Muscle thickness and neuron density in the caecum of horses with chronic recurrent caecal impaction

Abstract

Summary In this study, the hypothesis that caecal smooth muscle layers would be thinner and the linear neuron density of myenteric plexus greater was tested in normal horses compared to those with chronic recurrent caecal impaction. Four normal horses and 18 horses with chronic recurrent caecal impaction were subjected to euthanasia and 7 tissue samples were collected from each horse at different regions of the caecum (apex, dorsal body, cranial base, dorsal base, caudal base, caudal body, ventral body). Twelve horses with chronic recurrent caecal impaction were treated surgically. Only one tissue sample of the cranial part of the caecal base close to the caecocolic orifice was taken during surgery. The thickness of the circular muscle layer of all caecal regions measured in killed horses with chronic recurrent caecal impaction was significantly increased compared to the equivalent caecal region of normal horses. On the other hand, the longitudinal muscle layer was significantly thicker only in the cranial and caudal caecal base and in the dorsal region of the caecal body. The linear neuron densities of all caecal base areas and 2 caecal body regions, the caudal body region and of the apex, of killed horses with chronic recurrent caecal impaction were significantly lower compared with those in clinically normal horses. The circular muscle layer of all caecal regions was thickened (hypertrophied) probably as a consequence of chronic uncoordinated hypercontractility due to neuron deficit in the myenteric plexus of the caecal base.

Expression of PGP 9.5 by Enteric Neurons in Horses and Donkeys with and without Intestinal Disease

“…If the change observed is primary, it does beg the question as to whether certain animals are predisposed to developing signs of colic and ileus because of this characteristic. As mentioned above, it has been suggested that the reduction in enteric neurons in horses with chronic large intestinal lesions may be a predisposing cause of colic in these animals (Schusser and White, 1997;Schusser et al, 2000). Conversely, in the horse study of Pavone et al (2012), it was suggested that the enteric nervous system and ICC changes observed may have been secondary to the colic episodes.…”

“…However, there were two horses with a large colon obstructive disorder (left and right large colon displacement, respectively) that did have a marked reduction in PGP 9.5 immunoreactivity. Interestingly, one of these horses had a history of previous colic episodes including surgery (for the same lesion, a right large colon displacement) and it seems reasonable to speculate that this could be part of the disease process as proposed by Schusser et al (2000). These two horses also had a significant reduction in ICC density that could also have contributed to the motility problems.…”

“…Two previous studies have demonstrated a significant reduction in myenteric neuronal densities in horses with chronic obstructive disorders of the caecum and large colon (Schusser and White, 1997;Schusser et al, 2000). These investigators proposed that the changes observed were linked to the intestinal motility disorders of these animals (Schusser and White, 1997;Schusser et al, 2000).…”

“…These syndromes may be linked to alterations in the motility control systems, namely the enteric nervous system, the interstitial cells of Cajal (ICC) and the intestinal smooth muscle. Horses with chronic obstructive disorders of the large colon or recurrent caecal impactions have been shown to have reduced densities of neurons in the large colon or caecum (Schusser and White, 1997;Schusser et al, 2000). Additionally, a reduction in ICC density has been demonstrated in the pelvic flexure of horses with large intestinal obstructive disorders, suggesting a possible involvement of ICC in equine intestinal dysmotility (Fintl et al, 2004).…”

Idiopathic Fibrosis of the Tunica Muscularis of the Large Intestine in Five Horses with Colic

“…There are, however, reports of neuropathies associated with intestinal dysfunction in horses, including equine grass sickness (Scholes et al, 1993;Cottrell et al, 1999), impactions, displacements and volvulus/torsion of the large colon (Schusser et al, 1997) and chronic recurrent caecal impaction (Schusser et al, 2000).…”