C. Bertoni-Freddari, D. Platano, P. Fattoretti, B. Giorgetti, Y Grossi, M. Balietti, T. Casoli, G. Di Stefano, G. Aicardi

A computer-assisted morphometric study has been carried out on the synaptic junctional areas of perirhinal cortex isolated from adult (4-6 month-old) and old (25-27 month-old) Wistar rats exposed to an object-recognition training. The paradigm consisted of 6 sessions in which the animals could explore two identical objects. Rats were divided into the following groups: trained animals: adult trained (AT) and old trained (OT); untrained animals: adult control (AC) and old control (OC). The ultrastructural parameters measured on synapses preferentially stained by the ethanol phosphotungstic acid preferential technique (E-PTA) were: numeric density (number of synapses/mm3 of tissue: Nv), synaptic average area (size: S), and surface density (area of the synaptic contact zones/mm3 of tissue: Sv). Nv was significantly higher in OT, and AT vs. OC groups. S was significantly higher in OC vs. OT, AT and AC animals. Sv was significantly higher only in OT vs. AT. No significant difference was found as regards the percent of perforated synapses among the groups analysed. A percent distribution of S showed that in all the old animals (i.e. OC and OT) the fraction of oversized contacts (S>0.5 μm2) was higher than in the groups of adult rats (i.e. AC and AT). Moreover, in the OC group the fraction of these megasynapses accounted for about 8% vs. 3% in the OT group. Accordingly, the fraction of smaller junctional areas (S0.5 μm2) was almost the same in the two adult groups (it ranged from about 1 to 2%), while the small junctions (S

Keywords (Optional): 
Synaptic plasticity
Object-recognition test
Perirhinal cortex
Synaptic morphometry