3.4.2. Opioid Receptors
Early studies using the nonselective opioid ligand,
[3H]naltrexone, reported that castration increases
opioid receptors in whole brain relative to intact male rats, and this
effect is reversed by treatment with testosterone propionate (TP; Han
&Fishman, 1979; Han & Fishman, 1985). Later studies using ligands with
greater specificity reported androgenic effects on opioid receptors that
differ across subtype and brain region. In some but not all cases, there
are sufficient data to compare androgenic effects on both peptide and
receptor concentrations to draw functional inferences.