GDE5/Gpcpd1 activity determines phosphatidylcholine composition in skeletal muscle and regulates contractile force in mice.

Glycerophosphocholine (GPC) is an important precursor for intracellular choline supply in phosphatidylcholine (PC) metabolism. GDE5/Gpcpd1 hydrolyzes GPC into choline and glycerol 3-phosphate; this study aimed to elucidate its physiological function in vivo. Heterozygous whole-body GDE5-deficient mice reveal a significant GPC accumulation across tissues, while homozygous whole-body knockout results in embryonic lethality. Skeletal muscle-specific GDE5 deletion (Gde5 skKO) exhibits reduced passive force and improved fatigue resistance in electrically stimulated gastrocnemius muscles in vivo. GDE5 deficiency also results in higher glycolytic metabolites and glycogen levels, and glycerophospholipids alteration, including reduced levels of phospholipids that bind polyunsaturated fatty acids (PUFAs), such as DHA. Interestingly, this PC fatty acid compositional change is similar to that observed in skeletal muscles of denervated and Duchenne muscular dystrophy mouse models. These are accompanied by decrease of GDE5 expression, suggesting a regulatory role of GDE5 activity for glycerophospholipid profiles. Furthermore, a DHA-rich diet enhances contractile force and lowers fatigue resistance, suggesting a functional relationship between PC fatty acid composition and muscle function. Finally, skinned fiber experiments show that GDE5 loss increases the probability of the ryanodine receptor opening and lowers the maximum Ca2+-activated force. Collectively, GDE5 activity plays roles in PC and glucose/glycogen metabolism in skeletal muscle.

Anatomical variability, multi-modal coordinate systems, and precision targeting in the marmoset brain.

Localising accurate brain regions needs careful evaluation in each experimental species due to their individual variability. However, the function and connectivity of brain areas is commonly studied using a single-subject cranial landmark-based stereotactic atlas in animal neuroscience. Here, we address this issue in a small primate, the common marmoset, which is increasingly widely used in systems neuroscience. We developed a non-invasive multi-modal neuroimaging-based targeting pipeline, which accounts for intersubject anatomical variability in cranial and cortical landmarks in marmosets. This methodology allowed creation of multi-modal templates (MarmosetRIKEN20) including head CT and brain MR images, embedded in coordinate systems of anterior and posterior commissures (AC-PC) and CIFTI grayordinates. We found that the horizontal plane of the stereotactic coordinate was significantly rotated in pitch relative to the AC-PC coordinate system (10 degrees, frontal downwards), and had a significant bias and uncertainty due to positioning procedures. We also found that many common cranial and brain landmarks (e.g., bregma, intraparietal sulcus) vary in location across subjects and are substantial relative to average marmoset cortical area dimensions. Combining the neuroimaging-based targeting pipeline with robot-guided surgery enabled proof-of-concept targeting of deep brain structures with an accuracy of 0.2 mm. Altogether, our findings demonstrate substantial intersubject variability in marmoset brain and cranial landmarks, implying that subject-specific neuroimaging-based localization is needed for precision targeting in marmosets. The population-based templates and atlases in grayordinates, created for the first time in marmoset monkeys, should help bridging between macroscale and microscale analyses.

Comparative connectomics of the primate social brain.

Social interaction is thought to provide a selection pressure for human intelligence, yet little is known about its neurobiological basis and evolution throughout the primate lineage. Recent advances in neuroimaging have enabled whole brain investigation of brain structure, function, and connectivity in humans and non-human primates (NHPs), leading to a nascent field of comparative connectomics. However, linking social behavior to brain organization across the primates remains challenging. Here, we review the current understanding of the macroscale neural mechanisms of social behaviors from the viewpoint of system neuroscience. We first demonstrate an association between the number of cortical neurons and the size of social groups across primates, suggesting a link between neural information-processing capacity and social capabilities. Moreover, by capitalizing on recent advances in species-harmonized functional MRI, we demonstrate that portions of the mirror neuron system and default-mode networks, which are thought to be important for representation of the other's actions and sense of self, respectively, exhibit similarities in functional organization in macaque monkeys and humans, suggesting possible homologies. With respect to these two networks, we describe recent developments in the neurobiology of social perception, joint attention, personality and social complexity. Together, the Human Connectome Project (HCP)-style comparative neuroimaging, hyperscanning, behavioral, and other multi-modal investigations are expected to yield important insights into the evolutionary foundations of human social behavior.

