Protein Kinase C Is Required for Long-Lasting Synaptic Enhancement by the Neuropeptide DRNFLRFamide in Crayfish

Abstract

The FMRFamide-related neuropeptide AspArgAsnPheLeuArgPhe-NH2 (DRNFLRFamide, DF2) induces a long-lasting enhancement of synaptic transmission at neuromuscular junctions on the crayfish deep abdominal extensor muscles. Here we investigated the function of protein kinase C (PKC) in this effect because PKC has been implied in the control of long-term synaptic modulation in other systems. The general kinase antagonist staurosporine reduced both the initial increase in excitatory postsynaptic potential (EPSP) amplitude and the duration of synaptic enhancement. Unlike staurosporine, the selective PKC inhibitors, chelerythrine and bisindolylmaleimide, augmented the initial EPSP increase. However, like staurosporine, they also reduced the duration of synaptic enhancement. The PKC activator, phorbol-12-myristate 13-acetate, induced a long-lasting synaptic enhancement that was blocked by chelerythrine. These results show that synaptic enhancement by DF2 is mediated by different intracellular signaling systems that act in temporal sequence. The initial increase in EPSP amplitudes is negatively regulated by PKC and involves another, staurosporine-sensitive, kinase; whereas, the maintenance of synaptic enhancement requires PKC.

The Neuromuscular Junctions of the Slow and the Fast Excitatory Axon in the Closer of the CrabEriphia spinifronsAre Endowed with Different Ca2+Channel Types and Allow Neuron-Specific Modulation of Transmitter Release by Two Neuropeptides

“…FMRFamides enhance transmitter release at crustacean neuromuscular junctions (Kravitz et al, 1980;Mercier et al, 1990;Skerrett et al, 1995;Worden et al, 1995;Jorge-Rivera and Marder, 1996;Friedrich et al, 1998). Our finding that one of the FMRFamides, DF 2 , is effective in modulating release in the fast but not in the slow neuron innervating the same muscle, is new, and makes generalized statements on the role of modulators precarious.…”

“…The effect of Ni 2ϩ was largely reversible after 20 min of washing with saline. 15.0 Ϯ 6.4 (n ϭ 8) (n ϭ 7) (n ϭ 6) (n ϭ 8) (n ϭ 11) (n ϭ 5) I (nA) (%) 73.5 Ϯ 4.9 2.3 Ϯ 1.5 35.0 Ϯ 3.9 77.8 Ϯ 6.1 20.6 Ϯ 4.4 13.0 Ϯ 3.8 (n ϭ 10) (n ϭ 7) (n ϭ 6) (n ϭ 11) (n ϭ 10) (n ϭ 6) The modulation of transmitter release by the peptide DF 2 involves -conotoxin-sensitive Ca 2؉ channels As many as 12 LRFamide-like peptides have been identified in crustaceans (Weimann et al, 1993;Sithigorngul et al, 1998Sithigorngul et al, , 2001Mercier et al, 2001), of which four have been shown to modulate transmitter release from neuromuscular endings in crayfish and lobster (Kravitz et al, 1980;Mercier et al, 1990;Skerrett et al, 1995;Worden et al, 1995;Jorge-Rivera and Marder, 1996;Friedrich et al, 1998). Among them is DRNFLRFamide, also referred to as DF 2 , which enhances junction potential amplitudes by increasing the number of transmitter quanta released (Skerrett et al, 1995).…”

Phosphorylation-Dependent Low-Frequency Depression at Phasic Synapses of a Crayfish Motoneuron

“…Control recordings indicate that this concentration of DMSO does not alter LFD (data not shown). Drug concentration was chosen empirically based on dose-effect trials and on previous published concentrations used in crayfish [Rp-cAMPS, rapamycin (Beaumont et al, 2001), staurosporine, GF, PMA (Friedrich et al, 1998), OA (Swain et al, 1991;Lin and Fu, 2005), Sp-cAMPS, FK-506 (J. E. Swain and M. P. Charlton, unpublished observation)] or in other invertebrates such as Aplysia (FK-506) (Sharma et al, 2003), Mytilus (calcineurin autoinhibitory peptide) (Yamada et al, 2004), and Drosophila (FK-506) (Kuromi et al, 1997).…”

“…Inhibition of protein kinase A or protein kinase C accelerates LFD cAMP-dependent protein kinases A (PKA) and protein kinase C (PKC) were shown to be involved in LTF at crayfish neuromuscular junction (Atwood et al, 1989;Dixon and Atwood, 1989a) and in neuropeptide-induced potentiation (Friedrich et al, 1998). To examine the role of PKA, we applied the inhibitor Rp-cAMPS (300 M), which binds to the regulatory subunit of PKA (Dostmann et al, 1990) 10 min before 0.2 Hz stimulation.…”

Molecular physiology of crustacean and insect neuropeptides

“…88) It increases the amplitude of excitatory junction potentials (EJPs) in deep extensor muscles (DEMs) involving a presynaptic mechanism requiring calcium/calmodulin-dependent protein kinase, protein kinase C and cyclic nucleotide dependent protein kinases. [86][87][88][89] The synaptic modulation was shown to dependent on temperature and extracellular calcium. 91,92) DRNFLRFamide also induces contraction of superficial abdominal extensor muscles 93) and enhances hindgut contractions.…”