Female Squirrel Monkeys Research Articles

Birth synchrony in squirrel monkeys (Saimiri oerstedi)

The vigilance behaviors and association patterns of adult female squirrel monkeys (Saimiri oerstedi) in Parque Nacional Corcovado, Costa Rica were studied over the annual reproductive cycle to identify a possible adaptive function associated with the unusually close within-group birth synchrony prevalent in Saimiri populations. Raptor association with the troops, predation attempts, and monthly changes in food abundance were also documented. Seasonal fluctuations in food abundance probably constrained the timing of births among three contiguous troops to a two month period. The close within-troop birth synchrony (majority of births occurring within a week) is suggested to be advantageous because of intense predation pressure on neonate squirrel monkeys. Adult females with neonates cooperate in anti-predator vigilance and defense of neonates. Participation in these maternal associations may increase the probability of neonate survivorship. Variable gestation length in squirrel monkeys may reflect a lability in the duration of gestation to allow coordination of the timing of births among females in a troop.

Conversion of androgens to estrogens in the male squirrel monkey (saimiri sciureas)

Many New World primates such as the squirrel monkey have extraordinarily high plasma levels of steroid hormones including cortisol, testosterone, progesterone and vitamin D 3. While plasma estrogen levels in female squirrel monkeys apparently are approximately the same as those found in other species no information is available for males. The present results indicate that the plasma levels of estrone (E1), estradiol (E2), and E1 sulfate are approximately 10-fold higher than those found in men. Comparative in vitro studies of androgen metabolism in genital skin fibroblasts indicate that squirrel monkey cells have higher aromatase and lower 5-α-reductase activity than human cells. Estimation of aromatase activity in vivo by a radiometric assay indicates that the high plasma estrogens are derived by peripheral conversion from testicular and/or adrenal androgens.

Polymorphism of photopigments in the squirrel monkey: a sixth phenotype.

We describe here a trichromatic type of squirrel monkey that resembles Old World monkeys in having two well-separated photopigments in the red-green part of the spectrum; the cones of this phenotype have peak sensitivities close to 430, 536 and 564 nm. The existence of such animals is predicted by a genetic model that postulates three alleles for a single locus on the X-chromosome of the squirrel monkey. The three alleles correspond to three different photopigments in the red-green spectral range. A male monkey, or a homozygous female, will be dichromatic, combining short-wave cones with just one of the cone types in the red-green range. But a female monkey, if heterozygous at the locus, draws any two of the three alleles from the set. X-chromosome inactivation ensures that the two alleles are expressed in different subpopulations of retinal cone, giving the monkey the basis for trichromatic colour vision. This model requires three trichromatic types of female squirrel monkey. The photopigment complements of two types have previously been reported and microspectrophotometric data are now given for the third type. Behaviourally, this third type of trichromat gives precise Rayleigh matches that are intermediate between those of the other two types of trichromat. The polymorphism of photopigments in the squirrel monkey may be maintained by the heterozygous advantage enjoyed by the trichromatic females. This would be an instructive instance of heterozygous advantage because it is a case where X-chromosome inactivation plays a crucial role in segregating the two different gene-products into different cells.

Ovaries remain functional in squirrel monkeys (Saimiri sciureus) immunized with porcine zona pellucida 55,000 macromolecule.

Fifty female squirrel monkeys were each immunized with 200 micrograms of a purified preparation of the 55,000 macromolecule (ZP3) from porcine zona pellucida. The fertility status of these immunized monkeys, as well as the effect of ZP3 antibodies on ovarian function, was monitored. High anti-ZP3 titers were achieved (greater than 75% binding levels as determined by radioimmunoassay) and remained high (approximately 67% binding level) for the duration of this study. Hormonal evaluations indicated initial disturbances in normal ovarian steroid secretion and function that were confirmed by laparoscopic observation and oocyte production data. Histological examination of ovaries at 6-7 mo post-injection suggested an interference in folliculogenesis. No pregnancies were observed in the immunized monkeys during this period. By 10-15 mo post-immunization, hormonal and laparoscopic data indicated that ovarian function was recovering in injected monkeys despite the continued presence of high titers to ZP3. Collectively, these results demonstrate that although immunization with ZP3 initially produces disturbances in normal ovarian function that inhibit fertility, these effects are reversible. Such findings encourage the continued intensive investigation of purified porcine zona macromolecules for immunocontraceptive purposes.

