Distribution of P2X3 purinoceptor-immunoreactive sensory nerve endings in the carotid body of Japanese macaque (Macaca fuscata).

In the carotid body of laboratory rodents, adenosine 5'-triphosphate (ATP)-mediated transmission is regarded as critical for transmission from chemoreceptor type I cells to P2X3 purinoceptor-expressing sensory nerve endings. The present study investigated the distribution of P2X3-immunoreactive sensory nerve endings in the carotid body of the adult male Japanese monkey (Macaca fuscata) using multilabeling immunofluorescence. Immunoreactivity for P2X3 was detected in nerve endings associated with chemoreceptor type I cells immunoreactive for synaptophysin. Spherical or flattened terminal parts of P2X3-immunoreactive nerve endings were in close apposition to the perinuclear cytoplasm of synaptophysin-immunoreactive type I cells. Immunoreactivity for ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2), which hydrolyzes extracellular ATP, was localized in the cell body and cytoplasmic processes of S100B-immunoreactive cells. NTPDase2-immunoreactive cells surrounded P2X3-immunoreactive terminal parts and synaptophysin-immunoreactive type I cells, but did not intrude into attachment surfaces between terminal parts and type I cells. These results suggest ATP-mediated transmission between type I cells and sensory nerve endings in the carotid body of the Japanese monkey, as well as those of rodents.

[Posture Control Associated with Quadrupedal and Bipedal Gait in Japanese Monkeys (Macaca fuscata)].

How the CNS deals with instability of upright posture is the core in the control of bipedal gait. In this review, we summarize our recent findings comparing kinematics and EMG activity during quadrupedal and bipedal gait in Japanese macaques. Trunk/hindlimb muscles showed step cycle-modulated activity, which was more active in bipedal than in quadrupedal gait. For bipedal gait, enhanced activity during longer double support phase was predominantly observed in distal hindlimb muscles. Alternate burst activity in bilateral back muscles cyclically brought back the tilted trunk. In monkeys' quadrupedal gait, hindlimbs formed functional pairs with contralateral forelimbs, unlike in non-primate quadrupeds. These diagonal pairs acted differently on movements of the center of mass (COM). For bipedal gait, the hindlimbs solely carried the COM. Our results suggest that, compared to non-primate quadrupeds, hindlimbs in macaques contribute more critically to weight support and balance control even for quadrupedal gait. Additionally, for more unstable bipedal gait, the monkeys' CNS reinforces such hindlimb roles and actively controls the trunk posture in maintaining dynamic balance, in a manner similar to humans. Studies on Japanese macaques will further our understanding of the neural basis for the control of gait in mammals by bridging non-primate quadrupeds and humans.

Locomotor kinematics and EMG activity during quadrupedal versus bipedal gait in the Japanese macaque.

Several qualitative features distinguish bipedal from quadrupedal locomotion in mammals. In this study we show quantitative differences between quadrupedal and bipedal gait in the Japanese monkey in terms of gait patterns, trunk/hindlimb kinematics, and electromyographic (EMG) activity, obtained from 3 macaques during treadmill walking. We predicted that as a consequence of an almost upright body axis, bipedal gait would show properties consistent with temporal and spatial optimization countering higher trunk/hindlimb loads and a less stable center of mass (CoM). A comparatively larger step width, an ~9% longer duty cycle, and ~20% increased relative duration of the double-support phase were all in line with such a strategy. Bipedal joint kinematics showed the strongest differences in proximal, and least in distal, hindlimb joint excursions compared with quadrupedal gait. Hindlimb joint coordination (cyclograms) revealed more periods of single-joint rotations during bipedal gait and predominance of proximal joints during single support. The CoM described a symmetrical, quasi-sinusoidal left/right path during bipedal gait, with an alternating shift toward the weight-supporting limb during stance. Trunk/hindlimb EMG activity was nonuniformally increased during bipedal gait, most prominently in proximal antigravity muscles during stance (up to 10-fold). Non-antigravity hindlimb EMG showed altered temporal profiles during liftoff or touchdown. Muscle coactivation was more, but muscle synergies less, frequent during bipedal gait. Together, these results show that behavioral and EMG properties of bipedal vs. quadrupedal gait are quantitatively distinct and suggest that the neural control of bipedal primate locomotion underwent specific adaptations to generate these particular behavioral features to counteract increased load and instability. NEW & NOTEWORTHY Bipedal locomotion imposes particular biomechanical constraints on motor control. In a within-species comparative study, we investigated joint kinematics and electromyographic characteristics of bipedal vs. quadrupedal treadmill locomotion in Japanese macaques. Because these features represent (to a large extent) emergent properties of the underlying neural control, they provide a comparative, behavioral, and neurophysiological framework for understanding the neural system dedicated to bipedal locomotion in this nonhuman primate, which constitutes a critical animal model for human bipedalism.

