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Christine Gebhardt, Valentina Mosienko, Natalia Alenina, Doris Albrecht
This study focuses on analyzing long term potentiation (LTP) changes in the lateral nucleus of the amygdala (LA) and in the CA1 region of the hippocampus in slices derived from mice deficient in tryptophan hydroxylase 2 (TPH2-/- ), the rate-limiting enzyme for 5-HT synthesis in the brain. We found a reduced LTP in both brain structures in TPH2-/- mice. However, we found no changes in the magnitude of LTP in TPH2-/- mice compared to wildtype mice when it was preceded by a paired pulse protocol. Whereas the magnitude of long term depression (LTD) did not differ between wildtype and TPH2-/- mice, priming synapses by LTD-induction facilitated subsequent CA1-LTP in wildtype mice to a greater extent than in TPH2-/- mice...
November 20, 2018: Hippocampus
Matthew G Buckley, Tobias Bast
Watermaze tests of place learning and memory in rodents and corresponding reverse-translated human paradigms in real or virtual environments are key tools to study hippocampal function. In common variants, the animal or human participant has to find a hidden goal that remains in the same place over many trials, allowing for incremental learning of the place with reference to distal cues surrounding the circular, featureless maze. Although the hippocampus is involved in incremental place learning, rodent studies have shown that the delayed-matching-to-place (DMP) watermaze test is a more sensitive assay of hippocampal function...
November 19, 2018: Hippocampus
Molly S Hermiller, Stephen VanHaerents, Tommi Raij, Joel L Voss
Episodic memory is thought to rely on interactions of the hippocampus with other regions of the distributed hippocampal-cortical network (HCN) via interregional activity synchrony in the theta frequency band. We sought to causally test this hypothesis using network-targeted transcranial magnetic stimulation. Healthy humans participants completed four experimental sessions, each involving a different stimulation pattern delivered to the same individualized parietal cortex location of the HCN for all sessions...
November 17, 2018: Hippocampus
Robin Dard, Lionel Dahan, Claire Rampon
Hippocampal adult neurogenesis results in the persisting formation of new neurons that contribute to hippocampal-dependent learning and memory. This has led to the hypothesis that memory impairments associated with neurodegenerative diseases such as Alzheimer's disease may involve abnormal neurogenesis. Supporting this idea, evidence for decreased adult neurogenesis has been reported in the brain of Alzheimer's disease patients and in several mouse models of the disease. Thus, the development of strategies designed to stimulate the production of new neurons in the diseased brain has raised growing interest...
November 14, 2018: Hippocampus
Yue Liu, Zoran Tiganj, Michael E Hasselmo, Marc W Howard
Scale-invariant timing has been observed in a wide range of behavioral experiments. The firing properties of recently described time cells provide a possible neural substrate for scale-invariant behavior. Earlier neural circuit models do not produce scale-invariant neural sequences. In this article, we present a biologically detailed network model based on an earlier mathematical algorithm. The simulations incorporate exponentially decaying persistent firing maintained by the calcium-activated nonspecific (CAN) cationic current and a network structure given by the inverse Laplace transform to generate time cells with scale-invariant firing rates...
November 13, 2018: Hippocampus
Domilė Tautvydaitė, Aurélie L Manuel, Louis Nahum, Alexandra Adam-Darqué, Radek Ptak, Armin Schnider
Immediately repeated meaningful pictures in a continuous recognition task induce a positive frontal potential at about 200-300 ms, which appears to emanate from the medial temporal lobe (MTL) centered on the hippocampus, as concluded from inverse solutions, coherence measurements and depth electrode recordings in humans. In this study, we tested patients with unilateral MTL lesions due to stroke to verify the provenance of this signal and its association with the spacing effect (SE) - the improved learning of material encountered in spaced rather than massed presentation...
November 12, 2018: Hippocampus
Asaf Gilboa, Melanie Sekeres, Morris Moscovitch, Gordon Winocur
The hippocampus supports flexible decision-making through memory integration: bridging across episodes and inferring associations between stimuli that were never presented together (associative inference). A pre-requisite for memory integration is flexible representations of the relationships between stimuli within episodes (AB) but also of the constituent units (A,B). Here we investigated whether the hippocampus is required for parsing experienced episodes into their constituents to infer their re-combined within-episode associations (dissociative inference)...