Spontaneous Cryptococcosis of a Squirrel Monkey (Saimiri sciureus) in French Guyana

An old female squirrel monkey (Saimiri sciureus) with a tumor-like growth of the lower jaw died in shock after 2 months of illness. Histological studies of different tissue samples demonstrated that the pathological agent was Cryptococcus. Multiple foci of fungus existed in the thoracic cavity with essentially pulmonary and glandular localizations.

Crossed Renal Ectopia in a Squirrel Monkey (Saimiri sciureus) and an Owl Monkey (Aotus trivirgatus)

A 5-year-old female squirrel monkey, Saimiri sciureus, died with a ceco-colonic infarct. An incidental finding was renal ectopia: The left kidney was located between the common iliac arteries posterior to the bifurcation of the aorta and to the right of the body midline. An adult owl monkey, Aotus trivirgatus, was killed in renal failure due to end-stage glomerulonephritis. Fused kidneys were located on the right side and posterior to the normal position. These are examples of crossed renal ectopia with and without fusion.

Urogenital challenge of primate species with Mycoplasma genitalium and characteristics of infection induced in chimpanzees.

Eighteen male and eight female primates, representing five subhuman species, were inoculated urogenitally with Mycoplasma genitalium, a microorganism recovered from men with nongonococcal urethritis. Male rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) monkeys apparently were resistant. Female squirrel monkeys (Saimiri sciureus) and female tamarins (Saguinus mystax) exhibited low-level, genital-tract infections. Male chimpanzees (Pan troglodytes) developed an obvious genital-tract infection, with some shedding organisms for 21 weeks. M. genitalium was recovered from the blood of two of the male chimpanzees, usually when large numbers of organisms were in the urethra. Female chimpanzees generally shed organisms for 12-15 weeks. Most chimpanzees colonized with the organism exhibited increased numbers of polymorphonuclear leukocytes in the genital tract and developed a significant antibody response. The results offer substantial evidence for the pathogenicity of M. genitalium for the urogenital tract of higher primates and suggest the microorganism may have a role in human genital-tract infections.

Effects of social partners on pituitary-adrenal activity during novelty exposure in adult female squirrel monkeys

Adult female squirrel monkeys from established social groups were exposed to novel surroundings either while alone or while with an adult female partner. The partner was either familiar and judged to be affiliative with the subject, familiar and not judged to be affiliative with the subject, or unfamiliar. The females' plasma cortisol levels were higher at the end of the 25th hr of exposure than at the end of the first hr when the females were alone or with a familiar partner, but not when they were with an unfamiliar partner. In no instance were cortisol concentrations greater when females were tested alone than when they were tested in the presence of a companion. Behavioral signs of distress were greater during the first as compared to the 25th hr of exposure and showed no influence of the presence of a partner. Contact/proximity between monkeys was greater during the 25th than during the first hour of exposure in the familiar partner judged to be affiliative and in the unfamiliar partner conditions. These results contrast with those of studies investigating the disruption of the mother-infant relationship in squirrel monkeys, and provide further evidence that the pituitary-adrenal system of these animals is not responsive to the disruption of adult social relationships.

Temporal and Structural Analysis of Affiliative Vocal Exchanges in Squirrel Monkeys (Saimiri Sciureus)

AbstractAffiliative, aggressive, and vocal behaviors were observed in a group of five adult female squirrel monkeys. Affiliative partner preferences were correlated with use of the chuck vocalization. Mutually preferred partners exchanged chucks more often and with shorter latencies of response. Animals with few affiliative contacts were more likely to repeat themselves, and to obtain responses at longer latencies. Chuck exchanges neither follow nor precede changes in nonvocal behavior. Structural differences associated with the position of a chuck within a sequence were found. The peak frequency attained by several acoustic features of chucks was higher in chucks that followed closely another chuck compared with chucks that followed a silent period. We have termed these vocalizations "answer" and "question" chucks respectively. Among answer chucks, those that terminate an exchange have higher peak frequencies than those that become part of a longer sequence. These results are viewed as evidence for flexible use of signals in an exclusively linguistic context, and may be an example of categorical prosody.

