μ-opioid and 5-HT1A receptors heterodimerize and show signalling crosstalk via G protein and MAP-kinase pathways

► 5-HT1A- and μ-opioid receptors can form heterodimers in heterologous cell systems. ► μ-opioid receptor stimulates G protein‐dependent signaling by the 5-HT1A receptor. ► Both receptors can coexerce control of ERK1/2 phosphorylation ► No induction of co-internalization by both receptors is observed.