regions (Table 1). Chronic exposure to psychostimulants generally increases levels of RGS transcripts. Acute administration of morphine typically increases RGS expression, while chronic exposure reduces RGS expression – the opposite response of psychostimulants. Exceptions to these general observations, however, may reflect species differences or subtle variations in the treatment protocols. We found that chronic GHB treatment (injections twice-daily for one week) leads to a reduction of RGS2 mRNA in DA neurons of the VTA (Figure 2, [2]). In summary, addictive drugs lead to bidirectional changes in the levels of RGS transcripts and protein, suggesting complex changes in G-protein signaling, depending on the cell type and region of the brain.
