OFF midget bipolar cells in the retina of the marmoset, Callithrix jacchus, express AMPA receptors

Recent studies suggested that different types of OFF bipolar cells express specific types of ionotropic (AMPA or kainate) glutamate receptors (GluRs) at their contacts with cone pedicles. However, the question of which GluR type is expressed by which type of OFF bipolar cell in primate retina is still open. In this study, the expression of AMPA and kainate receptor subunits at the dendritic tips of flat (OFF) midget bipolar (FMB) cells was analyzed in the retina of the common marmoset, Callithrix jacchus. We used preembedding electron microscopy and double immunofluorescence with subunit-specific antibodies. The FMB cells were labeled with antibodies against the carbohydrate epitope CD15. Cone pedicles were identified with peanut agglutinin. Immunoreactivity for the GluR1 subunit and for CD15 is preferentially located at triad-associated flat contacts. Furthermore, the large majority of GluR1 immunoreactive puncta is localized at the dendritic tips of FMB cells. These results suggest that FMB cells express the AMPA receptor subunit GluR1. In contrast, the kainate receptor subunit GluR5 is not colocalized with the dendritic tips of FMB cells or with the GluR1 subunit. Immunoreactive puncta for the GluR1 subunit are found at all M/L-cone pedicles but are only rarely associated with S-cone pedicles. This is consistent with our recent findings in marmoset retina that FMB cells do not contact S-cone pedicles. The presence of GluR5 clusters at S-cone pedicles indicates that in primate retinas OFF bipolar cells expressing kainate receptor subunits receive some S-cone input.

Gonadotrophin-releasing hormone (GnRH) release in marmosets II: pulsatile release of GnRH and pituitary gonadotrophin in adult females

Unlike other mammals, including rodents, Old World primates and humans, common marmosets and probably all other New World primates synthesise and release chorionic gonadotrophin (CG), and not luteinising hormone (LH) from pituitary gonadotrophs. However, little is known about the physiological dynamics of gonadotrophin-releasing hormone (GnRH)-regulated CG release from gonadotrophs and whether such CG release has pulsatile release characteristics similar to those of LH in other mammalian species. Consequently, we performed a series of in vivo and in vitro studies in ovariectomised laboratory rats and female marmosets to compare GnRH-induced pituitary LH and CG release characteristics, respectively. Exogenous GnRH stimulated a slower onset of release of marmoset pituitary CG, both in vivo and in vitro, and induced an approximately 400% greater increase in the duration of marmoset pituitary CG release compared to that for rat LH. Not surprisingly, hypothalamic pulsatile release of GnRH in vivo was not obviously concordant with endogenous episodic changes in circulating levels of CG in marmosets, in contrast to the clear concordance observed between in vivo GnRH and LH release previously demonstrated in rats and other mammals. Pituitary CG release in marmosets thus demonstrates considerable divergence from the timely hypothalamic GnRH-regulated LH release in other female mammals, implying potentially different physiological dynamics in gonadotrophin regulation of marmoset ovarian function.

Expression of anti-Mullerian hormone protein during early follicular development in the primate ovary in vivo is influenced by suppression of gonadotropin secretion and inhibition of vascular endothelial growth factor

Anti-Mullerian hormone (AMH) plays a role during early follicular development and selection. The aim of this study was to determine the pattern of AMH protein expression in the marmoset ovary and to investigate the effects of inhibition of gonadotropins or vascular endothelial growth factor (VEGF) activity on AMH expression in vivo. GnRH antagonist or VEGF Trap, a soluble decoy receptor, was administered on d 0 or 5 of the follicular phase of the cycle, and ovaries were collected at the end of the follicular phase (d 10). AMH protein was expressed in the marmoset ovary in granulosa cells from the primary stage, with the most abundant staining at the preantral and early antral stages. Inhibition of gonadotropin secretion or VEGF activity between d 0-10 of the cycle decreased AMH expression in early preantral follicles (P < 0.01), and AMH expression was decreased in late preantral follicles in the presence of the VEGF Trap (P < 0.01), compared with controls. There was significantly less AMH expression in early antral follicles with both treatments (P < 0.01), and a decrease in the ratio of oocyte-associated/basement-membrane-associated granulosa cell expression of AMH (P < 0.05). When treatments were administered from d 5-10 of the cycle, both VEGF Trap and GnRH antagonist decreased AMH expression in preantral follicles (P < 0.01) but had no significant effect on early antral follicles. In conclusion, VEGF and gonadotropins are involved in the regulation of expression of AMH in the marmoset. This AMH expression may be a marker of abnormal folliculogenesis in the absence of gonadotropin stimulation or functional angiogenesis.

