Abstract
BackgroundElucidating specializations of the intrinsic neuronal network between the dorsal and the ventral hippocampus is a recently emerging area of research that is expected to help us understand the mechanisms underlying large scale functional diversification along the hippocampus. The aim of this study was to characterize spontaneous network activity between the dorsal and the ventral hippocampus induced under conditions of partial or complete blockade of GABAergic inhibition (i.e. disinhibition).ResultsUsing field recordings from the CA3 and CA1 fields of hippocampal slices from adult rats I found that ventral compared with dorsal hippocampus slices displayed higher propensity for and higher frequency of occurrence of spontaneous field potentials (spfps) at every level of disinhibition. Also NMDA receptor-depended spfps (spfps-nmda) occurred with higher probability more frequently and were larger in the ventral compared with the dorsal hippocampus. Importantly, blockade of GABAB receptors produced a stronger effect in enhancing the probability of generation of spfps and spfps-nmda in the dorsal compared with the ventral hippocampal slices and increased spfps-nmda only in dorsal slices.ConclusionThese results demonstrate a higher intrinsic neuronal excitability of the ventral compared with the dorsal local circuitry with the considerable contribution of NMDA receptors. Furthermore, the GABAB receptors control the total and the NMDA receptor-dependent excitation much less effectively in the ventral part of the hippocampus. It is proposed that NMDA and GABAB receptors significantly contribute to differentiate local network dynamics between the dorsal and the ventral hippocampus with important implications in the information processing performed along the long hippocampal axis.
Highlights
Elucidating specializations of the intrinsic neuronal network between the dorsal and the ventral hippocampus is a recently emerging area of research that is expected to help us understand the mechanisms underlying large scale functional diversification along the hippocampus
The results show that the intrinsic neuronal network of VH compared with DH exhibits higher excitability with the NMDA receptors having a significant contribution in the higher excitability of VH
Local network excitation is higher and less effectively controlled by GABABRs in VH compared with DH Spontaneous field potentials induced under conditions of blockade of GABAARs (Fig. 1b) were comparatively studied in DH and VH slices (Fig. 1c)
Summary
Elucidating specializations of the intrinsic neuronal network between the dorsal and the ventral hippocampus is a recently emerging area of research that is expected to help us understand the mechanisms underlying large scale functional diversification along the hippocampus. The first characteristic difference that was observed between the two hippocampal poles was the higher susceptibility of the ventral hippocampus in rodents and the anterior hippocampus in human to epileptic activities [19, 20] These early observations were repeatedly confirmed and extended by subsequent more thorough in vivo and in vitro studies performed in rats [4, 7, 21,22,23,24,25,26,27,28,29,30]. A typical experimental approach to study synchronous network activity is based on the induction of spontaneous activity in isolated brain preparations [32] This is achieved by changing the excitation/ inhibition balance through lowering inhibitory activity using the so-called disinhibition models [33]. GABABRs play a more important role in restricting network excitability in DH than in VH
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