Aim: 

Several subtypes of serotonin (5-HT) receptors are expressed in the hippocampus and various functions of 5-HT have been hypothesised.

Methods: 

Using whole-cell patch clamp on either rat or mouse brain slices, we tested 5-HT effects on AMPA receptor-mediated excitatory post synaptic currents (EPSCs) evoked in CA₁ pyramidal neurons by stimulation of Schaffer collaterals.

Results: 

At post natal (PN) day 10-20, 5-HT reduced the amplitude of AMPA-mediated EPSCs. This effect was mimicked by the 5-HT_1A agonist 8-OH PIPAT and by the mixed 5-HT_1A/5-HT₇ agonist 8-OH DPAT and was abolished by the 5-HT_1A antagonist NAN-190. 5-HT_1A agonists increased the paired-pulse facilitation (PPF) ratio, thus probably modified the synaptic release of glutamate. In contrast, at PN 7-9 8-OH DPAT enhanced AMPA-mediated EPSCs; such effect was not antagonised by NAN-190, suggesting the involvement of 5-HT₇ receptors. The PPF ratio was unchanged, indicating a post-synaptic effect. Similar results were obtained from rats and mice within the same age group.

Conclusion: 

We showed that 5-HT_1A and 5-HT₇ receptors exert opposite effects on CA₃-CA₁ transmission and suggest their different role during development. The balance between 5-HT_1A and 5-HT₇ effects might have important consequences on hippocampal-dependent learning, as pointed out by behavioural studies. Further developments of our study may contribute to the understanding of pathologies affecting hippocampal synaptic transmission and provide new suggestions for a pharmacological treatment of developmental cognitive disorders.