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.

Corticosubthalamic input zones from forelimb representations of the dorsal and ventral divisions of the premotor cortex in the macaque monkey: comparison with the input zones from the primary motor cortex and the supplementary motor area

Employing double anterograde axonal tracing in combination with intracortical microstimulation, we examined the distribution patterns of corticosubthalamic inputs from forelimb representations of the dorsal (PMd) and ventral (PMv) divisions of the premotor cortex in the macaque monkey. The inputs from the PMd and PMv were distributed mainly in the medial aspect of the subthalamic nucleus (STN), in which their distribution areas overlapped each other. By the same experimental approach, we further compared corticosubthalamic input zones from the PMd/PMv with those from the primary motor cortex (MI) and the supplementary motor area (SMA). The input zones from the PMd/PMv and SMA largely overlapped in the medial aspect of the STN, whereas the input zones from the PMd/PMv and MI were virtually segregated mediolaterally in the STN.

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.

Excitotoxic lesions of the pedunculopontine tegmental nucleus produce contralateral hemiparkinsonism in the monkey

Dopaminergic nigrostriatal neurons, degeneration of which causes Parkinson's disease, are known to receive excitatory input almost exclusively from the pedunculopontine tegmental nucleus (PPN). We report here that excitotoxic lesions of the PPN produce abnormal motor signs relevant to hemiparkinsonism in the macaque monkey. Under the guidance of extracellular unit recordings, the electrophysiologically identified PPN was injected unilaterally with kainic acid. These PPN-lesioned monkeys exhibited mild to moderate levels of flexed posture and hypokinesia in the upper and lower limbs contralateral to the lesion. In most of the monkeys, such pathophysiological events were gradually improved and became stationary in 1-2 weeks. The hemiparkinsonian symptoms observed after PPN destruction might be ascribed to a decrease in nigrostriatal neuron activity due to excitatory input ablation.

Patchy distribution of substance P receptor immunoreactivity in the' developing rat striatum

Developmental changes of the distribution pattern of substance P receptor (SPR) were investigated immunohistochemically in the rat striatum. The SPR immunoreactivity in the striatum first emerged at postnatal day 1 and transiently showed a patchy pattern of distribution until it displayed the adult pattern of homogeneous distribution by the third postnatal week. The SPR-immunoreactivity patches were most marked in the medial and dorsolateral parts of the striatum, as well as in the subcallosal streak. They matched tyrosine hydroxylase-enriched areas and, conversely, avoided calbindin-enriched zones. No neurons within the SPR-immunoreactive patches contained either choline acetyltransferase or somatostatin, which is known to be contained in intrinsic neurons in the striatum. The vast majority of SPR-immunoreactive patch neurons also contained DARPP-32, a phosphoprotein that is expressed in striatal projection neurons with D1 dopamine receptor. The results indicate that SPR-immunoreactive patches which appear transiently in the developing striatum are in register with the striatal patch compartment, and that SPR immunoreactivity within these patches may be expressed on projection neurons rather than intrinsic neurons. Such SPR immunoreactivity in projection neurons in striatal patches may fade out in adulthood.

Origin of thalamocortical projections to the presupplementary motor area (pre-SMA) in the macaque monkey

The presupplementary motor area (pre-SMA) is a recently defined cortical motor area that is located immediately rostral to the supplementary motor area (SMA) and is considered to play more complex roles in motor control than the SMA. In the present study, we examined the distribution of cells of origin of thalamocortical projections to the pre-SMA in the macaque monkey. Under the guidance of intracortical microstimulation mapping, the retrograde tracer biotinylated dextran amine was injected into the pre-SMA. Retrogradely labeled neurons were distributed primarily in the parvicellular division of the ventroanterior nucleus (VApc), oral division of the ventrolateral nucleus (VLo), area X, and mediodorsal nucleus (MD). Some labeled neurons were also observed in the medial and caudal divisions of the ventrolateral nucleus. The results indicate that the pre-SMA may receive not only basal ganglia inputs via the VApc, VLo, and MD, but also a cerebellar input via the X.

