Salt sensitivity and hydration behavior of the toad, Bufo marinus

Area of Science:

• Amphibian physiology
• Sensory biology
• Osmoregulation

Background:

• Toads rely on skin for water absorption, but the sensory mechanisms involved are not fully understood.
• The toad's ventral skin plays a role in evaluating hydration sources before water absorption.
• Dehydration significantly alters toad behavior in response to hydration sources.

Purpose of the Study:

• To investigate the sensory function of epithelial sodium channels in toad skin.
• To determine how toads differentiate between water and varying salt concentrations (NaCl, KCl).
• To understand the behavioral and neural responses of toads to osmotic challenges.

Main Methods:

• Behavioral observations of toads (Bufo marinus) on surfaces with water or hyperosmotic solutions (250/500 mM NaCl/KCl).
• Recording neural activity from spinal nerve #6 during skin perfusion with salt solutions.
• Administering amiloride to assess the role of epithelial sodium channels in sensory perception and behavior.

Main Results:

• Toads exhibit distinct 'seat patch down' (SPD) and 'water absorption response' (WR) behaviors to evaluate hydration.
• Dehydrated toads show altered SPD and WR behaviors compared to hydrated toads.
• Neural activity increases with 250 mM NaCl/KCl, with a stronger response to KCl; amiloride inhibits this neural response and increases WR behavior.

Conclusions:

• Epithelial sodium channels in toad skin possess a sensory function, aiding in the evaluation of hydration sources.
• Toads demonstrate a lower tolerance for potassium (K+) salts compared to sodium (Na+) salts.
• The sensory input from the skin influences both behavior and neural activity, guiding water absorption responses.