Interactive effects of fluid deprivation and testosterone on the expression of a sexually dimorphic conditioned taste aversion.

Conducted 3 experiments with 96 Wistar and 72 Sprague-Dawley rats to investigate the effects of fluid deprivation on the sexually dimorphic rate of extinction of a conditioned taste aversion. Under ad lib water conditions, males extinguished a conditioned taste aversion more slowly than females. However, when rats were fluid deprived, there was no difference in the extinction rates of females and males even when the more sensitive 2-bottle test was used. This absence of the sexual dimorphism was due to a differential effect of deprivation on females and males. Fluid deprivation increased the rate of extinction of the male but had no effect on the rate of the female. It is proposed that the more rapid extinction rate of the deprived male could be accounted for by a deprivation-induced change in a testosterone-dependent mechanism. This proposal was supported by demonstrating that injections of testosterone propionate blocked the effects of fluid deprivation on rate of extinction in the male rat. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Uterine position and conditioned taste aversion.

Three experiments investigated the influence of uterine position on the performance of female offspring of female Sprague-Dawley and male Long-Evans rats in a conditioned taste aversion paradigm. 49 females that had males caudal to them in the same uterine horn (MF), 48 females with no caudal males (FF), and 24 males that had occupied a variety of different positions in the uterine horn were examined. Exps I and II confirmed a differential behavioral response by males and females during acquisition and extinction of the conditioned taste aversion. However, no differences were found between MF and FF Ss. In Exp III, in which testosterone was administered to females throughout testing, MF females showed an increased sensitivity to testosterone and a more prolonged rate of extinction than FF females. Exposure to testosterone during prenatal development heightened postnatal responsiveness to testosterone in female Ss. Results are discussed in terms of the organizational and activational effects of testosterone on behavior in a conditioned taste aversion situation. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual differentiation of play behavior in the ferret.

Three experiments examined the endocrine mechanisms responsible for sex differences in prepubertal play behavior of ferrets. In Exp I, 6 gonadally intact adolescent males exhibited higher levels of "stand-over" behavior than 6 females did in tests between 63 and 123 days of age with gonadally intact female partners of the same age. In Exp II, with 69 Ss, those Ss exposed to androgen or to ovarian steroids over Days 5–20 of postnatal life subsequently exhibited significantly higher levels of stand-over behavior in tests with females than did control females gonadectomized on Day 5 and not given steroids. None of the Ss in Exp II exhibited levels of stand-over behavior comparable to those of the gonadally intact males in Exp I. In Exp III, with 36 Ss, males gonadectomized and implanted subcutaneously with testosterone capsules on Day 70 and tested with females at 84–96 days of age exhibited levels of stand-over behavior comparable to those observed in Exp I in gonadally intact males of the same age (Weeks 12–24). Males gonadectomized on Day 70 and given no hormone at testing exhibited significantly lower levels of this behavior. Significantly lower levels were also exhibited by males gonadectomized on Day 35 and females gonadectomized on Day 70, regardless of whether they were tested with testosterone present after Day 70. Sex differences in the expression of prepubertal play behavior of ferrets apparently result from differential exposure of males and females to androgen over an extended postnatal period. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in EEG in adult gonadectomized rats before and after hormonal treatment

EEG activity was recorded from the left and right parietal cortex in adult male and female Wistar rats that were gonadectomized (GNX) after puberty during 2 days without and 3 days with hormonal treatment (either testosterone propionate, 5 alpha-DHT or vehicle in males and progesterone, estradiol benzoate or vehicle in females). In contrast to EEG characteristics reported for intact rats, GNX abolished right over left parietal activation in both sexes and, sex differences in EEG interhemispheric correlation and in theta and delta relative power in the right parietal; additionally GNX males showed higher absolute power than females. Hormonal treatment reestablished interparietal asymmetry in both sexes and a lack of sex differences in absolute power, however, it was not enough to reestablish sex differences in delta and theta proportion in the right parietal nor in interhemispheric correlation. Differential effects were obtained with testosterone propionate and 5 alpha-DHT in males suggesting that activational effects of testosterone on EEG are probably exerted through testosterone or its aromatized metabolites. The results of our study indicate that the activational effects of gonadal steroids after puberty are necessary for maintaining sex differences in the EEG of the adult rat.     

