Ann S. Clark

Behavioral and physiological responses to anabolic-androgenic steroids.

Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone originally designed for therapeutic uses to provide enhanced anabolic potency with negligible androgenic effects. Although AAS continue to be used clinically today, the medical benefits of low therapeutic doses of AAS stand in sharp contrast to the potential health risks associated with the excessive doses self-administered not only by elite athletes and body builders, but by a growing number of recreational users, including adolescent boys and girls. The deleterious effects of AAS on peripheral organs and the incidence of altered behaviors in AAS abusers have been well documented in a number of excellent current reviews for clinical populations. However, a comparable synthesis of nonclinical studies has not been made. Our purpose in this review is to summarize the literature for animal models of the effects of supraphysiological doses of AAS (e.g. those that mimic human abuse regimes) on behaviors and on the neural circuitry for these behaviors. In particular, we have focused on studies in rodents that have examined how AAS alter aggression, sexual behaviors, anxiety, reward, learning, and locomotion and how AAS alter the expression and function of neurotransmitter systems and other signaling molecules that underlie these behaviors.

Stability of Spatial Working Memory across the Estrous Cycle of Long–Evans Rats

In the adult rat, hippocampal dendritic synaptic connectivity in region CA1 fluctuates across the estrous cycle. This study examined the potential functional impact of such fluctuations on spatial working memory in regularly cycling Long-Evans rats. Rats were trained in a delayed non-match-to-sample radial-arm maze task and performance was monitored across the estrous cycle. There were no significant alterations in the acquisition or performance of the working memory task across the estrous cycle, with 1- or 4-h delays imposed between training and testing sessions. However, rats performed the task significantly more slowly on proestrus than on any other estrous cycle day under both delay conditions. These results indicate that while working memory remains stable, sensorimotor or motivational aspects of the performance of this radial-arm maze task may vary across the estrous cycle.

Hormonal status and test condition, but not sexual experience, modulate partner preference in female rats

A series of experiments was conducted to determine the contributions of hormonal status, test condition, and sexual experience to the display of partner preference by female rats. Preference for a sexually active male rat over a sexually receptive female rat was assessed in independent groups of female rats tested in a condition limiting physical contact (No Contact) and a condition allowing for sexual interaction (Contact). Although hormonal status and test condition influenced the preference for a sexually active male, repeated testing and sexual experience had no effect. Experiment 1 demonstrated that independent of test condition, preference for the male is stronger in estrogen- and progesterone-primed rats than in rats receiving the vehicle. Moreover, independent of hormone condition, rats tested in the No Contact condition exhibit a stronger preference for the male than rats tested in the Contact condition, reflecting in part the active pacing of mating stimulation by sexually receptive rats tested in the Contact condition. Experiment 2 showed that the overall pattern of partner preference in proestrous and diestrous rats was similar to that observed in ovariectomized, estrogen- and progesterone-primed, and oil-treated rats, respectively. In Experiment 3, rats primed with estrogen alone did not exhibit a preference for the male even though fully receptive. Experiments 4 and 5 demonstrated that sexual experience does not affect the expression of preference for the male in estrogen- and progesterone-primed rats. The present findings demonstrate that the female rats preference for the male is stable across repeated tests and is not affected by sexual experience. Our results also confirm that gonadal hormones influence the expression of a preference for a sexually active male versus a sexually receptive female and demonstrate that the magnitude of preference is modulated by test conditions.

Anabolic-androgenic steroids and aggression in castrated male rats

The resident-intruder paradigm of aggression was utilized to evaluate the aggression-inducing properties of two anabolic-androgenic steroid (AAS) compounds, methyltestosterone and stanozolol, in castrated male rats. Three weekly tests were conducted. On test week three, castrated males treated with methyltestosterone displayed levels of aggression equivalent to the levels displayed by castrated males treated with testosterone propionate on most of the behavioral indices assessed. In contrast, treatment with stanozolol at the dose used in this study was completely ineffective in eliciting aggressive behavior. AAS effects on aggression were mirrored by their ability to stimulate seminal vesicle growth. There were no effects of AAS treatments on the levels of locomotor activity. These findings highlight the heterogeneity of AAS effects on the nervous system and behavior and indicate that the psychological effects reported by human AAS abusers may depend upon the distinct chemical structures of the abused steroids.

Paced mating behavior in the female rat following lesions of three regions responsive to vaginocervical stimulation.

The present study examines the effects of ibotenic acid lesions of the medial amygdala, the bed nucleus of the stria terminalis and the medial preoptic area on the display of paced mating behavior in female rats. Lesions of either the medial amygdala or the bed nucleus of the stria terminalis have no effect on the display of paced mating behaviors in ovariectomized, hormone-primed rats. In contrast, lesions of the medial preoptic area significantly lengthen contact-return latencies following intromissions and ejaculations and increase withdrawal from the male following intromissions. The present study demonstrates that the medial amygdala and the bed nucleus of the stria terminalis are not involved in the behavioral responses accompanying paced mating behavior, whereas the medial preoptic area is a critical component of the neural circuit mediating paced mating behavior as well as other appetitive aspects of mating.

Anabolic–Androgenic Steroid Effects on the Sexual Behavior of Intact Male Rats ☆

Six separate experiments were conducted which examined the effects of long-term administration of anabolic-androgenic steroid (AAS) compounds on the sexual behavior of gonadally intact male rats. The six AAS compounds analyzed in this study were 17alpha-methyltestosterone, methandrostenolone, nandrolone decanoate, stanozolol, oxymetholone, and testosterone cypionate. In each experiment, subjects received daily injections of a high, medium, or low dose of the AAS compound, or the oil vehicle, for 12 weeks. Sexual behavior was quantified weekly. Twelve weeks of administration of the high dose of three AAS compounds, 17alpha-methyltestosterone, stanozolol, and oxymetholone, eliminated male sexual behavior. These treatments also suppressed serum testosterone levels. The remaining compounds had minimal effects on sexual behavior at any dose. Thus, in intact male rats the six AAS compounds examined in these studies evoked a range of behavioral and endocrine responses that varied as a function of the specific compound and dose administered.

