Acute progesterone treatment impairs spatial working memory in intact male and female rats.

INTRODUCTION: The aim of this study was to determine if progesterone affects spatial and non-spatial working memory in intact male and female rats. METHODS: Rats received subcutaneous injections of progesterone (500 microg) or vehicle (sesame oil). Four hours after hormone treatments, spatial and non-spatial memories were tested using novel object recognition and spatial object recognition tasks. RESULTS: Vehicle-treated female rats had higher progesterone serum levels than males, but progesterone treatment produced equivalent progesterone serum levels in both sexes. In the object recognition task--a non-spatial memory task-females showed better performance than males, and progesterone had no effect on either sex. However, in the object replacement task--a spatial memory task-progesterone significantly impaired the retention in both male and female rats as compared with vehicle-treated groups. CONCLUSION: These results suggest that acute progesterone treatment interferes with spatial working memory consolidation, but not recognition (non-spatial) working memory. As such, the observed sexual incongruities in progesterone's effects on working memory suggest that progesterone-based hormone therapies have a negative impact on cognition.

Testosterone differentially alters cocaine-induced ambulatory and rearing behavioral responses in adult and adolescent rats.

Little is known about the physiological and behavioral effects of testosterone when co-administered with cocaine during adolescence. The present study aimed to determine whether exogenous testosterone administration differentially alters psychomotor responses to cocaine in adolescent and adult male rats. To this end, intact adolescent (30-days-old) and adult (60-day-old) male Fisher rats were pretreated with vehicle (sesame oil) or testosterone (5 or 10mg/kg) 45 min prior to saline or cocaine (20mg/kg) administration. Behavioral responses were monitored 1h after drug treatment, and serum testosterone levels were determined. Serum testosterone levels were affected by age: saline- and cocaine-treated adults in the vehicle groups had higher serum testosterone levels than adolescent rats, but after co-administration of testosterone the adolescent rats had higher serum testosterone levels than the adults. Pretreatment with testosterone affected baseline activity in adolescent rats: 5mg/kg of testosterone increased both rearing and ambulatory behaviors in saline-treated adolescent rats. After normalizing data to % saline, an interaction between hormone administration and cocaine-induced behavioral responses was observed; 5mg/kg of testosterone decreased both ambulatory and rearing behaviors among adolescents whereas 10mg/kg of testosterone decreased only rearing behaviors. Testosterone pretreatment did not alter cocaine-induced behavioral responses in adult rats. These findings suggest that adolescents are more sensitive than adults to an interaction between testosterone and cocaine, and, indirectly, suggest that androgen abuse may lessen cocaine-induced behavioral responses in younger cocaine users.

Effects of RU 486 and tamoxifen on cocaine-induced behavioral and endocrinologic activations in male and female Fischer rats.

Evidence suggests that sex differences in response to cocaine administration may be regulated by activation of progesterone and estrogen receptors. To test this hypothesis, rats were pretreated with either RU 486 (progesterone antagonist; 0, 3, or 25 mg/kg), tamoxifen (estrogen antagonist; 0, 1, or 3 mg/kg), or vehicle followed by saline or cocaine administration (15 mg/kg). Although RU 486 did not affect cocaine-induced locomotor activity in female rats, it dose-dependently decreased such activity in males (3 mg/kg significantly attenuated locomotor responses in cocaine-treated rats as compared with vehicle treatment or 25 mg/kg of RU 486). RU 486 also affected baseline serum levels of corticosterone. Males treated with 3 mg/kg of RU 486 plus cocaine had higher progesterone and corticosterone serum levels than vehicle-treated groups. In females, both doses (3 and 25 mg/kg) of RU 486 significantly attenuated corticosterone serum levels compared with vehicle treatment. For both sexes overall, tamoxifen neither significantly influenced cocaine-induced ambulatory and rearing responses nor altered cocaine-induced progesterone and corticosterone serum levels. Taken together, our results suggest that progesterone receptors have a sexually dimorphic role in cocaine-induced effects, but estrogen receptors have only a limited role. Moreover, both receptor antagonists modulate neurochemical responses differentially.

Testosterone plays a limited role in cocaine-induced conditioned place preference and locomotor activity in male rats.

Growing evidence suggests that sex differences in cocaine reward responses are regulated by endogenous gonadal hormones. However, few studies have addressed the role of testosterone on cocaine reward and psychomotor activation. This study aimed to determine whether testosterone influences the development of psychomotor and reward responses to cocaine. Castrated 8-week-old male Fisher rats received placebo or testosterone via Silastic capsules (1-3 capsules of 100% testosterone) or subcutaneous injections (400, 800, or 1200 microg/kg) concurrent with cocaine administration. Although chronic testosterone administration did not alter cocaine-induced conditioned place preference (CPP), concurrent administration of testosterone and cocaine affected the development of cocaine CPP dose-dependently; 400 microg/kg blocked the expression of cocaine-induced CPP. Testosterone did not affect cocaine-induced locomotor activity. Furthermore, testosterone-saline-treated controls did not develop CPP, suggesting that at these doses, testosterone does not produce rewarding or motor responses. These data suggest that testosterone may play a limited role in cocaine-induced reward associations and locomotor responses and thus has a limited effect in the previously reported sexually dimorphic responses to cocaine.

