Biomedical subjects

J David Sweatt

Publications and source records attributed to J David Sweatt.

59 records · Page 4Linked to original sources

PubMed2002

The other half of Hebb: K+ channels and the regulation of neuronal excitability in the hippocampus.

Historically, much attention has focused on the mechanisms of activity-dependent plasticity since the description of long-term potentiation by Bliss and Lomo in the early 1970s, while extrasynaptic changes have received much less interest. However, recent work has concentrated on the role of back-propagating action potentials in hippocampal dendrites in synaptic plasticity. In this review, we focus on the modulation of back-propagating action potentials by K+ currents in the dendrites of hippocampal cells. We described the primary K+-channel subunits and their interacting subunits that most likely contribute to these currents, and how these sites can be regulated by phosphorylation and other mechanisms. In conclusion, we provide a model for an alternative form of coincidence detection through K+ channels in the hippocampus.

Action Potentials↗

PubMed2002

Glutamate uptake in synaptic plasticity: from mollusc to mammal.

A great deal of research has been directed toward understanding the cellular mechanisms underlying synaptic plasticity and memory formation. To this point, most research has focused on the more "active" components of synaptic transmission: presynaptic transmitter release and postsynaptic transmitter receptors. Little work has been done characterizing the role neurotransmitter transporters might play during changes in synaptic efficacy. We review several new experiments that demonstrate glutamate transporters are regulated during changes in the efficacy of glutamatergic synapses. This regulation occurred during long-term facilitation of the sensorimotor synapse of Aplysia and long-term potentiation of the Schaffer-collateral synapse of the rat. We propose that glutamate transporters are "co-regulated" with other molecules/processes involved in synaptic plasticity, and that this process is phylogenetically conserved. These new findings indicate that glutamate transporters most likely play a more active role in neurotransmission than previously believed.

Amino Acid Transport System X-AG↗

PubMedDate not supplied

ERK/MAPK regulates hippocampal histone phosphorylation following contextual fear conditioning.

Long-term memory formation is regulated by many distinct molecular mechanisms that control gene expression. An emerging model for effecting a stable, coordinated pattern of gene transcription involves epigenetic tagging through modifications of histones or DNA. In this study, we investigated the regulation of histone phosphorylation in the hippocampus by the ERK/MAPK (extracellular signal-regulated kinase/mitogen-activated protein kinase) pathway. We found that activation of ERK/MAPK in vitro significantly increased histone H3 phosphorylation in hippocampal area CA1. Furthermore, we found that contextual fear conditioning in vivo leads to a rapid time-dependent increase in histone H3 phosphorylation in area CA1. This increase paralleled the time course of contextual fear-dependent activation of ERK, and was inhibited in vivo by a latent inhibition paradigm as well as by injection of an N-methyl-d-aspartic acid receptor (NMDA-R) antagonist. Finally, injection of an inhibitor of MEK (MAP kinase/ERK kinase), the unique dual-specificity kinase upstream of ERK, blocked the increase in histone H3 phosphorylation seen after contextual fear conditioning. These results demonstrate that changes in histone phosphorylation in the hippocampus are regulated by ERK/MAPK following a behavioral fear conditioning paradigm.

Animals↗

PubMedDate not supplied

Amnesia or retrieval deficit? Implications of a molecular approach to the question of reconsolidation.

Post-retrieval interference with a memory has uncovered a phenomenon known to the field as reconsolidation. In this article, we will review the specific molecular mechanisms that have been implicated in reconsolidation. As a result of numerous studies over the past five years, it can now be said with a fair amount of certainty that reconsolidation is not a recapitulation of the mechanisms underlying consolidation, despite what the term "reconsolidation" may suggest. Therefore, in addition to reviewing the known mechanisms of reconsolidation, we will propose that two experimental approaches involving the targeting of specific molecular mechanisms, and the study of these mechanisms during retrieval, may serve useful to the field as it is now able to advance beyond comparisons between consolidation and reconsolidation.

Algorithms↗

PubMedDate not supplied

A role for ERK MAP kinase in physiologic temporal integration in hippocampal area CA1.

Recent studies demonstrate a requirement for the Extracellular signal Regulated Kinase (ERK) mitogen-activated protein kinase (MAPK) cascade in both the induction of long-lasting forms of hippocampal synaptic plasticity and in hippocampus-dependent associative and spatial learning. In the present studies, we investigated mechanisms by which ERK might contribute to synaptic plasticity at Schaffer collateral synapses in hippocampal slices. We found that long-term potentiation (LTP) induced with a pair of 100-Hz tetani does not require ERK activation in mice whereas it does in rats. However, in mice, inhibition of ERK activation blocked LTP induced by two LTP induction paradigms that mimicked the endogenous theta rhythm. In an additional series of studies, we found that mice specifically deficient in the ERK1 isoform of MAPK showed no impairments in tests of hippocampal physiology. To investigate ERK-dependent mechanisms operating during LTP-inducing stimulation paradigms, we monitored spike production in the cell body layer of the hippocampus during the period of theta-like LTP-inducing stimulation. Theta-burst stimulation (TBS) produced a significant amount of postsynaptic spiking, and the likelihood of spike production increased progressively over the course of the three trains of TBS independent of any apparent increase in Excitatory Post-Synaptic Potential (EPSP) magnitude. Inhibition of ERK activation dampened this TBS-associated increase in spiking. These data indicate that, for specific patterns of stimulation, ERK may function in the regulation of neuronal excitability in hippocampal area CA1. Overall, our data indicate that the progressive increase in spiking observed during TBS represents a form of physiologic temporal integration that is dependent on ERK MAPK activity.

Action Potentials↗