title: Activity-dependent increases in [Ca2+]icontribute to digital-analog plasticity at a molluscan synapse.
abstract: In a type of short-term plasticity that is observed in a number of systems, synaptic transmission is potentiated by depolarizing changes in the membrane potential of the presynaptic neuron before spike initiation. This digital-analog form of plasticity is graded. The more depolarized the neuron, the greater the increase in the efficacy of synaptic transmission. In a number of systems, including the system presently under investigation, this type of modulation is calcium dependent, and its graded nature is presumably a consequence of a direct relationship between the intracellular calcium concentration ([Ca2+]i) and the effect on synaptic transmission. It is therefore of interest to identify factors that determine the magnitude of this type of calcium signal. We studied a synapse inAplysiaand demonstrate that there can be a contribution from currents activated during spiking. When neurons spike, there are localized increases in [Ca2+]ithat directly trigger neurotransmitter release. Additionally, spiking can lead to global increases in [Ca2+]ithat are reminiscent of those induced by subthreshold depolarization. We demonstrate that these spike-induced increases in [Ca2+]iresult from the activation of a current not activated by subthreshold depolarization. Importantly, they decay with a relatively slow time constant. Consequently, with repeated spiking, even at a low frequency, they readily summate to become larger than increases in [Ca2+]iinduced by subthreshold depolarization alone. When this occurs, global increases in [Ca2+]iinduced by spiking play the predominant role in determining the efficacy of synaptic transmission.NEW & NOTEWORTHYWe demonstrate that spiking can induce global increases in the intracellular calcium concentration ([Ca2+]i) that decay with a relatively long time constant. Consequently, summation of the calcium signal occurs even at low firing frequencies. As a result there is significant, persistent potentiation of synaptic transmission.
authors.affiliation: Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York; and.|Department of Biology and Environmental Sciences, Longwood University, Farmville, Virginia.
authors.forename: Bjoern Ch
authors.initials: BC
authors.lastname: Ludwar
authors.affiliation: Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York; and.
authors.forename: Colin G
authors.initials: CG
authors.lastname: Evans
authors.affiliation: Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York; and.
authors.forename: Monica
authors.initials: M
authors.lastname: Cambi
authors.affiliation: Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York; and elizabeth.cropper@gmail.com.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Cropper
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D005260:Female; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism*; D008297:Male; D008465:Mechanoreceptors / Q000166:cytology / Q000378:metabolism; D008839:Microelectrodes; D009473:Neuronal Plasticity / Q000502:physiology*; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D046509:Tissue Culture Techniques; D056969:Voltage-Sensitive Dye Imaging
chemical_list: D002413:Cations, Divalent; D002118:Calcium
keywords: Aplysia; calcium; invertebrate; synaptic plasticity; transmitter release