Maturation of NMDA receptor-mediated spontaneous postsynaptic currents in the rat locus coeruleus neurons

Introduction: During mammalian brain development, neural activity leads to maturation of glutamatergic innervations to locus coeruleus. In this study, fast excitatory postsynaptic currents mediated by N-methyl-Daspartate (NMDA) receptors were evaluated to investigate the maturation of excitatory postsynaptic currents in locus coeruleus (LC) neurons. Methods: NMDA receptor-mediated synaptic currents in LC neurons were evaluated using whole-cell voltage-clamp recording during the primary postnatal weeks. This technique was used to calculate the optimum holding potential for NMDA receptor-mediated currents and the best frequency for detecting spontaneous excitatory postsynaptic currents (sEPSC). Results: The optimum holding potential for detecting NMDA receptor-mediated currents was +40 to +50 mV in LC neurons. The frequency, amplitude, rise time, and decay time constant of synaptic responses depended on the age of the animal and increased during postnatal maturation. Conclusion: These findings suggest that most nascent glutamatergic synapses express functional NMDA receptors in the postnatal coerulear neurons, and that the activities of the neurons in this region demonstrate an age-dependent variation.