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Synthetic progestins such as medroxyprogesterone acetate (MPA) are used widely in the treatment of male sex offenders. In male cynomolgus monkeys (Macaca fascicularis) treated with testosterone (T), both MPA and progesterone (P) had comparable inhibitory effects on male sexual motivation and behavior. To determine if P, like MPA, decreases endogenous T levels, plasma T and P levels were analyzed in weekly blood samples (N=186) from eight intact males, each paired with a sexually receptive female before, during, and after treatment with subcutaneous Silastic P implants (336 behavior tests). P treatment decreased sexual activity but not plasma T levels. To ascertain if P, like MPA, acts by decreasing the nuclear uptake of T by brain, four P-treated and four control males were euthanized 60 min after intravenous injection of 3 mCi of [3H]T. The nuclear uptake of unchanged [3H]T and its metabolites [3H]E(2) and [3H]DHT was measured in samples of brain, pituitary gland, genital tract, and liver. P, unlike MPA, did not affect the nuclear uptake of [3H]androgens by brain, but reduced by 80% the nuclear accumulation of [3H]E(2) in tissue samples containing preoptic area and the anterior part of the bed nucleus of stria terminalis, although not in samples from hypothalamus or amygdala.

In male cynomolgus monkeys the synthetic progestin, medroxyprogesterone acetate (MPA), decreases testosterone (T) levels and sexual behavior, binds to progestin receptors in brain, and reduces by about 70% the uptake of [3H]androgens by both brain and genital tract tissues. To examine the behavioral effects of progesterone (P) itself, eight castrated, T-treated males were each tested twice weekly with an estrogenized female before, during, and after they were treated with two SC Silastic P implants. Data from six 4-week treatment periods were analyzed to facilitate comparisons with our previous data using MPA: i) baseline, ii) weeks 4-7 of P treatment, iii) weeks 8-11 of P treatment, iv) weeks 1-4 after P implants were removed, v) weeks 5-8 after P withdrawal, and finally vi) weeks 9-12 after P withdrawal (384 1 h behavior tests). Weekly blood samples (N = 192) were analyzed by radioimmunoassay to determine plasma levels of both T and P. P treatment, which resulted in high plasma P levels (about 44 ng/ml), produced decrements in measures of male sexual behavior and motivation that were both qualitatively and quantitatively similar to those produced by MPA treatment but, unlike MPA, P did not decrease plasma T levels or change them in any way (about 850 ng/100 ml throughout). The findings suggest that P implants may be preferable to weekly MPA injections in the treatment of male sex offenders because they require less patient compliance and may not have MPA's troubling side effects.

The distribution of androgen receptor immunoreactive-neurons, mapped with the PG21 anti-androgen receptor antibody, was compared in male rat brains with the distribution of Fos-immunoreactive neurons induced by mating. In gonadally intact, but not in castrated male rats, substantial numbers of androgen receptor-containing neurons were present in a variety of forebrain and midbrain regions. The PG21 antibody apparently had a higher affinity for occupied than for non-occupied androgen receptors. Androgen receptor-immunoreactive regions included the medial preoptic area and other forebrain areas previously identified as containing androgen receptors, the dorsal and ventral periaqueductal gray, and a midbrain region that included the lateral part of the central tegmental field, part of the caudal zona incerta, the subparafascicular nucleus of the thalamus and the peripeduncular nucleus. Fos-expressive neurons were essentially absent in non-mated males but were present in the brains of rats which mated to ejaculation. All brain regions in which androgen receptor-immunoreactive neurons were counted also expressed Fos immunoreactivity after mating, and there was considerable overlap between the distributions of androgen receptor- and Fos-immunoreactive neurons. In a second experiment, we used immunofluorescent techniques to document the intraneuronal co-localization of Fos with androgen receptor immunoreactivity in the medial preoptic area, medial amygdala, and central tegmental field. In these regions mating-induced Fos immunofluorescence was exclusively localized in androgen receptor-immunofluorescent neurons. However, not all androgen receptor neurons were Fos expressive, suggesting that only some androgen-sensitive neurons were activated during mating. These results are consonant with the view that hormone actions on forebrain and midbrain structures influence the neuronal activity correlated with mating.

