Fig. 3. Intracellular injection of apSyn enhances evoked neurotransmitter release from C1 neuron somata cultured under low-release conditions. (A) Phase-contrast image of the soma of a C1 neuron immediately after contact with a 5HT-sensitive sniffer cell (S). Bar, 50 µm. (B) Phase-contrast image of a C1-C3 soma-soma co-culture. Twenty-four hours after C1-C3 pairing, a sniffer cell (S) was micromanipulated to contact the membrane of the C1 soma to detect neurotransmitter release. Calibration as in A. (C) Sample intracellular recordings of the sniffer cell depolarization (upper trace) induced by a train of action potentials (10 Hz for 10 seconds) in the C1 soma (lower trace) under different experimental conditions. The basal membrane potential of the sniffer cell was kept at -80 mV. (D) The mean sniffer depolarization measured after stimulation of C3-paired C1 somata is significantly lower than the mean depolarization induced by stimulation of isolated C1. The amplitude of sniffer depolarization is significantly higher 24 hours after injection of the GST-apSyn fusion protein. No change is induced by injection of GST alone.