Figure 2
Optical quantal analysis with Ca2+ sensitive dyes. (A) Postsynaptic Ca2+ imaging. (Left) Activation of the axons within stratum radiatum (sr) with a stimulating electrode (SE) resulted in stochastic calcium signalling in several spines (a-g) of a dye-filled CA1 neuron in an acute hippocampal slice. (A; a-g) To enable rapid imaging of calcium events over time, laser scanning was restricted to a line (white vertical line) through responsive spines. The results from a line scan depicting successful transmitter release is presented next to each imaged spine; the broken vertical line indicates the point of stimulation. The probability of detecting a calcium event is displayed under each line scan and is used as a measure of the probability of transmitter release at the associated bouton. (B) Presynaptic Ca2+ imaging. (Left) Axonal projection of CA3 hippocampal neuron loaded with a Ca2+-sensitive dye. Laser scanning was restricted to a line through an axonal bouton in order to rapidly monitor fluorescence, in response to single action potentials, over time. (i) Three such line scans are presented, along with (ii) the quantified change in fluorescence (ΔF/F) and (iii) the recorded membrane potential. Note that in the second line scan, the action potential generates a larger calcium transient than in the first and second scan. This high-amplitude calcium transient reflects the additional activation of presynaptic NMDAR following the release of glutamate, and can be used as a measure of the probability of transmitter release at the associated bouton. Figure 2A: Reprinted from Neuron, 62(2), Enoki, R., Y.L. Hu, D. Hamilton, and A. Fine, Expression of long-term plasticity at individual synapses in hippocampus is graded, bidirectional, and mainly presynaptic: optical quantal analysis, p242-53., Copyright (2009), with permission from Elsevier. Figure 2B: Reprinted from Neuron, 68(6), McGuinness, L., C. Taylor, R.D. Taylor, C. Yau, T. Langenhan, M.L. Hart, H. Christian, P.W. Tynan, P. Donnelly, and N.J. Emptage, Presynaptic NMDARs in the Hippocampus Facilitate Transmitter Release at Theta Frequency, p1109-27., Copyright (2010), with permission from Elsevier.