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.

A novel phosphodiesterase 1 inhibitor reverses L-dopa-induced dyskinesia, but not motivation deficits, in monkeys

The enzyme phosphodiesterase 1 (PDE1) is highly expressed in the striatum and cortex. However, its role in corticostriatal function has not been fully investigated. The present study was aimed at evaluating the therapeutic potential of PDE1 inhibitors in treating motivation deficits and 3,4-dihydroxy-L-phenylalanine (L-dopa)-induced dyskinesia, which are pathological conditions of the corticostriatal system. We used a novel PDE1 inhibitor 3-ethyl-2-{[trans-4-(methoxymethyl)cyclohexyl]oxy}-7-(tetrahydro-2H-pyran-4-yl)-imidazo[5,1-f][1,2,4]triazin-4(3H)-one (DSR-143136), which was identified in our drug discovery program. Motivation in monkeys was measured using a progressive ratio task. L-Dopa-induced dyskinesia and disability scores were measured in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. DSR-143136 had a high selectivity for PDE1 over other PDE families and 67 other biologic targets. A dopamine D₁ receptor antagonist SCH-39166 at 0.01, 0.03 and 0.1 mg/kg potently decreased motivation in monkeys. However, DSR-143136 at 0.3 and 3 mg/kg did not affect motivation deficits induced by low-dose SCH-39166 (0.01 mg/kg). On the other hand, DSR-143136 at 3 mg/kg potently decreased L-dopa-induced dyskinesia in the Parkinsonian monkey model. Importantly, this antidyskinesic efficacy was NOT accompanied by detrimental effects on motor function. Further, this compound decreased on-time with marked or severe dyskinesia, without affecting on-time itself. These findings suggest that PDE1 inhibitor could be a therapeutic candidate for treating L-dopa-induced dyskinesia in Parkinson's disease, but not for motivation deficits.

An eye tracking system for monitoring face scanning patterns reveals the enhancing effect of oxytocin on eye contact in common marmosets

Eye tracking systems are used to investigate eyes position and gaze patterns presumed as eye contact in humans. Eye contact is a useful biomarker of social communication and known to be deficient in patients with autism spectrum disorders (ASDs). Interestingly, the same eye tracking systems have been used to directly compare face scanning patterns in some non-human primates to those in human. Thus, eye tracking is expected to be a useful translational technique for investigating not only social attention and visual interest, but also the effects of psychiatric drugs, such as oxytocin, a neuropeptide that regulates social behavior. In this study, we report on a newly established method for eye tracking in common marmosets as unique New World primates that, like humans, use eye contact as a mean of communication. Our investigation was aimed at characterizing these primates face scanning patterns and evaluating the effects of oxytocin on their eye contact behavior. We found that normal common marmosets spend more time viewing the eyes region in common marmoset's picture than the mouth region or a scrambled picture. In oxytocin experiment, the change in eyes/face ratio was significantly greater in the oxytocin group than in the vehicle group. Moreover, oxytocin-induced increase in the change in eyes/face ratio was completely blocked by the oxytocin receptor antagonist L-368,899. These results indicate that eye tracking in common marmosets may be useful for evaluating drug candidates targeting psychiatric conditions, especially ASDs.

The atypical antipsychotic blonanserin reverses (+)-PD-128907- and ketamine-induced deficit in executive function in common marmosets

Antagonism of the dopamine D3 receptor is considered a promising strategy for the treatment of cognitive impairment associated with schizophrenia. We have previously reported that the atypical antipsychotic blonanserin, a dopamine D2/D3 and serotonin 5-HT2A receptor antagonist, highly occupies dopamine D3 receptors at its antipsychotic dose range in rats. In the present study, we evaluated the effects of blonanserin on executive function in common marmosets using the object retrieval with detour (ORD) task. The dopamine D3 receptor-preferring agonist (+)-PD-128907 at 1mg/kg decreased success rate in the difficult trial, but not in the easy trial. Since the difference between the two trials is only cognitive demand, our findings indicate that excess activation of dopamine D3 receptors impairs executive function in common marmosets. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by (+)-PD-128907 in the difficult trial. This finding indicates that blonanserin has beneficial effect on executive function deficit induced by activation of the dopamine D3 receptor in common marmosets. Next, and based on the glutamatergic hypothesis of schizophrenia, the common marmosets were treated with the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine. Ketamine at sub-anesthetic doses decreased success rate in the difficult trial, but not in the easy trial. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by ketamine in the difficult trial. The findings of this study suggest that blonanserin might have beneficial effect on executive dysfunction in patients with schizophrenia.

