Rats selectively-bred for behavior related to affective disorders: proclivity for intake of alcohol and drugs of abuse, and measures of brain monoamines

Several lines of rats potentially useful for studying affective disorders have been developed in our laboratory though selective breeding for behavioral characteristics. The propensity of these lines to consume alcohol and other drugs of abuse (amphetamine and cocaine) was examined. Also, measurement of the concentration of brain monoamines - norepinephrine, dopamine, and serotonin - as well as estimation of their metabolism by measurement of the major extracellular metabolites of these monoamines was carried out to examine possible relationships of brain chemistry to the behavioral characteristics shown by these lines, as well as to their propensity for drug usage. The lines of rats are: Swim Low-active (SwLo) and Swim High-active (SwHi), which show either very low (SwLo) or very high (SwHi) amounts of motor activity in a swim test; Swim-test Susceptible (Susceptible or SUS) and Swim-test Resistant (Resistant or RES), which are highly susceptible (SUS) or highly resistant (RES) to having their swim-test activity depressed by being exposed to a stressful condition prior to the swim test; and Hyperactive (HYPER), which show spontaneous nocturnal hyperactivity compared to non-selectively bred (i.e., normal) rats as well as both extreme hyperactivity and behavioral depression after being exposed to a stressful condition. Regarding alcohol and drug usage, SUS rats readily consume alcohol while all other lines including non-selected, normal rats do not, and SwLo rats show a strong tendency to consume amphetamine and cocaine. Marked differences in brain monoamines were found between the various lines and normal rats, with salient differences seen in norepinephrine, particularly in the hippocampus, and in dopamine in forebrain regions (striatum and nucleus accumbens).

Depletion of brain norepinephrine does not reduce spontaneous ambulatory activity of rats in the home cage

6-Hydroxydopamine (6-OHDA) lesions of brain noradrenergic neurons and terminals were made in rats to assess the importance of forebrain norepinephrine (NE) for mediating circadian patterns of spontaneous ambulatory activity that rats show in the home cage. 6-OHDA was injected intracranially into the fibers of the ascending noradrenergic dorsal and ventral bundle pathways or infused into the lateral ventricle or both. Rats living in a 12/12 h light/dark cycle exhibit a marked increase in ambulatory activity during the dark period in comparison to the light period and a 'W-shaped' pattern of activity during the 12 h of the dark phase. Results showed that near-total depletion of brain NE did not impair the capacity to generate normal patterns of spontaneous ambulatory activity that occur in the home cage. In the animals that sustained the most complete NE lesions, the amounts of activity generated at times of peak activity were exaggerated in comparison to the control animals, which is consistent with the possibility that NE in the brain exerts a moderating influence on behavior.

Rats selectively bred for high and low swim-test activity show differential responses to dopaminergic drugs

RATIONALE

Selective breeding of Sprague-Dawley rats has been used to generate a line of animals with very low swim-test activity (SwLo) in an attempt to model certain characteristics of depression. For comparison with the SwLo animals, a line bred for high swim-test activity (SwHi) and a non-selectively bred line (SwNS) have been generated. Previous studies using these lines suggested an inverse relationship between dopamine (DA) function in the brain and inactivity in the swim test.

OBJECTIVES

The current experiments investigated the possibility that SwLo and SwHi rats show differences in central DA processes, as suggested by responsiveness to DA agonists.

RESULTS

The increase in ambulation produced by d-amphetamine (0.25-1.0 mg/kg) was largest in SwHi rats and smallest in SwLo rats, with SwNS rats showing an intermediate response. Amphetamine levels in plasma and brain tissue were similar in SwHi and SwLo rats, indicating that pharmacokinetic differences were not responsible for the behavioral differences. Repeated amphetamine administration produced enhancement in the ambulation-increasing effects of this drug (i.e., sensitization), with significant enhancement seen in all three lines. Apomorphine in doses that stimulate postsynaptic receptors (0.25-4.0 mg/kg) produced mainly increased sniffing behaviors in SwHi and SwNS rats and oral behaviors in SwLo rats, suggesting that the lines differ in proportions of D1, D2, and D3 postsynaptic receptors.

CONCLUSIONS

The findings suggest that DA function differs in lines of rats selectively bred for differences in swim behavior, a feature that may make these lines useful for studying certain depressive symptoms that might be related to DA function.

Galanin: a significant role in depression?

This paper describes a hypothesis that attempts to account for how changes in noradrenergic systems in the brain can affect depression-related behaviors and symptoms. It is hypothesized that increased activity of the locus coeruleus (LC) neurons, the principal norepinephrine (NE)-containing cells in the brain, causes release of galanin (GAL) in the ventral tegmentum (VTA) from LC axon terminals in which GAL is colocalized with NE. It is proposed that GAL release in VTA inhibits the activity of dopaminergic cell bodies in this region whose axons project to forebrain, thereby resulting in two of the principal symptoms seen in depression, decreased motor activation and decreased appreciation of pleasurable stimuli (anhedonia). The genesis of this hypothesis, which derives from studies using an animal model of depression, is described as well as recent data consistent with the hypothesis. The formulation proposed suggests that GAL antagonists may be of therapeutic benefit in the treatment of depression.

Behavioral responses to Depo-Provera, Fadrozole, and estradiol in castrated, testosterone-treated cynomolgus monkeys (Macaca fascicularis): the involvement of progestin receptors

Sexual motivation and behavior decreased in male cynomolgus monkeys given either Depo-Provera (medroxyprogesterone acetate, MPA), which reduces androgen uptake by brain, or the nonsteroidal aromatase inhibitor, Fadrozole, which virtually eliminates the conversion of testosterone (T) to estradiol (E2) in brain. This suggested that both unchanged T and E2 are important for the control of male primate sexual behavior, but combined treatment with MPA and Fadrozole did not have the anticipated summatory effects in intact males: the behavioral decrements when MPA-treated males were given Fadrozole were about half those observed when Fadrozole was given alone. The present study tested the hypothesis that Fadrozole suppressed the behavioral effects of MPA by preventing the induction by E2 of progestin receptors in the brain to which MPA binds. Eight castrated, T-treated males were each tested with an estrogenized female i) during baseline, ii) during MPA treatment, iii) during treatment with MPA and Fadrozole together, and iv) with E2 treatment added to condition (iii) (256 1-h behavior tests). All dosages were those used in previous studies. Sexual motivation, as reflected in mounting attempts and mounting attempt latencies, was further diminished by E2 treatment in males receiving both MPA and Fadrozole, but ejaculatory activity was not changed. Immunocytochemistry demonstrated that the distributions of progestin and androgen receptors were little affected by MPA treatment, and that progestin receptor immunoreactivity was almost completely abolished in the brains of males receiving both MPA and Fadrozole but present in those receiving additional E2 treatment, findings that supported the hypothesis.

