Histo-architectural Comparative Analysis of the Hypothalamus of Bat (Eidolon helvum) and Wistar Rat (Rattus norvegicus)

Abstract

Aims: The aim of this study was to compare the histo-architectural variation (if any) on hypothalamus of both Rat (Rattus norvegicus) and Bat (Eidolon helvum). Study Design:  The histological and histochemical investigations into the hypothalamus of two mammalian species were studied, to determine the possible differences in their thermoregulatory activities. Methodology: Six (6) rats and six (6) bats were used for this study, the animals were sacrificed under chloroform anaesthesia, after which the skulls of these animals were opened using bone forceps to expose the brains. The hypothalamus were excised from each brain and homogenized to determine the activities of lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PDH), acid phosphatase (ACP) and alkaline phosphatase (ALP). The tissue sample of hypothalamus for histological studies were fixed in 10% formol calcium and processed for paraffin wax embedding. Serial sections of 5 μm thickness were stained with Hematoxylin & Eosin, Cresyl fast violet and Gordon & sweet stains. The stained tissues were studied under the light microscope. Results: The results obtained from the macromorphometric study showed that, there are differences in the body and brain weights of the two mammalian species; bat (275.33±7.49, 3.60±0.09) and rat (193.33±5.30, 2.60±0.08) respectively.  The body weight of bat was observed to be higher than that of rat, and the brain weight of each mammal was found to be directly proportional to its body weight. The histological study showed that, neurones are well distributed in rat compared to bat, while the enzyme activity variables of G-6-PD, LDH and ACP were higher in rat with reliable proportion, except ALP that was found higher in bat (1022.00±0.91) compared to rat (829.75±1.31). This suggested that, the hypothalamus of rat performs more functions of thermoregulation, feeding and circadian rhythm control than bat, since the nuclei of hypothalamus such as; lateral hypothalamic nuleus, arcuate nucleus and suprachiasmatic nucleus control feeding, satiety and circadian rhythm respectively, which could be as a result of differences in their modes of behaviour, habitat and feeding. Conclusion: Considering the histological analysis and the enzyme activity, the hypothalamus of both animals are significantly different, being influenced by feeding and lifestyles.