Mechanisms of supraspinal correction of locomotor activity generator

Acute Basilar Artery Occlusion Presenting With Convulsive Movements: A Systematic Review

Background and Purpose: Convulsive seizures related to posterior circulation stroke are considered rare. However, some patients with acute basilar artery occlusion (BAO) can present with convulsive movements. Misdiagnosed as seizures may delay the reperfusion therapy for acute BAO. In this study, we have summarized the clinical features and possible mechanisms of BAO presenting with convulsive movements.

Methods: We performed an Institutional Review Board-approved institutional database query from 2015 to 2020 and a literature search of the online database PubMed. Clinical data were collected and analyzed.

Results: In total, 14 patients with acute BAO presented with convulsions. There were 10 men and 4 women, with a mean age of 53 (range, 23–77) years. All of these patients had different degrees of impaired consciousness (100.0%, 14/14). Convulsive movements were the initial symptoms in 78.6% (11/14) of patients. Further, 64.3% (9/14) of patients presented with paralysis or cranial nerve abnormalities, and 85.7% (12/14) of patients were treated with reperfusion therapy (thrombolysis, 35.7% [5/14]; endovascular thrombectomy, 64.3% [9/14]). The BAO etiology and mechanism were related to embolism, vessel dissections, and severe stenosis of the right vertebral artery in 57.1% (8/14), 21.4% (3/14), and 7.1% (1/14) of patients, respectively; they were undefined in 14.3% (2/14) of patients. Moreover, 42.9% (6/14) of patients had a 90-day modified Rankin Scale score of 0–2, and the mortality rate was 21.4% (3/14).

Conclusions: Acute BAO, especially that related to embolism or vessel dissection, may present with convulsive movements. Acute BAO is a devastating, but treatable disease if diagnosed in time. Considering the possibility of BAO is important when dealing with patients presenting with acute-onset convulsive movements. Prompt diagnosis and reperfusion therapy may help achieve a better prognosis.

Glutamatergic neurons of the gigantocellular reticular nucleus shape locomotor pattern and rhythm in the freely behaving mouse

Because of their intermediate position between supraspinal locomotor centers and spinal circuits, gigantocellular reticular nucleus (GRN) neurons play a key role in motor command. However, the functional contribution of glutamatergic GRN neurons in initiating, maintaining, and stopping locomotion is still unclear. Combining electromyographic recordings with optogenetic manipulations in freely behaving mice, we investigate the functional contribution of glutamatergic brainstem neurons of the GRN to motor and locomotor activity. Short-pulse photostimulation of one side of the glutamatergic GRN did not elicit locomotion but evoked distinct motor responses in flexor and extensor muscles at rest and during locomotion. Glutamatergic GRN outputs to the spinal cord appear to be gated according to the spinal locomotor network state. Increasing the duration of photostimulation increased motor and postural tone at rest and reset locomotor rhythm during ongoing locomotion. In contrast, photoinhibition impaired locomotor pattern and rhythm. We conclude that unilateral activation of glutamatergic GRN neurons triggered motor activity and modified ongoing locomotor pattern and rhythm.

Differential modulation of descending signals from the reticulospinal system during reaching and locomotion

We tested the hypothesis that the same spinal interneuronal pathways are activated by the reticulospinal system during locomotion and reaching. If such were the case, we expected that microstimulation within the pontomedullary reticular formation (PMRF) would evoke qualitatively similar responses in muscles active during both behaviors. To test this, we stimulated in 47 sites within the PMRF during both tasks. Stimulation during locomotion always produced a strongly phase-dependent, bilateral pattern of activity in which activity in muscles was generally facilitated or suppressed during one phase of activity (swing or stance) and was unaffected in the other. During reaching, stimulation generally activated the same muscles as during locomotion, although the modulation of the magnitude of the evoked responses was less limb dependent than during locomotion. An exception was found for some forelimb flexor muscles that were strongly facilitated by stimulation during the swing phase of locomotion but were not influenced by stimulation during the transport phase of the reach. We suggest that during locomotion the activity in interneuronal pathways mediating signals from the reticulospinal system is subject to strong modulation by the central pattern generator for locomotion. During reach, we suggest that, for most muscles, the same spinal interneuronal pathways are used to modify muscle activity but are not as strongly gated according to limb use as during locomotion. Finally, we propose that the command for movement during discrete voluntary movements suppresses the influence of the reticulospinal system on selected forelimb flexor muscles, possibly to enhance fractionated control of movement.

