Morphological and physiological characteristics of PNC neurons with spontaneous activity in vitro. A, B, Reconstruction drawings of two biocytin-filled PNC neurons, insets indicate the cells' position within the PNC. Horizontal lines mark the dorsal border of the PNC, arrowheads in A point to the cell's axon. C, in the absence of injected currents, spontaneous regular spiking was observed in this neuron. D, Responses to intracellular current injection identify this cell as regular non-adapting. E, continuous depolarization starting at a membrane potential of -90 mV revealed this cell's spike threshold at -66.4 mV. d, dorsal, m, medial, v, ventral, l, lateral.