Personality, subjective well-being, and the serotonin 1a receptor gene in common marmosets (Callithrix jacchus).

Studies of personality traits in common marmosets (Callithrix jacchus) indicate that there are five or six constructs-Sociability, Dominance, Neuroticism, Openness, and two related to Conscientiousness. The present study attempted to determine whether our earlier study of laboratory-housed individuals only yielded three-Dominance, Sociability, and Neuroticism-because of a low amount of between-subjects variance. To do so, we increased our sample size from 77 to 128. In addition, we ascertained the reliability and validity of ratings and whether polymorphisms related to the serotonin 1a receptor were associated with personality. We found Sociability, Dominance, and Negative Affect factors that resembled three domains found in previous studies, including ours. We also found an Openness and Impulsiveness factor, the latter of which bore some resemblance to Conscientiousness, and two higher-order factors, Pro-sociality and Boldness. In further analyses, we could not exclude the possibility that Pro-sociality and Boldness represented a higher-level of personality organization. Correlations between personality factors and well-being were consistent with the definitions of the factors. There were no significant associations between personality and genotype. These results suggest that common marmoset personality structure varies as a function of rearing or housing variables that have not yet been investigated systematically.

Versatile whole-organ/body staining and imaging based on electrolyte-gel properties of biological tissues.

Whole-organ/body three-dimensional (3D) staining and imaging have been enduring challenges in histology. By dissecting the complex physicochemical environment of the staining system, we developed a highly optimized 3D staining imaging pipeline based on CUBIC. Based on our precise characterization of biological tissues as an electrolyte gel, we experimentally evaluated broad 3D staining conditions by using an artificial tissue-mimicking material. The combination of optimized conditions allows a bottom-up design of a superior 3D staining protocol that can uniformly label whole adult mouse brains, an adult marmoset brain hemisphere, an ~1 cm3 tissue block of a postmortem adult human cerebellum, and an entire infant marmoset body with dozens of antibodies and cell-impermeant nuclear stains. The whole-organ 3D images collected by light-sheet microscopy are used for computational analyses and whole-organ comparison analysis between species. This pipeline, named CUBIC-HistoVIsion, thus offers advanced opportunities for organ- and organism-scale histological analysis of multicellular systems.

Common marmoset (Callithrix jacchus) personality, subjective well-being, hair cortisol level and AVPR1a, OPRM1, and DAT genotypes.

We studied personality, subjective well-being, and hair cortisol level, in common marmosets Callithrix jacchus, a small, cooperatively breeding New World monkey, by examining their associations with one another and genotypes. Subjects were 68 males and 9 females that lived in the RIKEN Center for Life Science Technologies. Personality and subjective well-being were assessed by keeper ratings on two questionnaires, hair samples were obtained to assay cortisol level and buccal swabs were used to assess AVPR1a, OPRM1 and DAT genotypes. Three personality domains-Dominance, Sociability, and Neuroticism-were identified. Consistent with findings in other species, Sociability and Neuroticism were related to higher and lower subjective well-being, respectively. Sociability was also associated with higher hair cortisol levels. The personality domains and hair cortisol levels were heritable and associated with genotypes: the short form of AVPR1a was associated with lower Neuroticism and the AA genotype of the A111T SNP of OPRM1 was related to lower Dominance, lower Neuroticism, and higher hair cortisol level. Some genetic associations were not in directions that one would expect given findings in other species. These findings provide insights into the proximate and ultimate bases of personality in common marmosets, other primates and humans.

