Morphometric analysis of the zona pellucida and ooplasm of squirrel monkey (Saimiri sciureus) eggs

The objective of this study was to correlate the thickness of the zona pellucida (zona) with egg (oocyte) maturity determined through a widely-used method of assessing oocyte maturation namely, the evidence for cumulus and corona cells expansion. Measurements of the zona of cultured oocytes were recorded at 0, 3, 6, 24, and 48 hr after laparoscopic oocyte retrieval from hormonallystimulated squirrel monkeys. The results indicated that at the time of oocyte retrieval, oocytes that were classified as mature had thicker zonae compared with immature oocytes. The zona layer of the mature oocyte expanded to a maximum after 6 hr of incubation while the zona layer of the immature oocyte became compressed. The diameter of the mature oocyte (minus the zona and perivitelline space) became smaller with time while the immature oocyte diameter remained relatively unchanged. The correlation between the maturational state of the oocyte and the thickness of the zona layer suggest the possible application of zona morphometric evaluations as an indicator of oocyte maturation.     

The effect of relative humidity on osmoregulation in the squirrel monkey (Saimiri sciureus)

Osmoregulatory balance was studied in four young, tamed squirrel monkeys (Saimiri sciureus, Columbia) after acclimatization to relative humidities (rh) commonly used in laboratories (30% and 50%) and to higher humidities representative of the dry and wet seasons in their natural environment (75% and 95%). The temperature was constant at 25°C and the light-dark cycle was 12:12 hours. The animals were maintained in large metabolism cages and were free moving. Water consumption and urine flow rates increased at each higher humidity from 30% rh to 75% rh and then decreased at 95% rh (p<0.05). Fecal water loss was greater with higher humidity (p<0.05). Evaporative water loss remained relatively constant until a break between 75% and 95% rh, at which point it decreased dramatically (p<0.05). Expressed relative to total water intake, evaporative water loss demonstrated a progressive decrease with increasing humidity: 65%, 56%, 51%, and 42%, at 30%, 50%, 75%, and 95% rh. This indicates that as the humidity approaches maximum saturation, not only is the evaporative water loss component necessarily diminished, but also the apparent precipitation of alternate strategies of thermoregulation leads to a reduction in the overall water requirements of the animals. Potassium/sodium excretion ratios were relatively constant at 30%, 50%, and 95% rh but decreased significantly at 75% rh (p<0.05). As a reflection of adrenocorticosteroid activity, this suggests that at 25°C, 75% rh is an optimal humidity in the maintenance of squirrel monkeys. The significant osmoregulatory alteration occurring between 75% and 95% rh provides further evidence that relative humidity may be an important factor in the seasonal physiological cycles of the squirrel monkey. In conducting the research described in this report the investigators adhered to the “Guide for Laboratory Animal Facilities and Care,” as promulgated by the Committee on the Guide for Laboratory Animal National Academy of Sciences, National Research Council.     

A study of correlates of hand preferences in squirrel monkeys (Saimiri sciureus)

The purpose of this study was to test the influence of sex, age, social rank, matriline membership, posture, and visual and tactual motor control on manual preferences inSaimiri sciureus. A well-established social group of 12 squirrel monkeys, aged 2 to 14 yrs and consisting of two matrilines with social rank known for each animal, was presented with four different food-reaching tasks and assessed for hand preferences with a minimum of 100 reaches per animal. Frequency of occurrence of hand preferences at the group level and degree of hand preferences at the individual level depended on posture and on whether the reaching act took place under visual or tactual guidance. Sex, age, social rank, and matriline membership were not found to determine frequency of occurrence, direction or degree of hand preferences with the exception of one task in which a significant negative correlation between the degree of hand preference and age was found. Nine out of 12 monkeys showed task-dependent changes in the hand they used preferentially while only three animals preferred the same hand in all four tasks. Significant preferences for the use of right or left hand on a given task were distributed almost equally between individuals. Thus, the results of this study suggest task-specific demands like posture and/or whether reaching was visually or tactually guided to be the major correlates of hand preferences in food-reaching tasks in squirrel monkeys.     

