Rapid rate magnetic stimulation of human sacral nerve roots alters excitability within the cortico-anal pathway.

Sacral nerve root stimulation (SNS) can produce dramatic symptomatic improvement in faecal incontinence (FI). However, the physiological mechanism behind this improvement remains unknown. One hypothesis is that SNS may modulate cortico-anal pathways and drive compensatory changes within the spinal cord or cerebral cortex that beneficially alter sphincter function. Our aim was to assess whether short-term experimental SNS can induce changes in the human cortico-anal pathway. Eight healthy volunteers (mean age 30 years) were studied. Subjects were investigated on three separate occasions and randomized to either active (5 and 15 Hz) or sham rapid-rate lumbosacral magnetic stimulation (rLSMS). Anal sphincter electromyograms (EMG) were recorded from an anal probe following single-pulse transcranial magnetic stimulation, at baseline, immediately, 30 and 60 min following rLSMS at either (i) 5 Hz for 15 min, (ii) 15 Hz for 15 min or (iii) sham stimulation for 15 min. In addition, manometry and anal sphincter sensation was measured in a subset of subjects. Interventions were compared to sham using anova. Fifteen hertz rLSMS increased cortico-anal EMG response amplitude in the 1 h postintervention (F(4, 28) = 3.2, P = 0.027), without a shift in response latency. This effect was not demonstrated with either 5 Hz or sham stimulation. rLSMS had no short-term effect on sensation or physiology. Short-term magnetic stimulation of the sacral nerve roots induces changes in cortico-anal excitability which is frequency specific. These data support the hypothesis that SNS produces some of its beneficial effect in patients with FI by altering the excitability of the cortico-anal pathway.

The effects of octreotide, soy polysaccharide, codeine and loperamide on nutrient, fluid and electrolyte absorption in the short-bowel syndrome.

Four agents, which could delay intestinal transit, were tested in six short-bowel patients (jejunal length 30-120 cm) on long-term nutritional/electrolyte replacement therapy. Intestinal transit time of a liquid test meal and nutrient, water and sodium absorption were measured during a control study and with each test agent on separate days. Soy polysaccharide tended to increase transit time, but decreased the absorption of water, sodium and nutrients. Codeine phosphate and loperamide caused inconsistent and clinically unimportant changes. Octreotide, a long-acting analogue of somatostatin, delayed transit and increased water, sodium and calorie absorption from the meal. Octreotide appears to have the potential to reduce the need for electrolyte and nutritional supplements in patients with the short-bowel syndrome.

Action of centrally mediated autonomic stimulation on human upper gastrointestinal transit: a comparative study of two stimuli.

Two well established experimental stressors, hand immersion in cold water, and mental stimulation with dichotomous listening, were applied to 37 normal subjects after the ingestion of a standard meal. Orocaecal transit was measured by serial exhaled breath hydrogen sampling. Cold water significantly delayed transit compared with warm water control (warm water 71.8 +/- 3.6 mins v cold water 93.2 +/- 5.7 mins p less than 0.01), with significant rises in blood pressure pulse rate perceived discomfort and plasma catecholamines. In contrast mental stimulation was unaccompanied by any change in transit (control; 67.4 +/- 4.7 v test 64.3 +/- 5.3 mins p greater than 0.1) despite a significant rise in pulse rate, skin conductance and plasma catecholamines. Repeated cold water immersion studies in eight individuals produced consistent orocaecal transit and autonomic responses, whereas mental stimulation showed reduced autonomic responses on repeat testing, suggesting that tolerance to the stimulus had occurred. The results of these studies show stimulus specific gastrointestinal response patterns to autonomic stimuli, and appear to have important implications for the design of future studies of human gastrointestinal autonomic physiology and for the investigation of patients with stress related gut dysfunction.