Abstract
Evidence for different physiological properties along the hippocampal longitudinal axis is emerging. Here, we examined the electrophysiological features of neurons at different dorso-ventral sites of the mouse CA1 hippocampal region. Cell position was defined with respect to longitudinal coordinates of each slice. We measured variations in neuronal excitability, subthreshold membrane properties and neurotransmitter responses along the longitudinal axis. We found that (i) pyramidal cells of the dorsal hippocampus (DH) were less excitable than those of the ventral hippocampus (VH). Resting Membrane Potential (RMP) was more hyperpolarized and somatic Input Resistance (Ri) was lower in DH compared to VH. (ii) The Paired-pulse ratio (PPR) of focally induced synaptic responses was systematically reduced from the DH to the VH; (iii) Long-term-potentiation was most pronounced in the DH and fell gradually in the intermediate hippocampus and in the VH; (iv) the frequency of miniature GABAergic events was higher in the VH than in the DH; (v) the PPR of evoked inhibitory post-synaptic current (IPSC) was higher in the DH than in the VH. These findings indicate an increased probability of both GABA and glutamate release and a reduced plasticity in the ventral compared to more dorsal regions of the hippocampus.
Highlights
Several studies based on gene expression, anatomical and behavioral measurements have suggested that the hippocampus has different functional organizations along its longitudinal axis
The longitudinal coordinates of the dorsal hippocampus (DH), IH and ventral hippocampus (VH) are presented in Fig. 1c together with representative Hoechst-stained slices at 5 different levels
We found that pyramidal cells of DH were less excitable than those of IH or VH, the short- and long-term plasticity were systematically reduced from the DH to the VH and GABAergic transmission was higher in VH than in DH, indicating an increased probability of both GABA and glutamate release in the VH compared to more dorsal regions of the hippocampus
Summary
Several studies based on gene expression, anatomical and behavioral measurements have suggested that the hippocampus has different functional organizations along its longitudinal axis. VH is significantly smaller than that induced in both DH14,16 and IH19 Though these results provide an electrophysiological characterization along the hippocampal longitudinal axis in the rat, only very limited amount of data is available for the mouse[20], prompting the need to extend the study to this species. We investigated in the mouse the electrophysiological properties of CA1 pyramidal cells along the hippocampal longitudinal axis. Neuronal properties, including subthreshold membrane behavior and firing activity, as well as short- and long-term plasticity at synapses that excites these cells were assessed. We examined for the first time the inhibitory GABAergic synaptic function in DH and VH To this purpose, we exploited an experimental strategy, based on isolating and straightening the hippocampus, to determine the coordinates of the neurons along the dorsal to ventral axis
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