Effects of gonadal steroid hormones on hypothalamic vasopressin mRNA level in male and female rats

Experiments were carried out in 10-11-week old gonadectomized male and female Sprague-Dawley rats. Dot-blot analysis and 3'-end digoxigenin-labeled 26 meroligonucleotide probe was used in detecting the mRNA level hypothalamic vasopressin (AVP). The basal hypothalamic AVP-mRNA level in the sham-operated intact males was 45% higher than that in the sham-operated intact females (P < 0.05). Plasma osmolality was also higher in the sham-operated intact males than in the sham-operated intact females (P < 0.05). The hypothalamic AVP-mRNA level in ovariectomized rats was 30% higher than that in sham-operated intact females (P < 0.05). Although the hypothalamic AVP mRNA level tended to be lower in castrated males than in sham-operated intact males, the difference was not statistically significant. The difference in plasma osmolality between gonadectomized males and females was statistically insignificant. In castrated males, hypothalamic AVP-mRNA level was decreased following sc injection of estradiol (P < 0.05), but testosterone, progesterone or a combination of estradiol and progesterone were without effect. In ovariectomized rats, sc injection of estradiol or a combination of estradiol and progesterone resulted in a decrease in hypothalamic AVP-mRNA level (P < 0.01), but progesterone or testosterone had no effect. The difference in plasma osmolality between gonadal steriod hormones-treated rats and vehicle-treated rats was not statistically significant. These findings indicate that gonadal steriod hormones can affect hypothalamic AVP-mRNA level in rats, through some central mechanism.     

Simultaneous second-order conditioning produces S-S learning in conditioned suppression.

Explored simultaneous 2nd-order conditioning of one stimulus (S2) by another (S1) in a conditioned suppression preparation. In Exps I (40 female Holtzman rats) and II (32 male Holtzman rats) 2nd-order conditioning of S2 was attenuated by subsequent extinction of S1. Sequential presentation of the same stimuli produced similar levels of conditioning of S2 that were not affected by extinction of S1, results that replicate previous findings (R. A. Rescorla, 1980). Exps III (32 females) and IV (32 males) found that sensitivity of a simultaneous S2 to changes in S1 depended on S1 receiving few separate reinforced or nonreinforced presentations prior to 2nd-order conditioning. Circumstances are suggested under which the typical stimulus–response learning observed in 2nd-order conditioned suppression can be converted into stimulus–stimulus learning. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Testosterone potentiates scopolamine-induced disruptions of nonspatial learning in gonadectomized male rats.

Whereas research into the effects of the gonadal hormones on learning and memory has primarily focused on estrogen in females, recent evidence suggests that testosterone can also modulate learning in males through an interaction with the cholinergic system. In the present study, the interactive effects of testosterone and scopolamine (0.1- 0.32 mg/kg), a muscarinic receptor antagonist, on complex behavioral processes were investigated in male rats trained to respond under a multiple schedule of repeated acquisition and performance. In the acquisition component, subjects acquired a different 3-response sequence each session, whereas in the performance component, they responded on the same 3-response sequence each session. Although gonadectomy did not disrupt responding in either component, gonadectomized rats were less sensitive to the disruptive effects of scopolamine on both response rate and accuracy. In contrast, after receiving exogenous testosterone replacement, these gonadectomized males were more sensitive to the behavioral disruptions produced by scopolamine (i.e., the effects of scopolamine were similar to those obtained in gonadally intact males). These results suggest that testosterone replacement can enhance scopolamine-induced behavioral effects in gonadectomized male rats responding under a multiple schedule of repeated acquisition and performance, a finding that is in contrast to those previously found for certain spatial tasks. Furthermore, the present findings suggest that testosterone may decrease the activity of the cholinergic system during nonspatial tasks and thereby work in concert with the antagonism produced by scopolamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Instrumental performance following a shift in primary motivation depends on incentive learning.

