Proceedings of The Physiological Society
University of Cambridge (2008) Proc Physiol Soc 11, PC112
Medial prefrontal cortex influences the control of normal and abnormal urinary bladder function in rats
Y. Mbaki1, V. Chapman1, R. Conley2, R. Mason1
1. School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom. 2. Discovery Biology, Pfizer Global R & D, Sandwich, United Kingdom.
Brain imaging studies have implicated the medial prefrontal cortex (mPFC) in the control of micturition and urinary continence in both humans and animals, although the exact role is still not fully understood. The present electrophysiological experiments investigated the contribution of the mPFC in the mediation of normal and abnormal bladder contractions in the anaesthetised rat. Female Sprague Dawley rats (250-300g; n=6) were anaesthetised with isoflurane (50%:50% N2O:O2 mixture) and maintained with urethane (1.2 g kg-1, i.v.). The bladder was infused (0.1 ml min-1) continuously with saline or citric acid (10 mg ml-1; pH 4) to evoke normal or abnormal bladder contractions respectively. Simultaneous recording of multiple single-unit and local field potential (LFP) activity using microelectrode arrays placed in the anterior cingulate gyrus of the mPFC measured bladder contraction-evoked neuronal activity. Single-unit and LFP activity, pre-voiding was compared with during/post-voiding-evoked activity using one-way ANOVA; p<0.05 was considered to be significant. Single-units (n = 13/28 neurones) correlating to voiding were identified in the anterior cingulate gyrus. Activity in these responsive units was suppressed (≥30%) shortly after saline-infusion-evoked bladder contractions. This was paralleled by an increase in LFP signal amplitude (~ 2 fold increase in the LFP signal amplitude; basal mean peak-to-peak amplitude = 0.7 mV). LFP frequency power was significantly (p<0.001) increased in the delta (1-4 Hz) band, and decreased (p<0.001) in the theta (4-8 Hz) band during/post-voiding compared to pre-voiding. Continuous infusion of citric acid produced abnormal bladder contractions and abolished bladder-evoked single-unit activity in 40% of previously responsive neurones. In contrast to saline infusion, citric acid altered the LFP power under pre-voiding, but not during/post-voiding conditions, by causing a significant increase (p<0.01) in the delta band and a significant decrease (p<0.05) in the theta band. These data provide evidence for a neuronal response to normal and abnormal bladder contractions in the anterior cingulate gyrus of the mPFC. The lag in response to voiding may imply a sensory involvement of the mPFC following normal/abnormal bladder contractions rather than a ‘motor drive’ role.
Where applicable, experiments conform with Society ethical requirements