Facilitation of morphine withdrawal symptoms and morphine-induced conditioned place preference by a glutamate transporter inhibitor DL-threo-beta-benzyloxyaspartate in rats

There is a body of evidence implying the involvement of the central glutamatergic system in morphine dependence. In this study, we examined the effect of intracerebroventricular (i.c.v.) administration of a potent glutamate transporter inhibitor, DL-threo-beta-benzyloxyaspartate (DL-TBOA), on acute morphine-induced antinociception, expression of somatic and negative affective components of morphine withdrawal, and acquisition of morphine-induced conditioned place preference in rats. I.c.v administration of DL-TBOA (10 nmol) to naive rats did not affect the acute antinociceptive effect of morphine. I.c.v. administration of DL-TBOA (10 nmol) to morphine-dependent rats significantly facilitated the expression of naloxone-precipitated somatic signs and conditioned place aversion. DL-TBOA (3 and 10 nmol) significantly facilitated acquisition of morphine-induced conditioned place preference. DL-TBOA itself produced neither conditioned place aversion nor place preference in naive rats. These results suggest that central glutamate transporters play inhibitory roles in the expression of somatic and negative affective components of morphine withdrawal and the reinforcing effect of morphine.