3.4.2.2. Delta Receptors
Androgens decrease delta opioid receptor expression in neuronal cells.
Nandrolone treatment decreases delta receptor binding and delta receptor
mRNA expression in hybrid cell lines naturally expressing delta
receptors. Interestingly, these effects are independent of androgen
receptors as evidenced by the observation that (1) androgenic decreases
in receptor density are observed in a cell line that does not express
androgen receptors and (2) androgenic decreases in receptor density are
observed in the presence of an androgen receptor antagonist
(Pasquariello et al., 2000). Androgen-induced decreases in delta opioid
receptor density is widespread across brain regions. In rats, for
instance, castration increases delta opioid receptor density in the
olfactory bulb, thalamus, midbrain, and hypothalamus, and this effect is
reversed completely by administration of testosterone (Takayama et al.,
1990). Similar to mu receptors, androgen-induced decreases in delta
receptors may be explained, in part, by receptor down-regulation induced
by androgenic increases in endogenous enkephalin concentrations.