Effects of the nonsteroidal aromatase inhibitor, fadrozole, on the sexual behavior of male cynomolgus monkeys (Macaca fascicularis)

In many vertebrates, castration and hormone replacement and, more recently, the use of aromatase inhibitors, have shown that male sexual activity is mediated by the aromatization of testosterone (T) to estradiol (E2). In macaques, however, the systemic administration of E2, either alone or in combination with androgen, failed either to maintain or to restore the sexual activity of castrated males. The present study examines the effects of administering the nonsteroidal aromatase inhibitor, Fadrozole, either alone or combined with E2, to castrated, T-treated male cynomolgus monkeys at a dose of 0.25 mg/kg/day. This dose inhibited by over 98% the conversion of T to E2 and the subsequent accumulation of the latter in hypothalamic cell nuclei. Castrated males bearing sc Silastic impants of T were each tested with an ovariectomized, E2-treated female partner before, during, and after being given minipumps delivering either Fadrozole or water (240 1-hr tests). Within 2 weeks, Fadrozole significantly reduced ejaculatory activity and male sexual motivation in the absence of changes in plasma T levels, which remained in the upper range for intact males. Additional estradiol treatment produced small but significant increases in ejaculations by three of the six males only, and measures of male sexual motivation remained unchanged (120 tests). The present results, which stand in contrast to our previous findings in macaques, support the view that aromatization of T is important for ejaculatory activity and sexual motivation in a male primate. They also suggest that exogenous E2, which reaches the brain from the systemic circulation, does not fully duplicate the behavioral effects of E2 produced locally in the brain by the aromatization of T.

Effects of the nonsteroidal aromatase inhibitor, Fadrozole, on sexual behavior in male rats

The new nonsteroidal aromatase inhibitor, Fadrozole (CGS 16949A, CIBA-Geigy Corp.), was tested for its ability (i) to inhibit the conversion of testosterone (T) to estradiol (E2) in brain and (ii) to suppress male sexual activity. Sprague-Dawley rats were castrated and immediately given sc Silastic T-implants and osmotic minipumps delivering 2.5 mg/kg/day Fadrozole (N = 4), 0.25 mg/kg/day Fadrozole (N = 4), or water (N = 4 controls). T-implants were removed after 6 days and, 3 days later, 3H-T (1 microCi/g) was given as an iv bolus. No 3H-E2 was detected in hypothalamic or amygdaloid nuclear pellets from Fadrozole-treated males but this metabolite predominated in controls. However, nuclear concentrations of 3H-T and [3H]dihydrotestosterone were similar in all groups. In another group of males (N = 18), brain aromatase activity was reduced by more than 96% at the 0.25 mg/kg dose level. Additional castrated, T-implanted males received minipumps delivering 0.25 mg/kg/day Fadrozole (six males) or water (six behaviorally matched controls) and were tested weekly with receptive females. After 2 weeks, ejaculations were reduced by 77% compared with controls (P less than 0.01) and, after 4 weeks, intromissions were also significantly reduced (P less than 0.05) but less so (48%). Radioenzymatic estimates of plasma aromatase inhibitor levels remained elevated throughout Fadrozole treatment. These males were then given Silastic E2 implants: intromissions increased significantly in 1 week (P less than 0.01), but ejaculations remained below control values. Results supported the view that aromatization is important for sexual behavior in male rats and suggested that Fadrozole has utility for studying the mechanisms by which testosterone affects behavior.

The interaction of testosterone with the brain of the orchidectomized primate fetus

At certain times during gestation, the testes of the fetal macaque produce plasma levels of testosterone (T) that are similar to those of adults. It is thought that testosterone acts on the brain via estrogen and androgen receptors to organize the development of sexually dimorphic neural structures that underlie sex differences in behavior. To test the proposition that there are male-female differences in the occupation of steroid receptor binding sites during fetal development in the cynomolgus macaque, we have compared the uptake of [3H]T and its metabolites in: (1) 5 intact males (plasma T 571.2 +/- 215.5 ng/100 ml); (2) 5 intact females (33.8 +/- 25.2 ng/100 ml); (3) in 5 males orchidectomized in utero (14.6 +/- 5.7 ng/100 ml). About 1 week after fetal gonadectomy or sham-operation, all fetuses were given 500 microCi [3H]T s.c. and were then delivered 60 min later by Cesarean section. Brains were removed and dissected into blocks containing the hypothalamus and preoptic area, amygdala, hippocampus, and midbrain. Samples of cerebral and cerebellar cortex were also obtained. Purified nuclear pellets were prepared by centrifugation through 2 M sucrose and were extracted into ether and analyzed by high performance liquid chromatography. Hypothalamic nuclear concentrations of [3H]E2 in intact males (847 +/- 195 dpm per mg DNA) were significantly lower than those in sham-operated females (2147 +/- 542 dpm per mg DNA) (P less than 0.05), but those in orchidectomized males (2233 +/- 345 dpm per mg DNA) were similar to concentrations in females.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in the uptake of testosterone by the primate brain

During the neonatal period in male macaques, the testis produces adult-like levels of plasma testosterone (T), but the function of this in development is not understood. To investigate the interaction of T with the neonatal brain, 4 male and 5 female cynomolgus monkeys were gonadectomized 2-5 days after birth, and were injected subcutaneously 3 days later with 500 microCi [3H]-testosterone ([3H]-T). 60 min later, brains and other tissue samples were removed. Purified nuclear pellets were prepared by centrifugation through 2 M sucrose, extracted into ether and analyzed by high-performance liquid chromatography. The aromatized metabolite, [3H]-estradiol [( 3H]-E2), was found only in the hypothalamus (HYP) and amygdala (AMG). In HYP, [3H]-E2 represented 55 +/- 3% of the radioactivity in males and 53 +/- 3% in females. In AMG, [3H]-E2 represented 40 +/- 9% of the radioactivity in males and 47 +/- 3% in females. Concentrations of unchanged [3H]-T were higher than those of [3H]-dihydrotestosterone [( 3H]-DHT). Both androgens were present in nuclear pellets from all 8 brain regions studied, and concentrations were significantly higher in females than in males (p less than 0.005). [3H]-T was also the main form of radioactivity in nuclear pellets from pituitary gland, adrenal gland, uterus and liver, but very high levels of [3H]-DHT were found in seminal vesicles, prostate and penis. Comparisons were made with previous results from orchidectomized fetuses at 122 days gestation and from fully adult male castrates, and the largest developmental changes occurred in the AMG where concentrations of [3H]-E2 were 20-fold higher in adults than in fetuses, and most of this increase took place after the neonatal stage. Nuclear concentrations of [3H]-T also increased markedly during development in most brain regions except the cerebellar cortex where they declined.

