Age-Induced Loss of Mossy Fibre Synapses on CA3 Thorns in the CA3 Stratum Lucidum

Table 1

Numerical values of the right dorsal hippocampal volume (top panel); asymmetric synaptic density (middle panel) and quantitative ultrastructural changes to microglia processes (bottom panel) within the CA3-SL with ageing. Total right dorsal hippocampal volume is significantly increased at 28 months of age. Changes are significant in the CA3 only. There is a significant reduction (~43–45%) in the density of mossy fibre asymmetric synapses on CA3 thorny excrescence at 12 and 28 months compared to 4-month-old rats. 12- and 28-month-old animals had a greater number (4-5-fold) of phagolysosome +ve glial processes compared to 4-month-old animals. The number of spherical phagolysosomes per microglial process was increased by 50% at 28 months compared to 12-month-old animals. Values represent mean ± SEM. Asterisks in top panel denote statistical significance (one-way ANOVA) as follows: *𝑃<0.05, **𝑃<0.01, ***𝑃<0.001. Synaptic density estimates were determined by one-way ANOVA, based on normalized 𝑁_𝑣 synaptic values compared to 4-month-old control.

	4 months	12 months	28 months
Right dorsal (anterior) hippocampal volume (mm^3)
CA3	2.69 ± 0.07	3.34 ± 0.14**	3.58 ± 0.017**
Total volume	11.64 ± 0.67	12.17 ± 0.08	13.22 ± 0.28
Asymmetric synaptic density (per μm^3)
Macular synapses	1.45 ± 0.27	0.80 ± 0.22*	0.82 ± 0.07***
Perforated synapses	0.18 ± 0.02	0.13 ± 0.05	0.08 ± 0.03*
Total 𝑁𝑣 (per μm^3)	1.63 ± 0.28	0.93 ± 0.26	0.90 ± 0.06***
Ultrastructural changes to microglial processes
Number of phagolysosome +ve glial processes per 100 μm^3	0.00 ± 0.00	4.21 ± 2.92	5.15 ± 1.23
Number of phagolysosomes per microglial cell process	0.00 ± 0.00	2.6 ± 1.03	5.18 ± 2.00