Title

Reticulospinal Neurons Receive Direct Spinobulbar Inputs During Locomotor Activity in Lamprey

Document Type

Article

Language

eng

Format of Original

7 p.

Publication Date

9-2004

Publisher

American Physiological Society

Source Publication

Journal of Neurophysiology

Source ISSN

0022-3077

Abstract

Reticulospinal neurons of the lamprey brain stem receive rhythmic input from the spinal cord during locomotor activity. The goal of the present study was to determine whether such spinal input has a direct component to reticulospinal neurons or depends on brain stem interneurons. To answer this question, an in vitro lamprey brain stem-spinal cord preparation was used with a diffusion barrier placed caudal to the obex, separating the experimental chamber into two baths. Locomotor activity was induced in the spinal cord by perfusion of D-glutamate or N-methyl-DL-aspartate into the spinal cord bath. The brain stem bath was first perfused with normal Ringer solution followed by a high-Ca2+, -Mg2+ solution, which reduced polysynaptic transmission. The amplitudes of membrane potential oscillations of reticulospinal neurons in the posterior and middle rhombencephalic reticular nuclei (PRRN and MRRN, respectively) recorded with sharp intracellular microelectrodes did not significantly change from normal to high-divalent solution. This finding suggests a large part of the spinal input creating the oscillations is direct to the reticulospinal neurons. Application of strychnine to the high-Ca2+, -Mg2+ solution decreased membrane potential oscillation amplitude, and injection of Cl- reversed presumed inhibitory postsynaptic potentials, indicating a role for direct spinal inhibitory inputs. Although reduced, the persistence of oscillations in strychnine suggests that spinal excitatory inputs also contribute to the oscillations. Thus it was concluded that both excitatory and inhibitory spinal neurons provide direct rhythmic inputs to reticulospinal cells of the PRRN and MRRN during locomotor activity. These inputs provide reticulospinal cells with information regarding the activity of the spinal locomotor networks.

Comments

Journal of Neurophysiology, Vol. 92, No. 3 (September 2004): 1384-1390. DOI.