Emergence of motor circuit activity.
In the developing nervous system, ordered neuronal activity patterns can occur even in the absence of sensory input and to investigate how these arise, we have used the model system of the embryonic chicken spinal motor circuit, focusing on motor neurons of the lateral motor column (LMC). At the earliest stages of their molecular differentiation, we can detect differences between medial and lateral LMC neurons in terms of expression of neurotransmitter receptor subunits, including CHRNA5, CHRNA7, GRIN2A, GRIK1, HTR1A and HTR1B, as well as the KCC2 transporter. Using patch-clamp recordings we also demonstrate that medial and lateral LMC motor neurons have subtly different activity patterns that reflect the differential expression of neurotransmitter receptor subunits. Using a combination of patch-clamp recordings in single neurons and calcium-imaging of motor neuron populations, we demonstrate that inhibition of nicotinic, muscarinic or GABA-ergic activity, has profound effects of motor circuit activity during the initial stages of neuromuscular junction formation. Finally, by analysing the activity of large populations of motor neurons at different developmental stages, we show that the asynchronous, disordered neuronal activity that occurs at early stages of circuit formation develops into organised, synchronous activity evident at the stage of LMC neuron muscle innervation. In light of the considerable diversity of neurotransmitter receptor expression, activity patterns in the LMC are surprisingly similar between neuronal types, however the emergence of patterned activity, in conjunction with the differential expression of transmitter systems likely leads to the development of near-mature patterns of locomotor activity by perinatal ages.
Institut de recherches cliniques de Montréal (IRCM), Montréal, Canada.
Chris
C
Law
Institut de recherches cliniques de Montréal (IRCM), Montréal, Canada.
Michel
M
Paquet
Institut de recherches cliniques de Montréal (IRCM), Montréal, Canada; Departments of Anatomy and Cell Biology, and Biology, Division of Experimental Medicine, McGill University Montréal, Montréal, Canada, and Faculté de Médecine, Université de Montréal, Montréal, Canada.
Artur
A
Kania
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D002490:Central Nervous System / Q000196:embryology*; D002642:Chick Embryo; D055724:Electrophysiological Phenomena; D018274:Electroporation; D017403:In Situ Hybridization; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D009469:Neuromuscular Junction / Q000196:embryology*; D009474:Neurons / Q000502:physiology; D018377:Neurotransmitter Agents / Q000502:physiology; D018408:Patch-Clamp Techniques
D018377:Neurotransmitter Agents; D002118:Calcium