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Differing synaptic strengths between homologous mechanosensory neurons
Kaitlin R Gibbons1, Michael J Baltzley
1Department of Biology, St. Mary's College of Maryland, St. Mary's City, MD, 20686-3001, USA.
Invertebrate Neuroscience : IN
|February 15, 2014
Summary
Neural circuits in leeches vary even in closely related species. Despite similar behaviors, Macrobdella decora leeches show different pressure cell (P cell) electrical responses compared to Hirudo verbana, highlighting neural plasticity.
Area of Science:
- Neuroscience
- Comparative neurobiology
- Invertebrate neurology
Background:
- Leeches possess four mechanosensory pressure neurons (P cells) per midbody ganglion.
- Interactions between P cells exhibit species-specific electrical and chemical signaling.
- Previous studies documented distinct P cell responses in Hirudo verbana (depolarization-hyperpolarization) and Erpobdella obscura (depolarization).
Purpose of the Study:
- To investigate the neural circuitry and intercellular communication between P cells in the American medicinal leech, Macrobdella decora.
- To compare P cell connectivity in Macrobdella decora with that of Hirudo verbana and Erpobdella obscura, considering their phylogenetic and behavioral similarities.
Main Methods:
- Intracellular stimulation of individual P cells in Macrobdella decora.
- Electrophysiological recordings of P cell responses in normal and modified saline solutions (high Mg2+, 0 Ca2+ and high Mg2+, high Ca2+).
- Analysis of synaptic connections, including monosynaptic excitation, polysynaptic inhibition, and electrical coupling.
Main Results:
- Intracellular stimulation of one P cell in Macrobdella decora elicited a net depolarization in other P cells.
- Experiments in modified saline solutions indicated monosynaptic excitatory and polysynaptic inhibitory connections, along with weak electrical coupling between P cells.
- The observed net depolarization in Macrobdella decora contrasts with the hyperpolarization seen in the closely related Hirudo verbana.
Conclusions:
- Despite close phylogenetic relationship and conserved behaviors with Hirudo verbana, Macrobdella decora exhibits distinct P cell network dynamics.
- Differences in the strengths of chemical connections, rather than the presence of connection types, likely account for the species-specific net responses.
- This study underscores that conserved behaviors do not always correlate with conserved underlying neural circuitry, demonstrating neural plasticity even in closely related species.
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