The dopamine D1 receptor agonist SKF-82958 effectively increases eye blinking count in common marmosets

Eye blinking is a spontaneous behavior observed in all mammals, and has been used as a well-established clinical indicator for dopamine production in neuropsychiatric disorders, including Parkinson's disease and Tourette syndrome [1,2]. Pharmacological studies in humans and non-human primates have shown that dopamine agonists/antagonists increase/decrease eye blinking rate. Common marmosets (Callithrix jacchus) have recently attracted a great deal of attention as suitable experimental animals in the psychoneurological field due to their more developed prefrontal cortex than rodents, easy handling compare to other non-human primates, and requirement for small amounts of test drugs. In this study, we evaluated the effects of dopamine D1-4 receptors agonists on eye blinking in common marmosets. Our results show that the dopamine D1 receptor agonist SKF-82958 and the non-selective dopamine receptor agonist apomorphine significantly increased common marmosets eye blinking count, whereas the dopamine D2 agonist (+)-PHNO and the dopamine D3 receptor agonist (+)-PD-128907 produced somnolence in common marmosets resulting in a decrease in eye blinking count. The dopamine D4 receptor agonists PD-168077 and A-41297 had no effect on common marmosets' eye blinking count. Finally, the dopamine D1 receptor antagonist SCH 39166 completely blocked apomorphine-induced increase in eye blinking count. These results indicate that eye blinking in common marmosets may be a useful tool for in vivo screening of novel dopamine D1 receptor agonists as antipsychotics.

Discovery of N-sulfonyl-7-azaindoline derivatives as potent, orally available and selective M(4) muscarinic acetylcholine receptor agonists

We designed and synthesized novel N-sulfonyl-7-azaindoline derivatives as selective M4 muscarinic acetylcholine receptor agonists. Modification of the N-carbethoxy piperidine moiety of compound 2, an M4 muscarinic acetylcholine receptor (mAChR)-preferring agonist, led to compound 1, a selective M4 mAChR agonist. Compound 1 showed a highly selective M4 mAChR agonistic activity with weak hERG inhibition in vitro. A pharmacokinetic study of compound 1 in vivo revealed good bioavailability and brain penetration in rats. Compound 1 reversed methamphetamine-induced locomotor hyperactivity in rats (1-10 mg/kg, po).

Discovery of novel N-substituted oxindoles as selective m1 and m4 muscarinic acetylcholine receptors partial agonists

Activation of the M1 and M4 muscarinic acetylcholine receptors is thought to play an important role in improving the symptoms of schizophrenia. However, discovery of selective agonists for these receptors has been a challenge, considering the high sequence homology and conservation of the orthosteric acetylcholine binding site among muscarinic acetylcholine receptor subtypes. We report in this study the discovery of novel N-substituted oxindoles as potent muscarinic acetylcholine receptor partial agonists selective for M1 and M4 over M2, M3, and M5. Among these oxindoles, compound 1 showed high selectivity for the M1 and M4 receptors with remarkable penetration into the central nervous system. Compound 1 reversed methamphetamine- and apomorphine-induced psychosis-like behaviors with low potency to extrapyramidical and peripheral side effects.

Restoration of holoceruloplasmin synthesis in LEC rat after infusion of recombinant adenovirus bearing WND cDNA

Wilson's disease, an autosomal recessive disorder, is characterized by the excessive accumulation of copper in the liver. WND (ATP7B) gene, which encodes a putative copper transporting P-type ATPase, is defective in the patients. To investigate the in vivo function of WND protein as well as its intracellular localization, WND cDNA was introduced to the Long-Evans Cinnamon rat, known as a rodent model for Wilson's disease, by recombinant adenovirus-mediated gene delivery. An immunofluorescent study and a subcellular fractionation study revealed the transgene expression in liver and its localization to the Golgi apparatus. Moreover, since the synthesis of holoceruloplasmin is disturbed in the Long-Evans Cinnamon rat, the plasma level of holoceruloplasmin, oxidase-active and copper-bound form, was examined to evaluate the function of WND protein with respect to the copper transport. Consequently, the appearance of holoceruloplasmin in plasma was confirmed by Western blot analysis and plasma measurements for the oxidase activity and the copper content. These findings indicate that introduced WND protein may function in the copper transport coupled with the synthesis of ceruloplasmin and that the Golgi apparatus is the likely site for WND protein to manifest its function.

A novel method for selective isolation of C-terminal peptides from tryptic digests of proteins by immobilized anhydrotrypsin: application to structural analyses of the tail sheath and tube proteins from bacteriophage T4

A novel method useful for selective isolation of the C-terminal peptide from a tryptic digestion mixture of a protein has been developed by taking advantage of a unique property of anhydrotrypsin, which has a strong specific affinity for the peptides containing arginine or lysine at their C-termini. Briefly, peptides produced by tryptic digestion of a protein are fractionated by affinity chromatography on a column of immobilized anhydrotrypsin. The C-terminal peptide is recovered in a breakthrough fraction, while the remainders are adsorbed on the column (unless the protein ends in arginine or lysine). The breakthrough fraction is then subjected to reversed-phase high-performance liquid chromatography in order to purify the C-terminal peptide. Using this method, we have successfully isolated the C-terminal peptides from tryptic digests of the sheath protein (gp 18) and the tube protein (gp 19) of bacteriophage T4. The analytical results on these peptides, together with the information on the N-terminal structures of the original proteins and on the nucleotide sequences of genes 18 and 19, allowed us to establish the complete primary structures of the two proteins.