Glutamate release and presynaptic action of AP4 during inspiratory drive to phrenic motoneurons.

High-performance liquid chromatography (HPLC) was used to detect the presence of excitatory amino acids released from bulbospinal axon terminals projecting to cervical spinal respiratory motoneurons during transmission of inspiratory drive in an in vitro neonatal rat brainstem-spinal cord preparation. Measurements were then repeated under paradigms where transmitter release was decreased by either depression of bulbospinal respiratory drive, or by adding DL-2-amino-4-phosphonobutyrate (AP4) to the solution bathing the spinal cord. The amounts of glutamate, but not aspartate, released decreased significantly with depressed brainstem inspiratory drive or the activation of AP4-sensitive receptors within the cervical (C) spinal cord.