Abstract
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. Whether CRH regulates SNS activity in nonmammals has not been well studied. Here we used the iris assay to determine the ability of ovine CRH (oCRH) to influence SNS activity in the Texas toad, Bufo speciosus. In the toad iris assay, relaxation of the sphincter pupillae muscles in the iris is determined by measuring treatment-related changes in pupillary dilatation. A single dose of oCRH administered via the dorsal lymph sac increased pupillary dilatation within 30 min after administration. The stimulatory effects of oCRH on pupillary dilatation were dose- and time-dependent, were blocked with the CRH-receptor antagonist α-helical CRH, were associated with elevated plasma norepinephrine, and were not blocked by hypophysectomy. Isoproterenol, a β-adrenergic receptor agonist, increased pupillary dilatation in a dose-related fashion. The effects of isoproterenol and oCRH were blocked by the β-adrenergic receptor antagonist propranolol. We conclude that the toad iris assay is a simple but effective method for assessing CRH receptor regulation of the SNS.
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