Serotonin signaling is a primary target of antidepressant medication, and may be dysregulated in psychiatric diseases. Serotonergic afferents and serotonin 5-HT1B receptors to the hippocampus are concentrated in stratum lacunosum-moleculare (SLM), where glutamatergic synaptic input from the entorhinal cortex, the temporo-ammonic (TA) pathway, also terminates. The TA pathway provides the only direct input to CA1 pyramidal neurons from the cortex and is thus a main source of sensory information. OBJECTIVE: to determine how 5-HT1B receptors regulate TA-CA1 synaptic transmission and determine how these processes are dysregulated in depression and restored by chronic antidepressant treatment. PRELIMINARY RESULTS: activation of 5-HT1B receptors potentiates excitatory postsynaptic potentials (field EPSPs and EPSPs) elicited by TA stimulation in CA1 SLM, but not by Schaffer collateral stimulation. The potentiation is mediated by increased postsynaptic AMPA receptor mediated transmission and accompanied by phosphorylation of the AMPA receptor GluR1 at the PKC/CaMKII Ser831 site. The effects of 5-HT1B receptor activation on TA-CA1 synaptic transmission are enhanced in rats subjected to chronic unpredictable stress (CUS), an accepted animal model of depression, and blocked by chronic antidepressant treatment.
SPECIFIC AIMS : 1. Test whether 5-HT1B receptor-induced potentiation and activity-dependent synaptic plasticity share common signaling mechanisms that lead to AMPA receptor insertion at TA-CA1 synapses. 2. Determine how potentiation of TA-CA1 synaptic transmission by 5-HT1B receptors is enhanced after chronic unpredictable stress. 3. Determine why potentiation of TA-CA1 synaptic transmission by 5-HT1B receptors is absent after chronic antidepressant treatment. 4. Test whether chronic antidepressant treatment can reverse a behavioral sign of depression, anhedonia, when 5-HT1B receptors are blocked pharmacologically or when serotonin-induced potentiation is absent in GluR1 S831A transgenic mice. RESEARCH DESIGN: we will combine electrophysiological techniques, including glutamate photolysis, with cell biological techniques such as transfection with constitutively active and dominant negative constructs, western blotting, and biotinylation assays, to investigate the actions of 5-HT1B receptors in hippocampal slices taken from control animals and animals subjected to CUS and chronic antidepressant treatment. OUTCOMES: The proposed project will expand our understanding of the physiological actions of serotonin and determine whether depression results, in part, from a dysregulation of the strength of excitatory synaptic transmission in multiple brain regions involved in cognitive and emotional function. A better understanding of serotonin actions and their alteration by stress will lead to improved antidepressant treatment strategies.

Public Health Relevance

Depression and other forms of mental illness are treated with drugs that act on a specific communication system in the brain that uses the substance serotonin. The normal function of this system is not well understood. Our experiments are designed to better understand the role played by this system in information processing in the healthy brain and how it may malfunction in mental illness.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
5R01MH086828-04
Application #
8442916
Study Section
Neurobiology of Learning and Memory Study Section (LAM)
Program Officer
Nadler, Laurie S
Project Start
2010-05-15
Project End
2015-01-31
Budget Start
2013-02-01
Budget End
2014-01-31
Support Year
4
Fiscal Year
2013
Total Cost
$359,361
Indirect Cost
$119,787
Name
University of Maryland Baltimore
Department
Physiology
Type
Schools of Medicine
DUNS #
188435911
City
Baltimore
State
MD
Country
United States
Zip Code
21201
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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
Kallarackal, Angy J; Kvarta, Mark D; Cammarata, Erin et al. (2013) Chronic stress induces a selective decrease in AMPA receptor-mediated synaptic excitation at hippocampal temporoammonic-CA1 synapses. J Neurosci 33:15669-74