Immunohistochemical labeling of androgen receptors in the brain of rat and monkey

Androgen receptor antibodies have recently been developed using fusion proteins containing fragments of human prostatic androgen receptor. We have used a polyclonal antibody raised in rabbits to label androgen receptors in brain sections from male and female rats and monkeys. Free-floating frozen sections were incubated in primary antibody, and processed by the peroxidase-avidin-biotin complex method using biotinylated anti-rabbit IgG. Nickel intensified diaminobenzidine was used as the chromagen, and neurons were labeled in the amygdala, hippocampus, bed nucleus of stria terminalis, septum, preoptic area, in several hypothalamic nuclei including the supraoptic and paraventricular nuclei, in several brain stem motor nuclei and in cerebral cortex. Staining was most intense in cell nuclei but also occurred in cytoplasm and in some neuronal processes. Labeling was more restricted in monkey than in rat brain. Omitting the primary antibody or pre-incubating the primary antibody with rat prostatic cytosol for control purposes demonstrated the specificity of staining.

Medroxyprogesterone acetate, aggression, and sexual behavior in male cynomolgus monkeys (Macaca fascicularis)

Medroxyprogesterone acetate (MPA) is used clinically to treat male sex offenders, but there are conflicting reports about its effects on aggression. To investigate these matters in a nonhuman primate, four intact male cynomolgus monkeys were studied in a testing paradigm that involved the presence of a caged, aggression-arousing stimulus male either immediately before or during a pair-test with an ovariectomized, untreated female partner. After two 4-week periods of pretreatment baseline, males received weekly injections of 40 mg MPA either alone (two 4-week treatment periods) or in combination with testosterone replacement with sc implants (one period) and additional daily injections of 2 mg testosterone propionate (two periods). MPA was then withdrawn while testosterone replacement continued (three periods). The testing paradigm was effective in maintaining aggression, especially male-male aggression, for many months. Male-male aggression increased with MPA treatment, and increased further with testosterone replacement, whereas male-female aggression tended to change in the opposite direction. As in earlier studies, MPA decreased both plasma testosterone and male sexual activity, but restoring plasma testosterone levels in treated males failed to restore their sexual activity. MPA therefore has behavioral effects that are not mediated primarily by its suppression of circulating androgens.

Medroxyprogesterone acetate and the nuclear uptake of testosterone and its metabolites by brain, pituitary gland and genital tract in male cynomolgus monkeys

The synthetic progestin, medroxyprogesterone acetate (MPA), is used to treat male sex offenders, and it is also suppresses sexual activity in male monkeys. To examine the possibility that MPA may act as an anti-androgen in the primate brain, 4 intact male cynomolgus monkeys were given MPA (40 mg i.m.) once a week for 16 weeks, while 4 control males received i.m. injections of vehicle. All males were then castrated and 3 days later were given 3 mCi [3H]testosterone ([3H]T) i.v.; 1 h after injection males were killed, and radioactivity in nuclear pellets obtained from the hypothalamus (HYP), preoptic area (POA), amygdala (AMG), septum, pituitary gland and genital tract was analyzed by HPLC. Concentrations of [3H]T and [3H]dihydrotestosterone in nuclear pellets were 65-96% lower in MPA-treated males than in controls (P less than 0.001), but the aromatized metabolite, [3H]estradiol, which was the major form of radioactivity present in nuclear pellets from HYP, POA and AMG, was unchanged. There were no differences in concentrations of [3H]T in supernatants from the tissues of MPA-treated and control males. Because the reduced nuclear uptake of androgen in brain occurred in males whose androgen-dependent behavior had been suppressed by MPA treatments, it is proposed that MPA may have anti-androgenic effects at the level of the cell nucleus in brain regions that control behavior.

Uptake of medroxyprogesterone acetate by progestin and androgen target neurons in the brain and pituitary gland of male cynomolgus monkeys

Medroxyprogesterone acetate (MPA), a synthetic progestin that reduces plasma testosterone levels, has been used in the treatment of male sex offenders. It also reduces the sexual activity of male macaques. To investigate its sites and mechanisms of action, 11 adult male cynomolgus monkeys were castrated and 7 and 21 h later were pretreated with 20 mg progesterone s.c. (Prog, n = 3), or 5 mg dihydrotestosterone propionate s.c. (DHTP, n = 3) or oil vehicle (controls, n = 5). Twenty-four hours after castration, all males were injected i.v. with 5 mCi [3H]-MPA, and killed after 60 min. Left halves of the brains were processed for thaw-mount autoradiography to identify the neurons accumulating radioactivity, and right halves were analyzed by high performance liquid chromatography (HPLC) to measure the uptake of [3H]-MPA in nuclear fractions. In males pretreated with oil, there were labeled neurons in the ventromedial nucleus (n.), arcuate n., medial preoptic n. and anterior hypothalamic area. In progesterone-pretreated males, labeling was reduced by 84-100% compared with controls (p less than 0.001), but in DHTP-pretreated males there was no effect, and labeling was not significantly different from control levels. Nuclear concentrations of [3H]-MPA measured by HPLC in controls were highest in the hypothalamus, amygdala, preoptic area and pituitary gland. Pretreatments with progesterone reduced the nuclear concentrations of [3H]-MPA in hypothalamus, preoptic area and pituitary gland by 82-95% compared with controls (p less than 0.05), but DHTP pretreatments had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

The uptake of tritiated diethylstilbestrol by the brain, pituitary gland, and genital tract of the fetal macaque: a combined chromatographic and autoradiographic study

To examine the possible sites of action of the synthetic estrogen diethylstilbestrol (DES) in the developing primate, [3H]DES (250 mu Ci, iv, or 500 mu Ci, sc) was administered directly into two rhesus and nine cynomolgus macaque fetuses at about 122 days gestation (range, 121-124 days). The location of cells accumulating radioactivity 60 min later was examined by autoradiography in two males and two females. In females, labeled neurons were observed in the hypothalamus, preoptic area, and amygdala, but not in the cerebral cortex. In one male a similar pattern of uptake was observed, but percentages of labeled neurons were lower, and in the other male very little labeling was observed in any region. The chemical identity of the radioactivity in cell nuclei was determined by high performance liquid chromatography in three males and four females. Concentrations of radioactivity in nuclear pellets were highest in the hypothalamus and lowest in the cerebral cortex. This regional variation was highly significant (P less than 0.001), but there was no significant difference between nuclear concentrations of radioactivity in males and females. In supernatant fractions, concentrations of radioactivity showed no significant variation between brain regions and after 60 min, 52-67% of the extracted radioactivity was no longer in the form of [3H]DES. Nuclear levels of radioactivity in pituitary glands and genital tracts of both male and female fetuses were 2-5 times higher than those in hypothalamus. The results demonstrated a direct interaction between DES and cell nuclei from specific regions of the brain, pituitary gland, and genital tract at this stage of gestation in a primate.

