Monoaminergic modulation of vegetative arousal in the snail helix pomatia
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1
Balaton Lymnological Research Institute, HAS, Hungary
In this study we investigated the firing activity of a group of serotonergic neurons (RPas), which neurons modulate the function of intestinal organs as the heart and the foregut, in isolated CNS preparations obtained from animals with different behavioral state as inactive aestivated, activated, active, feeding and satiated animals. Parallel, applying HPLC assay of monoamines we measured the level of 5HT and DA in the CNS and the heart. Furthermore, applying neurobiotin tracing through visceral nerves as well as immunocytochemistry we determined those putative sensory elements in the skin, and the foregut which may modulate the activity of RPas neurons. In the isolated CNS of Helix pomatia intracellular recording from RPas showed different activity patterns and firing frequencies depending on the behavioral state of the animal. In CNS preparations from osmotic stimulus activated or active animals ther firing frequency was significantly higher than in CNS from aestivated animals. The firing activity of RPas neurons of both feeding and satiated animals was higher than in active animals. The HPLC assay of 5-HT and DA content in the CNS and the heart showed that during activation both 5HT and DA levels decreased in the CNS while increased in the heart compared to the inactive aestivated animals. Contrary, in feeding animals 5HT and DA content increased in both the CNS and the heart compared to the active animals whereas in satiated animals both DA and 5HT levels decreased close to the level of active animals in the SG, whereas remained elevated in the heart. In semi-intact preparations (CNS-mantle collar interconnected via visceral nerves) obtained from aestivated animals, distilled water applied to the mantle collar increased their firing activity, while tactile stimulation evoked transient inhibition in their firing activity. In semi-intact preparations (CNS-foregut interconnected via intestinal nerve) obtained from active animals, the distension of the foregut transiently increased the activity of RPas neurons. Extracellular 5HT application mimicked the excitatory effect of osmotic stimulation and the foregut distension whereas DA mimicked the inhibitory effects of mechanical stimulation applied to the mantle collar or the skin. Co-application of DA and 5HT showed that 5HT antagonizes the inhibitory effects of DA, whereas DA application changes the tonic firing activity evoked by serotonin to an irregular, phasic pattern. Neurobiotin tracing revealed that a huge number of sensory axons reach CNS areas, where the RPas neurons are located, from the mantle collar and skin areas. Tyrosine-hydroxylase imunocytochemistry revealed numerous putative DA containing receptor cells among them. Neurobiotin tracing failed to reveal receptor cells sending sensory axons to the RPas neurons in the foregut, but revealed numerous neurobiotin labeled fibers in the vessels running circularly on the surface of the foregut suggesting a sensory function to them. The combination of intracellular labeling of the 5HTergic RPas neurons with immunolabeling of 5HT and DA elements showed that RPas neurons receive direct 5HT and DA inputs, as well as that 5HT neurons are interconnected, thus the liberated 5HT during increased arousal as locomotion and feeding excites them whereas DAergic inputs change their activity pattern. The RPas neurons by liberating increased amount of 5HT in both the CNS and intestinal organs during increased arousal, may contribute to the modulation of vegetative arousal.
Conference:
12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009.
Presentation Type:
Poster Presentation
Topic:
Homeostatic regulatory mechanisms
Citation:
Hernádi
L,
Hiripi
L and
Vehovszky
A
(2009). Monoaminergic modulation of vegetative arousal in the snail helix pomatia.
Front. Syst. Neurosci.
Conference Abstract:
12th Meeting of the Hungarian Neuroscience Society.
doi: 10.3389/conf.neuro.01.2009.04.110
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Received:
03 Mar 2009;
Published Online:
03 Mar 2009.
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Correspondence:
László Hernádi, Balaton Lymnological Research Institute, HAS, Tihany, Hungary, hernadi@tres.blki.hu