A whole-brain analysis of functional connectivity and immediate early gene expression reveals functional network shifts after operant learning.

Previous studies of operant learning have addressed neuronal activities and network changes in specific brain areas, such as the striatum, sensorimotor cortex, prefrontal/orbitofrontal cortices, and hippocampus. However, how changes in the whole-brain network are caused by cellular-level changes remains unclear. We, therefore, combined resting-state functional magnetic resonance imaging (rsfMRI) and whole-brain immunohistochemical analysis of early growth response 1 (EGR1), a marker of neural plasticity, to elucidate the temporal and spatial changes in functional networks and underlying cellular processes during operant learning. We used an 11.7-Tesla MRI scanner and whole-brain immunohistochemical analysis of EGR1 in mice during the early and late stages of operant learning. In the operant training, mice received a reward when they pressed left and right buttons alternately, and were punished with a bright light when they made a mistake. A group of mice (n = 22) underwent the first rsfMRI acquisition before behavioral sessions, the second acquisition after 3 training-session-days (early stage), and the third after 21 training-session-days (late stage). Another group of mice (n = 40) was subjected to histological analysis 15 min after the early or late stages of behavioral sessions. Functional connectivity increased between the limbic areas and thalamus or auditory cortex after the early stage of training, and between the motor cortex, sensory cortex, and striatum after the late stage of training. The density of EGR1-immunopositive cells in the motor and sensory cortices increased in both the early and late stages of training, whereas the density in the amygdala increased only in the early stage of training. The subcortical networks centered around the limbic areas that emerged in the early stage have been implicated in rewards, pleasures, and fears. The connectivities between the motor cortex, somatosensory cortex, and striatum that consolidated in the late stage have been implicated in motor learning. Our multimodal longitudinal study successfully revealed temporal shifts in brain regions involved in behavioral learning together with the underlying cellular-level plasticity between these regions. Our study represents a first step towards establishing a new experimental paradigm that combines rsfMRI and immunohistochemistry to link macroscopic and microscopic mechanisms involved in learning.

Structural Plastic Changes of Cortical Gray Matter Revealed by Voxel-Based Morphometry and Histological Analyses in a Monkey Model of Central Post-Stroke Pain.

Central post-stroke pain (CPSP) is a chronic pain caused by stroke lesions of somatosensory pathways. Several brain imaging studies among patients with CPSP demonstrate that the pathophysiological mechanism underlying this condition is the maladaptive plasticity of pain-related brain regions. However, the temporal profile of the regional plastic changes, as suggested by brain imaging of CPSP patients, as well as their cellular basis, is unknown. To investigate these issues, we performed voxel-based morphometry (VBM) using T1-weighted magnetic resonance imaging and immunohistochemical analysis with our established CPSP monkey model. From 8 weeks after a hemorrhagic lesion to the unilateral ventral posterolateral nucleus of the thalamus, the monkeys exhibited significant behavioral changes that were interpreted as reflecting allodynia. The present VBM results revealed a decrease in gray matter volume in the pain-related areas after several weeks following the lesion. Furthermore, immunohistochemical staining in the ipsilesional posterior insular cortex (ipsi-PIC) and secondary somatosensory cortex (ipsi-SII), where the significant reduction in gray matter volume was observed in the VBM result, displayed a significant reduction in both excitatory and inhibitory synaptic terminals compared to intact monkeys. Our results suggest that progressive changes in neuronal morphology, including synaptic loss in the ipsi-PIC/SII, are involved in theCPSP.

The Ventral Striatum is a Key Node for Functional Recovery of Finger Dexterity After Spinal Cord Injury in Monkeys.

