Cortical and striatal μ-opioid receptors are altered by gonadal hormone treatment but not by prenatal morphine exposure in adult male and female rats

Abstract

The cerebral cortex (CX), cingulate CX (cgCX), and striatum (STR) play an important role in locomotion, cognition, emotion, and reward-motivated behaviors, and are altered by prenatal morphine exposure. We have demonstrated that δ-opioid receptors in the CX and STR of adult male and female rats are altered by prenatal morphine exposure and gonadal hormonal treatment. Because morphine binds with greater affinity to μ- than δ-opioid receptors, the present study examined the effect of prenatal morphine exposure on μ-opioid receptor density in the CX, cgCX, and STR of adult male and female rats using receptor autoradiography. In Experiment 1, three groups of adult male rats were analyzed: intact, gonadally intact; GNX, gonadectomized; and TP, GNX and testosterone propionate (TP)-treated. In Experiment 2, four groups of adult females were analyzed: OVX, ovariectomized; EB, OVX and estradiol benzoate (EB)-treated; P, OVX and progesterone (P)-treated; and EB+P, OVX and EB- and P-treated. In male rats, GNX and TP males had lower μ-opioid receptor densities in all three brain regions than gonadally intact males regardless of prenatal drug exposure. In female rats, OVX, EB+P-treated females had lower μ-opioid receptor density in the STR than OVX only females regardless of prenatal drug exposure. There were no drug or gonadal hormone effects in the CX or in the cgCX of female rats. Thus, the present study demonstrates that gonadal hormones, and not prenatal morphine exposure, alter the density of μ-opioid receptors in the CX, cgCX, and STR of adult male and female rats.