Effects of streptozotocin diabetes on the ultrastructure of astrocytes in the cervical enlargement of rat spinal cord

A chronic complication of diabetes mellitus (DM), diabetic neuropathy, causes neurodegeneration leading to the development of neuropathic pain and sensation loss, particularly in the hands and arms. The cervical enlargement of the spinal cord sends the nerve supply to the hands and arms. Moreover, astrocytes effectively provide structural and functional maintenance of neurons in the spinal cord. Nevertheless, there is very little research concerning the ultrastructural changes of diabetic spinal astrocytes in the cervical enlargement. Thus, in this study, the ultrastructural changes of protoplasmic and fibrous astrocytes in streptozotocin (STZ)-induced diabetic and control rats using transmission electron microscopy (TEM) were examined and compared. Thirteen male diabetic and six male control rats were intraperitoneally administered with either STZ in citrate buffer or only the buffer solution, respectively. Rats were sacrificed at four (short term) and twenty-four weeks (long term) after induction of DM. Then, the cervical enlargements were collected for TEM processing. Under TEM, the morphologies of protoplasmic and fibrous astrocytes were similarly changed in each group. In the short-term DM model animals, hypertrophic nuclei with heterochromatin clumping were seen in both types of astrocytes. The rough endoplasmic reticulum (rER), Golgi complexes, and mitochondria were distended. Moreover, augmented glial fibrils were seen in astrocytic processes. In the long-term diabetes, increased heterochromatin clumping with severely disrupted nuclear membranes was seen in both types of astrocytes. The rER, Golgi complexes, and mitochondria were extremely degenerated. Disruptions of astrocytic processes were also observed. These results indicate that DM leads to abnormalities of both protoplasmic and fibrous astrocytes, which are possibly involved in the impairment of neuronal function that causes diabetic neuropathy. Thus, this basic knowledge can support better understanding of the pathogenesis in diabetic neuropathy.   Key words: Astrocytes, cervical enlargement, spinal cord, diabetes mellitus, streptozotocin.