ABSTRACT
Introduction. Social isolation has become an important public health issue since the COVID-19 pandemic outbreak. Lack of social contacts is especially challenging for adolescents because social interaction at this age is essential for healthy neuroendocrine system maturation. Aim. This study aimed to investigate the effect of adolescent social isolation on synaptic plasticity in the dorsal and ventral hippocampus of rats. Methods. Male Wistar rats were randomly assigned into either isolation-housing or group-housing immediately after weaning at postnatal day 23-25. After 4 weeks of different housing conditions, acute hippocampal slices (400 ±m thick) were prepared from dorsal (DH) and ventral (VH) poles of the hippocampus. Field excitatory postsynaptic potentials (fEPSP) were recorded from the stratum radiatum of the hippocampal CA1 region after stimulation of the Schaffer collateral. Long-term potentiation (LTP) was elicited by a high-frequency tetanic stimulation (HFS) train (100 Hz, 1 s), after which changes in the fEPSP were recorded. The period between 1 and 10 minutes after HFS was defined as short-term potentiation (STP). LTP was evaluated by averaging synaptic responses from 30 to 40 minutes after HFS. Results. We found that socially isolated rats had increased STP in the VH (166.4 ± 7.3 % vs. 137.1 ± 5.0 % in group-housed rats, p<0.05), while no changes were observed in the DH (165.3 ± 4.9 % vs. 162.3 ± 4.1 % in group-housed rats). Moreover, group-housed rats showed significant dorsoventral differences in STP (p<0.05), while fEPSP slopes in the DH and VH of isolated rats were similar. We also found that this dorsoventral heterogeneity was maintained in LTP of the group-housed rats (group-housed DH: 142.2 ± 8.3 % vs. group-housed VH: 110.9 ± 4.6 %, P<0.05), while there was no difference between DH and VH in the isolated group (isolated DH: 134.6 ± 8.9 % vs. isolated VH: 122.0 ± 5.6 %). Conclusions. Our results indicate that prolonged adolescent social isolation enhances short-term potentiation in the ventral hippocampus and abolishes dorsoventral heterogeneity in short-term and long-term potentiation. These alterations in hippocampal synaptic plasticity may have a role in the cognitive and behavioral disorders induced by social isolation.