugs tested were administered systemically, it is uncertain whether the effect of drugs on the micturition reflex was mediated centrally or peripherally. However, since S K F 38393 was effective on the micturition reflex only in MPTP-induced parkinsonian monkeys, the site of action of SKF 38393 appears in the central nervous system rather than in the periphery. This is also justified by the previous findings that an intracerebroventricular administration of SKF 38393 has inhibitory effects on reflex bladder contractions in the cat (Yoshimura et al., 1992). It is well documented that normal mictt,-!tion is mediated by the spino-bulbo-spinal reflex pathway passing through the pontine micturition center located in the dorsolaterai pontine tegmentum, including a region of the locus coeruleus (Yoshimura, Sasa, Yoshida and Takaori, 1990; Kruse, Mallory, Noto, Roppolo and de Groat, 1991). Lewin et al. (1967) reported that electrical stimulation of the basal ganglia including the substantia nigra inhibited the micturition reflex in cats. Thus, the dopaminergic system originating in the substantia nigra may be involved in the regulation of the spino--buibo-spinal micturition reflex. However, there is no histological evidence that dopaminergic neurons in the substantia
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N. YOSHIMURAet al.
nigra send their fibers to the dorsolateral pontine tegmentum or the spinal cord (Fallon and Loughlin, 1985). The dopaminergic efferents to the locus coeruleus area and the spinal cord were found to originate mainly from the ventral tegmental area (DeGueurce and Milon, 1983) and the diencephalic A l l area (Bj6rkund and Skagerberg, 1979), respectively. Therefore, it is possible that the dopaminergic system originating in the substantia nigra indirectly exerts its effect on the micturition reflex through dopamine Dj receptors, although the precise site of action is not clear at present. In contrast with the inhibitory effect of SKF 38393, quinpirole, a dopamine D 2 receptor agonist, and apomorphine, a dopamine D 1 and D 2 receptor agonist, reduced the bladder volume threshold for the micturition reflex by 15-30% in both normal and MPTPtreated groups. In normal rats, apomorphine and bromocriptine, a dopamine D 2 receptor agonist, induce detrusor hyperactivity (Kontani, Inoue and Sakai, 1990). These and our results suggest that the detrusor function can be enhanced by stimulation of dopamine D 2 receptors. Dopamine and apomorphine injected into the cat pontine micturition center reduced the bladder volume for the micturition reflex by 1 0 ~ 0 % as measured in the cystometrogram and increased the frequency of rhythmic bladder contractions (Roppolo, Noto, Mallory and de Groat, 1987). Therefore, it is likely that dopaminergic drugs act directly on the micturition reflex pathway through dopamine D 2 receptors in the pontine micturition center to induce their excitatory effects. The present study thus indicates that the D~ and D 2 dopaminergic receptors mediate opposite effects on the micturition reflex. In the behavioral study on MPTP-treated monkeys, parkinsonian symptoms such as akinesia and tremor were reversed by the administration of L-DOPA or dopamine D2 receptor agonists but not by SKF 38393 (Nomoto, Jenner and Marsden, 1985; Falardeau, Bouchard, B6dard, Boucher and Di Paolo, 1988). However, dopamine D~ receptor agonists might be effective for treatment of the detrusor hyperreflexia in patients with Parkinson's disease, since the detrusor hyperreflexia in MPTPtreated monkeys was suppressed by an administration of SKF 38393. Conversely, treatment of parkinsonian patients with dopamine D 2 receptor agonists might aggravate the symptoms such as urinary urgency or incontinence resulted from the detrusor hyperreflexia. In conclusion, the present study shows that hyperreflexia in the detrusor function commonly observed in patients with Parkinson's disease can be reproduced in MPTP-induced parkinsonism in monkeys. This appears to be due to a failure of activation of dopamine D~ receptors following the degeneration of dopaminergic neurons originating in the substantia nigra. Acknowledgements--Authors wish to than Professor W. C.