Two types of trichromatic squirrel monkey share a pigment in the red-green spectral region

Microspectrophotometric measurements have been obtained for individual photoreceptors from four female squirrel monkeys ( Saimiri sciureus) that had been shown behaviourally to be trichromatic. Relative to a normal human observer, two of the monkeys required more red light for a Rayleigh match; the other two required more green light than a normal human observer. In the red-green spectral region, the first type of monkey was found to have two cone pigments with peak sensitivities at approximately 536 and 549 nm, whereas the second type was found to have pigments with peak sensitivities at approximately 549 and 564 nm. By maximum likelihood estimation it was shown that the microspectrophotometric data could be described by a model that assumed only three underlying distributions, two of which were present in each type of monkey. The fit of this model was as good as one in which a “double normal” distribution was fitted individually to the data for each animal. This result is consistent with a genetic theory that postulates in Saimiri three possible alleles for a single locus on the X-chromosome; the heterozygous female enjoys trichromacy because Lyonisation ensures that only one photopigment is manufactured in any given cone.

Seasonal changes of serum concentrations of estradiol and progesterone in Bolivian squirrel monkeys (Saimiri sciureus).

Serial measurements of estradiol (E2) and progesterone (P) were used to describe the ovarian cycle of the Bolivian squirrel monkey. Group-caged, sexually mature female squirrel monkeys, housed with males, were sampled daily between 0900 and 1100 hr. Sampling was carried out during the breeding and nonbreeding seasons, for periods of 19-20 days from September 1981 to May 1982. Seasonal differences in serum concentrations of E2 and P were found with low levels of E2 and P and an absence of preovulatory surges of E2 during the nonbreeding season. This pattern was also observed in some animals during the breeding season. An abrupt increase in serum P concentrations in December appeared to signal the onset of cycling. Cycling animals had well-defined peaks of E2 (450-9,500 pg/ml) followed by increasing levels of P, which were >200 ng/ml in some animals. After the breeding season, E2 and P levels returned to their initially low levels. Levels of both steroids in cycling animals were higher than those reported for other primates and for previous measurements made in squirrel monkeys. Cycle length based on time interval between consecutive E2 peaks varied from 6-12 days.

Visualization of Bactericidal Concentrations of Nitrofurantoin Macrocrystals in Primate and Human Urinary Tract Tissue

The distribution of orally administered nitrofurantoin macrocrystals in the urinary tract was studied by whole body radioautography in female squirrel monkeys and by bioautography of excised human kidney. The drug was rapidly absorbed and widely distributed throughout the simian urinary tract and human kidney. Concentrations of 14C drug in simian renal cortex and renal pelvis were up to 5 times plasma levels. Nitrofurantoin-derived antibacterial activity was observed by bioautography throughout sections of human kidney at concentrations that killed susceptible human urinary tract pathogens.

Infection of female squirrel monkeys (Saimiri sciureus) with trichomonas vaginalis as a model of trichomoniasis in women.

Marmosets, tamarins, owl monkeys, and squirrel monkeys were inoculated intravaginally with Trichomonas vaginalis. The latter animal species was most susceptible, trichomonads being recovered from four of six monkeys for periods ranging usually up to one month. Vaginal discharge was seen in most infected animals but polymorphonuclear leucocytes were rare. Infected animals developed serum IgG antibody responses and also local IgG and IgA responses, the latter occurring sometimes on reinoculation in the absence of organism recovery. Antibody responses were, however, of short duration and, overall, immunity was weak because two animals were reinfected on a second or subsequent challenge. Some of the observations are relevant to vaginal trichomoniasis in women.

Motion-induced alterations in 2-deoxyglucose uptake in brainstem nuclei of squirrel monkeys: autoradiographic and liquid scintillation studies.