In 5 experiments the role of incentive learning in instrumental performance following a shift in primary motivation was examined. In Exps 1 and 2, rats trained to perform an instrumental action reinforced by either pellets or maltodextrin when in a low-deprivation state were shifted to a high-deprivation state and tested in extinction. This shift in deprivation increased performance only if the animals had been exposed to the reinforcer in the high deprivation state prior to instrumental training. Exps 3, 4, and 5 examined the reverse, shift training in a high-deprivation state and testing in a low-deprivation state, and found, similarly, that performance was only sensitive to this shift if animals were previously exposed to the reinforcer while in the low-deprivation state. These experiments support the conclusion that instrumental performance following revaluation of the reinforcer depends on a process of incentive learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence that physiologic levels of circulating estrogens and neonatal sex-imprinting modify postpubertal hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity

Intact, but sham-operated female rats had 2- to 3-fold higher levels of hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity than their male counterparts (15--21.5 vs. 6.7--8.7 nmol mevalonate/mg protein per h). The activity of the hepatic enzyme declined to about the same relative degree (40--60%) in male and female rats that were gonadectomized after puberty (53 days of age) and killed 5 weeks later. Implantation of silastic capsules containing 17 beta-estradiol increased the level of hepatic 3-hydroxy-3-methylglutaryl CoA reductase to levels found in sham-operated controls. In rats that were gonadectomized in infancy (12 h old) and killed 7--8 weeks later, the level of enzyme activity was not altered in females, but it was increased from 60--240% in males. Consequently, following neonatal gonadectomy, male-female differences in enzyme activity were no longer apparent. Implantation of silastic capsules containing estradiol in neonatally gonadectomized rats resulted in a doubling of enzyme activity in both males and females. Ovariectomy reduced plasma estrogen levels, but implantation of estradiol in gonadectomized males and females increased the hormone level to that found in sham-operated females. Thus, the results strongly suggest a role for physiologic levels of estrogen as a positive effector of 3-hydroxy-3-methylglutaryl CoA reductase activity. Neonatal sex imprinting also appears to modulate the enzyme activity since sex-mediated differences are effaced by gonadectomy in infancy, but not by gonadectomy following puberty.     

Effects of testosterone upon MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system of C57/B1 mice

We have recently reported that treatment of gonadectomized female and male C57/B1 mice with the gonadal steroid hormone, estrogen, reduced nigrostriatal dopaminergic neurotoxicity resulting from the Parkinson's-like inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the present report we examined whether the predominantly male gonadal steroid hormone, testosterone, would similarly modulate MPTP-induced neurotoxicity. Male C57/B1 mice were assigned to one of the following five treatment conditions: (1) Intact, (2) Orchidectomized, (3) Intact + MPTP, (4) Orchidectomized + Testosterone + MPTP and (5) Orchidectomized + MPTP. Corpus striatal and olfactory tubercle dopamine. DOPAC and norepinephrine concentrations were determined from the animals within each of the five treatment conditions. Orchidectomy alone failed to alter striatal dopamine and DOPAC concentrations, with levels obtained being similar to that of Intact animals. MPTP treatment significantly reduced striatal reduced striatal dopamine and DOPAC concentrations, regardless of hormonal condition of the animal. Similar results were obtained for olfactory tubercle determinations, with the exception that DOPAC levels from Orchidectomized mice were significantly greater than Intact males. No significant differences were obtained for norepinephrine within either brain area sampled. These results show that unlike estrogen, testosterone is devoid of any capacity to modulate nigrostriatal dopaminergic neurotoxicity resulting from MPTP. These findings may be related to the gender differences which exist in the prevalence of Parkinson's disease.     

Regulation of androgen receptor mRNA expression in hamster facial motoneurons: differential effects of non-aromatizable and aromatizable androgens