Gonadotrophin-releasing hormone (GnRH) release in marmosets I: in vivo measurement in ovary-intact and ovariectomised females

In vivo hypothalamic gonadotrophin-releasing hormone (GnRH) release was characterised for the first time in a New World primate. A nonterminal and repeatable push-pull perfusion (PPP) technique reliably measured GnRH in conscious common marmoset monkeys. Nineteen adult females (n = 8 ovary-intact in the mid-follicular phase; n = 11 ovariectomised) were fitted with long-term cranial pedestals, and a push-pull cannula was temporarily placed in unique locations within the pituitary stalk-median eminence (S-ME) 2 days prior to each PPP session. Marmosets underwent 1-3 PPPs (32 PPPs in total) lasting up to 12 h. Plasma cortisol levels were not elevated in these habituated marmosets during PPP, and PPP did not disrupt ovulatory cyclicity or subsequent fertility in ovary-intact females. GnRH displayed an organised pattern of release, with pulses occurring every 50.0 +/- 2.6 min and lasting 25.4 +/- 1.3 min. GnRH pulse frequency was consistent within individual marmosets across multiple PPPs. GnRH mean concentration, baseline concentration and pulse amplitude varied predictably with anatomical location of the cannula tip within the S-ME. GnRH release increased characteristically in response to a norepinephrine infusion and decreased abruptly during the evening transition to lights off. Ovary-intact (mid-follicular phase) and ovariectomised marmosets did not differ significantly on any parameter of GnRH release. Overall, these results indicate that PPP can be used to reliably assess in vivo GnRH release in marmosets and will be a useful tool for future studies of reproductive neuroendocrinology in this small primate.

Energy restriction initiated at different gestational ages has varying effects on maternal weight gain and pregnancy outcome in common marmoset monkeys (Callithrix jacchus)

With relatively high fertility and short lifespan, marmoset monkeys (Callithrix jacchus) may become useful primate models of prenatal nutritional effects on birth condition and adult disease risk. The present study determined the effects of energy restriction to 75% of expected ad libitum consumption during mid- (day 66) or late (day 99) gestation on maternal weight, fetal growth and pregnancy outcomes in this species. Mid-restriction reliably induced the loss of pregnancy before term, at 92 d, on average. Of the late-restricted pregnancies, four of seven were normal term length while three were preterm deliveries, at 101, 117 and 132 d. Control females had a mean mid-pregnancy weight gain of 0·67 g/d while mid-restricted females lost −0·65 g/d, on average. Control pregnancies averaged a 1·06 g/d gain during late pregnancy, while energy-restricted females lost −0·67 g/d, on average. Restriction-related weight change was highly variable, ranging from +0·55 to −2·56 g/d for mid-restriction pregnancies and from +0·79 to −3·91 g/d for late-restriction pregnancies. For mid-restriction pregnancies, the number of restriction days was best explained by linear weight change and total weight loss while the number of restriction days in late pregnancy was best explained by linear weight change alone. In late-restriction pregnancies, smaller females had higher daily weight losses. Restrictions did not induce litter-size reduction or growth restriction in those infants that were delivered at term but the size of aborted fetuses suggested that at least some pregnancies lost preterm may have involved impaired intra-uterine growth.

Demographic review of a captive colony of callitrichids (Callithrix kuhlii)

Although reports on colony demographics for a variety of callitrichid species are available in the literature, to date there has not been a detailed examination of Wied's black tufted-ear marmoset (Callithrix kuhlii). The purpose of this study is to present colony demographics for C. kuhlii from the University of Nebraska at Omaha's Callitrichid Research Center from 1991 to 2002. C. kuhlii are currently held in a number of zoological parks in the United States and abroad; however, the University of Nebraska at Omaha held the only breeding colony in North America. Here we report data on lifespan, sex ratio, litter size, and interbirth interval (IBI) for that captive breeding colony.

