Stochasticity in Ca2+ Increase in Spines Enables Robust and Sensitive Information Coding
A, Cerebellar Purkinje cells. Male mouse cerebellar Purkinje cells were doubly stained with anti-calbindin antibody to visualize whole cells (green) and with anti-mGluR (metabotropic glutamate receptor) antibody to specifically visualize the spines of the PF-Purkinje cell synapses (red). The inset in the left image is magnified in the right panel. The average volume of spines in cerebellar Purkinje cells has been reported to be 0.1 µm3, which is 104-fold smaller than a cell body (5,000 µm3). White circles in the left and right panels indicate a typical soma and spine, respectively. B, Schematic representation of PF and CF inputs-dependent Ca2+ increase in the simulation model  (Materials and Methods). Abbreviations: Glu; glutamate, mGluR; metabotropic glutamate receptor, IP3; inositol trisphosphate; AMPAR; α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor, VGCC; voltage-gated Ca2+ channels. Parentheses indicate initial numbers of the indicated molecules in the stochastic model. C, Ca2+ responses along the PF-CF interval in the experiments (black circles) , and mean Ca2+ responses in the stochastic simulation in a spine volume (0.1 µm3) (solid line) and in the stochastic simulation in a cell volume (5,000 µm3) (dashed line). The Ca2+ response was defined as the average relative change in fluorescence (ΔF/F0) of Magnesium Green 1, a Ca2+ indicator . Positive sign of the interval are given to Δt msec when PF inputs precede CF inputs; otherwise, a negative sign is given. Five PF inputs at 100 Hz and a single CF were given.