Neurourology and Urodynamics 28:549–554 (2009)

Effects of Electrical Stimulation of the Striatum onBladder Activity in Cats

Tatsuya Yamamoto,1* Ryuji Sakakibara,2 Ken Nakazawa,3

Tomoyuki Uchiyama,1 Eiji Shimizu,3 and Takamichi Hattori1

1Department of Neurology, Chiba University, Chiba, Japan2Neurology Division, Department of Internal Medicine, Sakura Medical Center, Toho University, Sakura, Japan

3Department of Integrative Neurophysiology, Chiba University, Chiba, Japan

Aims: Parkinson’s disease (PD) affects the nigrostriatal projections leading to micturition disturbance in mostcases. Overactive bladder (OAB) symptoms such as urinary urgency or urgent urinary incontinence are commonamongst PD patients. Several urodynamic studies have revealed that detrusor overactivity causes OAB symptomsin PD patients. We assert that striatal dysfunction might contribute to the pathogenesis of detrusor overactivity inPD patients. However, the role of the striatum in bladder contraction remains unclear. Methods: We generatedspontaneous isovolumetric bladder contractions in 12 ketamine-anesthetized adult male cats and subsequentlyperformed electrical stimulation and extracellular single-unit recording in the striatum. Results: Electricalstimulation applied to the posterior ventral caudate nucleus and the adjacent putamen educed inhibition of thespontaneous bladder contraction. None of the responses were facilitatory. Electrical stimulation was most effectiveat an amplitude of 70–400 mA. Forty-six neurons that exhibited correlation to spontaneous bladder contraction wererecorded in the striatum. Thirty-five neurons were found to be tonically active throughout the bladder relaxationphase, and the remaining 11 neurons were active during the bladder contraction phase. These particular neuronswere located within the area in which spontaneous bladder contraction was inhibited by electrical stimulation.Conclusions: Electrical stimulation was found to inhibit bladder contraction, and a correlation was observedbetween spontaneous bladder relaxation/contraction and neuronal firing in the posterior ventral striatum.Neurourol. Urodynam. 28:549–554, 2009. � 2009 Wiley-Liss, Inc.

Key words: basal ganglia; dopamine; micturition; Parkinson’s disease; striatum

INTRODUCTION

Autonomic dysfunction is prevalent amongst patientswith Parkinson’s disease (PD),1 and results in cardiovascular,gastrointestinal, urogenital, sudomotor, and thermoregula-tory symptoms. Many PD patients suffer from urinary urgencyalong with detrusor overactivity, a common urodynamicfinding.2–4 Because PD is caused by the degeneration of thenigrostriatal dopaminergic projections,5–7 the dysfunction ofthe nigrostriatal dopaminergic projections might be related tothe pathogenesis of detrusor overactivity. We have previouslyreported that PD patients with urinary symptoms demon-strated significant reduction in the uptake of [123I]-b-CIT bythe striatum, suggesting that nigrostriatal degenerationmight be related to the pathogenesis of urinary dysfunction.7

We have also established that electrical stimulation of thesubstantia nigra pars compacta (SNc) reduces inhibition ortermination of bladder contractions in cats.8 Additionally,striatal dopamine levels increased significantly during thebladder relaxation phase in cats.9 Although the striatum isknown to play a critical role in mediating visceral reflexes,little is known about the relationship between striatal neuro-nal activity and bladder function.10 Therefore, we examinedthe effects of electrical stimulation of the striatum on bladdercontractions and recorded spontaneous bladder contraction-related neuronal firing in the striatum in cats.

MATERIALS AND METHODS

Experiments were performed on 12 adult male cats(Shiraishi, Saitama, Japan) anesthetized with ketamine (initial

injection of 20 mg/kg IM with additional injections of 5 mg/kgin response to changes in blood pressure). We also adminis-tered pancronium bromide (0.2–0.4 mg/kg) to prevent truncalmovements. The trachea was intubated and catheters wereplaced in the femoral artery and the femoral vein to monitorblood pressure and administer drugs, respectively. A 20-gaugedouble-lumen urinary catheter with a three-way stopcock wasinserted into the bladder transurethrally to measure pressureand regulate volume in the bladder. Initial bladder contrac-tions were generated by filling the bladder with a relativelylarge amount of saline (20–50 ml). The bladder volume wasadjusted by the addition and withdrawal of fluid (2–5 ml) inorder to maintain isovolumetric spontaneous bladder con-tractions. The animals were positioned in a stereotaxic frameand their positions were adjusted to expose the surface oftheir left hemisphere. Artificial ventilation was appliedand end-tidal CO2 was maintained at 3–5%. A monopolartungsten microelectrode (FHC; Bowdoinham, ME, USA),25-05-3; tip diameter 25 mm, tip impedance 9–12 MO) wasinserted stereotaxically into the striatum (caudate nucleus