Neural coding strategies in auditory cortex

In contrast to the visual system, the auditory system has longer subcortical pathways and more spiking synapses between the peripheral receptors and the cortex. This unique organization reflects the needs of the auditory system to extract behaviorally relevant information from a complex acoustic environment using strategies different from those used by other sensory systems. The neural representations of acoustic information in auditory cortex can be characterized by three types: (1) isomorphic (faithful) representations of acoustic structures; (2) non-isomorphic transformations of acoustic features and (3) transformations from acoustical to perceptual dimensions. The challenge facing auditory neurophysiologists is to understand the nature of the latter two transformations. In this article, I will review recent studies from our laboratory regarding temporal discharge patterns in auditory cortex of awake marmosets and cortical representations of time-varying signals. Findings from these studies show that (1) firing patterns of neurons in auditory cortex are dependent on stimulus optimality and context and (2) the auditory cortex forms internal representations of sounds that are no longer faithful replicas of their acoustic structures.

Response to novel food and the role of social influences in common marmosets (Callithrix jacchus) and Goeldi's monkeys (Callimico goeldii)

Neophobia, defined as showing caution toward novel features of the environment, is widespread in birds and mammals; it can be affected by ecology, early experience, and social context. In this study, we aimed to (i) investigate the response to novel food in adult common marmosets and Goeldi's monkeys and (ii) assess the role of social influences. We used an experimental paradigm employed previously with capuchin monkeys and children, in which a subject (observer) was presented with a novel food under three conditions: (i) Presence: group members did not have food; (ii) Different color: group members received familiar food whose color differed from that of the observer's novel food; (iii) Same color: group members received familiar food of the same color as the observer's novel food. Although most common marmosets tasted and/or ate the novel food, none of the Goeldi's monkeys ate it and only two sampled it. Differences in home range size and early social experience might explain the divergent behavior of the two species. Observers of both species similarly attended to group members and their visual attention increased with the number of group members eating, especially when the observer's and group members' foods were perceptually similar. However, we observed social influences on explorative behavior in Goeldi's monkeys but not on explorative or eating behavior in common marmosets. This result might be explained by the different pattern of response to novel food observed in the two species. Moreover, social influences on Goeldi's monkeys' behavior were nonspecific, i.e. they were not based on an appreciation that the food is safe because eaten by group members.

Age-related Changes in Marmoset Trabecular and Cortical Bone and Response to Alendronate Therapy Resemble Human Bone Physiology and Architecture

In older humans, bone elongation ceases, periosteal expansion continues, and bone remodeling remains a dominant metabolic process. An appropriate animal model of type I and type II osteoporosis would be a species with sealed growth plates and persistence of bone remodeling. The rat is commonly used as a primary model, but due to delayed epiphyseal closure with continuous modeling and lack of Haversian remodeling, Food and Drug Administration guidelines recommend assessment of bone quality in an additional, non rodent, remodeling species. This study investigated the skeletal characteristics of senescent marmosets to evaluate their suitability as an osteoporosis model. Animals were randomized across three experimental groups; controls for both sexes and marmosets receiving alendronate for either 30 or 60 days (28 microg/kg, sc, twice per week). Outcome measures included serum chemistry and bone biomarkers, DEXA, histomorphometry, micro-computed tomography, and histopathology. Results showed that the adult marmoset skeleton has similar anatomical characteristics to the adult human, including the absence of growth plates, presence of Haversian system, and true remodeling of cancellous and cortical bone. Structural analyses of senescent marmoset cancellous bone demonstrated loss of trabecular mass and architecture similar to skeletal changes described for elderly men and women. Treatment with alendronate improved trabecular volume and number by reducing bone resorption, although bone formation was also reduced through coupling of bone remodeling. The common marmoset may provide a valuable model for research paradigms targeting human bone pathology and osteoporosis due to skeletal features that are similar to age-related changes and response to bisphosphonate therapy reported for humans.

