Membrane potential oscillations in reticulospinal and spinobulbar neurons during locomotor activity.
Feedback from the spinal locomotor networks provides rhythmic modulation of the membrane potential of reticulospinal (RS) neurons during locomotor activity. To further understand the origins of this rhythmic activity, the timings of the oscillations in spinobulbar (SB) neurons of the spinal cord and in RS neurons of the posterior and middle rhombencephalic reticular nuclei were measured using intracellular microelectrode recordings in the isolated brain stem-spinal cord preparation of the lamprey. A diffusion barrier constructed just caudal to the obex allowed induction of locomotor activity in the spinal cord by bath application of an excitatory amino acid to the spinal bath. All of the ipsilaterally projecting SB neurons recorded had oscillatory membrane potentials with peak depolarizations in phase with the ipsilateral ventral root bursts, whereas the contralaterally projecting SB neurons were about evenly divided between those in phase with the ipsilateral ventral root bursts and those in phase with the contralateral bursts. In the brain stem under these conditions, 75% of RS neurons had peak depolarizations in phase with the ipsilateral ventral root bursts while the remainder had peak depolarizations during the contralateral bursts. Addition of a high-Ca2+, Mg2+ solution to the brain stem bath to reduce polysynaptic activity had little or no effect on oscillation timing in RS neurons, suggesting that direct inputs from SB neurons make a major contribution to RS neuron oscillations under these conditions. Under normal conditions when the brain is participating in the generation of locomotor activity, these spinal inputs will be integrated with other inputs to RS neurons.
Einum
James F
JF
Department of Biological Sciences, Marquette University, P.O. Box 1881, Milwaukee, Wisconsin 53201, USA.
Buchanan
James T
JT
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D007839:Functional Laterality; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007798:Lampreys; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009043:Motor Activity / Q000502:physiology*; D016202:N-Methylaspartate / Q000494:pharmacology; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010507:Periodicity; D013116:Spinal Cord / Q000166:cytology* / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology
D018698:Glutamic Acid; D016202:N-Methylaspartate; D008274:Magnesium; D002118:Calcium