Neuroendocrine and behavioral effects of m-chlorophenylpiperazine administration in rhesus monkeys

The effects of m-chlorophenylpiperazine (mCPP), a serotonin receptor agonist, on the release of plasma prolactin (PRL), growth hormone (GH), and cortisol in the rhesus monkey were studied. mCPP was administered intravenously at doses of 0.5, 1.5, and 3.0 mg/kg. GH and cortisol were increased significantly at all doses whike PRL was significantly increased only following administration of 3.0 mg/kg mCPP. mCPP administration also produced behavioral alterations in each monkey, including sedation, penile erection, and defecation. PRL, GH and behavioral responses to mCPP were completely blocked by pretreatment with the serotonin anatgonist metergoline (MTG). However, pretreatment with MTG failed to entirely antagonize the cortisol response to mCPP. These data suggest that mCPP has prominent neuroendocrine and behavioral effects which are mediated, in part, by serotonergic mechanisms.     

Ovarian hormones and food intake in female guinea pigs and rhesus monkeys

Food intake was measured during ovarian cycles of female guinea pigs and rhesus monkeys. In both species, the period of lowest food intake occurred around the expected time of ovulation. Feeding levels were lowest in the guinea pig during the time of estrus, estrus being estimated on the basis of vaginal membrane changes. Minimum food intake in the rhesus occurred prior to the midpoint of the menstrual cycle, on Day 13, approximately 15–16 days before the next menstruation. In ovariectomized females of both species, either multiple or single estradiol injections significantly lowered food intake. Single progesterone injections to such females were found to have no significant effect on levels of feeding.     

Food preference of young rhesus monkeys fed marginally zinc deficient diets

Zinc deprivation has been shown to produce hypogeusia in rhesus monkeys but the possible consequences of altered taste sensitivity for food preference and selection is not known. We studied 13 rhesus monkeys (2.5 to 3 years of age) for food preference in a structured choice situation. These animals were fed two levels of dietary zinc: marginally zinc deprived (fed 4 μg zinc/g diet from conception and throughout development;N=6), or control (fed a 100 μg zinc/g diet throughout the study;N=7). Preference for familiar vs unfamiliar food items, order of food preferences, persistence in retrieval of preferred and nonpreferred foods, and preference under four deprivation periods were examined. Animals were offered a choice of two food items, both containing minimal zinc levels, and food choice and latency of choice were measured. Results indicate that animals fed the marginal zinc diets had reduced preference for unfamiliar foods relative to controls and different patterns of food preference. These results may be relevant to maintenance of appropriate food selection in marginally zinc deprived populations.     

Vitamin A intake of captive rhesus monkeys exceeds national research council recommendations

The specific vitamin A (VA) requirements of nonhuman primates have not been adequately determined via species-specific scientific experimentation. Recommendations are considered to be similar to human requirements, particularly for Old World monkeys. Manufacturers of primate diets add an excess of most nutrients in order to compensate for losses that occur during storage and handling. Moreover, the form of VA used in these diets is synthetic VA esters, which are readily absorbed and stored. Primates in the wild obtain much of their VA from provitamin A carotenoids, which are cleaved as needed to form active VA and are considered nontoxic, unlike preformed VA. The purpose of this study was to determine what types of feed are used at the National Primate Centers and to estimate the amount of VA that rhesus macaques are consuming. Five of the eight centers responded to a short survey that was administered through telephone and electronic mail contacts. VA intakes are well above those that are considered adequate for humans, and VA concentrations in commercially prepared standard primate diets exceed National Research Council (NRC) recommendations by as much as four times. Thus, the VA provided in primate diets should be reevaluated with regard to the concentration and form of the vitamin used.     

Reproductive capacity of rhesus monkeys following bilateral ovarian x-irradiation.

The effect of ovarian X-irradiation of the rhesus monkey upon menstrual cycle length, duration of menstrual bleeding, excretion of gonadotrophin in the urine, concentration of gonadotrophin in the pituitary gland, ovarian histology, and breeding performance was investigated. Doses below 4000 R had no significant effect upon the above criteria. By contrast, doses of 4000 to 7000 R rapidly induced amenorrhoea in most animals, but unexpectedly these animals did not excrete greater than normal amounts of gonadotrophin. The pituitary content of gonadotrophin in cyclic and non-cyclic animals was not significantly different. Some births occurred in the animals which had been X-irradiated.     

Self-agency in rhesus monkeys

Rhesus monkeys (Macaca mulatta) have shown the ability to monitor their own mental states, but fail the mirror self-recognition test. In humans, the sense of self-agency is closely related to self-awareness, and results from monitoring the relationship between intentional, sensorimotor and perceptual information. Humans and rhesus monkeys were trained to move a computer icon with a joystick while a distractor icon partially matched their movements. Both humans and monkeys were able to monitor and identify the icon they were controlling, suggesting they have some understanding of self-agency.     

Endocardiosis in rhesus monkeys

Endocardiosis was diagnosed as an incidental finding in two rhesus monkeys. The gross and histologic appearance of the lesions was described, and the similarity of this lesion to lesions of endocardiosis as found in dogs and man was discussed.The animals used in this study were handled in accordance with the Guide for Laboratory Animal Facilities and Care established by the National Academy of Science, National Research Council.     