Comparisons of the nuclear uptake of [3H]-testosterone and its metabolites by the brains of male and female macaque fetuses at 122 days of gestation

Testosterone secreted by the testis of the macaque fetus is thought to influence certain aspects of the brain's subsequent development which may be responsible for the ontogeny of sexually dimorphic patterns of behavior. To compare the interactions between testosterone and the receptors for androgens and estrogens in brain cell nuclei in the two sexes, 7 intact female fetuses and 5 intact male fetuses were injected in utero at about 120 days of gestation with [3H]-testosterone (250 microCi i.v. or 500 microCi s.c.). One hour later, fetuses were delivered by cesarean section, and samples of brain and peripheral tissues were homogenized and separated into purified nuclear and supernatant fractions. Fractions were analyzed by high performance liquid chromatography to measure levels of [3H]-testosterone and its metabolites. Concentrations of radioactivity extracted from cell nuclei were significantly higher in the hypothalamus-preoptic area than in other brain areas (p less than 0.001); [3H]-estradiol represented 65.0 +/- 5.7% of this radioactivity and nuclear concentrations of this metabolite were 73% lower in males than in females (p less than 0.001). Nuclear concentrations of [3H]-testosterone in the pituitary gland (68.9 +/- 8.8% of extracted radioactivity) were 48% lower in males than in females (p less than 0.001). There was no evidence of a sex difference in the tissue uptake of radioactive steroids from blood, but in males, levels of endogenous plasma testosterone (599.8 +/- 208.2 ng/100 ml) were significantly higher than in females (37.7 +/- 28.5 ng/100 ml; p less than 0.01), and the specific activity of [3H]-testosterone in blood was consequently lower in males than in females.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol administration and the sexual activity of castrated male rhesus monkeys (Macaca mulatta)

To examine whether estradiol might be effective in maintaining sexual behavior after castration or after testosterone withdrawal, we have observed male rhesus monkeys during daily 1-hr tests alternately with each of two ovariectomized, estradiol-treated females (four males, four females, eight male-female pairs, 798 tests). Estradiol (2-5 micrograms/kg sc/day) or vehicle was administered in counterbalanced order immediately after castration and again immediately after withdrawal of testosterone propionate treatments (800 micrograms and 1.6 mg sc/day). There were no significant differences in behavior during vehicle and estradiol treatments to indicate that estradiol helped to maintain male sexual activity. Instead, estradiol treatment tended to interfere with the capacity to intromit. This supported the results of other studies, namely, that the systemic administration of estradiol does not enhance the sexual behavior of castrated male macaques, and raises questions about the role of both aromatization and estrogen receptors in the male primate brain.

Sites in the male primate brain at which testosterone acts as an androgen

Quantitative autoradiographic analysis was used to identify regions in the brain of the male primate where androgen binding sites may be involved in the actions of testosterone. Three days after castration, adult male rhesus monkeys received a subcutaneous injection of either dihydrotestosterone propionate (DHTP, 20 mg, n = 6), testosterone propionate (TP, 100 mg, n = 2), or oil vehicle (control males, n = 4). Three hours later, 5 mCi [3H]testosterone was administered as an i.v. bolus. At 60 min, brains were rapidly removed and the left halves were used for autoradiography. In control males, highest percentages of labeled neurons (20-84% using a rigorous Poisson criterion) were observed in the ventromedial, arcuate and premammillary nuclei (n.) of the hypothalamus, medial preoptic n., bed n. of stria terminalis, intercalated mammillary n., lateral septal n. and the medial, cortical and accessory basal n. of the amygdala. Pretreatment with DHTP eliminated labeling in androgen target tissues of the genital tract, and reduced the percentages of labeled neurons to 4-22% of control values in the arcuate, lateral septal, premammillary and intercalated mammillary n., indicating that in these regions testosterone acted predominantly at androgen binding sites. However, in the medial preoptic n., the ventromedial hypothalamic n. and the accessory basal amygdaloid n., DHTP pretreatment resulted in much less blocking which, together with other data, suggested that in these sites, testosterone's actions involved aromatization and interaction with estrogen-binding sites.

Pretreatments with 5 alpha-dihydrotestosterone and the uptake of testosterone by cell nuclei in the brains of male rhesus monkeys

An in vivo competition method was used in adult male rhesus monkeys to determine if testosterone binds to high affinity binding agents, notably androgen receptors, in brain cell nuclei. Castrated males received 5 alpha-dihydrotestosterone propionate (DHTP, 20 mg, N = 6), testosterone propionate (TP, 100 mg, N = 3) or oil vehicle (controls, N = 6) followed 3 h later by 5 mCi [3H]testosterone [( 3H]T) as an intravenous bolus. Brain and peripheral tissue samples were removed after 60 min, homogenized and separated into supernatant and purified nuclear fractions. Radioactive metabolites of [3H]T [( 3H]estradiol, [3H]DHT) and unchanged [3H]T were identified by high performance liquid chromatography (HPLC). Androgen pretreatments reduced the nuclear uptake of [3H]T by 67-98% in hypothalamus (HYP), preoptic area (POA) and pituitary gland (PIT). This blockade was presumed to be due to prior occupation of nuclear androgen receptors by unlabeled androgens because pretreatments had no effects on levels of [3H]T in supernatants. Since [3H]T was the major radioactive androgen present in brain cell nuclei, results strongly suggested that the principal nuclear androgen receptor ligand in HYP, POA and PIT was unchanged [3H]T rather than [3H]DHT as occurs in the genital tract. In the amygdala the situation was quite different. Here, nuclear concentrations of [3H]T were reduced by 67% following TP pretreatment but were not changed following DHTP pretreatment, indicating a different uptake mechanism in this region that could have particular relevance for testosterone's central actions on behavior.

Identification of radioactivity in cell nuclei from brain, pituitary gland and genital tract of male rhesus monkeys after the administration of [3H]testosterone

Enzymes are present in the primate brain that convert testosterone into 17 beta-hydroxy-5 alpha-androstan-3-one (dihydrotestosterone), estradiol-17 beta and 4-androstene-3,17-dione. To identify the metabolites of testosterone that accumulate in cell nuclei obtained from different regions of the brain, 9 adult castrated male rhesus monkeys were injected with 5 mCi [3H]testosterone as an intravenous bolus. After 1 h, brains were rapidly removed and the left halves were used for autoradiography while the right halves were dissected to provide 14 samples. Radioactive metabolites in cell nuclei were identified by high-performance liquid chromatography (HPLC) and by repeated recrystallization. In autoradiograms of brain, most of the labeled neurons were in the hypothalamus, preoptic area and amygdala. These three regions also had the highest levels of radioactivity. The major form of this radioactivity was [3H]estradiol-17 beta (Type I tissues) and the major radioactive androgen present was [3H]testosterone. In all other brain regions and pituitary gland, the major form of radioactivity was unchanged [3H]testosterone (Type II tissues). In genital tract structures, [3H]dihydrotestosterone predominated (Type III tissues). These results suggested that, in contrast to its actions on genital tract structures, testosterone acts on neuronal nuclei mainly in unmetabolized form or after conversion to estradiol-17 beta.