de Groat and Professor M. Kuno for reading and correcting
the manuscript. This work was supported in part by a Grant-in-Aid for Scientific Research from Ministry of Education, Science and Culture, Japan (No. 03771039). REFERENCES
Albanese A., Jenner P., Marsden C. D. and Stephenson J. D. (1988) Bladder hyperreflexia induced in marmosets by l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine. Neurosci. Lett. 87: 46-50. Arnt J. and Hyttel J. (1984) Differential inhibition by dopamine D-I and D-2 antagonists of circling behaviour induced by dopamine agonists in rats with unilateral 6-hydroxydopamine lesions. Eur. J. Pharmac. 102: 349 -354. Berger Y., Blaivas J. G., DeLaRocha E. R. and Salinas J. M. (1987) Urodynamic findings in Parkinson's disease. J. Urol. 138: 836-838. Bernheimer H., Birkmayer W. and HornyckiewiczO, (1973) Brain dopamine and the syndromes of Parkinson and Huntington. Clinical, morphological correlations. 3. Neurol. Sci. 20: 415-455. Bj6rkund A. and Skagerberg G. (1979) Evidencefor a major spinal cord projection from the diencephalic All dopamine cell group in the rat using transmitter-specificfluorescent retrograde tracing. Brain Res. 177: 170-175. Burns R. S., Chiueh C. C., Markey S. P., Ebert M. H., Jacobitz D. M. and Kopin I. J. (1983) A primate model of parkinsonism: Selective destruction of dopaminergic neurons in the pars compacta of the substantia nigra by N-methyl-4-phenyl-l,2,3,6-tetrahydropyridine. Proc. Natn. Acad. Sci. 80: 4546-4550. D'Amato R. J., Lipman Z. P. and Snyder S. H. (1986) Selectivity of the parkinsonian neurotoxin MPTP: Toxic metabolite MPP ÷ binds to neuromelanin. Science 231: 987-989. DeGueurce A. M. and Milon H. (1983) Serotonin and dopamine afferents to the rat locus coeruleus: a biochemical study after lesioning of the ventral mesencephalic tegmental-A10 region and the raph~ dorsalis. Brain Res. 263: 344-347. Falardeau P., Bouchard S., B6dard P. J., Boucher R. and Di Paolo T. (1988) Behavioral and biochemical effect of chronic treatment with D-I and/or D-2 dopamine agonists in MPTP monkeys. Eur. J. Pharmac. 150: 59~6. Fallon J. H. and Loughlin S. E. (1985) Substantia nigra. In: The Rat Nervous System (Paxinos G., Ed.), Vol. 1, pp. 353 374. Academic Press, Australia. Graham W. C., Clarke C. E., Boyce S., Sambrook M. A., Crossman A. R. and Woodruff G. N. (1990) Autoradiographic studies in animal models of hemi-parkinsonism reveal D2 but not D, receptor supersensitivity. II. Unilateral intra-carotid infusion of MPTP in the monkey (Macaca fascicularis). Brain Res. 514: 103-110. de Groat W. C., Booth A. M. and Yoshimura N. (1992) Neurophysiology of micturition and its modification in animal models of human disease. In: The Autonomic Nervous System (Maggi C. A., Ed.), Vol. 2, pp. 227-290. Harwood Academic, London. Kontani H., Inoue T. and Sakai T. (1990) Dopamine receptor subtypes that induce hyperactive bladder response in anesthetized rats. Jap. J. Pharmac. 54: 482-486. Kruse M. N., Mallory B. S., Noto H., Roppolo J. R. and de Groat W. C. (1991) Properties of the descending limb of the spinobulbospinal micturition reflex pathway in the cat. Brain Res. 556: 6-12. Kuno S., Mizuta E., Nishida J. and Takechi M. (1992) Therapeutic effects of arotinolol, a fl-adrenergic blocker, on tremor in MPTP-induced parkinsonian monkeys. Clin. Neuropharmac. 15: 381-386. Lewin R. J., Dillard G. V. and Porter R. W. (1967) Extrapyramidal inhibition of the urinary bladder. Brain Res. 4: 301-307.
