Project Summary
Exposure to drugs of abuse, such as alcohol, induces plasticity in the brain and creates persistent drug-related
memories. These brain changes and persistent activation of drug memories are believed to be central in
contributing to drug addiction. A preponderance of literature has studied the tripartite synapse (pre- and
postsynaptic cells, and astrocytes) in addiction; however, mounting evidence has implicated the tetrapartite
synapse to indicate the additional involvement of extracellular matrix (ECM) molecules in this process. The ECM
is comprised of a complex network of glycoproteins, chondroitin sulfate proteoglycans (CSPG), and enzymes,
which interact to control underlying cell plasticity and excitability. Glycoproteins and CSPGs aggregate around
inhibitory fast-spiking parvalbumin (PVB) interneurons throughout the brain to form perineuronal nets (PNN)
which maintain and strengthen synapses. In rodents, PNNs are temporarily degraded after acute exposure to
drugs, a process that relies on the activity of glial cells which secrete endogenous proteases that cleave PNN
components. After persistent activation of reward memories (i.e., dependence), PNNs numbers are increased,
indicating that neuronal ensembles associated with drugs of abuse are enveloped by PNNs. While the findings
studying PNNs in preclinical addiction models are compelling, there are currently no data regarding PNNs in
humans with alcohol use disorder (AUD) or other substance use disorders. This proposal focuses on alcohol-
induced changes in PNNs and the molecules that regulate PNNs in humans, and how modifying neuron-
microglia signaling cascades in rodents alters the regulation of contextual alcohol reward memory and the
composition of PNNs. In Aim 1, we will evaluate PNN densities in human postmortem hippocampus tissue using
quantitative brightfield microscopy together with measures of protein and mRNA expression for several of the
endogenous ECM proteases, GABAergic neurons (e.g., PVB), and synaptic markers in tissue samples from the
same subject cohort. We predict that individuals with AUD will have increased numerical densities of PNNs and
increased PVB expression that coincide with decreased expression of ECM proteases. These findings will
delineate how PNNs are impacted in humans with AUD and provide a basis for evaluating whether PNN changes
in rodent models of substance use disorders are translatable to humans. In Aim 2, we will use mice to evaluate
how knockout of the interleukin-33 receptor, ST2, impacts reward memory using conditioned place preference.
Interleukin-33 is secreted by neurons in an experience-dependent manner, where it signals to its obligate ST2
receptor on microglia to mediate the release of several endogenous ECM proteases. We predict that knockout
of the interleukin-33 receptor will impede the proteolytic cascades that mediate memory formation and
consolidation, thereby curbing alcohol-induced place preference acquisition and consolidation. We believe the
proposed studies will inform the use of pharmacologic agents which target the ECM to treat AUD and other
substance use disorders, and will confirm and expand on findings from preclinical studies of the ECM in addiction.