A smooth muscle nodule producing 10-12 cycle/min regular contractions at the mesenteric border of the pacemaker area in the guinea-pig colon

At the boundary between the proximal and distal divisions of the colon in the guinea-pig is a ring-like section which rhythmically contracts. HUKUHARA and his co-researchers demonstrated that antiperistaltic movements in the proximal colon start from this ring-like section, the so-called pacemaker area. Tissue specimens, 0.1-0.3 mm in width/height x 4-7 mm in length, were prepared from various parts of this area. Significantly, in the circular muscle at the mesenteric border, a nodular structure spontaneously producing 10-12 cycle/min regular mechanical contractions was found. Moreover, histological investigations after physiological recording revealed that the presence of the inner-most and/or outermost portions of the circular muscle coat was not necessary for these spontaneous activities. Champy-Maillet (ZIO) staining showed that smooth muscle cells in this spontaneously contracting nodule were heavily innervated. Transmission electron microscopy showed that the smooth muscle tissue of this particular area was characterized by scanty interstitial elements such as fibroblasts. Plasma membranes of adjacent smooth muscle cells were frequently in direct contact with each other, forming many gap junctions. Scanning electron microscopy in the specimen prepared using a NaOH-maceration method revealed fine three-dimensional relationships between nerve terminals and smooth muscle cells. The nodular structure described in this paper may provide a useful experimental model for the investigation of colonic motility and its neural control.

Dual somatotopical representations in the primate subthalamic nucleus: evidence for ordered but reversed body-map transformations from the primary motor cortex and the supplementary motor area

The subthalamic nucleus (STN) is a key structure for somatic motor control via the basal ganglia. In the present study, we demonstrate that the STN of the macaque monkey has dual sets of body part representations. Each of the two separate portions of the STN is characterized with somatotopically arranged direct cortical inputs that are derived from the primary motor cortex (MI) and the supplementary motor area (SMA). The first set of body part representations is transformed from the MI to the lateral STN, whereas the second set is transformed from the SMA to the medial STN. Intracortical microstimulation mapping was carried out to guide paired injections of anterograde tracers into somatotopically corresponding regions of the MI and the SMA. We found that direct inputs from the MI were allocated mostly within the lateral half of the STN, whereas those from the SMA were distributed predominantly within its medial half. Of particular interest was that the arrangement of somatotopical representations from the SMA to the medial STN was reversed against the ordering of those from the MI to the lateral STN; the orofacial, forelimb, and hindlimb parts were represented from medial to lateral within the medial STN, whereas these body parts were represented, in the inverse order, mediolaterally within the lateral STN. Moreover, inputs from homotopical MI and SMA regions were found to converge only partially into the STN. The present findings could account for somatotopically specific involuntary movements manifested in hemiballism that is caused by destruction of the STN.

Nitrinergic nerves controlling pacemaker activities of the inner sublayer (P-layer) in the canine proximal colon circular muscles

The inner sublayer (P-layer) of the circular muscle coat in the canine proximal colon has been known to produce spontaneous mechanical contractions associated with characteristic electrical activities called slow waves. We recorded the mechanical activities of tissue preparations from this P-layer. Normal Krebs solution (K+; 6 mM) was used as the perfusate. Elevation of extracellular K+ concentrations in the range of 12 mM and 36 mM induced intensified phasic contractions. Administration of an NO-synthase inhibitor, N omega-nitro-arginine methyl ester (L-NAME, 50 microM), enhanced both the spontaneous mechanical rhythms and high extracellular K(+)-induced contractions. Administration of the substrate for NO synthases, L-arginine (400 microM) remarkably suppressed the effects of L-NAME on the amplitude of the spontaneous rhythms and on responses to extracellular high K+. Histological structures of nerves in the P-layer were investigated by an NADPH (nicotinamide adenine dinucleotide phosphate)-diaphorase technique and by the immunohistochemistry of NO-synthases, since NO-producing (nitrinergic) nerves usually, if not always, show a histochemical NADPH-diaphorase positive reaction in formaldehyde-fixed specimens, and since features of ganglia and nerve strands in the outer subdivision of the submucosal plexus (plexus submucosus externus; or so-called Henle's plexus) together with the delicate network of nerve terminal varicosities within the P-layer were clearly visualized by this method. The topographical arrangement of nitrinergic nerves supported the view that they produce nitric oxide (NO), being one of the major chemical mediators of the neural control of the spontaneous rhythms in the P-layer.