Hemodynamic Response of the Supplementary Motor Area during Locomotor Tasks with Upright versus Horizontal Postures in Humans.

To understand cortical mechanisms related to truncal posture control during human locomotion, we investigated hemodynamic responses in the supplementary motor area (SMA) with quadrupedal and bipedal gaits using functional near-infrared spectroscopy in 10 healthy adults. The subjects performed three locomotor tasks where the degree of postural instability varied biomechanically, namely, hand-knee quadrupedal crawling (HKQuad task), upright quadrupedalism using bilateral Lofstrand crutches (UpQuad task), and typical upright bipedalism (UpBi task), on a treadmill. We measured the concentration of oxygenated hemoglobin (oxy-Hb) during the tasks. The oxy-Hb significantly decreased in the SMA during the HKQuad task, whereas it increased during the UpQuad task. No significant responses were observed during the UpBi task. Based on the degree of oxy-Hb responses, we ranked these locomotor tasks as UpQuad > UpBi > HKQuad. The order of the different tasks did not correspond with postural instability of the tasks. However, qualitative inspection of oxy-Hb time courses showed that oxy-Hb waveform patterns differed between upright posture tasks (peak-plateau-trough pattern for the UpQuad and UpBi tasks) and horizontal posture task (downhill pattern for the HKQuad task). Thus, the SMA may contribute to the control of truncal posture accompanying locomotor movements in humans.

Functional properties of parietal hand manipulation-related neurons and mirror neurons responding to vision of own hand action.

Parietofrontal pathways play an important role in visually guided motor control. In this pathway, hand manipulation-related neurons in the inferior parietal lobule represent 3-D properties of an object and motor patterns to grasp it. Furthermore, mirror neurons show visual responses that are concerned with the actions of others and motor-related activity during execution of the same grasping action. Because both of these categories of neurons integrate visual and motor signals, these neurons may play a role in motor control based on visual feedback signals. The aim of this study was to investigate whether these neurons in inferior parietal lobule including the anterior intraparietal area and PFG of macaques represent visual images of the monkey's own hand during a self-generated grasping action. We recorded 235 neurons related to hand manipulation tasks. Of these, 54 responded to video clips of the monkey's own hand action, the same as visual feedback during that action or clips of the experimenter's hand action in a lateral view. Of these 54 neurons, 25 responded to video clips of the monkey's own hand, even without an image of the target object. We designated these 25 neurons as "hand-type." Thirty-three of 54 neurons that were defined as mirror neurons showed visual responses to the experimenter's action and motor responses. Thirteen of these mirror neurons were classified as hand-type. These results suggest that activity of hand manipulation-related and mirror neurons in anterior intraparietal/PFG plays a fundamental role in monitoring one's own body state based on visual feedback.

Hoffmann reflex in a rat bipedal walking model.

The rat bipedal walking model (RBWM) refers to rats that acquired anatomical and functional characteristics for bipedal walking after the completion of a long-term motor training program. We recorded the Hoffmann reflex (H-reflex) of the forelimb and hindlimb in RBWM and control (not trained, normal) rats to evaluate the effects of bipedal walking on central nervous system (CNS) activity. The H-reflex recorded from the hindlimbs of the RBWM was significantly inhibited compared with that in the control. Furthermore, the inhibition of the H-reflex recorded from both forelimbs and hindlimbs by paired pulse stimulation tended to be enhanced in RBWM. These results indicate that bipedal walking or bipedal walking training cause functional changes in spinal reflex pathways in the CNS.

[Cortical control in locomotion].

