Fig. 4. The spherical cells `phenotype'. (A,B) Biocytin-filled spherical cell characteristically firing a single spike when stimulated by long-lasting current step. (A) The spherical cells bear round smooth soma of about 15 µm diameter from which only one thin dendrite might emerge (not in this case) and a thick axon with a thin initial segment. (B) Traces from the same cell are displayed at a different magnification to show the shapes of the spikes (red and black traces) and the absence of repetitive firing with long lasting stimuli (inset). (C) Some cells (black and red traces) fire the spike on the falling face of a hump evoked by the stimulus step (stimuli in nA: violet 0.95; blue 0.75, green 0.60, black 0.50, red 0.40). (D) Spike latency was a hyperbolic function of the stimulus intensity (data from another cell).