Colorectal distention in the horse: visceral sensitivity, rectal compliance and effect of i.v. xylazine or intrarectal lidocaine

Animal Model of Video-Assisted Cecum and Ileum Instrumentation for Equine Visceral Pain Study

This study aimed to describe an animal model for studying equine visceral pain using minimally invasive and video-assisted cecum and ileum instrumentation. The access to the cecum and ileum was affected because of a previous typhlostomy. For video-assisted distention of the cecum and ileum, a distention device, which we developed using an endotracheal Rusch probe, was used, adapted, and coupled to a cuffometer to inflate and measure the pressure of the cuff attached to its distal portion. In a video-assisted manner, the distal portion of the device was introduced into the cecum and ileum, which contained the cuff in its distal portion, properly positioning it in the lumen. The cuff of the distension device was insufflated after the measurement of baseline physiological parameters of the animals and video-assisted confirmation of its right placement in the cecum and ileum lumen (M0). Was performed in one moment through two simultaneous cuff compressions and 1 minute of animal observation to evaluate the degree of abdominal discomfort manifestations (M1). To cease these stimuli, the cuff was deflated by disconnecting the extensor of the distension device attached to its proximal portion (M2). The procedure was easily performed in most cases. Slow and progressive insufflation allowed subjective adjustment of the intensity of the pain stimulus based on behavioral manifestations. Even with a low rate of complications, the model is feasible and reproducible for studies on visceral pain and the evaluation of analgesic effects.

Investigation of the effects of vatinoxan on somatic and visceral antinociceptive efficacy of medetomidine in dogs

OBJECTIVE

To determine whether concurrent vatinoxan administration affects the antinociceptive efficacy of medetomidine in dogs at doses that provide circulating dexmedetomidine concentrations similar to those produced by medetomidine alone.

ANIMALS

8 healthy Beagles.

PROCEDURES

Dogs received 3 IV treatments in a randomized crossover-design trial with a 2-week washout period between experiments (medetomidine [20 μg/kg], medetomidine [20 μg/kg] and vatinoxan [400 μg/kg], and medetomidine [40 μg/kg] and vatinoxan [800 μg/kg]; M20, M20V400, and M40V800, respectively). Sedation, visceral and somatic nociception, and plasma drug concentrations were assessed. Somatic and visceral nociception measurements and sedation scores were compared among treatments and over time. Sedation, visceral antinociception, and somatic antinociception effects of M20V400 and M40V800 were analyzed for noninferiority to effects of M20, and plasma drug concentration data were assessed for equivalence between treatments.

RESULTS

Plasma dexmedetomidine concentrations after administration of M20 and M40V800 were equivalent. Sedation scores, visceral nociception measurements, and somatic nociception measurements did not differ significantly among treatments within time points. Overall sedative effects of M20V400 and M40V800 and visceral antinociceptive effects of M40V800 were noninferior to those produced by M20. Somatic antinociception effects of M20V400 at 10 minutes and M40V800 at 10 and 55 minutes after injection were noninferior to those produced by M20.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested coadministration with vatinoxan did not substantially diminish visceral antinociceptive effects of medetomidine when plasma dexmedetomidine concentrations were equivalent to those produced by medetomidine alone. For somatic antinociception, noninferiority of treatments was detected at some time points.

Use of nociceptive threshold testing in cats in experimental and clinical settings: a qualitative review

OBJECTIVE

The objective of this study was to review the scientific articles on the use of nociceptive threshold testing (NTT) in cats and to summarize the clinical and experimental applications in this species.

DATABASES USED

Pertinent literature was searched with PubMed, Scopus, Web of Science, Universitätsbibliothek Basel (swissbib Basel Bern) and Google Scholar. The search was then refined manually based first on article titles and abstracts, and subsequently on full texts.

CONCLUSIONS

Of the four classical acute nociceptive models used for NTT, thermal and mechanical are most commonly used in cats. Thermal stimulation is applicable in experimental settings and has been used in pharmacodynamics studies assessing feline antinociception. Although mechanical stimulation is currently less used in cats, in the future it might play a role in the evaluation of clinical feline pain. However, the low response reliability after stimulus repetition within a narrow time interval represents a major limitation for the clinical use of mechanical thresholds in this species. Challenges remain when thermal thresholds are used to investigate analgesics that have the potential to affect skin temperature, such as opioids and α2-adrenergic agonists, and when a model of inflammatory pain is reproduced in experimental cats with the purpose of evaluating non-steroidal anti-inflammatory drugs as analgesics.

Thermal, mechanical and electrical stimuli in antinociceptive studies in standing horses: an update

OBJECTIVE

To perform a literature review of the thermal and mechanical antinociceptive devices used in pharmacological studies in standing horses published after 2011 (2012-2019). To complete a full literature review about electrical stimulation used for evaluation in similar studies.

DATABASES USED

PubMed, Google Scholar and Web of Science.

CONCLUSIONS

A high level of standardization has been reached in antinociceptive studies in standing horses using thermal and mechanical stimuli in most recent years. Commercially available testing devices to deliver thermal, mechanical and electrical stimuli, with observation of aversive responses to these stimuli, are reliable, sensitive and specific. For electrical stimulus testing, there is evidence that the resistance between the electrodes should be measured and should not exceed 3 kΩ to guarantee consistent and reproducible stimuli. The specific analysis of electromyographic activity after an electrical stimulus provides more detailed information about the neurons stimulated.