Although simple in appearance, bipedal (Bp) and even quadrupedal (Qp) locomotion are highly tuned motor behaviors that require coordinated control in the spatial and temporal domains of head, neck, trunk, and limbs. Seamless integration of limb movements and accompanying posture is a crucial determinant for the execution of desired locomotor movements. Recent functional brain imaging studies have shown that multiple cerebral sensorimotor cortices and the cerebellum are highly activated during human BP locomotion, suggesting that humans depend on the cerebrum and cerebellum for the elaboration of Bp locomotion. We have found that a young Japanese monkey, Macaca fuscata, acquires novel Bp walking capability with a long-term locomotor task and physical maturation. This model animal has kinematic features that are common with those of humans. Our imaging study showed that multiple cortical motor related areas are activated during monkey Bp walking, similar to that observed in humans. Furthermore, cortical inactivation studies revealed that each cortical region has an assigned functional role for the elaboration and refinements of its locomotor task. All these results show that selective yet multiple involvement of cortical motor regions are necessary for the elaboration of Bp locomotion in both humans and non-human primate models. Presumably, such multi-faceted recruitment of motor cortices is required to accommodate the limb movement and postural demands for Bp upright standing and walking. To cure locomotor dysfunctions due to CNS impairments, it is necessary to understand the CNS mechanisms involved in fine-tuning of limb movements and accompanying posture. Multi-comparative interdisciplinary studies should be initiated to reveal the CNS mechanisms involved in the control of Bp upright standing and locomotion in humans and non-human primate models.

Shared mapping of own and others' bodies in visuotactile bimodal area of monkey parietal cortex.

Parietal cortex contributes to body representations by integrating visual and somatosensory inputs. Because mirror neurons in ventral premotor and parietal cortices represent visual images of others' actions on the intrinsic motor representation of the self, this matching system may play important roles in recognizing actions performed by others. However, where and how the brain represents others' bodies and correlates self and other body representations remain unclear. We expected that a population of visuotactile neurons in simian parietal cortex would represent not only own but others' body parts. We first searched for parietal visuotactile bimodal neurons in the ventral intraparietal area and area 7b of monkeys, and then examined the activity of these neurons while monkeys were observing visual or tactile stimuli placed on the experimenter's body parts. Some bimodal neurons with receptive fields (RFs) anchored on the monkey's body exhibited visual responses matched to corresponding body parts of the experimenter, and visual RFs near that body part existed in the peripersonal space within approximately 30 cm from the body surface. These findings suggest that the brain could use self representation as a reference for perception of others' body parts in parietal cortex. These neurons may contribute to spatial matching between the bodies of the self and others in both action recognition and imitation.

Effects of salt concentration on the reaction rate of Glc with amino acids, peptides, and proteins.

The reaction between the amino group and the carbonyl group is important in food quality control. Furthermore, advanced glycation end products from foods are considered to relate to aging and diabetes. Thus, it is important to control this reaction. In this study, we investigated the effects of salt concentration on the rates of browning reaction of amino acid, peptides, and proteins. A high concentration of sodium chloride retarded the reaction rate of Glc with amino acids as measured with the absorbance at 470 nm, but did not change the browning rate of Glc with peptides. On the other hand, sodium chloride retarded the browning reaction rate of proteins as measured with polymerization degree or by the loss of Lys. It is hoped that the results of this study will be applied in the control of amino-carbonyl reaction rates in the food industry.

Obstacle clearance and prevention from falling in the bipedally walking Japanese monkey, Macaca fuscata.

BACKGROUND: studies are needed which consider CNS-controlled strategies for accommodating perturbed bipedal (Bp) posture and walking. OBJECTIVE: to demonstrate the suitability of the Japanese monkey, Macaca fuscata, for the above purpose. SETTING AND SUBJECTS: three adult monkeys were operantly trained to use Bp-walking on a moving treadmill belt. On one side of the belt, a rectangular adjustable-height obstacle confronted the ipsilateral leg every 4-6 steps, as determined by belt speed. METHODS: animal posture and walking patterns were captured and digitized by two high-speed video systems. Frame-by-frame analyses of side- and back-view kinematics were obtained. RESULTS: the monkeys learned quickly to proactively clear the in-coming obstacles by use of a flexible hip-knee-ankle flexion strategy. This featured an appropriate postural adjustment and leg trajectory. In cases where a monkey failed to clear the obstacle, it promptly adopted a defensive posture to avoid falling. There was then a quick return to a posture that allowed the resumption of a Bp gait. CONCLUSIONS: when Bp posture and gait are perturbed in a non-human primate model, the prompt adjustment of a flexible hip-knee-ankle flexion strategy and a defensive postural adjustment act together to prevent a fall and enable the speedy resumption of normal Bp posture and gait.

