Parkinson’s disease (PD) is characterized clinically by combination of bradykinesia, rigidity, and resting tremor. In addition, it is also well known that PD patients are usually suffering from overactive bladder (OAB) symptoms. Several studies suggested that subthalamic nucleus deep brain stimulation (STN-DBS) ameliorate OAB in PD patients. Although, detailed mechanisms regarding how STN-DBS improve OAB in PD patients are not well understood, functional brain imaging study reported that STN-DBS might normalize the afferent urinary information and thereby leading to the improvement of OAB [1]. It is also well known that medial prefrontal cortex (mPFC) play an important role in regulating micturition reflex based on urinary afferent information conveyed by periaqueductal grey (PAG) [2]. However, we do not know how STN-DBS affect the relationships between mPFC and PAG network which is important in regulating micturition reflex. We aimed to clarify how STN-DBS modulate the neuronal activity of mPFC induced by PAG stimulation (increased urinary afferent projections) and its effects on bladder contraction in PD model rat.

All experiments were performed on adult female Sprague–Dawley (SD) rats (14–16 weeks old, weighing 200–300 g), in accordance with the Guideline for the Care and Use of Laboratory Animals. PD model rat was constructed by a unilateral injection of 2 μg/ml 6-hydroxydopamine (6-OHDA)  dissolved in 5 μl of 0.9% sterile saline containing 0.1% ascorbic acid into the left medial forebrain bundle at a rate of 1 μl /min.
Experiments were performed under urethane anesthesia in 6-hydroxydopamine hemi-lesioned PD rats (n=6). A single-lumen catheter was trans-urethrally inserted into the bladder to measure bladder pressure. Stimulation electrodes were inserted into left subthalamic nucleus and ventrolateral PAG. Recording electrode was inserted into mPFC. Extracellular local field potential (LFP) recordings of mPFC were performed before stimulation, during PAG stimulation, during PAG+STN stimulation, and after cessation of stimulation. The power spectrum of mPFC was analyzed off-line using the Lab Chart software . Fast Fourier transforms (FFTs) were performed to analyze mPFC LFP in a frequency domain range of 0.3 to 50 Hz. Power spectral densities (PSDs) were estimated with 131072 FFT size, Hann window, and a 50% overlap, and normalized by log10 (PSD).

PAG stimulation significantly decreased bladder inter-contraction intervals from 568.07 ± 46.67 s (pre stimulation) to 342.15 ± 39.87 s (during PAG stimulation) (p =0.0004). Adding STN-DBS to PAG stimulation tended to increase bladder inter-contraction intervals from 342.15 ± 39.87 s to 412.06± 40.10 s (p =0.07) and cessation of stimulation changed bladder inter-contraction interval from 412.06± 40.10 s to 493.55± 50.04 s (p=0.08).
 Power spectrum analysis revealed that PAG stimulation significantly decreased the mean logarithmic power in mPFC alpha frequency (8-15Hz) from 7.80 ± 0.03 (a.u.) to 7.56± 0.03 (a.u.) (p<0.01) and adding STN-DBS to PAG stimulation significantly increased the mean logarithmic power in mPFC alpha frequency from 7.56± 0.03 (a.u.) to (a.u.) (p < 0.01) (Figure) and cessation of stimulation slightly increased the mean logarithmic power in mPFC alpha frequency from 7.56± 0.03 (a.u.) to 7.86 ± 0.03(a.u.) (p =0.12) during bladder relaxation phase. 
In addition, PAG stimulation significantly decreased the mean logarithmic power in mPFC alpha frequency (8-15Hz) from 8.23± 0.02 (a.u.) to 7.97± 0.03 (a.u.) (p<0.01) and adding STN-DBS to PAG stimulation significantly decreased the mean logarithmic power in mPFC alpha frequency from 7.97± 0.03 (a.u.) to 8.28 ± 0.03 (a.u.) (p < 0.01)(Figure) and cessation of stimulation decreased the mean logarithmic power in mPFC alpha frequency from 8.28 ± 0.03 (a.u.) to 7.75 ± 0.03(a.u.) (p < 0.01) during bladder contraction phase.

The present study revealed that PAG stimulation significantly decreased bladder inter-contraction interval with concomitant decrease in mPFC alpha power during storage and voiding phase, whereas adding STN stimulation tended to increase bladder inter-contraction interval with concomitant increase in mPFC alpha power during storage and voiding phase.
 The PAG stimulation is more likely to induce bladder contraction probably via activation of potine micturition centre (PMC)-sacral parasympathetic nucleus pathway and also induce urinary afferent projection from PAG to higher micturition centre located in cerebral cortex. The present study suggested that decreased mPFC alpha power might be related to urinary frequency observed during PAG stimulation, and adding STN stimulation tended to improve urinary frequency by increasing mPFC alpha power. This result also indicated that the activity of mPFC was influenced by afferent urinary information (stimulating PAG in this study) and STN-DBS might tend to increase bladder inter-contraction interval via increasing mPFC alpha power.

PAG stimulation decreased bladder inter-contraction interval and decreased the alpha power in mPFC in PD model rat. STN-DBS might increase bladder inter-contraction in interval by increasing the alpha power in mPFC in PD model rat.

Herzog J, Weiss PH, Assmus A, Wefer B, Seif C, Braun PM, Pinsker MO, Herzog H, Volkmann J, Deuschl G, Fink GR. Improved sensory gating of urinary bladder afferents in Parkinson's disease following subthalamic stimulation. Brain. 2008 ;131(Pt 1):132-45.
Fowler CJ, Griffiths D, de Groat WC. The neural control of micturition. Nat Rev Neurosci. 2008 :453-66. doi: 10.1038/nrn2401.