The composition of milk from free-living common marmosets (Callithrix jacchus) in Brazil

Common marmosets, one of the smallest anthropoid primates, have a relatively high reproductive rate, capable of producing twins or triplets twice per year. Growth and development of infants is relatively rapid, and lactation is relatively short at less than 3 months. Although mean values for the proximate composition (dry matter, protein, fat and sugar) of captive common marmoset milks fall within anthropoid norms, composition is highly variable among individual samples, with concentrations of milk fat ranging from below 1 to over 10%. To examine the extent to which this variation might be a consequence of captive conditions, we collected milk samples from wild common marmosets freely living on a farm in the state of Rio de Janeiro, Brazil. The proximate composition of the milk samples was assayed using identical techniques as used for the captive marmoset milks. The composition of the milk of wild common marmosets was also variable, but tended to be lower in dry matter, fat, protein and gross energy, and higher in sugar than milks from captive animals. Interestingly, the percentage of estimated gross energy from the protein fraction of the milks was relatively constant in both wild and captive marmosets and did not differ between wild and captive animals: 1 kcal of common marmoset milk contains on average (+/-SEM) 0.035+/-.001 g of protein regardless of the gross energy content of the milk or whether the milk was from a wild or captive animal. In contrast, in 1 kcal of low-energy milks, the amount of sugar was significantly higher and the amount of fat significantly lower than in 1 kcal of high-energy milks. Thus, common marmoset milk exhibits axes of variability (especially fat concentration) as well as a significant stability in the relative amount of protein.

Geniculocortical relay of blue-off signals in the primate visual system

A fundamental dichotomy in the subcortical visual system exists between on- and off-type neurons, which respectively signal increases and decreases of light intensity in the visual environment. In primates, signals for red-green color vision are carried by both on- and off-type neurons in the parvocellular division of the subcortical pathway. It is thought that on-type signals for blue-yellow color vision are carried by cells in a distinct, diffusely projecting (koniocellular) pathway, but the pathway taken by blue-off signals is not known. Here, we measured blue-off responses in the subcortical visual pathway of marmoset monkeys. We found that the cells exhibiting blue-off responses are largely segregated to the koniocellular pathway. The blue-off cells show relatively large receptive fields, sluggish responses to maintained contrast, little sign of an inhibitory receptive-field surround mechanism, and negligible functional input from an intrinsic (melanopsin-based) phototransductive mechanism. These properties are consistent with input from koniocellular or "W-like" ganglion cells in the retina and suggest that blue-off cells, as previously shown for blue-on cells, could contribute to cortical mechanisms for visual perception via the koniocellular pathway.

Processing of first-order motion in marmoset visual cortex is influenced by second-order motion

We measured the responses of single neurons in marmoset visual cortex (V1, V2, and the third visual complex) to moving first-order stimuli and to combined first- and second-order stimuli in order to determine whether first-order motion processing was influenced by second-order motion. Beat stimuli were made by summing two gratings of similar spatial frequency, one of which was static and the other was moving. The beat is the product of a moving sinusoidal carrier (first-order motion) and a moving low-frequency contrast envelope (second-order motion). We compared responses to moving first-order gratings alone with responses to beat patterns with first-order and second-order motion in the same direction as each other, or in opposite directions to each other in order to distinguish first-order and second-order direction-selective responses. In the majority (72%, 67/93) of cells (V1 73%, 45/62; V2 70%, 16/23; third visual complex 75%, 6/8), responses to first-order motion were significantly influenced by the addition of a second-order signal. The second-order envelope was more influential when moving in the opposite direction to the first-order stimulus, reducing first-order direction sensitivity in V1, V2, and the third visual complex. We interpret these results as showing that first-order motion processing through early visual cortex is not separate from second-order motion processing; suggesting that both motion signals are processed by the same system.

GnRH-antagonist mediated down-regulation of the estrous cycle in marmosets

BACKGROUND

Because of its small size and unproblematic captivity behavior the marmoset monkey is an attractive New World primate model for early developmental questions. However, superovulation protocols used in Old World monkeys and women are not successful in the female marmoset. A novel protocol is needed to utilize these New World monkeys as an efficient animal model for in vitro fertilization experiments or embryo stem cell research.

METHODS

To create such a protocol we first examined the effects of long-term estrous cycle control, secondly, in a dose-finding study, we determined the length of a down-regulation protocol with a gonadotropic releasing hormone (GnRH)-antagonist. Twenty-nine female marmosets were grouped according to the number of estrous cycles, which had been controlled for a period of 12 months in which 88 cycles were monitored. Application of PGF2alpha in the mid-luteal phase led to immediate onset of the follicular phase. The blood progesterone concentration rapidly declined and increased again on day 9-11.

