Skip to main content

Umbrella menu

  • SfN.org
  • eNeuro
  • The Journal of Neuroscience
  • Neuronline
  • BrainFacts.org

Main menu

  • HOME
  • CONTENT
    • Early Release
    • Featured
    • Current Issue
    • Issue Archive
    • Collections
  • ALERTS
  • FOR AUTHORS
    • Preparing a Manuscript
    • Submission Guidelines
    • Fees
    • Journal Club
    • eLetters
    • Submit
  • EDITORIAL BOARD
  • ABOUT
    • Overview
    • Advertise
    • For the Media
    • Rights and Permissions
    • Privacy Policy
    • Feedback
  • SUBSCRIBE
  • SfN.org
  • eNeuro
  • The Journal of Neuroscience
  • Neuronline
  • BrainFacts.org

User menu

  • Log in
  • Subscribe
  • My alerts

Search

  • Advanced search
Journal of Neuroscience
  • Log in
  • Subscribe
  • My alerts
Journal of Neuroscience

Advanced Search

Submit a Manuscript
  • HOME
  • CONTENT
    • Early Release
    • Featured
    • Current Issue
    • Issue Archive
    • Collections
  • ALERTS
  • FOR AUTHORS
    • Preparing a Manuscript
    • Submission Guidelines
    • Fees
    • Journal Club
    • eLetters
    • Submit
  • EDITORIAL BOARD
  • ABOUT
    • Overview
    • Advertise
    • For the Media
    • Rights and Permissions
    • Privacy Policy
    • Feedback
  • SUBSCRIBE
PreviousNext
This Week in The Journal

This Week in The Journal

Teresa Esch [Ph.D.]
Journal of Neuroscience 3 February 2016, 36 (5) i
Teresa Esch
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • ORCID record for Teresa Esch
  • Article
  • Figures & Data
  • Info & Metrics
  • eLetters
  • PDF
Loading

Hippocampal Neurons Encode Temporal Sequences

Timothy A. Allen, Daniel M. Salz, Sam McKenzie, and Norbert J. Fortin

(see pages 1547–1563)

The critical role of the hippocampus in episodic memory has long been recognized. In particular, the hippocampus is thought to encode spatial, temporal, and semantic relationships among objects and events (Eichenbaum and Cohen, 2014, Neuron 83:764). Numerous human and rodent studies have provided support for this hypothesis. First, the discovery of place cells, which exhibit changes in firing rate as animals move through an environment, provided evidence that the rodent hippocampus represents spatial sequences. More recently, cells that appear to encode the passage of time have been identified. Now Allen et al. present evidence that hippocampal neurons encode temporal relationships between nonspatial stimuli.

Figure1
  • Download figure
  • Open in new tab
  • Download powerpoint

A neuron that responded more to in-sequence odors (blue) than to out-of-sequence odors (red). Rasters (top) show spikes and odor sampling periods (shading) on individual trials. Perievent time histograms (bottom) show mean firing rates across all trials. See Allen et al. for details.

Rats were trained to recognize a sequence of five odors, after which they had to determine whether odors were presented in or out of order to earn a reward. Neuronal activity was recorded in CA1 as rats performed this task. The firing rate of ∼26% of recorded neurons (many more than would be expected by chance) differed depending on whether the odor being sniffed was in the learned sequence. Some neurons responded when the present odor was in the learned sequence—regardless of the odor's identity—and others responded whenever an odor was experienced out of order. Some neurons responded only when a particular odor was presented in the correct position, and still others responded only when a particular odor was presented out of order. Finally, some neurons responded when any wrong odor was presented at a particular temporal position. Overall, the analyses suggested that the firing of individual neurons contained sufficient information to distinguish whether an odor was in or out of sequence, and that neuronal ensemble activity reflected whether items were in the learned sequence on a trial-by-trial basis.

In these experiments, the location and overt behavior of rats were unchanged across trials, minimizing the likelihood that differences in neuronal firing were attributable to such confounds. Moreover, the proportion of cells that showed sequence-dependent changes in firing rate was correlated with accuracy on the task. Therefore, the results strongly suggest that hippocampal neurons encode temporal relationships between events—a central feature of episodic memories—and that this information is used to guide behavior.

Astrocytic NFAT Slows Synaptic Recovery after Injury

Jennifer L. Furman, Pradoldej Sompol, Susan D. Kraner, Melanie M. Pleiss, Esther J. Putman, et al.