Spontaneous limb movements and posturing secondary to acute basilar artery occlusion: a potentially devastating seizure mimic

Basilar artery occlusion is a devastating but treatable form of ischaemic stroke with high morbidity and mortality rates. The diagnosis is often challenging due to considerable heterogeneity of clinical signs and symptoms. We report a case of an acute basilar artery occlusion presenting with decreased level of consciousness associated with rhythmic tonic movements of the four extremities, mimicking seizure activity. The patient was treated with intravenous thrombolysis and subsequently gained good recovery. Awareness of this entity is required to recognise this potentially treatable, but otherwise devastating seizure mimic.

Contribution of the motor cortex to the structure and the timing of hindlimb locomotion in the cat: a microstimulation study

We used microstimulation to examine the contribution of the motor cortex to the structure and timing of the hindlimb step cycle during locomotion in the intact cat. Stimulation was applied to the hindlimb representation of the motor cortex in 34 sites in three cats using either standard glass-insulated microelectrodes (16 sites in 1 cat) or chronically implanted microwire electrodes (18 sites in 2 cats). Stimulation at just suprathreshold intensities with the cat at rest produced multi-joint movements at a majority of sites (21/34, 62%) but evoked responses restricted to a single joint, normally the ankle, at the other 13/34 (38%) sites. Stimulation during locomotion generally evoked larger responses than the same stimulation at rest and frequently activated additional muscles. Stimulation at all 34 sites evoked phase-dependent responses in which stimulation in swing produced transient increases in activity in flexor muscles while stimulation during stance produced transient decreases in activity in extensors. Stimulation with long (200 ms) trains of stimuli in swing produced an increased level of activity and duration of flexor muscles without producing changes in cycle duration. In contrast, stimulation during stance decreased the duration of the extensor muscle activity and initiated a new and premature period of swing, resetting the step cycle. Stimulation of the pyramidal tract in two of these three cats as well as in two additional ones produced similar effects. The results show that the motor cortex is capable of influencing hindlimb activity during locomotion in a similar manner to that seen for the forelimb.

Cortical and brainstem control of locomotion

While a basic locomotor rhythm is centrally generated by spinal circuits, descending pathways are critical for ensuring appropriate anticipatory modifications of gait to accommodate uneven terrain. Neurons in the motor cortex command the changes in muscle activity required to modify limb trajectory when stepping over obstacles. Simultaneously, neurons in the brainstem reticular formation ensure that these modifications are superimposed on an appropriate base of postural support. Recent experiments suggest that the same neurons in the same structures also provide similar information during reaching movements. It is suggested that, during both locomotion and reaching movements, the final expression of descending signals is influenced by the state and excitability of the spinal circuits upon which they impinge.

Contributions of the motor cortex to the control of the hindlimbs during locomotion in the cat

Although the corticospinal tract is not essential for the production of the basic locomotor rhythm in cats, it does contribute to the regulation of locomotion, particularly in situations in which there is a requirement for precise control over paw placement or limb trajectory. Lesions of the dorsolateral funiculi at the low thoracic level (T(13)) that completely interrupted both the cortico- and rubrospinal pathways produced long-term deficits in locomotion on a level surface. These deficits included a paw-drag that was probably caused both by a loss of cortico- and rubrospinal input to motoneurones controlling distal muscles as well as by a change in the relative timing of muscles acting around the hip and knee. Smaller lesions produced similar deficits from which the cats recovered relatively quickly. Cats with the largest lesions of the dorsolateral funiculi were unable to modify their gait sufficiently to step over obstacles attached to the treadmill belt even 3-5 months postlesion. These results imply that the medial pathways, the reticulo- and vestibulospinal pathways, are unable to fully compensate for damage to the lateral pathways. Single unit recordings from identified pyramidal tract neurones (PTNs) within the hindlimb representation of the primary motor cortex (area 4) showed that a substantial proportion of neurones (67%) significantly increased their discharge frequency when the cats modified their gait to step over obstacles attached to the treadmill belt. Of those PTNs that showed increased activity during the swing phase, populations of neurones were activated at different times. A large proportion of PTNS discharged early in swing, in phase with knee flexors such as the semitendinosus. Others discharged slightly later, in phase with the activity of ankle flexors, such as tibialis anterior, while still others discharged at the end of swing, in phase with digit dorsiflexors, such as the extensor digitorum brevis. We suggest that different populations of cortical neurones may specifically modify the activity of selected groups of close synergistic muscles during different parts of the swing phase. We further suggest that these modifications are mediated, in part, by groups of interneurones that are involved in determining the base locomotor rhythm. This provides a means by which the changes specified by the descending signal from the motor cortex may be smoothly, and appropriately, incorporated into the locomotor cycle.

