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MIP-immunoreactive innervation of the snail, Helix pomatia, heart. An ultrastructural study
1Department of Experimental Zoology, Balaton Limnological Research Institute of the Hungarian Academy of Sciences, Tihany.
Abstract:
The ultrastructural characteristics of the innervation established by MIP-(Mytilus inhibitory peptide) immunoreactive neurons was investigated in the heart of the snail, Helix pomatia, applying correlative light- and electron microscopic pre-embedding immunocytochemistry on Vibratome-slices. In both the auricle and ventricle, the muscle fibers receive a rich innervation by MIP-immunoreactive (IR) varicose fibers. However, the innervation is seasonally changing in the two parts of the heart. The varicosities, containing a morphologically uniform population of large (120-150 nm) electron-dense granules, can be found in three different positions in relation to the muscle fibers: (i) close (15-20 nm) but unspecialized membrane connections between MIP-(IR) varicosities and muscle fibers; (ii) MIP-IR varicosities located relatively far (0.5-several microm) from the muscles fibers; (iii) MIP-IR profiles localized freely in the extracellular space among the loosely arranged muscle fibers. A general modulatory role of MIP in regulating the heart activity of Helix is suggested.
Insights
Mytilus inhibitory peptide (MIP) neurons innervate the snail heart, with seasonal changes observed. These MIP-immunoreactive varicosities interact with muscle fibers in various ways, suggesting a modulatory role in heart activity.
Area of Science:
- Neurobiology
- Cardiovascular Physiology
- Molluscan Biology
Background:
- The heart of the snail Helix pomatia is regulated by neural input.
- Mytilus inhibitory peptide (MIP) is a known neuromodulator.
Purpose of the Study:
- To investigate the ultrastructural characteristics of MIP-immunoreactive innervation in the Helix pomatia heart.
- To determine the relationship between MIP-immunoreactive neurons and cardiac muscle fibers.
- To explore potential seasonal variations in cardiac innervation.
Main Methods:
- Correlative light and electron microscopy.
- Pre-embedding immunocytochemistry on Vibratome-dissected snail heart slices.
- Morphological analysis of MIP-immunoreactive varicosities and their association with muscle fibers.
Main Results:
- Rich innervation of both auricle and ventricle by MIP-immunoreactive varicose fibers was observed.
- Innervation patterns exhibit seasonal changes in different heart regions.
- MIP-immunoreactive varicosities contain large, electron-dense granules and are found in close proximity, distant, or free in the extracellular space relative to muscle fibers.
Conclusions:
- MIP-immunoreactive neurons extensively innervate the Helix pomatia heart.
- The observed seasonal variations suggest dynamic regulation of cardiac function.
- The varied positioning of MIP-IR varicosities indicates a potential modulatory role in regulating heart activity.