3.4.2.3. Kappa Receptors
Much of what is known about the effects of androgens on kappa receptors
is derived from a single investigation. In intact male rats, chronic
treatment with nandrolone decreases kappa opioid receptors in most brain
regions, with significant decreases observed in the nucleus accumbens
shell, hypothalamus, central amygdaloid nucleus, lateral globus
pallidus, and stria terminalis (Magnusson et al., 2009). In contrast,
chronic nandrolone treatment increases kappa receptor density in the
caudate putamen and dorsal endopiriform (Magnusson et al., 2009, also
see Ruka et al., 2015 for the effects of castration on hypothalamic
brain slices). In most of these regions, androgen-induced decreases in
kappa receptor density can be explained, in part, as compensatory
responses to androgen-induced increases in endogenous dynorphin
concentrations. One notable exception is the nucleus accumbens, which
exhibits decreases in both dynorphin concentrations and kappa opioid
receptor density following androgenic treatment. As noted above (Section
3.4.1), dynorphin negatively modulates dopamine release in the nucleus
accumbens, which is critically involved in motivated behavior and drug
addiction. Consequently, androgen-induced decreases in kappa opioid
signaling in the nucleus accumbens could account, in part, for the
positive-reinforcing and abuse-related effects of AAS in human
populations.