No conflict of interest reported by author(s).Abbreviations: DA, dopamine; EMG, electromyogram; GABA, m-aminobutyricacid; PAG, periaqueductal gray; PD, Parkinson’s disease; PET, positron emissiontomography; PMC, pontine micturition center; SNc, substantia nigra parscompacta; SNr, substantia nigra pars reticulata; SPECT, single-photon emissioncomputed tomography; STN, subthalamic nucleus.*Correspondence to: Tatsuya Yamamoto, MD, 1-8-1 Inohana Chuo-ku, Chiba 260-8670, Japan. E-mail: tatsuya-yamamoto@mbc.nifty.comReceived 21 July 2008; Accepted 27 October 2008Published online 12 February 2009 in Wiley InterScience(www.interscience.wiley.com)DOI 10.1002/nau.20682

� 2009 Wiley-Liss, Inc.

and putamen) using the Horsley–Clarke coordinates andthe electrode was moved in 1-mm steps when exploring anarea. When we moved the electrode to the next target, weremoved the electrode from the brain to confirm that theelectrode was not bending, and reinsert the electrode to thenext target. Electrical stimulation (stimulus parameters: 0.2msec duration, 70–400 mA, 100 Hz) was applied to determinewhether the stimulation initiated or terminated the bladdercontraction. In regards to the timing, the electrical stimulationfor evoking facilitatory responses was applied immediatelyafter the spontaneous bladder contraction had returned tobaseline. Responses were deemed facilitatory if a bladdercontraction was evoked during the bladder relaxation phase.The electrical stimulation for evoking inhibitory responseswas timed to occur just after the initial increase in sponta-neous bladder contraction. Electrical stimulation was sus-tained until the bladder pressure returned to baseline. Longerperiods of stimulation were applied (equivalent to one cycle ofbladder contraction/relaxation) to further confirm the inhib-itory response. Responses were defined as inhibitory when theduration and amplitude of bladder pressure decreased to<50% of the baseline bladder pressure. The threshold of theevoked bladder response was examined at each stimulationpoint during the period when the electrical current evokedbladder responses. We also performed extracellular single-unitrecordings with the same monopolar tungsten microelectrode.Electrical stimulation and extracellular single-unit recordingswere performed separately. The data recorded from theneurons along with the bladder pressure data were storedusing a Cambridge Electronic Design (CED) 1401-plus datainterface and Spike 2 software. We calculated the mean firingfrequencies within the respective spontaneous bladder con-tractions and relaxation phases. Neurons were defined asbladder relaxation phase-related neurons if their mean firingfrequencies in the relaxation phase were significantly higherthan those in the contraction phase during a period ofthree urinary cycles or more, and as bladder contractionphase-related neurons if their mean firing frequencies in thecontraction phase were significantly higher than those in therelaxation phase during a period of three urinary cycles ormore. At the end of the experiment, electrolytic lesions (30 mA,1 min) were created in order to mark the location of thesites of stimulation/recording. Thereafter, the brain wasquickly removed and fixed in 10% formalin solution. Thelocation of the electrode tips was checked by staining withhematoxylin–eosin (Fig. 1).

The two-tailed paired Student’s t-test was used for thecomparison of firing frequencies between the contraction andrelaxation phases. The above methods and definitions usedin this experiment were consistent to those applied in ourprevious study.8,11 At the end of the experiment, the animalswere administered an overdose of pentobarbital sodium. Allefforts were made to minimize the number of animals usedand all the experiments conformed to the internationalguidelines for the ethical use of animals.12

RESULTS

Electrical Stimulation of the Striatum

Electrical stimulation applied to the striatum educedinhibition of a spontaneous bladder contraction. None of theobtained responses were facilitatory. The typical bladderpressure response is shown in Figure 2, which illustrates thatelectrical stimulation inhibited a spontaneous bladder con-traction. Facilitatory responses were not obtained when thebladder was empty or under the threshold volume required togenerate continuous cycles. The threshold of the amplitude ofelectrical stimulation required for evoking the responses, witha given stimulation frequency of 100 Hz, was 70–400 mA.Stimulus-effective sites were located only in the posteriorventral region of the caudate nucleus and the adjacentputamen, as depicted in Figure 3. Each site is represented bya shaded circle.