Detrusor hyperreflexia in parkinsonism Nomoto M., Jenner P. and Marsden C. D. 0985) The dopamine D 2 agonist LY 141865, but not the D t agonist SKF 38393, reverses parkinsonism induced by l-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP) in the common marmoset. Neurosci. Lett. 57: 37-41. Pavlakis A. J., Siroky M. G., Goldstein 1. and Krane R. J. (1983) Neurourologic findings in Parkinson's disease. J. Urol. 129: 80-83. Rinne J. O., Rinne J. K., Laakso K., L6nnberg P. and Rinne U. K. (1985) Dopamine D-l receptors in the parkinsonian brain. Brain Res. 359: 306-310. Roppolo J. R., Noto H., Mallory B. and de Groat W. C. (1987) Dopaminergic and cholinergic modulation of bladder reflex at the level of the pontine
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micturition center in the cat. Abstr. Soc. Neurosci. 13: 733. Scatton B., Dennis T., L'Heureux R., Monfort J.-C., Duyckaerts C. and Javoy-Agid F. (1986) Degeneration of noradrenergic and serotonergic but not dopaminergic neurons in the lumber spinal cord of parkinsonian patients. Brain Res. 380: 181-185. Yoshimura N., Sasa M., Yoshida O. and Takaori S. (1990) Mediation of micturition reflex by central norepinephrine from the locus coeruleus in the cat. J. Urol. 143: 840-843. Yoshimura N., Sasa M., Yoshida O. and Takaori S. (1992) Dopamine D-I receptor-mediated inhibition of micturition reflex by central dopamine from the substantia nigra. Neurourol. Urodyn. l l : 535-545.
0028-3908/93 $6.00+ 0.00 Copyright © 1993 PergamonPress Ltd
THE DOPAMINE Di RECEPTOR AGONIST SKF 38393 SUPPRESSES D E T R U S O R HYPERREFLEXIA IN THE MONKEY WITH PARKINSONISM I N D U C E D BY 1-METHYL-4-PHENYL- 1,2,3,6-TETRAHYDROPYRIDINE (MPTP) N. YOSHIMURA,1 E. MIZUTA,2 S. KUNO,2. M. SASA3 and O. YOSHIDAl ~Department of Urology, Faculty of Medicine, Kyoto University, Kyoto 606, Japan, 2Department of Neurology, Center for Neurological Diseases, Utano National Hospital, Ukyo-ku, Kyoto 616, Japan and 3Department of Pharmacology, Faculty of Medicine, Hiroshima University, Hiroshima 734, Japan
(Accepted 13 January 1993) Sununary--A pharmacological study using monkeys, in which parkinsonism was induced by l-methyl-4phenyl-l,2,3,6-tetrahydropyridine (MPTP), was undertaken to elucidate the mechanism underlying urinary bladder dysfunctions in Parkinson's disease. Under ketamine anesthesia, cystometrograms showed that, in MPTP-treated monkeys, a contraction of the urinary bladder was induced with smaller bladder volume than that in normal monkeys. In MPTP-treated monkeys, subcutaneously injected SKF 38393, a dopamine D~ receptor agonist, significantly increased the bladder volume and pressure thresholds for inducing the micturition reflex without affecting those in normal monkeys. In contrast, subcutaneous injections of quinpirole, a dopamine D2 receptor agonist, and apomorphine, a dopamine D t and D2 receptor agonist, slightly, but significantly reduced the volume threshold of the bladder for the micturition reflex in both normal and MPTP-treated groups. These results indicate that, in parkinsonism, the degeneration of dopaminergic neurons in the substantia nigra leads to the detrusor hyperreflexia, probably due to a failure of activation of dopamine D~ receptors.
Key words--parkinsonism, MPTP, monkeys, detrusor hyperreflexia, dopamine D~ receptor.
