Elevated ovarian expression and serum concentration of α inhibin in the luteal phase during follicular development in the squirrel monkey (Saimiri boliviensis) compared to the human

The goal of the present investigation was to determine in the squirrel monkey the source and pattern of inhibin, a hormone known to effect reproductive steroid levels via pituitary and ovarian mechanisms. Since this seasonally polyestrous species is known to have elevated serum levels of reproductive steroids compared to other primates, the levels of ovarian alpha subunit mRNA expression and serum total alpha inhibin, estradiol, progesterone, and luteinizing hormone were measured and compared to human levels. Expression of the alpha subunit was robust in monkey luteal tissue compared to expression in human luteal tissue. Squirrel monkey serum inhibin peaked 4 days after the luteinizing hormone surge and correlated with progesterone changes. These luteal serum levels of inhibin were greater than 12 times higher than the human levels yet bio‐LH activities were less than in the human during the luteal phase. Inhibin concentrations during the non‐breeding season were generally half the levels measured in the breeding season and undetectable in ovariectomized animals. However, exogenous FSH stimulation induced a marked rise in inhibin, which correlated with an estradiol rise. In conclusion, abundant alpha inhibin subunit expression in the luteal ovary of the squirrel monkey and loss of serum delectability in ovariectomized animals indicates that the principle source of inhibin in the squirrel monkey is the ovary. Elevated serum inhibin levels during the luteal phase concurrent with ovulatory‐size follicular development is unique among species studied thus far. Possible simultaneous inhibin production from both follicular and luteal tissue may be responsible for the exceptionally high inhibin levels. Am. J. Primatol. 47:165–179, 1999. © 1999 Wiley‐Liss, Inc.     

Determination of lactogenic activity in the serum of the squirrel monkey (Saimiri boliviensis) using the Nb2 lymphoma bioassay

Determination of squirrel monkey prolactin by immunoassay has been hampered by the lack of antiserum specific to prolactin from this species. As an alternate method, we have investigated whether the Nb2 lymphoma bioassay could be adapted for routine measurement of the lactogenic activity of samples of squirrel monkey serum. The growth of the Nb2 cells is absolutely dependent on the presence of lactogens in the culture medium. The cells were maintained in Fisher's medium supplemented with 10% horse serum, 10% fetal calf serum (FCS), and 10^?4M β-mercaptoethanol. For each assay, the cells were plated at an initial density of 1 × 10⁵ cells/ml in 22-mm 12-well dishes in the above medium, but devoid of FCS. Serum samples were heated to 56°C for 20 minutes to abolish the unusually high cytolytic complement activity of squirrel monkey serum and were incubated for 72 hours with Nb2 cells at serial dilutions from 1/40 to 1/2,560. Growth curves were generated with pooled samples of squirrel monkey serum, and the level of lactogenic activity was estimated using a calibration growth curve generated with known concentrations of purified rhesus monkey prolactin standard. We have found that the Nb2 lymphoma bioassay provides a sensitive and adaptable means for determination of lactogenic activity in the serum of the squirrel monkey.     

Midcycle and luteal elevations of follicle stimulating hormone in squirrel monkeys (Saimiri boliviensis) during the estrous cycle

Follicle stimulating hormone (FSH) has fundamental importance in reproductive function, but its cyclic pattern has not previously been described in the squirrel monkey, due primarily to the lack of a suitable assay. An homologous radioimmunoassay (RIA) based on recombinant cynomolgus FSH measured changes in serum FSH relative to patterns of bioactive luteinizing hormone (LH), estradiol, and progesterone during the estrous cycle. FSH was observed to have a sharp peak during the late follicular phase coincident with the LH surge and then rose again during the luteal phase. Estradiol was low except for the midcycle rise, suggesting an inhibitory relationship. The rat granulosa cell in vitro FSH bioassay confirmed high levels of this hormone. Measurement of FSH in the squirrel monkey has found a pattern different from Old World primates in the luteal phase, which may provide insight into the reproductive mechanisms of this species.     

Adrenal 11-hydroxylase activity in a hypercortisolemic New World primate: adaptive intra-adrenal changes

The squirrel monkey, a representative New World primate, has high plasma cortisol and aldosterone concentrations when compared to Old World primates. We measured adrenal mitochondrial 11-hydroxylase (11-OHase) activity in squirrel monkeys and in two representative Old World species (cynomolgus and rhesus macaques) in an effort to explain these elevated plasma glucocorticoid and mineralocorticoid levels. The activity of 11-OHase was 5-fold higher in the squirrel monkey than in the Old World species tested. Calculated 11-OHase Vmax was different in the squirrel monkey and the cynomolgus. However, the Km values were similar in the New World primate when compared to cynomolgus. The ability of metyrapone to block 11-OHase was less in the former than in the latter. The data are consistent with the hypothesis that the squirrel monkey adrenal cortex possesses an increased number of 11-hydroxylase enzyme units compared to that of Old World primate species, and is therefore more efficient in producing cortisol. This difference in 11-OHase activity in the squirrel monkey, in addition to other previously reported adrenal steroidogenic enzyme alterations, may be adaptive in nature, favoring increased cortisol and aldosterone production in this and possibly other New World primate species.     