RESULTS

The results show that the controlled ovarian cycle length and progesterone response are not altered by the number of PGF2alpha injections. The rapid decline was similar in all groups, indicating that all animals, independent of the number of controlled cycles, react equally to multiple PGF2alpha injections. To determine the proper dosage for a GnRH-antagonist (Cetrorelix), 12 animals in three groups of four female marmosets were treated with two different dosages and a sham dosage. Cetrorelix was applied in the mid-luteal phase, three times over 2 days. In both Cetrorelix-treated animal groups the early progesterone levels matched those in the controls. In the low-dose treatment group [0.01 mg/100 g body weight (BW)] the expected progesterone rise on day 10 was delayed between 9 and 15 days whereas in the high-dose treatment group (0.1 mg/100 g BW) the progesterone rise was delayed between 21 and 41 days. In the low-dose group the steepness of the slope from day 20 onwards was almost identical to that of the control group. This was reflected in the bioCG levels measured.

CONCLUSIONS

Based on the GnRH-antagonist studies, complete ovarian down-regulation in female marmosets can be achieved by applying a low-dose regimen, and intrinsic gonadotropins would not interfere with an ovarian superstimulation protocol.

Preparing New World monkeys for laboratory research

New World monkeys represent an important but often poorly understood research resource. The relatively small size and low zoonotic risk of these animals make them appealing as research subjects in a number of areas. However, historic portrayal of many of these species as difficult to manage and handle is one of the factors that has limited their use. Basic guidelines are provided on management and handling approaches for the New World monkeys most commonly used in research: marmosets, squirrel monkeys, owl monkeys, and titi monkeys. Topics include transport and acclimation to a new facility, location changes within a facility, diet changes, removal from and return to social groups, capture and restraint, handling for anesthesia, postprocedural monitoring, and staff training.

Social suppression of cortisol in female marmosets: role of luteinizing hormone/chorionic gonadotropin

Behaviorally subordinate female common marmosets (Callithrix jacchus) undergo suppression of ovulation and chronic reductions in basal plasma cortisol concentrations. Indirect evidence suggests that hypophyseal chorionic gonadotropin (CG; the major pituitary luteinizing gonadotropin in marmosets) may elevate cortisol concentrations in female marmosets, and therefore that social suppression of CG may contribute to diminution of cortisol in subordinates. To test this hypothesis, we determined whether pharmacological inhibition of pituitary CG release decreases basal and adrenocorticotropin (ACTH)-stimulated cortisol secretion. We characterized cortisol and reproductive hormone concentrations in six ovary-intact and six ovariectomized marmosets during long-term treatment with leuprolide acetate, a gonadotropin-releasing hormone (GnRH) agonist, and vehicle. Leuprolide suppressed basal plasma CG concentrations, abolished the CG response to exogenous GnRH, and, in intact animals, blocked ovarian cyclicity. During treatment with vehicle, plasma cortisol concentrations were elevated during the periovulatory phase in intact females, compared to the follicular phase, the luteal phase, and ovariectomized females. Leuprolide suppressed basal cortisol concentrations of intact females as compared to the periovulatory phase, but did not affect basal cortisol in ovariectomized animals and did not alter responses to exogenous ACTH. These findings suggest that elevations in circulating CG concentrations are associated with elevated cortisol concentrations in female marmosets, and that this relationship requires simultaneous increases in ovarian hormones that occur only during the periovulatory period. Thus, suppression of CG release in anovulatory subordinate females may not play an important role in socially induced diminution of cortisol.

Hormonal regulation of apoptosis in the endometrium of common marmosets (Callithrix jacchus)

