Recombinant IGF-1/BP3 protects against intestinal injury in a neonatal mouse NEC model.

BACKGROUND: Recombinant human IGF-1/binding protein-3 (rhIGF-1/BP3) is currently being tested in phase II clinical trials in premature infants to prevent bronchopulmonary dysplasia, but its impact on the neonatal intestine remains unclear. The aim of this study was to determine whether rhIGF-1/BP3 protects against necrotizing enterocolitis (NEC) in mice and to investigate the mechanisms involved. METHODS: Neonatal mice were dam fed or injected intraperitoneally with rhIGF-1/BP3 (or vehicle) and submitted to an experimental NEC model. Serum IGF-1 was assessed by ELISA and intestinal vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) expression by Western blot. Intestinal endothelial cell proliferation, and enterocyte proliferation and migration were examined by immunofluorescence. Pup survival and histological intestinal injury were determined. RESULTS: In pups exposed to experimental NEC, serum IBP3-bound IGF-1 level was decreased. Exogenous rhIGF-1/BP3 preserved VEGF and VEGFR2 protein expression, decreased vascular permeability, and preserved endothelial cell proliferation in the small intestine. Furthermore, rhIGF-1/BP3 promoted enterocyte proliferation and migration, which effects were attenuated by inhibiting VEGFR2 signaling, decreased enterocyte apoptosis and decreased systemic and intestinal inflammation. rhIGF-1/BP3 improved survival and reduced the incidence of severe intestinal injury in experimental NEC. CONCLUSIONS: Exogenous rhIGF-1/BP3 protects neonatal mice against experimental NEC via multiple mechanisms. IMPACT: Exogenous rhIGF-1/BP3 preserves intestinal microvascular development and integrity, promotes enterocyte proliferation and migration, decreases local and systemic inflammation, and protects neonatal mice against NEC. The article adds pre-clinical evidence of a protective role for rhIGF-1/BP3 on the premature gut. It provides evidence supporting the use of rhIGF1/BP3 in premature neonates to protect against NEC.

Pilot dose-ranging of rhIGF-1/rhIGFBP-3 in a preterm lamb model of evolving bronchopulmonary dysplasia.

BACKGROUND: Low levels of insulin-like growth factor-1 (IGF-1) protein in preterm human infants are associated with bronchopulmonary dysplasia (BPD). We used our preterm lamb model of BPD to determine (1) dosage of recombinant human (rh) IGF-1 bound to binding protein-3 (IGFBP-3) to reach infant physiologic plasma levels; and (2) whether repletion of plasma IGF-1 improves pulmonary and cardiovascular outcomes. METHODS: Group 1: normal, unventilated lambs from 128 days gestation through postnatal age 5 months defined normal plasma levels of IGF-1. Group 2: continuous infusion of rhIGF-1/rhIGFBP-3 (0.5, 1.5, or 4.5 mg/kg/day; n = 2) for 3 days in mechanically ventilated (MV) preterm lambs determined that 1.5 mg/kg/day dosage attained physiologic plasma IGF-1 concentration of ~125 ng/mL, which was infused in four more MV preterm lambs. RESULTS: Group 1: plasma IGF-1 protein increased from ~75 ng/mL at 128 days gestation to ~220 ng/L at 5 months. Group 2: pilot study of the optimal dosage (1.5 mg/kg/day rhIGF-1/rhIGFBP-3) in six MV preterm lambs significantly improved some pulmonary and cardiovascular outcomes (p < 0.1) compared to six MV preterm controls. RhIGF-1/rhIGFBP-3 was not toxic to the liver, kidneys, or lungs. CONCLUSIONS: Three days of continuous iv infusion of rhIGF-1/rhIGFBP-3 at 1.5 mg/kg/day improved some pulmonary and cardiovascular outcomes without toxicity. IMPACT: Preterm birth is associated with rapid decreases in serum or plasma IGF-1 protein level. This decline adversely impacts the growth and development of the lung and cardiovascular system. For this pilot study, continuous infusion of optimal dosage of rhIGF-1/rhIGFBP-3 (1.5 mg/kg/day) to maintain physiologic plasma IGF-1 level of ~125 ng/mL during mechanical ventilation for 3 days statistically improved some structural and biochemical outcomes related to the alveolar formation that would favor improved gas exchange compared to vehicle-control. We conclude that 3 days of continuous iv infusion of rhIGF-1/rhIGFBP-3 improved some physiological, morphological, and biochemical outcomes, without toxicity, in mechanically ventilated preterm lambs.

