Abstract
Background: The changes in histological picture of gut during the post-natal period are an important factor that may be responsible for changes in gut motility during the developmental process.

Aims and Objectives: Histology of large gut is poorly understood, especially that of neonate. Therefore, the present study was undertaken to assess and confirm the histological differences in the neuronal and longitudinal muscle layers of colon and rectum of adult and neonate rats.

Materials and Methods: In the present study, isolated large gut segments (colon and rectum) from adult and neonate albino rats (4 to 6 months) were used to examine the histological differences using hematoxylin and eosin staining.

Results: The number of ganglion cells in the longitudinal muscle layer of adult colon was 16.31 ± 3.81 cells/mm2 and 8.86 ± 1.79 cells/mm2 in the rectum. In case of neonate, number of ganglion cells in the colon was 10.46 ± 1.82 cells/mm2 and in the rectum 13.85 ± 2.82 cells/mm2. Thus, no significant difference was observed in the number of ganglion cells in the colon and rectum of adult or neonate rat. Further, it was observed that the thickness of longitudinal muscle layer in adult rectum was more (108.75 ± 5.91 µm) as compared to colon (70 ± 16.83 µm). However, there was no difference in the thickness of colon (30 ± 2.89 µm) and rectum (27.5 ± 2.50 µm) neonates. Our data also indicated that the thickness of longitudinal muscle layer in colon and rectum increases with age.

Conclusion: It may be concluded that number of ganglion cells in colon and rectum does not increase with age. However, thickness of smooth muscle in both colon and rectum, increase over time from neonate to adulthood and may have some relation with the contractile characteristics of colon and rectum. Increased thickness of smooth muscle in adult rectum as compared to colon may be implicated for more contractile force required in the rectum of adult rats for evacuation of fecal matter in rats.