In a recent study, we demonstrated that the ventral striatum (VSt) controls finger movements directly during the early recovery stage after spinal cord injury (SCI), implying that the VSt may be a part of neural substrates responsible for the recovery of dexterous finger movements. The VSt is accepted widely as a key node for motivation, but is not thought to be involved in the direct control of limb movements. Therefore, whether a causal relationship exists between the VSt and motor recovery after SCI is unknown, and the role of the VSt in the recovery of dexterous finger movements orfinger movements in general after SCI remains unclear. In the present study, functional brain imaging in a macaque model of SCI revealed a strengthened functional connectivity between motor-related areas and the VSt during the recovery process for precision grip, but not whole finger grip after SCI. Furthermore, permanent lesion of the VSt impeded the recoveryof precision grip, but not coarse grip. Thus, the VSt was needed specifically for functional recovery of dexterous finger movements. These results suggest that the VSt is the key node of the cortical reorganization required for functional recovery of finger dexterity.

Premotor Cortical-Cerebellar Reorganization in a Macaque Model of Primary Motor Cortical Lesion and Recovery.

Neuromotor systems have the capacity for functional recovery following local damage. The literature suggests a possible role for the premotor cortex and cerebellum in motor recovery. However, the specific changes to interactions between these areas following damage remain unclear. Here, we demonstrate potential rewiring of connections from the ipsilesional ventral premotor cortex (ip-PMv) to cerebellar structures in a nonhuman primate model of primary motor cortex (M1) lesion and motor recovery. Cerebellar connections arising from the ip-PMv were investigated by comparing biotinylated dextran amine (BDA) between two groups of male Macaca mulatta: M1-lesion/motor recovery group and intact group. There were more BDA-labeled boutons and axons in all ipsilesional deep cerebellar nuclei (fastigial, interposed, and dentate) in the M1-lesion/recovery group than in the intact group. The difference was evident in the ipsilesional fastigial nucleus (ip-FN), and particularly observed in its middle, a putative somatosensory region of the ip-FN, which was characterized by absent or little expression of aldolase C. Some of the altered projections from the ip-PMv to ip-FN neurons were confirmed as functional because the synaptic markers, synaptophysin and vesicular glutamate transporter 1, were colocalized with BDA-labeled boutons. These results suggest that the adult primate brain after motor lesions can reorganize large-scale networks to enable motor recovery by enhancing sensorimotor coupling and motor commands via rewired fronto-cerebellar connections.SIGNIFICANCE STATEMENT Damaging the motor cortex causes motor deficits, which can be recovered over time. Such motor recovery may result from functional compensation in remaining neuromotor areas, including the ventral premotor cortex. We investigated compensatory changes in neural axonal outputs from ventral premotor to deep cerebellar nuclei in a monkey model of primary motor cortical lesion and motor recovery. The results showed an increase in premotor projections and synaptic formations in deep cerebellar nuclei, especially the sensorimotor region of the fastigial nucleus. Our results provide the first evidence that large-scale reorganization of fronto-cerebellar circuits may underlie functional recovery after motor cortical lesions.

Temporal plasticity involved in recovery from manual dexterity deficit after motor cortex lesion in macaque monkeys.

The question of how intensive motor training restores motor function after brain damage or stroke remains unresolved. Here we show that the ipsilesional ventral premotor cortex (PMv) and perilesional primary motor cortex (M1) of rhesus macaque monkeys are involved in the recovery of manual dexterity after a lesion of M1. A focal lesion of the hand digit area in M1 was made by means of ibotenic acid injection. This lesion initially caused flaccid paralysis in the contralateral hand but was followed by functional recovery of hand movements, including precision grip, during the course of daily postlesion motor training. Brain imaging of regional cerebral blood flow by means of H2 (15)O-positron emission tomography revealed enhanced activity of the PMv during the early postrecovery period and increased functional connectivity within M1 during the late postrecovery period. The causal role of these areas in motor recovery was confirmed by means of pharmacological inactivation by muscimol during the different recovery periods. These findings indicate that, in both the remaining primary motor and premotor cortical areas, time-dependent plastic changes in neural activity and connectivity are involved in functional recovery from the motor deficit caused by the M1 lesion. Therefore, it is likely that the PMv, an area distant from the core of the lesion, plays an important role during the early postrecovery period, whereas the perilesional M1 contributes to functional recovery especially during the late postrecovery period.

Brain activity changes after high/low frequency stimulation in a nonhuman primate model of central post-stroke pain.

