Activity of Reticulospinal Neurons During Locomotion in the Freely Behaving Lamprey

• Published in: Journal of neurophysiology Vol. 83; no. 2; pp. 853 - 863
• Main Authors: Deliagina, T. G, Zelenin, P. V, Fagerstedt, P, Grillner, S, Orlovsky, G. N
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-02-2000
• Subjects: Animals; Axons - physiology; Behavior, Animal - physiology; Electromyography - instrumentation; Electromyography - methods; Head - physiology; Lampetra; Lampreys; Medicin och hälsovetenskap; Neural Pathways; Neurons - physiology; Petromyzontidae; Physical Stimulation; Reticular Formation - cytology; Reticular Formation - physiology; reticular system; Spinal Cord - cytology; Spinal Cord - physiology; Swimming - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.83.2.853

  1 The Nobel Institute for Neurophysiology,
Department of Neuroscience, Karolinska Institute, SE-171 77 Stockholm,
Sweden; and   2 A. N. Belozersky Institute of
Physico-Chemical Biology, Moscow State University, Moscow 119 899, Russia
Deliagina, T. G.,
P. V. Zelenin,
P. Fagerstedt,
S. Grillner, and
G. N. Orlovsky.
Activity of Reticulospinal Neurons During Locomotion in the
Freely Behaving Lamprey. J. Neurophysiol. 83: 853-863, 2000. The reticulospinal (RS) system is the main
descending system transmitting commands from the brain to the spinal
cord in the lamprey. It is responsible for initiation of locomotion,
steering, and equilibrium control. In the present study, we
characterize the commands that are sent by the brain to the spinal cord
in intact animals via the reticulospinal pathways during locomotion. We
have developed a method for recording the activity of larger RS axons
in the spinal cord in freely behaving lampreys by means of chronically
implanted macroelectrodes. In this paper, the mass activity in the
right and left RS pathways is described and the correlations of this
activity with different aspects of locomotion are discussed. In
quiescent animals, the RS neurons had a low level of activity. A mild
activation of RS neurons occurred in response to different sensory
stimuli. Unilateral eye illumination evoked activation of the
ipsilateral RS neurons. Unilateral illumination of the tail dermal
photoreceptors evoked bilateral activation of RS neurons. Water
vibration also evoked bilateral activation of RS neurons. Roll tilt
evoked activation of the contralateral RS neurons. With longer or more
intense sensory stimulation of any modality and laterality, a sharp,
massive bilateral activation of the RS system occurred, and the animal
started to swim. This high activity of RS neurons and swimming could
last for many seconds after termination of the stimulus. There was a
positive correlation between the level of activity of RS system and the
intensity of locomotion. An asymmetry in the mass activity on the left
and right sides occurred during lateral turns with a 30% prevalence (on average) for the ipsilateral side. Rhythmic modulation of the
activity in RS pathways, related to the locomotor cycle, often was
observed, with its peak coinciding with the electromyographic (EMG)
burst in the ipsilateral rostral myotomes. The pattern of vestibular
response of RS neurons observed in the quiescent state, that is,
activation with contralateral roll tilt, was preserved during
locomotion. In addition, an inhibition of their activity with
ipsilateral tilt was clearly seen. In the cases when the activity of
individual neurons could be traced during swimming, it was found that
rhythmic modulation of their firing rate was superimposed on their
tonic firing or on their vestibular responses. In conclusion, different
aspects of locomotor activity initiation and termination, vigor of
locomotion, steering and equilibrium control are well reflected in the
mass activity of the larger RS neurons.