Direct projections from the orofacial region of the primary motor cortex to the superior colliculus in the macaque monkey

Employing anterograde axonal tracing combined with intracortical microstimulation, we have revealed in the macaque monkey that the orofacial region of the primary motor cortex sends projection fibers to the deep layers of the superior colliculus. The terminal site of these projection fibers was almost localized to the lateral part of the intermediate gray layer at its rostral level, and spatially segregated from that of projection fibers arising from the frontal eye field. The results indicate the existence of a discrete tectal region related specifically to the control of orofacial movements.

Postnatal development of cortical acetylcholinesterase-rich neurons in the rat brain: permanent and transient patterns

The development of acetylcholinesterase (AChE) activity within cortical neurons of the rat brain was investigated using a histochemical method. The fate of these neurons in later stages of development was studied in animals in which AChE within cortical axons (mostly cholinergic) had been depleted by lesions of the cholinergic neurons of the basal forebrain or by injections of diisopropyl fluorophosphate. We designated neurons with medium to high intensity of reaction product as AChEH and neurons with a low intensity of reaction product as AChEL. Four groups of AChEH cortical neurons were detected: (1) AChEH Cajal-Retzius cells were present in layer I at birth (P0) and decreased steadily in number until none could be detected at P17 or thereafter. (2) AChEH neurons within layer VI and underlying white matter were present at P0, peaked in number and staining intensity at P8-P9, showed a moderate decrease in number at P11-P13 and a further decrease into adulthood. (3) AChEH polymorphic intracortical neurons appeared at P3-P4 in deep cortical layers and by P9 were present in layers II-VI. They continued to increase in number through P11-P14 at which time they displayed the adult pattern and were found in all cortical areas. (4) A large population of AChEH pyramidal neurons appeared at P1-P4, peaked at P8-P10 and was no longer visible at P21. In the adult cerebral cortex, few pyramidal neurons displayed AChE activity and these were almost always of the AChEL type. These results indicate that the AChE within cortical neurons is developmentally regulated and that the content of this enzyme helps to differentiate cortical neurons into distinct populations. The transient expression of AChE activity within cortical neurons suggests a role for this enzyme in the development of the cerebral cortex.

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter muscle in the rat

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter and the external and sphincter muscles were examined in the rat by the tract-tracing methods utilizing retrograde transport of cholera toxin B subunit and anterograde transport of biotinylated dextran amine. The dorsolateral pontine tegmental region, corresponding to the micturition reflex center of Barrington, was confirmed to send bilaterally, with an ipsilateral dominance, projection fibers to the spinal parasympathetic nucleus (inferior intermediolateral nucleus). The micturition reflex center of Barrington, however, did not seem to send many projection fibers to the ventral horn of the lumbosacral cord segments, whereas the region immediately ventral to the micturition reflex center of Barrington was found to send bilaterally, with a contralateral dominance, projection fibers to the dorsolateral group of pudendal motoneurons in both the male and female rats. In the female rat, the dorsolateral group of pudendal motoneurons are comprised primarily of motoneurons that innervate the external urethral sphincter muscle. The dorsomedial group of pudendal motoneurons, which contain motoneurons that innervate the external and sphincter and the bulbocavernosus muscles, did not seem to receive major projections from the dorsolateral pontine tegmental regions. It was also observed that the locus coeruleus sent some projection fibers bilaterally to the spinal parasympathetic nucleus but only a few to the ventral horn of the lumbosacral cord segments. Thus, the present results indicate that the dorsolateral group of pudendal motoneurons containing those innervating the external urethral sphincter muscle receive pontospinal projection fibers mainly from the dorsolateral pontine tegmental region immediately ventral to the micturition reflex center of Barrington.