Central post-stroke pain (CPSP) is a chronic pain resulting from a lesion in somatosensory pathways. Neuromodulation techniques, such as repetitive transcranial magnetic stimulation (rTMS) that target the primary motor cortex (M1), have shown promise for the treatment of CPSP. High-frequency (Hf) rTMS exhibits analgesic effects compared to low-frequency (Lf) rTMS; however, its analgesic mechanism is unknown. We aimed to elucidate the mechanism of rTMS-induced analgesia by evaluating alterations of tactile functional magnetic resonance imaging (fMRI) due to Hf- and Lf-rTMS in a CPSP monkey model. Consistent with the patient findings, the monkeys showed an increase in pain threshold after Hf-rTMS, which indicated an analgesic effect. However, no change after Lf-rTMS was observed. Compared to Lf-rTMS, Hf-rTMS produced enhanced tactile-evoked fMRI signals not only in M1 but also in somatosensory processing regions, such as the primary somatosensory and midcingulate cortices. However, the secondary somatosensory cortex (S2) was less active after Hf-rTMS than after Lf-rTMS, suggesting that activation of this region was involved in CPSP. Previous studies showed pharmacological inhibition of S2 reduces CPSP-related behaviors, and the present results emphasize the involvement of an S2 inhibitory system in rTMS-induced analgesia. Verification using the monkey model is important to elucidate the inhibition system.

Effects of early versus late rehabilitative training on manual dexterity after corticospinal tract lesion in macaque monkeys.

Dexterous hand movements can be restored with motor rehabilitative training after a lesion of the lateral corticospinal tract (l-CST) in macaque monkeys. To maximize effectiveness, the optimal time to commence such rehabilitative training must be determined. We conducted behavioral analyses and compared the recovery of dexterous hand movements between monkeys in which hand motor training was initiated immediately after the l-CST lesion (early-trained monkeys) and those in which training was initiated 1 mo after the lesion (late-trained monkeys). The performance of dexterous hand movements was evaluated by food retrieval tasks. In early-trained monkeys, performance evaluated by the success rate in a vertical slit task (retrieval of a small piece of food through a narrow vertical slit) recovered to the level of intact monkeys during the first 1-2 mo after the lesion. In late-trained monkeys, the task success rate averaged ∼30% even after 3 mo of rehabilitative training. We also evaluated hand performance with the Klüver board task, in which monkeys retrieved small spherical food pellets from cylindrical wells. Although the success rate of the Klüver board task did not differ between early- and late-trained monkeys, kinematic movement analysis showed that there was a difference between the groups: late-trained monkeys with an improved success rate frequently used alternate movement strategies that were different from those used before the lesion. These results suggest that early rehabilitative training after a spinal cord lesion positively influences subsequent functional recovery.

Functional annotation of genes differentially expressed between primary motor and prefrontal association cortices of macaque brain.

DNA microarray-based genome-wide transcriptional profiling and gene network analyses were used to characterize the molecular underpinnings of the neocortical organization in rhesus macaque, with particular focus on the differences in the functional annotation of genes in the primary motor cortex (M1) and the prefrontal association cortex (area 46 of Brodmann). Functional annotation of the differentially expressed genes showed that the list of genes selectively expressed in M1 was enriched with genes involved in oligodendrocyte function, and energy consumption. The annotation appears to have successfully extracted the characteristics of the molecular structure of M1.

Expression of immediate-early genes reveals functional compartments within ocular dominance columns after brief monocular inactivation.

Visual inputs from the 2 eyes in most primates activate alternating bands of cortex in layer 4C of primary visual cortex, thereby forming the well-studied ocular dominance columns (ODCs). In addition, the enzymatic reactivity of cytochrome oxidase (CO) reveals "blob" structures within the supragranular layers of ODCs. Here, we present evidence for compartments within ODCs that have not been clearly defined previously. These compartments are revealed by the activity-dependent mRNA expression of immediate-early genes (IEGs), zif268 and c-fos, after brief periods of monocular inactivation (MI). After a 1-3-h period of MI produced by an injection of tetrodotoxin, IEGs were expressed in a patchy pattern that included infragranular layers, as well as supragranular layers, where they corresponded to the CO blobs. In addition, the expressions of IEGs in layer 4C were especially high in narrow zones along boundaries of ODCs, referred to here as the "border strips" of the ODCs. After longer periods of MI (>5 h), the border strips were no longer apparent. When either eyelid was sutured, changes in IEG expression were not evident in layer 4C; however, the patchy pattern of the expression in the infragranular and supragranular layers remained. These changes of IEG expression after MI indicate that cortical circuits involving the CO blobs of the supragranular layers include aligned groups of neurons in the infragranular layers and that the border strip neurons of layer 4C are highly active for a 3-h period after MI.