Discharge characteristics of neurons in the red nucleus during voluntary gait modifications: a comparison with the motor cortex

We have examined the contribution of the red nucleus to the control of locomotion in the cat. Neuronal activity was recorded from 157 rubral neurons, including identified rubrospinal neurons, in three cats trained to walk on a treadmill and to step over obstacles attached to the moving belt. Of 72 neurons with a receptive field confined to the contralateral forelimb, 66 were phasically active during unobstructed locomotion. The maximal activity of the majority of neurons (59/66) was centered around the swing phase of locomotion. Slightly more than half of the neurons (36/66) were phasically activity during both swing and stance. In addition, some rubral neurons (14/66) showed multiple periods of phasic activity within the swing phase of the locomotor cycle. Periods of phasic discharge temporally coincident with the swing phase of the ipsilateral limb were observed in 7/66 neurons. During voluntary gait modifications, most forelimb-related neurons (70/72) showed a significant increase in their discharge activity when the contralateral limb was the first to step over the obstacle (lead condition). Maximal activity in nearly all cells (63/70) was observed during the swing phase, and 23/63 rubral neurons exhibited multiple increases of activity during the modified swing phase. A number of cells (18/70) showed multiple periods of increased activity during swing and stance. Many of the neurons (35/63, 56%) showed an increase in activity at the end of the swing phase; this period of activity was temporally coincident with the period of activity in wrist dorsiflexors, such as the extensor digitorum communis. A smaller proportion of neurons with receptive fields restricted to the hindlimbs showed similar characteristics to those observed in the population of forelimb-related neurons. The overall characteristics of these rubral neurons are similar to those that we obtained previously from pyramidal tract neurons recorded from the motor cortex during an identical task. However, in contrast to the results obtained in the rubral neurons, most motor cortical neurons showed only one period of increased activity during the step cycle. We suggest that both structures contribute to the modifications of the pattern of EMG activity that are required to produce the change in limb trajectory needed to step over an obstacle. However, the results suggest an additional role for the red nucleus in regulating intra- and interlimb coordination.

Contributions of the reticulospinal system to the postural adjustments occurring during voluntary gait modifications

To test the hypothesis that reticulospinal neurons (RSNs) are involved in the formation of the dynamic postural adjustments that accompany visually triggered, voluntary modifications of limb trajectory during locomotion, we recorded the activity of 400 cells (183 RSNs; 217 unidentified reticular cells) in the pontomedullary reticular formation (PMRF) during a locomotor task in which intact cats were required to step over an obstacle attached to a moving treadmill belt. Approximately one half of the RSNs (97/183, 53%) showed significant changes in cell activity as the cat stepped over the obstacle; most of these cells exhibited either single (26/97, 26.8%) or multiple (63/97, 65.0%) increases of activity. There was a range of discharge patterns that varied in the number, timing, and sequencing of the bursts of modified activity, although individual bursts in different cells tended to occur at similar phases of the gait cycle. Most modified cells, regardless of the number of bursts of increased discharge, or of the discharge activity of the cell during unobstructed, control, locomotion, discharged during the passage of the lead forelimb over the obstacle. Thus, 86.9% of the modified cells increased their discharge when the forelimb ipsilateral to the recording site was the first to pass over the obstacle, and 72.2% when the contralateral limb was the first. Approximately one quarter of the RSNs increased their discharge during the passage of each of the four limbs over the obstacle in both the lead (27.1%) and trail (27.9%) conditions. In general, in any one cell, the number and relative sequencing of the subsequent bursts (with respect to the lead forelimb) was maintained during both lead and trail conditions. Patterns of activity observed in unidentified cells were very similar to the RSN activity despite the diverse population of cells this unidentified group may represent. We suggest that the increased discharge that we observed in these reticular neurons reflects the integration of afferent activity from several sources, including the motor cortex, and that this increased discharge signals the timing and the relative magnitude of the postural patterns that accompany the voluntary gait modification. However, based on the characteristics of the patterns of neuronal activity in these cells, we further suggest that while individual RSNs probably contribute to the selection of different patterns of postural activity, the ultimate expression of the postural response may be determined by the excitability of the locomotor circuits within the spinal cord.

