Steroids modulate the excitability of crayfish (Procambarus digueti) photoreceptors: long- and short-term actions

Short- and long-term actions of the steroids corticosterone, progesterone, and ecdysterone were analyzed upon excitability of crayfish retinular cells. The three hormones showed short-term actions, particularly during photoreceptor dark adaptation; effects were found to be dependent on the hour of the day. Corticosterone and progesterone had similar effects, i.e., resembled dark-adapted conditions; ecdysterone actions were opposite and resembled light adaptation. Long-term effects were opposed to short-term effects in all cases. Possible mechanisms underlying these effects are discussed.