Accounting for the valley of recovery during post-stroke rehabilitation training via a model-based analysis of macaque manual dexterity.

Background: True recovery, in which a stroke patient regains the same precise motor skills observed in prestroke conditions, is the fundamental goal of rehabilitation training. However, a transient drop in task performance during rehabilitation training after stroke, observed in human clinical outcome as well as in both macaque and squirrel monkey retrieval data, might prevent smooth transitions during recovery. This drop, i.e., recovery valley, often occurs during the transition from compensatory skill to precision skill. Here, we sought computational mechanisms behind such transitions and recovery. Analogous to motor skill learning, we considered that the motor recovery process is composed of spontaneous recovery and training-induced recovery. Specifically, we hypothesized that the interaction of these multiple skill update processes might determine profiles of the recovery valley. Methods: A computational model of motor recovery was developed based on a state-space model of motor learning that incorporates a retention factor and interaction terms for training-induced recovery and spontaneous recovery. The model was fit to previously reported macaque motor recovery data where the monkey practiced precision grip skills after a lesion in the sensorimotor area in the cortex. Multiple computational models and the effects of each parameter were examined by model comparisons based on information criteria and sensitivity analyses of each parameter. Result: Both training-induced and spontaneous recoveries were necessary to explain the behavioral data. Since these two factors contributed following logarithmic function, the training-induced recovery were effective only after spontaneous biological recovery had developed. In the training-induced recovery component, the practice of the compensation also contributed to recovery of the precision grip skill as if there is a significant generalization effect of learning between these two skills. In addition, a retention factor was critical to explain the recovery profiles. Conclusions: We found that spontaneous recovery, training-induced recovery, retention factors, and interaction terms are crucial to explain recovery and recovery valley profiles. This simulation-based examination of the model parameters provides suggestions for effective rehabilitation methods to prevent the recovery valley, such as plasticity-promoting medications, brain stimulation, and robotic rehabilitation technologies.

Pharmacological inactivation of the primate posterior insular/secondary somatosensory cortices attenuates thermal hyperalgesia.

BACKGROUND: We previously established a macaque model of central post-stroke pain (CPSP) and confirmed the involvement of increased activity of the posterior insular cortex (PIC) and secondary somatosensory cortex (SII) to somatosensory stimuli in mechanical allodynia by a combination of imaging techniques with local pharmacological inactivation. However, it is unclear whether the same intervention would be effective for thermal hyperalgesia. Therefore, using the macaque model, we examined behavioural responses to thermal stimuli following pharmacological inactivation of the PIC/SII. METHODS: Two CPSP model macaques were established based on collagenase-induced unilateral hemorrhagic lesions in the ventral posterolateral nucleus of the thalamus. To evaluate pain perception, withdrawal latencies to thermal stimuli of 37, 45, 50, 52, and 55 °C to hands were measured. Several weeks after the lesion induction, pharmacological inactivation of the PIC/SII by microinjection of muscimol was performed. The effect of inactivation on withdrawal latency was assessed by comparison with withdrawal latency after vehicle injection. RESULTS: Several weeks after induction of the thalamic lesions, both macaques demonstrated a reduction in withdrawal latencies to thermal stimulation (<50 °C) on the contralesional hand, indicating the occurrence of thermal hyperalgesia. When the PIC/SII were inactivated by muscimol, the withdrawal latencies to thermal stimuli of 50 and 52 °C were significantly increased compared to those after vehicle injection. CONCLUSIONS: Our data emphasize that increased activity in the PIC/SII after appearance of thalamic lesions can contribute to abnormal pain of multiple modalities, and the modulation of PIC/SII activity may be a therapeutic approach for thermal hyperalgesia. SIGNIFICANCE: CPSP is caused by stroke lesions in the sensory system and characterized by mechanical allodynia or thermal hyperalgesia. Inactivation of the PIC/SII has an analgesic effect on mechanical allodynia; however, it is not clear whether the same intervention could reduce thermal hyperalgesia. Here, using the macaque model, we demonstrated that inactivation of these cortices reduces hypersensitivity to thermal stimuli. This result emphasizes that increased PIC/SII activity can contribute to abnormal pain of multiple modalities.

