title: Wavelet transform-based de-noising for two-photon imaging of synaptic Ca2+ transients.
abstract: Postsynaptic Ca(2+) transients triggered by neurotransmission at excitatory synapses are a key signaling step for the induction of synaptic plasticity and are typically recorded in tissue slices using two-photon fluorescence imaging with Ca(2+)-sensitive dyes. The signals generated are small with very low peak signal/noise ratios (pSNRs) that make detailed analysis problematic. Here, we implement a wavelet-based de-noising algorithm (PURE-LET) to enhance signal/noise ratio for Ca(2+) fluorescence transients evoked by single synaptic events under physiological conditions. Using simulated Ca(2+) transients with defined noise levels, we analyzed the ability of the PURE-LET algorithm to retrieve the underlying signal. Fitting single Ca(2+) transients with an exponential rise and decay model revealed a distortion of τ(rise) but improved accuracy and reliability of τ(decay) and peak amplitude after PURE-LET de-noising compared to raw signals. The PURE-LET de-noising algorithm also provided a ∼30-dB gain in pSNR compared to ∼16-dB pSNR gain after an optimized binomial filter. The higher pSNR provided by PURE-LET de-noising increased discrimination accuracy between successes and failures of synaptic transmission as measured by the occurrence of synaptic Ca(2+) transients by ∼20% relative to an optimized binomial filter. Furthermore, in comparison to binomial filter, no optimization of PURE-LET de-noising was required for reducing arbitrary bias. In conclusion, the de-noising of fluorescent Ca(2+) transients using PURE-LET enhances detection and characterization of Ca(2+) responses at central excitatory synapses.
authors.affiliation: Medical Research Council Centre for Synaptic Plasticity, School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom. cezar.tigaret@bristol.ac.uk
authors.forename: Cezar M
authors.initials: CM
authors.lastname: Tigaret
authors.forename: Krasimira
authors.initials: K
authors.lastname: Tsaneva-Atanasova
authors.forename: Graham L
authors.initials: GL
authors.lastname: Collingridge
authors.forename: Jack R
authors.initials: JR
authors.lastname: Mellor
mesh_terms: D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D019706:Excitatory Postsynaptic Potentials; D006624:Hippocampus / Q000166:cytology; D008297:Male; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D059629:Signal-To-Noise Ratio; D013569:Synapses / Q000378:metabolism*; D058067:Wavelet Analysis
chemical_list: D002118:Calcium