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

Corticotectal Projections From the Premotor or Primary Motor Cortex After Cortical Lesion or Parkinsonian Symptoms in Adult Macaque Monkeys: A Pilot Tracing Study

The corticotectal projections, together with the corticobulbar (corticoreticular) projections, work in parallel with the corticospinal tract (CST) to influence motoneurons in the spinal cord both directly and indirectly via the brainstem descending pathways. The tectospinal tract (TST) originates in the deep layers of the superior colliculus. In the present study, we analyzed the corticotectal projections from two motor cortical areas, namely the premotor cortex (PM) and the primary motor cortex (M1) in eight macaque monkeys subjected to either a cortical lesion of the hand area in M1 (n = 4) or Parkinson's disease-like symptoms PD (n = 4). A subgroup of monkeys with cortical lesion was subjected to anti-Nogo-A antibody treatment whereas all PD monkeys were transplanted with Autologous Neural Cell Ecosystems (ANCEs). The anterograde tracer BDA was used to label the axonal boutons both en passant and terminaux in the ipsilateral superior colliculus. Individual axonal boutons were charted in the different layers of the superior colliculus. In intact animals, we previously observed that corticotectal projections were denser when originating from PM than from M1. In the present M1 lesioned monkeys, as compared to intact ones the corticotectal projection originating from PM was decreased when treated with anti-Nogo-A antibody but not in untreated monkeys. In PD-like symptoms' monkeys, on the other hand, there was no consistent change affecting the corticotectal projection as compared to intact monkeys. The present pilot study overall suggests that the corticotectal projection is less affected by M1 lesion or PD symptoms than the corticoreticular projection previously reported in the same animals.

Ipsilateral corticotectal projections from the primary, premotor and supplementary motor cortical areas in adult macaque monkeys: a quantitative anterograde tracing study

The corticotectal projection from cortical motor areas is one of several descending pathways involved in the indirect control of spinal motoneurons. In non-human primates, previous studies reported that cortical projections to the superior colliculus (SC) originated from the premotor cortex (PM) and the primary motor cortex, whereas no projection originated from the supplementary motor area (SMA). The aim of the present study was to investigate and compare the properties of corticotectal projections originating from these three cortical motor areas in intact adult macaques (n = 9). The anterograde tracer biotinylated dextran amine was injected into one of these cortical areas in each animal. Individual axonal boutons, both en passant and terminaux, were charted and counted in the different layers of the ipsilateral SC. The data confirmed the presence of strong corticotectal projections from the PM. A new observation was that strong corticotectal projections were also found to originate from the SMA (its proper division). The corticotectal projection from the primary motor cortex was quantitatively less strong than that from either the premotor or SMAs. The corticotectal projection from each motor area was directed mainly to the deep layer of the SC, although its intermediate layer was also a consistent target of fairly dense terminations. The strong corticotectal projections from non-primary motor areas are in position to influence the preparation and planning of voluntary movements.

Anatomical organization of descending cortical projections orchestrating the patterns of cortically induced rhythmical jaw muscle activity in guinea pigs

Repetitive electrical microstimulation to the cortical masticatory area (CMA) evokes distinct patterns of rhythmical jaw muscle activities (RJMAs) in animals. This study aimed to investigate the characteristics of the descending projections from the CMA, associated with distinct patterns of RJMAs, to the thalamus, midbrain, pons and medulla in guinea pigs. RJMAs with continuous masseter and digastric bursts (CB-RJMAs) and stimulus-locked digastric sub-bursts (SLB-RJMAs) were induced from the anterior and posterior areas of the rostral region of the lateral agranular cortex, and chewing-like RJMAs from the rostral region of the granular cortex. Anterograde tracer, biotinylated dextran amine, was injected into the three cortical areas. The cortical area inducing CB-RJMAs had strong ipsilateral projections to the motor thalamus, red nucleus, midbrain reticular formation, superior colliculus, parabrachial nucleus, and supratrigeminal region, and contralateral projections mainly to the lateral reticular formation around the trigeminal motor nucleus (Vmo). The cortical area inducing SLB-RJMAs had moderate projections to the motor thalamus and lateral reticular formation around the Vmo, but few projections to the midbrain nuclei. The cortical area inducing chewing-like RJMAs had strong projections to the ipsilateral sensory thalamus and contralateral trigeminal sensory nuclei, and moderate projections to the lateral reticular formation. The three cortical areas consistently had few projections to the ventromedial reticular formation. The present study demonstrates that multiple direct and indirect descending projections from the CMA onto the premotor systems connecting the trigeminal motoneurons represent the neuroanatomical repertoires for generating RJMAs during the distinct phases of natural ingestive behavior.

