Theta burst stimulation-induced LTP: Differences and similarities between the dorsal and ventral CA1 hippocampal synapses.

The hippocampal synapses display a conspicuous ability for long-term plasticity, which is thought to contribute to learning and memory. Previous research has shown that long-term potentiation (LTP) greatly differs between the dorsal (DH) and ventral (VH) CA1 hippocampal synapses when induced by high-frequency stimulation. In this study, using rat hippocampal slices and more physiologically relevant activity patterns based on the frequency of the theta rhythm (i.e., theta-burst stimulation, TBS) we found that the DH compared with the VH displayed a higher ability for induction and stability of NMDA receptor-dependent LTP of the field excitatory postsynaptic potential. Nevertheless, the maximal magnitude of LTP was similar in the two hippocampal segments. Blockade of GABA receptors prevented the LTP induction by the minimal effective TBS and reduced the magnitude of LTP induced by longer TBS. TBS produced a three-fold higher facilitation of the synaptic burst responses in the DH compared with the VH, accompanied by a strong enhancement in the postsynaptic excitation in the DH but mostly depression in the VH. The DH displayed NMDA receptor-dependent and NMDA receptor-independent facilitation, but the facilitation in the VH was only NMDA receptor-dependent. Also, the TBS-associated activity of GABA receptors was higher in the DH than in the VH. The different response profiles during TBS could underlie the differences in LTP between the two hippocampal segments. L-type voltage-dependent calcium channels (L-VDCC) and the metabotropic glutamate receptor-5 (mGluR5) equally contributed in DH and VH to compound LTP induced by relatively long TBS. We propose that these dorsoventral differences in synaptic plasticity reflect specializations of the intrinsic circuitry of the hippocampus, that are involved in the distinct information processing performed by the two hippocampal segments and could effectively support the contribution of the dorsal and the ventral hippocampal segment to single event memory and to emotional memory respectively. © 2016 Wiley Periodicals, Inc.