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The toad iris assay: a simple method for evaluating CRH action on the sympathetic nervous system
James A Carr1, Paula E Zozzaro
1Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA. james.carr@ttu.edu
General and Comparative Endocrinology
|December 4, 2003
Summary
Corticotropin-releasing hormone (CRH) activates the sympathetic nervous system (SNS) in Texas toads, as shown by pupillary dilation. This study demonstrates CRH
Area of Science:
- Comparative physiology
- Neuroendocrinology
- Amphibian research
Background:
- Corticotropin-releasing hormone (CRH) is vital for stress responses in mammals.
- Its role in regulating sympathetic nervous system (SNS) activity in nonmammals is less understood.
Purpose of the Study:
- To investigate the effect of ovine CRH (oCRH) on SNS activity in the Texas toad (Bufo speciosus).
- To validate the toad iris assay for assessing CRH receptor regulation of the SNS.
Main Methods:
- Utilized the toad iris assay to measure pupillary dilatation in response to oCRH.
- Administered oCRH and measured changes in pupillary size, plasma norepinephrine, and effects of receptor antagonists/agonists.
- Investigated the role of the pituitary by performing hypophysectomy.
Main Results:
- oCRH administration led to dose- and time-dependent increases in pupillary dilatation.
- CRH-induced effects were blocked by a CRH-receptor antagonist and associated with elevated norepinephrine.
- Beta-adrenergic pathways mediated the pupillary response, as shown by isoproterenol and propranolol effects.
Conclusions:
- The toad iris assay effectively assesses CRH receptor regulation of the SNS in amphibians.
- CRH influences SNS activity in nonmammals, similar to its role in mammals.
- This study provides a model for studying CRH-SNS interactions across vertebrates.