Insulin-Like Growth Factor 1 in the Preterm Rabbit Pup: Characterization of Cerebrovascular Maturation following Administration of Recombinant Human Insulin-Like Growth Factor 1/Insulin-Like Growth Factor 1-Binding Protein 3.

Following preterm birth, serum levels of insulin-like growth factor 1 (IGF-1) decrease compared to corresponding in utero levels. A recent clinical trial indicated that supplementation with recombinant human (rh) IGF-1/rhIGF-binding protein 3 (rhIGF-1/rhIGFBP-3) prevents severe intraventricular hemorrhage (IVH) in extremely preterm infants. In a preterm rabbit pup model, we characterized endogenous serum and hepatic IGF-1, along with brain distribution of IGF-1 and IGF-1 receptor (IGF1R). We then evaluated the effects of rhIGF-1/rhIGFBP-3 on gene expression of regulators of cerebrovascular maturation and structure. Similar to preterm infants, serum IGF-1 concentrations decreased rapidly after preterm birth in the rabbit pup. Administration of rhIGF-1/rhIGFBP-3 restored in utero serum levels but was rapidly eliminated. Immunolabeled IGF1R was widely distributed in multiple brain regions, displaying an abundant density in the choroid plexus and sub-ependymal germinal zones. Increased IGF-1 immunoreactivity, distributed as IGF1R, was detected 4 h after rhIGF-1/rhIGFBP-3 administration. The rhIGF-1/rhIGFBP-3 treatment led to upregulation of choroid plexus genes involved in vascular maturation and structure, with corresponding protein translation for most of these genes. The preterm rabbit pup model is well suited for evaluation of IGF-1-based prevention of IVH. Administration of rhIGF-1/rhIGFBP-3 affects cerebrovascular maturation, suggesting a role for it in preventing preterm IVH.

Zebrafish behavioral profiling identifies multitarget antipsychotic-like compounds.

Many psychiatric drugs act on multiple targets and therefore require screening assays that encompass a wide target space. With sufficiently rich phenotyping and a large sampling of compounds, it should be possible to identify compounds with desired mechanisms of action on the basis of behavioral profiles alone. Although zebrafish (Danio rerio) behavior has been used to rapidly identify neuroactive compounds, it is not clear what types of behavioral assays would be necessary to identify multitarget compounds such as antipsychotics. Here we developed a battery of behavioral assays in larval zebrafish to determine whether behavioral profiles can provide sufficient phenotypic resolution to identify and classify psychiatric drugs. Using the antipsychotic drug haloperidol as a test case, we found that behavioral profiles of haloperidol-treated zebrafish could be used to identify previously uncharacterized compounds with desired antipsychotic-like activities and multitarget mechanisms of action.

Evaluation of recombinant human IGF-1/IGFBP-3 on intraventricular hemorrhage prevention and survival in the preterm rabbit pup model.

Insulin-like growth factor-1 (IGF-1) is essential for normal brain development and regulates processes of vascular maturation. The pathogenesis of intraventricular hemorrhage (IVH) relates to the fragility of the immature capillaries in the germinal matrix, and its inability to resist fluctuations in cerebral blood flow. In this work, using different experimental setups, we aimed to (i) establish an optimal time-point for glycerol-induction of IVH in relation to time-point of recombinant human (rh) IGF-1/rhIGFBP-3 administration, and (ii) to evaluate the effects of a physiologic replacement dose of rhIGF-1/rhIGFBP-3 on prevention of IVH and survival in the preterm rabbit pup. The presence of IVH was evaluated using high-frequency ultrasound and post-mortem examinations. In the first part of the study, the highest incidence of IVH (> 60%), occurred when glycerol was administered at the earliest timepoint, e.g., 6 h after birth. At later time-points (18 and 24 h) the incidence decreased substantially. In the second part of the study, the incidence of IVH and mortality rate following rhIGF-1/rhIGFBP-3 administration was not statistically different compared to vehicle treated animals. To evaluate the importance of maintaining intrauterine serum levels of IGF-1 following preterm birth, as reported in human interventional studies, additional studies are needed to further characterize and establish the potential of rhIGF-1/rhIGFBP-3 in reducing the prevalence of IVH and improving survival in the preterm rabbit pup.

