Microbial Biofilms as Regulators of Amphetamine Use Disorders

Project Summary: Amphetamines (AMPHs) are a class of psychostimulants that includes compounds commonly used for the treatment of neuropsychiatric disorders (e.g. attention deficit disorders) as well as drugs of abuse. The abuse liability of AMPHs stems from their capacity to elevate synaptic levels of dopamine (DA) and activate natural reward pathways in the brain. AMPH does this, at least in part, via reversal of the dopamine transporter (DAT), a membrane protein physiologically responsible for import of DA into presynaptic neurons. Reversal of DAT leads to mobilization of cytoplasmic DA through non-vesicular DA release (DA efflux). The psychomotor stimulant properties of AMPH, as well as induction of reward, are dependent upon this efflux. In fact, inhibition of DA efflux reduces both the ability of AMPH to increase locomotion as well as AMPH preference. A growing amount of data shows reciprocal communication between the microbiome and the brain. Fusobacterium nucleatum (F. nucleatum) is a member of the human microbiome that enhances behavioral responses to AMPH by secreting butyrate, inhibiting histone deacetylase complex activity, and increasing expression of the dopamine transporter. Interestingly, not only does F. nucleatum enhance host responses to AMPH, AMPH increases abundance of F. nucleatum in both rodents, and humans, suggesting a feedforward paradigm that reinforces both imbalances in the microbiome (dysbiosis) as well as amphetamine use disorders. How AMPH enhances the abundance of F. nucleatum is not known. F. nucleatum is a gram-negative anaerobic rod that uses biofilm formation with aerobic or facultative partners to generate a protective barrier that stabilizes F. nucleatum colonies in the host. Our data demonstrates that AMPH enhances biofilm formation between F. nucleatum and the facultative bacteria Streptococcus mutans (S. mutans). Of note, F. nucleatum and S. mutans are both bacterial species that are highly associated with dental caries and gingivitis, periodontal diseases commonly comorbid with AMPH use disorders. Interestingly, biofilm formation in S. mutans is dependent upon glucosyl transferases (Gtfs), enzymes that aid in assembly and organization of the extracellular matrix of biofilms, and AMPH enhances expression of these Gtfs. We hypothesize that Gtfs, expressed by S. mutans, are required for formation of F. nucleatum:S. mutans mixed species biofilms, increases in abundance of F. nucleatum, and enhancement of host responses to AMPH. We test this hypothesis in the following aims: S.A. #1: Determine how Gtf activity regulates AMPH-enhanced biofilm formation, between F. nucleatum and S. mutans, and host colonization. S.A. #2: Define how Gtf activity alters AMPH-induced behavioral responses.