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.

One group of male rats was trained to associate novel odors with three different environmental conditions: the presence of (i) a sexually receptive female (RF), (ii) an unreceptive female (UF) and (iii) no other rat (NO). A second group of males received no training. Single units in nucleus accumbens (NAC) were then recorded in anesthetized animals and their responsiveness to various odors was tested. Odors that had been associated with receptive females during training evoked significantly more unit responses in NAC than did the same odors in untrained males. There were no differences between trained and untrained males in the numbers of units responsive to odors associated with unreceptive females and with the empty training chamber. In trained animals, both the percentage of responding units and the magnitude of olfactory-evoked responses were significantly larger with RF-associated odors than with either UF or NO odors. Both of these effects were more pronounced in rats that had ejaculated with females during training than in rats that had not. Findings demonstrated that pairing odors with the presentation of sexually receptive females enhanced the responsiveness of NAC neurons to those odors and indicated a role for NAC in associating environmental stimuli with natural reward processes.

Rats were implanted with stimulating electrodes in the medial forebrain bundle-lateral hypothalamus (MFB-LH). After recovery from surgery, they were assigned to one of two groups equalized for body weight. One group was housed four animals to a cage and animals in the other group were housed individually. After four weeks in these housing conditions, animals were tested during the fifth week for locomotor activity in five daily 15-min sessions, and their reactivity to handling was also measured. During the sixth and seventh weeks, animals were allowed to self-train for brain stimulation (ICSS) during daily 15-min sessions. Animals housed in groups had higher levels of locomotor activity and were less reactive to handling than were animals housed individually. When tested for the acquisition of ICSS, animals housed as a group made more responses than did animals housed individually. These results indicate that, within the time frame of a few weeks, the housing conditions of adult animals caused differences in both unconditioned behavior, such as locomotor activity, and in the acquisition of a highly reinforcing brain self-stimulation task.

Microinjections of substance P (SP) into the ventral tegmental area (VTA) increase locomotor activity in rats, and this effect is thought to be produced by activation of the mesolimbic dopamine system. In the present study, firing rates of neurons in areas receiving projections from the mesolimbic dopamine system were recorded during injections of SP (3 microgram in 0.5 microliters saline) into the VTA of rats anesthetized with chloral hydrate. Significant changes in firing rates were observed in 84% of the units recorded in nucleus accumbens and olfactory tubercle. There were mostly decreases in nucleus accumbens (NAC, 21 of 25 units affected by SP) and mostly increases in olfactory tubercle (OT, 13 of 18 units affected by SP). In contrast, neither saline injections into VTA nor SP injections 2 mm dorsal to VTA had any effect on NAC or OT neurons. Haloperidol (0.5 mg/kg IV) blocked the effects of SP, suggesting that effects were mediated, at least in part, by the mesolimbic dopamine system. Results indicated that activation of dopaminergic neurons by SP injections into VTA can produce changes in the activity of neurons in NAC and OT, areas which receive mesolimbic dopaminergic projections.

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.

It is well known that neurons of the nigrostriatal dopamine (DA) system respond to sensory stimuli, and our primary objective here was to ascertain if neurons in the terminal regions of the mesolimbic DA system respond to sensory input also. In addition, the effects of electrical stimulation of the ventral tegmentum, which contains the DA cells of origin of the mesolimbic system, on sensory-evoked responses in mesolimbic neurons was studied. In rats anesthetized with chloral hydrate, responses of single units to olfactory and somatosensory stimuli were recorded in 6 forebrain regions including nucleus accumbens and olfactory tubercle. Both increases and decreases in spontaneous firing rates were evoked in 225 of 336 units by one or more of the 8 types of sensory stimuli employed (5 olfactory, 3 somatosensory). Excitatory responses occurred twice as frequently as inhibitory responses, but a few units responded with excitatory responses to some stimuli and inhibitory responses to others. The proportions of units responsive to olfactory and/or somatosensory stimuli were different in different regions. After electrical stimulation of the ventral tegmentum, sensory-evoked responses were changed in 30 of the 49 units tested (61%). There were increases, decreases or combinations of a decrease followed by an increase in sensory-evoked responses, which persisted for 1–10 min after the application of a single electrical stimulus train. Haloperidol (0.3 mg/kg, i.p.) either blocked the effect of tegmental stimulation or decreased all responses. The present results demonstrated that units in the terminal regions of the mesolimbic DA system are responsive to sensory input and that these responses can be affected by prior electrical stimulation of the ventral tegmentum.