Arousal of cerebral cortex electroencephalogram consequent to high-frequency stimulation of ventral medullary reticular formation.

We have theorized that large neurons in the ventral and medial reticular formation of the medulla are critical for both autonomic and cortical arousal. To test this theory, we anesthetized rats with urethane, lowered concentric bipolar stimulating electrodes into the medullary reticular formation, and implanted electroencephalogram (EEG) and ECG recording electrodes. We stimulated in the medulla with pulse frequencies ranging from 50 to 300 Hz while recording cortical EEG and ECG. These female rats were ovariectomized, and one subgroup was administered estradiol. Electrical stimulation at either 200 or 300 Hz among the large medullary reticular neurons in nucleus paragigantocellularis (PGi) caused a significant reduction in the portion of the EEG power spectrum represented by delta-waves (0.1-4 Hz) and -waves (4.1-8 Hz). Correspondingly, there were increases in gamma-wave power (22-50 Hz), especially when using 300 Hz. Stimulation at

Progesterone receptors activation after acute cocaine administration.

Cocaine modulates serum levels of progesterone in intact female and male rats, as well as in pregnant dams, and progesterone decreases or attenuates cocaine-induced behavioral and reward responses. It has been postulated that cocaine's modulation of serum progesterone levels may in turn alter progesterone receptor activity, thereby contributing to cocaine-induced alterations of neuronal functions and genomic regulations. To test this hypothesis, intact male rats received acute injections of saline or cocaine (15 or 30 mg/kg, dissolved in 0.9% saline, intraperitoneal). Progesterone serum levels, progesterone receptor (PR) protein levels, and PR-DNA binding complexes were measured in the striatum by radioimmunoassay, Western blot, and gel shift analyses, respectively. After injection of 15 mg/kg of cocaine, induction of progesterone serum levels was closely followed by an increase in receptor protein levels and DNA binding complexes. After injection of 30 mg/kg of cocaine, similar effects were observed along with an attenuation of receptor protein levels and DNA binding complexes at 60 min. Our results suggest that activation of progesterone receptors may be a mechanism by which cocaine mediates behavior through molecular alterations in the central nervous system.

Cocaine-induced sex differences in D1 receptor activation and binding levels after acute cocaine administration.

Although it is established that female rats have a more robust behavioral response to acute cocaine administration than male rats, the neurobiological mechanisms underlying these differences remain unclear. The purpose of the present study was to determine whether dopamine (DA) receptor activation influences sex differences in cocaine-induced behaviors. A second study was performed to determine sex differences in D1/D2 receptor levels prior to and post-cocaine administration. Male and female Fischer rats were pre-treated with the D1 antagonist SCH-23390 (0.05, 0.1, and 0.25 mg/kg, i.p.), the D2 antagonist eticlopride (0.03, 0.1 mg/kg, i.p.), or vehicle (saline) 15 min before acute cocaine (20 mg/kg, i.p.) or saline administration. Cocaine-induced ambulatory and rearing activity was greater in female than male rats. Pre-treatment with SCH-23390 affected cocaine-induced ambulatory, rearing, and stereotypic activity in a sex-dependent manner; cocaine-induced ambulatory and stereotypic behavior in female rats was reduced by the lowest dose of SCH-23390. Eticlopride did not alter behavioral responses to cocaine in male or female rats. These results suggest that in both male and female rats, activation of the D1, but not the D2, receptor modulates cocaine's motor effects. There were no sex differences in baseline levels of D1, D2, and DA transporter binding in the caudate putamen (CPu) and the nucleus accumbens (NAc). Cocaine administration reduced D1 binding levels in the CPu only in male rats. Our findings suggest that the regulation of striatal D1 binding levels after acute cocaine administration is a sexually dimorphic process. We also hypothesize that the greater sensitivity to D1 receptor blockade in female rats, as compared to male rats, may contribute to their overall increased hyperactivity in response to acute cocaine. Taken together, the D1 receptor may be an important substrate in the regulation of sex differences to cocaine-induced locomotor activity.

Estradiol and progesterone differentially regulate formalin-induced nociception in ovariectomized female rats.

