Differentially expressed genes among motor and prefrontal areas of macaque neocortex

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.

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.

Selective gene expression in regions of primate neocortex: implications for cortical specialization

The neocortex, which is characteristic of mammals, has evolved to play important roles in cognitive and perceptual functions. The localization of different functions in different regions of the neocortex was well established within the last century. Studies on the formation of the neocortex have advanced at the molecular level, thus clarifying the mechanisms that control neural or glial cell differentiation and sensory projections. However, mechanisms that underlie cortical area specialization remain unsolved. To address this problem, our approach has been to isolate and characterize the genes that are selectively expressed in particular subsets of neocortical areas in primates; these areas are most distinctive among mammals. By differential display and restriction landmark cDNA scanning (RLCS) methods, we have identified two major classes of genes that are specifically expressed in the adult macaque monkey neocortical areas: one is expressed in the primary sensory areas, particularly, in the primary visual cortex (V1) and the other is expressed in the association areas. The genes that show these specific expression patterns are limited to only several gene families among our large-scale screening. In this review, I first describe the isolation and characterization of these genes, along with another class of genes specifically expressed in motor areas. Then, I discuss their functional significance in the primate neocortex. Finally, I discuss the implication of these gene expression patterns in neocortical specialization in primates and possible future research directions.

Compensatory changes at the cerebral cortical level after spinal cord injury

Neurorehabilitation is based on the concept that rehabilitative training recruits neuronal systems that remain intact after the brain and/or spinal cord injury to take over the impaired function. Understanding the neural mechanism of recovery will surely contribute to the development of evidence-based rehabilitation therapies. Recent studies have shown that after a lesion of the lateral corticospinal tract at midcervical segments, the remaining pathways can compensate for finger dexterity in macaque monkeys in a few weeks to months. Combined brain imaging and reversible pharmacological inactivation of motor cortical regions suggested that the recovery involves the bilateral primary motor cortex during the early recovery stage and more extensive regions of the contralesional primary motor cortex and bilateral premotor cortex during the late stage. Thus, contribution of each cortical region changes depending on the recovery stage, suggesting that the brain uses available pre-existing neural systems by reducing inhibition during the early stage and enhances the original systems or recruits other systems by plastic change of the neural circuits during the late stage. These changes in the activation pattern of motor-related areas represent an adaptive strategy for functional compensation after spinal cord injury.

Japanese macaques as laboratory animals

The Japanese macaque (Macaca fuscata), along with rhesus and long-tailed macaques, is one of the macaca species. In Japan, it has been preferred for use as a laboratory animal, particularly in the field of neuroscience, because of its high level of intelligence and its gentle nature. In addition, the species has a relatively homogeneous genetic background and field researchers have accumulated abundant information on the social behavior of wild Japanese macaques. As future neuroscience research will undoubtedly be more focused on the higher cognitive functions of the brain, including social behavior among multiple individuals, the Japanese macaque can be expected to become even more valuable as a laboratory animal in the near future. The Ministry of Education, Culture, Sports, Science and Technology has launched a National BioResource Project (NBRP) to establish a stable breeding and supply system for Japanese macaques for laboratory use. The project is in progress and should lead to the establishment of a National Primate Center in Japan, which will support the supply of monkeys as well as social outreach and handling of animal welfare issues.

Paraneoplastic antigen-like 5 gene (PNMA5) is preferentially expressed in the association areas in a primate specific manner

To understand the relationship between the structure and function of primate neocortical areas at a molecular level, we have been screening for genes differentially expressed across macaque neocortical areas by restriction landmark cDNA scanning (RLCS). Here, we report enriched expression of the paraneoplastic antigen-like 5 gene (PNMA5) in association areas but not in primary sensory areas, with the lowest expression level in primary visual cortex. In situ hybridization in the primary sensory areas revealed PNMA5 mRNA expression restricted to layer II. Along the ventral visual pathway, the expression gradually increased in the excitatory neurons from the primary to higher visual areas. This differential expression pattern was very similar to that of retinol-binding protein (RBP) mRNA, another association-area-enriched gene that we reported previously. Additional expression analysis for comparison of other genes in the PNMA gene family, PNMA1, PNMA2, PNMA3, and MOAP1 (PNMA4), showed that they were widely expressed across areas and layers but without the differentiated pattern of PNMA5. In mouse brains, PNMA1 was only faintly expressed and PNMA5 was not detected. Sequence analysis showed divergence of PNMA5 sequences among mammals. These findings suggest that PNMA5 acquired a certain specialized role in the association areas of the neocortex during primate evolution.