Quantification of receptor activation by oxytocin and vasopressin in endocytosis-coupled bioluminescence reduction assay using nanoKAZ.

Oxytocin (OXT) and arginine vasopressin (AVP) are structurally similar neuropeptide hormones that function as neurotransmitters in the brain, and have opposite key roles in social behaviors. These peptides bind to their G protein-coupled receptors (OXTR and AVPRs), inducing calcium ion-dependent signaling pathways and endocytosis of these receptors. Because selective agonists and antagonists for these receptors have been developed as therapeutic and diagnostic agents for diseases such as psychiatric disorders, facile methods are in demand for the evaluation of selectivity between these receptors. In this study, we developed a quantitative assay for OXT- and AVP-induced endocytosis of their receptors. The mutated Oplophorus luciferase, nanoKAZ, was fused to OXTR and AVPRs to enable rapid quantification of agonist-induced endocytosis by bioluminescence reduction. Agonist stimulation significantly decreases bioluminescence of nanoKAZ-fused receptors in living cells. Using this system, we evaluated clinically used OXTR antagonist atosiban and a reported pyrazinyltriazole derivative, hereby designated as PF13. Atosiban acted as an antagonist of AVPR1a, as well as an agonist for AVPR1b, whereas PF13 antagonized OXTR more selectively than atosiban, as reported previously. This paper shows a strategy for quantification of agonist-induced endocytosis of OXTR and AVPRs, and confirms its potent utility in the evaluation of agonists and antagonists.

Individual identity and affective valence in marmoset calls: in vivo brain imaging with vocal sound playback.

As with humans, vocal communication is an important social tool for nonhuman primates. Common marmosets (Callithrix jacchus) often produce whistle-like 'phee' calls when they are visually separated from conspecifics. The neural processes specific to phee call perception, however, are largely unknown, despite the possibility that these processes involve social information. Here, we examined behavioral and whole-brain mapping evidence regarding the detection of individual conspecific phee calls using an audio playback procedure. Phee calls evoked sound exploratory responses when the caller changed, indicating that marmosets can discriminate between caller identities. Positron emission tomography with [18F] fluorodeoxyglucose revealed that perception of phee calls from a single subject was associated with activity in the dorsolateral prefrontal, medial prefrontal, orbitofrontal cortices, and the amygdala. These findings suggest that these regions are implicated in cognitive and affective processing of salient social information. However, phee calls from multiple subjects induced brain activation in only some of these regions, such as the dorsolateral prefrontal cortex. We also found distinctive brain deactivation and functional connectivity associated with phee call perception depending on the caller change. According to changes in pupillary size, phee calls from a single subject induced a higher arousal level compared with those from multiple subjects. These results suggest that marmoset phee calls convey information about individual identity and affective valence depending on the consistency or variability of the caller. Based on the flexible perception of the call based on individual recognition, humans and marmosets may share some neural mechanisms underlying conspecific vocal perception.

Distinct roles for primate caudate dopamine D1 and D2 receptors in visual discrimination learning revealed using shRNA knockdown.

The striatum plays important motor, associative and cognitive roles in brain functions. However, the rodent dorsolateral (the primate putamen) and dorsomedial (the primate caudate nucleus) striatum are not anatomically separated, making it difficult to distinguish their functions. By contrast, anatomical separation exists between the caudate nucleus and putamen in primates. Here, we successfully decreased dopamine D1 receptor (D1R) or D2R mRNA expression levels selectively in the marmoset caudate using shRNA knockdown techniques, as determined using positron emission tomography imaging with specific D1R and D2R ligands and postmortem in situ hybridization analysis. We then conducted a voxel-based correlation analysis between binding potential values of PET imaging and visual discrimination learning task performance in these genetically modified marmosets to find a critical role for the caudate D2R but no apparent role for the caudate D1R. This latter finding challenges the current understanding of the mechanisms underlying D1R activation in the caudate.

