The dynamic regulation of nitric oxide synthase (NOS) activity and cGMP levels suggests a functional role in the development of nervous systems. We report evidence for a key role of the NO/cGMP signalling cascade on migration of postmitotic neurons in the enteric nervous system of the embryonic grasshopper. During embryonic development, a population of enteric neurons migrates several hundred micrometers on the surface of the midgut. These midgut neurons (MG neurons) exhibit nitric oxide-induced cGMP-immunoreactivity coinciding with the migratory phase. Using a histochemical marker for NOS, we identified potential sources of NO in subsets of the midgut cells below the migrating MG neurons. Pharmacological inhibition of endogenous NOS, soluble guanylyl cyclase (sGC) and protein kinase G (PKG) activity in whole embryo culture significantly blocks MG neuron migration. This pharmacological inhibition can be rescued by supplementing with protoporphyrin IX free acid,an activator of sGC, and membrane-permeant cGMP, indicating that NO/cGMP signalling is essential for MG neuron migration. Conversely, the stimulation of the cAMP/protein kinase A signalling cascade results in an inhibition of cell migration. Activation of either the cGMP or the cAMP cascade influences the cellular distribution of F-actin in neuronal somata in a complementary fashion. The cytochemical stainings and experimental manipulations of cyclic nucleotide levels provide clear evidence that NO/cGMP/PKG signalling is permissive for MG neuron migration, whereas the cAMP/PKA cascade may be a negative regulator. These findings reveal an accessible invertebrate model in which the role of the NO and cyclic nucleotide signalling in neuronal migration can be analyzed in a natural setting.

Over the past few years, molecular studies of phylogeny have challenged the traditional view of evolutionary relationships among protostomian animal phyla. Based on analysis of 18S ribosomal RNA gene sequences, it has been suggested that some traditional groups, like the articulata and the pseudocoelomata, should be completely abandoned and that instead the protostomians should be split into two major clades: the Ecdysozoa and the Lophotrochozoa. However, this new molecular phylogeny still awaits confirmation by independent methods. In this study, we present a cytological feature that supports the new classification. The carbohydrate epitope that is recognised by antisera against the plant glycoprotein horseradish peroxidase (HRP) is known to be selectively expressed by membrane proteins on the surface of neural tissue in insects. We found that the major ecdysozoan phyla show neural expression of HRP immunoreactivity, which is completely absent in the nervous tissue of lophotrochozoans, deuterostomians, and cnidarians. This suggests that the presence of anti-HRP-reactive glycoproteins in neural tissue is an ecdysozoan autapomorphy.

Female strawberry poison frogs (Dendrobates pumilio) exhibit highly evolved maternal care, including tadpole transport and tadpole provisioning with unfertilized eggs. We observed that tadpole-rearing and mating activity are mutually exclusive behavioura l states in a Costa Rican population. Tadpole-rearin g females did not engage in courtship activity. Only non-rearing females courted. Non-rearing females occupied larger home ranges than tadpole-rearing females, which may be related to female selection of mates. For the rst time aggressive female-female interactions were observed in the eld. Tadpole-rearing females were signi cantly more aggressive than non-rearing females, especially in the vicinity of their offspring-rearin g sites.Resumen. Las hembras de la ranita roja Dendrobates pumilio ejecutan cuidado parental altamente desarrollado que incluye el transporte y la alimentación de los renacuajos. En una población costaricense encontramo s que el cuido materno y la actvidad sexual son comportamientos mutualmente exclusivos: Las hembras que estan cuidando a su cría son sexualmente inactivas, solamente las hembras sin renacuajos se aparean. Las hembras sexualmente activas poseian un rango de actividad más grande que las hembras cuidando a renacuajos. Los rangos de actividad en el primer grupo de hembras eran más grandes probablement e porque ellas visitan los territorios de varios machos con el n de seleccionar una pareja. Además, por la primera vez interacciones aggressivas entre las hembras de la ranita roja fueron observado s en el campo, siendo más aggressivas las hembras con rencuajos, particularment e en la vencidad de los hábitats de su cría.

We examined the expression of acetylcholinesterase (AChE) in the nervous system and epidermal body structures during embryonic and larval development of two grasshopper species: Locusta migratoria and Schistocerca americana. Histochemical labelling was blocked by the enzyme inhibitors eserine and BW284c51, but not by iso-OMPA, showing that the staining reflected true AChE activity. The majority of staining was localized on the cell surface but granular intracellular staining was also visible in many cell bodies. In both species, the cellular expression of AChE followed a similar but complex spatiotemporal staining pattern. Initially, mainly epidermal tissue structures were stained in the various body appendages (stages 25%-30%). Labelling subsequently appeared in outgrowing neurons of the central nervous system (CNS) and in the nerves innervating the limbs and dorsal body wall (stages 30%-40%). The latter staining originated in motoneurons of the ventral nerve cord. In a third phase (after 45%), the somata of certain identified mechanosensory neurons started to express AChE activity, presumably reflecting cholinergic differentiation. Staining was also found in repo-positive glial cells of the CNS, longitudinal glia of connectives, glia of the stomatogastric nervous system and glial cells ensheathing peripheral nerves. Glial cells remained AChE-positive during larval to adult development, whereas motoneurons lost their AChE expression. The expression pattern in non-neuronal cells and glutamatergic motoneurons and the developmental appearance of AChE prior to synaptogenesis in the CNS suggest non-cholinergic functions of AChE during grasshopper embryogenesis.

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