Arm movements induced by electrical microstimulation in the superior colliculus of the macaque monkey

Neuronal activity in the deep layers of the macaque (Macaca mulatta) superior colliculus (SC) and the underlying reticular formation is correlated with the initiation and execution of arm movements (Werner, 1993). Although the correlation of this activity with EMGs of proximal arm muscles is as strong as in motor cortex (Werner et al., 1997a; Stuphorn et al., 1999), little is known about the influence of electrical microstimulation in the SC on the initiation and trajectories of arm movements. Our experiments on three macaque monkeys clearly show that arm movements can be elicited by electrical microstimulation in the deep layers of the lateral SC and underlying reticular formation. The most extensively trained monkey, M1, extended his arm toward the screen in front of him more or less stereotypically upon electrical SC stimulation. In two other monkeys, M2 and M3, a larger repertoire of arm movements were elicited, categorized into three movement types, and compared before (M3) and after (M2 and M3) training: twitch (56% vs. 62%), lift (6% vs. 5%), and extend (37% vs. 32%), respectively. Therefore, arm movements induced by electrical stimulation in the monkey SC represent a further component of the functional repertoire of the SC using its impact on motoneurons in the spinal cord, probably via premotor neurons in the brainstem, as well as on structures involved in executing more complex movements such as target-directed reaching. Therefore, the macaque SC could be involved directly in the initiation, execution, and amendment of arm and hand movements.

Input-output organization of jaw movement-related areas in monkey frontal cortex

The brain mechanisms underlying mastication are not fully understood. To address this issue, we analyzed the distribution patterns of cortico-striatal and cortico-brainstem axon terminals and the origin of thalamocortical and intracortical fibers by injecting anterograde/retrograde tracers into physiologically and morphologically defined jaw movement-related cortical areas. Four areas were identified in the macaque monkey: the primary and supplementary orofacial motor areas (MIoro and SMAoro) and the principal and deep parts of the cortical masticatory area (CMaAp and CMaAd), where intracortical microstimulation produced single twitch-like or rhythmic jaw movements, respectively. Tracer injections into these areas labeled terminals in the ipsilateral putamen in a topographic fashion (MIoro vs. SMAoro and CMaAp vs. CMaAd), in the lateral reticular formation and trigeminal sensory nuclei contralaterally (MIoro and CMaAp) or bilaterally (SMAoro) in a complex manner of segregation vs. overlap, and in the medial parabranchial and Kölliker-Fuse nuclei contralaterally (CMaAd). The MIoro and CMaAp received thalamic projections from the ventrolateral and ventroposterolateral nuclei, the SMAoro from the ventroanterior and ventrolateral nuclei, and the CMaAd from the ventroposteromedial nucleus. The MIoro, SMAoro, CMaAp, and CMaAd received intracortical projections from the ventral premotor cortex and primary somatosensory cortex, the ventral premotor cortex and rostral cingulate motor area, the ventral premotor cortex and area 7b, and various sensory areas. In addition, the MIoro and CMaAp received projections from the three other jaw movement-related areas. Our results suggest that the four jaw movement-related cortical areas may play important roles in the formation of distinctive masticatory patterns.

Neural pathways underlying vocal control

Vocalization is a complex behaviour pattern, consisting of essentially three components: laryngeal activity, respiratory movements and supralaryngeal (articulatory) activity. The motoneurones controlling this behaviour are located in various nuclei in the pons (trigeminal motor nucleus), medulla (facial nucleus, nucl. ambiguus, hypoglossal nucleus) and ventral horn of the spinal cord (cervical, thoracic and lumbar region). Coordination of the different motoneurone pools is carried out by an extensive network comprising the ventrolateral parabrachial area, lateral pontine reticular formation, anterolateral and caudal medullary reticular formation, and the nucl. retroambiguus. This network has a direct access to the phonatory motoneurone pools and receives proprioceptive input from laryngeal, pulmonary and oral mechanoreceptors via the solitary tract nucleus and principal as well as spinal trigeminal nuclei. The motor-coordinating network needs a facilitatory input from the periaqueductal grey of the midbrain and laterally bordering tegmentum in order to be able to produce vocalizations. Voluntary control of vocalization, in contrast to completely innate vocal reactions, such as pain shrieking, needs the intactness of the forebrain. Voluntary control over the initiation and suppression of vocal utterances is carried out by the mediofrontal cortex (including anterior cingulate gyrus and supplementary as well as pre-supplementary motor area). Voluntary control over the acoustic structure of vocalizations is carried out by the motor cortex via pyramidal/corticobulbar as well as extrapyramidal pathways. The most important extrapyramidal pathway seems to be the connection motor cortex-putamen-substantia nigra-parvocellular reticular formation-phonatory motoneurones. The motor cortex depends upon a number of inputs for fulfilling its task. It needs a cerebellar input via the ventrolateral thalamus for allowing a smooth transition between consecutive vocal elements. It needs a proprioceptive input from the phonatory organs via nucl. ventralis posterior medialis thalami, somatosensory cortex and inferior parietal cortex. It needs an input from the ventral premotor and prefrontal cortex, including Broca's area, for motor planning of longer purposeful utterances. And it needs an input from the supplementary and pre-supplementary motor area which give rise to the motor commands executed by the motor cortex.