We have previously shown inherent sex differences in the levels of androgen receptor mRNA (AR mRNA) in hamster facial motor neurons (FMN). FMN of intact females contained approximately 50% less AR mRNA than their male counterparts. Gonadectomy in males down-regulated AR mRNA levels in FMN by approximately 50%, whereas no effects of gonadectomy were observed in females. Sex differences in the regulation of AR mRNA levels by exogenous testosterone propionate (TP) were also observed. In those studies, AR mRNA levels were up-regulated after 1 day of treatment with exogenous TP in FMN of gonadectomized (GDX) males and after 7 days in FMN of intact females, with no effects in GDX females. Since TP is aromatizable to estrogen, and given recent findings of transient expression of estrogen receptors (ER) in rodent FMN, the effects of dihydrotestosterone (DHT), a non-aromatizable form of the steroid, on AR mRNA expression in hamster FMN were examined in the present study. If testosterone (TES) were the active hormone regulating AR mRNA levels in FMN, DHT treatment should render a similar regulatory pattern as TP, but if metabolism of TES to estradiol plays a role in AR mRNA regulation, effects of the two treatments should differ. In situ hybridization and computerized image analysis were used to quantify the regulation of AR mRNA by DHT in individual FMN of hamsters of both sexes. Exogenous DHT was administered to intact and gonadectomized (GDX) male and female hamsters by implantation of one 10-mm Silastic capsule for 1, 2 or 7 days. AR mRNA levels were significantly up-regulated in intact females at all time points of DHT exposure, with no effects in GDX groups. These results differ from previous work using TP, in which a modest up-regulation in AR mRNA levels was observed in FMN of intact females only after 7 days. As with TP, DHT exposure gradually down-regulated AR mRNA levels in FMN of intact males. Thus, DHT only regulated AR mRNA levels in intact animals, with endogenous sources of estrogen available, but not in GDX animals, with endogenous estrogens reduced by gonadectomy. Taken together, these results substantiate our previous findings of sex differences in AR mRNA levels/regulation and suggest a synergism between estrogen and androgen in the regulation of AR mRNA levels in peripheral motor neurons.     

Role of cholecystokinin in the motivational control of instrumental action in rats.

In 4 experiments, the role of cholecystokinin (CCK) in the motivational control of instrumental performance in rats was assessed. Following instrumental training with food rewards, injections of CCK (either 2 μg/kg or 4 μg/kg) had no effect on instrumental performance in extinction, even when the opportunity was given to learn about the incentive value of the food outcome under CCK. These results contrasted markedly with the effects of shifts in food deprivation. Rewarded instrumental performance was, however, reduced by both doses of CCK, suggesting that CCK may mediate deprivation-related shifts in incentive value. Tests of this hypothesis found that the alimentary CCK antagonist devazepide (MK329) attenuated the devaluation of a food outcome produced by exposure to the outcome in a nondeprived state. These data are interpreted as suggesting that CCK may act as a satiety-specific incentive signal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to extinction in rats as a function of deprivation level and schedule of reward in acquisition.

Conducted 3 straight-alley investigations with 84 male and 44 female Holtzman albino rats. 2 levels of deprivation were combined factorially with 2 schedules of reward (50 or 100%) in acquisition. Deprivation level in extinction was equated. When extinction deprivation level was low either there was no difference in extinction due to acquisition deprivation level or groups trained under high deprivation were more resistant to extinction than groups trained under low deprivation, as they were when deprivation level was high in extinction. It is suggested that at least 2 factors influence resistance to extinction as a function of acquisition deprivation level deprivation-related stimuli and some factor which produces greater resistance to extinction following high deprivation in acquisition. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some experimental tests of the functional significance of scent-marking by gerbils (Meriones unguiculatus).

Investigated the functional significance of male gerbil scent-marks in 4 experiments with 60 male and female Mongolian gerbils. In Exps I and II, males in a novel test environment marked more, groomed more, and urinated less in the presence of odors of a strange male than in their absence. Female odors elicited male marking more than did male odors. In Exps III and IV, females were selectively less aggressive toward familiar-smelling males in comparison with unfamiliar-smelling males. These results, in conjunction with field observations of related species, call into question the hypothesis that gerbil scent-marks function territorially and instead suggest that the primary targets are adult females. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regulation of preoptic area gonadotrophin-releasing hormone (GnRH) mRNA expression by gonadal steroids in the long-term gonadectomized male rat

