This study tested whether the glial cells are involved in the exciting effects of doxapram on brainstem slice in vitro. Experiments were performed in brainstem slice preparations from neonatal rats. The medial area of nucleus retrofacialis (mNRF) and the hypoglossal nerve (XII nerve) were contained in the preparations. The slices were perfused with modified Kreb's solution (MKS), and the rhythmical respiratory discharge activity (RRDA) was simultaneously recorded from the XII nerve by using suction electrodes, including the discharge time course of inspiratory (Ti), expiratory (Te), respiratory cycle (RC), and integrity amplitude of inspiratory discharge (IA). After applying of doxapram (5 mu M) to the MKS for 10 min, Ti and IA increased significantly (85.0 +/- A 25.0%, 13.2 +/- A 2.5%, respectively, P < 0.05), the Te and the RC decreased significantly (19.0 +/- A 1.4%, 12.8 +/- A 1.4%, respectively, P < 0.05) when compared with control group. When the methionine sulfoximine (MS, 10 mu M), a blockage of glutamine synthetase, was applied, all the exciting effects of doxapram on RRDA were reversed. After the glutamine (20 mu M) was applied to the MKS for 10 min, the exciting effects were revealed again. Our results suggest that the normal metabolism of glial cells takes a key role in the modification of the RRDA in the slices. In conclusion, glial cells are involved in the exciting effects of doxapram on brainstem slice in vitro.