The effects of amphetamine on the extinction of intracranial self-stimulation (ICSS) and on postextinction ICSS performance were examined in rats implanted with electrodes either in medial prefrontal cortex (mPFC) or in the posterior hypothalamus-ventral tegmental area (PH-VTA). Lever-pressing for ICSS was allowed to stabilize in daily 15-minute sessions before each animal was exposed to 5 minutes of extinction (responding without reward). Animals were administered either 0.25 mg/kg d-amphetamine or saline before baseline, extinction and lower in PH-VTA animals compared with saline-treated controls. Rates did not change immediately after extinction but, one day later, postextinction sessions. After amphetamine treatment, the number of lever presses during extinction was higher in mPFC animals and rates had increased in all saline-treated animals (both PH-VTA and mPFC animals) and had decreased in all amphetamine-treated animals. These findings demonstrated that the effects of amphetamine on the extinction of ICSS were different in cortical and hypothalamic sites, possibly because of regional differences in stimulus-evoked reinforcement and inhibitory processes.

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.

The Publisher regrets that this article was published containing an error. Fc-fos_ should appear as Fc-fos [4]_ in the second line of the abstract. Please see the complete corrected abstract as it should appear below. In contrast to some other species, the numbers of activated neurons in the brains of male and female macaques are high in both mated and unmated animals. Dual labeling with the 1D5 anti-estrogen receptor antibody and the Fc-fos [4]_ polyclonal anti-c-fos antibody was used in 19 female cynomolgus monkeys to examine whether mating selectively increases the activation of neurons containing estrogen receptors (ER). Mated females, and social controls exposed to males without mating, were euthanized about 75 min after the start of the test, exactly 60 min after the first ejaculation (mated females, N =7) and 75 min after the start of exposure to a male (social controls

Rats were implanted with stimulating electrodes in the medial forebrain bundle-lateral hypothalamus, and trained in one of two brain self-stimulation (ICSS) procedures. One group of animals was trained in the auto-titration procedure which measured response rates and reinforcement thresholds for ICSS. When trained, the animals were tested with d -amphetamine (0.03–1.0 mg/kg) and saline. The second group of animals was trained in a procedure which established the discriminative properties of brain stimulation and which also measured the detection threshold for ICSS. When trained, the animals were tested with d -amphetamine and saline, and were subsequently tested with amphetamine and saline in an activity monitor. A graded decrease in mean reinforcement thresholds was produced by d -amphetamine. The two lower doses (0.03, 0.10 mg/kg) increased the rate of lever-pressing, but the highest dose (1.0 mg/kg) decreased it. No reliable changes in detection threshold occurred, although at the 0.3 mg/kg dose reductions were seen in two of five animals. Animals also showed a graded increase in motor activity with dose as well as increases in several performance measures. These results demonstrated that although amphetamine lowers reinforcement thresholds, it does not reliably alter detection thresholds, suggesting that the motivation to respond for ICSS is changed without any corresponding changes in the capacity to detect the presence of the stimulus.

(1) In a double-blind study using a new tampon method, 682 samples of vaginal secretions were collected from 50 healthy young women attending a university. (2) Samples were analyzed by gas chromatography for the volatile fatty acids (C2-C6) that have sex-attractant properties in infra-human primates. (3) All subjects produced some acids but acetic predominated; however, 30% of women provided samples containing more than 10 μg of other acids in addition to acetic, and these women formed a sub-group termed ‘producers’. (4) The content of volatile acids increased significantly during the first half of the cycle and declined during the second half of the cycle. (5) Increases in propanoic, methylpropanoic, butanoic, methylbutanoic and methylpentanoic acids contributed especially to the increased content during the first half of the cycle. (6) Women taking oral contraceptives had a lower overall content of acids in their vaginal secretions, and the mid-cycle increase was absent. (7) The mid-cycle increase was particularly well-marked in women ‘producers’. (8) The biosynthesis of the acids is discussed.