Each of 8 young adult female squirrel monkeys were injected via a femoral vein cannula with 167 microCi/100 g body weight of 2-(1,2-3H)-deoxy-D-glucose (2-DG) (New England Nuclear, 37.3 Ci/mmol) in 0.5 ml sterile saline. 4 additional female squirrel monkeys were injected in the same manner with 100 microCi/100 g body weight of the (3H)-2-DG. 2 h after this initial injection the original 8 animals were injected with 16.7 microCi/100 g body weight of 2-(1-14C)-deoxy-D-glucose (51.3 mCi/mmol) in 0.5 ml sterile saline. The 4 additional animals were injected with 25 microCi/100 g body weight of the (14C)-2-DG. Half of the animals each dose level were restrained in the upright position with Velcro straps and a nontraumatic moulded plastic head holder on a modified animal restraint board [Withrow and Devine, 1972] with the head in the sagittal plane but tilted forward about 20 degrees. They were then subjected to horizontal rotary motion at 25 rpm together with a vertical movement of 6 inches at 0.5 Hz for 1 h in a lighted room. The other half of the animals at each dose were restrained in the same manner and maintained in a quiescent state. At the end of this period each animal was anesthetized with ketamine, and the brain was quickly dissected out and frozen in isopentane cooled to -60 degrees C with dry ice. Transverse cryostat sections (-15 degrees C) of the brainstem were cut alternately at 200 and 20 microns from the nucleus gracilis caudally through the superior vestibular nucleus rostrally. Micropunch samples of the individual vestibular nuclei, and other brainstem nuclei and areas were obtained from the 200-microns sections with a modification of the method of Eik-Nes and Brizzee with a small stainless steel punch measuring 850 microns in diameter. The frozen punch samples were prepared for liquid scintillation counting (Beckman LS7500 system). Differential (3H) and (14C) counts (cpm) were made employing external standards. The 20-microns sections were prepared for 14C autoradiography by standard methods employing Kodak SB-5 X-ray film. The (14C) autoradiographs from the motion-stimulated animals revealed a selectively high uptake of 2-DG in all of the vestibular nuclei, the lateral cuneate nucleus and the lateral reticular nucleus as compared with the corresponding structures in the control animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in spectral response properties of LGN cells in male and female squirrel monkeys.

The spectral response patterns of single cells recorded from the lateral geniculate nucleus (LGN) of the squirrel monkey (Saimiri sciureus) were examined in light of recent behavioral evidence indicating that there are significant variations in visual sensitivity and color vision within this species. The principal results from an analysis of data obtained from 1084 LGN cells were that (a) a significantly higher proportion of cells showing spectrally-opponent response patterns were recorded from female subjects, and (b) the proportion of spectrally-opponent units showing RG response patterns is very much higher in females than in males. These gender-related differences in the response patterns of LGN cells are discussed in the context of the behavioral results.

Oral ethanol intake and levels of blood alcohol in the squirrel monkey

Oral alcohol ingestion and blood alcohol levels were examined in adult female squirrel monkeys to assess the feasibility of using this primate as a model for fetal alcohol effects, In one experiment, alcohol intake was evaluated in nonpregnant animals under conditions in which the concentration of ethanol, length of ethanol exposure, and degree of liquid deprivation were varied. In another experiment blood alcohol levels were measured in pregnant animals of two subtypes that had been drinking ethanol. In a third experiment, time-dependent blood alcohol levels and behavior were evaluated in nonpregnant monkeys following intubation of specific doses of ethanol. Results showed that nonpregnant monkeys drank ethanol at concentrations of 5 to 10%, and that the amount of ethanol consumed was related to the concentration and length of time ethanol was available. When given access to a 5% ethanol solution, pregnant animals drank quantities that varied between individuals and subtypes, with maximum blood levels, measured up to 6 hr after presentation, ranging from 1 to 196 mg%. Intubation of ethanol resulted in blood alcohol levels and incoordination scores that were linearly related to dose, with maximum effects occurring 1 hr after administration. Elimination of ethanol from the blood at levels above 50 mg% occurred at a rate of about 35 mg%/hr, while the rate of clearance from the body was calculated to be approximately 250 mg/kg/hr.

Behavior and plasma cortisol following brief peer separation in juvenile squirrel monkeys.