The uptake of [3H]testosterone and its metabolites by the brain and pituitary gland of the fetal macaque

Testosterone is secreted by the fetal testis during gestation, and this is thought to influence certain aspects of the brain's subsequent development. To study this action at the neuronal level, nine macaque fetuses were injected with 250 microCi [3H]testosterone via the umbilical vein at about 120 days gestation. After 60 min, samples of brain and peripheral tissue were studied by autoradiography or HPLC. Purified nuclear pellets were prepared, and radioactivity in ether extracts was fractionated by HPLC and identified by coelution with internal standard steroids. Concentrations of radioactivity were significantly higher (P less than 0.05) in the hypothalamus-preoptic area than in amygdala, hippocampus, midbrain, and cerebral and cerebellar cortexes, and most of the radioactivity (75%) in the hypothalamus-preoptic area coeluted with 17 beta-estradiol. Radioactivity coeluting with 17 beta-estradiol was also detected in nuclear fractions from amygdala (44%). In contrast, 80% of the radioactivity extracted from pituitary gland nuclei coeluted with testosterone. Most of the neurons labeled in autoradiograms were located in the hypothalamus and preoptic area, fewer were found in the amygdala, and labeling in the frontal or motor cortex did not exceed chance levels. Results suggested that aromatization and, consequently, estrogen receptors play a role in the effects of testosterone on the hypothalamus and amygdala of the primate fetus at this stage of development.

Localization and identification of nuclear radioactivity in the pituitary gland and genital tract after administering 3H-testosterone, 3H-dihydrotestosterone, or 3H-estradiol to male rhesus monkeys

Target cells for testosterone, dihydrotestosterone, and estradiol in the pituitary gland and genital tract of the male primate were localized by thaw-mount autoradiography, and high performance liquid chromatography was used to identify the metabolites of these steroids in cell nuclei. Castrated rhesus monkeys were injected with 3H-testosterone, 3H-dihydrotestosterone, or 3H-estradiol and killed 60 min later. In the anterior pituitary gland, fewer cells were labeled and less radioactivity was taken up by cell nuclei following the administration of either 3H-testosterone (4% of pars distalis cells and 5 dpm/micrograms DNA) or 3H-dihydrotestosterone (5% of cells and 13 dpm/micrograms DNA) than following the administration of 3H-estradiol (43% of cells and 214 dpm/micrograms DNA). Most of the radioactivity in nuclei was in the form of the unmetabolized parent compound (78-94%). In prostate, seminal vesicles, and penis, 3H-dihydrotestosterone was the predominant form of nuclear radioactivity following both 3H-testosterone (67-90%) and 3H-dihydrostestosterone (94-97%) administration, and both androgens labeled epithelial and smooth muscle cells. In contrast, 3H-estradiol was taken up in unchanged form, by cell nuclei of the genital tract and it labeled connective tissue fibroblasts, but not epithelial cells. Thus, the distributions of target cells for androgens and estrogens were clearly different in all these tissues, and the uptake of testosterone resembled that of its androgenic rather than that of its estrogenic metabolite.

Estrogen binding and the actions of testosterone in the brain of the male rhesus monkey

Autoradiography and high performance liquid chromatography (HPLC) were used to determine where metabolites of testosterone interact with estrogen binding sites in the brain of the male primate. Three days after castration, animals received a subcutaneous injection of either estradiol benzoate (EB, 200 micrograms/kg, n = 4) or oil vehicle (controls, n = 4). Three hours later, 5 mCi [3H]testosterone was administered as an intravenous bolus. At 60 min, brains were rapidly removed, left halves were used for autoradiography and right halves were dissected into 14 samples for HPLC of nuclear and supernatant fractions. In control males, labeled neurons were observed in preoptic area, hypothalamus and amygdala. In EB-pretreated males, the number of labeled neurons was reduced by 35% in the anterior hypothalamus and ventromedial nucleus, and by 65% in the cortical and accessory basal amygdaloid nuclei, but was not significantly reduced in other brain regions. In hypothalamus, preoptic area and amygdala, EB-pretreatment reduced nuclear concentrations of [3H]estradiol to 37-55% of control levels, but reduced neither the nuclear concentrations of [3H]testosterone nor the supernatant concentrations of [3H]estradiol and [3H]testosterone. The data suggest that the actions of testosterone in regions such as the arcuate nucleus and lateral septal nucleus primarily involve unchanged testosterone or dihydrotestosterone, while in regions such as the amygdala, aromatization and interaction with estrogen receptors is involved also.

Brain self-stimulation, locomotor activity and tissue concentrations of ethanol in male rats

These studies were aimed at correlating the effects of ethanol on operant behavior and on locomotor activity with its distribution in selected tissues in the body. One group of male rats was trained on a continuous reinforcement schedule for intracranial self-stimulation (ICSS) with electrodes in the lateral hypothalamus. Another group was studied in a locomotor activity apparatus, and both groups were given ethanol intraperitoneally over the dose-range 0.3-1.7 g/kg. Urine was collected 15 min and 60 min after ethanol administration and samples of blood, brain, heart, lung, liver, muscle and testis were obtained at both time points. Depressions of ICSS and of locomotor activity occurred, and these changes in behavior were correlated with increasing concentrations of ethanol in blood, urine and tissue. Thus, the disrupting effects of ethanol on behavior which occurred shortly after its acute administration were closely linked to its concentrations throughout the body.

Sites at which testosterone may act as an estrogen in the brain of the male primate

Testosterone is converted to estradiol in specific regions of the primate brain and accumulates as such in the nuclei of cells in hypothalamus, preoptic area, and amygdala. To locate more precisely those neurons in which nuclear estrogen receptors were occupied by estrogenic metabolites of testosterone, we injected 8 castrated male rhesus monkeys with [3H]-estradiol. Four were injected with oil for control purposes, and 4 were pretreated for 3 days with 2 mg/day testosterone propionate. This dose raised plasma testosterone levels into the high physiological range for intact males. After 60 min, brains were rapidly removed, the levels of [3H]-estradiol in nuclei were measured in the right halves of the brains by high-performance liquid chromatography, and labeled neurons were located in the left halves by autoradiography. Compared with the 4 control animals, nuclear levels of [3H]-estradiol in testosterone-treated males were reduced by 77% in the hypothalamus (p less than 0.001), by 93% in the preoptic area (p less than 0.001), and by 90% in the amygdala (p less than 0.05). In autoradiograms from testosterone-treated males, the labeling of neurons was reduced by 72-96% in most of the regions in which the control males showed high percentages of labeled cells. However, there were only small reductions in the number of labeled neurons in lateral septum (by 31%) and arcuate nucleus (by 23%). These two regions, therefore, contained estrogen receptors that were not blocked by pretreatment with testosterone. The simplest explanation for these results is that estrogenic metabolites of testosterone prevented the uptake of [3H]-estradiol by prior occupation of estrogen receptor sites. The rather precise neuroanatomical localization of the effects pointed to the existence of two populations of estrogen target neurons in the primate brain depending on the presence or absence of local aromatase activity.

