The dentate gyrus as a filter or gate: a look back and a look ahead
Introduction
The dentate gyrus, sitting between the entorhinal cortex and area CA3, is both anatomically well positioned and physiologically predisposed to play the role of a gate, blocking or filtering excitatory activity from the entorhinal cortex and controlling the amount of excitation that gets through to the hippocampus. Normal adult granule cells rarely generate action potentials. In part this is because there is little direct interconnectivity between dentate granule cells under normal conditions (reviewed in Chapter 1 of this volume). In addition, granule cells have a high resting membrane potential (Fricke and Prince, 1984; Scharfman, 1992; Staley et al., 1992; Williamson et al., 1993), and strong GABA receptor-mediated inhibition (Mody et al., 1992; Coulter, 1999; Nusser and Mody, 2002; Stell and Mody, 2002; Cohen et al., 2003; Mody, 2005).
Section snippets
History of the idea
Data that the dentate gyrus may serve as a gate appeared in at least as early as 1966 in work by Andersen et al. (1966). In these experiments, the hippocampal formation of adult rabbits was exposed by removal of the overlying neocortex and corpus callosum. Stimulating electrodes were placed into entorhinal cortex or in the perforant pathway. Extracellular as well as intracellular recordings were made from electrodes placed in the transverse plane of the hippocampus, piercing CA1 and both blades
The idea of dentate gate vs. filter
In summary, there is now a series of studies, which suggest that activity in the entorhinal cortex is often halted, delayed, or diminished at the dentate gyrus. The decreased excitability appears to be related at least in part to the strong, prolonged dentate granule cell IPSP first described by Andersen et al. (1966). Further, as also found in that study, repetitive perforant pathway stimulation for a prolonged period of time (a few seconds or longer) results in facilitation of succeeding
Dentate-hilar filtering function: a hypothesis
Various ways in which mossy cells can help the dentate gyrus function as a filter have been proposed. Buckmaster and Schwartzkroin (1994) have suggested a granule cell association hypothesis, wherein the mossy cells help to link subpopulations of granule cells. They suggested that the dentate-hilar role is one of pattern recognition, where the role of the mossy cells is to fill in missing components of perforant pathway input. For example, if the dentate-hilar complex learns to recognize a
A look ahead
Our conjecture for dentate-hilar function is speculative, but testable. The simplest type of experiment would be to monitor all EPSPs from the dentate granular layer in one lamella, and to calculate the initial slope of each EPSP, denoted E in units of volts per second. One would also keep track of which E's result in population spikes. Then a distribution function can be constructed, G(E), giving the probability of observing each value of E (Fig. 2, filled squares). One can also determine the
Acknowledgments
I am grateful to Drs. Helen Scharfman and Thomas Sutula for helpful advice and for the opportunity to write this chapter. I also thank the American Epilepsy Society for support, and the National Institutes of Health and National Center for Research Resources K12 Roadmap, Project number 8K12RR023268-02.
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2022, Behavioural Brain ResearchCitation Excerpt :The mammalian hippocampus is mainly divided into the CA1, CA3, and the dentate gyrus (DG), and each subregion exhibits differing functions in spatial learning and memory [13,14]. Among them, the DG is a highly plastic region located at the entrance of the hippocampal tri-synaptic loop [15]. Moreover, evidences indicate that the DG lesions in rats impair the formation of spatial memory, and the morphological damage and impairment of synaptic plasticity in the DG are appeared in AD rats [16–18].
Epilepsy
2022, Neurobiology of Brain Disorders: Biological Basis of Neurological and Psychiatric Disorders, Second EditionIn vitro Oscillation Patterns Throughout the Hippocampal Formation in a Rodent Model of Epilepsy
2021, NeuroscienceCitation Excerpt :At 60 days post-SE, although the duration of ictal events was shorter in DG from epileptic animals, the susceptibility to generate ictal events was higher, when compared to control group; and the duration of ictal events increased when compared to the 30 days post-SE group, demonstrating a higher ictogenesis in the DG at established epilepsy. DG plays an important role in battling the epileptiform discharges propagation from EC to hippocampus (Barbarosie et al., 2000; Hsu, 2007). As observed in animal models and patients with TLE, the DG undergoes a variety of pathological changes that may disrupt the gating function, contributing to the development of epilepsy (Scharfman, 2019).