Mechanically evoked cortical potentials: A physiological approach to assessment of anorectal sensory pathways

Background The rat has served usefully as a model for fecal incontinence and exploration of the mechanism of action of sacral neuromodulation (SNM). There remains a deficit in information regarding the location and type of spinal neurons which receive anorectal input and the effect of SNM on those neurons. Methods Single neuronal extracellular recordings of neurons receiving anorectal input were made at the S1 level of the spinal cord using sharp glass electrodes. SNM at S1 was delivered at 2 Hz for 3 minutes and its effect on discharge was quantified. Key Results In total, 31 units (n = 14 animals) receiving anorectal synaptic input were recorded at the first sacral (S1) segmental level in either lamina III or IV of the dorsal horn. The inputs were classified according to afferent fiber conduction speed (16 Aδ, 11 Aβ, and 4 C‐fiber). The baseline firing frequency (ie, the mean firing frequency before the application of SNM) was 0.48 Hz ± 0.49 (mean ± SD) and 58% of units responded to acute SNM with either an increase or decrease in mean firing frequency. Conclusions & Inferences In this study, the majority of spinal neurons receiving anorectal input changed their activity in response to SNM. These findings provide the basis for future studies which aim to explore the precise cellular mechanism of action of SNM on this fecal continence pathway.

Section: Methodsmentioning

confidence: 99%

The projection of anorectal afferents to spinal cord and effect of sacral neuromodulation on dorsal horn neurons which receive such input in the rat

Turner

O'Connell

Jones

2019

“…11,12 CEPs provide a useful assessment of afferent brain responses to visceral stimulation from various regions of the GI tract and normative data has been established. 11,[13][14][15][16][17][18][19] CEP latency is used to define the presence or absence of neuropathy. For example, shorter CEP latencies are seen in IBS patients, indicating accelerated afferent gut-brain signaling.…”

Section: Introductionmentioning

confidence: 99%

“…Cortical evoked potentials (CEPs) in response to rectal electrical stimulation are a validated and reproducible measure of the afferent neural pathway of the gut‐brain axis 11,12 . CEPs provide a useful assessment of afferent brain responses to visceral stimulation from various regions of the GI tract and normative data has been established 11,13–19 . CEP latency is used to define the presence or absence of neuropathy.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of bidirectional gut‐brain axis and anorectal function in Parkinson's disease with constipation

Yan,

Tennekoon,

Eubanks

et al. 2023

BackgroundParkinson's disease (PD) is a neurodegenerative movement disorder with prodromal and highly prevalent gastrointestinal (GI) symptoms, especially constipation. Although PD models suggest gut‐brain axis dysfunction, the mechanistic underpinnings and their correlation with GI symptoms are poorly understood.AimTo examine the bidirectional gut‐brain axis function in PD and correlate it with constipation severity, PD duration, and severity.MethodsRectal sensory thresholds and afferent cortical evoked potentials (CEP) were assessed using a 4‐ring EMG electrode probe. Efferent anal and rectal motor evoked potentials (MEPs) were obtained following transcranial and lumbosacral magnetic stimulation. Bowel symptoms were assessed by prospective stool diary. The CEP and MEP latencies, rectal sensory thresholds, and anorectal sensorimotor data were compared between PD subjects and age‐adjusted healthy subjects.Key ResultsTwenty‐five PD subjects with constipation (F/M = 6/19) and 20 healthy subjects (F/M = 14/6) were enrolled. The first and pain sensation thresholds were higher in PD subjects than healthy subjects (p < 0.002) but lost significance after adjustment for age. Age‐adjusted rectal CEP and right‐sided cortico‐anal MEP latencies were prolonged in PD subjects compared to healthy subjects (p < 0.04). Also, half (4 of 8) age‐adjusted spino‐anal and rectal MEP latencies in PD subjects were significantly longer. In multivariate linear analysis, first rectal sensation and right‐sided MEP latencies showed moderate correlation with constipation severity.Conclusions & InferencesParkinson's disease is associated with significant bidirectional gut‐brain axis dysfunction as evidenced by prolonged afferent and efferent neuronal signaling. Constipation severity in PD is correlated to abnormal rectal sensation and lateralized disturbance of efferent brain‐gut signaling.

“…The representation of the anorectum on the somatosensory cortex of the rat has, until recently, been overlooked. Following positive confirmation that electrical stimulation of the anorectal evokes a measurable signal from the somatosensory cortex, a 32‐channel multi‐electrode array has been used to pinpoint the cortical representation of the anorectum, using both electrical stimulation of the anorectum and mechanical stimulation of the anal canal and rectum . However, an expanded rodent map of cortical activation may assist studies which analyze the action of sacral neuromodulation at the level of the sensory cortex .…”

Section: Introductionmentioning

confidence: 99%

“…Following positive confirmation that electrical stimulation of the anorectal evokes a measurable signal from the somatosensory cortex, 1 a 32-channel multi-electrode array has been used to pinpoint the cortical representation of the anorectum, using both electrical stimulation of the anorectum and mechanical stimulation of the anal canal and rectum. 2 However, an expanded rodent map of cortical activation may assist studies which analyze the action of sacral neuromodulation at the level of the sensory cortex. 3,4 The study of anorectal afferent projection to cerebral cortex is valuable because it is pertinent to chronic sacral neuromodulation for syndromes of fecal incontinence wherein patients appear to lose cortical awareness of the pelvic floor.…”

Section: Introductionmentioning

confidence: 99%

The projection of anorectal afferents to cortex of the rat: Comparison of two methods of cortical mapping

Turner

Pickering

O'Connell

et al. 2019

Background The rat has served usefully as a model for fecal incontinence and exploration of the mechanism of action of sacral neuromodulation. However, there is a gap in knowledge concerning representation(s) on the primary sensory cortex of this anatomical region. Methods Multi‐electrode array (32 channels) and intrinsic optical signal (IOS) processing were used to map cortical activation sites following anorectal electrical stimulation in the rat. A simple method for expanding a 32‐electrode array to a virtual 2700 array was refined. Key Results The IOS method identified activation of parietal cortex following anorectal or first sacral nerve root (S1) stimulation; however, the signal was poorly localized and large spontaneous vasomotion was observed in pial vessels. In contrast, the resulting high‐density maps showed two anatomically distinct cortical activation sites to anorectal stimulation. Conclusions & Inferences There are two distinct sites of activation on the parietal cortex following anorectal stimulation in the rat. The implications for sacral neuromodulation as a therapy for fecal incontinence are discussed.