Development of Calcium Signaling in Postsynaptic Neurons of the Medial Nucleus of the Trapezoid Body in the Mouse

Abstract Purpose In the central nervous system, Ca 2 ⁺ signaling plays a pivotal role in various cellular processes, including neuronal development and maturation. Disruption of Ca 2 ⁺ homeostasis impairs auditory circuit formation, compromising auditory processing and behavior. Here, we aimed to investigate systematically the development of Ca 2 ⁺ signaling in neurons of the medial nucleus of the trapezoid body (MNTB), a brainstem nucleus critical for sound localization. Methods Using Ca 2 ⁺ imaging in brain slices from mice genetically expressing the Ca 2 ⁺ indicator GCaMP in glycinergic cells, we studied Ca 2 ⁺ signaling in MNTB neurons from mice of either sex at three developmental milestone stages, in response to both bath-applied agonists of various neurotransmitter receptors and synaptic activation of glutamatergic afferents. Results Prior to hearing onset at postnatal 7 days (P7), robust Ca 2 ⁺ responses were evoked in MNTB neurons upon activation of glutamate receptors (NMDARs, AMPARs, and group I (Gp-I) mGluRs by 200 μM NMDA, 100 μM AMPA, and 200 μM 3,5-DHPG, respectively), whereas after hearing onset (P14 and P21), responses induced by NMDA and 3,5-DHPG declined markedly while AMPA-induced responses remained relatively strong. Ca 2 ⁺ responses upon application of GABA (100 μM) and glycine (200 μM) were detected in neonatal mice, diminished in a few days after birth, and almost completely disappeared by P7. Whole-cell patch-clamp recordings showed that stimulation of excitatory afferents evoked action potentials across all ages with no differences in firing frequency up to 100 Hz, but Ca 2 ⁺ responses varied in a stimulus intensity- and frequency-dependent manner and exhibited developmental downregulation. Conclusion Ca 2 ⁺ signaling induced by activation of the major transmitter receptors in MNTB neurons is highly developmentally down-regulated.