Mechanisms and functional impact of Group I metabotropic glutamate receptor modulation of excitability in mouse MNTB neurons |
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Authors: | Éverton dos Santos e Alhadas Ana Maria Bernal Correa Ligia Araújo Naves Christopher Kushmerick |
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Institution: | 1. Graduate Program in Physiology and Pharmacology, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil;2. Department of Physiology and Biophysics, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil |
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Abstract: | We examined effects of Group I metabotropic glutamate receptors on the excitability of mouse medial nucleus of the trapezoid body (MNTB) neurons. The selective agonist, S-3,5-dihydroxyphenylglycine (DHPG), evoked a dose-dependent depolarization of the resting potential, increased membrane resistance, increased sag depolarization, and promoted rebound action potential firing. Under voltage-clamp, DHPG evoked an inward current, referred to as IDHPG, which was developmentally stable through postnatal day P56. IDHPG had low temperature dependence in the range 25–34°C, consistent with a channel mechanism. However, the I-V relationship took the form of an inverted U that did not reverse at the calculated Nernst potential for K+ or Cl−. Thus, it is likely that more than one ion type contributes to IDHPG and the mix may be voltage dependent. IDHPG was resistant to the Na+ channel blockers tetrodotoxin and amiloride, and to inhibitors of iGluR (CNQX and MK801). IDHPG was inhibited 21% by Ba2+ (500 μM), 60% by ZD7288 (100 μM) and 73% when the two antagonists were applied together, suggesting that KIR channels and HCN channels contribute to the current. Voltage clamp measurements of IH indicated a small (6%) increase in Gmax by DHPG with no change in the voltage dependence. DHPG reduced action potential rheobase and reduced the number of post-synaptic AP failures during high frequency stimulation of the calyx of Held. Thus, activation of post-synaptic Group I mGlu receptors modifies the excitability of MNTB neurons and contributes to the reliability of high frequency firing in this auditory relay nucleus. |
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Keywords: | HCN channel KIR channel metabotropic glutamate receptor MNTB resting potential |
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