Caudate electrochemical response following amphetamine administration in pigtail monkeys

In vivo electrochemical and heart rate (HR) recordings following amphetamine (AMPH) (0.8 mg/kg) and saline administration were made from caudate in four young adult pigtail (M. nemestrina) monkeys using linear sweep voltammetry. One hour following drug injection, two familiar humans served as test stimuli, and were visually exposed to the animals for 15-minute epochs each. One was threatening to the animals, and one was not. AMPH produced a significant increase in height of the electrochemical peak thought to represent oxidation of dopamine and its metabolites. Heart rate (HR) decreased during the time the peak height was increasing. HR and peak height increased during presentation of both humans under both AMPH and saline conditions. However, peak height increase under AMPH, but not saline, conditions discriminated the negative from neutral stimulus. The findings demonstrate that AMPH administration induces a significant increase in the height of a major electroactive peak in the caudate nucleus of pigtail monkeys, and further that such amphetamine-induced increases can be manipulated by altering the affective and/or emotional state of the animal.     

Salmon calcitonin reduces food intake through changes in meal sizes in male rhesus monkeys

Amylinergic mechanisms are believed to be involved in the control of appetite. This study examined the effects of the amylin agonist, salmon calcitonin, on food intake and meal patterns in adult male rhesus monkeys. Fifteen minutes before the onset of their 6-h daily feeding period, monkeys received intramuscular injections of various doses of salmon calcitonin (0.032, 0.056, 0.1, 0.32, and 1 microg/kg) or saline. Salmon calcitonin dose dependently reduced total daily and hourly food intake, with significant decreases at the 0.1, 0.32, and 1 microg/kg doses. Daily food intake was reduced by approximately 35%, 62%, and 96%, at these doses, respectively. An analysis of meal patterns revealed that size of the first meal was significantly reduced across the dose range of 0.056 to 1 microg/kg, while average meal size was reduced with the 0.32 and 1 microg/kg doses. Meal number was only affected at the 1 microg/kg dose. Repeated 5-day administration of the 0.1 microg/kg dose resulted in a reduction in daily food intake only on injection day 2, while significant reductions in food intake were observed on all five injection days with a 0.32 microg/kg dose. Daily food intake was also reduced for 1 day after the termination of the 5-day injections of the 0.32 microg/kg salmon calcitonin dose. These sustained reductions in intake were expressed through decreases in meal size. These data demonstrate that salmon calcitonin acutely and consistently decreases food intake mainly through reductions in meal sizes in nonhuman primates.     

Malignant uterine mesotheliomas in squirrel monkeys following diethylstilbestrol administration

10 adult female squirrel monkeys were implanted subcutaneously with 4 60 mg pellets of diethylstilbestrol (DES); 4 animals were implanted with cholesterol pellets to serve as controls. Animals were killed at 5, 9, 11, and 14 months after insertion of pellets. All animals implanted with DES had evidence of extreme estrogenic stimulation, including marked edema of the labia, heavy vaginal cornification, and enlargement of the uterine corpus. There were several stages of uterine lesions, in general in proportion to the duration of treatment. The less advanced lesions were restricted to hyperplasia and hyperthrophy of the serosal cells. In more advanced lesions the myometrium was infiltrated; in the most advanced cases there was invasion of the endometrium. The 7 most advanced uterine tumors were classified as malignant mesotheliomas. Cholesterol-treated controls did not have any significant lesions. These observations indicate that DES is carcinogenic in the squirrel monkey, as it has been demonstrated to be in other lower mammalian species.     

Changes in the behavior of laboratory-reared rhesus monkeys following the threat of separation

Four heterosexual pairs of three-year-old rhesus monkeys were either repeatedly separated from each other for 30-min or not separated. Prior to each separation, a transfer cage was displayed at the front of the cage to serve as a cue that the pair would be separated. After only a few trials, the animals displayed disturbance, particularly in the form of stereotyped pacingprior to the separation. Practical considerations related to laboratory methodology, a theoretical discussion concerning the fear of separation in monkeys and man, and the need for attention to individual differences in response to separation were emphasized.Supported by NIH grants MH22253, HD04335, and RR00169, to Dr.Gary Mitchell; whose assistance is gratefully acknowledged.     

Menopause in female rhesus monkeys

Fifteen female rhesus monkeys (Macaca mulatto), ranging in age from 8 to 34 years, were studied for one year to characterize the endocrine and menstrual changes associated with menopause in this species. Five monkeys were premenopausal; these younger monkeys, ages 8–11 years, menstruated and showed cyclic ovarian activity during the 12–month study period, as evidenced by menses and periodic elevations of serum estradiol (E₂) and luteinizing hormone (LH) concentrations. Four females, ages 24–26 years, were in transition to menopause. Two of these perimenopausal females menstruated and secreted E₂ and LH in a periodic fashion; the other two females showed elevated LH concentrations, consistently low E₂ levels, and no evidence of menstruation. Six females, ages 27–34 years, were clearly postmenopausal; LH concentrations were high, whereas E₂ concentrations were uniformly low. There was a significant inverse correlation between basal E₂ concentrations and age, and a significant positive correlation between age and LH concentrations across all 15 animals. Hormonal changes indicative of ovulation, when they occurred, were generally restricted to the winter and early spring months. Histological analysis of ovaries from four postmenopausal females revealed little or no evidence of active folliculogenesis. These data indicate that menopause in female rhesus monkeys does not occur until the second half of thethird decade of life. © 1995 Wiley-Liss, Inc.