Phase-dependent apoptotic changes in the human endometrium during an ovarian cycle imply a potential role of steroids in the regulation of apoptosis. The present study was undertaken to determine the direct role of hormones in endometrial apoptosis in marmosets (Callithrix jacchus), a primate species which shows similarity to humans in terms of the cycle length and pattern. Endometrial apoptosis was detected by 3'-end labeling (TUNEL) in various phases of ovarian cycle in naturally cycling healthy marmosets (n=14) and also in ovariectomized marmosets (n=13) treated with either estradiol alone (E) or progesterone alone (P) or estradiol followed by progesterone (E+P). Expressions of apoptosis associated genes such as Bcl-2 family members (Bax and Bcl-2), proliferating cell nuclear antigen (PCNA)--a proliferation marker and steroid receptors, ERalpha and PR A were analysed by immunohistochemical methods. Apoptosis was intense in the glandular epithelial cells of endometrium during the mid-luteal phase as compared to other phases in naturally cycling animals; in the E+P group as compared to other groups of ovariectomized animals (P<0.05). Pronounced apoptosis in the mid-luteal phase was accompanied by the increased expression of Bax in glandular epithelial cells; while Bcl-2 immunoreactivity remained unchanged. PCNA expression was higher in the naturally cycling animals in the follicular phase and in the E group of the ovariectomized animals as compared those in the other groups. Immunoreactive ERalpha and PR A in glandular epithelial cells were most abundant during early follicular phase in naturally cycling animals and in both E and E+P groups among the ovariectomized animals. The present study highlights the importance of apoptosis in endometrial remodeling during the ovarian cycle and secondly, the role of both estradiol and progesterone in the regulation of apoptosis.

Acoustic analysis of vocal development in a New World primate, the common marmoset (Callithrix jacchus)

In contrast to humans and songbirds, there is limited evidence of vocal learning in nonhuman primates. While previous studies suggested that primate vocalizations exhibit developmental changes, detailed analyses of the extent and time course of such changes across a species' vocal repertoire remain limited. In a highly vocal primate, the common marmoset (Callithrix jacchus), we studied developmental changes in the acoustic structure of species-specific communication sounds produced in a social setting. We performed detailed acoustic analyses of the spectral and temporal characteristics of marmoset vocalizations during development, comparing differences between genders and twin pairs, as well as with vocalizations from adult marmosets residing in the same colony. Our analyses revealed significant changes in spectral and temporal features as well as variability of particular call types over time. Infant and juvenile vocalizations changed progressively toward the vocalizations produced by adult marmosets. Call types observed early in development that were unique to infants disappeared gradually with age, while vocal exchanges with conspecifics emerged. Our observations clearly indicate that marmoset vocalizations undergo both qualitative and quantitative postnatal changes, establishing the basis for further studies to delineate contributions from maturation of the vocal apparatus and behavioral experience.

Perception of the stereokinetic illusion by the common marmoset (Callithrix jacchus)

Stereokinetic illusions have never been investigated in non-human primates, nor in other mammalian species. These illusions consist in the perception of a 3D solid object when certain 2D stimuli are rotated slowly in the plane perpendicular to the line of sight. The ability to perceive the stereokinetic illusion was investigated in the common marmoset (Callithrix jacchus). Four adult marmosets were trained to discriminate between a solid cylinder and a solid cone for food reward. Once learning criterion was reached, the marmosets were tested in sets of eight probe trials in which the two solid objects used at training were replaced by two rotating 2D stimuli. Only one of these stimuli produced, at least to the human observer, the stereokinetic illusion corresponding to the solid object previously reinforced. At test, the general behaviour and the total time spent by the marmosets observing each stimulus were recorded. The subjects stayed longer near the stimulus producing the stereokinetic illusion corresponding to the solid object reinforced at training than they did near the illusion corresponding to the previously non-rewarded stimulus. Hence, the common marmosets behaved as if they could perceive stereokinetic illusions.

Changes in endocrine profile and reproductive organs during puberty in the male marmoset monkey (Callithrix jacchus)