(see pages 1502–1515)

Nuclear factor of activated T cells (NFAT) is a transcription factor that resides in the cytoplasm under baseline conditions. When intracellular calcium levels rise, the calcium/calmodulin-dependent phosphatase calcineurin dephosphorylates NFAT, unmasking a nuclear translocation signal. Consequently, NFAT enters the nucleus where it regulates expression of various genes, most notably those involved in lymphocyte activation during immune responses. Calcineurin-dependent activation of NFAT also occurs during activation of astrocytes and microglia, and it is thus thought to contribute to neuroinflammation after brain injury and in neurodegenerative diseases. Consistent with this hypothesis, astrocytic NFAT expression was elevated in a mouse model of Alzheimer's disease (AD), and inhibiting NFAT activation selectively in astrocytes—by expressing the inhibitory peptide VIVIT—reduced astrocytic hypertrophy, plaque formation, synaptic deficits, and cognitive impairment (Furman et al., 2012, J Neurosci 32:16129).

Following these promising results, Furman et al. asked whether astrocytic NFAT activation also contributes to synaptic disruption after traumatic brain injury in rats. Previous work showed that unilateral controlled cortical impact (CCI) causes loss of synaptic inputs from hippocampal CA3 to CA1. Although synapses re-emerge within a week, they remain weak, and long-term depression (LTD) is easier to induce in the injured hippocampus than in the contralateral hippocampus. When VIVIT was expressed in hippocampal astrocytes beginning ∼8 weeks before injury, however, synaptic strength and the ability to induce LTD were similar in CCI-treated and uninjured rats. Furthermore, VIVIT expression attenuated CCI-induced loss of the scaffolding protein PSD-95 and an AMPA receptor subunit, and it enhanced astrocytic production of the synapse-promoting protein hevin. Surprisingly, however, VIVIT did not reduce expression of glial fibrillary acidic protein (GFAP)—a marker of astrocyte activation—after CCI, as it did in AD-model mice.

These data suggest that NFAT-dependent transcriptional regulation in astrocytes contributes to synaptic impairment after CCI injury independently of astrocyte activation (or at least independently of GFAP expression). They also indicate that different transcriptional programs underlie astrocyte activation in AD mice, in which NFAT is required, and after traumatic injury in rats, in which NFAT is dispensable. Finally, they suggest that preventing activation of NFAT may promote recovery of brain function after traumatic injury while sparing protective functions of activated astrocytes.

Footnotes

  • This Week in The Journal is written by Teresa Esch, Ph.D.

Back to top

In this issue

The Journal of Neuroscience: 36 (5)
Journal of Neuroscience
Vol. 36, Issue 5
3 Feb 2016
  • Table of Contents
  • Table of Contents (PDF)
  • About the Cover
  • Index by author
  • Advertising (PDF)
  • Ed Board (PDF)
Email

Thank you for sharing this Journal of Neuroscience article.

NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. We do not retain these email addresses.

Enter multiple addresses on separate lines or separate them with commas.
This Week in The Journal
(Your Name) has forwarded a page to you from Journal of Neuroscience
(Your Name) thought you would be interested in this article in Journal of Neuroscience.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Print
View Full Page PDF
Article Alerts
Sign In to Email Alerts with your Email Address
Citation Tools
This Week in The Journal
Journal of Neuroscience 3 February 2016, 36 (5) i

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Respond to this article
Request Permissions
Share
This Week in The Journal
Journal of Neuroscience 3 February 2016, 36 (5) i
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
  • Tweet Widget
  • Facebook Like
  • Google Plus One

Jump to section

  • Article
    • Hippocampal Neurons Encode Temporal Sequences
    • Astrocytic NFAT Slows Synaptic Recovery after Injury
    • Footnotes
  • Figures & Data
  • Info & Metrics
  • eLetters
  • PDF

Responses to this article

Respond to this article

Jump to comment:

No eLetters have been published for this article.

Related Articles

Cited By...

More in this TOC Section

  • This Week in The Journal
  • This Week in The Journal
  • This Week in The Journal
Show more This Week in The Journal
  • Home
  • Alerts
  • Visit Society for Neuroscience on Facebook
  • Follow Society for Neuroscience on Twitter
  • Follow Society for Neuroscience on LinkedIn
  • Visit Society for Neuroscience on Youtube
  • Follow our RSS feeds

Content

  • Early Release
  • Current Issue
  • Issue Archive
  • Collections

Information

  • For Authors
  • For Advertisers
  • For the Media
  • For Subscribers

About

  • About the Journal
  • Editorial Board
  • Privacy Policy
  • Contact
  • Feedback
(JNeurosci logo)
(SfN logo)

Copyright © 2021 by the Society for Neuroscience.
JNeurosci Online ISSN: 1529-2401

The ideas and opinions expressed in JNeurosci do not necessarily reflect those of SfN or the JNeurosci Editorial Board. Publication of an advertisement or other product mention in JNeurosci should not be construed as an endorsement of the manufacturer’s claims. SfN does not assume any responsibility for any injury and/or damage to persons or property arising from or related to any use of any material contained in JNeurosci.