Ano-rectal motility responses to pelvic, hypogastric and pudendal nerve stimulation in the Göttingen minipig

The effect of colonic tissue electrical stimulation and celiac branch of the abdominal vagus nerve neuromodulation on colonic motility in anesthetized pigs

BACKGROUND

Knowledge on optimal electrical stimulation (ES) modalities and region-specific functional effects of colonic neuromodulation is lacking. We aimed to map the regional colonic motility in response to ES of (a) the colonic tissue and (b) celiac branch of the abdominal vagus nerve (CBVN) in an anesthetized porcine model.

METHODS

In male Yucatan pigs, direct ES (10 Hz, 2 ms, 15 mA) of proximal (pC), transverse (tC), or distal (dC) colon was done using planar flexible multi-electrode array panels and CBVN ES (2 Hz, 0.3-4 ms, 5 mA) using pulse train (PT), continuous (10 min), or square-wave (SW) modalities, with or without afferent nerve block (200 Hz, 0.1 ms, 2 mA). The regional luminal manometric changes were quantified as area under the curve of contractions (AUC) and luminal pressure maps generated. Contractions frequency power spectral analysis was performed. Contraction propagation was assessed using video animation of motility changes.

KEY RESULTS

Direct colon ES caused visible local circular (pC, tC) or longitudinal (dC) muscle contractions and increased luminal pressure AUC in pC, tC, and dC (143.0 ± 40.7%, 135.8 ± 59.7%, and 142.0 ± 62%, respectively). The colon displayed prominent phasic pressure frequencies ranging from 1 to 12 cpm. Direct pC and tC ES increased the dominant contraction frequency band (1-6 cpm) power locally. Pulse train CBVN ES (2 Hz, 4 ms, 5 mA) triggered pancolonic contractions, reduced by concurrent afferent block. Colon contractions propagated both orally and aborally in short distances.

CONCLUSION AND INFERENCES

In anesthetized pigs, the dominant contraction frequency band is 1-6 cpm. Direct colonic ES causes primarily local contractions. The CBVN ES-induced pancolonic contractions involve central neural network.

The minipig as nonrodent species in toxicology--where are we now?

Over the past 3 decades minipigs have moved from being an obscure alternative to dogs and nonhuman primates to being a standard animal model in regulatory toxicity studies. This article covers the use of minipigs as a model in the context of nonclinical drug safety and provides an overview of the minipig's developmental history and relates minipigs to other animal species commonly used in toxicology; and the minipig's translational power is supported by 43 case studies of marketed drug products covered. Special focus is given to criteria for selecting minipigs in nonclinical programs supporting the development of new medicines; the use of swine in the assessment of food additives, agrochemicals, and pesticides; as well as a regulatory perspective on the use of minipigs in Food and Drug Administration (FDA)-regulated products. This article presents the main points conveyed at a symposium held at the 2010 American College of Toxicology meeting in Baltimore, Maryland.

Selective pelvic autonomic nerve stimulation with simultaneous intraoperative monitoring of internal anal sphincter and bladder innervation

BACKGROUND

Pelvic autonomic nerve preservation avoids postoperative functional disturbances. The aim of this feasibility study was to develop a neuromonitoring system with simultaneous intraoperative verification of internal anal sphincter (IAS) activity and intravesical pressure.

METHODS

14 pigs underwent low anterior rectal resection. During intermittent bipolar electric stimulation of the inferior hypogastric plexus (IHP) and the pelvic splanchnic nerves (PSN), electromyographic signals of the IAS and manometry of the urinary bladder were observed simultaneously.

RESULTS

Stimulation of IHP and PSN as well as simultaneous intraoperative monitoring could be realized with an adapted neuromonitoring device. Neurostimulation resulted in either bladder or IAS activation or concerted activation of both. Intravesical pressure increase as well as amplitude increase of the IAS neuromonitoring signal did not differ significantly between stimulation of IHP and PSN [6.0 cm H(2)O (interquartile range [IQR] 3.5-9.0) vs. 6.0 cm H(2)O (IQR 3.0-10.0) and 12.1 μV (IQR 3.0-36.7) vs. 40.1 μV (IQR 9.0-64.3)] (p > 0.05).

CONCLUSIONS

Pelvic autonomic nerve stimulation with simultaneous intraoperative monitoring of IAS and bladder innervation is feasible. The method may enable neuromonitoring with increasing selectivity for pelvic autonomic nerve preservation.

Intraoperative pelvic nerve stimulation performed under continuous electromyography of the internal anal sphincter

PURPOSE

The aim of this animal study was to investigate the effect of intraoperative pelvic nerve stimulation on internal anal sphincter electromyographic signals in order to evaluate its possible use for neuromonitoring during nerve-sparing pelvic surgery.

METHODS

Eight pigs underwent low anterior rectal resection. The intersphincteric space was exposed, and the internal (IAS) and external anal sphincter (EAS) were identified. Electromyography of both sphincters was performed with bipolar needle electrodes. Intermittent bipolar electric stimulation of the inferior hypogastric plexus and the pelvic splanchnic nerves was carried out bilaterally. The recorded signals were analyzed in its frequency spectrum.

RESULTS

In all animals, electromyographic recordings of IAS and EAS were successful. Intraoperative nerve stimulation resulted in a sudden amplitude increase in the time-based electromyographic signals of IAS (1.0 (0.5-9.0) μV vs. 4.0 (1.0-113.0) μV) and EAS (p < 0.001). The frequency spectrum of IAS in the resting state ranged from 0.15 to 5 Hz with highest activity in median at 0.77 Hz (46 cycles/min). Pelvic nerve stimulation resulted in an extended spectrum ranging from 0.15 to 20 Hz. EAS signals showed higher frequencies mainly in a range of 50 to 350 Hz. However, after muscle relaxation with pancuronium bromide, only the low frequency spectrum of the IAS signals was still present.

CONCLUSIONS

Intraoperative verification of IAS function by stimulation of pelvic autonomic nerves is possible. The IAS electromyographic response could be used to monitor pelvic autonomic nerve preservation.

Pelvic nerve stimulation evokes nitric oxide mediated distal rectal relaxation in pigs

PURPOSE

Pelvic nerve stimulation evokes a complex motility response in the pig rectum with a proximal decrease and a distal increase in cross-sectional area. This study investigated whether the distal increase in the cross-sectional area is because of smooth muscle relaxation mediated by nitric oxide.

METHODS

The pelvic nerves were stimulated with cuff electrodes in ten chloralose-anesthetized minipigs. Pressure, volume, and cross-sectional areas at five positions in the rectum were obtained during stimulation to examine the effect of N(G)-nitro-L-arginine (an inhibitor of nitric oxide synthase) injection.

RESULTS

Stimulation evoked a median pressure decrease of 13 cm H(2)O (range, 0-27; P < 0.05; n = 10) in the anal canal, a pressure increase of 6 cm H(2)O (range,-15 to 30; P < 0.05; n = 10) in the rectum and a decrease of 39 mL (range, 30-63; P < 0.05; n = 6) in rectal volume. Rectal cross-sectional areas decreased 33 percent (range, 5-56; P < 0.02; n = 7) in the proximal part and increased 32 percent (range, 9-67; P < 0.02; n = 8) in the distal part. N(G)-nitro-L-arginine eliminated the increase in the distal rectal cross-sectional area (n = 5) and the decrease in anal canal pressure (n = 9) in all tested animals.

CONCLUSION

Pelvic nerve stimulation evokes distal rectal relaxation in pigs, sensitive to N(G)-nitro-L-arginine, which suggests that this smooth muscle response is mediated by nitric oxide.