Evidence that glutamate is the transmitter mediating respiratory drive from medullary premotor neurons to phrenic motoneurons: a double labeling study in the rat.

Glutamate immunoreactivity was found in 81-84% of the bulbospinal neurons projecting to the phrenic motoneuron pool, which were located in the para-ambiguous nucleus and the ventral vicinity of the retrofacial nucleus. Their glutamate contents were identified by a double labeling technique in combination with the retrograde transport of horseradish peroxidase and immunocytochemistry of the glutamate. The remaining 16-19% of the bulbospinal neurons projecting to the phrenic motoneuron pool did not contain glutamate immunoreactivity. Thus it appears that glutamate may be a major transmitter of the inspiratory drive from the medullary respiratory neurons to the phrenic motoneurons.