Paced mating behavior in the naturally cycling and the hormone-treated female rat.

During a sexual encounter with a male rat, a female rat will display both receptive (lordosis) and proceptive (hopping, darting, and ear-wiggling) behaviors. Additionally, if mating occurs in an environment where the female rat may approach and withdraw from the male rat, she will control the timing of the receipt of mounts, intromissions, and ejaculations. This temporal patterning by the female rat is known as paced mating behavior. The present experiment compared paced mating behavior in rats during an intact, proestrous phase and an ovariectomized phase, during which they were treated with estradiol benzoate (10 microg per rat) and progesterone (0.5 mg per rat). Though no differences in sexual receptivity were observed across the two phases, patterns of paced mating behavior were found to differ. Specifically, female rats exhibited significantly longer contact-return latencies when hormone treated than when intact.

Paced mating behavior in female rats in response to different hormone priming regimens

A female rat will display a repertoire of behaviors during a sexual encounter with a male rat including sexually receptive (the lordosis response) and proceptive (hopping, darting) behaviors. In addition, when given the opportunity, a sexually receptive female rat will approach and withdraw from the male rat, controlling the timing of the receipt of mounts, intromissions, and ejaculations, a behavior known as paced mating behavior. The present experiments tested the hypotheses (1) that progesterone regulates paced mating behavior, and (2) that multiple hormone regimens used previously to induce sexual receptivity have the same effect on paced mating behavior. Paced mating behavior was assessed in sexually receptive ovariectomized female rats after treatment with: (1) estradiol benzoate (EB; 30.0 mg/kg) followed by a range of doses of progesterone (P; 1.0-8.0 mg/kg), (2) two pulses of unesterified estradiol (E2; 2.0 microg/rat) followed by 1.0 mg/rat of P, and (3) EB alone (5.0 microg/rat) for 6 days. No differences in sexual receptivity or in paced mating behavior were observed across doses of P (1.0-8.0 mg/kg). In contrast, the number of hops and darts per min increased with the dose of P administered. E2 + P administration resulted in slightly, but significantly, lower levels of sexual receptivity along with significantly longer contact-return latencies following an intromission in relation to the other treatment conditions. In addition, female rats exhibited fewer hops and darts per min in response to E2 + P than in response to EB + 8.0 mg/kg of P. The administration of EB alone for 6 days induced levels of receptivity and paced mating behavior indistinguishable from EB + P, while eliciting significantly fewer hops and darts per min than the EB + 8.0 mg/kg P treatment condition. Hormone priming regimen had no effect on the percentage of exits displayed during the paced mating tests in any experimental phase. Dose of P had no effect on paced mating behavior in sexually receptive rats. In addition, P does not appear to be necessary for the display of paced mating behavior following long-term treatment with EB. In contrast, the pulsatile administration of E2 + P induced a different pattern of paced mating behavior in sexually receptive rats.

Female rats exhibit a conditioned place preference for nonpaced mating

Paced, but not nonpaced, mating behavior is reported to induce a conditioned place preference (CPP) in female rats. Contrary to these previous findings, Experiment 1 showed that female rats that received 15 intromissions from a single male rat during each of five conditioning sessions exhibited a CPP for the compartment associated with mating when the intromissions were delivered via a paced or nonpaced paradigm. Experiment 2 demonstrated that nonpaced mating induced a CPP when a single male delivered the 15 intromissions but not when the male was replaced following ejaculation and a new male allowed to complete the requisite number of intromissions. These findings invite reevaluation of the reinforcing aspects of mating behavior in female rats.

Anabolic androgenic steroids and forebrain GABAergic transmission.

Anabolic androgenic steroids are synthetic derivatives of testosterone designed for therapeutic purposes, but now taken predominantly as drugs of abuse. The most common behavioral effects associated with anabolic androgenic steroid use are changes in anxiety, aggression and reproductive behaviors, including the onset of puberty and sexual receptivity. GABAergic circuits in the forebrain underlie these behaviors and are regulated by gonadal steroids. Work from our laboratories has shown that the expression and function of GABA(A) receptors in the rat and mouse forebrain varies between the sexes and across the estrous cycle. We have also shown that there are significant changes in GABA(A) receptor expression that occur with the progression through puberty to adulthood. Because GABAergic systems are both steroid-sensitive and critical for the expression of behaviors altered with anabolic androgenic steroid use, forebrain GABA(A) receptors are an attractive candidate to assess how molecular actions of anabolic androgenic steroids may be translated to known behavioral outcomes. Our studies demonstrate that anabolic androgenic steroids elicit both acute modulation of GABA(A) receptor-mediated currents, as well as chronic regulation of GABA(A) receptor expression and forebrain GABAergic transmission. Because anabolic androgenic steroid use has now become prevalent not only among adolescent boys, but in an increasing number of adolescent girls, we have also been particularly interested in determining age- and sex-specific effects of anabolic androgenic steroids. Our data show that the effects of chronic anabolic androgenic steroid exposure can be greater for adolescent than adult animals and are more marked in females than in males. These data have particularly important implications with respect to studies we have done demonstrating that chronic anabolic androgenic steroid exposure alters the onset of puberty, estrous cyclicity and sexual receptivity.