Table 1

Means, SE, and sample sizes for 2D TEM morphological analyses

	Age	Total boutons	Total synapses	PSD length (μm)	Bouton area (μm²)	% SBBs	Spinule area (μm²)	Spinule:bouton area (%)

	p21	70	74	0.29	0.34	4%	0.04	12%
	p28	71	78	0.27	0.42	7%	0.02	6%
Group sum Group mean ± SEM (n = animals)		141	152	0.28 ± 0.01	0.38 ± 0.03	6 ± 1.4%	0.03 ± 0.01	9 ± 3.1%
Cumulative mean ± SEM (n = sampled structures)				0.28 ± 0.01	0.38 ± 0.03	6 ± 1.4%	0.03 ± 0.01	6 ± 1.5%

	p46	102	102	0.28	0.19	6%	0.02	6%
	p47	94	94	0.29	0.21	6%	0.03	12%
Group sum Group mean ± SEM (n = animals)		196	196	0.29 ± 0.01	0.20 ± 0.01	6 ± 0.3%	0.03 ± 0.001	9 ± 3.2%
Cumulative mean ± SEM (n = sampled structures)				0.29 ± 0.01	0.20 ± 0.01	6 ± 0.3%	0.02 ± 0.004	8 ± 3.2%

	p60_1	25	29	0.28	0.21	10%	0.04	14%
	p60_2	111	113	0.29	0.28	13%	0.01	4%
	p66_1	118	124	0.31	0.28	11%	0.04	14%
Group sum Group mean ± SEM (n = animals)		254	266	0.30 ± 0.01	0.26 ± 0.02	11 ± 0.8%	0.03 ± 0.01	11 ± 3.4%
Cumulative mean ± SEM (n = sampled structures)				0.30 ± 0.01	0.27 ± 0.01	11 ± 0.8%	0.03 ± 0.01	10 ± 1.7

	>p90_1	61	61	0.32	0.29	16%	0.06	16%
	>p90_2	149	150	0.36	0.33	15%	0.02	5%
	>p90_3	109	112	0.34	0.35	22%	0.04	4%
Group sum Group mean ± SEM (n = animals)		319	323	0.35 ± 0.01	0.32 ± 0.01	18 ± 2.1%	0.04 ± 0.01	8 ± 4%
Cumulative mean ± SEM (n = sampled structures)				0.35 ± 0.01	0.33 ± 0.01	18 ± 2.1%	0.04 ± 0.01	8 ± 1%

Means and SEM for individual animals and developmental age groups are listed for each 2D TEM analysis measurement (column titles). Population sizes are listed for individual animals and age groups under total boutons and total synapses columns. % SBBs = percentage of sampled excitatory presynaptic boutons that contained spinules. Spinule: bouton area % = percentage of bouton area occupied by spinule area.