Neuronal background of activation of estivated snails,with special attention to the monoaminergic system: a biochemical,physiological, and neuroanatomical study |
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Authors: | L Hernádi Á Vehovszky J Gy?ri L Hiripi |
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Institution: | (1) Department of Experimental Zoology, Balaton Limnological Research Institute, Hungarian Academy of Sciences, P.O. Box 35, Tihany, 8237, Hungary |
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Abstract: | Osmotic stimulation activates both estivated and inactivated specimens of Helix pomatia and increases their central arousal. High-pressure liquid chromatography has shown that, during activation, the level of
both serotonin and dopamine decreases in the central nervous system (CNS) but increases in the foot and heart, organs that
are involved in the eversion of the body. In isolated CNS from activated animals, the firing frequency of the heart-modulator
serotonergic (RPas) neurons is significantly higher than that in the CNS of estivated or inactivated animals. These neurons
innervate both the heart and the anterior aorta. In semi-intact preparations, distilled water (an osmotic stimulus) applied
to the mantle collar increases their firing frequency, whereas tactile stimulation evokes their inhibition. Extracellularly
applied monoamines mimic the effect of peripheral stimuli: serotonin (0.1–10 μM) increases the activity of the RPas neurons,
whereas dopamine (0.1–10 μM) inhibits their activity. Tyrosine-hydroxylase immunocytochemistry and retrograde neurobiotin
tracing have revealed similar bipolar receptor cells in the mantle collar and tail, organs that are exposed to environmental
stimuli in estivated animals. Serotonin immunocytochemistry carried out on the same tissues does not visualize receptor cells
but labels a dense network of fibers that appear to innervate neurobiotin-labeled receptor cells. The combination of neurobiotin-labeling
of RPas neurons and immunolabeling suggests that RPas neurons receive direct dopaminergic inputs from receptor cells and serotonergic
inputs from central serotonergic neurons, indicating that central serotonergic neurons are interconnected. Thus, the RPas
neurons may belong to neuronal elements of the arousal system.
This work was supported by Hungarian OTKA grants T037389, T046580, T037505, and K63451. |
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Keywords: | Serotonin Dopamine Arousal Immunocytochemistry Helix pomatia (Mollusca) |
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