Rats were implanted with stimulating electrodes either in the medial forebrain bundle-lateral hypothalamus (MFB-LH) or the midbrain-central gray area (MID-CG), and were trained to lever-press for electrical brain self-stimulation (ICSS). The animals were made tolerant to morphine (15 mg/kg) by twice daily injections for a four-day period. Withdrawal was then induced either by substituting saline (spontaneous withdrawal) or by administering naloxone (1.0 mg/kg) (precipitated withdrawal). Changes in body weight, in the incidence of diarrhea, and in rates of lever-pressing for ICSS were recorded during the five-day withdrawal period. In both the MFB-LH implanted and the MID-CG implanted groups, the duration and magnitude of changes in lever-pressing were greater when withdrawal was precipitated than when it was spontaneous. Independently of the type of withdrawal, however, the behavioral disruption was greater for animals implanted in the MFB-LH than for animals implanted in the MID-CG. The changes in body weight were similar for both electrode sites and both types of withdrawal. Diarrhea only occurred in the precipitated withdrawal group and its incidence was similar for animals implanted in the two sites. Three additional groups of animals were implanted in the MFB-LH, made tolerant to morphine, and given naloxone as above. They were administered clonidine (10, 30 or 100 micrograms/kg) 30 min prior to naloxone to attenuate the effects of withdrawal. The 30 micrograms/kg dose of clonidine produced maximal attenuation of the disruption in lever-pressing. None of the doses of clonidine attenuated weight loss, but all three doses reduced the incidence of diarrhea. The ICSS procedure demonstrated that the behavior during withdrawal can be related to the brain area that is stimulated.

(1) Hypothalamic and cortical macro-electrode (EEG) records were telemetered from freely-moving, ovariectomized cats treated with estrogen during mating tests with males, and records were analysed for EEG energy changes in 3 frequency bands (4–8, 8–16 and 16–32 Hz). The methods used for telemetry and EEG analysis are fully described. (2) Synchronous with the male's intromission, there was a flattening of the amplitude of the already activated EEG (Suppression response) in hypothalamic ventromedial nucleus (Hvm) which was not observed in other hypothalamic or cortical sites. (3) EEG energy analysis showed that the effect was most marked in the 16–32 Hz band, and confirmed that it was localized to Hvm. (4) Similar, but not identical, suppression responses were observed during vaginal probing both before and during estrogen treatment: the response was not, therefore, a hormone-dependent one. (5) The suppression response in Hvm was considered to be a neural correlate of intromission by the male and, together with changes in the background level of the EEG, may play a role in determining the affective responses of the female cat to the male's copulatory activity.

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.

(1) Hypothalamic and cortical EEG activities were telemetered from freely-moving ovariectomized female cats during mating tests with a vigorous male conducted over periods of many weeks. (2) Records were analyzed for long-term energy changes in 3 frequency bands: 4–8, 8–16 and 16–32 Hz. In Hvm, energy levels (Voltage Indices) were higher in the higher frequency bands while the reverse trend was observed in anterior and posterior hypothalamus. (3) Estrogen treatment had widespread effects on energy levels in the brain, but consistently depressed energy levels in Hvm, particularly in the highest frequency band. (4) Estrogen treatment did not consistently exert this effect in anterior and posterior hypothalamus or in cortical sites. (5) Behavioral factors also contributed to the effects observed. Although these were difficult to interpret, the particular depression observed in Hvm during mating activity did not occur elsewhere. (6) There is evidence that these localized changes in EEG activity relate to the regulation of estrous behavior.