Hydrodynamics of defecation

Animals discharge feces within a range of sizes and shapes. Such variation has long been used to track animals as well as to diagnose illnesses in both humans and animals. However, the physics by which feces are discharged remain poorly understood. In this combined experimental and theoretical study, we investigate the defecation of mammals from cats to elephants using the dimensions of large intestines and feces, videography at Zoo Atlanta, cone-on-plate rheological measurements of feces and mucus, and a mathematical model of defecation. The diameter of feces is comparable to that of the rectum, but the length is double that of the rectum, indicating that not only the rectum but also the colon is a storage facility for feces. Despite the length of rectum ranging from 4 to 40 cm, mammals from cats to elephants defecate within a nearly constant duration of 12 ± 7 seconds (N = 23). We rationalize this surprising trend by our mathematical model, which shows that feces slide along the large intestine by a layer of mucus, similar to a sled sliding down a chute. Larger animals have not only more feces but also thicker mucus layers, which facilitate their ejection. Our model accounts for the shorter and longer defecation times associated with diarrhea and constipation, respectively. This study may support clinicians use of non-invasive procedures such as defecation time in the diagnoses of ailments of the digestive system.

Measurement of Gastrointestinal and Colonic Motor Functions in Humans and Animals

Accurately measuring the complex motor behaviors of the gastrointestinal tract has tremendous value for the understanding, diagnosis and treatment of digestive diseases. This review synthesizes the literature regarding current tests that are used in both humans and animals. There remains further opportunity to enhance such tests, especially when such tests are able to provide value in both the preclinical and the clinical settings.

Effect of systemic lidocaine on visceral and somatic nociception in conscious horses

REASONS FOR PERFORMING STUDY

Commonly used analgesics (nonsteroidal anti-inflammatory agents, opioids and alpha2-agonists) have unwanted side effects. An effective alternative with minimal adverse effects would benefit clinical equine pain management.

OBJECTIVES

To compare the effect of lidocaine or saline on duodenal and rectal distension threshold pressure and somatic thermal threshold in conscious mature horses.

HYPOTHESIS

Systemically administered lidocaine would increase somatic and visceral nociceptive thresholds.

METHODS

Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min for 2 h) or saline was administered to 6 horses each carrying a permanently implanted gastric cannula, in a randomised, blinded cross-over design. Thermal threshold was measured using a probe containing a heater element placed over the withers which supplied heat until the horse responded. A barostatically controlled intraduodenal balloon was distended until a discomfort response was obtained. A rectal balloon was inflated until extruded or signs of discomfort noted.

RESULTS

Thermal threshold was increased significantly 30 and 90 mins after the start of lidocaine infusion. There was no change in duodenal distension pressure and a small but clinically insignificant change in colorectal distension pressure in the lidocaine group.

CONCLUSIONS

At the dose used, systemically administered lidocaine produced thermal antinociception but minimal changes in visceral nociception.

POTENTIAL RELEVANCE

At these doses, lidocaine may play a role in somatic analgesia in horses.

Effect of detomidine on visceral and somatic nociception and duodenal motility in conscious adult horses

OBJECTIVE

To evaluate the effects of detomidine on visceral and somatic nociception, heart and respiratory rates, sedation, and duodenal motility and to correlate these effects with serum detomidine concentrations.

STUDY DESIGN

Nonrandomized, experimental trial.

ANIMALS

Five adult horses, each with a permanent gastric cannula weighing 534 +/- 46 kg.

METHODS

Visceral nociception was evaluated by colorectal (CRD) and duodenal distension (DD). The duodenal balloon was used to assess motility. Somatic nociception was assessed via thermal threshold (TT). Nose-to-ground (NTG) height was used as a measure of sedation. Serum was collected for pharmacokinetic analysis. Detomidine (10 or 20 microg kg(-1)) was administered intravenously. Data were analyzed by means of a three-factor anova with fixed factors of treatment and time and random factor of horse. When a significant time x treatment interaction was detected, differences were compared with a simple t-test or Bonferroni t-test. Significance was set at p < 0.05.

RESULTS

Detomidine produced a significant, dose-dependent decrease in NTG height, heart rate, and skin temperature and a significant, nondose-dependent decrease in respiratory rate. Colorectal distension threshold was significantly increased with 10 microg kg(-1) for 15 minutes and for at least 165 minutes with 20 microg kg(-1). Duodenal distension threshold was significantly increased at 15 minutes for the 20 microg kg(-1) dose. A significant change in TT was not observed at either dose. A marked, immediate decrease in amplitude of duodenal contractions followed detomidine administration at both doses for 50 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Detomidine caused a longer period of visceral anti-nociception as determined by CRD but a shorter period of anti-nociception as determined by DD than has been previously reported. The lack of somatic anti-nociception as determined by TT testing may be related to the marked decrease in skin temperature, likely caused by peripheral vasoconstriction and the low temperature cut-off of the testing device.