Immunodetection and localization of nitric oxide synthase in the olfactory center of the terrestrial snail, Helix pomatia

Nitric oxide-coupled signaling in odor elicited molecular events in the olfactory center of the terrestrial snail, Helix pomatia

Olfaction, a chemosensory modality, plays a pivotal role in the orientation and behavior of invertebrates. The central olfactory processing unit in terrestrial stylomatophoran snails is the procerebrum, which contains NO synthesizing interneurons, whose oscillatory currents are believed to be the base of odor evoked memory formation. Nevertheless, in this model the up- and downstream events of molecular cascades that trigger and follow NO release, respectively, have not been studied. Immunocytochemistry and flow cytometry studies performed on procerebral neural perikarya isolated from the snail Helix pomatia revealed cell populations with discrete DAF-2 fluorescence, indicating the release of different amounts of NO. Glutamate increased the intensity of DAF-2 fluorescence, and the number of DAF-2 positive non-bursting interneurons, through a mechanism likely to involve an NMDA-like receptor. Similarly to glutamate, NO activation induced an increase in intracellular cGMP levels through activation of soluble guanylyl cyclase. Immunohistochemical localization of proteins possessing the phosphorylated target sequence of AGC family kinases (RXXS/T-P), among them protein kinase A (RRXS/T-P), showed striking similarities to the distribution of NOS/cGMP. Activators of cyclic nucleotide synthesis increased the AGC-kinase-dependent phosphorylation of discrete proteins with 28, 45, and 55kDamw. Importantly, exposure of snails to an attractive odorant induced hyperphosphorylation of the 28kDa protein, and increased levels of cGMP synthesis. Protein S-nitrosylation and intercellular activation of protein kinase G were also suggested as alternative components of NO signaling in the snail procerebrum. The present results from Helix pomatia indicate an important role for procerebrum NO/cGMP/PKA signaling pathways in the regulation of olfactory (food-finding) behavior.

Report on the 13th symposium on invertebrate neurobiology held 26-30 August 2015 at the Balaton Limnological Institute, MTA Centre for ecological research of the Hungarian Academy of Sciences, Tihany, Hungary

This report summarizes the lectures and posters presented at the International Society for Invertebrate Neurobiology's 13th symposium held 26-30 August 2015, at the Balaton Limnological Institute, MTA Centre for Ecological Research, Tihany, Hungary. The symposium provided an opportunity for scientists working on a range of topics in invertebrate neurobiology to meet and present their research and discuss ways to advance the discipline.

The 5-HT immunoreactive innervation of the Helix procerebrum

In the procerebrum of terrestrial snails, 5-HT is a key modulatory substance of the generation of synchronous oscillatory activity and odor learning capability. In this study, we have analyzed the characteristics of the 5-HT-immunoreactive (5-HT-IR) innervation of the distinct anatomical regions of the procerebrum of Helix pomatia, applying correlative light- and electron microscopic immunocytochemistry. A dense network of 5-HT-IR innervation was demonstrated in the cell body layer, meanwhile a varicose fiber system of different density occurred in the different neuropil regions. At the ultrastructural level, labeled varicosities were found to contact both procerebral cell bodies, and different unlabeled axon profiles in the neuropils. The labeled structures established mostly close non-specialized membrane contacts with the postsynaptic profiles. The overall dense distribution of 5-HT-IR innervation supports a general modulatory role of 5-HT in processing different olfactory events.