Under laboratory conditions, pairs of rhesus monkeys show at least four different patterns of sexual behavior in relation to the stage of the menstrual cycle. The most interesting of these is characterized by a distinct mid-cycle peak followed by a secondary pre-menstrual rise. High doses of progesterone administered to ovariectomized females receiving estrogen replacement treatment resulted in a marked reduction of the sexual behavior of the pair either because the female refused the male or because the male made fewer mounting attempts. Males were shown by operant conditioning and nose-blocking procedures to detect the hormonal status of theier female partners by olfactory mechanisms. Shortchain fatty acids in the vaginal secretions of females were found to be responsible for this effect. The same acids have been shown to be normal constituents of human vaginal secretions, and levels were highest in the late follicular phase but declined progressively during the luteal phase of the menstrual cycle. In women taking oral contraceptives, levels of volatile acids in the secretions were lower than normal and rhythmic production during the menstrual cycle was abolished.

To determine the threshold doses of testosterone propionate (TP) that cause clear-cut behavioral changes in the sexual behavior of castrated male cynomolgus monkeys, observations were made on three males during successive 5-week treatment periods while they received daily subcutaneous doses of 100 micrograms TP increasing in octaves to 25.6 mg TP. Males were tested with each of the same two ovariectomized, estrogen-treated females (6 pairs, 330 1-hr behavior tests). To mimic the diurnal plasma testosterone rhythm, TP injections were given at 1600 hr and blood samples were obtained at 0800 hr (141 samples). Male ejaculatory activity increased at the threshold dose of 200 micrograms TP per day giving plasma testosterone levels of 830 ng/100 ml, which is in the physiological range of 600-1600 ng/100 ml for intact males. This threshold dose was eight times higher than in rhesus monkeys on a dose per kilogram body weight basis. There was a further marked increase in ejaculatory performance at higher doses (6.4 to 25.6 mg) giving supraphysiological plasma levels of 4000-9000 ng/100 ml. There were individual differences in the behavioral changes occurring with TP treatment, and the female partner modulated the effects. These findings were generally similar to those obtained with male rhesus monkeys, but certain species differences were noted.

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 μg/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.

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.

Changes in direct and redirected aggression and in plasma testosterone levels were studied during a 39-month period in eight male rhesus monkeys maintained under laboratory conditions in a constant photoperiod. Males were tested with the same four ovariectomized, estrogen-treated females (32 pairs, 6357 one-hour tests), and plasma samples were obtained weekly at 0800 and 1600 hr and every two weeks at 2200 hr (2630 samples). Four males remained intact throughout and four males were castrated and received testosterone implants subcutaneously at the start of the second year. Annual changes in male aggression continued to occur at the expected time in the autumn in both intact and castrated males which indicated a degree of independence of the behavior from the photoperiod and from changes in plasma testosterone. There was a highly significant temporal association between 0800 hr testosterone and direct aggression occurring 3–4 weeks later during the first year, but this association was lost in subsequent years. Although the annual rhythms in plasma testosterone persisted for three years in the intact group, the maxima for the hormonal and the behavioral changes drifted apart in the constant photoperiod. The view is propounded that essentially independent long-term endocrine and behavioral rhythms are normally entrained by exteroceptive factors.

Pairs of adult rhesus monkeys of opposite sexes (12 pairs) were studied during 1-h mating tests (986 tests). Ovariectomized females received 5 μg oestradiol intravaginally throughout to keep them attractive to males and maintain a relatively constant level of male sexual activity. Females were given subcutaneous silastic implants of testosterone to change their sexual receptivity. A threefold change in sexual invitations resulted from the implantation and removal of testosterone in the absence of any major changes in the behaviour of their male partners. These changes in invitational behaviour therefore reflected an action of the hormone upon an internal mechanism within the female subserving sexual motivation which was independent of changes in the behaviour of the male. Radioimmunoassay of plasma testosterone (109 samples) and plasma oestradiol (86 samples), and gas-liquid chromatography of vaginal secretions (306 samples), facilitated the monitoring of variables needed to interpret the results.

