Impairment of Retrograde Neuronal Transport in Cardiac Vagal Motoneurons in Streptozotocin-Induced Diabetic Rats: A Wheat Ger Agglutinin-Horseradish Peroxidase Neurohistochemical study

Central projections of vagal motoneurons to the heart were studied in diabetic rats using Wheat germ Agglutinin-Horseradish peroxidase (WGA-HRP). Experimental rats were rendered diabetic by intraperitoneal injection of streptozotocin in citrate buffer. The diabetic rats were maintained in a stable diabetic state by daily injection of insulin for 24 weeks. Age-matched control rats were injected intraperitoneally with citrate buffer not containing streptozotocin. Control rats were also kept alive for 24 weeks after citrate buffer injection. At the end of 24 weeks the two groups were prepared for injection with WGA-HRP. Following anesthesia with sodium pentobarbitone, thoracotomy was performed on the left aspect of the thorax to expose the heart. The atrial and ventricular walls were then injected with 5% WGA-HRP by multiple intramuscular penetrations. Experimental and control rats were sacrificed 72 h after tracer injection by transcardial perfusion first with normal saline followed by fixative and then buffered sucrose. Transverse serial frozen sections of the brainstem were then taken and processed for WGA-HRP neurohistochemistry and analyzed under light and dark-field microscopy. Analysis of the sections taken from diabetic rats revealed fewer WGA-HRP labeled neurons in the nucleus ambiguus (nA) than sections taken from control rats. Sporadic labeling of the dorsal motor nucleus of the vagus nerve was observed in control rat but not in the diabetic rats. It was concluded that the depletion of labeled neurons in the diabetic rats compared with the normoglycaemic rats is indicative of impairment of retrograde neuronal transport of WGAHRP in chronic diabetic state.