Data on pubertal maturation in male marmoset, a model for human reproduction, are scant and conflicting. We collected data on novel parameters to characterize puberty. Twenty-five marmoset monkeys were assigned to five age groups by weeks (wk): 21 (pre-pubertal), 43 (onset of puberty), 52 (fully pubertal), 70 (mature), and 116 (fully adult). Serum and intratesticular testosterone and pituitary bioactive chorionic gonadotropin (bioCG) were measured. Testicular development was assessed by ultrasonography, histology, and flow cytometry. Three consecutive blood samples revealed extreme fluctuations in testosterone concentrations, suggesting an erratic secretion. Age-related changes in serum testosterone and pituitary bioCG concentrations were observed. Intratesticular androgens (ITAs) showed high fluctuations within groups at all ages and were high in some animals by 21 wk. Unexpectedly, no correlation between pituitary bioCG and serum testosterone or ITAs was found, but these parameters significantly correlated with testicular weight and volume. These observations were consistent a dependence on the testis growth on bioCG. Unfortunately, the low serum levels of bioCG were not measurable in this study. At 43 wk, the animals reached puberty. At 52 wk of age, animals attained maximum body and epididymal weights and qualitatively normal spermatogenesis, but testes continued growing, reaching a maximum of all parameters at 70 wk of age, without further major changes at the age of 116 wk. It is concluded that (1) gonadal activation is evident at wk 21, (2) the male marmoset reaches the pubertal threshold around 43 wk of age, attains qualitative parameters at 52 wk, matures further to sexual maturity at 70 wk, and (3) serum testosterone and ITAs are highly variable without any identifiable correlation with pituitary bioCG.

Individual olfactory signatures in common marmosets (Callithrix jacchus)

Individual discrimination is likely a prerequisite for most primate social interactions. Olfactory cues are one set of stimuli used by primates to discriminate between individuals. Despite the importance of these olfactory signatures, there is little published research assessing the existence or function of individually unique odors among primates. This review systematically assesses behavioral and biochemical aspects of individual odors in a New World primate, the common marmoset (Callithrix jacchus). There are three objectives to this review: First, behavioral evidence for odors unique to the individual is evaluated in the context of results demonstrating that marmosets are able to discriminate between the scents from a familiar and a novel individual conspecific in behavioral bioassays under a variety of conditions. Second, biochemical evidence for individual scent signatures is debated with reference to studies examining qualitative and quantitative differences between the chemical compositions of scent-mark pools from adult females. A combined gas chromatography (GC) and mass spectrometry (MS) analysis demonstrated that each female had a unique ratio of highly volatile chemicals in the scent mark that could affect individual discrimination. Finally, the possible adaptive significance of individual odors in marmosets is debated. Individual odors may play a key role in regulating both female intrasexual competition and intersexual communication by providing a basis for the assessment of individual quality.

Background pathology of the common marmoset (Callithrix jacchus) in toxicological studies

Two hundred common marmosets (Callithrix jacchus) from control groups (100 males, 100 females) of toxicological studies were examined histopathologically to evaluate the spectrum of spontaneous lesions in this species. Frequent findings were extramedullary hematopoiesis affecting adrenal glands, liver, kidney and spleen, cystic Brunner's glands in the duodenum, acute or subacute inflammation in the large intestine and gall bladder, renal mineralization and pigmentation, hepatic Ito-cell vacuolation, microgranuloma and glycogen storage, pituitary cysts, C-cell hyperplasia and lymphocytic foci of the thyroid gland, luteal hyperplasia of the ovary and inflammatory cell foci in various organs.

Thalamic connections of the auditory cortex in marmoset monkeys: core and medial belt regions

In this study and its companion, the cortical and subcortical connections of the medial belt region of the marmoset monkey auditory cortex were compared with the core region. The main objective was to document anatomical features that account for functional differences observed between areas. Injections of retrograde and bi-directional anatomical tracers targeted two core areas (A1 and R), and two medial belt areas (rostromedial [RM] and caudomedial [CM]). Topographically distinct patterns of connections were revealed among subdivisions of the medial geniculate complex (MGC) and multisensory thalamic nuclei, including the suprageniculate (Sg), limitans (Lim), medial pulvinar (PM), and posterior nucleus (Po). The dominant thalamic projection to the CM was the anterior dorsal division (MGad) of the MGC, whereas the posterior dorsal division (MGpd) targeted RM. CM also had substantial input from multisensory nuclei, especially the magnocellular division (MGm) of the MGC. RM had weak multisensory connections. Corticotectal projections of both RM and CM targeted the dorsomedial quadrant of the inferior colliculus, whereas the CM projection also included a pericentral extension around the ventromedial and lateral portion of the central nucleus. Areas A1 and R were characterized by focal topographic connections within the ventral division (MGv) of the MGC, reflecting the tonotopic organization of both core areas. The results indicate that parallel subcortical pathways target the core and medial belt regions and that RM and CM represent functionally distinct areas within the medial belt auditory cortex.

