Male Sprague-Dawley rats were injected with 55 mg/kg streptozotocin (STZ) (DM group) or with citrate buffer (control). After 2 weeks, 2 months, 6 months and 12 months, sections of their hearts were analyzed in five areas鈥攍eft ventricle, interventricular septum, right ventricle, anterior and posterior wall. Nerve fibers were visualized immunohistochemically, using antibody against a general neuronal marker, protein gene product 9.5 (PGP 9.5).
Significant increase in total nerve fibers from all heart areas was observed 2 weeks and 2 months after diabetes induction, followed by a decrease at 6 months and again increase at 12 months was observed in both control and diabetic rats. Significant difference between control and diabetic rats was visible after 2 weeks and 2 months, with diabetic rats exhibiting significantly more nerve fibers. There were no consistent differences in quantity of nerve fibers in different areas of the heart within a particular age-related group of animals.
In conclusion, cardiac innervation undergoes dynamic changes both in control and in diabetic rats, with a time-dependent significant increase in neuronal fiber density in diabetic animals. This novel information may contribute to our understanding of pathophysiological changes associated with diabetic cardiac neuropathy.