Vestibulospinal and reticulospinal neuronal activity during locomotion in the intact cat. II. Walking on an inclined plane

The experiments described in this report were designed to determine the contribution of vestibulospinal neurons (VSNs) in Deiters' nucleus and of reticulospinal neurons (RSNs) in the medullary reticular formation to the modifications of the walking pattern that are associated with locomotion on an inclined plane. Neuronal discharge patterns were recorded from 44 VSNs and 63 RSNs in cats trained to walk on a treadmill whose orientation was varied from +20 degrees (uphill) to -10 degrees (downhill), referred to as pitch tilt, and from 20 degrees roll tilt left to 20 degrees roll tilt right. During uphill locomotion, a majority of VSNs (25/44) and rhythmically active RSNs (24/39) showed an increase in peak discharge frequency, above that observed during locomotion on a level surface. VSNs, unlike some of the RSNs, exhibited no major deviations from the overall pattern of the activity recorded during level walking. The relative increase in discharge frequency of the RSNs (on average, 31.8%) was slightly more than twice that observed in the VSNs (on average, 14.4%), although the average absolute change in discharge frequency was similar (18.2 Hz in VSNs and 21.6 Hz in RSNs). Changes in discharge frequency during roll tilt were generally more modest and were more variable, than those observed during uphill locomotion as were the relative changes in the different limb muscle electromyograms that we recorded. In general, discharge frequency in VSNs was more frequently increased when the treadmill was rolled to the right (ear down contralateral to the recording site) than when it was rolled to the left. Most VSNs that showed significant linear relationships with treadmill orientation in the roll plane increased their activity during right roll and decreased activity during left roll. Discharge activity in phasically modulated RSNs was also modified by roll tilt of the treadmill. Modulation of activity in RSNs that discharged twice in each step cycle was frequently reciprocal in that one burst of activity would increase during left roll and the other during right roll. The overall results indicate that each system contributes to the changes in postural tone that are required to adapt the gait for modification on an inclined surface. The characteristics of the discharge activity of the VSNs suggest a role primarily in the overall control of the level of electromyographic activity, while the characteristics of the RSNs suggest an additional role in determining the relative level of different muscles, particularly when the pattern is asymmetric.

Vestibulospinal and reticulospinal neuronal activity during locomotion in the intact cat. I. Walking on a level surface

To examine the function of descending brain stem pathways in the control of locomotion, we have characterized the discharge patterns of identified vestibulo- and reticulospinal neurons (VSNs and RSNs, respectively) recorded from the lateral vestibular nucleus (LVN) and the medullary reticular formation (MRF), during treadmill walking. Data during locomotion were obtained for 44 VSNs and for 63 RSNs. The discharge frequency of most VSNs (42/44) was phasically modulated in phase with the locomotor rhythm and the averaged peak discharge frequency ranged from 41 to 165 Hz (mean = 92.8 Hz). We identified three classes of VSNs based on their discharge pattern. Type A, or double peak, VSNs (20/44 neurons, 46%) showed two peaks and two troughs of activity in each step cycle. One of the peaks was time-locked to the activity of extensor muscles in the ipsilateral hindlimb while the other occurred anti-phase to this period of activity. Type B, or single pause, neurons (13/44 neurons, 30%) were characterized by a tonic or irregular discharge that was interrupted by a single pronounced and brief period of decreased activity that occurred just before the onset of swing in the ipsilateral hindlimb; some type B VSNs also exhibited a brief pulse of activity just preceding this decrease. Type C, or single peak, neurons (9/44 neurons, 23%) exhibited a single period of increased activity that, in most cells, was time-locked to the burst of activity of either extensor or flexor muscles of a single limb. The population of RSNs that we recorded included neurons that showed phasic activity related to the activity of flexor or extensor muscles [electromyographically (EMG) related, 26/63, 41%], those that were phasically active but whose activity was not time-locked to the activity of any of the recorded muscles (13/63, 21%) and those that were completely unrelated to locomotion (24/63, 38%). Most of the EMG-related RSNs showed one (15/26) or two (11/26) clear phasic bursts of activity that were temporally related to either flexor or extensor muscles. The discharge pattern of double-burst RSNs covaried with ipsilateral and contralateral flexor muscles. Peak averaged discharge activity in these EMG-related RSNs ranged from 4 to 98 Hz (mean = 35.2 Hz). We discuss the possibility that most VSNs regulate the overall activity of extensor muscles in the four limbs while RSNs provide a more specific signal that has the flexibility to modulate the activity of groups of flexor and extensor muscles, in either a single or in multiple limbs.