The effects of 30-min separation from peers on behavior and plasma cortisol levels were studied in juvenile, mother-reared, female squirrel monkeys, housed in triads. Juveniles vocalized much more frequently when isolated in a novel room than they did when either undisturbed, handled only, placed with both peers in a novel room, or separated from one peer and housed with the other in the home cage. When separated from one peer in the home cage, the monkeys engaged in putative scent-marking behaviors more frequently than when undisturbed. Exposure to the novel room resulted in increased vocalizing, and decreased locomotor activity and scent marking, regardless of whether the subject was isolated or with peers. Plasma cortisol levels were elevated following all manipulations and no effects could be attributed specifically to separation or exposure to novelty. These results demonstrate that brief separation from peers can evoke a behavioral reaction in juvenile squirrel monkeys that resembles the behavioral "protest" response of maternally-separated infants, and that the response of juveniles, like that of infants, varies greatly with the separation procedure employed.

Cortisol responses under different housing conditions in female squirrel monkeys

Adult female squirrel monkeys were housed in a group, in pairs or individually. Plasma levels of cortisol obtained under basal and stress conditions once weekly for four weeks were significantly lower in pair-housed females than in those living in a social group or individually. The increment in cortisol levels after stress (induced by handling and ether anesthesia) also was smaller in females housed in pairs. The cortisol values of the pair-housed females were positively correlated with those of their partners. Basal cortisol levels in the group-living females showed a significant rank-order correlation with dominance status. This indicated that social interactions in group-living animals can influence cortisol levels in a complex manner, either increasing or decreasing them. The relatively lower pituitary — adrenal activation when a single partner was present also indicated that the social environment can affect an individual's general level of arousal and subsequently alter the response to stressful stimuli.

Hormonal and behavioral changes at puberty in the squirrel monkey

Developmental changes in the reproductive behavior and physiology of 9 male and 15 female juvenile squirrel monkeys were evaluated in a 20-month study. Plasma levels of gonadal steroids remained relatively low for this species until most animals reached puberty between 2.5 and 3 years of age. Longitudinal assessment of plasma progesterone levels indicated that the onset of ovarian cycles tended to be synchronized between females although the 5 heaviest females began to cycle earlier than the rest. The heavier females reached puberty at a time which was appropriate to their birth in the wild, whereas most of the remaining females conceived 6 months later during a second period of reproductive activity that coincided with the laboratory mating season. Pubescent males underwent their first seasonal elevation in plasma testosterone levels during the second period and its onset was synchronized across all males. Thus, even in the absence of adults, pubertal processes in the squirrel monkey were strongly influenced by the seasonal breeding pattern. In addition, behavioral observations revealed that social maturation closely parallels reproductive ability in females, whereas males enter a protracted subadult stage after puberty.

Anatomical distribution and sensory properties of brain stem and posterior diencephalic neurons responding to genital, somatosensory, and nociceptive stimulation in the squirrel monkey

In chloralose-urethane-anesthetized female squirrel monkeys, 325 single units sampled from a region extending from the caudal medulla to the posterior diencephalon were examined for responsiveness to genital, rectal, innocuous somatosensory, and various forms of nociceptive stimulation. The units were highly responsive, with 84% responding to at least one stimulus type. The responsive units were widely distributed in the brain stem tegmentum, deep tectum, and posterior diencephalon. Very few neurons responded to only one type of stimulation. The patterns of convergent responsiveness to the various stimulus types were not, however, a simple random function of unit responsiveness to each type of stimulus per se. Unit responses to vaginal stimulation consisted of simple increases or decreases in firing which outlasted the duration of the probing stimulus in most cases. Some units responded more strongly to cervical than to vaginal tract stimuli. The somatic receptive fields of units responding to touch-pressure stimuli were typically bilateral and quite extensive. A forceps pinch of nociceptive intensity elicited a response from 64% of the cells, and of these, 11% showed significant linear correlations between their firing rates and increasing pinch pressure in the nociceptive intensity range. Brief, localized nociceptive thermal stimuli and needle pricks failed to elicit responses from the neurons tested. Based on a comparison between the response properties of monkey brain stem neurons and the previous findings for rat and cat neurons, it was concluded that brain stem cells display species-typical sensory characteristics which have parallels in the properties of behavioral responses of these three species to genital and other sensory stimuli. Properties of unit responses to nociceptive stimuli have implications in relation to the neural mechanisms of first and second pain.