Distribution of median, ulnar and radial motoneurons in the monkey spinal cord: a retrograde triple-labeling study.

Topographic distribution of motoneurons innervating hand muscles through the median (Mn), ulnar (Ul), or radial (Rd) nerves was examined using a retrograde multiple-labeling technique in the macaque monkey. The Mn and Ul motoneurons, i.e. flexor motoneurons, were distributed from C6 to T2 and from C7 to T2 segments of the spinal cord, respectively, while the Rd motoneurons, i.e. extensor motoneurons, were distributed from C4 to T2. The present study further revealed partial intermingling of the cell bodies and partial overlap of the dendritic fields among the motoneurons projecting through different nerves, indicating that subregions of motoneuronal pool participate in coordination between the flexor and extensor, or among the flexor muscles. It was suggested that there exists a control mechanism for precise hand movements in the spinal cord.

Somatotopic arrangement and corticocortical inputs of the hindlimb region of the primary motor cortex in the macaque monkey.

Using Japanese monkeys, we examined the somatotopic organization of the hindlimb region of the primary motor cortex (MI) with intracortical microstimulation. In the hindlimb region of the MI, areas representing distal movements (digits and ankle joints) were basically surrounded by those representing proximal movements (knee and hip joints). Thus, the hindlimb region of the MI has a nested or horseshoe-like somatotopic representation. We then examined the topographic organization of corticocortical projections to the hindlimb region of the MI by the retrograde double-labeling technique: one monkey received paired injections of Fast blue (FB) and Diamidino yellow (DY) into hindlimb or forelimb representation of the MI, respectively, while two monkeys received those of FB and DY into proximal or distal representation of the hindlimb region of the MI, respectively. The neurons projecting to the hindlimb region of the MI were located in cortical areas largely separate from those projecting to the forelimb region of the MI. On the other hand, we found a substantial overlap of corticocortical neurons projecting to the proximal and distal parts of the hindlimb region of the MI in the dorsal division of the premotor cortex and the cingulate motor areas.

Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation (TMS) provides a noninvasive method of examining cortical inhibitory and excitatory processes and cortical excitability in awake subjects. There is evidence from clinical and electroencephalographic (EEG) data that cortical excitability may be abnormal in some psychiatric populations. Chronic cocaine abuse influences a number of neurotransmitters that are involved in the excitatory/inhibitory balance of the cerebral cortex. This pilot study was conducted to ascertain the possible utility of TMS in examining cortical excitability in a population of chronic cocaine abusers. METHODS: The right and left motor thresholds of ten cocaine-dependent subjects, according to DSM-IV, and ten normal control subjects were examined using single pulse TMS. RESULTS: The resting motor thresholds resulting from stimulation of the right or the left motor cortical regions were significantly elevated in cocaine-dependent subjects compared with matched control subjects. CONCLUSIONS: These pilot data suggest that chronic cocaine use significantly alters cortical excitability in the direction of increased inhibition or decreased excitability. We hypothesize that this observation reflects adaptation to those effects of cocaine intoxication that promote cortical excitability and seizures.

Organization of inputs from cingulate motor areas to basal ganglia in macaque monkey.

The cingulate motor areas reside within regions lining the cingulate sulcus and are divided into rostral and caudal parts. Recent studies suggest that the rostral and caudal cingulate motor areas participate in distinct aspects of motor function: the former plays a role in higher-order cognitive control of movements, whereas the latter is more directly involved in their execution. Here, we investigated the organization of cingulate motor areas inputs to the basal ganglia in the macaque monkey. Identified forelimb representations of the rostral and caudal cingulate motor areas were injected with different anterograde tracers and the distribution patterns of labelled terminals were analysed in the striatum and the subthalamic nucleus. Corticostriatal inputs from the rostral and caudal cingulate motor areas were located within the rostral striatum, with the highest density in the striatal cell bridges and the ventrolateral portions of the putamen, respectively. There was no substantial overlap between these input zones. Similarly, a certain segregation of input zones from the rostral and caudal cingulate motor areas occurred along the mediolateral axis of the subthalamic nucleus. It has also been revealed that corticostriatal and corticosubthalamic input zones from the rostral cingulate motor area considerably overlapped those from the presupplementary motor area, while the input zones from the caudal cingulate motor area displayed a large overlap with those from the primary motor cortex. The present results indicate that a parallel design underlies motor information processing in the cortico-basal ganglia loop derived from the rostral and caudal cingulate motor areas.