Organization of projections from the medial agranular cortex to the superior colliculus in the rat: a study using anterograde and retrograde tracing methods

The organization of corticotectal projections from the medial agranular cortex (AGm), which has been considered to contain rat's frontal eye field, was examined using anterograde and retrograde tracing techniques. When biotinylated dextranamine (BDA) injections were made into the rostral part of the AGm, small numbers of BDA-labeled axons were found in the rostral two-thirds of the superior colliculus (SC) while some labeled axons were seen in the caudal one-third of the SC. These labeled axons were distributed mainly in the lateral part of the stratum griseum intermediale. On the other hand, after BDA injections into the caudal part of the AGm, moderate to dense plexuses of labeled axons were found in the rostral two-thirds of the SC while some labeled axons were seen in the caudal one-third of the SC. These labeled axons were distributed in the ventromedial and dorsolateral marginal zones of the stratum griseum intermediale as well as in the stratum griseum profundum. The corticotectal projections were largely uncrossed. After combined injections of BDA into the caudal part of the AGm on one side and cholera toxin B subunit (CTb) into the paramedian pontine reticular formation on the opposite side or into the interstitial nucleus of Cajal on the same side, the overlapping distributions of BDA-labeled axons and CTb-labeled neurons were found in the ventromedial marginal zone of the stratum griseum intermediale ipsilateral to the site of BDA injection. These results suggest that the caudal part of the AGm plays a more significant role in the oculomotor function than does the rostral part of the AGm.

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.

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.

Demonstration of the corticotectobulbar pathway from the orofacial motor cortex to the parvicellular reticular formation in the rat

We examined a corticotectobulbar pathway from the orofacial motor cortex (OfM) to the parvicellular reticular formation (RFp), where numerous premotor neurons for the orofacial motor nuclei were known to be distributed, light and electron microscopically by using a combination of anterograde and retrograde tracing techniques. After contralateral injections of biotinylated dextranamine (BDA) into the OfM and cholera toxin B subunit (CTb) into the RFp, the overlapping distribution of ipsilateral axon terminals labeled with BDA and contralateral neurons labeled with CTb was found in the lateralmost part of the superior colliculus (SC). Furthermore, contralateral injections of BDA into the OfM and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the RFp resulted in that ipsilateral axons labeled with BDA made asymmetrical synaptic contacts with the dendrites of contralateral SC neurons labeled with WGA-HRP.

Efferents from the lateral frontal cortex to spinomedullary target areas, trigeminal nuclei, and spinally projecting brainstem regions in the hedgehog tenrec

This study was done in the Madagascan lesser hedgehog tenrec, an insectivore with a very poorly differentiated neocortex. The cortical region, known to give rise to spinal projections, was injected with tracer, and the cortical efferents to brainstem and spinal cord were analyzed. Bulbar reticular fields, in addition, were identified according to their cells of origin and the laterality of their spinal projections after injection of tracer. Only few cortical fibers could be traced from the bulbar pyramid into the ipsilateral spinal cord, particularly to the lateral funiculus. The projections to the dorsal column nuclei and the classical spinally projecting brainstem regions were also weak. Faint projections were demonstrated to the nucleus of the posterior commissure and the nucleus of Darkschewitsch. In comparison to other mammals, there was no evidence that the contralateral cortico-bulbo-spinal pathway was strengthened, substituting for the almost non-existent contralateral corticospinal projection. Unlike the sensorimotor apparatus controlling limb and body movements, the brainstem regions controlling the head and neck received prominent cortical projections. Direct corticotrigeminal projections and indirect pathways were well represented. The projections to the trigeminal nuclei and the lateral reticular fields were clearly bilateral; those to the superior colliculus were predominantly ipsilateral. The corticobulbar fibers left the pyramid along its entire extent; the principal trigeminal nucleus and the dorsolateral pontine tegmentum were supplied by additional fibers of the corticotegmental tract. The lateral frontal cortex also projected densely to the dorsolateral hypothalamus, the periaqueductal gray, and the adjacent mesencephalic tegmentum, components of the emotional motor system.