Genetically determined antigens of squirrel monkey (Saimiri sciureus) IgG

Alloantigens of squirrel monkey (Saimiri sciureus) IgG were studied using alloantisera prepared by cross-immunizations among four subspecies. The results demonstrated the occurrence of IgG antigenic polymorphism. Three distinct Fd fragment allotypes were detected. Greater alloantigenic complexity occurred among Colombian and Peruvian squirrel monkeys, which occupy the more central regions of the geographic range; Bolivian and Guyanan monkeys, which occupy the extremes of the range, expressed less alloantigenic complexity.     

Relative taste preferences for food-associated sugars in the spider monkey (Ateles geoffroyi)

The purpose of the present study was to determine relative taste preferences for five food-associated sugars inAteles geoffroyi. Using two-solution choice tests of brief duration (5 min) four adult spider monkeys were given the choice between all binary combinations of sucrose, fructose, glucose, lactose, and maltose presented in equimolar concentrations of 20, 50, 100, and 200 mM respectively. Preferences for individual sugars were stable across the concentrations tested and indicate an order of relative effectiveness (sucrose>fructose>glucose≥lactose≥maltose) which is similar to results obtained with the same method in the squirrel monkey and to findings on relative sweetness in man. These results support the assumption that the order of relative effectiveness of the sugars under investigation found in the present study may represent a general pattern of preference in frugivorous and perhaps all primates.     

Characterization of Gilbert-like syndrome in squirrel monkeys (Saimiri sciureus)

Bolivian squirrel monkeys, unlike those of Brazilian origin, exhibit a marked fasting hyperbilirubinemia (FH) similar to that observed in Gilbert's syndrome in man. Since no delays in the hepatic clearance of sulfobromophthalein or indocyanine green are present, the Bolivian monkey appears to be similar to Gilbert's type I syndrome. FH can be significantly decreased by either phenobarbital or tin-protoporphyrin pretreatment. Nicotinic acid-induced hyperbilirubinemia and delayed tolbutamide clearance were not observed as in the human syndrome.     

Neuronal cytoplasmic inclusions in the dorsal horn and supraoptic nucleus of the squirrel monkey,Saimiri sciureus

In the squirrel monkey (Saimiri sciureus) two types of cytoplasmic inclusion bodies have been observed sporadically in neurons of both the dorsal horn (Rexed's laminae I-III in the lumbosacral region) and the supraoptic nucleus. One of these, designated here the "vesicular body", is a round inclusion which measures up to 1.4 mu in diameter. It occurs only in perikarya and is composed of vesicular-like chambers 300-400 A in diameter. We have not found previous references to this structure in the literature, but its 50 A substructural particles are similar in size to those described in nematosomes. The other inclusion, a "filamentous whorl", is found in nerve cell bodies and dendrites and it is structurally similar to the Hirano body. The structure measures up to 2.2 mu in diameter and is composed of circularly arrayed filaments which vary in configuration and size depending on the plane of section. There are no indications that the vesicular body and the filamentous whorl are in any way related to each other; and usually both are not found in the same cell profiles.     

Gustatory thresholds for food-associated sugars in the spider monkey (Ateles geoffroyi)

The purpose of this study was to determine gustatory thresholds for five different food-associated sugars in Ateles geoffroyi. Using a two-bottle test, three adult spider monkeys were found to significantly prefer concentrations as low as 3 mM sucrose, 15 mM fructose, 20 mM glucose, and 10 mM lactose over tap water. Maltose was significantly discriminated down to 20 mM with individual animals showing either a preference or an aversion, or an inverted U-shaped function of preference toward higher concentrations of this carbohydrate. The results showed the spider monkey to respond to lower sugar concentrations compared to other nonhuman primates tested so far and thus support the assumptions that Ateles geoffroyi may use sweetness as a criterion for food selection, and that the remarkably high sweet-taste sensitivity of this frugivorous species might be correlated with its dietary specialization. © 1996 Wiley-Liss, Inc.     

Susceptibility of squirrel monkey (Saimiri sciureus) to infection by mammalian schistosomes.

