Sex, sensitivity, and second messengers: differential effect of cyclic nucleotide mediated inhibition in the chemosensory system of fiddler crabs.

Fiddler crabs (Uca spp.) exhibit sex-specific responses food-related chemical cues, constituting a natural experiment regarding the regulation of chemosensitivity. To understand the mechanisms that underlie these broad differences, chemosensory neurons from the claws were challenged with stimulants in the presence of various agents that activate or inhibit the adenylate cyclase-cAMP transduction cascade. Stimulants mixed with agents that increase intracellular cAMP (forskolin, 3-isobutyl-1-methylxanthine, and Ro 20-1724) elicited decreased response magnitudes from neurons, compared to drug-free controls, whereas the adenylate cyclase inhibitor SQ 22536 increased the response. These effects were dose dependent and reversible, and, in all cases, were more dramatic in male than in female neurons. Similar to other crustaceans, the adenylate cyclase-cAMP second-messenger system appears to regulate inhibition in fiddler crab chemosensory neurons. The perturbations of this pathway reveal that the degree of inhibition is greater in male than in female neurons, consistent with the lower behavioral and physiological sensitivity typically displayed by males. Changes in the expression of the second messenger system may be causal in the production of sex-specific patterns of chemosensitivity that underlie behavior. Alternately, experimental perturbations using adenylate cyclase-cAMP pathway modulators may unmask sex-specific differences in electrical properties of peripheral neurons affecting action potential generation.