The Hippocamposeptal Pathway Generates Rhythmic Firing of GABAergic Neurons in the Medial Septum and Diagonal Bands: An Investigation Using a Complete Septohippocampal Preparation In Vitro

Abstract : The medial septum diagonal band area (MS/DB) projects to the hippocampus through the fornix/fimbria pathway and is implicated in generating hippocampal theta oscillations. The hippocampus also projects back to the MS/DB, but very little is known functionally about this input. Here, we investigated the physiological role of hippocamposeptal feedback to the MS/DB in a complete in vitro septohippocampal preparation containing the intact interconnecting fornix/fimbria pathway. We demonstrated that carbachol-induced rhythmic theta-like hippocampal oscillations recorded extracellularly were synchronized with powerful rhythmic IPSPs in whole-cell recorded MS/DB neurons. Interestingly, we found that these IPSPs evoked rebound spiking in GABAergic MS/DB neurons. In contrast, putative cholinergic and glutamatergic MS/DB neurons responded only weakly with rebound spiking and, as a result, were mostly silent during theta-like oscillations. We next determined the mechanism underlying the rebound spiking that followed the IPSPs in MS/DB GABAergic neurons using phasic electrical stimulation of the fornix/fimbria pathway. We demonstrate that the increased rebound spiking was attributable to the activation of I(h) current, because it was significantly reduced by low concentrations of the I(h) antagonist ZD7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyridinium chloride]. Together, these results suggest that rhythmical activity in hippocampus is transferred to the MS/DB and can preferentially phase the spiking of GABAergic MS/DB neurons because of their significant expression of I(h) currents. Our data demonstrate that hippocamposeptal inhibition facilitates theta rhythmic discharges in MS/DB GABAergic neurons while favoring the inhibition of most ACh and glutamate neurons.
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https://hal.archives-ouvertes.fr/hal-02349374
Contributor : Romain Goutagny <>
Submitted on : Tuesday, November 5, 2019 - 4:14:19 PM
Last modification on : Wednesday, November 6, 2019 - 1:36:25 AM

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Frédéric Manseau, Romain Goutagny, Marc Danik, Sylvain Williams. The Hippocamposeptal Pathway Generates Rhythmic Firing of GABAergic Neurons in the Medial Septum and Diagonal Bands: An Investigation Using a Complete Septohippocampal Preparation In Vitro. Journal of Neuroscience, Society for Neuroscience, 2008, 28 (15), pp.4096-4107. ⟨10.1523/JNEUROSCI.0247-08.2008⟩. ⟨hal-02349374⟩

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