Structural plasticity of motor cortices assessed by voxel-based morphometry and immunohistochemical analysis following internal capsular infarcts in macaque monkeys.

Compensatory plastic changes in the remaining intact brain regions are supposedly involved in functional recovery following stroke. Previously, a compensatory increase in cortical activation occurred in the ventral premotor cortex (PMv), which contributed to the recovery of dexterous hand movement in a macaque model of unilateral internal capsular infarcts. Herein, we investigated the structural plastic changes underlying functional changes together with voxel-based morphometry (VBM) analysis of magnetic resonance imaging data and immunohistochemical analysis using SMI-32 antibody in a macaque model. Unilateral internal capsular infarcts were pharmacologically induced in 5 macaques, and another 5 macaques were used as intact controls for immunohistochemical analysis. Three months post infarcts, we observed significant increases in the gray matter volume (GMV) and the dendritic arborization of layer V pyramidal neurons in the contralesional rostral PMv (F5) as well as the primary motor cortex (M1). The histological analysis revealed shrinkage of neuronal soma and dendrites in the ipsilesional M1 and several premotor cortices, despite not always detecting GMV reduction by VBM analysis. In conclusion, compensatory structural changes occur in the contralesional F5 and M1 during motor recovery following internal capsular infarcts, and the dendritic growth of pyramidal neurons is partially correlated with GMV increase.

Diffuse Optical Tomography Using fNIRS Signals Measured from the Skull Surface of the Macaque Monkey.

Diffuse optical tomography (DOT), as a functional near-infrared spectroscopy (fNIRS) technique, can estimate three-dimensional (3D) images of the functional hemodynamic response in brain volume from measured optical signals. In this study, we applied DOT algorithms to the fNIRS data recorded from the surface of macaque monkeys' skulls when the animals performed food retrieval tasks using either the left- or right-hand under head-free conditions. The hemodynamic response images, reconstructed by DOT with a high sampling rate and fine voxel size, demonstrated significant activations at the upper limb regions of the primary motor area in the central sulcus and premotor, and parietal areas contralateral to the hands used in the tasks. The results were also reliable in terms of consistency across different recording dates. Time-series analyses of each brain area revealed preceding activity of premotor area to primary motor area consistent with previous physiological studies. Therefore, the fNIRS-DOT protocol demonstrated in this study provides reliable 3D functional brain images over a period of days under head-free conditions for region-of-interest-based time-series analysis.

Non-human Primate Models to Explore the Adaptive Mechanisms After Stroke.

The brain has the ability to reconstruct neural structures and functions to compensate for the brain lesions caused by stroke, although it is highly limited in primates including humans. Animal studies in which experimental lesions were induced in the brain have contributed to the current understanding of the neural mechanisms underlying functional recovery. Here, I have highlighted recent advances in non-human primate models using primate species such as macaques and marmosets, most of which have been developed to study the mechanisms underlying the recovery of motor functions after stroke. Cortical lesion models have been used to investigate motor recovery after lesions to the cortical areas involved in movements of specific body parts. Models of a focal stroke at the posterior internal capsule have also been developed to bridge the gap between the knowledge obtained by cortical lesion models and the development of intervention strategies because the severity and outcome of motor deficits depend on the degree of lesions to the region. This review will also introduce other stroke models designed to study the plastic changes associated with development and recovery from cognitive and sensory impairments. Although further validation and careful interpretation are required, considering the differences between non-human primate brains and human brains, studies using brain-lesioned non-human primates offer promise for improving translational outcomes.

