A region-specific increase in Gαq and Gα11 proteins in brains of rats during cocaine withdrawal

Serotonin 2A (5-HT2A) receptor-mediated increases in plasma hormone levels become supersensitive after 42 h of withdrawal from cocaine treatment. The present study investigated which components of the 5-HT2A receptor signaling system are associated with this supersensitivity. Rats were injected daily for 14 days with either saline or cocaine ( 15 mg/kg i.p.) twice a day or were injected using a "binge" protocol ( three injections per day, 1 h apart). Rats were sacrificed 2 or 7 days after the last cocaine injection, and the levels of membrane and cytosolassociated 5-HT2A receptors, Galpha(q), Galpha(11), regulators of G protein signaling (RGS) 4, and RGS7 proteins were assayed in the hypothalamic paraventricular nucleus, amygdala, and frontal cortex using Western blot analysis. Two days of withdrawal from cocaine, administered twice a day or using a binge protocol, produced an increase in membrane-associated Galpha(q) and Galpha(11) proteins in the paraventricular nucleus and the amygdala ( but not in the frontal cortex). This effect was reversible after 7 days of withdrawal. The protein levels of the 5-HT2A receptor, Galpha(z) protein, and RGS4 or RGS7 proteins were not altered by cocaine withdrawal in any of the above-mentioned brain regions. These findings suggest that the supersensitivity of the 5-HT2A receptors, during withdrawal from chronic cocaine, is associated with an increase in membrane-associated Galpha(q) and Galpha(11) proteins and not with changes in the expression of 5-HT2A receptors.