Seasonal rhythm of red pigment concentrating hormone in the crayfish

Repeated applications of high potassium elicit long-term changes in a motor circuit from the crab, Cancer borealis

We examined the effects of altered extracellular potassium concentration on the output of the well-studied pyloric circuit in the crab, Cancer borealis. Pyloric neurons initially become quiescent, then recover spiking and bursting activity in high potassium saline (2.5x[K⁺]). These changes in circuit robustness are maintained after the perturbation is removed; pyloric neurons are more robust to subsequent potassium perturbations even after several hours of wash in control saline. Despite this long-term "memory" of the stimulus history, we found no differences in neuronal activity in control saline. The circuit's adaptation is erased by both low potassium saline (0.4x[K⁺]) and direct hyperpolarizing current. Initial sensitivity of PD neurons to high potassium saline also varies seasonally, indicating that changes in robustness may reflect natural changes in circuit states. Thus, perturbation, followed by recovery of normal activity, can hide cryptic changes in neuronal properties that are only revealed by subsequent challenges.

Neuronal correlates of the visually elicited escape response of the crab Chasmagnathus upon seasonal variations, stimuli changes and perceptual alterations

When confronted with predators, animals are forced to take crucial decisions such as the timing and manner of escape. In the case of the crab Chasmagnathus, cumulative evidence suggests that the escape response to a visual danger stimulus (VDS) can be accounted for by the response of a group of lobula giant (LG) neurons. To further investigate this hypothesis, we examined the relationship between behavioral and neuronal activities within a variety of experimental conditions that affected the level of escape. The intensity of the escape response to VDS was influenced by seasonal variations, changes in stimulus features, and whether the crab perceived stimuli monocularly or binocularly. These experimental conditions consistently affected the response of LG neurons in a way that closely matched the effects observed at the behavioral level. In other words, the intensity of the stimulus-elicited spike activity of LG neurons faithfully reflected the intensity of the escape response. These results support the idea that the LG neurons from the lobula of crabs are deeply involved in the decision for escaping from VDS.

Circadian oscillations of RPCH gene expression in the eyestalk of the crayfish Cherax quadricarinatus

The RPCH and beta-actin cDNAs from the crayfish Cherax quadricarinatus were amplified, cloned and sequenced. The primary structure sequences of these cDNAs were compared to other members of the AKH/RPCH family. Fluctuations in the amount of the C. quadricarinatus RPCH and beta-actin mRNAs, as cDNAs, were quantified every 3h by RT-PCR. Single cosinor analysis supports the notion of beta-actin and RPCH mRNA circadian behavior in animals subjected to 12h:12h light/dark regimes. In constant darkness RPCH mRNA concentration changes to ultradian cycles.

Circadian rhythm of pigment migration induced by chromatrophorotropins in melanophores of the crab Chasmagnathus granulata

The circadian rhythm of black pigment migration of melanophores of the crab Chasmagnathus granulata and the variation in responsiveness of these cells to pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide (CCAP), and red pigment-concentrating hormone (RPCH) were investigated. Melanophores of C. granulata possess an endogenous circadian rhythm of pigment migration, with black pigments staying more dispersed during the day period and more aggregated during the night period. This rhythm seems to be largely dependent on an endogenous release of neurohormones from eyestalks, and to a lesser extent on a primary response to illumination. beta-PDH was the most potent PDH isoform to induce pigment dispersion in both in vivo (EC50 = 0.4 pmol/animal) and in vitro (EC50 = 0.18 microM) assays. CCAP also induced pigment dispersion in vivo and in vitro assays (EC50 = 12 microM), but it was less potent than beta-PDH. In vivo, RPCH induced a low and nondose-dependent pigment aggregation, while in vitro, it had no effect on pigment migration. The responsiveness of melanophores of C. granulata to beta-PDH was significantly higher during the day period when compared to the night period in both assays, in vitro and in vivo. These results suggest that the endogenous circadian rhythm of black pigment migration is dependent on both endogenous circadian rhythm of beta-PDH synthesis and/or release from eyestalks and on an endogenous rhythm of responsiveness of melanophores to beta-PDH.

Corazonin promotes tegumentary pigment migration in the crayfish Procambarus clarkii

The undecapeptide corazonin (pGlu-Thr-Phe-Gln-Tyr-Ser-His-Gly-Trp-Thr-AsnNH(2)) elicits a retraction of erythrophore pigment granules and dispersion of leucophore pigment granules in the crayfish Procambarus clarkii. The effects are dose-dependent from 10(-10) to 10(-5)M. Influence on erythrophores is lower than that of Red Pigment Concentrating Hormone (RPCH), which is inactive on leucophores. Corazonin effects are partly blocked by an anti-corazonin antibody, and even less by an anti-RPCH antibody. Corazonin effects are completely suppressed by the calcium chelator BAPTA. Immunoreactive somata and fibers were identified in various regions of the eyestalk (medulla terminalis, medulla interna and medulla externa) with the anti-corazonin antibody. These results suggest the possible existence of a corazonin-like peptide in crustaceans.