Idiopathic parkinsonism is known to be a disorder primarily caused by degeneration of dopaminergic neurons originating in the substantia nigra (Bernheimer, Birkmayer and Hornyckiewicz, 1973). It has been clinically documented that patients with Parkinson's disease often exhibit lower urinary tract dysfunctions such as urinary urgency or incontinence, and that the most commonly observed urodynamic manifestation is detrusor hyperreflexia (Pavlakis, Siroky, Goldstein and Krane, 1983; Berger, Blaivas, DeLaRocha and Salinas, 1987). The underlying mechanism for inducing detrusor hyperactivity in parkinsonism remains unclear, although it has been reported that the basal ganglia including substantia nigra has an inhibitory effect on the micturition reflex in the cat (Lewin, Dillard and Porter, 1967; Yoshimura, Sasa, Yoshida and Takaori, 1992). It has been well documented that repeated intravenous injections of a neurotoxin, 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP), induce irreversible degeneration of dopamine-containing cells in the substantia nigra in the primate, thereby producing typical and stable parkinsonian symptoms (Burns, Chiueh, Markey, Ebert, Jacobitz and Kopin, 1983). In addition, the urinary bladder function was *To whom correspondence should be addressed.
found to be hyperreflexic after MPTP treatment in marmosets (Albanese, Jenner, Marsden and Stephenson, 1988). Therefore, the present study was undertaken to elucidate the underlying mechanism for dysfunctions of the urinary bladder in parkinsonism using MPTP-induced parkinsonian monkeys.
METHODS
Eight adult male cynomolgus monkeys (Macaca fascicularis) weighing 4.2-5.8 kg were used. Four animals were treated with three consecutive injections of MPTP hydrochloride (0.3 mg/kg, i.v.; Aldrich) at an interval of 3 or 4 days, followed by several injections of the same dose of MPTP at 7 days intervals, with the cumulative dose of MPTP ranging between 26 and 34mg. These 4 monkeys were confirmed to develop persistent parkinsonian symptoms such as mild to severe degree of postural tremor and poverty of movements, which continued more than 20 months after the last MPTP injection. Further details of MPTP treatment were described previously (Kuno, Mizuta, Nishida and Takechi, 1992). Four other monkeys, which received no injections of MPTP, were used as normal controls. Under ketamine anesthesia (initial dose of 10mg/kg, i.m., and supplemental doses of each 5 mg/kg, i.m., when 315
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Table 1. Parameters of cystometrogramsin normal and MPTP-treatedmonkeys Volume Pressure Maximumintravesical Animal number threshold(ml) threshold(cm H20) pressure(cm H20) Normal monkey No. I 85 7 41 No. 2 141 7 36 No. 3 94 5 36 No. 4 68 6 51 Mean + SEM 97.0 + 15.6 6.3 + 0.5 41.0 ± 3.5 MPTP-treated monkey No. 1 22 9 No. 2 55 7 No. 3 34 8 No. 4 36 6 Mean + SEM 36.8 + 6.8* 7.5 + 0.6 *P < 0.05; compared with normal monkeys(unpaired t-test). required), a cystometrogram was obtained with a 6 Fr. dual lumen catheter inserted into the bladder transurethrally. The changes of the intravesical pressure induced by continuous infusion of physiological saline into the urinary bladder at a rate of 6 ml/min were recorded using a pressure transducer (Nihon Kohden, TP-200T) connected to an amplifier (Nihon Kohden, AP-600G) on a pen recorder (Rikadenki Kogyo, R-031). In order to compare changes among cystometrograms, three parameters including volume and pressure thresholds of the bladder for inducing reflex bladder contractions, and the maximum intravesical pressure during bladder contractions were measured on each cystometrogram. Cystometrograms examining the effect of dopaminergic drugs were carried out 20, 50 a n d 90 min after each drug injection, and were also obtained 120 and 150min after the drug application when the effect of the drug had continued in the last cystometrogram. Drugs used were as follows; apomorphine (Sigma), a nonspecific dopamine receptor agonist, SKF 38393 (Research Biochemicals Inc.), a dopamine Dl receptor agonist, and quinpirole (Eli-Lilly), a dopamine D 2 receptor agonist. Each dose of all these drugs was subcutaneously injected after dissolved with physiological saline. Statistical significance (P <0.05) was determined using Student's t-test for paired or unpaired values. RESULTS
Control Prior to the drug application, three consecutive cystometrograms in each animal were obtained at an interval of 15 min, and found to be fairly consistent. Table 1 shows the three parameters including volume and pressure thresholds, and maximum intravesical pressure for the bladder contraction in the first cystometrogram of each animal. In normal monkeys,
38 29 32 36 33.8 + 2.0
a contraction of the urinary bladder with a maximum intravesical pressure of 41.0+3.5 cmH20 (mean _ SEM, n = 4) was induced with the volume and pressure thresholds of 9 7 . 0 _ 1 5 . 6 m l and 6.3 4- 0.5 cm H20, respectively [Fig. I(A) and Table 1]. In contrast, in MPTP-treated monkeys, a bladder contraction was elicited with a significantly (P < 0.05) smaller volume threshold of 36.8 + 6.8 ml (n = 4) than that in normal monkeys, although the pressure threshold and maximum intravesical pressure did not differ between two groups [Fig. I(B) and Table 1].
