Regional c-Fos and FosB/ΔFosB expression associated with chronic methamphetamine self-administration and methamphetamine-seeking behavior in rats

Abstract

The regional expression of the transcription factors c-Fos and FosB/ΔFosB was examined in rats given acute exposure to intravenous methamphetamine (METH) or repeated intravenous METH self-administration. One group of rats self-administered METH via lever pressing in 2 h sessions every day for 3 weeks and on a final test day received self-administered METH as usual. A second group with the same METH self-administration history received saline infusions on the test day, to induce drug-seeking behavior. Other rats were trained with infusions of intravenous saline that were yoked to the passive delivery of METH in the other two groups. On test day, half of these yoked rats received passive METH infusions for the first time, whereas the others received saline as usual. The results showed that acute METH produced a characteristic signature of Fos expression with elevations in striatal, cortical, and extended amygdala regions. Importantly, rats with a 3-week history of METH self-administration displayed similar regional Fos expression to rats receiving METH for the first time. Rats seeking, but not receiving, METH on the test day had augmented Fos in the lateral hypothalamus, septum, and vertical limb of the diagonal band of Broca, suggesting a primary role for these regions in METH-seeking behavior. Both acute and chronic METH activated orexin-positive cells in the perifornical area of the hypothalamus. FosB/ΔFosB was elevated in the lateral hypothalamus, posterior ventral tegmental area, central amygdala, and dorsal raphe of all the rats with a history of METH self-administration. This occurred regardless of whether they received METH on test day, suggesting presence of the long-lived FosB isoform, ΔFosB. Overall, these results show persistent upregulated regional brain Fos and FosB/ΔFosB expression with chronic METH self-administration and indicate a role for the lateral hypothalamus and lateral septum in METH-seeking behavior.