Increased production of 11beta-hydroxysteroid dehydrogenase type 2 in the kidney microsomes of squirrel monkeys (Saimiri spp.)

In squirrel monkeys (Saimiri spp.), cortisol circulates at levels much higher than those seen in man and other Old World primates, but squirrel monkeys exhibit no physiologic signs of the mineralocorticoid effects of cortisol. These observations suggest that squirrel monkeys have mechanisms for protection of the mineralocorticoid receptor (MR) from these high levels of cortisol. We previously showed that the serum cortisol to cortisone ratio in these animals is low relative to that in human serum, suggesting that production of the MR protective enzyme, 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), is increased in squirrel monkeys. Here, we directly evaluate whether increased production of 11beta-HSD2, which inactivates cortisol to cortisone, is a mechanism for protection of MR. In vitro assays showed that 11beta-HSD2 activity in squirrel monkey kidney microsomes was 3 to 7 times higher than that seen in kidney microsomes from pig or rabbit. 11beta-HSD2 protein detected by Western blot analysis was 4 to 9 times greater in squirrel monkey microsomes than in pig or rabbit microsomes. Comparison of the effect of expression of either human or squirrel monkey 11beta-HSD2 on MR transactivation activity showed similar inhibition of MR response to cortisol by both enzymes, indicating that the intrinsic activities of the human and squirrel monkey enzymes are similar. These findings suggest that one mechanism by which squirrel monkeys protect the MR from activation by high cortisol levels in the kidney is by upregulation of 11beta-HSD2 activity through increased production of the enzyme.     

Postnatal changes of IgG and IgM levels in squirrel monkeys (Saimiri sciureus)

Serum IgG and IgM levels were measured in domestically bred squirrel monkeys (Saimiri sciureus) ranging in age from 0 days to 42 months, as well as in adult squirrel monkeys from the wild estimated to be 60 months or older. The results indicated that the transplacental transfer of IgG occurs in the squirrel monkey but the transferability is lower in the squirrel monkey than in the cynomolgus monkey. Immune response in the squirrel monkey occurs just after birth, as shown by IgM production.     

Impaired transactivation of the glucocorticoid receptor cloned from the Guyanese squirrel monkey

Squirrel monkeys are among a diverse group of New World primates that demonstrate unusually high levels of circulating corticosteroids and glucocorticoid receptor (GR) insensitivity. Recent evidence suggests that overexpression of an immunophilin impairs dexamethasone binding to GR in the Bolivian squirrel monkey (Saimiri boliviensis). Here we describe the cloning, expression, and functional characterization of GR from the closely related Guyanese squirrel monkey (S. sciureus). The cloned Guyanese squirrel monkey GR (gsmGR) cDNA closely resembles human GR (hGR) cDNA, and yields a high affinity dexamethasone binding receptor when expressed in COS-1 cells. Transactivation analysis of hGR and gsmGR expressed in CV-1 cells and cultured squirrel monkey kidney (SMK) cells indicates that: (1) SMK cells elaborate a functional high activity GR from human GR cDNA; (2) gsmGR is an order of magnitude less efficient than hGR at transactivation in CV-1 and SMK cells; and (3) maximal transactivation by gsmGR is attenuated in both cell lines. Glucocorticoid resistance in S. sciureus is at least partly attributable to a naturally occurring mutation in the GR gene that results in impaired GR transactivation.     

Immunofluorescence study of the hypothalamo-infundibular LRH tract and serum gonadotropin levels in the female squirrel monkey during the estrous cycle

Summary The study of LRH reactive neurons of the medial basal hypothalamic group was made with rabbit antisera to unconjugated synthetic LRH, in normally cycling female squirrel monkeys.The specifically immunoreactive material present along the hypothalamo-infundibular LRH tract shows significant modifications that are particularly distinct in the lateral, posterior and anterior labia of median eminence, with a maximum concentration during the early and middle follicular phases, a sudden fall to a minimum concentration during the late follicular and ovulatory phases and with a progressive increase during the luteal and early follicular phases.Serum FSH and LH levels show a progressive decrease from the luteal phase to the late follicular phase, with differential modifications suggesting that a double regulation might take place in cycling squirrel monkeys.A parallel is suggested between the specifically reactive material along the hypothalamo-infundibular tract, serum gonadotropin levels and variations in the medial basal hypothalamic and infundibular LRH concentrations during the estrous cycle in the squirrel monkey.This work was supported by the D.G.R.S.T. (contrat 76-7-1536) and U.E.R. 3 (Faculty of Medicine). We acknowledge the help of A. Pillez (C.N.R.S.) for sectioning and staining the genital tracts     