Marmoset Serotonin 5-HT1A Receptor Mapping with a Biased Agonist PET Probe 18F-F13714: Comparison with an Antagonist Tracer 18F-MPPF in Awake and Anesthetized States.

BACKGROUND: In vivo mapping by positron emission tomography of the serotonin 1A receptors has been hindered by the lack of suitable agonist positron emission tomography probes. 18F-labeled F13714 is a recently developed biased agonist positron emission tomography probe that preferentially targets subpopulations of serotonin 1A receptors in their "active state," but its brain labeling pattern in nonhuman primate has not been described. In addition, a potential confound in the translatability of PET data between nonhuman animal and human arise from the use of anesthetics that may modify the binding profiles of target receptors. METHODS: Positron emission tomography scans were conducted in a cohort of common marmosets (n=4) using the serotonin 1A receptor biased agonist radiotracer, 18F-F13714, compared with a well-characterized 18F-labeled antagonist radiotracer, 18F-MPPF. Experiments on each animal were performed under both consciousness and isoflurane-anesthesia conditions. RESULTS: 18F-F13714 binding distribution in marmosets by positron emission tomography differs markedly from that of the 18F-MPPF. Whereas 18F-MPPF showed highest binding in hippocampus and amygdala, 18F-F13714 showed highest labeling in other regions, including insular and cingulate cortex, thalamus, raphe, caudate nucleus, and putamen. The binding potential values of 18F-F13714 were about one-third of those observed with 18F-MPPF, with marked individual- and region-specific differences under isoflurane-anesthetized vs conscious conditions. CONCLUSIONS: These findings highlight the importance of investigating the brain imaging of serotonin 1A receptors using agonist probes such as 18F-F13714, which may preferentially target subpopulations of serotonin 1A receptors in specific brain regions of nonhuman primate as a biased agonist.

Positron emission tomography imaging of the social brain of common marmosets.

Positron emission tomography (PET) is a molecular imaging modality that can visualize functional neurochemical processes throughout the brain in the living condition, and is useful in bridging the gap between experimental animals and humans. We applied PET to common marmosets to study the brain mechanisms underlying social behaviors. Common marmosets are known for their high level of sociality within a cooperative breeding system, which is rare among non-human primates, and they could represent valuable animals for studying human-like social behaviors. PET successfully revealed a brain-molecular relationship underlying social traits and a functional brain network associated with social situations in common marmosets. Marmoset PET appears likely to prove useful in understanding the neurobiological mechanisms underpinning social behaviors in both physiological and pathological conditions, and has potential for simulating psychiatric disorders.

A voxel-based analysis of brain activity in high-order trigeminal pathway in the rat induced by cortical spreading depression.

Cortical spreading depression (SD) is a self-propagating wave of depolarization that is thought to be an underling mechanism of migraine aura. Growing evidence demonstrates that cortical SD triggers neurogenic meningeal inflammation and contributes to migraine headaches via subsequent activation of trigeminal afferents. Although direct and indirect evidence shows that cortical SD activates the trigeminal ganglion (peripheral pathway) and the trigeminal nucleus caudalis (TNC, the first central site of the trigeminal nociceptive pathway), it is not yet known whether cortical SD activates the high-order trigeminal nociceptive pathway in the brain. To address this, we induced unilateral cortical SD in rats, and then examined brain activity using voxel-based statistical parametric mapping analysis of FDG-PET imaging. The results show that approximately 40h after the induction of unilateral cortical SD, regional brain activity significantly increased in several regions, including ipsilateral TNC, contralateral ventral posteromedial (VPM) and posterior thalamic nuclei (Po), the trigeminal barrel-field region of the primary somatosensory cortex (S1BF), and secondary somatosensory cortex (S2). These results suggest that cortical SD is a noxious stimulus that can activate the high-order trigeminal nociceptive pathway even after cortical SD has subsided, probably due to prolonged meningeal inflammation.

