Eyestalk

Li S., C.A. Wagner, J.A. Freisen, and D.W. Borst (2003). 3-Hydroxy-3-methylglutaryl-coenzyme A reductase in the lobster mandibular organ Regulation by the eyestalk. General and Comparative Endocrinology 134 147-155. 

The similarity of the crustacean blanching substance (Factor A) found in crustacean sinus glands and insect corpora cardiaca has been confirmed by the structural identification of a family of neuropeptides common to arthropods. The first identified member of this family is RPCH (red pigment concentrating hormone), an octapeptide (pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-amide) isolated from eyestalks of the shrimp Pandalus borealis (28). Shortly thereafter, a related peptide--designated as adipokinetic hormone (AKH)--was purified from locust... 

In tests for melanophore pigment dispersion in eyestalkless individuals of the fiddler crab Uca pugilator, head extracts from the cockroach Periplaneta americana and the honey bee Apis mellifera showed strong activity, as did the crustacean eyestalk extracts 36). Head extracts of the butterfly Danaus plexippus and the mealworm Tenebrio molitor fere, however, inactive in the chromatophoral dispersion assay. 

For many years, scientists were aware that peptide factors from the eyestalks of decapod crustaceans regulated glucose metabolism, moulting and female reproduction. It was only much later when these peptides were isolated from the XO-SG complex and structurally elucidated, that it became apparent that the peptides controlling these diverse processes were structurally homologous to each other and, hence, warranted inclusion as members of one peptide family. 

It has been reported that synthesis of cHH is not restricted to the XO in the eyestalks of crustaceans, but is also shown by immunocytochemistry to be localized to the suboesophageal ganglion and thoracic second roots in H. americanus [89], in the POs of C. maenas [90] and is transiently expressed in gut paraneurons of C. maenas where it is involved with water uptake to facilitate ecdysis [91]. Interestingly, the PO-cHH of C. maenas has a free C-terminus, its first 40 amino acid residues are identical to the SG-cHH and, not surprisingly, it displays no functional activity in the cHH bioassay [90]. 

Few studies have looked at the expression of MIH apart from the classical XO-SG distribution, and the results are not all in agreement. Northern blots, PCRs and immunocytochemistry with antisera raised to recombinant MIH-B of M. ensis showed that MIH-B is expressed in the eyestalk (XO) and ventral nerve cord [106], whereas PCRs and Northern blots showed expression of a putative MIH only in the eyestalks of M rosenbergii [107]. In C. pagurus, MIH-like transcripts were detected by Northern blotting only in XOs, whereas the more-sensitive nested PCR approach revealed that MIH could be amplified from optic nerve and the... 

Factors from the eyestalks of H americanus, specifically cHH, have been implicated in playing a role in osmoregulation too [132]. The involvement of cHH in osmoregulation was confirmed in another decapod crustacean, viz in the crayfish Astacus leptodactylus, where the injection of cHH into eyestalk-ablated specimens caused a significant increase in the haemolymph osmolality and Na+ concentration, whereas the concentration of Cl remained unchanged [133]. 

Fig. 7.2 Schematic representations of chemosensory pathways in the brain, (a) Lateral antennular neuropil (LAN) pathway. dCRNs and MRNs from sensilla on the lateral (LF) and medial (MF) antennular flagellum project somatotopically into both lobes of the LAN and couple directly to antennular motoneurons (MN), (b) Olfactory pathway. ORNs project nontopographically into the olfactory lobe (OL) which is organized into glomeruli. Information is processed by various types of multiglomerular local intemeurons (LN) and output is provided by multiglomerular projections neurons (PN) ascending to the lateral protocerebrum in the eyestalk ganglia...

Fig. 13.2 Photograph showing chemical communication during aggressive interaction of two male Astacus leptodactylus. Both males were blindfolded using opaque film wrapped around the eyestalks. Urine signals were visualized using Fluorescein dye injected into the heart (for methodology see Breithaupt and Eger 2002)...

Fig. 21.4 Effects of eyestalk ablation on lobster growth. The larger animal (upper) had both of its eyestalks removed 2 months after hatching. The intact control animal (lower) was its full sibling. Both lobsters were kept in the same aquatic system for 1 year and fed excess amounts of food. From Conklin and Chang (1983)...

A dramatic rise in CHH in C. maenas was observed in late premolt compared to intermolt values (over 100-fold). This surge in CHH triggers the massive ion and water uptake during ecdysis and mediates the body s expansion necessary for successful ecdysis. The mechanism of this uptake is unknown, but the sources of this premolt surge in CHH are the fore- and hindguts. The structure of this intestinal CHH is different from the eyestalk form of CHH. 

In addition to its effects on the molt interval previously described, there are observations that MF is a female gonadotropin. Early, indirect studies involved eyestalk ablation and subsequent ovarian maturation. For example, MOs (the... 

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