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex. To determine the extent to which the rubrospinal tract is capable of modifying locomotion in the intact cat, we applied microstimulation (cathodal current, 330 Hz; pulse duration 0.2 ms; maximal current, 25 microA) to the red nucleus during locomotion. The stimuli were applied either as short trains (33 ms) of impulses to determine the capacity of the rubrospinal tract to modify the level of electromyographic (EMG) activity in different flexors and extensors at different phases of the step cycle or as long trains (200 ms) of pulses to determine the effect of the red nucleus on cycle timing. Stimuli were also applied with the cat at rest (33-ms train). This latter stimulation evoked short-latency (average = 11.8-19.0 ms) facilitatory responses in all of the physiological flexor muscles of the forelimb that were recorded; facilitatory responses were also common in the elbow extensor, lateral head of triceps but were rare in the physiological wrist and digit extensor, palmaris longus. Responses were still evoked in most muscles when the current was decreased to near threshold (3-10 microA). Stimulation during locomotion with the short trains of stimuli evoked shorter-latency (average = 6.0-12.5 ms) facilitatory responses in flexor muscles during the swing phase of locomotion and, except in the case of the extensor digitorum communis, evoked substantially smaller responses in stance. The same stimuli also evoked facilitatory responses in the extensor muscles during swing and produced more complex effects involving both facilitation and suppression in stance. Increasing the duration of the train to 200 ms modified the amplitude and duration of the EMG activity of both flexors and extensors but had little significant effect on the cycle duration. In contrast, whereas stimulation of the motor cortex with short trains of stimuli during locomotion had very similar effects to that of the red nucleus, increasing the train duration to 200 ms frequently produced a marked reset of the step cycle by curtailing stance and initiating a new period of swing. The results suggest that whereas both the motor cortex and the red nucleus have access to the interneuronal circuits responsible for controlling the structure of the EMG activity in the step cycle, only the motor cortex has access to the circuits responsible for controlling cycle timing.

Cerebellar terminations in the red nucleus of Macaca fascicularis: an electron-microscopic study utilizing the anterograde transport of WGA:HRP

The red nucleus (RN) of the macaque monkey is divided into a rostral two-thirds, the parvicellularis (RNp), which projects to the cerebellum by way of the inferior olivary nucleus, and a caudal third, the magnocellularis (RNm), which projects to the spinal cord via the rubrospinal tract. The RNp and RNm receive afferents from two principal sources: the cerebral motor cortices and the deep cerebellar nuclei. The terminations of these two afferent projections tend to be spatially segregated on rubral neurons, in that most corticorubral afferents terminate on more distal dendrites, and those from the deep cerebellar nuclei terminate more proximally. The present electron-microscopic analysis of the cerebellar terminations in the macaque RN provides anatomical evidence for the presence of labeled afferents in both divisions of this motor nucleus, following injection of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the deep cerebellar nuclei and the anterograde transport of the tracer to the RN. The cerebellar terminal afferents are large; contain numerous mitochondria and primarily rounded synaptic vesicles; and form asymmetric synaptic contacts with rubral neurons. Unlike other terminals in the nucleus, they possess an electron-lucent cytoplasmic matrix and less densely packed synaptic vesicles. They are termed "large, round, pale" (LRP) terminals because of the morphological characteristics that distinguish them from other afferent terminal types found in RN. Labeled cerebellar afferents in RNp and RNm contact primarily neuronal somata, proximal dendrites emerging from the cell body, large-diameter dendrites, and the spines of rubral neurons that arise from somata and proximal dendrites.(ABSTRACT TRUNCATED AT 250 WORDS)