Fig. 5.

Dynamics of spine-like protrusions on well developed pyramidal cell dendrites (12 d in vitro).A, Single-focal-plane view of a CA1 neuron showing the characteristic pyramidal shape with a primary apical dendrite (arrow). The tissue was prepared from a P6 animal and cultured for 12 d. B, Higher-magnification, extended-focus view (combining 6 optical sections spanning 30 μm) of the distal portion of the apical dendrites. Note the complexity of the dendritic arbor and spiny appearance of the oblique dendrite branches (arrows). C, Time-lapse sequence of a region (top box) in B showing both stable, spine-like structures and transient filopodial extensions. A short, knobby spine-like protrusion (arrowhead 1) persists with little change in length or shape. Directly adjacent to this spine, a filopodia-like protrusion (arrowhead 2) extends transiently from the dendrite shaft. Time is shown in minutes. D, Time-lapse sequence of a region (lower box) inB showing rapid formation of a knobby, spine-like protrusion (arrowhead 5). The new spine forms and persists adjacent to an existing spine (arrowhead 4). Note also another spine (arrowhead 3) that persists for the entire observation period but does not change shape or length significantly. Scale bar inC also applies to D. The plots of length versus time for spiny protrusions 1, 2, and 5 correspond to traces 12, 9, and 11, respectively, in Figure 7.