[125I]β-endorphin bound to high affinity (K(d) = 0.25 nM) receptors in the caudal dorsomedial medulla of rats with a B(max) of 97 fmol/mg protein. The relative potency for displacement of [125I]β-endorphin binding was: β-endorphin1-31 β-endorphin1-27 > DAMGO > naloxone > N- acetyl-β-endorphin1-31 > U50488 > DPDPE. The B (max) for [3H]DAMGO binding was 81 fmol/mg protein, indicating that most [125I]β-endorphin binding corresponds to μ-opioid receptors. [3H]DAMGO binding was not influenced by lesioning noradrenergic nerve terminals in the caudal dorsomedial medulla. Our findings indicate that β-endorphin interacts primarily with μ-opioid receptors in the caudal dorsomedial medulla. These receptors are not affected by noradrenergic denervation.
- Nucleus of the solitary tract
- Opioid receptor