Submitted on December 12, 2008
Revised on March 11, 2009
Accepted on March 11, 2009
Paraplegia Increased Cardiac NGF Content, Sympathetic Tonus and the Susceptibility to Ischemia-Induced Ventricular Tachycardia in Conscious Rats
Heidi L. Lujan1, Ying Chen1, and Stephen E. DiCarlo1*
1 Wayne State University School of Medicine
* To whom correspondence should be addressed. E-mail: sdicarlo{at}med.wayne.edu.
Mid-thoracic spinal cord injury is associated with ventricular arrhythmias that are mediated, in part, by enhanced cardiac sympathetic activity. Furthermore, it is well known that sympathetic neurons have a lifelong requirement for nerve growth factor (NGF). NGF is a neurotrophin that supports the survival and differentiation of sympathetic neurons and enhances target innervation. Therefore, we tested the hypothesis that paraplegia is associated with an increased cardiac NGF content, sympathetic tonus and susceptibility to ischemia-induced ventricular tachyarrhythmias. Intact and paraplegic (6-9 weeks post transection, T5X) rats were instrumented with a radio-telemetry device for recording arterial pressure, temperature and ECG and a snare was placed around the left main coronary artery. Following recovery, the susceptibility to ventricular arrhythmias (coronary artery occlusion) was determined in intact and paraplegic rats. In additional groups of matched intact and paraplegic rats, cardiac nerve growth factor content (ELISA), and cardiac sympathetic tonus were determined. Paraplegia, compared to intact, increased cardiac nerve growth factor content (2146 ± 286 pg/ml vs 180 ± 36 pg/ml, P<0.05), cardiac sympathetic tonus (154 ± 4 vs 68 ± 4 bpm, P<0.05), and decreased the ventricular arrhythmia threshold (3.6 ± 0.2 min vs 4.9 ± 0.2 min, P<0.05). Thus, altered autonomic behavior increases the susceptibility to ventricular arrhythmias in paraplegic rats.
