OBJECTIVETo explore the role of group II metabotropic glutamate receptors in the modulation of basic respiratory rhythm.

METHODSNeonatal (0-3 days) SD rats of either sex were used. The medulla oblongata brain slice containing the medial region of the nucleus retrofacialis (mNRF) and the hypoglossal nerve rootlets was prepared, and the surgical procedure was performed in the modified Kreb's solution (MKS) with continuous carbogen (95% O2 and 5% CO2) within 3 min. The brain slices were quickly transferred to a recording chamber and continuously perfused with oxygen-saturated MKS at a rate of 4-6 ml/min at 27-29 degrees celsius. Eighteen medulla oblongata slices were divided into 3 groups and treated for 10 min with group II metabotropic glutamate receptor-specific agonist 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (APDC) (at concentrations of 10, 20, 50 micromol/L), group II metabotropic glutamate receptor antagonist (2S)-alpha-ethylglutamic acid (EGLU) (300 micromol/L), or APDC (50 micromol/L)+EGLU (300 micromol/L) after a 10 min APDC (50 micromol/L) application. Respiratory rhythmical discharge activity (RRDA) of the rootlets of the hypoglossal nerve was recorded by suction electrodes.

RESULTSAPDC produced a dose-dependent inhibitory effect on the RRDA, prolonging the respiratory cycle and expiratory time and decreasing the integral amplitude and inspiratory time. EGLU induced a significant decrease in the respiratory cycle and expiratory time. The effect of APDC on the respiratory rhythm was partially reversed by the application of APDC+EGLU.

CONCLUSIONGroup II metabotropic glutamate receptors are probably involved in the modulation of the RRDA in isolated neonatal rat brainstem slice.