Rats were implanted with stimulating electrodes in the medial forebrain bundle-lateral hypothalamus and were trained in an auto-titration brain self-stimulation paradigm. When response rates and reinforcement thresholds were stable, the animals were implanted with subcutaneous osmotic minipumps (Alzet, 2ML1) which continually delivered morphine (1.2 mg/kg/hr as the base, n = 16) or saline (10.0 microliter/hr, n = 11). After one week the pumps were removed, and the animals were again tested in the auto-titration paradigm following the daily administration of either saline (spontaneous withdrawal) or 1.0 mg/kg naloxone (precipitated withdrawal). During the eight-day withdrawal phase there was a decrease in the rate of lever-pressing for the morphine dependent animals and this was greatest on the first day. The magnitude of the decrease was greater in the precipitated withdrawal group than in the spontaneous withdrawal group and an increase in the reinforcement threshold occurred only with precipitated withdrawal. Animals in both groups lost weight when measured each morning, but the precipitated group showed greater weight loss during the day. In addition, animals in the precipitated withdrawal group had diarrhea and showed a higher incidence of withdrawal signs than both the non-dependent (control) and spontaneous withdrawal groups. These experiments provide a detailed account of opiate withdrawal following the continuous subcutaneous infusion of a small dose of morphine for one week.

In a preliminary study, autoradiography was used to localize target cells for 3H-dihydrotestosterone (DHT), a non-aromatizable androgen, in the brain of the rhesus monkey. One castrated male was injected intravenously with 2 mCi of 3H-DHT (0.42 microgram/kg), and was killed one hour later. Neurons that concentrated radioactivity in their nuclei were located in widespread areas of the brain, which included the medial and suprachiasmatic preoptic nuclei, bed nucleus of the stria terminalis, lateral septal nucleus, anterior hypothalamic area, ventromedial, arcuate, dorsomedial, and paraventricular hypothalamic nuclei, ventral premammillary nucleus, and medial, cortical, basal accessory, and lateral amygdaloid nuclei. These results indicate that the topographic distribution of androgen target neurons is considerably wider than that observed in a study using 3H-testosterone (T) in the male rhesus monkey (1). However, further work is needed to elucidate these differences before attempting correlations between behavioral activity and androgen receptors in the brain.

Rats implanted with electrodes in the lateral hypothalamus were trained in a discrete trial procedure to make a differential response (right or left lever press) in the presence or absence of brain stimulation. When a high level of accuracy (95% correct) was attained in the discrimination, testing with vehicle, RO 15–4513, diazepam (1.0–10 mg/kg), diazepam plus RO 15–4513 (1.0 mg/kg), pentobarbital (1.0–17.5 mg/kg) and pentobarbital plus RO 15–4513 began. Diazepam, at 10 mg/kg, disrupted the discrimination behavior, and it also decreased the total number of lever-presses and increased the time to complete the session. These effects were blocked by the coadministration of 1.0 mg/kg RO 15–4513. Pentobarbital produced effects similar to those of diazepam, but these effects were only reversed to a limited extent by RO 15–4513. By itself, however, RO 15–4513 also decreased the total number of lever presses and increased the time to complete the session. Results were consistent with our previous findings with alcohol and RO 15–4513, and supported the notion that diazepam and alcohol have some similar effects at the GABA-benzodiazepine receptor complex.

In six female squirrel monkeys anesthetized with a chloralose-urethane mixture, single midbrain and pontine units were tested for their responsiveness to somatosensory, vaginal, and rectal stimulation. Three monkeys (two ovariectomized, one intact) were given a series of estradiol injections that produced full cornification of vaginal smears. The other three animals, all ovariectomized, received only the oil vehicle and their smears remained uncornified throughout. Single-unit activity was sampled from comparable regions in both groups of monkeys. Units responding to tactile stimuli tended to have large receptive fields, and in the estrogen-treated monkeys they comprised a larger proportion of the sample than in the untreated monkeys (89 and 49%, respectively). Similarly, a greater proportion of the units responded to vaginal stimulation (65%) in the estrogen-treated animals than in those receiving the oil vehicle alone (40%). In contrast to the effect of estradiol treatment on neuronal responsiveness to vaginal and tactile cutaneous stimulation, units responding to nociceptive stimulation of the foot were found with equal frequency (48%) in both groups of monkeys. The finding that unit responses to tactile stimuli occurred with a greater frequency in estrogen-treated monkeys is consistent with results previously reported for midbrain and pontine units is estrous and anestrous cats. Unlike the cat, however, in the squirrel monkey there was no indication that the sizes of the peripheral receptive fields were altered by estradiol treatment.