In a study of host-schistosome relationships, the squirrel monkey (Saimiri sciureus) was exposed to 500 cercariae of Schistosoma bovis (Kenya), S. intercalation (Cameroon), S. mattheei (South Africa), 2 strains of S. mansoni (Puerto Rico and South Africa), 2 strains of S. rodhaini (Uganda and Kenya), and Schistosomatium douthitti (North America). It is apparent that the squirrel monkey can be employed as an experimental host for a broad range of mammalian schistosomes. Based upon cercariae-adult worm ratios, it is a good host for S. intercalatum, S. mattheei, the Puerto Rico and South Africa strains of S. mansoni, and Schistosomatium, but only a fair host for S. bovis and the Uganda and Kenya strains of S. rodhaini. Individuality of host-parasite relationships is borne out by the great ranges recorded for egg deposits in different organs as well as by total body egg counts and eggs/worm pair.     

Experimental American leishmaniasis in the Brazilian squirrel monkey (Saimiri sciureus): lesions, hematology, cellular, and humoral immune responses

Unulcerated cutaneous lesions appeared and persisted in squirrel monkeys experimentally infected with Leishmania braziliensis braziliensis or L. b. panamensis. Peripheral blood mononuclear cell (PBMC) numbers increased following infection, and cultured PBMCs from infected monkeys proliferated in response to parasite antigens. The responses of PBMCs to mitogens were not suppressed in infected monkeys. Elevated levels of leishmania-specific immunoglobulins M and G were also observed. Thus, the squirrel monkey is susceptible to American leishmaniasis and is capable of responding to the infection with measurable cellular and humoral immunity.     

Detection and cultivation of intestinal trichomonads of squirrel monkeys (Saimiri sciureus)

Routine examinations of fecal samples from squirrel monkeys suggested that intestinal trichomonads might be common inhabitants of these animals. In pursuit of these observations, microscopic examination of fecal suspensions and cultures have demonstrated a 100% incidence of trichomonads in 30 arbitrarily selected animals from a colony of more than 300 housed in groups of ten. The most prominent species was Pentatrichomonas hominis. A not yet fully characterized tritrichomonad was also found on several occasions. The main obstacle in establishing individual strains in culture was the presence of bacterial and fungal flora in the samples. Nevertheless, abundant cultures were obtained from 28 animals by inoculation of fecal suspensions into tissue cultures with appropriately formulated medium and high concentration of antibiotics. In several unattended cultures maintained at room temperature, the flagellates retained motility for at least 4 months. This long survival may explain the widespread occurrence of the parasites within a confined animal community.     

Gustatory Responsiveness to food-associated acids in the spider monkey (Ateles geoffroyi)

The gustatory responsiveness of four adult spider monkeys to five food-associated acids was assessed in two-bottle preference tests of brief duration (3 min). The animals were given the choice between a 30 mM sucrose solution and defined concentrations of citric acid, ascorbic acid, malic acid, acetic acid, or tannic acid dissolved in a 30 mM sucrose solution. With this procedure,Ateles geoffroyi was found to significantly discriminate concentrations as low as 5 mM ascorbic acid, citric acid, and acetic acid, 10 mM malic acid, and 0.1 mM tannic acid from the alternative stimulus. With the latter two substances, the monkeys rejected all suprathreshold concentrations tested, whereas with the former three substances, the animals showed an inverted U-shaped function of preference, i.e. they rejected high concentrations, but significantly preferred low but detectable concentrations of these acidic tastants over the alternative sweet stimulus. The results showed (1) the spider monkey to respond to the same range of acid concentrations as other nonhuman primate species; (2) thatAteles geoffroyi, is able to detect food-associated acids at concentrations well below those present in most fruits; and (3) that unlike most other primate species tested so far, spider monkeys do not generally reject acidic tastants but show a substanceand concentration-dependent change in responsiveness that may range from rejection to preference. The results support the assumptions that spider monkeys may use sourness and/or astringency of food-associated acids as a criterion for food selection, and that the gustatory responsiveness ofAteles geoffroyi to acidic tastants might reflect an evolutionary adaptation to frugivory.     

