Proceedings of The Physiological Society

Physiology 2015 (Cardiff, UK) (2015) Proc Physiol Soc 34, C66

Oral Communications

The effect of 2 and 14Hz sacral neuromodulation on cortical evoked potentials and polysialated neural cell adhesion modecule expression in a rodent model of pudendal nerve injury

J. Evers1, P. R. O'Connell2,1, J. F. Jones1

1. School for Medicine and Medical Science, UCD, Ireland, Dublin, Ireland. 2. Centre for Colorectal Disease, St Vincent's University Hospital, Dublin, Ireland.

  • Figure 1:A. Anti PSA-NCAM Immunocytochemistry of the anorectal representation in the primary somatosensory cortex. Cell nuclei are stained red (propidium iodine) and PSA-NCAM green.B. Close up of PSA-NCAM positive cells. Cells where greater than

  • Table 1<\#13>

Severe faecal incontinence, a common and debilitating disorder affecting mostly multiparous women, is routinely treated with sacral neuromodulation (SNM). It is hypothesized that SNM acts upon somatosensory afferent fibres, but its mechanism of action is not yet fully understood. This study aims to elucidate its effects on afferent transmission to the somatosensory cortex by utilizing a model of pudendal nerve injury, designed to mimic the trauma of childbirth(1), and cortical evoked potential (EP) recording. Two stimulation frequencies, the clinically used one (14Hz) and an experimentally derived optimum (2Hz(2)), were tested. Using 24 urethane (1.5g/kg, i.p.) anaesthetized female Wistar rats anal EPs were recorded by a 32-channel multi-electrode array over the primary somatosensory cortex before, during and after a 60min inflation of 2 retro-uterine balloons(1.5mls each). Two or 14Hz SNM was applied after balloon deflation (left S1, 10min, 1ms pulse duration, at motor threshold: 4.8V±0.5V). Four groups (N=8 each) were studied: Sham, balloon, 2 and 14Hz SNM. Immunohistochemistry for polysialylated neural cell adhesion molecule (PSA-NCAM) was performed on harvested brains (N=4/group) as described by Griffin et al.(3). Data are mean±S.E.M. The criterion for statistical significance was P<0.05. EP amplitude diminished during balloon inflation to -69%±6% in balloon, 2 and 14Hz groups. Recovery in the balloon group was partial (-35%±2%), while 14Hz SNM increased EPs to (-3%±3%) and 2Hz SNM above the initial level (33%±4%). In the recovery period, EPs in SNM groups were larger than in the balloon group and in the 2Hz group larger than in the 14Hz group (two-way repeated-measures ANOVA, group factor: P<0.0001). The frequency of PSA-NCAM positive cells per field of view (250μmx250μm) was Poisson distributed. Their number was increased in the right (stimulated) hemisphere of both SNM groups (P<0.0001, Poisson test), but not in the Sham or balloon group (P=0.43, P=0.74 respectively). Their numerical density incl. P values (Student's t-test) are shown in Table 1. Their location changed after SNM: Unstimulated cortex showed a small cluster in layer IV and stimulated cortices in layer I/II, IV and V (Fig. 1). SNM causes a long term potentiation like phenomenon in the somatosensory cortex. Increased PSA-NCAM expression was seen in layer I/II, IV and V. In electrophysiological experiments 2Hz is more effective in ameliorating diminished EPs than 14Hz SNM, but on a cellular level changes in PSA-NCAM expression were similar for both frequencies.

Where applicable, experiments conform with Society ethical requirements