Characterization of choroid plexus in the preterm rabbit pup following subcutaneous administration of recombinant human IGF-1/IGFBP-3.

Insulin-like growth factor-1 (IGF-1) is essential for normal brain development and regulates essential processes of vascular maturation and stabilization. Importantly, preterm birth is associated with reduced serum levels of IGF-1 as compared to in utero levels. Using a preterm rabbit pup model, we investigated the uptake of systemic recombinant human (rh) IGF-1 in complex with its main binding protein IGF-binding protein 3 (BP-3) to the brain parenchyma via the choroid plexus. Five hours after subcutaneous administration, labeled rhIGF-1/rhIGFBP-3 displayed a widespread presence in the choroid plexus of the lateral and third ventricle, however, to a less degree in the fourth, as well as in the perivascular and subarachnoid space. We found a time-dependent uptake of IGF-1 in cerebrospinal fluid, decreasing with postnatal age, and a translocation of IGF-1 through the choroid plexus. The impact of systemic rhIGF-1/rhIGFBP-3 on IGF-1 receptor activation in the choroid plexus decreased with postnatal age, correlating with IGF-1 uptake in cerebrospinal fluid. In addition, choroid plexus gene expression was observed to increase with postnatal age. Moreover, using choroid plexus in vitro cell cultures, gene expression and protein synthesis were further investigated upon rhIGF-1/rhIGFBP-3 stimulation as compared to rhIGF-1 alone, and found not to be differently altered. Here, we characterize the uptake of systemic rhIGF-1/rhIGFBP-3 to the preterm brain, and show that the interaction between systemic rhIGF-1/rhIGFBP-3 and choroid plexus varies over time.

Clinical outcome and gut development after insulin-like growth factor-1 supplementation to preterm pigs.

Background: Elevation of circulating insulin-like growth factor-1 (IGF-1) within normal physiological levels may alleviate several morbidities in preterm infants but safety and efficacy remain unclear. We hypothesized that IGF-1 supplementation during the first 1-2 weeks after preterm birth improves clinical outcomes and gut development, using preterm pigs as a model for infants. Methods: Preterm pigs were given vehicle or recombinant human IGF-1/binding protein-3 (rhIGF-1, 2.25 mg/kg/d) by subcutaneous injections for 8 days (Experiment 1, n = 34), or by systemic infusion for 4 days (Experiment 2, n = 19), before collection of blood and organs for analyses. Results: In both experiments, rhIGF-1 treatment increased plasma IGF-1 levels 3-4 fold, reaching the values reported for term suckling piglets. In Experiment 1, rhIGF-1 treatment increased spleen and intestinal weights without affecting clinical outcomes like growth, blood biochemistry (except increased sodium and gamma-glutamyltransferase levels), hematology (e.g., red and white blood cell populations), glucose homeostasis (e.g., basal and glucose-stimulated insulin and glucose levels) or systemic immunity variables (e.g., T cell subsets, neutrophil phagocytosis, LPS stimulation, bacterial translocation to bone marrow). The rhIGF-1 treatment increased gut protein synthesis (+11%, p < 0.05) and reduced the combined incidence of all-cause mortality and severe necrotizing enterocolitis (NEC, p < 0.05), but had limited effects on intestinal morphology, cell proliferation, cell apoptosis, brush-border enzyme activities, permeability and levels of cytokines (IL-1ß, IL-6, IL-8). In Experiment 2, rhIGF-1 treated pigs had reduced blood creatine kinase, creatinine, potassium and aspartate aminotransferase levels, with no effects on organ weights (except increased spleen weight), blood chemistry values, clinical variables or NEC. Conclusion: Physiological elevation of systemic IGF-1 levels for 8 days after preterm birth increased intestinal weight and protein synthesis, spleen weight and potential overall viability of pigs, without any apparent negative effects on recorded clinical parameters. The results add further preclinical support for safety and efficacy of supplemental IGF-1 to hospitalized very preterm infants.

