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Localization of a FMRFamide‐related peptide in efferent neurons and analysis of neuromuscular effects of DRNFLRFamide (DF 2 ) in the crustacean Idotea emarginata .

2003; Wiley; Volume: 17; Issue: 2 Linguagem: Inglês

10.1046/j.1460-9568.2003.02455.x

1460-9568

Torsten Weiß, Sabine Kreissl, W. Rathmayer,

Cholinesterase and Neurodegenerative Diseases

Abstract In the ventral nerve cord of the isopod Idotea emarginata , FMRFamide‐immunoreactive efferent neurons are confined to pereion ganglion 5 where a single pair of these neurons was identified. Each neuron projects an axon into the ipsilateral ventral and dorsal lateral nerves, which run through the entire animal. The immunoreactive axons form numerous varicosities on the ventral flexor and dorsal extensor muscle fibres, and in the pericardial organs. To analyse the neuromuscular effects of a FMRFamide, we used the DRNFLRFamide (DF 2 ). DF 2 acted both pre‐ and postsynaptically. On the presynaptic side, DF 2 increased transmitter release from neuromuscular endings. Postsynaptically, DF 2 depolarized muscle fibres by approximately 10 mV. This effect was not observed in leg muscles of a crab. The depolarization required Ca 2+ , was blocked by substituting Ca 2+ with Co 2+ , but not affected by nifedipine or amiloride. In Idotea , DF 2 also potentiated evoked extensor muscle contractions. The amplitude of high K + contractures was increased in a dose dependent manner with an EC 50 value of 40 n m . In current‐clamped fibres, DF 2 strongly potentiated contractions evoked by current pulses exceeding excitation‐contraction threshold. In voltage‐clamped fibres, the inward current through l ‐type Ca 2+ channels was increased by the peptide. The observed physiological effects together with the localization of FMRFamide‐immunoreactive efferent neurons suggest a role for this type of peptidergic modulation for the neuromuscular performance in Idotea . The pre‐ and postsynaptic effects of DF 2 act synergistically and, in vivo , all should increase the efficacy of motor input to muscles resulting in potentiation of contractions.