Clinical and preclinical studies have found sex-specific differences in the discrimination and perception of inflammatory stimuli. The emerging picture suggests that the biological basis of these differences resides in the regulatory activity of gonadal hormones in the central nervous system. This study describes the effects of ovarian hormones in inflammatory pain processes. Ovariectomized rats received estradiol and/or progesterone, and the number of paw flinches was measured after 1, 2.5 or 5% formalin administration. Both estradiol and progesterone altered the number of flinches only after 1% formalin administration. Estradiol significantly reduced the overall number of flinches during Phase II of the formalin nociceptive response while progesterone attenuated Phase I of the response. After co-administration of estradiol and progesterone, progesterone reversed estradiol's analgesic effect in Phase II, however, estradiol did not reverse progesterone's analgesic activity in Phase I. To determine if estradiol effects are receptor-mediated, tamoxifen (selective estrogen receptor mediator, 15 mg/kg) or alpha-estradiol (an inactive isomer of estradiol, 20 microg) were utilized. Tamoxifen decreased the number of formalin-induced flinches during Phase II while alpha-estradiol did not affect any formalin-induced responses. When co-administered with estradiol, tamoxifen failed to reverse estradiol's effect, suggesting both tamoxifen and estradiol activate similar intracellular mechanisms. Although Western blot analysis detected the presence of estradiol alpha and beta and progesterone B receptors in the spinal cord, hormone replacement treatments had no effects on the levels of these receptors. We postulate that the mechanisms by which estradiol and progesterone induce analgesia occur through the activation of their receptor at the spinal cord level.

Cocaine induction of ERK proteins in dorsal striatum of Fischer rats.

Cocaine is an addictive psychostimulant that induces fos and opioid gene expression by activating the dopamine receptors and the PKA pathways in dopamine D1 and a glutamate NMDA-dependent mechanisms in the striatum. In this study, we show that a single cocaine administration induces ERK phosphorylation in the caudate/putamen of Fischer rats. This increase in Phospho-ERK is diminished by pre-administration of SCH23390, or MK801 but not with pre-administration of eticlopride. Furthermore, this single cocaine administration does not alter the levels of phospho-CREB protein or CREB-DNA bindings in the caudate/putamen protein extracts but does increase phospho-Elk-1 protein levels in the same extracts.

MK-801 attenuates cocaine induction of c-fos and preprodynorphin mRNA levels in Fischer rats.

This study shows that single (15 mg/kg) or binge (3x15 mg/kg) cocaine administration increases c-fos mRNA levels, but only binge cocaine administration increases preprodynorphin mRNA levels in the caudate/putamen of Fischer rats. This increase in both c-fos and preprodynorphin mRNA levels is attenuated by the noncompetitive NMDA antagonist MK-801 (0.25 mg/kg), suggesting a preferential role for NMDA receptor co-activation in cellular events leading to cocaine-induced behaviors.

Endogenous gonadal hormones modulate behavioral and neurochemical responses to acute and chronic cocaine administration.

Recent evidence demonstrates that there are sex differences in behavioral responses to cocaine. Further, reproductive gonadal hormones (estrogen, progesterone and testosterone) have been further implicated in mediating some of the cocaine-induced alterations. To better understand sex differences and the role of gonadal hormones in cocaine-induced locomotor and stereotypic behavior, intact and gonadectomized male and female Fischer rats were randomly assigned to either chronic cocaine (15 mg/kg) or saline treatments for 14 days followed by a challenge administration (7 days after the last cocaine/saline administration). Locomotor (ambulatory and rearing) and stereotypic activities were measured on days 1, 7 and 14 as well as after withdrawal/challenge with cocaine. Overall, intact female rats consistently showed a rapid (acquired by day 7) and longer lasting (persistent through the challenge dose) sensitization for all locomotor behaviors than any of the other groups. In contrast, intact males developed sensitization of these locomotor activities only in response to chronic cocaine administration, and after withdrawal and drug challenge the sensitization to cocaine-induced locomotor activity was no longer present. In female rats, gonadectomy affected ambulatory activity but not total and rearing responses after acute, sub-acute, chronic and challenge response to cocaine. On the other hand, castrated male rats were affected in cocaine-induced ambulatory activity but not rearing activity. In intact male rats, cocaine-induced stereotypic activity was rapidly and persistently sensitized after 7 days of cocaine administration, where gonadectomized male rats developed sensitization to cocaine-induced stereotypic activity only after a challenge cocaine administration. Although cocaine induced stereotypic activity, no statistically significant differences were observed between intact and ovariectomized female rats or throughout the different lengths of cocaine administration. After a challenge of cocaine, corticosterone levels were induced in all experimental groups. Moreover, no differences in levels of benzoylecgonine, a cocaine metabolite, were observed. Similar to our previous observations after acute cocaine administration, after challenge of cocaine, an increase in progesterone and a decrease in testosterone levels were observed in intact females and males, respectively. In summary, endogenous hormones seem to be involved in the behavioral activation and development of sensitization to cocaine.