Time- and area-dependent macrophage/microglial responses after focal infarction of the macaque internal capsule.

We quantitatively investigated temporal changes of macrophages and microglia (MΦ/MG) after focal infarction of the internal capsule using a macaque model we recently established. Immunoreactivity for Iba1, a general marker for MΦ/MG, in the periinfarct core gradually increased from 0 days to 2-3 weeks after infarction, and the increased immunoreactivity continued at least until 6 months; no study in rodents has reported increased Iba1-immunoreactive cells for so long. Retrograde atrophy or degeneration of neurons in layer V of the primary motor cortex, where the descending motor tract originates, was seen as secondary damage. Here we found that Iba1-positive MΦ/MG transiently increased in layer V during several weeks after the infarction. Therefore, the time course of MΦ/MG activation differs between the perilesional area and the remote brain area where secondary damage occurs to tissue initially preserved after the infarct. Detailed analyses using the functional phenotype markers CD68, CD86, and CD206, as well as cytokines released by cells with each phenotype, suggest an anti-inflammatory role for activated MΦ/MG both in the periinfarct core during the chronic phase and in the primary motor cortex.

Enriched expression of serotonin 1B and 2A receptor genes in macaque visual cortex and their bidirectional modulatory effects on neuronal responses.

To study the molecular mechanism how cortical areas are specialized in adult primates, we searched for area-specific genes in macaque monkeys and found striking enrichment of serotonin (5-hydroxytryptamine, 5-HT) 1B receptor mRNA, and to a lesser extent, of 5-HT2A receptor mRNA, in the primary visual area (V1). In situ hybridization analyses revealed that both mRNA species were highly concentrated in the geniculorecipient layers IVA and IVC, where they were coexpressed in the same neurons. Monocular inactivation by tetrodotoxin injection resulted in a strong and rapid (<3 h) downregulation of these mRNAs, suggesting the retinal activity dependency of their expression. Consistent with the high expression level in V1, clear modulatory effects of 5-HT1B and 5-HT2A receptor agonists on the responses of V1 neurons were observed in in vivo electrophysiological experiments. The modulatory effect of the 5-HT1B agonist was dependent on the firing rate of the recorded neurons: The effect tended to be facilitative for neurons with a high firing rate, and suppressive for those with a low firing rate. The 5-HT2A agonist showed opposite effects. These results suggest that this serotonergic system controls the visual response in V1 for optimization of information processing toward the incoming visual inputs.

Brain activity changes in a monkey model of central post-stroke pain.

Central post-stroke pain (CPSP) can occur after stroke in the somatosensory pathway that includes the posterolateral region of the thalamus. Tactile allodynia, in which innocuous tactile stimuli are perceived as painful, is common in patients with CPSP. Previous brain imaging studies have reported plastic changes in brain activity in patients with tactile allodynia after stroke, but a causal relationship between such changes and the symptoms has not been established. We recently developed a non-human primate (macaque) model of CPSP based on thalamic lesions, in which the animals show behavioral changes consistent with the occurrence of tactile allodynia. Here we performed functional magnetic resonance imaging under propofol anesthesia to investigate the changes in brain activation associated with the allodynia in this CPSP model. Before the lesion, innocuous tactile stimuli significantly activated the contralateral sensorimotor cortex. When behavioral changes were observed after the thalamic lesion, equivalent stimuli significantly activated pain-related brain areas, including the posterior insular cortex (PIC), secondary somatosensory cortex (SII), anterior cingulate cortex (ACC), and amygdala. Moreover, when either PIC/SII or ACC was pharmacologically inactivated, the signs of tactile allodynia were dampened. Our results show that increased cortical activity plays a role in CPSP-induced allodynia.

Functional near-infrared-spectroscopy-based measurement of changes in cortical activity in macaques during post-infarct recovery of manual dexterity.