Cortical connections of the auditory cortex in marmoset monkeys: core and medial belt regions

The auditory cortex of primates contains a core region of three primary areas surrounded by a belt region of secondary areas. Recent neurophysiological studies suggest that the belt areas medial to the core have unique functional roles, including multisensory properties, but little is known about their connections. In this study and its companion, the cortical and subcortical connections of the core and medial belt regions of marmoset monkeys were compared to account for functional differences between areas and refine our working model of the primate auditory cortex. Anatomical tracer injections targeted two core areas (A1 and R) and two medial belt areas (rostromedial [RM] and caudomedial [CM]). RM and CM had topographically weighted connections with all other areas of the auditory cortex ipsilaterally, but these were less widespread contralaterally. CM was densely connected with caudal auditory fields, the retroinsular (Ri) area of the somatosensory cortex, the superior temporal sulcus (STS), and the posterior parietal and entorhinal cortex. The connections of RM favored rostral auditory areas, with no clear somatosensory inputs. RM also projected to the lateral nucleus of the amygdala and tail of the caudate nucleus. A1 and R had topographically weighted connections with medial and lateral belt regions, infragranular inputs from the parabelt, and weak connections with fields outside the auditory cortex. The results indicated that RM and CM are distinct areas of the medial belt region with direct inputs from the core. CM also has somatosensory input and may correspond to an area on the posteromedial transverse gyrus of humans and the anterior auditory field of other mammals.

Suppression of prolactin does not reduce infant care by parentally experienced male common marmosets (Callithrix jacchus)

High levels of prolactin have been found to correlate with the expression of paternal care in a variety of taxa. However, in mammals, there is little experimental evidence that prolactin is causally involved in the stimulation or maintenance of paternal care. Here, we suppressed prolactin production in paternally experienced common marmoset fathers in their family groups during the first 2 weeks after their infants were born. Circulating prolactin levels were suppressed using cabergoline (Dostinex: Pfizer), a long acting dopamine (D2) agonist with minimal behavioural side-effects. A within-subject design was used to compare behavioural and hormonal data on 5 paternally experienced fathers during two consecutive births. Cabergoline reduced prolactin to negligible levels in all fathers without effecting testosterone, DHT and cortisol and without adverse side-effects. However, lowering prolactin had no significant effect on the expression of majority of the behaviour patterns associated with paternal care. These included infant carrying, infant grooming and the frequency with which fathers retrieved and rejected infants. The only infant-related behaviour to be affected was the frequency with which fathers touched, licked and investigated infants. We noted a marginally significant increase in this behaviour during cabergoline treatment. Despite the lack of effect on paternal care, cabergoline did exert an effect on the affiliative/sexual behaviour of fathers as there was a significant increase in the grooming behaviour fathers directed at and received from their mates during drug treatment. This study showed that experienced male marmosets can express paternal behaviour in the absence of the high prolactin levels normally seen after infants are born.

Contested dominance modifies the anovulatory consequences of social subordination in female marmosets

Dominance status among female marmosets is reflected in agonistic behavior and ovarian function. Socially dominant females receive submissive behavior from subordinates, while exhibiting normal ovulatory function. Subordinate females, however, receive agonistic behavior from dominants, while exhibiting reduced or absent ovulatory function. Such disparity in female fertility is not absolute, and groups with two breeding females have been described. The data reported here were obtained from 8 female-female pairs of captive female marmosets, each housed with a single unrelated male. Pairs were classified into two groups: "uncontested" dominance (UD) and "contested" dominance (CD), with 4 pairs each. Dominant females in UD pairs showed significantly higher frequencies (4.1) of agonism (piloerection, attack and chasing) than their subordinates (0.36), and agonistic behaviors were overall more frequently displayed by CD than by UD pairs. Subordinates in CD pairs exhibited more agonistic behavior (2.9) than subordinates in UD pairs (0.36), which displayed significantly more submissive (6.97) behaviors than their dominants (0.35). The data suggest that there is more than one kind of dominance relationship between female common marmosets. Assessment of progesterone levels showed that while subordinates in UD pairs appeared to be anovulatory, the degree of ovulatory disruption in subordinates of CD pairs was more varied and less complete. We suggest that such variation in female-female social dominance relationships and the associated variation in the degree and reliability of fertility suppression may explain variations of the reproductive condition of free-living groups of common marmosets.