Differential effect of amphetamine over the corticotropin-releasing factor CRF 2 receptor, the orexin OX 1 receptor and the CRF 2 -OX 1 heteroreceptor complex.

Stress is one of the factors underlying drug seeking behavior that often goes in parallel with loss of appetite. We here demonstrate that orexin 1 receptors (OX ₁ R) may form complexes with the corticotropin releasing factor CRF ₂ receptor. Two specific features of the heteromer were a cross-antagonism and a blockade by CRF ₂ of OX ₁ R signaling. In cells expressing one of the receptors, agonist-mediated signal transduction mechanisms were potentiated by amphetamine. Sigma 1 (σ ₁ ) and 2 (σ ₂ ) receptors are targets of drugs of abuse and, despite sharing a similar name, the two receptors are structurally unrelated and their physiological role is not known. We here show that σ ₁ receptors interact with CRF ₂ receptors and that σ ₂ receptors interact with OX ₁ R. Moreover, we show that amphetamine effect on CRF ₂ receptors was mediated by σ ₁ R whereas the effect on OX ₁ receptors was mediated by σ ₂ R. Amphetamine did potentiate the negative cross-talk occurring within the CRF ₂ -OX ₁ receptor heteromer context, likely by a macromolecular complex involving the two sigma receptors and the two GPCRs. Finally, in vivo microdialysis experiments showed that amphetamine potentiated orexin A-induced dopamine and glutamate release in the ventral tegmental area (VTA). Remarkably, the in vivo orexin A effects were blocked by a selective CRF ₂ R antagonist. These results show that amphetamine impacts on the OX ₁ R-, CRF ₂ R- and OX ₁ R/CRF ₂ R-mediated signaling and that cross-antagonism is instrumental for in vivo detection of GPCR heteromers. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.
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