Effects of removal and reapplication of K(+) and Cl(-) on spontaneous electrical activity, slow wave, in the circular muscle of the guinea-pig gastric antrum.

In the circular muscle of guinea-pig gastric antrum, the effects of removal and reapplication of K(+) and Cl(-) were studied on the slow wave, which consists of the lower, first and upper, second components. The first component appeared to be triggered by the driving potential generated in the interstitial cells. K(+) removal slightly depolarized the membrane, increased frequency, and shortened the first component and driving potential, and K(+) reapplication hyperpolarized and prolonged these potentials transiently. Ouabain abolished the K(+)-induced hyper-polarization but had no inhibitory effect on the K(+)-induced potentiation. The K(+)-induced prolongation was much reduced in Ca(2+)-deficient and increased in Ca(2+)-excess solution. BAPTA-AM, thapsigargin, and cyclopiazonic acid shortened the slow wave and inhibited the K(+)-induced prolongation but did not block the slow wave. Effects of Cl(-) removal were stronger than K(+) removal in shortening and increasing the frequency. In Cl(-)-deficient solution, no prolongation was observed on K(+) reapplication. Although no conclusive evidence was obtained as to the ionic mechanism involved in the effects of K(+) or Cl(-) removal and reapplication, a possibility is considered that the sarcoplasmic reticulum is involved in determining the duration of the driving potential and the first component of the slow wave.

Excitatory cortical inputs to pallidal neurons via the subthalamic nucleus in the monkey.

How the motor-related cortical areas modulate the activity of the output nuclei of the basal ganglia is an important issue for understanding the mechanisms of motor control by the basal ganglia. In the present study, by using awake monkeys, the polysynaptic effects of electrical stimulation in the forelimb regions of the primary motor and primary somatosensory cortices on the activity of globus pallidus (GP) neurons, especially mediated by the subthalamic nucleus (STN), have been characterized. Cortical stimulation induced an early, short-latency excitation followed by an inhibition and a late excitation in neurons of both the external and internal segments of the GP. It also induced an early, short-latency excitation followed by a late excitation and an inhibition in STN neurons. The early excitation in STN neurons preceded that in GP neurons. Blockade of STN neuronal activity by muscimol (GABA(A) receptor agonist) injection resulted in abolishment of both the early and late excitations evoked in GP neurons by cortical stimulation. At the same time, the spontaneous discharge rate of GP neurons decreased, pauses between the groups of spikes of GP neurons became prominent, and the firing pattern became regular. Injection of (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) [N-methyl-D-aspartate (NMDA) receptor antagonist], but not 1,2,3, 4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium [NBQX (non-NMDA receptor antagonist)], into the STN attenuated the early and late excitations in GP neurons, suggesting that cortico-subthalamic transmission is mediated mainly by NMDA receptors. Interference with the pallido-subthalamic transmission by bicuculline (GABA(A) receptor antagonist) injection into the STN made the inhibition distinct without affecting the early excitation. The present results indicate that the cortico-subthalamo-pallidal pathway conveys powerful excitatory effects from the motor-related cortical areas to the GP with shorter conduction time than the effects conveyed through the striatum.

Organization of somatic motor inputs from the frontal lobe to the pedunculopontine tegmental nucleus in the macaque monkey.

To reveal the somatotopy of the pedunculopontine tegmental nucleus that functions as a brainstem motor center, we examined the distribution patterns of corticotegmental inputs from the somatic motor areas of the frontal lobe in the macaque monkey. Based on the somatotopical map prepared by intracortical microstimulation, injections of the anterograde tracers, biotinylated dextran amine and wheat germ agglutinin-conjugated horseradish peroxidase, were made into the following motor-related areas: the primary motor cortex, the supplementary and presupplementary motor areas, the dorsal and ventral divisions of the premotor cortex, and the frontal eye field. Data obtained from the present experiments were as follows: (i) Corticotegmental inputs from orofacial, forelimb, and hindlimb representations of the primary motor cortex tended to be arranged orderly from medial to lateral in the pedunculopontine tegmental nucleus. However, the distribution areas of these inputs considerably overlapped; (ii) The major input zones from distal representations of the forelimb and hindlimb regions of the primary motor cortex were located medial to those from their proximal representations, although there was a substantial overlap between the distribution areas of distal versus proximal limb inputs; (iii) The main terminal zones from the forelimb regions of the primary motor cortex, the supplementary and presupplementary motor areas, and the dorsal and ventral divisions of the premotor cortex appeared to overlap largely in the mediolaterally middle aspect of the pedunculopontine tegmental nucleus; and (iv) Corticotegmental input from the frontal eye field was scattered over the pedunculopontine tegmental nucleus.Thus, the present results indicate that the pedunculopontine tegmental nucleus is likely to receive partly separate but essentially convergent cortical inputs not only from multiple motor-related areas representing the same body part, but also from multiple regions representing diverse body parts. This suggests that somatotopical representations are intermingled rather than segregated in the pedunculopontine tegmental nucleus.

