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Thiago C Moulin, Lyvia L Petiz, Danielle Rayêe, Jessica Winne, Roberto G Maia, Rafael V Lima da Cruz, Olavo B Amaral, Richardson N Leão
Prolonged increases in excitation can trigger cell-wide homeostatic responses in neurons, altering membrane channels, promoting morphological changes, and ultimately reducing synaptic weights. However, how synaptic downscaling interacts with classical forms of Hebbian plasticity is still unclear. In this study, we investigated whether chronic optogenetic stimulation of hippocampus CA1 pyramidal neurons in freely moving mice could (a) cause morphological changes reminiscent of homeostatic scaling, (b) modulate synaptic currents that might compensate for chronic excitation, and (c) lead to alterations in Hebbian plasticity...
February 15, 2019: Hippocampus
Emily A Mankin, Kay Thurley, Alireza Chenani, Olivia V Haas, Luca Debs, Josephine Henke, Melissa Galinato, Jill K Leutgeb, Stefan Leutgeb, Christian Leibold
Large parts of our knowledge about the physiology of the hippocampus in the intact brain are derived from studies in rats and mice. While many of those findings fit well to the limited data available from humans and primates, there are also marked differences, for example, in hippocampal oscillation frequencies and in the persistence of theta oscillations. To test whether the distinct sensory specializations of the visual and auditory system of primates play a key role in explaining these differences, we recorded basic hippocampal physiological properties in Mongolian gerbils, a rodent species with high visual acuity, and good low-frequency hearing, similar to humans...
February 12, 2019: Hippocampus
David Clewett, Sarah DuBrow, Lila Davachi
Our daily lives unfold continuously, yet when we reflect on the past, we remember those experiences as distinct and cohesive events. To understand this phenomenon, early investigations focused on how and when individuals perceive natural breakpoints, or boundaries, in ongoing experience. More recent research has examined how these boundaries modulate brain mechanisms that support long-term episodic memory. This work has revealed that a complex interplay between hippocampus and prefrontal cortex promotes the integration and separation of sequential information to help organize our experiences into mnemonic events...
February 7, 2019: Hippocampus
Guo-Rong Zhang, Hua Zhao, Eui M Choi, Michael Svestka, Xiaodan Wang, Aarti Nagayach, Anshuman Singh, Robert G Cook, Alfred I Geller
Advanced cognitive tasks are encoded in distributed neocortical circuits that span multiple forebrain areas. Nonetheless, synaptic plasticity and neural network theories hypothesize that essential information for performing these tasks is encoded in specific ensembles within these circuits. Relatively simpler subcortical areas contain specific ensembles that encode learning, suggesting that neocortical circuits contain such ensembles. Previously, using localized gene transfer of a constitutively active protein kinase C (PKC), we established that a genetically-modified circuit in rat postrhinal cortex, part of the hippocampal formation, can encode some essential information for performing specific visual shape discriminations...
February 7, 2019: Hippocampus
Karola Kaefer, Hugo Malagon-Vina, Desiree D Dickerson, Joseph O'Neill, Svenja V Trossbach, Carsten Korth, Jozsef Csicsvari
Aberrant proteostasis of protein aggregation may lead to behavior disorders including chronic mental illnesses (CMI). Furthermore, the neuronal activity alterations that underlie CMI are not well understood. We recorded the local field potential and single-unit activity of the hippocampal CA1 region in vivo in rats transgenically overexpressing the Disrupted-in-Schizophrenia 1 (DISC1) gene (tgDISC1), modeling sporadic CMI. These tgDISC1 rats have previously been shown to exhibit DISC1 protein aggregation, disturbances in the dopaminergic system and attention-related deficits...
February 5, 2019: Hippocampus
Iva K Brunec, Jessica Robin, Eva Zita Patai, Jason D Ozubko, Amir-Homayoun Javadi, Morgan D Barense, Hugo J Spiers, Morris Moscovitch
As London taxi drivers acquire "the knowledge" and develop a detailed cognitive map of London, their posterior hippocampi (pHPC) gradually increase in volume, reflecting an increasing pHPC/aHPC volume ratio. In the mnemonic domain, greater pHPC/aHPC volume ratios in young adults have been found to relate to better recollection ability, indicating that the balance between pHPC and aHPC volumes might be reflective of cross-domain individual differences. Here, we examined participants' self-reported use of cognitive map-based navigational strategies in relation to their pHPC/aHPC hippocampal volume ratio...
February 3, 2019: Hippocampus
Annika Hanert, Anya Pedersen, Thorsten Bartsch
Day-to-day life involves the perception of events that resemble one another. For the sufficient encoding and retrieval of similar information, the hippocampus provides two essential computational processes. Pattern separation refers to the differentiation of overlapping memory representations, whereas pattern completion reactivates memories based on noisy or degraded input. Evidence from human and rodent studies suggest that pattern separation specifically relies on neuronal ensemble activity in hippocampal subnetworks in the dentate gyrus and CA3...