Because compensatory changes in brain activity underlie functional recovery after brain damage, monitoring of these changes will help to improve rehabilitation effectiveness. Functional near-infrared spectroscopy (fNIRS) has the potential to measure brain activity in freely moving subjects. We recently established a macaque model of internal capsule infarcts and an fNIRS system for use in the monkey brain. Here, we used these systems to study motor recovery in two macaques, for which focal infarcts of different sizes were induced in the posterior limb of the internal capsule. Immediately after the injection, flaccid paralysis was observed in the hand contralateral to the injected hemisphere. Thereafter, dexterous hand movements gradually recovered over months. After movement recovery, task-evoked hemodynamic responses increased in the ventral premotor cortex (PMv). The response in the PMv of the infarcted (i.e., ipsilesional) hemisphere increased in the monkey that had received less damage. In contrast, the PMv of the non-infarcted (contralesional) hemisphere was recruited in the monkey with more damage. A pharmacological inactivation experiment with muscimol suggested the involvement of these areas in dexterous hand movements during recovery. These results indicate that fNIRS can be used to evaluate brain activity changes crucial for functional recovery after brain damage.

Neuronal and microglial localization of secreted phosphoprotein 1 (osteopontin) in intact and damaged motor cortex of macaques.

We previously reported that mRNA encoding secreted phosphoprotein 1 (SPP1), also known as osteopontin, is preferentially expressed in large neurons in layer V of the macaque motor cortex, most of which are presumed to be corticospinal tract neurons. As a first step to elucidating the cellular function of SPP1 in macaque neurons, we examined the localization of SPP1 in the primary motor cortex (M1) of the macaque by using immunohistochemistry. SPP1 immunoreactivity was found to be localized in the cell bodies of neurons, but not outside the cells, indicating that SPP1 was not secreted from these neurons. The results of electron microscope analysis and double-labeling analysis with marker proteins suggested that SPP1 was localized in the mitochondria of neurons. The distributions of SPP1 in the neurons corresponded to those of integrin αV, a putative receptor for SPP1. The distribution of SPP1 was also investigated in macaques whose M1 had been lesioned. We found that SPP1 was secreted by proliferated microglia in the lesioned area. Double-labeling analysis indicated that SPP1 immunoreactivity in the microglia was colocalized with CD44, another putative receptor for SPP1. Success rates in the small-object-retrieval task were positively correlated with SPP1 immunoreactivity in the neurons in the perilesional area. SPP1 has multiple roles in the macaque motor cortex, and it may be a key protein during recovery of hand movement after brain damage.

Difference in sensory dependence of occ1/Follistatin-related protein expression between macaques and mice.

occ1/Follistatin-related protein (Frp) is strongly expressed in the primary visual cortex (V1) of macaque monkeys, and its expression is strongly down-regulated by intraocular tetrodotoxin (TTX) injection. The pronounced area selectivity of occ1/Frp mRNA expression occurs in macaques and marmosets, but not in mice, rabbits and ferrets, suggesting that occ1/Frp is an important clue to the evolution of the primate cerebral cortex. To further determine species differences, we examined the sensory-input dependency of occ1/Frp mRNA expression in mice in comparison with macaque V1. In macaque V1, occ1/Frp mRNA expression level significantly decreased with even 1-day monocular deprivation (MD) by TTX injection. In contrast to that in macaques, however, the occ1/Frp mRNA expression in the visual cortex in mice was not down-regulated by 1- to 7-day MD by TTX injection. Similarly, MD had no effect on occ1/Frp mRNA expression level in the dorsal lateral geniculate nucleus of mice. In addition, the extirpation of the cochlear or olfactory epithelium had no effect on occ1/Frp mRNA expression in either the cochlear nucleus or the olfactory bulb in mice. Thus, occ1/Frp mRNA expression is independent of sensory-input in mice. The results suggest that activity-dependent occ1/Frp mRNA expression is not common between mice and monkeys, and that primate V1 has acquired a unique gene regulatory mechanism that enables a rapid response to environmental changes. The characteristic feature of the activity dependency of occ1/Frp mRNA expression is discussed, in comparison with that of the expression of the immediate-early genes, c-fos and zif268.