Abstract
Cocaine dysregulates tumor necrosis factor (TNF) signaling in mesolimbic substrates, suggesting a role for TNF in cocaine-induced hyperlocomotion, a signature preclinical effect of cocaine. Inhibition of TNF signaling by genetic deletion or with a brain-penetrable TNF antagonist enhances cocaine-induced hyperlocomotion in male mice, but roles for sex and peripheral TNF are unclear. Also unknown is how peripherally restricted etanercept, the world's most widely prescribed TNF inhibitor, affects cocaine-induced locomotor responses. We determined effects of etanercept on a triad of cocaine-induced locomotor responses (e.g., ambulation, stereotypy, distance traveled) in male and female rats and impacts of etanercept-cocaine exposure on tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA levels in the ventral tegmental area (VTA). Etanercept (20 mg/kg, IP) and a submaximal dose of cocaine (10 mg/kg, IP) were used initially, and etanercept was injected 48 h before cocaine to capture peak plasma concentrations. Etanercept itself did not affect spontaneous locomotor responses in male or female rats. In male rats, etanercept increased cocaine-induced ambulatory and stereotypical activities and enhanced cocaine-induced distance traveled. Etanercept modestly reduced TH mRNA levels in the VTA of cocaine-naïve and cocaine treated male rats. Locomotor responses in male rats that were evoked by a higher dose of cocaine (20 mg/kg, IP) were not affected by etanercept. In female rats, etanercept did not affect any cocaine-induced locomotor responses. These results show that etanercept exerts effects on locomotor behaviors induced by cocaine that depend on both sex and cocaine dose and suggest that peripheral inhibition of TNF influences cocaine-induced behaviors. Key words: etanercept; TNF; cocaine; dopamine; tyrosine hydroxylase; DAT; locomotor.