Testosterone and its metabolites in male cynomolgus monkeys (Macaca fascicularis): behavior and biochemistry

To extend our previous study on the behavioral effects of testosterone propionate (TP) and dihydrotestosterone propionate (DHTP) to a dose-range producing supra-physiological plasma androgen levels, 4 castrated cynomolgus monkeys were tested with the same 4 females during successive 4-week treatment periods while receiving 800 micrograms, 1.6 mg, 3.2 mg, 6.4 mg and 12.8 mg of TP or DHTP SC/day in counterbalanced order (16 pairs, 828 1-hr tests). Both androgens increased male sexual activity, but DHTP was less effective than TP in increasing the numbers of ejaculations per test and failed to restore ejaculations to intact levels. Giving androgen-treated males single injections of 50 micrograms and 100 micrograms estradiol benzoate (EB) was without any additional effect on behavior (16 pairs, 256 tests). To examine hormonal effects in the brain, castrated males were given either 3H-T or 3H-DHT, and tissues were examined by high performance liquid chromatography (hplc). After 3H-T, 3H-E2 and unchanged 3H-T were the major forms of radioactivity in nuclei from hypothalamus, preoptic area and amygdala. After 3H-DHT, unchanged 3H-DHT predominated. The lower behavioral effectiveness of DHT could not be ascribed to its failure to enter the brain. The data suggested a role for unchanged T in the regulation of ejaculatory behavior in a male primate.

Pre-optic and hypothalamic neurons accumulate [3H]medroxyprogesterone acetate in male cynomolgus monkeys

Medroxyprogesterone acetate (MPA) is a synthetic progestin that is reported to be effective in the treatment of paraphilic behavior, including paraphilic aggression, in men. The mechanisms and sites of action for its behavioral effects are not known. Thaw-mount autoradiography was used to help identify sites in the brain at which MPA may act in a male primate. Two adult, castrated male cynomolgus monkeys were administered [3H]MPA and killed one hour later. Radioactivity was concentrated in the nuclei of many neurons in the medial preoptic nucleus (n.), anterior hypothalamic area, ventromedial hypothalamic n., and arcuate n. Virtually no labeled cells were observed in the bed n. of the stria terminalis, lateral septal n., or amygdala. Analysis by high performance liquid chromatography of brain samples from the same animals demonstrated that 84% of the extractable radioactivity in cell nuclei from the hypothalamus and preoptic area was in the form of unmetabolized [3H]MPA. The localization of MPA-concentrating neurons in regions of the brain known to be implicated in regulating both sexual behavior and pituitary function suggests that, among other sites of action, MPA may act directly upon the brain.

Sites of action of testosterone in the brain of the female primate

Thaw-mount autoradiography was used to map target neurons for tritiated steroids in the brains of ovariectomized rhesus monkeys. In five females, studies were performed 60 min after the administration of 3H-estradiol. Of these, two females were pretreated for five days with daily injections of 2 mg testosterone propionate, one female was pretreated with daily injections of 2 mg dihydrotestosterone propionate, and two females were pretreated with oil vehicle. For comparison, two additional females were administered 3H-testosterone and were killed 30 min later. Following 3H-estradiol administration in females pretreated with oil, there were numerous labeled neurons in the medial preoptic nucleus (n.), anterior hypothalamic area, ventromedial hypothalamic n., arcuate n., bed n. of stria terminalis, lateral septal n., and regions of the amygdala. In females pretreated with testosterone propionate, labeling was virtually abolished in all these areas with the exceptions of the lateral septal n. and arcuate n., presumably because estradiol formed from testosterone competed with 3H-estradiol for estrogen-binding sites. Pretreatment with dihydrotestosterone propionate had no effect on the labeling following the administration of 3H-estradiol. Areas where labeling was blocked, therefore, represent regions where testosterone acted as an estrogen, and it would appear that regional differences in the activity of aromatizing enzymes determine which estrogen target sites in the brain can interact with estrogenic metabolites of testosterone in female primates.

The nuclear accumulation of [3H]testosterone and [3H]estradiol in the brain of the female primate: evidence for the aromatization hypothesis

To identify the metabolites of estradiol (E2) and testosterone (T) in nuclei obtained from the female primate brain and, hence, to investigate the mechanism of their actions on behavior, 9 ovariectomized adult rhesus monkeys were studied. Two of these females were injected with 5.5 mCi [3H]T, and 30 min later, samples of 14 brain areas, pituitary gland, and peripheral tissues were removed and homogenized. Purified cell nuclei and a crude cytosol fraction were prepared, extracted with ether, and fractionated by HPLC to identify steroid metabolites. In nuclei from the hypothalamus, preoptic area, and amygdala, [3H]E2 formed locally was the major form of radioactivity. In nuclei from the clitoris, [3H]dihydrotestosterone was the major form of radioactivity, and in nuclei in all other brain samples and in the pituitary gland and uterus, [3H]T predominated. Two females (controls) were pretreated for 5 days with oil sc, injected with 1 mCi [3H]E2, and killed 60 min later. In these females, elevated nuclear concentrations of [3H]E2 were found in the hypothalamus, preoptic area, amygdala, pituitary gland, and uterus. Similar results were obtained in 2 females that were pretreated for 5 days with 2 mg/day dihydrotestosterone propionate, sc, and then injected with 1 mCi [3H]E2. In 3 females that were pretreated for 5 days with 2 mg/day T propionate, sc, and then injected with 1 mCi [3H]E2, levels of [3H]E2 were reduced by 100% (P less than 0.01) in nuclei from preoptic area and amygdala compared with control values and by 78% (P less than 0.05) in nuclei from the hypothalamus. There were no comparable reductions in steroid levels in cerebral cortex, pituitary gland, or uterus. This is the first direct evidence in the brain of a female primate that the actions of T and E2 involve the same receptor systems.

[3H]estradiol and its metabolites in the brain, pituitary gland, and reproductive tract of the male rhesus monkey. A combined autoradiographic and chromatographic study

Previous studies have shown that [3H]estradiol is the major nuclear metabolite of [3H]testosterone in the hypothalamus, preoptic area and amygdala of the male rhesus monkey, and it has been proposed that some of the stimulatory effects of testosterone on male sexual behavior may be mediated by estradiol-concentrating neurons. To map these neurons and identify metabolites, 4 castrated male rhesus monkeys were each injected with 0.47 mCi/kg [3H]estradiol, and the brains were removed 60 min later. Left halves were frozen for thaw-mount autoradiography, and right halves were used to isolate cell nuclei from different brain regions. A fifth animal was used to validate the methodology. Radioactive steroids were identified and measured by high performance liquid chromatography. Brain areas previously shown to contain labeled neurons after [3H]testosterone administration were also labeled after [3H]estradiol, including medial preoptic nucleus (n.), anterior hypothalamic area, bed n. of stria terminalis, ventromedial n., premammillary n., and corticomedial amygdala. Some areas not labeled after [3H]testosterone were labeled after [3H]estradiol, including lateral septal n., arcuate n., paraventricular n., claustrum, entorhinal cortex, and spinal cord. The pars distalis of the pituitary gland was heavily labeled. Most (83%) of the radioactivity in cell nuclei was [3H]estradiol while [3H]estrone was a major metabolite (25%) in supernatants. In the brain, the highest nuclear concentration of [3H]estradiol was in the hypothalamus (249.2 +/- 20.0 fmol/mg DNA), although in the previous experiments with [3H]testosterone, the highest nuclear concentrations of [3H]estradiol were found in the amygdala. We interpret these results to indicate that local metabolic differences in the brain may underlie some of the different behavioral effects of gonadal steroids in primates.

