Are the catecholestrogens involved in estrogen-induced striatal dopamine receptor supersensitivity?

Disruption of latent inhibition induced by ovariectomy can be reversed by estradiol and clozapine as well as by co-administration of haloperidol with estradiol but not by haloperidol alone

INTRODUCTION

Epidemiological and clinical life cycle studies have indicated that the more favorable illness course and the better response to antipsychotic drugs (APDs) in women with schizophrenia correlate with high levels of estrogen, whereas increased vulnerability to exacerbation and relapse and reduced sensitivity to treatment are associated with low estrogen levels. Accordingly, the estrogen hypothesis of schizophrenia proposes that estrogen has a neuroprotective effect in women vulnerable to schizophrenia.

MATERIALS AND METHODS

Latent inhibition (LI), the capacity to ignore stimuli that received nonreinforced preexposure prior to conditioning, is disrupted in acute schizophrenia patients and in rats and humans treated with the psychosis inducing drug amphetamine. Disruption of LI is reversible by typical and atypical APDs. The present study tested whether low levels of estrogen induced by ovariectomy (OVX) would lead to disruption of LI in female rats and whether such disruption would be normalized by estrogen replacement treatment and/or APDs.

RESULTS

Results showed that OVX led to LI disruption, which was reversed by 17beta-estradiol (150 microg/kg) and the atypical APD clozapine (5 mg/kg), but not by the typical APD haloperidol (0.1, 0.2, 0.3 mg/kg). Haloperidol regained efficacy when administered with 17beta-estradiol (50 microg/kg).

DISCUSSION

These results provide the first demonstration in rats that low levels of hormones can induce a pro-psychotic state that is resistant to at least typical antipsychotic treatment. This constellation may mimic states seen in schizophrenic women during periods associated with low levels of hormones such as the menopause.

Maternal exposure to diphenhydramine during the fetal period in rats: Effects on physical and neurobehavioral development and on neurochemical parameters

Previous research from our laboratory suggested that the administration of antihistaminics (H(1) receptor antagonists) to pregnant Wistar rats throughout pregnancy altered brain sexual differentiation and dopaminergic physiology of the offspring. In the present study, we assessed the effects of 20 mg/kg diphenhydramine (DPH) administration to pregnant rats during the fetal period of pregnancy [Gestation Days (GDs) 16-21], a critical period for brain sexual differentiation and central nervous system (CNS) maturation. Maternal body weight and water and food consumption were measured during pregnancy and offspring physical and behavioral development were evaluated during lactation. Offspring open-field behavior was assessed at 21 and 100 days of age. After the final open-field test, male and female sexual behavior, stereotypy following an apomorphine challenge, striatal content of dopamine (DA), the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), serotonin (5-HT) and the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were assessed. There were no significant treatment-related changes in maternal reproductive parameters, but DPH treatment decreased maternal body weight gain during the treatment period. Offspring physical parameters were not altered in the treated group, and no significant treatment-related changes were found in female open-field measures, sexual behavior or in striatal neurochemical measurements. However, delayed testis descent and altered patterns of sexual behavior occurred in male offspring accompanied by increased striatal DA, decreased striatal DOPAC as well as reduced DOPAC/DA, HVA/DA and 5-HIAA/5-HT ratios. Taken together, these data suggest that exposure to DPH during the fetal period of rat development altered postnatal CNS maturation and sexual development of male offspring via changes in striatal bioamine systems.