Protection against dopaminergic nigrostriatal cell death by excitatory input ablation.

The importance of enhanced glutamatergic neurotransmission in the basal ganglia and related structures has recently been highlighted in the development of Parkinson's disease. The pedunculopontine tegmental nucleus (PPN) is the major origin of excitatory, glutamatergic input to dopaminergic nigrostriatal neurons of which degeneration is well known to cause Parkinson's disease. Based on the concept that an excitatory mechanism mediated by glutamatergic neurotransmission underlies the pathogenesis of neurodegenerative disorders, we made an attempt to test the hypothesis that removal of the glutamatergic input to the nigrostriatal neurons by PPN lesions might prevent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in the macaque monkey. The PPN was lesioned unilaterally with microinjection of kainic acid, and, then, MPTP was administered systemically. In these monkeys, the degree of parkinsonian motor signs was behaviourally evaluated, and the histological changes in the dopaminergic nigrostriatal system were analysed by means of tyrosine hydroxylase immunohistochemistry. The present results revealed that nigrostriatal cell loss and parkinsonian motor deficits were largely attenuated in the MPTP-treated monkey group whose PPN had been lesioned, compared with the control, MPTP-treated monkey group with the PPN intact. This clearly indicates that the onset of MPTP neurotoxicity is suppressed or delayed by experimental ablation of the glutamatergic input to the nigrostriatal neurons. Such a protective action of excitatory input ablation against nigrostriatal cell death defines evidence that nigral excitation driven by the PPN may be implicated in the pathophysiology of Parkinson's disease.

Direct projections from the magnocellular division of the basal nucleus of the amygdala to the principal part of the cortical masticatory area in the macaque monkey.

Direct projections from the amygdala to the cortical masticatory area were found in the macaque monkey. Under the guidance of intracortical microstimulation, retrograde tracers were injected into multiple jaw movement-related regions of the frontal lobe. The cortical masticatory area, especially its principal part, stimulation of which elicited rhythmic jaw movement, was the only site of injection that produced neuronal labeling in the amygdala. The cells of origin of such projections were localized in the medial aspect of the magnocellular division of the basal nucleus through its rostral level. No labeled neurons were observed in the amygdala after tracer injection into any other cortical jaw movement-related region. The present results suggest that the amygdaloid input to the cortical masticatory area may exert some modulatory influence on the generation of masticatory rhythm.

B-mode and color Doppler ultrasound imaging for localization of microelectrode in monkey brain.

Using alert monkeys, we attempted ultrasound imaging after partial craniotomy to localize a metal microelectrode in the brain. B-mode ultrasonography provided images of sulcus and gyrus patterns of the cerebral cortex, and locations of the ventricles and subarachnoid cisterns. As the microelectrode proceeded in the brain, the position of the microelectrode was clearly identified. Electrolytic microlesions generated by delivering direct currents via the microelectrode could also be detected. Color Doppler imaging of blood vessels of the brain was helpful to demarcate deep brain structures and to avoid accidental injury of the blood vessels by the microelectrode. The ultrasonography will make it possible to place recording microelectrodes or injection needles accurately in target regions of the brain in physiological, anatomical or behavioral experiments.

A cortical motor region that represents the cutaneous back muscles in the macaque monkey.

A cortical motor region that represented the cutaneous muscles on the back was identified on the medial wall of the frontal lobe in the macaque monkey. In this region, neurons responded to somatosensory stimuli such as light touch or squeezing of the back skin, and intracortical microstimulation elicited contraction of the back skin. Such a region was located primarily on the dorsal bank of the cingulate sulcus, corresponding to the dorsal cingulate motor area.

Organization of nonprimary motor cortical inputs on pyramidal and nonpyramidal tract neurons of primary motor cortex: An electrophysiological study in the macaque monkey.