Neurourology and Urodynamics DOI 10.1002/nau

Fig. 1. a: Position of the tip of the electrode (white arrow). b: A higher

magnification of the area limited by a square in (a).

Fig. 2. Bladder pressure response to electrical stimulation of the striatum.

a: Electrical stimulation of the striatum reduced bladder pressure when

the stimulation was applied just after the initiation of an increase in

spontaneous bladder pressure. b: Longer stimulation successfully sup-

pressed bladder contraction. Stimulus parameters as shown here: pulse

duration 0.2 msec, 150 mA, 100 Hz.

550 Yamamoto et al.

Single-Unit Recording in the Striatum

Forty-six neurons that exhibited correlation to urinarycycles were recorded in the striatum. Thirty-five neurons werefound to be tonically activated during the bladder relaxationphase, and the remaining 11 neurons were activated duringthe bladder contraction phase. The neuron activated duringthe bladder relaxation phase exhibited 9.3 � 3.5 and 2.1 � 1.5Hz mean firing frequencies during the relaxation andcontraction phases, respectively. The difference between thesevalues was statistically significant (P < 0.01). The neuronactivated during the bladder contraction phase exhibited thefollowing mean firing frequencies during the relaxation andcontraction phases: 1.6 � 1.9 and 9.6 � 3.9 Hz, respectively.The difference between these values was statistically signifi-cant (P < 0.01). The typical firing pattern with respect tourinary cycles is shown in Figure 4. None of the neuronsexhibited phasic patterns. Both types of the neurons wereall located within the area in which electrical stimulationinhibited the bladder contraction, as shown in Figures 5and 6.

DISCUSSION

The basal ganglia are known to play a critical role inextrapyramidal motor control. Recent reports have suggestedthat the basal ganglia modulate the micturition reflex in bothexperimental animals13 and humans,14 since lesions in thebasal ganglia can cause severe urinary urge incontinence.Several previous studies have examined the role of the basalganglia on the micturition reflex by electrical stimulation ofthe globus pallidus and subthalamic nucleus.15,16 However,the role of the striatum on bladder activity remains unknown.This study is the first demonstration of the fact that electricalstimulation of the striatum inhibits spontaneous bladdercontractions. Moreover, this study also validates the occur-rence of a spontaneous bladder contraction-related neuronalfiring in the posterior ventral striatum in ketamine-anesthe-tized cats.

The results of the present study also revealed that electricalstimulation only induced inhibition of spontaneous bladder

contractions, specifically no facilitatory responses wereobserved. These results indicated that the net effect ofelectrical stimulation on spontaneous bladder contractionwas inhibitory. It should be noted that electrical stimulationcould stimulate both the neuron cell body and the axon. Sincethe axon usually have a lower threshold than the neuron cellbody, some of the axons in passage whose neuron cell bodiesare located in other regions of the brain may also be activated.Therefore, we might say that the activation of the striatalregion including the striatal neuron cell body and the axonspassing through the striatum may lead to the inhibition ofthe spontaneous bladder contraction. Although we didnot obtain facilitatory responses on bladder contraction inelectrical stimulation, these negative results might be attrib-uted to our experimental method. Since the bladder nervoussystem is in a relatively inhibitory state immediately afterbladder contraction, testing excitatory effect on bladdercontraction must be performed at a relatively full bladdervolume that does not induce isovolumetric bladder contrac-tion. This could be the reason that electrical stimulation onlyinduced inhibitory effect on bladder contraction.

In contrast, neuronal activity in both the bladder relaxationphase (n ¼ 35) and the bladder contraction phase (n ¼ 11) wasrecorded in the posterior ventral striatum via single-unitrecording.

It should be recognized that both the activity of the neuroncell body and the axon could be caught by single-unitrecording, as electrical stimulation could stimulate both theneuron cell body and the axon. Although many brain neuronsmight participate in regulating the bladder contraction, it isgenerally considered that when bladder contraction occurs,some brain neurons participate in this bladder contractionevent by increasing firing, but other brain neurons participateby decreasing or ceasing its firing. We might say that theneurons activated during bladder relaxation phase induced abladder contraction by decreasing their activity duringbladder contraction phase so that the other neurons includingthe neurons activated during bladder contraction phasein the present study lead to bladder contraction. Similarly,the neurons increasing its firing during bladder relaxationphase might participate in inhibiting bladder contraction.On the contrary, the neurons activated during bladdercontraction phase might contribute to inducing bladdercontraction.

