Fig. 1

Calcium imaging of MC and Neuronal activity. a Phase-contrast image on the left panel of a hippocampal neuron (asterisk) at 2 weeks in culture following 24 h coculture with mast cells (black arrows). A glass micropipette of 1 μm ϕ was positioned very close to the neuronal soma before pressure ejection (2.5 psi) pulses of 5 s. The right panel shows the same cells loaded with the Ca²⁺ sensitive dye Fura-2 AM (MCs selected by dashed circles and neuron by the dotted polygon). Scale bar is 5 μm. b Traces of [Ca²⁺]_i transients in three mast cells (blue, red, and green traces) and a hippocampal neuronal cell body (black trace) triggered by the initial neuronal depolarization by microperfusion (70 mM [K⁺] Locke solution). Note the [Ca²⁺]_i oscillation pattern elicited in MCs after initial neuronal activation and the short [Ca²⁺]_i transient (*) evoked in neuron later. Both responses were reproduced in a second stimulation. c Percentage of responding cells. d Mean [Ca²⁺]_i peak obtained in MC- and neuron-evoked responses. e Latencies measured from the beginning of neuronal [Ca²⁺]_i transient induced by depolarization (a) to the origin of MC oscillations (b) and from the latter to the second rise in neuronal trace (c) (*)