Table 2.

Percentages of SBBs, perforated PSDs, spinule origins, and sampled structures for FIBSEM analyses

FIBSEM
Age	Total boutons	Total synapses	% SBBs	% Perforated PSDs	% PS spine	% Adj axon	% Adj spine	% Adj dendrite	% Adj glia	% Unknown
>p90	223	237	24.2	29.5	37.0	35.2	7.4	14.8	5.6	3.7
p60	235	256	14.5	18.4	14.7	55.9	8.8	17.7	0.0	0.0
p46	157	163	6.4	16.6	10.0	50.0	0.0	40.0	0.0	0.0
p21	61	62	6.6	16.1	25.0	25.0	0.0	25.0	0.0	25.0

Total sampled boutons and synapses for each age are listed under total boutons and total synapses columns for FIBSEM analyses at each age examined. Percentages of SBBs and perforated PSDs in FIBSEM analyses are listed in their respective columns for each age examined. Percentages of SBBs containing at least one spinule from a neurite/glial source are listed in their respective columns for each age examined. PS = postsynaptic; adj = adjacent (i.e., not synaptic); unknown = spinules whose origin could not be determined (for details, see Materials and Methods). Since some SBBs contained spinules from multiple sources, percentages of spinules from all origins may sum to greater than 100%.