Comparison of the effects of testosterone and dihydrotestosterone on the behavior of male cynomolgus monkeys (Macaca fascicularis)

To compare the behavioral effects of testosterone propionate (TP) and diyhdrotestosterone propionate (DHTP) at doses producing plasma levels of androgens within the physiological rage, observations were made on 4 castrated male cynomolgus monkeys during successive 4-week treatment periods while they received 25, 50, 100, 200, 400 and 800 micrograms of either TP or DHTP SC/day in counterbalanced order. Males were tested with each of the same 4 female partners (16 pairs, 1024 1-hr behavior tests). Males were injected at 1600 hr and blood samples were obtained at 0800 hr (256 samples, 456 hormone determinations). Physiological plasma levels of T resulted from the 200 micrograms and 400 micrograms TP treatments, and were associated with significantly increased ejaculatory behavior. Physiological plasma levels of DHT resulted from the 50 micrograms and 100 micrograms DHTP treatments, but there were no changes in ejaculatory behavior over the entire DHTP dose range used. This difference in the behavioral effects of TP and DHTP, not previously reported for a primate, could not be accounted for by the effects of treatment order, season, long-term behavioral testing, female sexual motivation or behavior reflecting the peripheral action of androgens.

An automatic device for measuring speed of movement and time spent at rest: its application to testing dopaminergic drugs

We describe a device to measure speed of movement and time at rest for use with a commercially available infrared photobeam activity monitor. This system is a reliable substitute for a human observer and provides additional measures of activity that can help in interpreting how psychoactive drugs alter behavior. The effects of graded doses of d-amphetamine, haloperidol and (-)3-(3-hydroxyphenyl)-N-n-propylpiperidine, (-)-3-PPP, were studied with the device, and the results confirmed that these drugs differentially alter speed of movement and time at rest.

The distribution, nuclear uptake and metabolism of [3H]dihydrotestosterone in the brain, pituitary gland and genital tract of the male rhesus monkey

Three adult male rhesus monkeys were castrated and administered 2 mCi [3H]dihydrotestosterone ([3H]DHT) intravenously. Brain and peripheral organs were removed after 60 min and were examined either by thaw-mount autoradiography or by subcellular fractionation and high performance liquid chromatography. Neurons that accumulated radioactivity in their nuclei were distributed widely in many regions of the brain including the preoptic area, hypothalamus, septal area-bed nucleus, amygdala, thalamus, and brain stem. Several brain areas which were labeled after [3H]DHT injection had not been labeled in earlier experiments after [3H]testosterone ([3H]T) injection. The major metabolite of [3H]DHT in extranuclear fractions from brain was [3H]androstanediol, but [3H]DHT alone was detected in cell nuclei. There was no evidence of any [3H]estradiol in cell nuclei, confirming that DHT can also be regarded as a non-aromatizable androgen in the primate brain. Since the nuclear concentrations of androgens were 2-3 times higher in the brain following [3H]DHT than they were in the earlier [3H]T experiments, the relative lack of effectiveness of DHT in restoring the sexual behavior of male castrates cannot be related to an inability of DHT to enter brain cell nuclei.

Localization of the synthetic progestin 3H-ORG 2058 in neurons of the primate brain: evidence for the site of action of progestins on behavior

The location of neurons that concentrate progestin in the brains of female cynomolgus monkeys was mapped by autoradiography using the specific synthetic progestin receptor ligand 3H-ORG 2058. Three females were ovariectomized and treated with estrogen (20 micrograms estradiol benzoate daily for 7 days), and one of them was also pretreated with progesterone. Each received an i.v. injection of 1 mCi 3H-ORG 2058 and was killed 1 hour later. Thaw-mount autoradiograms revealed intense accumulation of radioactivity in the nuclei of many neurons in the mediobasal hypothalamus, particularly in the ventromedial nucleus (n.), arcuate n., and premammillary n. Neuronal labeling was also observed frequently in the medial preoptic n., and occasionally in the anterior hypothalamic area, paraventricular n., and organum vasculosum of the lamina terminalis. In the pituitary gland, about 5% of cells in the pars distalis were intensely labeled. In the female pretreated with progesterone, however, labeling was almost completely blocked. Analysis of samples by high-performance liquid chromatography demonstrated that the radioactivity extracted from brain and pituitary gland cell nuclei was almost entirely unmetabolized 3H-ORG 2058. The nuclear concentration of progestin was much greater in the pituitary gland than in the brain, and was greater in the hypothalamus than in any other brain area. These results revealed well-localized groups of progestin-concentrating neurons in the primate brain which presumably mediate the effects of progesterone on both gonadotropin secretion and female sexual behavior.

The behavioral thresholds of testosterone in castrated male rhesus monkeys (Macaca mulatta)

To determine the lowest doses of testosterone propionate (TP) that cause clearcut behavioral changes in castrated male rhesus monkeys (behavioral thresholds), observations were made on eight males during successive 4-week treatment periods while they received daily doses of TP ranging from 25 micrograms to 12.8 mg subcutaneously. Males were tested with each of the same four ovariectomized females (32 pairs, 1408 one-hour behavior tests). Two females were untreated and the other two received either 5 or 15 micrograms estradiol benzoate sc per day. TP injections were given at 1600 hr, and plasma samples were obtained at 0800 hr (352 samples). Individual males had widely different behavioral thresholds from 50 micrograms up to 3.2 mg TP per day. Males showed two types of response: A, a graded increase in ejaculatory activity as plasma testosterone values increased, and B, an all-or-none type of response in which there were no further increases in ejaculation with increasing plasma levels once the behavioral threshold had been reached. At levels below the physiological range, small changes in plasma testosterone were associated with marked changes in behavior. The female partner exerted a pronounced effect upon the responses of males to TP treatment.