Male behavior through the breeding season in Saimiri boliviensis boliviensis

The Bolivian squirrel monkey (Saimiri boliviensis boliviensis) is a seasonal breeder. Male squirrel monkeys show distinct morphological and behavioral changes prior to and during the breeding season. A “fatting syndrome” includes increased body weight, increased levels of androgens, and in the Bolivian subspecies, an increasingly active role in the social organization of the group. In this study, the behavior of ten adult male Bolivian squirrel monkeys was analyzed over a 6-month period prior to, during, and after the breeding season. Each was housed as the only adult male in a breeding unit with six to ten adult females and one juvenile male. Employing a principle components method, 11 behavioral clusters were generated from 27 responses. Their activity clusters were identified as follows: sexual activity that showed a peak around the time of peak conceptions; excitatory activity that was initially high but decreased throughout the breeding season; and maintenance activity that did not change across the breeding season. The changing social behavior of the male squirrel monkey parallels physiological changes and is correlated with changing androgen levels.     

An immunoradiometric assay for squirrel monkey prolactin.

Determination of immunoreactive prolactin in squirrel monkeys has been hampered by the lack of specific antibodies. We investigated the adaptability of a commercially available immunoradiometric assay for human prolactin, which employs two separate monoclonal antibodies (MAb I and II) to human prolactin, to determine the presence of squirrel monkey prolactin. We found that immunoreactivity curves for prolactin in squirrel monkey pituitary homogenates and serum were parallel to human prolactin standards, suggesting that the epitopes recognized by these antibodies were common to both human and squirrel monkey prolactin. Both nonglycosylated (23 kD) and glycosylated (26 kD) forms of squirrel monkey prolactin were detected in squirrel monkey pituitary homogenates by Western blot analysis using [125I]-MAb II. Neither sheep nor rat prolactin was recognized by Western blot analysis, indicating that the assay may be specific for primate prolactins. We examined the effect of ketamine HCl, an anesthetic that has been shown to elevate serum prolactin levels in other primates, on prolactin secretion in squirrel monkeys. Serum prolactin levels increased greater than fourfold after the administration of ketamine HCl (30 mg/kg b.w., i.m.) compared with control levels. Serum prolactin levels were unaffected by anesthesia with pentobarbital sodium (15 mg/kg b.w., i.v.). This assay provides a reliable and sensitive method for determining immunoreactive squirrel monkey prolactin.     

The origin of four squirrel monkey cell lines established by karyotype analysis

The squirrel monkey is a neotropical primate genus which is widely used in biomedical research but includes individual species and subspecies that respond differently to experimental perturbations. GTG-banding patterns of chromosomes 15 and 16, which are distinct among different squirrel monkey species and subspecies, were used to determine the origin of three lung fibroblast cell lines from squirrel monkeys of unknown genetic background (DPSO 114/74, SqMkLu/68, and 7603830) and to confirm the origin of a lymphoblast cell line (GSML) recently established from Guyanese squirrel monkey. DPSO 114/74 cells are from Peruvian squirrel monkey, SqMkLu/68 cells are Bolivian squirrel monkey, and 7603830 cells are from a Peruvian/Bolivian hybrid. Chromosome analysis of GSML cells confirmed that they are from Guyanese squirrel monkey.     

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.     

Cortisol metabolism in the Bolivian squirrel monkey (Saimiri boliviensis boliviensis)

New World squirrel monkeys (Saimiri spp.) have high circulating cortisol levels but normal electrolytes and blood pressures. The goal of the present study was to gain insight into adaptive mechanisms used by Bolivian squirrel monkeys to minimize the effects of high cortisol on mineralocorticoid receptor (MR) activity and electrolyte and water balance. Aldosterone levels in serum from 10 squirrel monkeys were 17.7 +/- 3.4 ng/dl (normal range in humans, 4 to 31 ng/dl), suggesting that squirrel monkeys do not exhibit a compensatory increase in aldosterone. The squirrel monkey MR was cloned and expressed in COS-7 cells and found to have similar responsiveness to cortisol and aldosterone as human MR, suggesting that squirrel monkey MR is not inherently less responsive to cortisol. To determine whether altered metabolism of cortisol might contribute to MR protection in squirrel monkeys, serum and urinary cortisol and cortisone were measured, and a comprehensive urinary corticosteroid metabolite profile was performed in samples from anesthetized and awake squirrel monkeys. The levels of cortisone exceeded those of cortisol in serum and urine, suggesting increased peripheral 11beta-hydroxysteroid dehydrogenase 2 activity in squirrel monkeys. In addition, a significant fraction (approximately 20%) of total corticosteroids excreted in the urine of squirrel monkeys appeared as 6beta-hydroxycortisol, compared with that in man (1%). Therefore, changes in cortisol metabolism likely contribute to adaptive mechanisms used by Bolivian squirrel monkeys to minimize effects of high cortisol.     