Supplemental Insulin-Like Growth Factor-1 and Necrotizing Enterocolitis in Preterm Pigs.

Background: Recombinant human IGF-1/binding protein-3 (rhIGF-1/BP-3) is currently tested as a therapy in preterm infants but possible effects on the gut, including necrotizing enterocolitis (NEC), have not been tested. The aim of this study was to evaluate if rhIGF-1/BP-3 supplementation in the first days after birth negatively affects clinical variables like growth, physical activity, blood chemistry and hematology and gut maturation (e.g., intestinal permeability, morphology, enzyme activities, cytokine levels, enterocyte proliferation, NEC lesions), using NEC-sensitive preterm pigs as a model for preterm infants. Methods: Preterm pigs were given twice daily subcutaneous injections of rhIGF-1/BP-3 or vehicle. Blood was collected for IGF-1 measurements and gut tissue for NEC evaluation and biochemical analyses on day 5. Results: Baseline circulating IGF-1 levels were low in preterm pigs compared with near-term pigs reared by their mother (<20 vs. 70 ng/ml). Injection with rhIGF-1/BP-3 resulted in increased plasma IGF-1 levels for up to 6 h after injection (>40 ng/mL). rhIGF-1/BP-3 treatment reduced the incidence of severe NEC lesions (7/24 vs.16/24, p = 0.01) and overall NEC severity (1.8 ± 0.2 vs. 2.6 ± 0.3, p < 0.05, with most lesions occurring in colon). In the small intestine, villi length (405 ± 25 vs. 345 ± 33 µm) and activities of the brush border peptidases aminopeptidase N and dipeptidylpeptidase IV were increased in rhIGF-1/BP-3 treated pigs, relative to control pigs (+31-44%, both p < 0.05). The treatment had no effects on body weight, blood chemistry or hematology, except for an increase in blood leucocyte and neutrophil counts (p < 0.05, i.e., reduced neonatal neutropenia). Likewise, rhIGF-1/BP-3 treatment did not affect intestinal tissue cytokine levels (IL-1ß, IL-6, IL-8, TNFα,), enterocyte proliferation, goblet cell density, permeability or bacterial translocation to the bone marrow. Conclusion: Supplemental rhIGF-1/BP-3 did not negatively affect any of the measured variables of clinical status or gut maturation in preterm pigs. Longer-term safety and efficacy of exogenous rhIGF-1/BP-3 to support maturation of the gut and other critical organs in preterm newborns remain to be investigated in both pigs and infants.

The anxiolytic-like effects of the novel, orally active nociceptin opioid receptor agonist 8-[bis(2-methylphenyl)methyl]-3-phenyl-8-azabicyclo[3.2.1]octan-3-ol (SCH 221510).

Orphanin FQ/nociceptin (OFQ/N) is the endogenously occurring peptide ligand for the nociceptin opioid receptor (NOP) that produces anxiolytic-like effects in mice and rats. The present study assessed the anxiolytic-like activity of 8-[bis(2-methylphenyl)-methyl]-3-phenyl-8-azabicyclo[3.2.1]octan-3-ol (SCH 221510), a novel potent piperidine NOP agonist (EC(50) = 12 nM) that binds with high affinity (K(i) = 0.3 nM) and functional selectivity (>50-fold over the mu-, kappa-, and delta-opioid receptors). The anxiolytic-like activity and side-effect profile of SCH 221510 were assessed in a variety of models and the benzodiazepine, chlordiazepoxide (CDP), was included for comparison. The effects of chronic dosing of SCH 221510 were also assessed. Furthermore, the specificity of the anxiolytic-like effect of SCH 221510 was investigated with the NOP receptor antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) and the opioid receptor antagonist naltrexone. Like CDP (1-30 mg/kg i.p.), SCH 221510 (1-30 mg/kg p.o.) produced anxiolytic-like effects in the elevated plus-maze (rat and gerbil), Vogel conflict (rat), conditioned lick suppression (rat), fear-potentiated startle (rat), and pup separation-induced vocalization (guinea pig) assays. In the Vogel conflict, the anxiolytic-like effect of SCH 221510 (10 mg/kg) was attenuated by J-113397 (3-10 mg/kg p.o.), but not naltrexone (3-30 mg/kg i.p.). Additionally, the anxiolytic-like effects of SCH 221510 did not change appreciably following 14-day b.i.d. dosing in rats (10 mg/kg). Furthermore, unlike CDP, SCH 221510 (3-30 mg/kg) produced anxiolytic-like activity at doses that did not disrupt overt behavior. Collectively, these data suggest that NOP agonists such as SCH 221510 may have an anxiolytic-like profile similar to benzodiazepines, with a reduced side-effect liability.

