Differential effect of amphetamine over the corticotropin-releasing factor CRF receptor, the orexin OX receptor and the CRF-OX 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 (OXR) may form complexes with the corticotropin releasing factor CRF receptor. Two specific features of the heteromer were a cross-antagonism and a blockade by CRF of OXR signaling. In cells expressing one of the receptors, agonist-mediated signal transduction mechanisms were potentiated by amphetamine. Sigma 1 (σ) and 2 (σ) 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 receptors interact with CRF receptors and that σ receptors interact with OXR. Moreover, we show that amphetamine effect on CRF receptors was mediated by σR whereas the effect on OX receptors was mediated by σR. Amphetamine did potentiate the negative cross-talk occurring within the CRF-OX 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 CRFR antagonist. These results show that amphetamine impacts on the OXR-, CRFR- and OXR/CRFR-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'.