Tai S, Leung L (2009) Facilitation of dentate gyrus population spike may involve septohippocampal GABAergic input. Neuroscience 2009 Abstracts 566.18/EE33. Society for Neuroscience, Chicago, IL.
Summary: The medial septum (MS) is known to modulate the neural circuitry in the hippocampus. It have been demonstrated that, in anaesthetized rats, MS stimulation prior to perforant path stimulation facilitated the population spike in the dentate gyrus and such facilitation was unaffected by muscarinic and nicotinic cholinergic antagonists, suggesting that this facilitation may be mediated by septohippocampal GABAergic neurons. To study the effects of septohippocampal neurons in modulating neural circuitry in the dentate gyrus, selective lesion of septohippocampal GABAergic cells was made by infusion of orexin-saporin in the MS. Evoked field potentials were recorded in the dentate gyrus following stimulation of the medial perforant path in urethane-anesthetized rats using multichannel silicon probes and analyzed as current source density. High-frequency stimulation of the pontis oralis (PnO) activated a hippocampal theta rhythm. Theta peak power was attenuated in lesion rats as compared to control (sham lesion) rats. PnO stimulation resulted in a larger average increase in dentate population spike (pSpike) in control rats compared to lesion rats (26.4 ± 8.8 % vs 5.1 ± 8.7 %) but the difference was not significant (P = 0.1082; control n = 9, lesion n = 8). The number of choline acetyltransferase-immunopositive (cholinergic) cells in the MS was not significantly different (P = 0.88, unpaired t-test) between lesion and control rats, while a significant decrease (about 50%) of the number of parvalbumin-immunopositive GABAergic cells in the MS was observed in lesion as compared to control rats (P<0.05, unpaired t-test). The effect of PnO stimulation on the paired-pulse pSpike response versus interpulse interval (30 - 400 ms) was not different between control and lesion rats. No difference between control and lesion rats was detected in the pSpike enhancement after PnO stimulation following scopolamine (5 mg/kg i.p.). Additional studies were needed to demonstrate the facilitation of dentate gyrus population spike by septohippocampal GABAergic neurons.
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