[A case report of dural sinus thrombosis: direct thrombolytic therapy using endovascular surgery]

Dural sinus thrombosis, a relatively rare disease, is difficult to diagnose because of variable symptomatic manifestations. We successfully treated a case of dural sinus thrombosis by direct thrombolysis using an endovascular technique in combination with postoperative anticoagulant therapy. The patient, a 19-year-old female, developed a headache affecting her whole head on December 13, 1993. She was admitted to our hospital the next day. Neurological examination upon admission revealed no neurological abnormalities, nor was there any abnormality in CT scan, either plain or enhanced, taken on the day of admission. The patient's consciousness deteriorated in the early morning of December 22. MRI and cerebral angiography revealed thrombi from the confluence of the sinuses to the right transverse and sigmoid sinus, with disturbed circulation through deep cerebral veins. Systemic thrombolytics, steroid and mannitol were started, but, on the next day, the third ventricle was compressed by bilateral swelling of the basal ganglia, with hydrocephalus. Since her consciousness deteriorated further despite ventricular drainage and barbiturate therapy, direct thrombolytic therapy was performed on December 25. A catheter was placed in the superior sagittal sinus, and 600,000 units of urokinase was locally injected, followed by postoperative anticoagulant therapy. The patient's condition improved rapidly. On CT scan, the bilateral swelling of the basal ganglia disappeared along with the hydrocephalus. At about 1 month after endovascular surgery, MRI and cerebral angiography revealed recanalization of the deep cerebral veins, straight sinus and confluence of sinuses with improved opacification of the left transverse sinus, although the right transverse sinus was found to be re-occluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotopical projections from the supplementary motor area to the red nucleus in the macaque monkey

Direct projections from the supplementary motor area (SMA) to the red nucleus were investigated in the Japanese monkey (Macaca fuscata). The anterograde tracer, horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), was injected into various regions of the SMA after intracortical microstimulation mapping. After WGA-HRP injection into the orofacial, forelimb, or hindlimb region of the SMA, anterogradely labeled axon terminals were found, respectively, in the medial, intermediate, or lateral portion of the parvocellular part of the red nucleus, bilaterally with an ipsilateral predominance. The results indicate the clear somatotopical arrangement of corticorubral projections from the SMA.

Effects of intracellular pH on calcium currents and intracellular calcium ions in the smooth muscle of rabbit portal vein

In smooth muscle cells freshly dispersed from the rabbit portal vein, effects of intracellular pH (pHi) on Ca2+ channel currents were studied with the whole-cell clamp method using nystatin in the pipette. pHi was modified with ammonium chloride (NH4Cl) and propionate. Changes in intracellular Ca2+ concentration ([Ca2+]i) and pHi were also measured with the fluorescent indicator fura-2 and a pH-sensitive dye, respectively, together with the mechanical response in intact tissues. Intracellular alkalinization caused by an application of NH4Cl (20 mM) markedly potentiated and acidification caused by propionate (20 mM) inhibited inward Ca2+ channel currents, without much change in the kinetics. Tension development induced by 60 mM K- was inhibited by NH4Cl (20 mM) and potentiated by propionate (20 mM), whereas the peak [Ca2+]i level reached during K+ contracture was reduced in the presence of NH4Cl and increased in the presence of propionate. It was concluded that the modification of Ca2+ channel currents caused by pHi is not directly related to the effects of pHi on the mechanical response to excess K+. The direct effects of pHi on [Ca2+]i and on contractile machinery are considered to be mainly responsible for the mechanical effect of pHi.

Single retinal ganglion cells projecting bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals in the cat

In most mammals with frontalized eyes, retinal ganglion cells in the nasal or temporal retina send their axons to the contralateral or ipsilateral half, respectively, of the brain. Previous studies in the cat, however, have indicated a retinal region of "nasotemporal overlap" from which arise the retinal projections to both the contralateral and ipsilateral halves of the brain. The present study thus examined in the cat whether any retinal ganglion cells give rise to bifurcating axons that innervate both halves of the brain. By employing fluorescent retrograde double labeling, we investigated whether or not single retinal ganglion cells project bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. After Fast Blue was injected into the lateral geniculate nucleus on one side and Diamidino Yellow was injected contralaterally into the lateral geniculate nucleus, 100-200 ganglion cells in each retina were double labeled with both tracers. These double-labeled cells were distributed primarily in the temporal retina, including the region around the vertical meridian and, additionally, in the nasal retina. About 60-80% of the double-labeled cells had large cell bodies (more than 25 microns in diameter), and the others had medium-sized ones (15-25 microns in diameter). The pattern of distribution of double-labeled cells, which was observed after the combined injection into both superior colliculi, was similar to that seen after the combined injection into both lateral geniculate nuclei; more than 90% of double-labeled cells, however, were large.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct projections from the ventral premotor cortex to the hindlimb region of the supplementary motor area in the macaque monkey