Lumbar commissural interneurons with reticulospinal inputs in the cat: morphology and discharge patterns during fictive locomotion.

The purpose of this study was 1). to characterize the morphology of lumbar commissural neurons (CNs) with reticulospinal inputs and 2). to quantitate their activity during locomotor rhythm generation. Intraaxonal recordings at the L4-7 level of the spinal cord were obtained in 67 neurons in the decerebrate, paralyzed cat. Fourteen of them were subsequently nearly fully visualized following their intraaxonal injection with the tracer neurobiotin. All 14 were CNs with axons projecting across the midline of the spinal cord. Their somata were located mainly in lamina VIII and additionally in laminae VII-VI. Most of the lamina VIII CNs were excited monosynaptically from reticulospinal pathways. They were judged to be interneuronal CNs if they had no, or a short, rostral projection. These CNs commonly gave off multiple axon collaterals in and around their somata's segmental level. They projected mainly to laminae VIII-VII and some additionally to lamina IX. Some laminae VIII and the laminae VII-VI CNs were excited polysynaptically from reticulospinal pathways or were not excited. They were judged to be long propriospinal or ascending tract CNs because they had only an ascending axon. Most lamina VIII CNs discharged rhythmically during fictive locomotion evoked by stimulation of the mesencephalic locomotor region, exhibiting one peak per locomotor cycle. The peak was in phase with neurographic activity of either a left or a right hindlimb extensor nerve. These results suggested that lamina VIII CNs are reciprocally connected bilaterally at each segmental level. Such an arrangement suggests their participation in the generation and coordination of reciprocal and bilateral locomotor activity.

Biomechanical constraints in hindlimb joints during the quadrupedal versus bipedal locomotion of M. fuscata.

The operant-trained Japanese monkey, Macaca fuscata, can walk with both a quadrupedal (Qp) and a bipedal (Bp) gait on the surface of a treadmill belt, which moves at different speeds. The animal can also learn to transform its locomotor pattern from Qp to Bp, and vice versa, without a break in forward walking speed. This nonhuman primate model provides an intriguing opportunity to compare the kinematics of multiple body segments during Qp and Bp walking of the same subject. We found that M. fuscata selects a postural strategy and limb-kinematic parameters appropriate for the execution of both gaits. We propose that the basic locomotor rhythm-generating mechanisms of the brainstem and spinal cord, which are genetically endowed and relatively automatized, are used for the execution of both the Qp and Bp gait. The latter requires in addition, however, some higher-level circuitry which is shaped substantially by motor learning mechanisms.

Reactive and anticipatory control of posture and bipedal locomotion in a nonhuman primate.

Bipedal locomotion is a common daily activity. Despite its apparent simplicity, it is a complex set of movements that requires the integrated neural control of multiple body segments. We have recently shown that the juvenile Japanese monkey, M. fuscata, can be operant-trained to walk bipedally on moving treadmill. It can control the body axis and lower limb movements when confronted by a change in treadmill speed. M. fuscata can also walk bipedally on a slanted treadmill. Furthermore, it can learn to clear an obstacle attached to the treadmill's belt. When failing to clear the obstacle, the monkey stumbles but quickly corrects its posture and the associated movements of multiple motor segments to again resume smooth bipedal walking. These results give indication that in learning to walk bipedally, M. fuscata transforms relevant visual, vestibular, proprioceptive, and exteroceptive sensory inputs into commands that engage both anticipatory and reactive motor mechanisms. Both mechanisms are essential for meeting external demands imposed upon posture and locomotion.

Locomotor role of the corticoreticular-reticulospinal-spinal interneuronal system.

In vertebrates, the descending reticulospinal pathway is the primary means of conveying locomotor command signals from higher motor centers to spinal interneuronal circuits, the latter including the central pattern generators for locomotion. The pathway is morphologically heterogeneous, being composed of various types of inparallel-descending axons, which terminate with different arborization patterns in the spinal cord. Such morphology suggests that this pathway and its target spinal interneurons comprise varying types of functional subunits, which have a wide variety of functional roles, as dictated by command signals from the higher motor centers. Corticoreticular fibers are one of the major output pathways from the motor cortex to the brainstem. They project widely and diffusely within the pontomedullary reticular formation. Such a diffuse projection pattern seems well suited to combining and integrating the function of the various types of reticulospinal neurons, which are widely scattered throughout the pontomedullary reticular formation. The corticoreticular-reticulospinal-spinal interneuronal connections appear to operate as a cohesive, yet flexible, control system for the elaboration of a wide variety of movements, including those that combine goal-directed locomotion with other motor actions.