Whole-brain imaging with single-cell resolution using chemical cocktails and computational analysis.

Systems-level identification and analysis of cellular circuits in the brain will require the development of whole-brain imaging with single-cell resolution. To this end, we performed comprehensive chemical screening to develop a whole-brain clearing and imaging method, termed CUBIC (clear, unobstructed brain imaging cocktails and computational analysis). CUBIC is a simple and efficient method involving the immersion of brain samples in chemical mixtures containing aminoalcohols, which enables rapid whole-brain imaging with single-photon excitation microscopy. CUBIC is applicable to multicolor imaging of fluorescent proteins or immunostained samples in adult brains and is scalable from a primate brain to subcellular structures. We also developed a whole-brain cell-nuclear counterstaining protocol and a computational image analysis pipeline that, together with CUBIC reagents, enable the visualization and quantification of neural activities induced by environmental stimulation. CUBIC enables time-course expression profiling of whole adult brains with single-cell resolution.

New index based on the physical separation of motion into three categories for characterizing the effect of cocaine in mice.

Characterization of open-field behavior and locomotor activity is widely used to assess the influence of a drug on mouse or rat behavior. In this study, we developed an index for characterizing the behavior of cocaine-administered mice (C57BL/6, DBA/2, and BALB/c). Because a three-exponential-model exhibited the best fit to the obtained data among the different probability density functions, we divided each walking episode into three categories according to the duration of movement. We found a significant difference in decay variation of mean speed with time in the case of long walking duration. To clarify this difference quantitatively, we developed an index for the changes in locomotion control, based on a heuristic argument regarding the ratio of the coefficients of the drag term obtained by the biphasic motion-equation model. The index had a significant dose-related effect in each strain and a significant strain effect in high-concentration drug. Therefore, it would thus be useful for examining the effect of the drug on locomotor activity in mice. Moreover, evaluating other characters suggested previously, the proposed index had good advantage to differentiate the dose-related response in the three species of inbred mice.

Linkage between the midline cortical serotonergic system and social behavior traits: positron emission tomography studies of common marmosets.

Serotonin is known to play an important role not only in regulating emotional behaviors, but also in the formation of social behavior traits. To determine the location and serotonin function of brain areas involved in social behavior traits, we tested serotonin transporter (SERT) binding and neural activity linked with the social behaviors of common marmosets with positron emission tomography using [(11)C]-3-amino-4-(2-dimetylaminomethyl-phenylsulfanyl)-benzonitrile and [(18)F]fluorodeoxyglucose, respectively. Factor analysis of behavioral measures during a direct encounter between unfamiliar adult males identified three classes of social behavioral traits: (1) aggressive, (2) anxious, and (3) unfriendly (opposite of friendly). Voxel-based analysis revealed a significant association between SERT binding with the social behavioral traits in the midline cortical subregions. Aggressive and friendly traits are localized to the posterior cingulate cortex, and the anxious trait is localized to the anterior cingulate cortex. In addition, neural activity and functional connectivity of the posterior and anterior cingulate cortices appear to be altered depending on the social situation. These results suggest that the midline cortical serotonergic system is crucial in social behavior traits and its subregions are functionally segregated in socio-emotional processing.

Evaluation of dopamine D2/D3 and serotonin 5-HT2A receptor occupancy for a novel antipsychotic, lurasidone, in conscious common marmosets using small-animal positron emission tomography.

