Synaptic stimulation of cholinergic afferents evokes calcium waves that invade the nucleus.a, A fluorescent image of a cell loaded with 50 μm Oregon Green BAPTA-1. b, The selected pseudocolor frames are baseline-subtracted images (ΔF) taken at 300 msec intervals after synaptic stimulation (10 pulses at 33 Hz). c, Rises in calcium, plotted as ΔF/F, measured at the soma (s), nucleus (n), and different distances from the soma (in micrometers), are shown in thetop traces. The bottom trace shows the whole-cell current over the same time period. A 30 mV hyperpolarizing step was applied during the tetanus to ensure that voltage-gated channels were not activated during the tetanus. d, In neurons in which calcium waves evoked by brief (10–20 pulses at 33 Hz) synaptic stimulation did not propagate to the nucleus, the propagation distance could be increased by increasing the number of stimuli (data not shown) or application of eserine. e, Synaptic stimulation of cholinergic afferents amplifies of action potential-induced calcium transients. The nuclear calcium rise to a train of four action potentials, plotted as ΔF/F, was greater when action potentials immediately followed synaptic stimulation (33 Hz, 1 sec;thick traces) than without previous synaptic stimulation (thin traces). Sequential application of eserine, MCPG, and atropine in the presence of CNQX and APV demonstrate that the amplification was attributable to activation of cholinergic synapses.