Spinal networks encode the motor outputs that generate all behaviors, therefore it is not surprising that spinal interneurons (INs) are highly complex and that our knowledge is rather incomplete about how many classes of spinal INs exist, their properties, connections and mechanisms of differentiation. This information is essential not only to understand motor function, but also how genetic alterations, disease or injury affects these circuits in adults and newborns. A few years ago a new conceptual framework to understand spinal INs was prompted by the discovery of a few canonical embryonic classes that diversify into the large variety of adult phenotypes. With previous funding we established that temporal control of neurogenesis and transcription factor (TF) expression correlates with specific IN phenotypes within a class known as V1. V1-INs include those that mediate recurrent inhibition of motoneurons (Renshaw cells) and many that mediate reciprocal inhibition of motoneurons with antagonist actions on a single joint (Ia inhibitory interneurons, IaINs). Thus, we divided V1s in an early generated group (that includes Renshaw cells and expression of MafB) and a late generated group (that includes IaINs and expression of Foxp2). However, V1 diversity is much larger and there is not yet a complete scheme of V1 IN variety and function, in part because lack of information about their output in terms of axon projections, connections and firing. Here we hypothesize that V1s of different birthdates express different combinations of TFs with specific roles in defining axonal projections and firing properties.
In aim 1 we will analyze V1 axon projections and relate them to TF expression and time of birth.
Aim 2 will analyze whether Foxp2 controls axon length and therefore the extent of rostro-caudal projections of different V1's.
Aim 3 will analyze the firing properties of V1 groups, their relation to specific voltage-gated channels and whether these are determined by specific TFs. Validation of our hypotheses would suggest that birth-date and TF expression differentiate V1 groups with distinct connections and firing modulation. The results will also provide a more complete picture of V1s that will contribute to improve our understanding of spinal local motor circuits.

Public Health Relevance

Our goal is to understand the organization and development of the spinal cord during the maturation of motor behaviors like locomotion. Human infants, similar to mice, undergo a long period of motor function maturation that ultimately reflects the development of the neural control circuits that generate them. The work will use mouse models to investigate the development of these circuits. This information is essential to understand normal motor development and also the many newborn motor syndromes that currently have unknown etiologies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS047357-12
Application #
9041032
Study Section
Sensorimotor Integration Study Section (SMI)
Program Officer
Riddle, Robert D
Project Start
2004-06-01
Project End
2018-04-30
Budget Start
2016-05-01
Budget End
2017-04-30
Support Year
12
Fiscal Year
2016
Total Cost
Indirect Cost
Name
Emory University
Department
Physiology
Type
Schools of Medicine
DUNS #
066469933
City
Atlanta
State
GA
Country
United States
Zip Code
30322
Alvarez, Francisco J (2018) Spinal Interneurons ""à La Carte"". Neuron 100:3-6
Alvarez, Francisco J (2017) Gephyrin and the regulation of synaptic strength and dynamics at glycinergic inhibitory synapses. Brain Res Bull 129:50-65
Bikoff, Jay B; Gabitto, Mariano I; Rivard, Andre F et al. (2016) Spinal Inhibitory Interneuron Diversity Delineates Variant Motor Microcircuits. Cell 165:207-219
Siembab, Valerie C; Gomez-Perez, Laura; Rotterman, Travis M et al. (2016) Role of primary afferents in the developmental regulation of motor axon synapse numbers on Renshaw cells. J Comp Neurol 524:1892-919
Zhang, Jingming; Lanuza, Guillermo M; Britz, Olivier et al. (2014) V1 and v2b interneurons secure the alternating flexor-extensor motor activity mice require for limbed locomotion. Neuron 82:138-50
Richards, Dannette S; Griffith, Ronald W; Romer, Shannon H et al. (2014) Motor axon synapses on renshaw cells contain higher levels of aspartate than glutamate. PLoS One 9:e97240
Wootz, Hanna; Fitzsimons-Kantamneni, Eileen; Larhammar, Martin et al. (2013) Alterations in the motor neuron-renshaw cell circuit in the Sod1(G93A) mouse model. J Comp Neurol 521:1449-69
Alvarez, Francisco J; Benito-Gonzalez, Ana; Siembab, Valerie C (2013) Principles of interneuron development learned from Renshaw cells and the motoneuron recurrent inhibitory circuit. Ann N Y Acad Sci 1279:22-31
Wootz, Hanna; Fitzsimons-Kantamneni, Eileen; Larhammar, Martin et al. (2013) Alterations in the motor neuron-renshaw cell circuit in the Sod1(G93A) mouse model. J Comp Neurol 521:1449-69
van Zundert, Brigitte; Izaurieta, Pamela; Fritz, Elsa et al. (2012) Early pathogenesis in the adult-onset neurodegenerative disease amyotrophic lateral sclerosis. J Cell Biochem 113:3301-12

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