November 12, 2018: Hippocampus
Eric D Melonakos, John A White, Fernando R Fernandez
Sharp wave-ripples (140-220 Hz) are patterns of brain activity observed in the local field potential of the hippocampus which are present during memory consolidation. As rodents switch from memory consolidation to memory encoding behaviors, cholinergic inputs to the hippocampus from neurons in the medial septum-diagonal band of Broca cause a marked reduction in ripple incidence. The mechanism for this disruption in ripple power is not fully understood. In isolated neurons, the major effect of cholinergic input on hippocampal neurons is depolarization of the membrane potential, which affects both hippocampal pyramidal neurons and inhibitory interneurons...
November 12, 2018: Hippocampus
Max Anstötz, Meliha Karsak, Gabriele M Rune
Cajal-Retzius (CR) cells are early-born glutamatergic neurons that are primarily known as the early main source of the signal protein Reelin. In the reeler mutant, the absence of Reelin causes severe defects in the radial migration of neurons, resulting in abnormal cortical layering. To date, the exact morphological properties of CR-cells independent of Reelin are unknown. With this in view, we studied the ontogenesis, density and distribution of CR-cells in reeler mice that were cross-bred with a CXCR4-EGFP reporter mouse line, thus enabling us to clearly identify CR-cells positions in the disorganized hippocampus of the reeler mouse...
November 5, 2018: Hippocampus
Jui-Jui Lin, Gray Umbach, Michael D Rugg, Bradley Lega
The question of whether the anterior and posterior hippocampus serve different or complementary functional roles during episodic memory processing has been motivated by noteworthy findings in rodent experiments and from noninvasive studies in humans. Researchers have synthesized these data to postulate several models of functional specialization, However, the issue has not been explored in detail using direct brain recordings. We recently published evidence that theta power increases during episodic memory encoding occur in the posterior hippocampus in humans...
November 5, 2018: Hippocampus
Hidenori Ito, Rika Morishita, Makoto Mizuno, Hidenori Tabata, Koh-Ichi Nagata
The hippocampus is generally considered as a brain center for learning and memory. We have recently established an electroporation-mediated gene transfer method to investigate the development of neonatal dentate granule cells in vivo. Using this new technique, we introduced knockdown vectors against Rac1 small GTPase into precursors for dentate granule cells at postnatal day 0. After 21 days, Rac1-deficient cells were frequently mispositioned between the granule cell layer (GCL) and hilus. About 60% of these mislocalized cells expressed a dentate granule cell marker, Prox1...
November 2, 2018: Hippocampus
Ahmed T Hussin, Timothy K Leonard, Kari L Hoffman
Sharp-wave ripples (SWRs) are spontaneous, synchronized neural population events in the hippocampus widely thought to play a role in memory consolidation and retrieval. They occur predominantly in sleep and quiet immobility, and in primates they also appear during active visual exploration. Typical measures of SWRs in behaving rats include changes in rate of occurrence, or in the incidence of specific neural ensemble activity contained within the categorical SWR event. Much less is known about the relevance of spatiotemporal SWR features, though they may index underlying activity of specific cell types including ensemble-specific internally generated sequences...
October 29, 2018: Hippocampus
Tetsuya Imura, Yasuyuki Kobayashi, Ken Suzutani, Naoki Ichikawa-Tomikawa, Hideki Chiba
Neural progenitors acquire GFAP expression during the perinatal period and continue to generate granule cells (GCs) in the hippocampal dentate gyrus throughout adulthood. Cellular characteristics of GFAP+ progenitor-derived late-born GCs in comparison with early-born GCs remain unknown. Using genetic fate mapping in mice, we show that early- and late-born GCs are concentrated in the outer and inner side of the GC layer, respectively. We then identify that a nuclear orphan receptor Nr4A2 is preferentially expressed by early-born GCs...
October 26, 2018: Hippocampus
Neha Sinha, Zachariah M Reagh, Nicholas J Tustison, Chelsie N Berg, Ashlee Shaw, Catherine E Myers, Diane Hill, Michael A Yassa, Mark A Gluck
Using high-resolution resting state fMRI, the present study tested the hypothesis that ABCA7 genetic risk differentially affects intra-medial temporal lobe (MTL) functional connectivity between MTL subfields, versus internetwork connectivity of the MTL with the medial prefrontal cortex (mPFC), in non-demented older African Americans. Although the association of ABCA7 risk variants with Alzheimer's disease (AD) has been confirmed worldwide, its effect size on the relative odds of being diagnosed with AD is significantly higher in African Americans...