A retrograde tracer, Diamidino yellow, was injected into the hindlimb region of the supplementary motor area after intracortical microstimulation mapping in the Japanese monkey. As a result, a cluster of retrogradely labeled neurons was found in the caudal bank of the arcuate sulcus, which corresponds to the ventral premotor cortex. The present findings suggest that there exists a hindlimb representation in the ventral premotor cortex.

Direct projections from the entopeduncular nucleus to the lower brainstem in the rat

The present study reports the existence of projection fibers from the entopeduncular nucleus to the superior colliculus and lateral parts of the pontobulbar tegmental regions (so-called lateral tegmental field) in the rat, suggesting that the entopeduncular nucleus may control eye-head and orofacial movements via these projection fibers. The anterograde axonal tracing with Phaseolus vulgaris-leucoagglutinin has revealed that the entopedunculotectal fibers terminate, bilaterally, with an ipsilateral predominance, in the deep layers of the superior colliculus through its rostral one-third level and that the entopedunculotegmental fibers terminate, bilaterally, with an ipsilateral predominance, in the parabrachial area, reticular formation surrounding the trigeminal motor nucleus, and parvicellular, dorsal, and ventral reticular nuclei. The cells of origin of the entopedunculotectal and entopedunculotegmental projections have been identified by retrograde axonal tracing with Fluoro-Gold and cholera toxin B subunit. The entopedunculotectal or entopedunculotegmental fibers originate, respectively, from the dorsal or ventral part of the entopeduncular nucleus. Additionally, a series of fluorescent retrograde double-labeling experiments with Fast Blue and Diamidino Yellow have indicated that single entopeduncular nucleus neurons projecting to the superior colliculus or lateral tegmental field often send their axon collaterals to the lateral habenular nucleus. The entopedunculotectal fibers are assumed to control head movements, which may be provoked via the tectospinal fibers, and further to participate in eye movements as the nigrotectal fibers that have been known to arise from the substantia nigra pars reticulata to end in the deep layers of the superior colliculus primarily through its caudal two-thirds level. The entopedunculotegmental fibers are presumed to be involved in control of orofacial movements, because the sites of termination of the entopedunculotegmental fibers correspond well with the reported areas of distribution of premotor interneurons for the trigeminal motor, facial, and hypoglossal nuclei.

Direct projections from the deep layers of the superior colliculus to the subthalamic nucleus in the rat

Direct projections from the superior colliculus to the subthalamic nucleus were found in the rat in antero- and retrograde tracing experiments; these projections arose mainly from the deep layers of the superior colliculus at its middle to caudal levels. The present findings suggest that signals from the deep layers of the superior colliculus may modulate the basal ganglia activity during orienting behavior.

Inhibitory effects of propiverine on rat and guinea-pig urinary bladder muscle

In muscle strips isolated from guinea-pig and rat urinary bladder, propiverine (3-10 microM) inhibited carbachol-induced contractions in the presence of verapamil and Ca(2+)-induced contractions in excess K+ medium containing atropine, suggesting it has both anticholinergic and Ca2+ channel blocking actions. The Ca2+ channel blocking action was also demonstrated by recording inward Ca2+ currents in single cells dispersed from both species. The inhibition of inward currents by propiverine was three times stronger in the rat than the guinea-pig, ID50 being 7 microM for rat and 21 microM for guinea-pig. The recovery of the current after washout was faster than that of mechanical inhibition. It is concluded that propiverine blocks not only muscarinic receptors, but also Ca2+ channels at similar concentrations.

