Abstract
The dorsoventral axis of the hippocampus exhibits functional differentiations with regard to (spatial Vs emotional) learning and information retention (rapid encoding Vs long‐term storage), as well as its sensitivity to neuromodulation and information received from extrahippocampal structures. The mechanisms that underlie these differentiations remain unclear. Here, we explored neurotransmitter receptor expression along the dorsoventral hippocampal axis and compared hippocampal synaptic plasticity in the CA1 region of the dorsal (DH), intermediate (IH) and ventral hippocampi (VH). We observed a very distinct gradient of expression of the N‐methyl‐D‐aspartate receptor GluN2B subunit in the Stratum radiatum (DH< IH< VH). A similar distribution gradient (DH< IH< VH) was evident in the hippocampus for GluN1, the metabotropic glutamate receptors mGlu1 and mGlu2/3, GABAB and the dopamine‐D1 receptor. GABAA exhibited the opposite expression relationship (DH > IH > VH). Neurotransmitter release probability was lowest in DH. Surprisingly, identical afferent stimulation conditions resulted in hippocampal synaptic plasticity that was the most robust in the DH, compared with IH and VH. These data suggest that differences in hippocampal information processing and synaptic plasticity along the dorsoventral axis may relate to specific differences in the expression of plasticity‐related neurotransmitter receptors. This gradient may support the fine‐tuning and specificity of hippocampal synaptic encoding.
Highlights
Over the past 50 years, the functional organization of the hippocampal longitudinal axis has been a focus of intensive research
Synaptic plasticity profiles expressed by the Schaffer collateral– CA1 synapses differ between these three domains, whereby long-term potentiation (LTP) exhibits the highest magnitude in the dorsal compared with intermediate and ventral subdivisions
We found that mGlu5 was equivalently expressed across the hippocampal dorsoventral axis, suggesting that this receptor contributes little to the differences in LTP that we observed
Summary
Over the past 50 years, the functional organization of the hippocampal longitudinal axis has been a focus of intensive research. A gradual functional shift from the dorsal towards the ventral hippocampal pole has been reported (Kjelstrup et al, 2008; Strange et al, 2014), whereby the intermediate hippocampus (IH) subserves a transitional role between the two hippocampal poles. This intermediate hippocampal subdivision is postulated to play a specific role in the translation of new rapid learning into efficient behavioral performance (Bast, Wilson, Witter, & Morris, 2009).
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