Colonic enteric nervous system analysis during parenteral nutrition

Abstract

Introduction: Parenteral nutrition (PN) is a necessary therapy used to feed patients with gastrointestinal dysfunction. Unfortunately, PN results in intestinal atrophy and changes to host immune function. PN may also induce additional effects on gut motility that we hypothesized would result from changes in the enteric nervous system.

Methods: Mice received an intravenous (i.v.) catheter and were randomized to chow (n = 5), i.v. PN (n = 6), or i.v. PN + bombesin (BBS, 15 μg/kg, 3×/d) (n = 6) for 5 d. Colons were removed and dissected to measure the length and circumference. Enteric neuronal density and neurotransmitter expression were determined by co-immunostaining whole-mount tissue with Hu and neuronal nitric oxide synthase (nNOS).

Results: The number of myenteric neurons expressing Hu and nNOS increased per unit length in the mid-colon during PN treatment compared with chow. This increase was abrogated by the addition of BBS to the PN regimen. However, the percentage of nNOS-expressing neurons was not significantly altered by PN. Morphometric analysis revealed a decrease in the length and circumference of the colon during PN administration that was partially normalized by supplementation of PN with BBS. A significant reduction in total fecal output was observed in PN animals compared with chow and was increased by mice receiving BBS in addition to PN.

Conclusions: PN causes a constriction of the bowel wall, reducing not only the length but also the circumference of the colon. These changes cause a condensation of enteric neurons but no difference in neurotransmitter expression. BBS supplementation partially restores the constriction and increases the fecal output during PN treatment compared with PN treatment alone.

Keywords: Bombesin; Enteric nervous system; Motility; Neurotransmitter; Parenteral nutrition; TPN; nNOS.

Figure 1

Schematic representation of the experimental protocol utilized. Mice were catherized IV, allowed two days of ad libitum standard rodent chow before being randomized to Chow, PN or PN+BBS (15μg/kg, TID) for five days.

Figure 2

Increased colonic myenteric neuronal density and number of nNOS expressing cells during PN treatment is abrogated by supplementation of PN with BBS. (A) Immunostaining of the myenteric plexus within the colon of Chow, PN and PN+BBS treated animals with Hu (upper panel), nNOS (middle panel) and Hu/nNOS (lower panel). Scale bar equals 200 μm. (B) Bar graphs showing the neuronal density (mm²), number of nNOS expressing cells (mm²) and the proportion of nNOS cells within the Hu+ population of neurons.

Figure 3

PN reduces the length and circumference of the colon, which is partially restored by the addition of BBS. (A) Length and (B) circumference of the colon (cm) measured in Chow, PN and PN+BBS animals.

Figure 4

Total fecal ouput is reduced during PN treatment compared to Chow and is increased with BBS supplementation of PN. Bar graph showing the total fecal output (gm) measured from Chow, PN and PN+BBS animals.