N-methyl-D-aspartate receptors (NMDARs) play critical roles in information processing and in the synaptic plasticity that underlies learning and memory. Depending upon the pattern of activation, NMDARs can promote long-term potentiation (LTP) or long-term synaptic depression (LTD), two leading candidates for synaptic memory mechanisms. When activated excessively, however, NMDARs can also cause several forms of neurodegeneration. We have observed that there are also conditions in which NMDAR activation produces no change in synaptic responses or neuronal injury, but impairs the ability to generate LTP. This NMDAR-mediated LTP inhibition is observed with low level activation of NMDARs, certain patterns of synaptic stimulation and exposure to sub-lethal stressful conditions (brief hypoxia and low glucose). Because of the role that synaptic plasticity plays in memory processing, this NMDAR-mediated LTP inhibition may be important for understanding the cognitive defects that accompany untimely NMDAR activation in neuropsychiatric disorders. In recent studies, we found that low level NMDAR activation promotes the production of GABA-enhancing neurosteroids in hippocampal pyramidal neurons and these neurosteroids play a key role in LTP inhibition. In this proposal, we will extend our work on NMDAR LTP inhibition by pursuing three aims: 1. To determine conditions under which NMDAR activation promotes neurosteroid production and how steroids contribute to LTP modulation;2. To determine signaling mechanisms underlying NMDAR-induced neurosteroid production;and 3. To determine the effects of NMDA and neurosteroids on GABAergic inhibition and the mechanisms underlying these effects. These studies will be conducted in the CA1 region of rat hippocampal slices, an area known to be important for memory processing. Our long-term goal is to identify ways to preserve and restore synaptic function in individuals with neuropsychiatric illnesses.
Psychiatric disorders involve dysfunction in neural circuits underlying cognition, emotion and motivation. Although the biology of these disorders is poorly understood, the hippocampus has emerged as a major hub in several disorders and plays a critical role in brain systems involved in mental function and declarative memory formation. In these studies, we will examine mechanisms underlying hippocampal dysfunction in stressful conditions, including the role of neurosteroids. These studies have potential to shed new light on the role of the hippocampus in neuropsychiatric illnesses and to identify novel approaches to treatment.
|Jiang, Xiaoping; Shu, Hong-Jin; Krishnan, Kathiresan et al. (2016) A clickable neurosteroid photolabel reveals selective Golgi compartmentalization with preferential impact on proximal inhibition. Neuropharmacology 108:193-206|
|Zorumski, Charles F; Izumi, Yukitoshi; Mennerick, Steven (2016) Ketamine: NMDA Receptors and Beyond. J Neurosci 36:11158-11164|
|Izumi, Yukitoshi; Zorumski, Charles F (2016) GABA and Endocannabinoids Mediate Depotentiation of Schaffer Collateral Synapses Induced by Stimulation of Temperoammonic Inputs. PLoS One 11:e0149034|
|Sun, Min-Yu; Linsenbardt, Andrew J; Emnett, Christine M et al. (2016) 24(S)-Hydroxycholesterol as a Modulator of Neuronal Signaling and Survival. Neuroscientist 22:132-44|
|Emnett, Christine; Li, Hairong; Jiang, Xiaoping et al. (2016) A Clickable Analogue of Ketamine Retains NMDA Receptor Activity, Psychoactivity, and Accumulates in Neurons. Sci Rep 6:38808|
|Sun, Min-Yu; Izumi, Yukitoshi; Benz, Ann et al. (2016) Endogenous 24S-hydroxycholesterol modulates NMDAR-mediated function in hippocampal slices. J Neurophysiol 115:1263-72|
|Ishikawa, Makoto; Yoshitomi, Takeshi; Zorumski, Charles F et al. (2016) 24(S)-Hydroxycholesterol protects the ex vivo rat retina from injury by elevated hydrostatic pressure. Sci Rep 6:33886|
|Ishikawa, Makoto; Yoshitomi, Takeshi; Covey, Douglas F et al. (2016) TSPO activation modulates the effects of high pressure in a rat ex vivo glaucoma model. Neuropharmacology 111:142-159|
|Stein, Liana R; O'Dell, Kazuko A; Funatsu, Michiyo et al. (2016) Short-term environmental enrichment enhances synaptic plasticity in hippocampal slices from aged rats. Neuroscience 329:294-305|
|Izumi, Yukitoshi; Zorumski, Charles F (2015) Sensitivity of N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potentials and synaptic plasticity to TCN 201 and TCN 213 in rat hippocampal slices. J Pharmacol Exp Ther 352:267-73|
Showing the most recent 10 out of 53 publications