Visual sensitivity in the squirrel monkey

Several indices of visual sensitivity have been obtained from behavioral experiments conducted on the squirrel monkey (Saimiri sciureus). In this species, the photopic spectral sensitivity functions determined by increment-threshold and flicker discrimination procedures are substantially different; the involvement of two different neural processes in the two tasks is suggested. When tested similarly, the thresholds for rod and cone-based vision are not substantially different for squirrel monkeys and humans; however, above cone threshold, for a 500 nm test light, increment threshold is some 0.3 to 0.4 log₁₀ units higher for the squirrel monkey. Rod saturation has also been demonstrated to occur in the squirrel monkey.     

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 D₃. 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 studies of androgen metabolism in genital skin fibroblasts indicate that squirrel monkey cells have higher aromatase and lower 5--reductase activity than human cells. Estimation of aromatase activity by a radiometric assay indicates that the high plasma estrogens are derived by peripheral conversion from testicular and/or adrenal androgens.     

The Distribution of Enzymes Which Synthesize Nicotinamide Adenine Dinucleotide and Nicotinamide Adenine Dinucleotide Phosphate in Monkey, Rabbit, and Ground Squirrel Retinas

The activity of adenosinetriphosphate:nicotinamide adenylyltransferase (EC 2.7.7.1) was measured in all the layers of monkey, rabbit, and ground squirrel retinas. Nicotinamide adenine dinucleotide (NAD) kinase (EC 2.7.1.23) distribution was measured in monkey and rabbit retinas. An attempt was made to measure NAD synthetase (EC 6.3.5.1), but the activities in the retinal layers were too low to produce a reliable increment in the levels of endogenous NAD. In monkey retina the adenylyl transferase was highest by far in the outer and inner nuclear layers, lower and variable in ganglion cell and fiber layers, and almost absent elsewhere. Rabbit retina differed in that activity was nearly absent in the outer nuclear layer, whereas in the ground squirrel outer nuclear layer activity was double that of the inner nuclear layer. The species differences suggest that adenylyl transferase is almost absent from cone cell nuclei and high in rod cell nuclei. NAD kinase distribution in monkey retina was almost the mirror image of that of adenylyl transferase.     

Enzyme-histochemical studies on the muscle spindle

Summary Detailed studies have been made on the distribution of several enzymes in the muscle spindles of the hand and foot interosseous muscles and M. longissimus dorsi of the rhesus monkey as well as in those of the hand interosseous muscles of the squirrel monkey. The intrafusal muscle fibers (IMF) of the rhesus monkey can be classified into two types by the reaction intensity at the polar regions for adenosine triphosphatases and by the enzymes concerning the carbohydrate metabolism except glucose-6-phosphate dehydrogenase, while the extrafusal muscle fibers (EMF) show three types of reactions for the enzymes of the Embden-Meyerhof pathway and the tricarboxylic acid (TCA) cycle. The IMF and EMF of the squirrel monkey are more variable than those of the rhesus monkey for the glycogen breakdown enzyme. It is possible that the small IMF are more capable of energy production through the TCA cycle than the large IMF and the EMF in both species. The positive cholinesterases reactions are found around the polar regions of the IMF, while only the rim of the equator of the IMF shows monoamine oxidase activity. The pericapsular epithelial cells of the muscle spindle seem to be metabolically similar to the perineural epithelial cells.Visiting scientist from the Department of Anatomy, Tokyo Medical and Dental University, Tokyo, Japan. T. R. Shanthaveerappa in previous publications.     

Comparison of antigenicity of serum immunoglobulin G among human, cynomolgus monkey, African green monkey and squirrel monkey

Antigenicity of IgG was compared among human, the cynomolgus monkey, the African green monkey and the squirrel monkey by the quantitative precipitation test using purified IgG of and rabbit anti-IgG serum to each species. Clear cross-antigenicity was observed between the cynomolgus monkey and the African green monkey and less clear cross-antigenicity between human and the cynomolgus monkey or the African green monkey. The cross-antigenicity observed between the squirrel monkey and the other three species examined was evidently weak.