Comparative Histological Studies of the Esophagus Wall of Oryctolagus cuniculus Rabbit Adult, Young and Lactating Using Light Microscope

Background: As the different parts of the alimentary canal, the esophagus is an important part of it, because it facilitate the passage of food material to the stomach. The purpose of this study was to compare the structure of the esophageal wall of rabbit before weaning (lactating) and after weaning (young and adult) to determine the structural changes that accompany the changes of the feeding pattern from lactating to adult.


Introduction
Many previous authors describe the digestive organs l of other mammals such as Egyptian bats in which showed some differences between them [1,2].
In vertebrate animals the secretion from the gastrointestinal wall contains mucoid substances [3][4][5][6][7][8][9]. The histological structure of the esophagus rabbit and guinea pig incomplete. Therefore, the present study was concentrated on rabbit and rat with different stages. The esophagus wall has four layers from inside to outside (mucosa, submucosa, muscularis and serosa). The mucosa is composed of three layers, the stratified squamous epithelium, a lamina propria and a lamina muscularis. The keratinization is different in different mammals in pig and in ruminants.
In African Giant Rats (AGRs), the epithelial lining of the esophagus was non keratinized stratified squamous cells. The mucous glands were absent. Give with Alcian Blue (AB), Periodic Acid Schiff (PAS) and Alcian Blue-Periodic Acid Schiff (ABPAS) negative [10].
The present work aims to illustrate the differences in the histological structure of the esophagus wall of rabbit through lactating and after weaning by the use of light microscope.

Animals
Fifteen animals of Oryctolagus cuniculus collected alive from Abu-Rawash, Giza Governorate. Five animals were lactating and depend only on suckling milk from their mothers average weighs were 257 g. five animals were after weaning but before maturity feed on different kinds of food and had free access to water. Their weighs were about 1.0 kg. Five adult animals also were procured also feed on different kinds of food and had free access to water. Their weighs average was 1.99 kg.

Histological examination
Animals were anesthesied and esophagus of adult, Young, and lactating animals were removed. The esophagus were fixed in 10% neutral buffered formalin for 24 h. Dehydrated in ascending grades of ethyl alcohol, cleared by xylene and embedded in paraffin. Sections of 5 lm thickness were mounted and stained with Haematoxylin and Eosin method [11].

Statistical analysis
Statistical presentation and analysis of the present study was conducted, using below.
is the sum of squares of the difference between each observation (X) and the mean value of all observations(X) Standard student "t test": test of significance of the difference between two means: The calculated "t" was compared with tabulated one at different levels of significance at the degree of freedom (DF): Where: X=The mean value of group L, X 2=The mean value of group II.
SD1=The standard deviation of group I. SD2=The standard deviation of group II. n1=the number of observations of group L, n2=The number of observations of group II.

Analysis of variance [ANOVA] tests:
According to the computer program SPSS for Windows. ANOVA test was used for comparison among different times in the same group in quantitative data.

Morphometric study
The esophageal length of rabbit was in lactating 3.62 ± 0.97 cm, in Young 6.97 ± 0.46 cm and in adult 8.19 ± 0.26 cm (Table 1).

Microscopic study
Histolgogically, the esophageal wall is composed of mucosa, sub mucosa, muscularis and serosa. The mucosa characterized with a nonkeratinized squamous.

Lactating rabbit
The esophageal wall composed of serosa of loose connective tissue, the muscularis of three layers (outer longitudinal muscle layermiddle circular muscle layer-inner longitudinal), sub mucosa of loose connective tissue (Lamina propria) and the mucosa of non-keratinized squamous epithelium. All the above layers were poorly developed by using hematoxylin and eosin stain (Figure 1). By using Periodic acid Schiff reagent for mucus secretion, we observed that the muscular layer give strong purple color reaction, weak reaction with inner layer of mucosa and very weak reaction with lamina propria (Figure 2). With azan stain the lamina propria react with aniline blue give weak reaction but the muscular layer react with azocamine and give moderate reaction (Figure 3).

Young rabbit
The esophog wall composed of serosa of loose connective tissue, the muscularis three layers (outer longitudinal muscle layer and the inner longitudineal) more thickness than lactating rabbit, submucosa of loose connective tissue (Lamina propria) containing blood vessels and nerve ending, thin muscularis mucosa and mucosa of nonkeratinized squamous epithelium more thickness than lactating rabbit. The entire above developed layer give moderately. All the above layers were developed by using hematoxylin and eosin stain (Figure 4). By using Periodic acid Schiff reagent for mucus secretion, we observed that the muscular layer give negative reaction, very weak reaction with inner layer of mucosa and very weak also reaction with lamina propria ( Figure 5). With azan stain the lamina propria react with aniline blue give negative reaction but the muscular layer react with azocamine and give moderate reaction ( Figure 6).

Adult rabbit
The esophageal wall composed of serosa of loose connective tissue, the muscularis three layers (outer longitudinal muscle layer and the inner longitudineal ) more thickness than young rabbit, submucosa of loose connective tissue (Lamina propria), thin muscularis mucosa and mucosa of non-keratinized squauamous epithelium more thickness than young rabbit. All the above layers were well developed by using hematoxylin and eosin stain (Figure 7). By using Periodic acid Schiff reagent for mucus secretion, we observed that the muscular layer give poor reaction, strong reaction with inner layer of mucosa and moderate reaction with lamina propria (Figure 8). With azan stain the lamina propria react with aniline blue give negative reaction but the muscular layer react with azocamine and give moderate reaction (Figures 9 and 10).

Discussion
The esophagus is the first part of the alimentary canal and was divided into the cervical, thoracic and abdominal portions. As observed for rabbit [13]. However, Rudolf and Strombery [14] noticed that the esophagus of the rat deviated slightly to the left around the cervical region.
The inner wall of the esophagus in the present animals show non keratinized stratified squamous epithelium as the same observed of the African Giant Rat [8] (Cricetomys gambianus-Waterhouse, 1840) [10,15].
The esophagus is important organ [16] for passage of food from the mouth to the stomach. The present animals (Rabbit -herbivorous needs this mucous to increase the viscosity of the esophagus which is important allowing the passage of large food. The mucous barrier is also an important factor in the protection of the esophagus from damage. In the lactating rabbit the mucus which secreted from the mucosal layer