Dendritic spines undergo synaptic pruning during adolescence, a process which is dysregulated in autism and schizophrenia. The mechanism underlying this synaptic pruning is not known, but is likely to involve reductions in NMDA receptor activation. We recently found that, during the pubertal period (~PND 35-45), extrasynaptic ?4?? GABAA receptors (GABARs) emerge on dendritic spines of CA1 hippocampal pyramidal cells of mice for ~10d. Moreover, activation of NMDA receptors is impaired in +/+ but not ?4 or ?-/- mice, implicating ?4?? in the reduction of NMDAR function during puberty. In this proposal, we will test the hypothesis that synaptic pruning in adolescence is indeed due to this increased expression of ?4?? GABARs, and we will explore the cellular, circuit and behavioral consequences of this effect. The proposed experiments will use a wide combination of techniques, including two-photon imaging, two-photon uncaging, electrophysiological, pharmacological, anatomical and immunocytochemical assays to directly assess the functional outcome of this novel form of inhibition on the spines at puberty. Initially, optochemical techniques with RuBiGABA, a novel caged GABA compound, will be used to map GABAergic currents in spines at puberty. Preliminary data with this technique show that spines have GABAergic currents. Then, the impact of these receptors on NMDA receptor-induced Ca2+ influx from individual spines will be examined using two-photon Ca2+ imaging along with local uncaging of Rubi-GABA. These experiments will also use acute pharmacological (agonists, modulators) and genetic manipulation (knock-out, adenovirus-shRNA knock-down) of ?4?? to explore the role of these receptors in regulating NMDA receptor function. In parallel, to determine the impact of ?4??-mediated inhibition during puberty on spine density post-pubertally, we will chronically manipulate ?4?? function (as above) over the 10 days when ?4?? receptors are elevated (~PND 35-45) and quantify spine density at 8-wks of age. Preliminary data shows that spine density is indeed decreased post-pubertally in +/+ but not ?4-/- mice, implicating ?4?? GABARs in pubertal synaptic pruning. Both immunocytochemical and electrophysiological correlates of spine density changes will be examined. Finally, to explore the effect of this pruning on circuit and behavioral plasticity, we will also determine the impact of these alterations on synaptic plasticity (long-term potentiation (LTP), long-term depression (LTD), reversal of LTP), and on behaviorally flexibility in two hippocampal-dependent spatial learning tasks. The findings from the proposed studies will directly address the functional role of GABAergic inhibition on dendritic spines at puberty, and will also provide mechanisms for the process of synaptic pruning in adolescence, as well as explore functional outcomes of alterations in this process. These results will be relevant for cognitive disorders such as autism, where reduced synaptic pruning and reduced behavioral flexibility are associated with single nucleotide polymorphisms of the ?4 gene, suggesting a genetic link.

Public Health Relevance

Synaptic pruning of dendritic spines occurs in adolescence and is thought to be dysregulated in cognitive disorders such as autism and schizophrenia, suggesting that there is an optimal spine density for normal cognitive processes. This proposal will examine novel, potential mechanisms underlying this pruning of connections, using two-photon imaging and optochemical activation of individual spines and electrophysiological correlates, which our preliminary data suggest is dependent upon inhibitory receptors, ?4??, that emerge at puberty on dendritic spines. The proposed experiments will also identify changes in circuit plasticity and learning flexibility associated with alterations in spine pruning, which ay suggest new therapeutic strategies for these cognitive disorders, where alterations in the ?4 gene have been reported.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
1R01MH100561-01
Application #
8493627
Study Section
Special Emphasis Panel (ZRG1-MDCN-P (57))
Program Officer
Asanuma, Chiiko
Project Start
2013-04-23
Project End
2018-02-28
Budget Start
2013-04-23
Budget End
2014-02-28
Support Year
1
Fiscal Year
2013
Total Cost
$653,088
Indirect Cost
$134,135
Name
Suny Downstate Medical Center
Department
Physiology
Type
Schools of Medicine
DUNS #
040796328
City
Brooklyn
State
NY
Country
United States
Zip Code
11203
Liou, Jyun-You; Ma, Hongtao; Wenzel, Michael et al. (2018) Role of inhibitory control in modulating focal seizure spread. Brain 141:2083-2097
Agetsuma, Masakazu; Hamm, Jordan P; Tao, Kentaro et al. (2018) Parvalbumin-Positive Interneurons Regulate Neuronal Ensembles in Visual Cortex. Cereb Cortex 28:1831-1845
Izquierdo-Serra, Mercè; Hirtz, Jan J; Shababo, Ben et al. (2018) Two-Photon Optogenetic Mapping of Excitatory Synaptic Connectivity and Strength. iScience 8:15-28
Parato, Julie; Shen, Hui; Smith, Sheryl S (2018) ?4?? GABAA Receptors Trigger Synaptic Pruning and Reduce Dendritic Length of Female Mouse CA3 Hippocampal Pyramidal Cells at Puberty. Neuroscience 398:23-36
Kwon, Taekyung; Sakamoto, Masayuki; Peterka, Darcy S et al. (2017) Attenuation of Synaptic Potentials in Dendritic Spines. Cell Rep 20:1100-1110
Afroz, Sonia; Shen, Hui; Smith, Sheryl S (2017) ?4?? GABAA receptors reduce dendritic spine density in CA1 hippocampus and impair relearning ability of adolescent female mice: Effects of a GABA agonist and a stress steroid. Neuroscience 347:22-35
Baird-Daniel, Eliza; Daniel, Andy G S; Wenzel, Michael et al. (2017) Glial Calcium Waves are Triggered by Seizure Activity and Not Essential for Initiating Ictal Onset or Neurovascular Coupling. Cereb Cortex 27:3318-3330
Fang, Wei-Qun; Yuste, Rafael (2017) Overproduction of Neurons Is Correlated with Enhanced Cortical Ensembles and Increased Perceptual Discrimination. Cell Rep 21:381-392
Wenzel, Michael; Hamm, Jordan P; Peterka, Darcy S et al. (2017) Reliable and Elastic Propagation of Cortical Seizures In Vivo. Cell Rep 19:2681-2693
Jayant, Krishna; Hirtz, Jan J; Plante, Ilan Jen-La et al. (2017) Targeted intracellular voltage recordings from dendritic spines using quantum-dot-coated nanopipettes. Nat Nanotechnol 12:335-342

Showing the most recent 10 out of 29 publications