Alterations of prenatal morphine exposure in mu-opioid receptor density in hypothalamic nuclei associated with sexual behavior.

Our previous work demonstrated that prenatal morphine exposure twice daily during gestational days 11-18 differentially alters male and female sexual behavior. One possible explanation may be that prenatal morphine exposure alters the sexual behavior via alterations of mu-opioid receptors in brain regions involved in reproductive function and behavior, including the ventromedial nucleus of the hypothalamus (VMH), arcuate nucleus (ARC), and medial preoptic area (mPOA). In experiment 1, mu-opioid receptor density was analyzed in three groups of adult male rats: gonadally intact, gonadectomized (GNX), and GNX and testosterone 17beta-propionate-treated (TP). In experiment 2, mu-opioid receptor density was analyzed in four groups of adult female rats: ovariectomized (OVX), OVX and estradiol benzoate-treated (EB), OVX and progesterone-treated (P), and OVX and EB- and P-treated (EB+P). Experiment 1 demonstrated that prenatal morphine exposure lowered the mu-opioid receptor density in the mPOA of adult, gonadally intact and in TP males, while this difference was not apparent in GNX male rats. Experiment 2 demonstrated that prenatal morphine exposure increased mu-opioid receptor density in OVX females, while decreasing it in EB females in the VMH. When compared to our previous sexual behavior data, the present results demonstrate that at least some changes in sexual behavior of adult male and female rats prenatally exposed to morphine may be related to alterations in mu-opioid receptors in brain regions controlling sexual behavior.

Hyperfunctionality of serotonin-2C receptor-mediated inhibition of accumbal dopamine release in an animal model of depression is reversed by antidepressant treatment.

Dopamine release in the nucleus accumbens mediates motivation and reward, making it a likely candidate to be involved in anhedonia, one of the major symptoms of depression. In the current study, alterations in basal extracellular dopamine levels and 5HT2C receptor-mediated inhibition of accumbal dopamine release in Flinders Sensitive Line (FSL) rats, an animal model of depression, were investigated. We found that FSL rats have decreased extracellular dopamine levels in the nucleus accumbens and an increased inhibitory-like effect of 5HT2C receptors on accumbal dopamine release. However, neither basal 5HT levels nor the accumbal 5HT response to the local 5HT2C receptor antagonist (RS 102221) differed between Sprague-Dawley and FSL rats. Seven-day treatment with the nefazodone (a serotonin/noradrenaline reuptake inhibitor and 5HT2C antagonist) as well as 7-day and 14-day treatments with a tricyclic antidepressant desipramine increased extracellular dopamine levels in the nucleus accumbens of FSL rats. However, only 14-day treatment with desipramine or 7-day treatment with nefazodone, but not 7-day treatment with desipramine, decreased 5HT2C receptor-mediated inhibition of accumbal dopamine release. Based on a possible correlation between the onset of 5HT2C receptor-mediated inhibition and the behavioral effects of desipramine and nefazodone treatment that was described in our previous studies, we suggest that 5HT2C receptor activation may be important for the onset of the behavioral effects of antidepressant treatment.

Cholera toxin B decreases bicuculline seizures in prenatally morphine- and saline-exposed male rats.

Prenatal morphine exposure on gestation days 11-18 alters bicuculline-induced seizures in rats during development and in adulthood. Adult, morphine-exposed male progeny exhibit an increased latency to bicuculline seizures, which can be reversed by administration of the opioid receptor antagonist naloxone. In chronically morphine-treated adult mice, cholera toxin B (CTX-B) can reverse the effects of chronic morphine administration. Therefore, the present study investigated whether prenatally morphine-exposed rats show a similar response to CTX-B as chronically morphine-treated adult rodents. Prenatally morphine-, saline- and unexposed male progeny were tested for seizure susceptibility with a 7.5-mg/kg intraperitoneal injection of bicuculline in adulthood. CTX-B or saline was injected subcutaneously at 24, 12, and 0.5 h before bicuculline injection. CTX-B decreased the occurrence of bicuculline-induced seizures in both prenatally saline- and morphine-exposed but not unexposed rats. Furthermore, three, but not one, saline injections administered at 12-h intervals prior to bicuculline administration reversed the increase in seizure latency in prenatally morphine-exposed adult males, suggesting an altered responsiveness of the stress system. The present study demonstrates that CTX-B can decrease the occurrence of bicuculline seizures in prenatally stressed rats and that increased seizure latencies in prenatally morphine-exposed male rats may be related to stress responses.

Transplantation of glial cell line-derived neurotrophic factor-expressing cells into the striatum and nucleus accumbens attenuates acquisition of cocaine self-administration in rats.

