Mewes & Cheney (1991)

Facilitation and suppression of wrist and digit muscles from single rubromotoneuronal cells in the awake monkey.

K Mewes, PD Cheney.

1. The output effects of 214 cells in the magnocellular red nuclei of two rhesus monkeys (Macaca mulatta) were tested with spike-triggered averaging of electromyogram (EMG) activity from six forearm extensor and six flexor muscles. The monkeys performed an alternating wrist movement task (auxotonic paradigm) or generated wrist torque trajectories alternating between flexion and extension (isometric paradigm). 2. Sixty-five cells (30%) were identified as rubromotoneuronal (RM) cells on the basis of their postpike effects on forearm flexor and extensor muscles. Three major types of RM cell output organization were identified: 1) pure facilitation (28 cells), 2) reciprocal (18 cells), and 3) cofacilitation (16 cells). 3. RM cell output showed a strong preference for facilitation of extensor forearm muscles. This preference was reflected in the fact that 69% (43 of 62) of RM cells facilitated extensors exclusively or most strongly; 27% facilitated flexors exclusively or most strongly; and 5% facilitated flexors and extensors equally. Postspike facilitation (PSpF) was observed in 45% of the extensor muscles and 20% of the flexors tested. In contrast, postpike suppression (PSpS) was observed in 3% of the extensors and 7% of the flexors. 4. The mean number of extensors facilitated per RM cell was 3.1 (53% of tested) compared with 2.8 (51% of tested) flexors facilitated per cell. The extensor and flexor PSpS muscle field sizes were both 2.0 (35% of extensors and 36% of flexors tested). The mean number of muscles facilitated by cofacilitation cells was 5.8 (48%) per cell. No clear preference was found for facilitation of particular combinations of synergist muscles. 5. PSpF magnitude was assessed by measuring both the percent change of facilitation or suppression from baseline and the signal-to-noise ratio of effects. The overall average magnitudes of RM PSpF and PSpS were 4.1 +/- 2.0 and 4.0 +/- 2.3% change from baseline, respectively. The average magnitude of PSpF in flexors was not significantly different from that of extensors; neither was there a difference in the average magnitude of PSpS in flexors and extensors. 6. The mean onset latency of RM cell PSpS was greater than PSpF (9.2 +/- 3.0 vs. 5.7 +/- 1.8 ms; P less than or equal to 0.05). This can be attributed to an underlying minimal disynaptic linkage to motoneurons for suppression effects, whereas most PSpFs are probably mediated by underlying monosynaptic connections. The mean onset latency of flexor PSpFs was greater than that of extensors (6.4 +/- 2.3 vs. 5.4 +/- 1.5 ms; P less than or equal to 0.05).(ABSTRACT TRUNCATED AT 400 WORDS) - J Neurophysiol (1991) vol. 66 (6) pp. 1965-77

Lavoie & Drew (2002)

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

S Lavoie, T Drew.

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. - J Neurophysiol (2002) vol. 88 (4) pp. 1791-814

Hongo et al. (1969)

The rubrospinal tract. I. Effects on alpha-motoneurones innervating hindlimb muscles in cats.

T Hongo, E Jankowska, A Lundberg.

Experimental brain research Experimentelle Hirnforschung Expérimentation cérébrale (1969) vol. 7 (4) pp. 344-64