Reticulospinal neurons controlling forward and backward swimming in the lamprey

Abstract

Zelenin PV. Reticulospinal neurons controlling forward and backward swimming in the lamprey. J Neurophysiol 105: 1361-1371, 2011. First published January, 19, 2011 doi:10.1152 doi:10. /jn.00887.2010brates are capable of two forms of locomotion, forward and backward, strongly differing in the patterns of motor coordination. Basic mechanisms generating these patterns are located in the spinal cord; they are activated and regulated by supraspinal commands. In the lamprey, these commands are transmitted by reticulospinal (RS) neurons. The aim of this study was to reveal groups of RS neurons controlling different aspects of forward (FS) and backward (BS) swimming in the lamprey. Activity of individual larger RS neurons in intact lampreys was recorded during FS and BS by chronically implanted electrodes. It was found that among the neurons activated during locomotion, 27% were active only during FS, 3% only during BS, and 70% during both FS and BS. In a portion of RS neurons, their mean firing frequency was correlated with frequency of body undulations during FS (8%), during BS (34%), or during both FS and BS (22%), suggesting their involvement in control of locomotion intensity. RS activity was phasically modulated by the locomotor rhythm during FS (20% of neurons), during BS (29%), or during both FS and BS (16%). The majority of RS neurons responding to vestibular stimulation (and presumably involved in control of body orientation) were active mainly during FS. This explains the absence of stabilization of the body orientation observed during BS. We discuss possible functions of different groups of RS neurons, i.e., activation of the spinal locomotor CPG, inversion of the direction of propagation of locomotor waves, and postural control. supraspinal commands; reticulospinal system; backward locomotion; forward locomotion; posture

Necessary, Sufficient and Permissive: A Single Locomotor Command Neuron Important for Intersegmental Coordination

“…Similar control schemes are seen in the lamprey (Buchanan and Cohen, 1982; McClellan and Grillner, 1984; Deliagina et al, 2002). Some reticulospinal neurons, for example, are dedicated to forward or backward locomotion (Zelenin, 2005), although the majority participates in both behaviors (Zelenin, 2011). Thus heterogeneity of function within cell populations and shared usage of command cells across behavioral routines appear to be a common theme emerging in the control of patterned behaviors in invertebrates and vertebrates.…”

Activity of motor cortex neurons during backward locomotion

“…Recently, it was shown that during simple, unobstructed locomotion, this modulation is caused by signals coming from the spinal mechanisms generating stepping movements of individual limbs (limb controllers), and different combinations of limb controllers can affect an individual motor cortex neuron and contribute to its modulation (Zelenin et al 2011). …”

“…Activity of motor cortex neurons during backward locomotion. J Neurophysiol 105: 2698-2714, 2011. First published March 23, 2011doi:10.1152/jn.00120.2011 and backward walking (BW) are two important forms of locomotion in quadrupeds.…”

“…However, descending commands controlling forward and backward locomotion were recently studied in the lamprey, a lower vertebrate. Recording the activity of reticulospinal neurons during forward and backward locomotion revealed several groups of these neurons with different activity patterns, suggesting their different functions, including activation of the locomotor CPG in the forward or backward mode (Zelenin 2011).…”

“…To reveal the sources of rhythmical modulation of the neurons, we used the previously developed method (Zelenin et al 2011) and recorded individual neurons, not only during quadrupedal locomotion but also during bipedal locomotion. We found that limb controllers of both girdles contributed to modulation in the majority of neurons.…”