October 14, 2018: Hippocampus
Ana Pocivavsek, Greg I Elmer, Robert Schwarcz
A combination of genetic and environmental factors contributes to schizophrenia (SZ), a catastrophic psychiatric disorder with a hypothesized neurodevelopmental origin. Increases in the brain levels of the tryptophan metabolite kynurenic acid (KYNA), an endogenous antagonist of α7 nicotinic acetylcholine and NMDA receptors, have been implicated specifically in the cognitive deficits seen in persons with SZ. Here we evaluated this role of KYNA by adding the KYNA precursor kynurenine (100 mg/day) to chow fed to pregnant rat dams from embryonic day (ED) 15 to ED 22 (control: ECon; kynurenine treated: EKyn)...
October 12, 2018: Hippocampus
Eugénie E Suter, Craig Weiss, John F Disterhoft
Many studies have focused on the function of hippocampal region CA1 as a critical site for associative memory, but much less is known about changes in the afferents to CA1. Here we report the activity of multiple single neurons from perirhinal and entorhinal cortex and from dentate gyrus during trace eyeblink conditioning as well as consolidated recall, and in pseudo-conditioned control rabbits. We also report an analysis of theta activity filtered from the local field potential (LFP). Our results show early associative changes in single-neuron firing rate as well as theta oscillations in lateral entorhinal cortex (EC) and dentate gyrus (DG), and increases in the number of responsive neurons in perirhinal cortex...
October 12, 2018: Hippocampus
Esther M C van Leijsen, Jonathan Tay, Ingeborg W M van Uden, Eline C M Kooijmans, Mayra I Bergkamp, Helena M van der Holst, Mohsen Ghafoorian, Bram Platel, David G Norris, Roy P C Kessels, Hugh S Markus, Anil M Tuladhar, Frank-Erik de Leeuw
BACKGROUND: White matter hyperintensities (WMH) constitute the visible spectrum of cerebral small vessel disease (SVD) markers and are associated with cognitive decline, although they do not fully account for memory decline observed in individuals with SVD. We hypothesize that WMH might exert their effect on memory decline indirectly by affecting remote brain structures such as the hippocampus. We investigated the temporal interactions between WMH, hippocampal atrophy and memory decline in older adults with SVD...
October 11, 2018: Hippocampus
P Lopes da Cunha, M E Villar, F Ballarini, R Tintorelli, H Viola
Stress is known to have a critical impact on memory processes. In the present work, we focus on the effects of an acute stress event closely associated to an unrelated learning task. Here we show that acute stress (elevated platform session, EP) experienced one hour after a weak spatial object recognition training (SOR), which only induces a short-term memory (STM), promoted the formation of SOR-long term memory (SOR-LTM) in rats. The effect induced by stress was dependent on the activation of glucocorticoid- and mineralocorticoid-receptors, brain-derived neurotrophic factor (BDNF) and protein synthesis in the dorsal hippocampus...
October 8, 2018: Hippocampus
Wing K L Witharana, Benjamin J Clark, Vivek Trivedi, Lilia Mesina, Bruce L McNaughton
Immediate-early genes (IEGs) exhibit a rapid, transient transcription response to neuronal activation. Fluorescently-labeled mRNA transcripts appear as bright intranuclear transcription foci (INF) which have been used as an all-or-nothing indicator of recent neuronal activity; however, it would be useful to know whether INF fluorescence can be used effectively to assess relative activations within a neural population. We quantified the Homer1a (H1a) response of hippocampal neurons to systematically varied numbers of exposures to the same places by inducing male Long-Evans rats to run laps around a track...
September 28, 2018: Hippocampus
K Liu, J Sibille, G Dragoi
Spontaneous neuronal ensemble activity in the hippocampus is believed to result from a combination of preconfigured internally-generated dynamics and the unique patterns of activity driven by recent experience. Previous research has established that preconfigured sequential neuronal patterns (i.e., preplay) contribute to the expression of future place cell sequences, which in turn contribute to the sequential neuronal patterns expressed post-exploration (i.e., replay). The relative contribution of preconfigured and of experience-related factors to replay and to overall sequential activity during post-run sleep is believed to be highly biased toward the recent run experience, despite never being tested directly...
September 27, 2018: Hippocampus
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