Sensitivity of transformed (phasic to tonic) motor neurons to the neuromodulator 5-HT.
Long-term adaptation resulting in a 'tonic-like' state can be induced in phasic motor neurons of the crayfish, Procambarus clarkii, by daily low-frequency stimulation [Lnenicka, G.A., Atwood, H.L., 1985b. Long-term facilitation and long-term adaptation at synapses of a crayfish phasic motoneuron. J. Neurobiol. 16, 97-110]. To test the hypothesis that motor neurons undergoing adaptation show increased responses to the neuromodulator serotonin (5-HT), phasic motor neurons innervating the deep abdominal extensor muscles of crayfish were stimulated at 2.5 Hz, 2 h/day, for 7 days. One day after cessation of conditioning, contralateral control and conditioned motor neurons of the same segment were stimulated at 1 Hz and the induced excitatory post-synaptic potentials (EPSPs) were recorded from DEL(1) muscle fibers innervated by each motor neuron type. Recordings were made in saline without and with 100 nM 5-HT. EPSP amplitudes were increased by 5-HT exposure in all cases. Conditioned muscles exposed to 5-HT showed a 2-fold higher percentage of increase in EPSP amplitude than did control muscles. Thus, the conditioned motor neurons behaved like intrinsically tonic motoneurons in their response to 5-HT. While these results show that long-term adaptation (LTA) extends to 5-HT neuromodulation, no phenotype switch could be detected in the postsynaptic muscle. Protein isoform profiles, including the myosin heavy chains, do not change after 1 week of conditioning their innervating motor neurons.
Griffis
B
B
Thomas Hunt Morgan School of Biological Sciences, University of Kentucky, 100 T.H. Morgan Building, Lexington, KY 40506-0225, USA.
Bonner
P
P
Cooper
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RL
D000818:Animals; D003400:Astacoidea; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009124:Muscle Proteins / Q000302:isolation & purification / Q000378:metabolism; D018482:Muscle, Skeletal / Q000294:innervation; D018995:Myosin Heavy Chains / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*
D009124:Muscle Proteins; D012701:Serotonin; D018995:Myosin Heavy Chains