Localization of the myomodulin-like immunoreactivity in the leech CNS

Keating, Heather H.; Sahley, Christie L.

doi:10.1002/(sici)1097-4695(199607)30:3<374::aid-neu6>3.0.co;2-1

Cited by 23 publications

(23 citation statements)

References 43 publications

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“…For example, the increased stimulus-induced activity of the S-cell could selectively augment the release of neuropeptides, as described for other systems (Dutton and Dyball, 1979;Vilim et al, 1996). Consistent with this, the presynaptic terminals of the S-cell within the ganglion contain large dense core vesicles, purported to contain peptide transmitters, in addition to small clear vesicles (Muller and C arbonetto, 1979), and the neuropeptide myomodulin (Cropper et al, 1987) appears by immunocytochemistry to be present in the S-cell (Keating and Sahley, 1996). Thus the postsynaptic action of myomodulin or other peptides might mediate the sensitization-induced increase in behavior.…”

Section: Discussionsupporting

confidence: 58%

Regeneration of a Central Synapse Restores Nonassociative Learning

1997

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Sensitization is a form of nonassociative learning in which a strong or noxious stimulus persistently enhances the response produced by a weaker stimulus. In the leech Hirudo medicinalis, the S-interneuron is required for sensitization of the shortening response. A single S-cell axon was surgically separated from its sole synaptic partner, the neighboring S-cell. This consistently eliminated sensitization without impairing reflexive shortening itself, as measured in semi-intact specimens. Sensitization of the shortening reflex returned after 3 weeks when the severed axon grew and regenerated its specific electrical synapse within the nerve cord, as shown by restored conduction of impulses between S-cells. This confirms the essential role of one neuron, the S-cell, in sensitization, and it demonstrates that regeneration of the synapse between S-cells restores this example of nonassociative learning.Key words: invertebrate learning; leech; regeneration; nerve repair; nonassociative conditioning; plasticity; axotomy; Hirudo medicinalis; S-cell; synapse regeneration A major challenge in repair of the damaged C NS is to restore sensory f unction and motor performance (Freed et al., 1985;

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Section: Discussionsupporting

confidence: 58%

Regeneration of a Central Synapse Restores Nonassociative Learning

1997

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“…The increased action-potential frequency could also enhance firing in neurons that the S cell excites through electrical synapses, such as the L motor neurons, by temporal summation with other excitatory inputs. Finally, increases in S-cell actionpotential frequency could enhance release of the neuropeptide myomodulin, a neuromodulator that is present in the S cell and has been shown to increase excitability of the Retzius cells (Keating and Sahley 1996;Wang et al 1999).…”

Section: Functional Consequences Of the Increase In Instantaneous Frementioning

confidence: 99%

Serotonin Modulates Axo-Axonal Coupling Between Neurons Critical for Learning in the Leech

Moss

Fuller

Sahley

et al. 2005

Journal of Neurophysiology

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modulates axo-axonal coupling between neurons critical for learning in the leech. J Neurophysiol 94: [2575][2576][2577][2578][2579][2580][2581][2582][2583][2584][2585][2586][2587][2588][2589] 2005. First published June 29, 2005; doi:10.1152/jn.00322.2005. S cells form a chain of electrically coupled neurons that extends the length of the leech CNS and plays a critical role in sensitization during wholebody shortening. This process requires serotonin, which acts in part by altering the pattern of activity in the S-cell network. Serotonincontaining axons and varicosities were observed in Faivre's nerve where the S-to-S-cell electrical synapses are located. To determine whether serotonin modulates these synapses, S-cell action-potential (AP) propagation was studied in a two-ganglion chain containing one electrical synapse. Suction electrodes were placed on the cut ends of the connectives to stimulate one S cell while recording the other, coupled S cell's APs. A third electrode, placed en passant, recorded the APs near the electrical synapse before they propagated through it. Low concentrations of the gap junction inhibitor octanol increased AP latency across the two-ganglion chain, and this effect was localized to the region of axon containing the electrical synapse. At higher concentrations, APs failed to propagate across the synapse. Serotonin also increased AP latency across the electrical synapse, suggesting that serotonin reduced coupling between S cells. This effect was independent of the direction of propagation and increased with the number of electrical synapses in progressively longer chains. Furthermore, serotonin modulated instantaneous AP frequency when APs were initiated in separate S cells and in a computational model of S-cell activity after mechanosensory input. Thus serotonergic modulation of S-cell electrical synapses may contribute to changes in the pattern of activity in the S-cell network.

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“…The increased S-cell excitability enhances the activity of the interneuron during evoked whole-body shortening responses. Increased S-cell activity (1) may enhance synaptic transmission from the S-cell by synaptic facilitation, temporal summation, or both; (2) may increase the probability of transmitter release at synapses that have a high rate of failure (Lisman, 1997), allowing the S-cell to excite a neuron that it might not excite in the unsensitized state; and (3) may enhance release of a modulatory neuropeptide (Vilim et al, 1996(Vilim et al, , 2000, such as myomodulin, which is found in the S-cell and known to have excitatory effects on the R-cells (Keating and Sahley, 1996;Wang et al, 1999). All of these changes could increase the participation of the S-cell in whole-body shortening and explain the enhanced contribution of the S-cell to the shortening reflex during sensitization or dishabituation.…”

Section: Relevance Of the Effects Of 5ht For Non-associative Learningmentioning

confidence: 99%

Non-Associative Learning and Serotonin Induce Similar Bi-Directional Changes in Excitability of a Neuron Critical for Learning in the Medicinal Leech

2001

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In studies of the cellular basis of learning, much attention has focused on plasticity in synaptic transmission in terms of transmitter release and the number or responsiveness of neurotransmitter receptors. However, changes in postsynaptic excitability independent of receptors may also play an important role. Changes in excitability of a single interneuron in the leech, the S-cell, were measured during non-associative learning of the whole-body shortening reflex. This interneuron was chosen because it is known to be necessary for sensitization and full dishabituation of the shortening response. During sensitization, S-cell excitability increased, and this enhancement corresponded to facilitation of the shortening reflex and increased S-cell activity during the elicited response. During habituation training, there was a decrement in both the shortening reflex and the elicited S-cell activity, along with decreased S-cell excitability. Conversely, dishabituation facilitated both the shortening response and S-cell activity during shortening, with an accompanying increase in S-cell excitability. Bath application of 1-10 M serotonin (5HT), a modulatory neurotransmitter that is critical for sensitization, for full dishabituation, and for associative learning, increased S-cell excitability. S-cell excitability also increased after stimulation of the serotonergic Retzius cells. However, focal application of serotonin onto the S-cell soma hyperpolarized the interneuron, and bath application of a lower dose of serotonin (0.1 M) decreased excitability. The observed changes in postsynaptic excitability appear to contribute to non-associative learning, and modulatory neurotransmitters, such as serotonin, evidently help regulate excitability. Such changes in S-cell excitability may also be relevant for more complex, associative forms of learning.

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Localization of the myomodulin-like immunoreactivity in the leech CNS

Cited by 23 publications

References 43 publications

Regeneration of a Central Synapse Restores Nonassociative Learning

Regeneration of a Central Synapse Restores Nonassociative Learning

Serotonin Modulates Axo-Axonal Coupling Between Neurons Critical for Learning in the Leech

Non-Associative Learning and Serotonin Induce Similar Bi-Directional Changes in Excitability of a Neuron Critical for Learning in the Medicinal Leech

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