Heteromorphic antennules protect the olfactory midbrain from atrophy following chronic antennular ablation in freshwater crayfish

Histological organization of the central nervous system and distribution of a gonadotropin-releasing hormone-like peptide in the blue crab, Portunus pelagicus

We present a detailed histological description of the central nervous system (CNS: brain, subesophageal ganglion, thoracic ganglia, abdominal ganglia) of the blue crab, Portunus pelagicus. Because the presence of gonadotropin-releasing hormone (GnRH) in crustaceans has been disputed, we examine the presence and localization of a GnRH-like peptide in the CNS of the blue crab by using antibodies against lamprey GnRH (lGnRH)-III, octopus GnRH (octGnRH) and tunicate GnRH (tGnRH)-I. These antibodies showed no cross-reactivity with red-pigment-concentrating hormone, adipokinetic hormone, or corazonin. In the brain, strong lGnRH-III immunoreactivity (-ir) was detected in small (7-17 μm diameter) neurons of clusters 8, 9 and 10, in medium-sized (21-36 μm diameter) neurons of clusters 6, 7 and 11 and in the anterior and posterior median protocerebral neuropils, olfactory neuropil, median and lateral antenna I neuropils, tegumentary neuropil and antenna II neuropil. In the subesophageal ganglion, lGnRH-III-ir was detected in medium-sized neurons and in the subesophageal neuropil. In the thoracic and abdominal ganglia, lGnRH-III-ir was detected in medium-sized and small neurons and in the neuropils. OctGnRH-ir was observed in neurons of the same clusters with moderate staining, particularly in the deutocerebrum, whereas tGnRH-I-ir was only detected in medium-sized neurons of cluster 11 in the brain. Thus, anti-lGnRH-III shows greater immunoreactivity in the crab CNS than anti-octGnRH and anti-tGnRH-I. Moreover, our functional bioassay demonstrates that only lGnRH-III has significant stimulatory effects on ovarian growth and maturation. We therefore conclude that, although the true identity of the crab GnRH eludes us, crabs possess a putative GnRH hormone similar to lGnRH-III. The identification and characterization of this molecule is part of our ongoing research.

Amputation-induced activity of progenitor cells leads to rapid regeneration of olfactory tissue in lobsters

Lobsters have a self-renewing olfactory system and, like many animals, continuously replace old or dying olfactory receptor neurons. In addition, lobsters are able to regenerate the peripheral olfactory system even after complete loss. The olfactory sensors in lobsters are located distally on a pair of antennules. These antennules are often damaged, but this has little impact on the lobster's sense of smell because damaged olfactory tissue is rapidly replaced. In this study, we investigated damage-induced regeneration of the olfactory system by measuring cell proliferation following controlled amputation. We show that amputation-induced regeneration occurs as a result of up-regulating the normal development of olfactory sensors. A unique feature of up-regulated development is the formation of patches of proliferating cells within the antennular epithelium. Epithelial patches were typically formed between 3 and 10 days postamputation on the amputated side. They were characterized by their: proximal position with respect to developing clusters of olfactory receptor neurons (ORNs); tendency to form two discrete patches within the borders of each existing annulus; cell size, which was approximately twice that of mature ORNs; and location within the ventral epithelium. The development of epithelial patches was immediately followed by proliferation of clusters of ORNs and associated glial cells, and the level of this proliferation increased significantly during the premolt stage of the lobster's molt cycle. These epithelial patches may represent populations of precursor cells, because they develop in response to amputation and immediately precede development of cell clusters composed of ORNs and glia. Possible regulatory signals controlling epithelial patch development are discussed.

Neurogenesis in the central olfactory pathway of the adult shore crab Carcinus maenas is controlled by sensory afferents

The number of olfactory projection neurons (OPNs) in the brain of the juvenile and adult shore crab Carcinus maenas continues to increase during the life of the animal. In vivo labeling of adult crabs with the proliferation marker bromodeoxyuridine (BrdU) revealed a group of proliferating neuronal precursor cells in the lateral soma clusters (LCs) and in the soma clusters of the hemiellipsoid bodies (HBCs). The LCs contain the cell bodies of the olfactory projection neurons and the HBCs house the cell bodies to which the OPNs project. The aim of the present study was to examine whether the input from primary olfactory afferents has any influence on the rate of proliferation and survival of the neuronal precursors in the central olfactory pathways of C. maenas. Different sets of experiments involving BrdU injection and its immunocytochemical detection combined with unilateral amputation of the antennule that houses the olfactory organ were carried out. Our results show that the missing olfactory sensory input affects the rate of proliferation and the survival of postmitotic cells in the LC and in the HBC compared with control animals. The effect on the survival of postmitotic cells tested by BrdU injection followed by unilateral ablation is lateralized. Proliferation of neuronal precursor cells tested by the reversed experimental order was drastically impaired bilaterally. We conclude that the olfactory sensory input is necessary for a normal rate of proliferation of neuronal precursors and the survival of their progeny in the LC and in the HBC of C. maenas.