SKF 38393 In normal animals, subcutaneous injections of SKF 38393 at doses of 5 and 10 mg/kg did not alter the three parameters in cystometrogram [Figs I(A), 2 and 3]. However, in MPTP-treated monkeys, subcutaneously injected SKF 38393 significantly increased the volume and pressure thresholds for the micturition reflex without affecting the maximum intravesical pressure during bladder contractions [Fig. I(B)]. The percent volume threshold was elevated to 153.4-t- 14.3 (P <0.05)and 170.2 4- 12.0% (P <0.01) of the predrug value 20 min after the injection of SKF 38393 at doses of 5 and 10 mg/kg, respectively (Fig. 2). In MPTP-treated monkeys, SKF 38393 at doses of 5 and 10 mg/kg also significantly (P <0.05) increased respectively the pressure threshold to 132.6 _ 7.9 and 199.6 4- 17.6% of the value before the drug application (Fig. 3). The inhibitory effect of SKF 38393 on the micturition reflex in the MPTPtreated group was observed 20 min after the injection, and maintained for 50 and 90 min at doses of 5 and 10 mg/kg, respectively.
Quinpirole and apomorphine In contrast with an inhibitory effect of SKF 38393 on the micturition reflex in MPTP-treated animals,
Fig. 1. (A) Cystometrograms in a normal monkey. 1: Control; 2, 3 and 4:20 min after subcutaneous injections of SKF 38393 (I0 mg/kg), quinpirole (1 mg/kg) and apomorphine (0.5 mg/kg), respectively. (B) Cystometrograms in a MPTP-treated monkey. 1: Control; 2-6:20 min after subcutaneous injections of dopamine receptor agonists; 2: SKF 38393 (5mg/kg); 3: SKF 38393 (10mg/kg); 4: quinpirole (0.2 mg/kg); 5: quinpirole (1 mg/kg); 6: apomorphine (0.5 mg/kg). The threshold volume for inducing the bladder contraction was indicated by an arrow in each trace.