Stillbirth of twins in a squirrel monkey (Saimiri boliviensis peruviensis)

This is the first published report of twinning in a squirrel monkey (genus Saimiri). The mother survived but the twins, both male and close to full term, were stillborn     

Pentastomid nymph from the brain of a squirrel monkey (Saimiri sciureus). II. Morphology of the host response

A Porocephalus nymph found in the meninges of a squirrel monkey was encapsulated by connective tissue cells and fibrils presumably derived from the pia mater. The capsule was composed of an inner layer (IL) adjacent to the nymphal integument and an outer layer (OL) adherent to the brain surface. Separating the two layers was a capsular space. The IL was lined by a granular material adjacent to the nymph surface and possessed impressions of annulae and the apical pits of chloride cells. The surface of IL facing the capsular space was characterized by a monolayer of cells possessing extensive anastomosing plasmalemmal processes. The OL was composed of several tiers of fibroblasts and associated collagen fibrils that adhered to the brain surface in the form of a thickened pia mater. It is suggested that the capsule was formed by a modification of the pia that isolated the nymph and created an "intracapsular space" with specialized lining cells to facilitate fluid exchange.     

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.     

Adaptation of the Plasmodium falciparum FCB strain for in vitro and in vivo analysis in squirrel monkeys (Saimiri sciureus)

The asexual blood stages of the Plasmodium falciparum parasite are responsible for inducing the clinical symptoms and the most severe presentations of malaria infection that causes frequent mortality and morbidity in tropical and subtropical areas of the world, making the blood stages of infection a key target of new malaria treatment and prevention strategies. Progress towards the development of more effective treatment and prevention strategies has been hindered by the limited availability of infection models that permit the sequential analysis of blood stage parasites in vitro followed by in vivo analysis to confirm therapeutic benefits. To advance a model for in vitro and in vivo analysis of blood stage parasites, we examined nine laboratory strains of P. falciparum to determine which strains could adapt to growth in vivo in splenectomized squirrel monkeys (Saimiri sciureus). Only one of the nine laboratory strains tested, the FCB strain, adapted to in vivo growth. Morphological analysis show that the adapted ring-stage parasites have a different morphology from original parasites cultured in vitro, and more often they were found to localize at the edge of the infected red blood cell. No remarkable differences were observed for both trophozoites and schizonts. The adapted strain can be cultured back in vitro similar to the original parasite, indicating that the adapted parasite can develop both in vitro and in vivo. This squirrel monkey-adapted P. falciparum parasite is expected to be suitable and is advantageous for the research and development of vaccines and antimalarial drugs.     

Chuck Vocalizations of Wild Female Squirrel Monkeys (Saimiri sciureus) Contain Information on Caller Identity and Foraging Activity

Analysis of the acoustic signal of the chuck vocalizations of adult female squirrel monkeys (Saimiri sciureus) in Parque Nacional de Manu, Peru, revealed consistent differences within and between individuals. We quantified four peak frequency parameters: (a) the peak frequency of single chucks, (b) the first and (c) the second peak frequencies of double chucks, and (d) the peak difference: the difference between the first and the second double chuck peaks. One-way ANOVAs and a posteriori comparisons of these variables revealed that each distinguished more than 70% of all possible pairs of females. When all double chuck measures were included in a discriminant analysis, 57% of double chucks were correctly assigned to the caller. Another category of information potentially encoded in the acoustic structure of chuck vocalizations is foraging activity. When the chucks of squirrel monkeys during foraging and nonforaging activities were compared, the single chuck peak frequency, and the first peak frequency and the peak difference of double chucks, were significantly reduced during foraging contexts. Previously Boinski and Mitchell (1992) concluded that chucks facilitate group cohesion among widely dispersed troop members by providing information of the location of callers; the rate of chucks produced by an adult female increases as she becomes more spatially and visually separated from other adult females. The additional information potentially conveyed by chucks on caller identity and foraging activity documented in these new analyses further emphasizes the role chucks serve to enhance group coordination and cohesion.     

Case report: Esophageal Spirura infection in a squirrel monkey (Saimiri sciureus)

Necropsy of an adult, wild-born squirrel monkey (Saimiri sciureus) revealed 30 to 40 esophageal nematodes. The anterior end of each nematode was firmly attached to the mucosa, with the remaining portion free in the lumen. Histologic changes were limited to the superficial mucosa, where the epithelium adjacent to the nematode was hyperplastic and increased keratin formed a bridge over the body of the parasite. The nematode was identified as belonging to the genus Spirura. The number of parasites in this animal was considered significant and contributed to the death of the animal.