Decreased depressor response mediated by calcitonin gene-related peptide (CGRP)-containing vasodilator nerves to spinal cord stimulation and levels of CGRP mRNA of the dorsal root ganglia in spontaneously hypertensive rats

The depressor response to electrical stimulation of the spinal cord and the level of calcitonin gene-related peptide (CGRP) mRNA in the dorsal root ganglion (DRG) in the spontaneously hypertensive rat (SHR) was compared with the normotensive Wistar Kyoto rat (WKY) and Wistar rat (WR). The animals were pithed by inserting a stainless-steel rod into the spinal cord. Pithed rats were treated with hexamethonium (2 mg/kg/min i.v.) to block autonomic outflow, and mean arterial blood pressure (MBP) was maintained at approximately 100 mmHg with continuous infusion of methoxamine (10 to 15 μg/kg/min i.v.). Electrical stimulation (2 and 4 Hz for 30 s) of the lower thoracic spinal cord (T9-12) via the pithing rod caused a frequency-dependent depressor response without a change in heart rate. The depressor response to spinal cord stimulation was significantly smaller in SHR than in WKY and WR. Long-term treatment of 8 week-old SHR with captopril (0.1% in drinking water) for 7 weeks restored the reduced depressor response to spinal cord stimulation. The level of CGRP mRNA in DRG of SHR was significantly lower than that in WKY. These results suggest that the function of CGRP-containing nerves from the spinal cord decreases in SHR and captopril treatment prevents its reduction.