Detrusor hypcrreflcxia in parkinsonism
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subcutaneous injections of quinpirole and apomorphine produced facilitatory effects on the micturition reflex in both normal and MPTP-treated groups (Fig. 1). In normal monkeys, subcutaneously injected quinpirole at a dose of l mg/kg significantly (P <0.05) reduced the volume threshold for the micturition reflex to 82.7 ___2.7% of the value obtained before the drug application (Fig. 2). When apomorphine at a dose of 0.5 mg/kg was subcutaneously injected, the volume threshold again decreased to 80.9 + 3.9% (P <0.05) of the predrug value (Fig. 2). In MPTP-treated monkeys, the relative volume threshold was significantly (P<0.05) reduced to 77.0 + 6.9 and 75.7 + 6.5% of the predrug value by subcutaneous injections of quinpirole (1 mg/kg) and apomorphine (0.5 mg/kg), respectively (Fig. 2). The quinpirole- and apomorphine-induced reductions of the volume threshold for the micturition reflex occurred 20 min after the drug application, and lasted for 90min in both normal and MPTP-treated monkeys. Neither quinpirole nor apomorphine had any effect on the pressure threshold and maximum intravesical pressure in the two groups of animals (Fig. 3). DISCUSSION In the present study, the micturition reflex was evoked with much smaller bladder volume in MPTP-
treated monkeys than in untreated animals, indicating hyperreflexia of the detrusor function in MPTP-induced parkinsonism. These findings are similar to those observed in marmosets by Albanese et al. (1988). Idiopathic parkinsonism is known to be caused by the degeneration of dopamine-containing cells of pars compacta of the substantia nigra (Bernheimer et al., 1973). A neurotoxin, MPTP, has been demonstrated to selectively destroy dopaminergic cell bodies in the melanin-containing substantia nigra of primates, resulting in the development of the typical parkinsonian symptoms, which are identical to those seen in humans with parkinsonism (Burns et al., 1983; D'Amato, Lipman and Snyder, 1986). Clinical urodynamic studies have also shown that the detrusor hyperreflexia is most commonly observed in patients with Parkinson's disease (Pavlakis et al., 1983; Berger et al., 1987). Therefore, it is likely that a loss of dopaminergic neurons in the substantia nigra is related to the detrusor hyperreflexia in parkinsonism. In addition, the postmortem study in patients with Parkinson's disease revealed the degeneration of noradrenergic and serotonergic, but not dopaminergic, pathways in the lumber spinal cord (Scatton, Dennis, L'Heureux, Monfort, Duyckaerts and Javoy-Agid, 1986). Since the spinal noradrenergic and serotonergic systems reportedly play important roles in modulation of the detrusor function (de Groat, Booth and Yoshimura, 1992), the changes in such spinal
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Fig. 2. Effects of dopamine receptor agonists on the volume threshold for inducing reflex bladder contractions in normal (n = 4) and MPTP-treated (n = 4) monkeys. The responses are expressed as percent (mean 4- SEM) of control volume threshold prior to the drug application. Statistical significances using paired t-test are determined by comparisons between respective controls (100%) in normal and MPTP-treated groups, and the values after drug application in each group. *P < 0.05, **P < 0.01.
Detrusor hyperreflexia in parkinsonism
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Fig. 3. Effects of dopamine receptor agonists on the pressure threshold for inducing reflex bladder contractions in normal (n = 4) and MPTP-treated (n = 4) monkeys. The responses are expressed as percent (mean +_SEM) of control pressure threshold prior to the drug application. Statistical significances using paired t-test are determined by comparisons between respective controls (100%) in normal and MPTP-treated groups, and the values after drug application in each group. *P < 0.05. neuronal pathways might also be involved in the detrusor dysfunction observed in parkinsonism. The major finding in this study was that the reduction in the bladder volume threshold for the micturition reflex in MPTP-induced parkinsonian monkeys is antagonized by subcutaneously injected S K F 38393, a dopamine D~ receptor agonist, in a dose-dependent manner. These results suggest that the detrusor hyperreftexia in parkinsonism results from a failure of activation of dopamine D~ receptors due to the degeneration of dopaminergic neurons in the substantia nigra. However, S K F 38393 had no effects on the cystometrogram in normal monkeys. The marked effect of SKF 38393 in MPTP-treated animals might be explained by receptor supersensitivity following the denervation of dopaminergic neurons. In the rat with unilateral legions by 6-hydroxydopamine of the nigrostriatal pathway, SKF 38393 has been shown to induce contralateral rotational behavior due to supersensitive striatal dopamine D I receptors on the lesion side (Arnt and Hyttel, 1984). Rinne, Rinne, Laakso, L6nnberg and Rinne (1985) also found that dopamine D l receptor binding sites increased in the striatum, especially in the putamen, of patients with Parkinson's disease, although dopamine D~ receptors were reportedly less susceptible than D2 receptors to changes after dopaminergic denervation (Graham, Clarke, Boyce, Sambrook, Crossman and Woodruff, 1990). These
observations are consistent with our assumption that SKF 38393 increases the bladder volume threshold for the micturition reflex in MPTP-treated monkeys because of supersensitive dopamine DI receptors. Since all drugs tested were administered systemically, it is uncertain whether the effect of drugs on the micturition reflex was mediated centrally or peripherally. However, since S K F 38393 was effective on the micturition reflex only in MPTP-induced parkinsonian monkeys, the site of action of SKF 38393 appears in the central nervous system rather than in the periphery. This is also justified by the previous findings that an intracerebroventricular administration of SKF 38393 has inhibitory effects on reflex bladder contractions in the cat (Yoshimura et al., 1992). It is well documented that normal mictt,-!tion is mediated by the spino-bulbo-spinal reflex pathway passing through the pontine micturition center located in the dorsolaterai pontine tegmentum, including a region of the locus coeruleus (Yoshimura, Sasa, Yoshida and Takaori, 1990; Kruse, Mallory, Noto, Roppolo and de Groat, 1991). Lewin et al. (1967) reported that electrical stimulation of the basal ganglia including the substantia nigra inhibited the micturition reflex in cats. Thus, the dopaminergic system originating in the substantia nigra may be involved in the regulation of the spino--buibo-spinal micturition reflex. However, there is no histological evidence that dopaminergic neurons in the substantia