To elucidate the functions of nonprimary motor cortical (nPMC) areas whose afferents synapse onto output neurons of the primary motor cortex (PMC), we examined the responses of pyramidal tract neurons (PTNs) and non-PTNs (nPTNs) to electrical stimulation in the three nPMCs, the supplementary motor area (SMA) and the dorsal and ventral divisions of the premotor cortex (PMd and PMv), with extracellular unit recording in alert monkeys. Typical responses of PTNs to nPMC stimulation were early orthodromic excitatory responses followed by inhibitory responses. Among 27 PTNs tested by constructing peri-stimulus time histograms, 19 (70.4%) showed inhibitory responses to stimulation in all of the nPMC areas. In contrast, 5/33 PTNs (15.2%) and 10/72 nPTNs (13.9%) showed excitatory responses to stimulation in all of the nPMCs. The inhibitory responses of PTNs were mediated by inhibitory interneurons, some of which may correspond to nPTNs in the superficial layers of the PMC. These interneurons probably possess widely extended axons and nonspecifically inhibit multiple PTNs in layer V. The excitatory and inhibitory influences, and the patterns of convergence of inputs from the nPMCs onto the PTNs, are important to understand motor control by the nPMC-PMC-spinal cord pathway.

Corticostriatal and corticosubthalamic input zones from the presupplementary motor area in the macaque monkey: comparison with the input zones from the supplementary motor area.

The presupplementary motor area (pre-SMA) is a cortical motor-related area which lies in the medial wall of the frontal lobe, immediately anterior to the supplementary motor area (SMA). This area has been considered to participate in the control of complex forelimb movements in a way different from the SMA. In an attempt to analyze the patterns of projections from the pre-SMA to the basal ganglia, we examined the distributions of pre-SMA inputs in the striatum and the subthalamic nucleus and compared them with the SMA input distributions. To detect morphologically the terminal fields from the pre-SMA and the forelimb region of the SMA, anterograde tracers were injected into such areas that had been identified electrophysiologically in the macaque monkey. Corticostriatal inputs from the pre-SMA were distributed mainly in the striatal cell bridges connecting the rostral aspects of the caudate nucleus and the putamen, as well as in their neighboring striatal portions. These input zones were located, with no substantial overlap, rostral to corticostriatal input zones from the SMA forelimb region. Corticosubthalamic input zones from the pre-SMA were almost localized in the medial aspect of the nucleus, where corticosubthalamic inputs from the SMA forelimb region were also distributed predominantly. However, the major terminal fields from the pre-SMA were centered ventrally to those from the SMA. The present results indicate that the corticostriatal and corticosubthalamic input zones from the pre-SMA appear to be segregated from the SMA-derived input zones. This implies the possibility of parallel processing of motor information from the pre-SMA and SMA in the cortico-basal ganglia circuit.

Monkey globus pallidus external segment neurons projecting to the neostriatum.

Experiments were performed to assess the number and parvalbumin (PV) immunoreactivity of neurons participating in the pallidostriatal projection in macaque monkeys. Injection of WGA-HRP into the right caudate nucleus and the left putamen of a Macaca mulatta and a M. fuscata labeled a large number of the globus pallidus external segment (GPe) neurons. Counting neurons labeled with WGA-HRP and those stained with neuronal markers indicated that approximately 30% of GPe neurons project to neostriatum. Approximately 2/3 of the pallidostriatal neurons are PV-immunoreactive. This study revealed that a significant number of primate GPe PV immunoreactive neurons project to the neostriatum, and suggest that the pallidostriatal projection should be taken into account in the analysis of functional roles of the basal ganglia circuitry.

Long-term use-dependent enhancement of impulse-induced exocytosis by adrenaline at frog motor nerve terminals.

Adrenaline (5-20 microM) use-dependently increased end-plate potentials (EPPs) in normal Ringer solution (containing d-tubocurarine to partially block acetylcholine receptors) and a low Ca2+, high Mg2+ solution for more than several hours and decreased the coefficient of variation of EPP amplitude in the latter solution in frog neuromuscular junctions. The amplitude and frequency of miniature EPPs and impulse-induced increases in intraterminal Ca2+ concentration were unaffected. Adrenaline thus causes sustained enhancement of impulse-induced exocytosis by acting at a mechanism of exocytosis downstream to Ca2+ entry.

Corticostriatal projections from distal and proximal forelimb representations of the monkey primary motor cortex.

