The superior colliculus (SC) is a visuomotor center involved in the autonomic reflex adjustments of eye movements in response to visual stimuli. Diabetes mellitus (DM) is known to affect some visual pathway structures, but few studies have assessed the effects of diabetes on the SC. The aim of this study was to investigate the ultrastructural changes of SC neurons in the early period of streptozotocin (STZ)-induced diabetes. The ultrastructure was assessed by transmission electron microscopy (TEM). Twenty male Sprague–Dawley rats were divided into two groups (n=10 per group) and were intraperitoneally injected with either STZ (60 mg/kg) in citrate buffer (pH 4.5) to induce DM or with buffer alone as a positive control. The rats were sacrificed 4 weeks after injection and the SC was processed for TEM. Most of the SC neurons in the DM group exhibited either chromatolysis or pyknosis. Chromatolytic neurons had an enlarged nucleus with some chromatin clumping and disruption of the cell membrane. These neurons also exhibited mitochondrial enlargement with rupture of the cristae, distended Golgi complexes and rough endoplasmic reticulum, and numerous secondary lysosomes. By contrast, the pyknotic neurons in the DM group exhibited severe chromatic condensation and dark electron-dense structures in the cytoplasm. The organelles were smaller and had an irregular outline. The neuropil of DM rats had coarse, irregular, swollen dendrites and axons, together with demyelination. In conclusion, this study has provided clear evidence of ultrastructural degeneration in the SC of STZ-induced DM rats. These ultrastructural changes might contribute to the impairments of autonomic eye movement, optokinetic and vestibulo-ocular reflexes, and vision-related learning and memory in patients with DM.
Key words: Superior colliculus, diabetes mellitus, streptozotocin.