HISTOLOGICAL AND HISTOCHEMICAL STUDIES ON THE GASTROINTESTINAL TRACT AND ACCESSORY DIGESTIVE GLANDS OF THE GRASSCUTTER (Thryonomys swinderianus)

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Department of Medicine

ABSTRACT
The gastrointestinal (GIT) morphology and the distribution of the different types of mucin secreting cells were investigated in the grasscutter (Thryonomys swinderianus). Previous research studies carried out on the GIT have only focused on the gross morphology and histology, The aim of the study was to provide a comprehensive morphological assessment of the GIT, some accessory digestive glands, identify and characterise the distribution of mucin (neutral and acidic) in the GIT of this rodent. Seven (7), apparently, healthy grasscutters were purchased from a farm in Zaria. The animals were anaesthesised and sacrificed, with the stomach, small and large intestines, liver, pancreas and gall bladder dissected. The weight, shape and length of the accessory digestive glands, stomach, small and large intestines were taken. The organs were fixed in neutral buffered formalin and routinely processed for histological and histochemical studies. Histomorphological characteristics of the different parts of the GIT and accessory digestive glands were studied using Hematoxylin and Eosin staining technique. Histochemical staining methods were used to detect and distinguish between neutral and acidic mucins using Alcian Blue (AB), Periodic Acid Schiff (PAS) and Alcian Blue and Periodic Acid Schiff combined (AB-PAS) techniques while PAS with diastase control technique was used to study the histochemistry of the liver. The result of the macroscopic observations in the stomach revealed three distinct parts; the cardia, fundus and pylorus, while the small intestine also revealed three regions, namely; the duodenum, the jejunum and the ileum. The large intestine revealed three distinct regions; the caecum, the colon and the rectum. The result of the morphometric studies showed sexual dimorphism with male values higher in most of the parameters measured than in the females. The body weight of 1582.25 ± 207.95g was recorded in the males and 1089.67 ± 276.93g in the females. The mean GIT length in the males was 253.13 ± 10.68cm and 243.63 ± 6.73cm in the females. The mean liver weight of 45.65 ± 3.20g and 37.43 ± 5.84g were recorded in the males and the females respectively. The result of the microscopic observations of the GIT and the gall bladder of the grasscutter revealed simple columnar epithelial cells across all the regions while intestinal glands were observed for the secretion of mucus and in the stomach, glands were observed for the secretion of mucus and gastric juice. The liver cells (hepatocytes) were closely packed and arranged from a diffuse to radial pattern. The pancreas was made up of lightly stained pancreatic islands (islets of Langerhans) and darkly stained serous acinar cells. The result of the histochemical studies revealed the presence of acid and neutral mucins across the segments of the gastrointestinal tract with the stomach positive for only neutral mucins while the small and large intestines were positive for both acid and neutral mucins. The acid mucins were dominant across the regions of the intestines. Histochemical studies of the liver revealed PAS positive hepatocytes which suggested the presence of glycogen deposits within their cytoplasm. In conclusion, the grasscutter showed a unique pattern in the distribution of acid and neutral mucins across the GIT which could be as a result of difference in the quality of biofilm required in the various segments of the GIT. This not too far from what is seen in the Wistar rats except for the total absence of acidic mucins in the stomach.