Testosterone exerts important feedback actions on the hypothalamus and pituitary of the male rat to control reproductive hormone secretion. Marked fluctuations occur in plasma-luteinizing hormone (LH) concentrations, hypothalamic gonadotrophin-releasing hormone (GnRH) content and GnRH mRNA expression following castration and it appears as though a stable post-castration equilibrium is not attained until 3-4 weeks after gonadectomy. In the present study, we have investigated the effects of long-term (7 week) gonadectomy on GnRH mRNA expression in the male rat and determined whether estrogen or androgen receptor-mediated mechanisms are involved in regulating its expression. Accordingly, in situ hybridization was undertaken using a 35S-labelled antisense oligonucleotide probe complementary to bases 102-149 of the rat GnRH cDNA to quantify cellular GnRH mRNA expression in the medial septum (MS), diagonal band of Broca (DBB) and rostral preoptic area (rPOA) of intact males, rats gonadectomized for 7 weeks and gonadectomized animals implanted with silastic capsules containing testosterone (T), estrogen (E) or dihydrotestosterone (DHT). We found no difference between any of the treatment groups in the number of cells expressing GnRH mRNA in the MS/DBB or rPOA. Similarly, the GnRH mRNA content of cells in the MS/DBB was not different between the treatment groups. In contrast, cellular GnRH mRNA expression in the rPOA was elevated 7 weeks following castration (intact: 0.95 +/- 0.07 silver grains/microm2/cell; gonadectomized: 1.26 +/- 0.03; mean +/- S.E.M., P < 0.05) and this was restored to intact levels by either T (1.02 +/- 0.07) or E (1.02 +/- 0.08) treatment. DHT replacement had no effect on cellular levels of GnRH mRNA in gonadectomized rats (1.26 +/- 0.03). Frequency analysis of relative GnRH mRNA expression/cell showed that the rostral preoptic GnRH population responded to the steroid treatment in an homogeneous manner. These results show that GnRH mRNA expression is elevated specifically within the rPOA of the long-term gonadectomized male rat when LH secretion has stabilized at a constant high level. Further, we show that the gonadal steroid regulation of cellular GnRH mRNA content at such time occurs only through an estrogen receptor-mediated pathway.     

Hormonal dynamics during mate choice in the northern pintail: a test of the 'challenge' hypothesis

In previous mate choice experiments, we found no relationship between dominance rank and pairing success in male northern pintails, Anas acutaOnce chosen by a female, however, males became aggressive, initiated fights with higher-ranked males and quickly established dominance. In the present study, we tested a variation of the 'challenge' hypothesis, that the behavioural stimuli associated with acquiring and defending a mate induce an increase in testosterone level, which in turn facilitates aggressive behaviours required for males to establish dominance. We measured plasma hormone levels (testosterone, dihydrotestosterone, luteinizing hormone and corticosterone) before and after mate choice in two experiments in which males competed for a single female (experiments 1 and 2) and in a control experiment in which no female was introduced (experiment 3). We used groups of either three adult males (experiment 1) or one adult and two yearling males (experiments 2 and 3). Contrary to expectation, in experiment 1, plasma levels of corticosterone increased significantly and testosterone levels decreased in chosen males following mate choice. The magnitude of change in corticosterone was positively correlated with the rate of aggression by males. Chosen adult males in experiment 2 showed similar patterns of hormone change (corticosterone increase and testosterone decrease), although not all changes were significant. Hormone levels of unchosen yearlings in experiment 2 and control adults and yearlings in experiment 3 showed no changes. The results are consistent with the hypothesis that behavioural stimuli associated with successful pair formation induce a transitory increase in circulating levels of corticosterone, which in turn mediates the behavioural response of increased aggression leading to the establishment of dominance following mate choice. A short-term increase in corticosterone may be adaptive in this situation because it would mobilize energy stores needed by the male to defend the new pair bond and establish dominance.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour     

Sex-dependent relations of grasp-reflex strengths from right and left hands to serum gonadotropin (FSH and LH) levels in human neonates with regard to cerebral lateralization

The relation of grasp-reflex strength to serum FSH and LH levels were studied in human neonates. The grasp-reflex strengths from the right and left hands were found to be negatively linearly correlated with serum FSH level in males without familial sinistrality (-FS), but there was no significant correlations between these parameters in females. Serum LH levels were not correlated with grasp reflex in -FS neonates. The grasp-reflex strength from the right hand showed a significant negative linear correlation with LH only in +FS males. The right minus left (R-L) grasp-reflex strength decreased linearly with serum LH levels only in +FS males. These results did not support the testosterone hypothesis of cerebral lateralization. It was suggested that FSH and LH may indirectly influence the brain development according to sex and genetically pre-determined cerebral organization.     

