Characterization of NO/cGMP-Mediated Responses in Identified Motoneurons |
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Authors: | Ricardo M Zayas Barry A Trimmer |
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Institution: | (1) Department of Biology, Dana Laboratory, Tufts University, Medford, MA 02155, USA;(2) University of Illinois at Urbana-Champaign, Department of Cell & Developmental Biology, B107 CLSL (MC-123), 601 S. Goodwin Avenue, Urbana, IL 61801, USA |
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Abstract: | 1. Nitric oxide (NO) is thought to play a neuromodulatory role in the nervous system of vertebrate and invertebrate species.
In the hornworm Manduca sexta, NO-mediated signaling has been implicated in behavioral and developmental processes, but its exact function in neurons is
unknown. In this study, we identify specific neurons in the CNS of Manduca larvae that accumulate cGMP in response to treatment with NO donors in the presence of cGMP-phosphodiesterase inhibitors.
Subsets of these neurons were identified as motoneuron-12 (MN12) and intersegmental motoneurons (ISMs), which innervate dorsal
oblique muscles of the larvae.
2. To investigate the physiological role of NO-evoked increases in cGMP in these motoneurons we performed intracellular recordings;
we found that application of NO donors caused an increase in neuronal excitability that was characterized by an increase in
the spontaneous firing frequency. When action potentials and EPSPs were blocked, NO treatment evoked a depolarization of the
resting membrane potential and a decrease in the measured input resistance in both MN12 and the ISMs.
3. Additional experiments with MN12 showed that treatment with the cGMP analogue, 8-Br-cGMP mimicked the NO effect on the
resting potential and the input resistance. Furthermore, MN12 incubation with the NOS inhibitor, L-NNA, resulted in a small
hyperpolarization of the resting potential and an increase in the input resistance, and incubation with the sGC inhibitor,
ODQ blocked the NO-evoked depolarization of MN12. Finally, NO treatment during voltage clamping of MN12 evoked an inward positive
current.
4. Taken together, these results suggest that NO can act as a “gain control” of neuronal excitability, which might have an
important role in insect behavior. |
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Keywords: | nitric oxide phosphodiesterase inhibitors soluble guanylyl cyclase insect manduca |
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