Research

Functional neuroanatomy of the rhinophore of Aplysia punctata

Adrian Wertz^1,2,3 , Wolfgang Rössler² , Malu Obermayer² and Ulf Bickmeyer¹

¹  Biologische Anstalt Helgoland, Alfred Wegener Institute for Polar and Marine Research in Helmholtz Society, Kurpromenade 201, 27483 Helgoland, Germany

²  Behavioural Physiology and Sociobiology, Biocenter, University of Würzburg, Am Hubland, 97074 Würzburg, Germany

³  Max Planck Institute of Neurobiology, Department of Systems and Computational Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany

author email corresponding author email

Frontiers in Zoology 2006, 3:6doi:10.1186/1742-9994-3-6

Published:	6 April 2006

Abstract

Background

For marine snails, olfaction represents a crucial sensory modality for long-distance reception, as auditory and visual information is limited. The posterior tentacle of Aplysia, the rhinophore, is a chemosensory organ and several behavioural studies showed that the rhinophores can detect pheromones, initiate orientation and locomotion toward food. However the functional neuroanatomy of the rhinophore is not yet clear. Here we apply serotonin-immunohistochemistry and fluorescent markers in combination with confocal microscopy as well as optical recording techniques to elucidate the structure and function of the rhinophore of the sea slug Aplysia punctata.

Results

With anatomical techniques an overview of the neuroanatomical organization of the rhinophore is presented. Labelling with propidium iodide revealed one layer of cell nuclei in the sensory epithelium and densely packed cell nuclei beneath the groove of the rhinophore, which extends to about two third of the total length of the rhinophore. Serotonin immunoreactivity was found within the olfactory glomeruli underneath the epithelium as well as in the rhinophore ganglion. Retrograde tracing from the rhinophore ganglion with 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA) demonstrated the connection of glomeruli with the ganglion. Around 36 glomeruli (mean diameter 49 μm) were counted in a single rhinophore. Fluorimetric measurements of intracellular Ca²⁺ levels using Fura-2 AM loading revealed Ca²⁺-responses within the rhinophore ganglion to stimulation with amino acids. Bath application of different amino acids revealed differential responses at different positions within the rhinophore ganglion.

Conclusion

Our neuroanatomical study revealed the number and position of glomeruli in the rhinophore and the rhinophore ganglion as processing stage of sensory information. Serotonin-immunoreactive processes were found extensively within the rhinophore, but was not detected within any peripheral cell body. Amino acids were used as olfactory stimuli in optical recordings and induced sensory responses in the rhinophore ganglion. The complexity of changes in intracellular Ca²⁺-levels indicates, that processing of odour information takes place within the rhinophore ganglion. Our neuroanatomical and functional studies of the rhinophore open up a new avenue to analyze the olfactory system in Aplysia.