RATIONALE: Lurasidone is a novel antipsychotic drug with potent binding affinity for dopamine D(2) and serotonin (5-hydroxytryptamine, 5-HT)(2A), 5-HT(7), and 5-HT(1A) receptors. Previous pharmacological studies have revealed that lurasidone exhibits a preferable profile (potent antipsychotic activity and lower incidence of catalepsy) to other antipsychotic drugs, although the contribution of receptor subtypes to this profile remains unclear. OBJECTIVES: To compare target engagements of lurasidone with those of an atypical antipsychotic, olanzapine, we performed evaluation of dopamine D(2)/D(3) and serotonin 5-HT(2A) receptor occupancy in vivo by positron emission tomography (PET) with conscious common marmosets. METHODS: We measured brain receptor occupancies in conscious common marmosets after oral administrations of lurasidone or olanzapine by PET with [(11)C]raclopride and [(11)C]R-(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine methanol (MDL 100907) for D(2)/D(3) and 5-HT(2A) receptors, respectively. RESULTS: Increases in brain D(2)/D(3) receptor occupancies of both lurasidone and olanzapine, which reached >80 % at maximum, were observed in the striatum with significant correlations to plasma drug levels. However, lurasidone showed lower 5-HT(2A) receptor occupancy in the frontal cortex within the same dose range, while olanzapine showed broadly comparable 5-HT(2A) and D(2)/D(3) receptor occupancies. CONCLUSIONS: Compared with olanzapine, lurasidone preferentially binds to D(2)/D(3) receptors rather than 5-HT(2A) receptors in common marmosets. These results suggest that the contribution of in vivo 5-HT(2A) receptor blocking activity to the pharmacological profile of lurasidone might differ from olanzapine in terms of the low risk of extrapyramidal syndrome and efficacy against negative symptoms.

The food reaching test: a sensitive test of behavioral improvements by deep brain stimulation in MPTP-treated monkey.

We modified an objective behavioral test, namely the food reaching test (FRT), for quantitative assessment of motor performance improved by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the Parkinsonian monkeys. The symptomatic features and their severity in 3 monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were evaluated with a subjective monkey Parkinson's disease rating scale (PDRS). We then performed STN-DBS with the minimum current intensity that stopped the tremor. The time required for the monkeys to pick up all 5 pieces of potato (FRT time) was measured as a major index to evaluate bradykinesia. The success rate was adopted as another index for assessing overall motor impairments. Although both FRT time and PDRS score were similarly improved by STN-DBS, change of FRT time appeared more sensitive than that of PDRS scores. FRT is an easily trained behavioral test with high objectivity and sensitivity that can be applied for assessing motor performance in MPTP-treated monkeys during experiments in a restrained condition such as functional imaging of the brain.

Disruption of programmed masticatory movements in unilateral MPTP-treated monkeys as a model of jaw movement abnormality in Parkinson's disease.

While motor disturbance in Parkinson's disease can affect innate, programmed processes, such as masticatory mandibular movements, the pathophysiology of such abnormalities remains unclear. This study applies digital analysis by high-speed video signal processing that tracks three dots placed around the mouth for recording masticatory movements in unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. The system analyzes displacement, velocity and cycle duration of the topography of mandibular movement during mastication of sweet potato slices. In monkeys receiving MPTP into the right carotid artery (n = 3), positron emission tomography indicated significant reduction in the binding of (E)-N-(3-iodoprop-2-enyl)-2ß-carbo[(11)C]methoxy-3ß-(4-methylphenyl)nortropane ([(11)C]PE2I) to the dopamine transporter in the right caudate, putamen, nucleus accumbens and substantia nigra relative to the contralateral hemisphere. These monkeys showed hypokinesia of the left forelimbs and hindlimbs. During mastication, MPTP-treated monkeys chewed preferentially on the left side, while untreated monkeys (n = 3) showed no preference for chewing side. The amplitude of vertical opening and closing movements was reduced in MPTP-treated monkeys, with a slight but significant increase in the lateral component of mandibular movements. The velocity of all phases of horizontal mandibular movements was reduced. In consequence, duration of the occlusal phase was increased, while duration of the closing phase was decreased in MPTP-treated monkeys. These findings indicate that during masticatory movements MPTP-treated monkeys chew preferentially on the side contralateral to loss of dopamine neurons, with reduced amplitude and velocity of mandibular movements. High-speed digital movement analysis is able to define and quantify abnormalities of orofacial movement topography as a sign of parkinsonism.