Neurotrophic factors, such as glial cell line-derived neurotrophic factor (GDNF), may play a role in drug-induced biochemical and behavioural adaptations that characterize addiction. We found that GDNF mRNA levels are lower in the striatum of rats that chronically self-administered cocaine. Therefore, we examined the effect of transplanted cells used as a biodelivery system for GDNF on cocaine self-administration in rats. A human astrocyte-like cell line, which produces and excretes GDNF, was transplanted into the striatum and nucleus accumbens of rats. These rats showed a significantly lower number of active lever presses in the cocaine self-administration paradigm compared with control rats. Moreover, rats that received a chronic infusion of GDNF via a micro-osmotic pump also exhibited weak cocaine self-administration. Therefore, we conclude that exogenous augmentation of GDNF repositories may be useful in suppressing cocaine self-administration.

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

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 delta-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 mu- than delta-opioid receptors, the present study examined the effect of prenatal morphine exposure on mu-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 mu-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 mu-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 mu-opioid receptors in the CX, cgCX, and STR of adult male and female rats.

Density of mu-opioid receptors in the hippocampus of adult male and female rats is altered by prenatal morphine exposure and gonadal hormone treatment.

The present in vitro autoradiography study demonstrates that prenatal exposure to morphine alters the density of mu-opioid receptors in the hippocampus of adult female but not adult male rats. Prenatal morphine exposure increased the mu-opioid receptor density in the CA1 of ovariectomized (OVX) females and in the CA3 of OVX, estradiol benzoate-plus progesterone (EB+P)-treated females, but decreased it in CA3 of OVX females. There were also hormonal effects on mu-opioid receptor density in adult female rats. In the CA1, only morphine-exposed but not saline-exposed, hormone-treated females (EB, P, or EB+P) had a decrease in mu-opioid receptor density relative to OVX females. Both saline-exposed and morphine-exposed, OVX females after gonadal hormone replacement had a lower density of mu-opioid receptors in the CA3 and in the dentate gyrus (DG) than OVX females. In male rats, there was a decrease in mu-opioid receptor density in the CA1 and CA3 of gonadectomized (GNX), testosterone 17beta-proprionate (TP)-treated males relative to GNX males regardless of prenatal morphine exposure. In the DG, the mu-opioid receptor density was reduced only in morphine-exposed but not in saline-exposed, TP-treated males compared with GNX males. Thus, our data demonstrate that mu-opioid receptor density in the hippocampus is affected by prenatal morphine exposure and by male and female gonadal hormones.

Mu-opioid receptors in seizure-controlling brain structures are altered by prenatal morphine exposure and by male and female gonadal steroids in adult rats.

The present study used autoradiography to examine the effect of prenatal morphine exposure on mu-opioid receptor density in epileptic seizure-controlling brain structures including the substantia nigra pars compacta (SNC), substantia nigra pars reticulata (SNR), superior colliculus (SC), and subthalamic nucleus (STN) of adult male and female rats. The results demonstrate that prenatal morphine exposure increases the mu-opioid receptor density in the SNC and STN, but not in the SNR or in the SC of gonadally intact adult male rats. The density of mu-opioid receptors in the SNC and STN is, however, decreased following gonadectomy in morphine-exposed males, and testosterone treatment fails to restore this decrease to the level of gonadally intact males. Further, in the SC, the density of mu receptors was lower in both saline-exposed, gonadectomized (GNX) and GNX, TP-treated males and in morphine-exposed, GNX, TP-treated males relative to gonadally intact saline- and morphine-exposed males, respectively. In ovariectomized (OVX) female rats, the same prenatal morphine exposure increases the mu-opioid receptor density in the SNC and SNR, but decreases it in the STN. The density of mu-opioid receptors is also decreased in the SNC and SC of OVX estrogen-treated females and in the SNR and SC of OVX, progesterone-treated females. Thus, the present study demonstrates that mu-opioid receptors in seizure-controlling brain structures are sex-specifically altered by prenatal morphine exposure in adult progeny. Further, prenatal morphine exposure alters gonadal hormone effects on the density of mu receptors in adult, OVX females.

Impact of maternal morphine and saline injections on behavioral responses to a cold water stressor in adult male and female progeny.

The purpose of the present study was to test the effects of maternal morphine and saline injections on chronic cold water stress responses in three groups of adult male and female rats: prenatally morphine-exposed adult progeny, prenatally saline-exposed adult progeny, and control groups. All male rats were gonadally intact, and female rats were ovariectomized (OVX) in adulthood, and half of them were injected with estradiol benzoate (EB). All animals were exposed to a cold water stressor daily for 2 weeks and tested before (baseline) and after (stress effects) the chronic cold water stressor in a swim test and an open field test. In the swim test, both adult males and OVX, EB-treated adult females born to mothers injected with morphine or saline displayed more floating behavior during the swim test than their controls, both before and after the cold water stressor. Male rats exposed to morphine or saline prenatally also spent more time struggling during the swim tests than controls, and this was further increased after the cold water stressor. In the open field test, males and OVX, EB-treated females born to morphine- or saline-injected mothers were less active and displayed fewer rearings than controls. No differences were observed in OVX females as a result of prenatal injections. Thus, the present study demonstrates that maternal injections, regardless of injection content, induce long-lasting effects on stress responsiveness in adult progeny.