Since the striatum is not directly connected to the spino-bulbo-spinal micturition circuit, it is necessary to discusshow striatum activity affects spontaneous bladder contrac-tions. The spino-bulbo-spinal micturition reflex is organizedas follows: the bladder sends a signal to the sacral cord via A-delta fibers about its content. This information is sent via adistinct cell group in the sacral cord, which is then relayed tothe central parts of the periaqueductal gray, where it issubsequently relayed to the lateral PAG.17 These lateral PAGcells have access to the pontine micturition center (PMC),18

which controls micturition by exciting the parasympatheticbladder motoneurons in the sacral cord. Moreover, viainhibitory interneurons, these PAG cells relax the bladdersphincter motoneurons.19

However, micturition is not only based on the bladdercontent, but also on the location of the individual; the brainshould have total control on the spino-bulbo-spinal micturi-tion reflex to determine when and where micturition takeplace. This control, in all likelihood, is exerted by the prefrontalcortex, which has very strong connections with the PAG.20

In this sense, the PAG ‘‘decides’’ the time for micturition basedon the bladder volume and whether voiding is desired by

Neurourology and Urodynamics DOI 10.1002/nau

Fig. 3. Sites of electrical stimulation in the striatum. A11–A19 are

designated according to the Horsley–Clarke coordinates. The larger filled

circles represent the lower threshold (70–200 mA), whereas the smaller filled

circles represent a higher threshold (200–400 mA). All of the bladder

responses were inhibitory. Stimulation of the posterior ventral portion of the

caudate nucleus and the putamen was most effective at suppressing bladder

contraction.

Role of the Striatum on Bladder Activity 551

the person and is socially appropriate.21 Almost certainly, thestriatum affects the prefrontal cortex. When this section of thecortex, along with the motor, premotor, and other frontalcortical regions in PD patients, does not receive the properinformation from the striatum, it cannot properly activate or

inhibit the PAG, and thus, the PAG activates the PMCincorrectly leading to detrusor overactivity.

Since the striatum receives projections from the SNc, therole played by the SNc in spontaneous bladder contraction isalso of importance. In our previous study, the results obtained

Neurourology and Urodynamics DOI 10.1002/nau

Fig. 4. Typical recording of neuronal firing in the striatum. a: The neurons activated during bladder relaxation

phase. b: The neurons activated during bladder contraction phase.

552 Yamamoto et al.

Neurourology and Urodynamics DOI 10.1002/nau

Fig. 6. Distribution of neurons recorded in the bladder contraction phase. Eleven neurons were recorded in the

bladder contraction phase. These neurons were also localized to the posterior ventral caudate nucleus. A11–A19

are designated according to the Horsley–Clarke coordinates.

Fig. 5. Distribution of neurons recorded in the bladder relaxation phase. Thirty-five neurons were recorded in the

bladder relaxation phase. These neurons were localized to the posterior ventral portion of the caudate nucleus and

the putamen, corresponding to the sites of electrical stimulation. A11–A19 are designated according to the

Horsley–Clarke coordinates.

Role of the Striatum on Bladder Activity 553

with regard to the SNc were similar to those of the presentstudy; specifically, electrical stimulation of the SNc educedinhibition of spontaneous bladder contractions and nofacilitatory responses were observed in the cats.8 However,both the bladder relaxation phase-related (78%) and contrac-tion phase-related (22%) neurons were obtained in the SNc.These results suggest that both the SNc and the striatummight have participated in the regulation of the spontaneousbladder contraction in a similar way. It is also important tomention the role played by dopamine in spontaneous bladdercontraction. We previously reported that striatal dopaminelevels increased significantly during the bladder relaxationphase.9 Therefore, it is possible that the activation of bladderrelaxation phase-related neurons in the SNc leads to increaseddopamine levels in the striatum, which in turn might lead tothe activation of bladder relaxation phase-related neurons inthe striatum. It is possible that the degenerated nigrostriataldopaminergic pathway failed to inhibit bladder contraction, aresult which could be recognized as detrusor overactivity inpatients with PD.7

CONCLUSIONS

In this study, we demonstrated that electrical stimulationinhibits spontaneous bladder contraction and that bladdercontraction-related neuronal firing takes place in the posteriorventral striatum.

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