Effects of Ageing and Alloxan- Induced Diabetes Mellitus on the Structure of Inferior Colliculus in male Albino Rats: a Light and Electron Microscopic Study

Background: The inferior colliculus (IC) is an important relay centre in the acoustic pathway that can influence the motor neurons in the brain stem and spinal cord. Aim of the Work: This research was conducted to study the structural changes in the inferior colliculus of the senile and adult diabetic male albino rats compared to the adult control one using both the light and transmission electron microscopy. Material and Methods: A total of 30 male albino rats were divided into 3 equal groups including adult (3 - 4 months) and senile (24 months), adult diabetic (3 - 4 months) rats. To induce diabetes, a single dose of alloxan (200mg/kg body weight) dissolved in distilled water was injected intraperitoneally. Two months later, the animals of all groups were anaesthetized with ether and sacrificed, followed by removal of the inferior colliculi, which were processed for microscopic examination. Results: The histological examination of the inferior colliculus in adult control rats revealed that the nerve processes were relatively abundant than the neuronal somata. The nerve fibers were myelinated, arranged in clusters, and the majority had thick, uniform and regular myelin sheath. The inferior colliculus was constituted of a superficial cortex and a deep central part. The nerve cells in the cortex were few in number and rounded in shape. In the center, many cells of different sizes which exhibited unipolar, bipolar or multipolar processes were observed. In the senile rats, variable degrees of degeneration were observed in both the nerve cells and fibers. The nerve cells were either appeared swollen or showed small size with dense cytoplasm and dark pyknotic nuclei. The myelinated nerve fibers showed thickened myelin sheaths, disrupted sheaths, separation of their lamellae and sometimes showed shrunken degenerated nerve axon. In diabetic rats, most of the neuronal somata appeared small in size with small, dark and pyknotic nuclei. The neuropil showed extensive vacuolation and congested blood vessels with thickened basement membrane. Thin myelinated and unmyelinated nerve fibers were observed with vacuolated cytoplasmic matrix. Silverstained sections showed irregular-shaped thin nerve fibers. Conclusions: Diabetic state induced severe degenerative changes in the inferior colliculus, which were worse than those detected in the senile rats. Such changes may contribute in hearing loss of the young diabetics. So, the auditory health and early clinical testing of the diabetics are highly important for early prevention of deleterious complications of diabetes