Direct and indirect pathways for corticospinal control of upper limb motoneurons in the primate.

In the macaque monkey and in humans, the monosynaptic cortico-motoneuronal system is well developed. It allows the cortical motor areas to make an important direct contribution to the pattern of muscle activity during upper limb movements. There is, in addition, good anatomical evidence for descending corticospinal inputs being able to influence the premotoneuronal networks of the cervical spinal cord, and especially those operating at the segmental level of upper limb motoneurons. While oligosynaptic inhibition has been easy to demonstrate in the macaque, and may be a very important component of descending corticospinal control, it has proved much more difficult to detect signs of oligosynaptic excitation. In contrast, in the squirrel monkey, in which the cortico-motoneuronal system is far less developed, oligosynaptic excitation is prominent. There are important changes in the interplay between direct and indirect pathways in different primates, which may provide important clues on the nature of the corticospinal control of upper limb function.

Integration of multiple motor segments for the elaboration of locomotion: role of the fastigial nucleus of the cerebellum.

This chapter provides a conceptual overview of the role and operation of higher structures of the central nervous system (CNS) in the control of posture and locomotion in the mammal, including the nonhuman primate and the human. Both quadrupedal and bipedal locomotion require the integrated neural control of multiple body segments against gravity. During development, and in selected instances in the adult, motor learning is required, particularly for merging anticipatory and reactive CNS processes, the latter being necessary after tripping and stumbling. We have recently found that the fastigial nucleus (FN) of the cerebellum in the cat plays a particularly important role in the control of locomotion, by virtue of its critical position in uniting the cerebro-cerebellar and the spino-cerebellar loops of neural activity that participate in the integrated control of multiple body segments. Further understanding of the CNS structures that achieve this integration has come from our recent study of an intact nonhuman primate, the Japanese monkey, Macaca fuscata, as it learns to elaborate bipedal locomotion rather than its normal quadrupedal fashion. Based on findings from these two animal species, we now present a model of the overall integrated control of posture and locomotion that features the combined operation of parallel and distributed neural circuitry throughout the CNS.

Acquisition of operant-trained bipedal locomotion in juvenile Japanese monkeys (Macaca fuscata): a longitudinal study.

This study investigated developmental aspects of the acquisition of operant-trained bipedal (Bp) standing and Bp walking in the normally quadrupedal (Qp) juvenile Japanese monkey (M. fuscata). Four male monkeys (age: 1.6 to 2.4 years, body weight: 3.3 to 4.6 kg) were initially operantly trained to stand upright on a smooth floor and a stationary treadmill belt (width = 60 cm, walking length = 150 cm). They were then trained to walk bipedally on the moving treadmill belt (speed: 0.4-0.7 m/s). A regular training program (5 days/week; 30-60 min/day) was given to each monkey for the first 40 to 60 days, followed by less intensive training. After the beginning of locomotor training, upright postural stability and Bp walking capability were assessed kinematically for 592, 534, 526, and 537 days on monkeys A, B, C, and D, respectively. Left side- and back-views of the walking monkey were photographed (10 frames/s) and videotaped (250 frames/s). Stick figures of the head, body, and hindlimbs were drawn with reference to ink-marks positioned in front of the ear and over the pivot points of hindlimb joints. All kinematic data were digitized and analyzed using image-analyzing software. After sufficient physical growth and locomotor training, all the monkeys gradually acquired: (a) a more upright and a more stable posture with a constant body axis orientation during Bp locomotion; (b) a more stable and a stronger functional coupling between the body and hindlimb movements with a less anterior (A)-posterior (P) fluctuation of a body axis; (c) a smaller leftward (Lt)-rightward (Rt) displacement of the midline pelvic position, allowing the monkey to walk along a straight course; (d) a more coordinated relationship among hip-knee, knee-ankle, and ankle-metatarsophalangeal (MTP) joints; and finally (e) the acquisition of well-coordinated Bp walking even at high treadmill belt speeds up to 1.5 m/s. All of these results demonstrated the capability of the physically developing monkey to integrate the neural and musculoskeletal mechanisms required for sufficient coordination of upper (head, neck, trunk) and lower (hindlimbs) motor segments so that Bp standing and Bp walking could be elaborated.