Serum insulin-like growth factor-I, insulin-like growth factor binding protein-3, sex steroids, osteocalcin and bone mineral density in male and female rats

Although it has been reported that the rate of weight gain and linear growth increases markedly during puberty in rats, little is known about the relationship between endocrine changes and bone mineral density (BMD) changes upon sexual maturation in these animals. The aim of this study was to examine the levels of serum insulin-like growth factor-I (IGF-I), IGF binding protein (IGFBP)-3, sex steroids and osteocalcin, and the changes in BMD in normal aging male and female rats. Male rats exhibited increases in serum IGF-I and IGFBP-3 concentrations before increases in serum testosterone levels. IGF-I and testosterone peaked at 9 weeks of age, and thereafter remained in a steady state, whereas IGFBP-3 reached a peak at 7 weeks of age, and then gradually declined. A strong correlation between serum IGF-I and IGFBP-3 levels was found in subjects 3-9 weeks old. A highly significant correlation between serum IGF-I and testosterone levels was also found. In females, serum 17 beta-estradiol, IGF-I and IGFBP-3 levels increased gradually from 3 to 5 weeks old, peaked at 9 weeks, and then decreased slowly thereafter. The correlation coefficient between serum IGF-I and IGFBP-3 was highly significant. The correlation coefficient between serum IGF-I and 17 beta-estradiol levels was weak, although it was strongest when the subjects were 3-9 weeks old. Serum osteocalcin is a marker of bone formation; its level remained relatively high from 3 to 9 and from 3 to 7 weeks of age in males and females, respectively, although osteocalcin in both sexes declined gradually with age. As for bone mass, sharp increases in BMD in the tibia, femur and lumbar vertebrae appeared earlier in female than in male rats, and the BMD in females tended to be higher than in males between 5 and 9 weeks old. After 9 weeks of age, BMD in males was higher than that in females, as BMD in males continued to increase whereas females tended to remain in a steady state after this stage. The correlation coefficients between tibial BMD and serum IGF-I or IGFBP-3 levels were highly significant when the subjects were from 3 to 9 weeks old. Taken together, these results suggest that BMD development occurs earlier in female than in male rats. This sex-related difference in changes in the BMD pattern may result from the earlier onset of puberty in females, and from sex-specific differences in concentrations of IGF-I, IGFBP-3 and sex steroids during maturation.     

Estradiol replacement in gonadectomized male rats alters scopolamine-induced disruptions of nonspatial learning.

Recent evidence indicates that testosterone can modulate learning in males through an interaction with the cholinergic system. However, the mechanism for this interaction between testosterone and the cholinergic system on learning remains uncharacterized and may involve several of testosterone's active metabolites. In the present study, two of the active metabolites of testosterone, 5α-dihydrotestosterone and estradiol, were administered in combination with the muscarinic receptor antagonist scopolamine (0.1-1 mg/kg, i.p.) to adult gonadectomized male rats that were trained to respond under a multiple schedule of repeated acquisition and performance of response sequences. In the acquisition component, subjects acquired a different three-response sequence each session, whereas in the performance component they responded on the same three-response sequence each session. When scopolamine was administered, it produced greater rate-decreasing and error-increasing effects in gonadally intact subjects than in gonadectomized subjects, even though gonadectomy had little or no effect on these measures under control conditions. In gonadectomized rats receiving 5α-dihydrotestosterone replacement, the disruptions produced by scopolamine were also smaller than those produced in gonadally intact subjects. In contrast, gonadectomized rats receiving estradiol replacement were as sensitive, or more sensitive, to scopolamine-induced disruptions of response rate and accuracy than those under the gonadally intact condition. These results suggest that testosterone's interactive effects with the cholinergic system on learning in gonadectomized male rats may not be mediated directly via androgen receptors, but rather by estrogen receptors following the aromatization of testosterone to estradiol. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual dimorphism in ultrasonic vocalizations of mice (Mus musculus): Gonadal hormone regulation.

Male mice, during courtship and sexual behavior, vocalize substantially more 70-kHz ultrasounds than do females. Four experiments conducted with 109 male and female DBA/2J and ADK2F? mice demonstrated that testosterone propionate (TP) substantially increased ultrasonic emissions and mounting by ovariectomized females and that long-term gonadectomized males and females increased their amount of ultrasound production in response to TP to approximately the same levels. From these results it is suggested that the sexual dimorphism normally seen in ultrasonic vocalizations can be accounted for by the activational effects of androgen in adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)