Relaxin-3-deficient mice showed slight alteration in anxiety-related behavior.

Relaxin-3 is a neuropeptide belonging to the relaxin/insulin superfamily. Studies using rodents have revealed that relaxin-3 is predominantly expressed in neurons in the nucleus incertus (NI) of the pons, the axons of which project to forebrain regions including the hypothalamus. There is evidence that relaxin-3 is involved in several functions, including food intake and stress responses. In the present study, we generated relaxin-3 gene knockout (KO) mice and examined them using a range of behavioral tests of sensory/motor functions and emotion-related behaviors. The results revealed that relaxin-3 KO mice exhibited normal growth and appearance, and were generally indistinguishable from wild genotype littermates. There was no difference in bodyweight among genotypes until at least 28 weeks after birth. In addition, there were no significant differences between wild-type and KO mice in locomotor activity, social interaction, hot plate test performance, fear conditioning, depression-like behavior, and Y-maze test performance. However, in the elevated plus maze test, KO mice exhibited a robust increase in the tendency to enter open arms, although they exhibited normal performance in a light/dark transition test and showed no difference from wild-type mice in the time spent in central area in the open field test. On the other hand, a significant increase in the acoustic startle response was observed in KO mice. These results indicate that relaxin-3 is slightly involved in the anxiety-related behavior.

Developmental changes in P-glycoprotein function in the blood-brain barrier of nonhuman primates: PET study with R-11C-verapamil and 11C-oseltamivir.

UNLABELLED: P-glycoprotein (P-gp) plays a pivotal role in limiting the penetration of xenobiotic compounds into the brain at the blood-brain barrier (BBB), where its expression increases with maturation in rats. We investigated developmental changes in P-gp function in the BBB of nonhuman primates using PET with R-(11)C-verapamil, a PET radiotracer useful for evaluating P-gp function. In addition, developmental changes in the brain penetration of (11)C-oseltamivir, a substrate for P-gp, was investigated as practical examples. METHODS: PET studies in infant (age, 9 mo), adolescent (age, 24-27 mo), and adult (age, 5.6-6.6 y) rhesus monkeys (Macaca mulatta) were performed with R-(11)C-verapamil and also with (11)C-oseltamivir. Arterial blood samples and PET images were obtained at frequent intervals up to 60 min after administration of the PET tracer. Dynamic imaging data were evaluated by integration plots using data collected within the first 2.5 min after tracer administration. RESULTS: R-(11)C-verapamil rapidly penetrated the brain, whereas the blood concentration of intact R-(11)C-verapamil decreased rapidly in all subjects. The maximum brain uptake in infant (0.033% ± 0.007% dose/g of brain) and adolescent (0.020% ± 0.002% dose/g) monkeys was 4.1- and 2.5-fold greater, respectively, than uptake in adults (0.0082% ± 0.0007% dose/g). The clearance of brain R-(11)C-verapamil uptake in adult monkeys was 0.056 ± 0.010 mL/min/g, significantly lower than that in infants (0.11 ± 0.04 mL/min/g) and adolescents (0.075 ± 0.023 mL/min/g). (11)C-oseltamivir showed little brain penetration in adult monkeys, with a clearance of R-(11)C-verapamil uptake of 0.0072 and 0.0079 mL/min/g, slightly lower than that in infant (0.0097 and 0.0104 mL/min/g) and adolescent (0.0097 and 0.0098 mL/min/g) monkeys. CONCLUSION: These results suggest that P-gp function in the BBB changes with development in rhesus monkeys, and this change may be closely related to the observed difference in drug responses in the brains of children and adult humans.