Discovery of N-[(3R)-1-azabicyclo[2.2.2]oct-3-yl]furo[2,3-c]pyridine-5-carboxamide, an agonist of the alpha7 nicotinic acetylcholine receptor, for the potential treatment of cognitive deficits in schizophrenia: synthesis and structure--activity relationship.

N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]furo[2,3-c]pyridine-5-carboxamide (14, PHA-543,613), a novel agonist of the alpha7 neuronal nicotinic acetylcholine receptor (alpha7 nAChR), has been identified as a potential treatment of cognitive deficits in schizophrenia. Compound 14 is a potent and selective alpha7 nAChR agonist with an excellent in vitro profile. The compound is characterized by rapid brain penetration and high oral bioavailability in rat and demonstrates in vivo efficacy in auditory sensory gating and, in an in vivo model to assess cognitive performance, novel object recognition.

The gerbil elevated plus-maze I: behavioral characterization and pharmacological validation.

Several neurokinin NK1 receptor antagonists currently being developed for anxiety and depression have reduced affinity for the rat and mouse NK1 receptor compared with human. Consequently, it has proven difficult to test these agents in traditional rat and mouse models of anxiety and depression. This issue has been overcome, in part, by using non-traditional lab species such as the guinea pig and gerbil, which have NK1 receptors closer in homology to human NK1 receptors. However, there are very few reports describing the behavior of gerbils in traditional models of anxiety. The aim of the present study was to determine if the elevated plus-maze, a commonly used anxiety model, could be adapted for the gerbil. Using a specially-designed elevated plus-maze, gerbils exhibited an 'anxious' behavioral profile similar to that observed in rats and mice, i.e., reduced entries into, and time spent exploring, an open, aversive arm. The anxiolytic drugs diazepam (0.03-3 mg/kg i.p.), chlordiazepoxide (0.3-10 mg/kg i.p.), and buspirone (0.3-30 mg/kg s.c.) increased open arm exploration and produced anxiolytic-like effects on risk-assessment behaviors (reduced stretch-attend postures and increased head dips). Of particular interest, the antidepressant drugs imipramine (1-30 mg/kg p.o.), fluoxetine (1-30 mg/kg, p.o.) and paroxetine (0.3-10 mg/kg p.o.) each produced some acute anxiolytic-like activity, without affecting locomotor activity. The antipsychotic, haloperidol, and the psychostimulant, amphetamine, did not produce any anxiolytic-like effects (1-10 mg/kg s.c). The anxiogenic beta-carboline, FG-7142, reduced time spent in the open arm and head dips, and increased stretch-attend postures (1-30 mg/kg, i.p.). These studies have demonstrated that gerbils exhibit an anxiety-like profile on an elevated plus-maze, and that the gerbil elevated plus-maze may have predictive validity for anxiolytics, and antidepressants with potential anxiolytic-like effects.

The gerbil elevated plus-maze II: anxiolytic-like effects of selective neurokinin NK1 receptor antagonists.