Sexual behavior correlates with the diurnal plasma testosterone range in intact male rhesus monkeys

There is evidence that androgens are necessary for the full expression of sexual behavior in male primates, but it has proved difficult to relate sexual activity to circulating androgens levels in comparisons between intact males. In the present study, 4423 behavior tests of 32 pairs of rhesus monkeys were conducted in a constant photoperiod over a 2-year period, and there was no significant relationship between the frequency of ejaculation and plasma testosterone levels in samples collected at 0800, 1600 or 2200 h. However, the magnitude of the diurnal range between the lowest and highest levels correlated negatively with sexual behavior. As the seasonal increase in sexual activity occurred, there was a corresponding decrease in the diurnal range of plasma testosterone. Furthermore, those males with the highest numbers of ejaculations showed the smallest diurnal plasma testosterone ranges. An additional experiment with 32 males revealed that neither behavior testing nor the occurrence of ejaculation influenced the diurnal testosterone range. Consequently, we have concluded that if any causality operated it would be in the direction of a hormonal influence on behavior. These findings suggest that increased nocturnal levels of testosterone do not enhance behavior and that a threshold level maintained throughout the 24 h may be a critical endocrine factor.

Characterization by high performance liquid chromatography of nuclear metabolites of testosterone in the brains of male rhesus monkeys

Testosterone (T) restores the potency of castrated male rhesus monkeys, and our autoradiographic data have demonstrated that 3H-T or its metabolites concentrate in cell nuclei in the corticomedial amygdala, bed nucleus of stria terminalis, preoptic area, and hypothalamus. In rat, 3H-estradiol (3H-E2) is a major nuclear metabolite of 3H-T in areas of the limbic system, but comparable data are lacking for the primate. We have therefore developed an improved technique using high performance liquid chromatography for investigating metabolites of 3H-T that accumulate in cell nuclei in small amounts of tissue obtained from the brain of the rhesus monkey. Two castrated male rhesus monkeys were injected with 5 mCi of 3H-T and were killed 30 min later. In amygdala, preoptic area-bed nucleus of stria terminalis, and hypothalamus, 48-70% of the nuclear radioactivity was in the form of 3H-E2 (Type I tissues). In six other brain areas and in pituitary, 35-85% of the nuclear radioactivity was in the form of 3H-T (Type II tissues), whereas in genital tract tissues, 86-99% of the nuclear radioactivity was in the form of 3'-dihydrotestosterone (3H-DHT) (Type III tissues). In plasma and in supernatants from both Type I and Type II tissues, the proportions of 3H-T were high, and 3H-E2 did not exceed 10% of the total extractable radioactivity. These data suggest that, as in rodents, some of the central actions of T in primates may be mediated by estrogen target neurons.

Behavior of rhesus monkeys during 28-day cycles of estrogen treatment

Sixteen ovariectomized rhesus monkeys were paired, each with two males, during thirty-two 28-day periods during which they received one or more of the following schedules of daily injections: (a) different mixtures of estradiol benzoate, progesterone, and testosterone propionate (artificial menstrual cycles), (b) the doses of estradiol benzoate given in artificial cycles but without the other hormones (cyclic estradiol regimens), and (c) appropriate control treatments (625 one-hour behavioral tests). Hormone doses were adjusted to give plasma levels in the physiological range (335 blood samples). Measures of male sexual activity during artificial cycles and during cyclic estradiol regimens showed significant cyclic changes, but these changes were indistinguishable from each other. In four females studied in an operant conditioning paradigm, there was a midcycle dip in the times taken to obtain access to males during the cyclic estradiol regimens. The data indicated that the estrogen state of the female plays a preponderant role in determining the cyclic changes in the behavioral interactions of the pair independently of the effects of other ovarian hormones.

Behavior of rhesus monkeys during 28-day cycles of estrogen treatment

Sixteen ovariectomized rhesus monkeys were paired, each with two males, during thirty-two 28-day periods during which they received one or more of the following schedules of daily injections: (a) different mixtures of estradiol benzoate, progesterone, and testosterone propionate (artificial menstrual cycles), (b) the doses of estradiol benzoate given in artificial cycles but without the other hormones (cyclic estradiol regimens), and (c) appropriate control treatments (625 one-hour behavioral tests). Hormone doses were adjusted to give plasma levels in the physiological range (335 blood samples). Measures of male sexual activity during artificial cycles and during cyclic estradiol regimens showed significant cyclic changes, but these changes were indistinguishable from each other. In four females studied in an operant conditioning paradigm, there was a midcycle dip in the times taken to obtain access to males during the cyclic estradiol regimens. The data indicated that the estrogen state of the female plays a preponderant role in determining the cyclic changes in the behavioral interactions of the pair independently of the effects of other ovarian hormones.

Behavior of rhesus monkeys during artificial menstrual cycles

Daily subcutaneous injections of estradiol, progesterone, and testosterone were given to ovariectomized rhesus monkeys in amounts that imitated accurately the changing plasma levels of hormones in intact females with natural menstrual cycles. Because these cycles in ovariectomized, treated females were terminated by normal vaginal bleeding every 28 days and showed a mid-cycle gonadotropin surge, we termed them "artificial menstrual cycles." In dyadic mating tests, changes in the females' access times (lever pressing) for males, and in the males' ejaculatory performance, were closely similar during natural and artificial cycles, and there were well-marked behavioral rhythms. These rhythms were lost during 28-day control periods when ovariectomized females received injections of vehicle alone. Differences in ejaculatory performance during natural and artificial cycles could be accounted for by an order effect. It is concluded that the artificial cycle provides a valid and useful paradigm for a more detailed study of the neuroendocrine regulation of primate reproductive behavior.

An easily constructed biphasic constant-current stimulator for intracranial self-stimulation

This paper describes a biphasic, constant-current stimulator that is appropriate for intracranial self-stimulation (ICSS) studies. The stimulator is made from components that are readily available in electronic supply stores at low cost. A printed circuit board has also been designed for the stimulator which facilitates its production. The device has proven extremely reliable in various ICSS paradigms.

Menstrual cycle influences on operant behavior of female rhesus monkeys

Nine female rhesus monkeys were paired with males throughout 63 menstrual cycles. The females' motivation to approach males was studied with an operant conditioning paradigm that required the female to press a lever 250 times to gain access to the male. Sexual behavior was scored during standard 60-min tests that followed the attainment of access (17 pairs, 1,440 tests). In the overall data, mean times to access were shortest at mid-cycle and longest just before and after the onset of menstruation, and a model-fitting method showed that 45% of cycles from individual pairs were significantly correlated with a V-shaped model of the overall pattern. Male sexual activity was highest at mid-cycle and lowest in the last quarter of the cycle, but the changes in access times could not be attributed entirely to the rewarding effects of the ejaculations. In the combined data from five females (9 pairs, 33 cycles), high estradiol levels and low progesterone levels were statistically associated with short access times and short ejaculation times. The overall effect was for operant performance and sexual activity to be synchronized and maximized in the periovulatory period of the menstrual cycle.

Human vaginal secretions: volatile fatty acid content

Vaginal samples (682) were collected by a tampon method from 50 healthy young women. Samples were analyzed by gas chromatography. The volatile aliphatic acids increased during the late follicular phase of the menstrual cycle and declined progressively during the luteal phase. Women on oral contraceptives had lower amounts of volatile acids and did not show any rhythmic changes in acid content during the menstrual cycle. These same substances possess sex-attractant properties in other primate species.