Role of estrogen in the acquisition of intravenously self-administered cocaine in female rats

Previous work from this laboratory has revealed that female rats acquired cocaine self-administration at a faster rate than male rats and that a greater percentage of females acquired self-administration [Psychopharmacology 144 (1999) 77.]. It has been suggested that sex differences in stimulant self-administration may be related to ovarian hormones, particularly estrogen. To investigate this possibility, we compared four groups (n = 10) of female rats: ovariectomized (OVX) treated with either estradiol benzoate (EB) or vehicle (VEH), and sham-operated intact (SH) females treated with either the antiestrogen tamoxifen (TAM) or VEH. An autoshaping procedure was used to train rats to lever press for intravenous infusions of cocaine (0.2 mg/kg). The criterion for cocaine acquisition was a mean of 100 self-administered infusions over five consecutive 6-h sessions. Results revealed that 70% of the OVX + EB group and 80% of the SH + VEH group acquired self-administration, while only 30% of the OVX + VEH group and 50% of the SH + TAM group met the acquisition criterion. Rats that had estrogen chemically or surgically blocked exhibited significantly less responding for cocaine over the acquisition testing period, and fewer of these rats met the acquisition criterion compared to intact rats and to OVX rats with estrogen (EB) replacement. The percentages for females with estrogen (70% and 80%) vs. those without (OVX, 30%) were similar to those reported for intact females (70%) and males (30%) in the previous study [Psychopharmacology (2000)]. Taken together, these results suggest that estrogen is a key factor influencing drug-seeking behavior in female rats, and it may underlie sex differences in drug-reinforced responding.

Menstrual cycle affects functional cerebral asymmetries

Cerebral lateralization in females is probably modulated by the menstrual cycle such that a part of hemispheric asymmetries are diminished with an increase of the steroids estrogen and progesterone during the follicular and luteal phase and enhanced with steroid decreases during the menstrual phase. However, previous data were contradictory with regard to the hemispheric side of modulation and could not analyze which steroid is mainly responsible for cycle dependent lateralization shifts. Therefore, in the present study estrogen and progesterone changes were assessed separately and related to changes in cerebral asymmetry. Plasma levels of estrogen and progesterone were measured once during luteal and once during menstrual cycle phase while 20 females subjects performed a verbal and a figural lateralized matching task. The results showed a significant cycle phase x lateralization interaction for the right hemisphere dominated figural comparison task but not for the left hemispheric lexical condition. Although the lateralization was modulated by the menstrual cycle, a within-subject regression analysis demonstrated that the asymmetry shift was not under direct influence of estrogen or progesterone. Thus, the present study provides further empirical support for cycle dependent alterations in lateralization but makes it unlikely that this effect is directly caused by estrogen or progesterone plasma level variations.

Effects of estradiol on the ontogenesis of striatal dopamine D1 and D2 receptor sites in male and female rats

Since estradiol (E2) either increases or reduces the number of dopamine receptors in the corpus striatum of adult rats, depending on the dose and length of administration, the sensitivity of the two receptor subpopulations (D1 and D2) to E2 during ontogenesis was investigated. Rats of both sexes received either 10 micrograms/kg E2 for 3 days or 50 micrograms/kg for 6 days, and were sacrificed at the age of 15, 21, 40 and 120 days. D1 receptors (identified by [3H]SCH 23390 binding) displayed no changes in density and affinity in function of age, sex or E2 dose, whereas the D2 receptors (identified by [3H]spiperone binding) fell after the lower dose in all groups, and the higher dose resulted in supersensitivity in males of all ages, but only in the 15-day-old females. These findings show that the effect of E2 is bivalent on D2 density only. The effect of its brief administration at a low dose is not sex-dependent, whereas at higher doses administered for longer periods it appears to involve mechanisms linked to sexual differentiation after birth.

Effect of sex steroids on cocaine lethality in male and female mice

1. Endogenous sex steroid levels were altered in mice via gonadectomy, via physiological or supraphysiological doses of testosterone and/or estradiol, and via tamoxifen dosing to antagonize estrogens. 2. The role of sex hormones in susceptibility to cocaine lethality was examined via the response of mice after endocrine alterations to an intraperitoneal (i.p.) cocaine HCl (75 mg/kg). Incidence of deaths was significantly decreased only in sham-operated males receiving estradiol or tamoxifen and in ovariectomized or sham-operated females receiving doses of estradiol. 3. The levels of estradiol in both sexes appeared to be more influential than were levels of testosterone as a determinant of susceptibility to cocaine.