Major hypothesis of this project: The endogenous opioid, cannabinoid, and CCK systems mutually interact via hippocampal interneurons and thereby jointly regulate the excitability of pyramidal cells. Low frequency neuronal population oscillations (especially theta "?", 4-12 Hz, and gamma "?", 30-80 Hz, rhythms) represent brain states that are crucial for high order cognitive processing. Activity in GABAergic basket cell microcircuits is required for several forms of rhythm generation, yet many questions regarding the underlying cellular mechanisms are unresolved, largely because available tools are inadequate for selectively investigating the sparse and widely dispersed cellular circuits. Model phenomena, called low frequency oscillations (LFOs), capture some of the properties of the much more complex in vivo brain rhythms. The present application will use new optogenetic methods to address questions about mechanisms of LFOs at the microcircuit level. The goal is to elucidate fundamental cell circuit properties that may help illuminate the in vivo phenomena. Molecular biological tools will be used to introduce light-sensitive molecules ("opsins") into targeted cell groups via viral vectors. The vectors contain a double-floxed, inverted gene for a fusion protein consisting of an opsin plus a fluorescent marker protein. Vectors are introduced into the brains of transgenic mice expressing Cre-recombinase under the control of cell-specific promoters. We will target the opsins to either the parvalbumin (PV) - expressing, or cholescystokinin (CCK) - expressing interneurons in hippocampus, or acetylcholine (ACh) - expressing cells in the medial septum. Depending on its molecular properties, light-activation of a particular opsin will either excite or inhibit the cell expressing it. We will use the excitatory opsin, Channelrhodopsin2, and the inhibitory opsin, Halorhodopsin in the proposed experiments. Flashes of light of an appropriate wavelength will either excite or inhibit defined networks of cells, even though the cells are scattered in the tissue. Optogenetic methods will complement high resolution electrophysiological analysis of individual neurons. In the hippocampus, the mu-opioid receptor, ?OR, or the cannabinoid receptor, CB1R, are segregated at high density on the PV or CCK cells, respectively. We will ask how the individual microcircuits regulated by ?ORs and CB1Rs interact to foster inhibitory LFOs.
The Specific Aims are to:
Aim #1 : Test the hypothesis that CCK and PV cells mutually influence each other.
Aim #2 : Test the hypothesis that CCK and PV cell IPSPs collectively generate LFO-LFPs.
Aim #3 : Test the hypothesis that LFO-IPSCs and LFO-LFPs can be triggered by endogenous ACh.

Public Health Relevance

Health Relevance: Disordered function of inhibitory microcircuits has been implicated in psychiatric disorders such as schizophrenia, autism, and Alzheimer's Disease, among others. In addition, opiate and cannabinoid drugs have actions that interact in affecting behavior, and yet the ways in which they interact is not known. A detailed understanding of the cross-talk between PV and CCK cell microcircuits will impact on important neurological problems.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
2R01MH077277-06A1
Application #
8282190
Study Section
Neurobiology of Learning and Memory Study Section (LAM)
Program Officer
Nadler, Laurie S
Project Start
2006-04-01
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2014-06-30
Support Year
6
Fiscal Year
2012
Total Cost
$383,750
Indirect Cost
$133,750
Name
University of Maryland Baltimore
Department
Physiology
Type
Schools of Medicine
DUNS #
188435911
City
Baltimore
State
MD
Country
United States
Zip Code
21201
Mattison, Hayley A; Bagal, Ashish A; Mohammadi, Michael et al. (2014) Evidence of calcium-permeable AMPA receptors in dendritic spines of CA1 pyramidal neurons. J Neurophysiol 112:263-75
Nagode, Daniel A; Tang, Ai-Hui; Yang, Kun et al. (2014) Optogenetic identification of an intrinsic cholinergically driven inhibitory oscillator sensitive to cannabinoids and opioids in hippocampal CA1. J Physiol 592:103-23
Alger, Bradley E (2012) Endocannabinoids at the synapse a decade after the dies mirabilis (29 March 2001): what we still do not know. J Physiol 590:2203-12
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Alger, Bradley E; Tang, Ai-Hui (2012) Do cannabinoids reduce brain power? Nat Neurosci 15:499-501
Tang, Ai-Hui; Karson, Miranda A; Nagode, Daniel A et al. (2011) Nerve terminal nicotinic acetylcholine receptors initiate quantal GABA release from perisomatic interneurons by activating axonal T-type (Cav3) Ca²? channels and Ca²? release from stores. J Neurosci 31:13546-61
Zhang, Longhua; Wang, Meina; Bisogno, Tiziana et al. (2011) Endocannabinoids generated by Ca2+ or by metabotropic glutamate receptors appear to arise from different pools of diacylglycerol lipase. PLoS One 6:e16305
Nagode, Daniel A; Tang, Ai-Hui; Karson, Miranda A et al. (2011) Optogenetic release of ACh induces rhythmic bursts of perisomatic IPSCs in hippocampus. PLoS One 6:e27691
Alger, Bradley E; Kim, Jimok (2011) Supply and demand for endocannabinoids. Trends Neurosci 34:304-15
Zhang, Longhua; Alger, Bradley E (2010) Enhanced endocannabinoid signaling elevates neuronal excitability in fragile X syndrome. J Neurosci 30:5724-9

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