During my postdoctoral training at MUSC I began to investigate the use of viral vector mediated astrocyte-specific expression of DREADD receptors. In these studies I used glutamate biosensor recordings to determine if activation of NAcore astrocytes produced detectable glutamate release. Following cocaine self-administration and extinction, I found that activation of glial DREADD receptors, and subsequent inhibited cue-induced cocaine seeking, in part by restoring tone on presynaptic mGluR2/3 autoreceptors (study a.). Becoming more interested in astrocytes, I began to implement the use another glial cell-specific viral vector (GFAP-LCK-GFP) designed to restrict expression of GFP to the astrocyte plasma membrane. Using this viral vector, I labeled, imaged, and digitally reconstructed NAcore astrocytes to examine their morphological characteristics following cocaine self-admin and extinction. These studies demonstrated reduced volume and surface area of astrocytes following cocaine self-administration and extinction. By combining the astrocyte viral signal with fluorescent detection of a synaptic marker, I also observed decreased contact of NAcore astrocytes with a synaptic marker, which paralleled decreases in surface area and volume and previously reported decreases in glutamate clearance. Interestingly, decreased synaptic contact was reversed with ceftriaxone treatment, a drug that restores cocaine-induced alterations in glutamate homeostasis by enhancing expression of glial proteins responsible for uptake and release of glutamate (study b.). While setting up my laboratory at MUSC in the department of Anesthesiology I have continued to explore the microscopic investigation of astrocytes and their interaction with neurons, compiling some additional optogenetics-based glutamate biosensor data with super-resolution images of the astrocyte plasma membrane and corresponding glial fibrillary acid protein arbor in a recent publication where I compile recent results from the field with the conclusions made from my earlier astrocyte work (study c.). These studies are ongoing in the laboratory and we have begun to develop a series of new assays and techniques that take advantage of our new super resolution microscope.
a. Scofield MD, Boger HA, Smith RJ, Li H, Haydon PG and Kalivas PW (2015). Gq-DREADD Selectively Initiates Glial Glutamate Release and Inhibits Cue-induced Cocaine Seeking. Biol Psychiatry 78:441-451 (PMC4547911)
b. Scofield MD, Li H, Siemsen B, Healy KL, Tran PK, Woronoff N, Boger HA, Kalivas PW and Reissner KJ. (2016) Cocaine self-administration and extinction leads to reduced GFAP expression and morphometric features of astrocytes in the nucleus accumbens core. Biol Psychiatry 80:207-215 (PMC4930433)
c. Scofield MD. (2017). Exploring the role of astroglial glutamate release and association with synapses in neuronal function and behavior. Biol Psychiatry [Epub Ahead of Print] (PMC5948108)