ZOZZARO, P.E.; CARR, J.A.: Peripheral Administration of Ovine Corticotropin-releasing Hormone Activates the Sympathetic Nervous System in Toads.

Corticotropin-releasing hormone (CRH) plays a key role in the regulation of stress and arousal associated behaviors in mammals, and contributes to hyperglycemia and activation of the sympathetic nervous system (SNS) during stress. Work in mammals suggests that the effects of CRH on SNS activity are mediated via receptors in the central nervous system. Whether CRH regulates SNS activity in nonmammals has not been well studied. Here we report that dorsal lymph sac (DLS) administration of ovine CRH (oCRH) activates the SNS in the Texas toad, Bufo speciosus. Percent increase in pupil diameter was used as an indirect measure of SNS activity. Isoproterenol, a beta-adrenergic receptor agonist, increased pupil diameter in a dose-related fashion after DLS injection. The effects of isoproterenol were blocked by the beta-adrenergic receptor antagonist propranolol. DLS administration of oCRH also increased pupil diameter in a dose- and time-dependent manner, with a maximal effect occurring within 30 min after administration. The effects of oCRH were entirely blocked by propranolol. We conclude that percent change in pupil diameter can be used as a convenient and non-invasive marker of SNS activation in toads and is sensitive enough to detect SNS activation after peripheral administration of oCRH. (Supported in part by a Howard Hughes Medical Institute grant through the Undergraduate Biological Sciences Education Program to TTU).