320
N. YOSHIMURAet al.
nigra send their fibers to the dorsolateral pontine tegmentum or the spinal cord (Fallon and Loughlin, 1985). The dopaminergic efferents to the locus coeruleus area and the spinal cord were found to originate mainly from the ventral tegmental area (DeGueurce and Milon, 1983) and the diencephalic A l l area (Bj6rkund and Skagerberg, 1979), respectively. Therefore, it is possible that the dopaminergic system originating in the substantia nigra indirectly exerts its effect on the micturition reflex through dopamine Dj receptors, although the precise site of action is not clear at present. In contrast with the inhibitory effect of SKF 38393, quinpirole, a dopamine D 2 receptor agonist, and apomorphine, a dopamine D 1 and D 2 receptor agonist, reduced the bladder volume threshold for the micturition reflex by 15-30% in both normal and MPTPtreated groups. In normal rats, apomorphine and bromocriptine, a dopamine D 2 receptor agonist, induce detrusor hyperactivity (Kontani, Inoue and Sakai, 1990). These and our results suggest that the detrusor function can be enhanced by stimulation of dopamine D 2 receptors. Dopamine and apomorphine injected into the cat pontine micturition center reduced the bladder volume for the micturition reflex by 1 0 ~ 0 % as measured in the cystometrogram and increased the frequency of rhythmic bladder contractions (Roppolo, Noto, Mallory and de Groat, 1987). Therefore, it is likely that dopaminergic drugs act directly on the micturition reflex pathway through dopamine D 2 receptors in the pontine micturition center to induce their excitatory effects. The present study thus indicates that the D~ and D 2 dopaminergic receptors mediate opposite effects on the micturition reflex. In the behavioral study on MPTP-treated monkeys, parkinsonian symptoms such as akinesia and tremor were reversed by the administration of L-DOPA or dopamine D2 receptor agonists but not by SKF 38393 (Nomoto, Jenner and Marsden, 1985; Falardeau, Bouchard, B6dard, Boucher and Di Paolo, 1988). However, dopamine D~ receptor agonists might be effective for treatment of the detrusor hyperreflexia in patients with Parkinson's disease, since the detrusor hyperreflexia in MPTPtreated monkeys was suppressed by an administration of SKF 38393. Conversely, treatment of parkinsonian patients with dopamine D 2 receptor agonists might aggravate the symptoms such as urinary urgency or incontinence resulted from the detrusor hyperreflexia. In conclusion, the present study shows that hyperreflexia in the detrusor function commonly observed in patients with Parkinson's disease can be reproduced in MPTP-induced parkinsonism in monkeys. This appears to be due to a failure of activation of dopamine D~ receptors following the degeneration of dopaminergic neurons originating in the substantia nigra. Acknowledgements--Authors wish to than Professor W. C.
de Groat and Professor M. Kuno for reading and correcting
the manuscript. This work was supported in part by a Grant-in-Aid for Scientific Research from Ministry of Education, Science and Culture, Japan (No. 03771039). REFERENCES
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