Autoradiography was used to map sites in the primate brain at which testosterone may have sexual differentiating actions on brain function and behavior during fetal development. Two female rhesus monkey fetuses were injected in utero on days 112 and 114 of gestation respectively with 3H-testosterone, and were killed 30 and 60 minutes later. Thaw-mount autoradiography of the brains revealed the accumulation of radioactivity, representing 3H-testosterone or its metabolites, in neurons of the medial preoptic-anterior hypothalamic area, bed nucleus (n.) of the stria terminalis, ventromedial hypothalamic n., and corticomedial amygdala. Thus, it appears that steroid receptors are present in a circumscribed system in the brain of the primate fetus at this stage of development.

Rats were trained to lever-press for intracranial self-stimulation (ICSS) with electrodes in the midbrain central gray area. The effects of naloxone (0.1–30.0 mg/kg, SC) on a continous reinforcement (CRF) schedule were determined. Rats were then re-trained on higher fixed-ratio (FR) schedules, and naloxone was re-tested at FR: 5, 10, 15 and 20. Only moderate reductions in lever-pressing rates were obtained at the highest dose of naloxone under CRF and FR: 5 schedules. In contrast, pronounced, dose-dependent reductions in ICSS rates occured at FR: 10, 15 and 20. The time-course for this reduction at FR: 20 was consistent with an opiate-antagonistic action of naloxone. The modest decrease in locomotor activity produced by naloxone in a matched group of control rats was not sufficient to account for the effects on ICSS. The threshold of naloxone for reducing the rate of ICSS lever-pressing was lowered by increasing the effort and/or time requirement for each reinforcement.

(1) Available data on breeding seasonality in primates are summarized. (2) When intact female rhesus monkeys, whose Fallopian tubes had been ligated to prevent pregnancy, were paired with intact males in a laboratory in London, the timing of the annual increase (autumn) in mating activity was closely similar to that in India. (3) When ovariectomized, estrogentreated females were paired with intact males in a laboratory in Atlanta, where the photoperiod was strictly controlled, the annual increase in mating activity persisted during the first year, although it was less well-circumscribed. (4) During the second year in a fixed photoperiod, in a sham-castrated group, the annual increase in sexual activity virtually disappeared. (5) During the second year in a fixed photoperiod, however, in a castrated, testosterone-treated group, a brief increase in sexual activity occurred at the expected time. (6) When ovariectomized, estrogen-treated female rhesus monkeys were paired with castrated, testosterone-treated males in a laboratory in London, the seasonal increase in sexual activity occurred at the expected time, indicating that it was not entirely dependent upon pituitary activation of the gonads. (7) Seasonal factors operating in the female are also considered.

Sexual behaviour was studied quantitatively in eight male and seven female adult rhesus monkeys, paired in sixteen oppositely-sexed combinations, during regular test sessions conducted over a period of 13 months. Results indicated that the overall level of sexual interaction of pairs was determined largely by the male partner. The range of variation between males was large across all the indices of sexual behaviour used. Highly significant differences were found in the indices of behaviour of different males tested with the same group of females, whereas differences were smaller when different females were tested with a single male, indicating the predominant role of the latter. Paired tests showed that the menstrual cycle of the female did not influence the differences in the behaviour of males. Successive ejaculations in a test resulted in a progressive decline in sexual performance and an increase in refractory periods. The relevance of these findings for the design of experiments concerned with the control of mating behaviour in the rhesus monkey is discussed.

This paper describes a simple commutatory by which electrical stimuli can be delivered to the brain of freely moving animals studied in a self-stimulation operant conditioning paradigm. The device is inexpensive and can be constructed in the laboratory. It has proven reliable in continued use and does not distort the stimulus parameters of waveforms.