Neurokinin NK1 receptor antagonists may have therapeutic potential in the treatment of anxiety and depression. Species variants in the NK1 receptor result in reduced affinity of NK1 receptor antagonists at rat and mouse NK1 receptors, making it difficult to test NK1 antagonists in traditional preclinical models of anxiety and depression. Gerbil NK1 receptors are similar in homology to the human NK1 receptor. In a companion article, we described the anxiety-like behavioral profile of gerbils on an adapted elevated plus-maze, and the ability of anxiolytic drugs to produce anti-anxiety effects in the gerbil elevated plus-maze. The aim of the present study was to determine whether oral (p.o.) administration of the NK1 receptor antagonists MK-869, L-742,694, L-733,060, CP-99,994, and CP-122,721 produced anxiolytic-like effects in the gerbil elevated plus-maze. Upon testing, all five NK1 antagonists produced anxiolytic-like effects. MK-869 (0.01-3 mg/kg) was the most potent NK1 antagonist, producing anxiolytic-like effects on percentage of open arm time, percentage of open arm entries, stretch-attend postures, and head dips at 0.03-0.3 mg/kg doses. L-742,694 (1-30 mg/kg) and L-733,060 (1-10 mg/kg) produced anxiolytic-like effects on percentage of open arm time and stretch-attend postures at 3-10 mg/kg doses. CP-99,994 (3-30 mg/kg) only produced an anxiolytic-like effect on stretch-attend postures. CP-122,721 (3-30 mg/kg) produced an anxiolytic-like effect on percentage of open arm time at 30 mg/kg. The order of potency of the NK1 antagonists to increase percentage of open arm time was very similar to their potency to block NK1 agonist-induced foot-tapping. These studies demonstrate that neurokinin NK1 receptor antagonists produce anxiolytic-like effects in a novel gerbil elevated plus-maze, and suggest that this is an appropriate model to test NK1 antagonists for preclinical anxiolytic activity.

Antidepressant-like activity of corticotropin-releasing factor type-1 receptor antagonists in mice.

The development of selective corticotropin-releasing factor type-1 (CRF1) receptor antagonists represents a potential novel treatment for depression. These studies evaluated CRF1 receptor antagonists for antidepressant-like activity in mice. Subchronic dosing of both R 121919 (3-[6-(dimethylamino)-4-methyl-pyrid-3-yl]-2,5-dimethyl-N,N-dipropyl-pyrazolo[2,3-a]pyrimidin-7-amine) and DMP 696 (4-(1,3-dimethoxyprop-2-ylamino)-2,7-dimethyl-8-(2,4-dichlorophenyl)-pyrazolo[1,5-a]-1,3,5-triazine) significantly decreased immobility time in the tail suspension test (at 30 and at 3 and 10 mg/kg, i.p., respectively). These antidepressant-like effects were observed at doses that did not impair general locomotor activity. Neither antalarmin (N-butyl-N-ethyl-[2,5,6-trimethyl-7-(2,4,6)trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amine) nor DMP 904 (4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1,5-a]-pyrimidine) had an effect indicative of antidepressant-like activity. These results suggest that the tail suspension assay may have utility to identify CRF1 receptor antagonists with antidepressant-like activity. Moreover, the results lend support to the theory that some nonpeptidic CRF1 receptor antagonists may possess antidepressant-like activity and therefore represent a promising novel pharmacotherapeutic strategy in the treatment of depression.

Models of neurological disease (substance abuse): self-administration in monkeys.

Drug self-administration is a procedure in which a subject performs a specified response that results in the delivery of a drug injection. This procedure is viewed as a relevant model for the study of human drug-taking behavior. Drug self-administration in primates has several characteristics that resemble drug-taking behavior in humans, and agents commonly abused by humans also generally maintain self-administration behavior in monkeys. Self-administration procedures allow for the study of a variety of drug properties. For instance, they can be used to investigate the abuse potential of new compounds and to study the effects of candidate medications for the treatment of drug addiction. These procedures can also be employed for examining drug reinforcement mechanisms. Described in this unit are procedures for studying intravenous drug self-administration in large primates, such as rhesus macaques, and smaller primates, such as squirrel monkeys.

Intravenous self-administration techniques in monkeys.

Drug self-administration is a procedure in which a subject performs a response, called an operant, that results in the delivery of a drug injection. This procedure is viewed as a relevant model for the study of human drug-taking behavior. Drug self-administration in primates has several characteristics that resemble drug-taking behavior in humans, and drugs that are commonly abused by humans also typically maintain self-administration behavior in monkeys. Drug self-administration procedures allow for the study of a variety of drug properties. For instance, they are used to investigate the abuse potential of new compounds and to study the effects of candidate medications for the treatment of drug addiction. These procedures also can be used to study the process of drug reinforcement. This unit describes intravenous drug self-administration in large primates, such as rhesus macaques, and smaller primates, such as squirrel monkeys.