Corticostriatal projections from one distal and two proximal subregions in the forelimb representation of the primary motor cortex (MI) were examined in the macaque monkey. The distal and proximal subregions in the anterior bank of the central sulcus (distal and proximal-bank subregions) and the proximal subregion in the surface of the precentral gyrus (proximal-surface subregion) of the MI were identified using intracortical microstimulation. Different anterograde tracers were then injected into two of these three forelimb subregions of the MI. In the ipsilateral putamen, the distribution areas of corticostriatal fibers from the distal, proximal-bank and proximal-surface subregions were arranged from ventrolateral to dorsomedial in this order. These corticostriatal input zones were largely segregated from one another.

A modified microsyringe for extracellular recording of neuronal activity.

We describe a modified Hamilton microsyringe that allows extracellular recording of neuronal activity and subsequent injections. It is assembled with a Hamilton removable needle and a syringe for injection, a Teflon-coated tungsten wire for recording, and polyimide tubing as a sheath. The device is inexpensive and easy to handle in anatomical and physiological experiments in awake monkeys.

Corticostriatal projections from the somatic motor areas of the frontal cortex in the macaque monkey: segregation versus overlap of input zones from the primary motor cortex, the supplementary motor area, and the premotor cortex.

It is an important issue to address the mode of information processing in the somatic motor circuit linking the frontal cortex and the basal ganglia. In the present study, we investigated the extent to which corticostriatal input zones from the primary motor cortex (MI), the supplementary motor area (SMA), and the premotor cortex (PM) of the macaque monkey might overlap in the putamen. Intracortical microstimulation was performed to map the MI, SMA, and dorsal (PMd) and ventral (PMv) divisions of the PM. Then, two different anterograde tracers were injected separately into somatotopically corresponding regions of two given areas of the MI, SMA, PMd, and PMv. With respect to the PMd and PMv, tracer injections were centered on their forelimb representations. Corticostriatal input zones from hindlimb, forelimb, and orofacial representations of the MI and SMA were, in this order, arranged from dorsal to ventral within the putamen. Dense input zones from the MI were located predominantly in the lateral aspect of the putamen, whereas those from the SMA were in the medial aspect of the putamen. On the other hand, corticostriatal inputs from forelimb representations of the PMd and PMv were distributed mainly in the dorsomedial sector of the putamen. Thus, the corticostriatal input zones from the MI and SMA were considerably segregated though partly overlapped in the mediolateral central aspect of the putamen, while the corticostriatal input zone from the PM largely overlapped that from the SMA, but not from the MI.

Corticostriatal input zones from the supplementary motor area overlap those from the contra- rather than ipsilateral primary motor cortex.

To investigate the degree of convergence of corticostriatal inputs from the primary motor cortex (MI) and the supplementary motor area (SMA), we analyzed the extent to which corticostriatal inputs from forelimb representations of these motor-related areas spatially overlap in the macaque monkey. Of particular interest was that corticostriatal input zones from SMA overlapped those from MI of the contralateral hemisphere more extensively than from MI of the ipsilateral hemisphere.

Reevaluation of ipsilateral corticocortical inputs to the orofacial region of the primary motor cortex in the macaque monkey.

An anatomical approach to possible areas in the cerebral cortex involved in somatic motor behavior is to analyze the cortical areas containing neurons that connect directly to the primary motor cortex (MI). To define the cortical areas related to orofacial movements, we examined the distribution of cortical neurons that send their axons to the orofacial region of the MI in the macaque monkey. Injections of retrograde tracers into the electrophysiologically identified orofacial region of the MI revealed that labeled neurons were distributed in the following cortical areas: the orbital cortex (area 12), insular cortex, frontoparietal operculum (including the deep part of the cortical masticatory area and the secondary somatosensory cortex), ventral division of the premotor cortex (especially in its lateral part), orofacial region of the supplementary motor area, rostral division of the cingulate motor area (CMA), and CMA on the ventral bank. A number of labeled neurons were also seen in the MI around the injection sites and in the parietal cortex (including the primary somatosensory cortex and area 7b). No labeled neurons were found in the dorsal division of the premotor cortex. Fluorescent retrograde double labeling further revealed virtually no overlap of distribution between cortical neurons projecting to the orofacial and forelimb regions of the MI. Based on the present results, we discuss the functional diversity of the cortical areas related to orofacial motor behavior and the somatotopical organization in the premotor areas of the frontal cortex.