Submitted on April 8, 2003
Accepted on August 11, 2003
Cocaine- and amphetamine-regulated transcript peptideattenuates phenylephrine-induced bradycardia in anesthetized rats
Phouangmala Scruggs1, Siok L Dun1, and Nae J Dun1*
1 Department of Pharmacology, East Tennessee State University, Johnson City, TN, USA
* To whom correspondence should be addressed. E-mail: dunnae{at}mail.etsu.edu.
The present study was undertaken to investigate the origin of cocaine- and amphetamine-regulated transcript peptide immunoreactive (irCART) fibers observed in the nucleus of the solitary tract (NTS) and assess the role of CART peptide on phenylephrine-induced baroreflex. Immunohistochemical and retrograde tract-tracing studies showed that some of the irCART-fibers observed in the NTS may have their cell bodies in the nodose ganglia. In urethane-anesthetized rats, intracisternal or bilateral intra-NTS microinjection of the CART peptide fragment 55-102 (0.1- 3 nmol), referred to herein as CARTp, consistently and dose-dependently attenuated phenylephrine (PE)-induced bradycardia. CARTp, in the doses used here, caused no significant changes of resting blood pressure or heart rate. Bilateral intra-NTS injections of CART-antibody (1:500) potentiated PE-induced bradycardia. Injections of saline, normal rabbit serum, or concomitant injection of CARTp and CART-antiserum into the NTS caused no significant changes of PE-induced baroreflex. The result suggests that endogenously released CARTp from primary afferents or exogenously administered CARTp modulates phenylephrine-induced baroreflex.