January 31, 2019: Hippocampus
Swati Jain, John J LaFrancois, Justin J Botterill, David Alcantara-Gonzalez, Helen E Scharfman
Previous studies suggest that reducing the numbers of adult-born neurons in the dentate gyrus (DG) of the mouse increases susceptibility to severe continuous seizures (status epilepticus; SE) evoked by systemic injection of the convulsant kainic acid (KA). However, it was not clear if the results would be the same for other ways to induce seizures, or if SE-induced damage would be affected. Therefore, we used pilocarpine, which induces seizures by a different mechanism than KA. Also, we quantified hippocampal damage after SE...
January 23, 2019: Hippocampus
Joonyeup Lee, Miru Yun, Eunjae Cho, Jong Won Lee, Doyun Lee, Min Whan Jung
Strong hippocampal mossy fiber synapses are thought to function as detonators, imposing "teaching" signals onto CA3 neurons during new memory formation. For an empirical test of this long-standing view, we examined effects of optogenetically stimulating mossy fibers on spatial firing of CA3 neurons in freely-moving mice. We found that spatially restricted mossy fiber stimulation drives novel place-specific firing in some CA3 pyramidal neurons. Such neurons comprise only a minority, however, and many more CA3 neurons showed inhibited spatial firing during mossy fiber stimulation...
January 4, 2019: Hippocampus
Emma Delhaye, Dawn Mechanic-Hamilton, Laura Saad, Sandhitsu R Das, Laura E M Wisse, Paul A Yushkevich, David A Wolk, Christine Bastin
Unitization, that is, the encoding of an association as one integrated entity, has been shown to improve associative memory in populations presenting with associative memory deficit due to hippocampal dysfunction, such as amnesic patients with focal hippocampal lesions and healthy older adults. One reason for this benefit is that encoding of unitized associations would rely on the perirhinal cortex (PrC) and thus minimize the need for hippocampal recruitment. Mild cognitive impairment (MCI) is accompanied by a deficit in associative memory...
December 26, 2018: Hippocampus
Diego Garibay-Pulido, Leopoldo Cendejas-Zaragoza, Robert Dawe, Marvin A Rossi
Parametric subtracted post-ictal diffusion tensor imaging (pspiDTI) is a novel imaging technique developed at our center to visualize transient, patient-specific, ictal-associated water diffusion abnormalities in hippocampal-associated axonal tissue. PspiDTI can elucidate putative connectivity patterns, tracing ictal propagation following a partial-onset seizure without generalization secondarily. PspiDTI compares two DTI volumes acquired during the early post-ictal period (<4 hr), and baseline inter-ictal interval (>24 hr post-seizure)...
December 26, 2018: Hippocampus
Kazuki Okamoto, Yuji Ikegaya
Recurrent excitatory synapses have theoretically been shown to play roles in memory storage and associative learning and are well described to occur in the CA3 region of the hippocampus. Here, we report that the CA2 region also contains recurrent excitatory monosynaptic couplings. Using dual whole-cell patch-clamp recordings from CA2 pyramidal cells in mouse hippocampal slices under differential interference contrast microscopic controls, we evaluated monosynaptic excitatory connections. Unitary excitatory postsynaptic potentials occurred in 1...
December 26, 2018: Hippocampus
Misun Kim, Eleanor A Maguire
Head direction cells are critical for navigation because they convey information about which direction an animal is facing within an environment. To date, most studies on head direction encoding have been conducted on a horizontal two-dimensional (2D) plane, and little is known about how three-dimensional (3D) direction information is encoded in the brain despite humans and other animals living in a 3D world. Here, we investigated head direction encoding in the human brain while participants moved within a virtual 3D "spaceship" environment...
December 18, 2018: Hippocampus
Liqin Zhang, Calvin Wu, David T Martel, Michael West, Michael A Sutton, Susan E Shore
Here, we investigate remodeling of hippocampal cholinergic inputs after noise exposure and determine the relevance of these changes to tinnitus. To assess the effects of noise exposure on the hippocampus, guinea pigs were exposed to unilateral noise for 2 hr and 2 weeks later, immunohistochemistry was performed on hippocampal sections to examine vesicular acetylcholine transporter (VAChT) expression. To evaluate whether the changes in VAChT were relevant to tinnitus, another group of animals was exposed to the same noise band twice to induce tinnitus, which was assessed using gap-prepulse Inhibition of the acoustic startle (GPIAS) 12 weeks after the first noise exposure, followed by immunohistochemistry...
November 24, 2018: Hippocampus
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
Christopher R Doxey, Cooper B Hodges, Ty A Bodily, Nathan M Muncy, C Brock Kirwan
No abstract text is available yet for this article.
February 2019: Hippocampus
Marlena Wosiski-Kuhn, Mihail Bota, Christina A Snider, Steven P Wilson, Kannan U Venkataraju, Pavel Osten, Alexis M Stranahan
Diabetes increases adrenal steroids in humans and animal models, but potential interactions with psychological stress remain poorly understood. Diabetic rodents exhibit anxiety and reductions in hippocampal brain-derived neurotrophic factor (BDNF) expression, and these studies investigated whether loss of BDNF-driven hippocampal activity promotes anxiety and disinhibits the HPA axis. Mice with genetic obesity and diabetes (db/db) received intrahippocampal injections of lentivirus for BDNF overexpression (db/db-BDNFOE), and Wt mice received lentiviral constructs for BDNF knockdown (Wt-BDNFKD)...
December 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
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