Comparative anatomy of serotonin‐like immunoreactive neurons in isopods: Putative homologues in several species

Abstract

It is now commonly accepted that the arthropod nervous system has evolved only once, and so homologies between crustacean and insect nervous systems can be meaningfully sought. To do this, we have examined the distribution of serotonin (5-hydroxytryptamine)-like immunoreactive neurons in the central nervous system (CNS) of four common British isopods. Two species of terrestrial woodlouse, Oniscus asellus and Armadillidium vulgare, the littoral sea slater, Ligia oceanica, and the aquatic water hoglouse, Asellus meridianus, all possess approximately 40 pairs of serotonin-like immunoreactive neurons, distributed throughout the CNS in a very similar pattern. Interspecific homology is clearly suggested. Serotonin-like immunoreactive neurons in the first (T1) and fourth (T4) thoracic ganglia are particularly prominent in each of the four species studied. Whole-mount immunohistochemistry shows that the pair of T1 neurons have large dorsolateral cell bodies and prominent neurites that project medially and then anteriorly, whereas the pair of T4 neurons have ventrolateral cell bodies and neurites that bifurcate to form a thin axon projecting anteriorly to terminate in T3 and a thick medial axon that projects posteriorly into the abdominal neuromeres of the terminal ganglion. Intracellular cobalt staining of these neurons reveals more of their arborizations: the T1 neurons send three processes anteriorly, which arborize in the brain and exist from the CNS via peripheral nerves, whereas the T4 neurons contribute considerably to the extensive pattern of serotonin-like immunoreactive fibres in T3-T6 ganglia. The overall pattern of serotonin-like immunoreactive neurons in the isopods is similar to that in decapod crustacea, and a number of putative homologies can be assigned. It is more difficult to homologize the isopod serotonin-like immunoreactive neurons with those in the insect CNS, but some stained brain and thoracic neurons share common cell body positions and axon trajectories in isopods, decapods, and insects and may therefore be homologous.

Effects ofMicrophallus papillorobustus(Platyhelminthes: Trematoda) on serotonergic immunoreactivity and neuronal architecture in the brain ofGammarus insensibilis(Crustacea: Amphipoda)

“…After a partial anterior loop, the axon projects posteriorly through the circumoesophageal connective. Serotonin immunoreactivity has not been described in the brain of amphipods but the TGN is clearly homologous to the large tritocerebral serotonergic neuron described by Thompson et al (1994) …”

Cytological organization of the central gelatinosa in the turtle spinal cord

“…Specificity was tested preincubating the diluted antiserum with 1.5 mM serotonin. Immunostaining was almost abolished by preincubation with serotonin (Thompson et al, 1994). The antibody was also tested by us in well-known serotoninergic neuronal systems such as the raphe nuclei of turtles and the nerve cord of isopods.…”

“…The antibody was also tested by us in well-known serotoninergic neuronal systems such as the raphe nuclei of turtles and the nerve cord of isopods. The stained neuronal and axons patterns were identical to those described for turtles (Kiehn et al, 1992) and isopods (Thompson et al, 1994). The antibody was used at a 1/500 dilution.…”

A crustacean serotonin receptor: Cloning and distribution in the thoracic ganglia of crayfish and freshwater prawn

“…It is well documented that the serotonergic system is highly conserved among arthropods (Thompson et al, 1994;Beltz, 1999;Monastirioti, 1999;Harzsch, 2003). An important question is whether the conservation of the serotonergic system extends to effector molecules.…”