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FMRFamide produces biphasic modulation of the LFS motor neurons in the neural circuit of the siphon withdrawal reflex of Aplysia by activating Na+ and K+ currents


, : FMRFamide produces biphasic modulation of the LFS motor neurons in the neural circuit of the siphon withdrawal reflex of Aplysia by activating Na+ and K+ currents. Journal of Neuroscience 13(12): 5139-5152

The molluscan neuropeptide FMRFamide has an inhibitory effect on transmitter release from the presynaptic sensory neurons in the neural circuit for the siphon withdrawal reflex. We have explored whether FMRFamide also acts postsynaptically in motor neurons in this circuit, focusing on the LFS motor neurons. FMRFamide typically produces a biphasic response in LFS neurons: a fast excitatory response followed by a prolonged inhibitory response. We have analyzed these postsynaptic actions and compared them with the mechanism of FMRFamide's inhibition of the presynaptic sensory neurons. The transient excitatory effect of FMRFamide, which desensitizes rapidly, is due to activation of a TTX-insensitive, Na(+)-dependent inward current. The late hyperpolarizing phase of the FMRFamide response results from activation of at least two K+ currents. One component of the hyperpolarizing response is active at rest and at more hyperpolarized membrane potentials, and is blocked by 5 mM 4-aminopyridine, suggesting that it differs from the previously described FMRFamide-modulated K+ currents in the presynaptic sensory neurons. In addition, FMRFamide increases a 4-aminopyridine-insensitive K+ current. Presynaptically, FMRFamide increases K+ conductance, acting via release of arachidonic acid. In the LFS motor neurons, application of arachidonic acid mimicked the prolonged, hyperpolarizing phase of the FMRFamide response; 4-bromophenacyl bromide, an inhibitor of phospholipase A2, selectively blocked this component of the FMRFamide response. Thus, FMRFamide may act in parallel pre- and post-synaptically to inhibit the output of the siphon withdrawal reflex circuit, producing this inhibitory effect via the same second messenger in the sensory neurons and motor neurons, though a number of the K+ currents modulated in these two types of neurons are different.


Accession: 008670375

PMID: 8254364

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Related references

Belkin K.J.; Abrams T.W., 1990: Fmrfamide acts in parallel presynaptically and postsynaptically via arachidonic acid to inhibit the neural circuit of the siphon withdrawal reflex of aplysia. Society for Neuroscience Abstracts 16(1): 627

Lieb, J.R.; Frost, W.N., 1997: Realistic simulation of the Aplysia siphon-withdrawal reflex circuit: roles of circuit elements in producing motor output. The circuitry underlying the Aplysia siphon-elicited siphon-withdrawal reflex has been widely used to study the cellular substrates of simple forms of learning and memory. Nonetheless, the functional roles of the different neurons and synaptic con...

Fischer T.M.; Carew T.J., 1991: Activation of the facilitory interneuron l29 produces inhibition of reflex input to siphon motor neurons in aplysia. Society for Neuroscience Abstracts 17(1-2): 1302

Hawkins, R.D.; Frost, L., 1996: Contribution of monosynaptic EPSPS from LE siphon sensory neurons to mediation and habituation of the gill- and siphon withdrawal and reflex in Aplysia. Society for Neuroscience Abstracts 22(1-3): 1445

Frost W.N.; W.L.G.; Lieb J., 1991: Simulation of the aplysia siphon withdrawal reflex circuit slow components of interneuronal synapses contribute to the mediation of reflex duration. Society for Neuroscience Abstracts 17(1-2): 1390

Cooper J.; Clark G.A., 1991: Effects of fmrfamide on inputs to peripheral siphon motor neurons in aplysia. Society for Neuroscience Abstracts 17(1-2): 1591

Stopfer, M.; Chen, X.; Carew, T.J., 1993: Evoked ink release in Aplysia produces inhibition of the siphon withdrawal reflex in neighboring conspecifics. Aplysia californica exhibit a dramatic defensive reaction, the release of a cloud of dark purple ink, in response to noxious stimuli. Although the neural control of this behavior has been studied rather extensively, the functional significance of...

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Frost, L.; Kaplan, S.W.; Cohen, T.E.; Henzi, V.; Kandel, E.R.; Hawkins, R.D., 1997: A simplified preparation for relating cellular events to behavior: contribution of LE and unidentified siphon sensory neurons to mediation and habituation of the Aplysia gill- and siphon-withdrawal reflex. We have begun to analyze several elementary forms of learning in a simple preparation consisting of the isolated mantle organs and abdominal ganglion of Aplysia. Previous studies suggested that plasticity at siphon sensory neuron synapses contribu...

Small, S.A.; Cohen, T.E.; Kandel, E.R.; Hawkins, R.D., 1992: Identified FMRFamide-immunoreactive neuron LPL16 in the left pleural ganglion of Aplysia produces presynaptic inhibition of siphon sensory neurons. The gill- and siphon-withdrawal reflex of Aplysia undergoes transient inhibition following noxious stimuli such as tail shock. This behavioral inhibition appears to be due in part to transient presynaptic inhibition of the siphon sensory cells, wh...