Local Change in Urinary Bladder Contractility Following CNS Dopamine Denervation in the 6-OHDA Rat Model of Parkinson's Disease

Abstract

Background: Urinary problems, including urinary frequency, urgency, and nocturia are some of the non-motor symptoms that correlate most with poor quality of life in Parkinson's disease. However, the mechanism behind these symptoms is poorly understood, in particular regarding peripheral bladder pathophysiology following dopamine degeneration.

Objective: In this study, we compared the contractile responsiveness of urinary bladder from the 6-OHDA unilateral rat model of Parkinson's disease with that of normal untreated animals.

Methods: The contractility of the urinary detrusor muscle was evaluated in bladder strip preparations using electrical field stimulation, and muscarinic and purinoceptor stimulations in an vitro organ bath setup.

Results: Our data show that the overall contractile response following electrical field stimulation was significantly higher (43% at maximum contraction by 20-40 Hz stimulation) in the 6-OHDA-lesioned rats as compared to control animals. This increase was associated with a significant increase in the cholinergic contractile response, where the muscarinic agonist methacholine produced a 44% (at 10 -4 M concentration) higher response in the 6-OHDA-treated rats as compared to controls with a significant left-shift of the dose response. This indicates an altered sensitivity of the muscarinic receptor system following the specific central 6-OHDA-induced dopamine depletion. In addition a 36% larger contraction of strips from the 6-OHDA animals was also observed with purinoceptor activation using the agonist ATP (5×10 -3 M) during atropine treatment.

Conclusions: Our data shows that it is not only the central dopamine control of the micturition reflex that is altered in Parkinson's disease, but also the local contractile function of the urinary bladder. The current study draws attention to a mechanism of urinary dysfunction in Parkinson's disease that has previously not been described.

Keywords: Urinary bladder pathophysiology; detrusor muscle; muscarinic receptor; parasympathetic nervous system.

Fig.1

The effect of 6-OHDA lesion on striatal tyrosine hydroxylase (TH)-positive fibers, bladder weight and contractile response to high K ⁺ Krebs. Following unilateral 6-OHDA lesion TH-positive fibers in the striatum were >95% abolished as compared to the untreated side (A). The bladder strip weight in the 6-OHDA-lesioned animals showed a trend to be larger (10.0±0.8 mg, n = 17) as compared to normal (8.4±0.8 mg, n = 34), however this 20% increase was not significant (p = 0.20, unpaired t-test; B). Testing the viability of the strips by using high K ⁺ Krebs solution revealed a significantly (36% ) higher response in the 6-OHDA-lesioned animals as compared to the untreated controls; 22.1±1.8 mN (n = 34) vs. 16.2±1.5 mN (n = 17) respectively (unpaired t-test p = 0.022; C). Scale bar in Panel A represents 2 mm.  ^* = significantly different from control.

Fig.2

EFS-induced bladder responses in bladder strips in controls and 6-OHDA-lesioned rats. Following EFS the bladder strips from 6-OHDA-lesioned rats (n = 16) showed an overall significantly higher contractile response as compared to controls (n = 26; A, B). In the presence of atropine the EFS response was reduced in both groups by 31% and 33% for controls and 6-OHDA respectively (C). However a significant difference could still be observed at 40 Hz. Following administration of phentolamine (10 ^{− 5}M) together with suramin and atropine, no change in contraction in the control (n = 7) as compared to 6-OHDA (n = 7) was observed (p = 0.094; D). The grey thin line under the responses in panel C represent the duration of the electric stimulation.  ^* = significantly different from control group. [Two-way repeated ANOVAs; (A) interaction: F(5, 200) = 3.86, p = 0.00023, Group: F(1, 40) = 4.15, p = 0.048; (C) interaction: F(5, 200) = 2.86, p = 0.016, Group: F(1, 40) = 1.96, p = 0.17; (D) interaction: F(5, 60) = 1.98, p = 0.094, Group: F(1, 12) = 3.09, p = 0.10. All ANOVAS are followed by a Bonferroni multiple comparison test].

Fig.3

Methacholine-induced responses in bladder strips from controls and 6-OHDA-lesioned rats. Following cumulative administration of methacholine the bladder strips from the 6-OHDA-lesioned rats (n = 10) showed an overall significantly increased contractile response as compared to controls (n = 27; A). This response could specifically be observed at a concentration of 10 ^{− 4} M (A, C). The EC₅₀ showed also a significant left-shift in the 6-OHDA group as compared to controls (Insert, Panel A) Further, in the presence of atropine (10 ^{− 6} M) the methacholine response was almost completely blocked (B). Significance was nevertheless still observed at the highest dose administered (10 ^{− 3} M).  ^* = significantly different from control. [Two-way repeated ANOVAs; (A) interaction: F(5, 175) = 2.71, p = 0.022, Group: F(1, 35) = 5.24, p = 0.028; (B) interaction: F(5, 175) = 3.93, p = 0.0021, Group: F(1, 35) = 5.79, p = 0.022; All ANOVAS are followed by a Bonferroni multiple comparison test].

Fig.4

ATP-induced bladder responses in bladder strips from controls and 6-OHDA-lesioned rats. Cumulative administration of ATP showed a trend to yield an overall higher contraction in the 6-OHDA-lesioned rats (n = 10) as compared to controls (n = 27; A). This was evident in particular at the highest concentration (5×10 ^{− 3} M; A, C). A significant difference was observed following atropine administration, where a higher response was shown in the bladder strips from the 6-OHDA-lesioned animals (n = 10) as compared to control animals (n = 26; B).  ^* = significantly different from control group. [Two-way repeated ANOVAs; (A) interaction: F(6, 210) = 1.69, p = 0.12, (B) interaction: F(6, 204) = 1.85, p = 0.092, Group: F(1, 34) = 8.40, p = 0.0065; All ANOVAS are followed by a Bonferroni multiple comparison test].