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Development/Plasticity/Repair Differential Postnatal Maturation of GABAA, Glycine

Summary: Development/Plasticity/Repair
Differential Postnatal Maturation of GABAA, Glycine
Receptor, and Mixed Synaptic Currents in Renshaw Cells and
Ventral Spinal Interneurons
David Gonzalez-Forero and Francisco J. Alvarez
Department of Anatomy and Physiology, Wright State University, Dayton, Ohio 45435
Renshaw cells (RCs) receive excitatory inputs from motoneurons to which then they inhibit. The gain of this spinal recurrent inhibitory
circuit is modulated by inhibitory synapses on RCs. Inhibitory synapses on RCs mature postnatally, developing unusually large postsyn-
aptic gephyrin clusters that colocalize glycine and GABAA receptors. We hypothesized that these features potentiate inhibitory currents
in RCs. Thus, we analyzed glycinergic and GABAergic "inhibitory" miniature postsynaptic currents (mPSCs) in neonatal [postnatal day
1 (P1) to P5] and mature (P9P15) RCs and compared them to other ventral interneurons (non-RCs). Recorded neurons were Neurobi-
otin filled and identified as RCs or non-RCs using post hoc immunohistochemical criteria. Glycinergic, GABAergic, and mixed glycine/
GABA mPSCs matured differently in RCs and non-RCs. In RCs, glycinergic and GABAA mPSC peak amplitudes increased 230 and 45%,
respectively, from P1P5 to P9P15, whereas in non-RCs, glycinergic peak amplitudes changed little and GABAA amplitudes decreased.
GABAA mPSCs were slower in RCs (P1P5, 58 ms; P9P15, 43 ms) compared with non-RCs (P1P5, 27 ms; P9P15, 14
ms).Thus,fastglycinergiccurrentsdominated"mixed"mPSCpeakamplitudesinmatureRCs,andGABAA currentsdominatedtheirlong
decays. In non-RCs, GABAergic and mixed events had shorter durations, and their frequencies decreased with development. Functional
maturation of inhibitory synapses on RCs correlates well with increased glycine receptor recruitment to large gephyrin patches, colocal-
ization with 3/ 5-containing GABAA receptors, and maintenance of GABA/glycine corelease. As a result, charge transfer in GABA,
glycine, or mixed mPSCs was larger in mature RCs than in non-RCs, suggesting RCs receive potent inhibitory synapses.


Source: Alvarez, Francisco J. - Department of Neuroscience, Cell Biology, and Physiology, Wright State University


Collections: Biology and Medicine