Developmentally transient expression of acetylcholinesterase within cortical pyramidal neurons of the rat brain

Using a histochemical method for the visualization of cholinesterase activity in neurons, we have observed developmentally transient expression of acetylcholinesterase (AChE) in cortical pyramidal neurons of the rat brain. Depending on the extent of the deposition of AChE reaction product, several types of cortical neurons could be visualized. We designated neurons with moderate-to-high staining intensity as AChEH and neurons with relatively lower staining intensity as AChEL. At birth (P0), very little AChE activity was found within cortical neurons. Between P1-P4, there was a gradual emergence of AChE-stained cortical neurons. At this stage, the majority of these neurons were of the AChEL type. At P5-P7 we observed an abrupt increase in AChE-stained cortical neurons. The number and the staining intensity of these neurons was at a peak at P8-P10. At this age range, the majority of these neurons were of the AChEH variety and displayed morphological characteristics of cortical pyramidal neurons. At P11-P15, there was an abrupt decrease in the number of AChEH neurons. After P15, the density and staining intensity of cortical AChE-positive (cholinergic) axons gradually increased. Nevertheless, AChEL pyramidal neurons were detected through these fibers up to P21. At P21, a dense plexus of AChE-positive axons was observed in all cortical areas while very little AChE reaction product was visible in pyramidal neurons, and this pattern continued into adult life. When the adult cortex was denervated from its AChE-positive axons by lesions of the nucleus basalis magnocellularis, many AChEL pyramidal neurons were uncovered.(ABSTRACT TRUNCATED AT 250 WORDS)

[A case of metastatic spinal tumor from renal cancer reduced by interferon-alpha]

A case of metastatic spinal tumor from renal cancer reduced by interferon-alpha is reported. A 54-year-old man was admitted to Tane General Hospital on April 12, 1990, with the complaint of difficulty in walking. Abdominal CT scan revealed right renal carcinoma, and MRI demonstrated metastatic spinal tumor at Th6, which was mainly occupying the entire lamina, spinous process and right pedicle of Th6. Nephrectomy was performed and, instead of operating on the spinal lesion, the patient was given follow-up treatment with administration of interferon-alpha (5 million units twice a week) and steroid. 1 year and 6 months later the patient's walking ability began to deteriorate and paraparesis progressed, although the size of the metastatic spinal tumor had gradually reduced. This was thought to be because of atrophy of the legs due to prolonged bed rest and steroid administration. Laminectomy with total removal of the tumor was performed on January 16, 1992. In the 12 months postoperatively, there has been neither recurrence nor remote metastasis seemingly due to the administration of interferon-alpha. This appears to be the first report of metastatic spinal tumor from renal cancer reduced by interferon-alpha.

Input organization of distal and proximal forelimb areas in the monkey primary motor cortex: a retrograde double labeling study

The present double-labeling study was designed to demonstrate the morphological framework for motor control in coordinated distal and proximal forelimb movements, which may partly, at least, depend on corticocortical and thalamocortical inputs to the forelimb area in the primary motor cortex. After intracortical microstimulation mapping of the forelimb area in the primary motor cortex of four macaque monkeys, a retrograde tracing study with fluorescent dyes was attempted to label simultaneously neurons in cortical and subcortical sites projecting to the distal forelimb representation area and those projecting to the proximal representation area of the primary motor cortex. Neurons projecting to distal and proximal forelimb parts of the primary motor cortex were largely separate in the following areas: the premotor area, primary somatosensory area, secondary somatosensory area, area 5, and thalamus. In contrast, there was no precise topographic organization of labeled projection neurons in the following areas: the supplementary motor area, cingulate motor area, primary motor cortex adjacent to the injection sites, claustrum, and basal nucleus of Meynert. The present study revealed that the forelimb area of the primary motor cortex receives both segregated and intermixed inputs from cortical and subcortical sources. In particular, the fact that the forelimb area of the primary motor cortex receives topographically organized inputs from the premotor area and nontopographically organized inputs from the supplementary motor area and cingulate motor area indicates possible different functional roles of frontal premotor areas in control of coordinated distal and proximal forelimb movements.