Carbachol, glycine and gamma aminobutyric acid also activate cardiovascular neurons of pontomedulla responsive to glutamate.

Thirty-three cats under intraperitoneal chloralose (40 mg/kg) and urethane (400 mg/kg) anesthesia were used to explore the effect of microinjections (100 nl) of carbachol (CCh, 0.5 M), a cholinergic analogue, glycine (Gly, 1 M) and gamma aminobutyric acid (GABA, 0.4 M) on the cardiovascular-reactive sites in the pontomedulla that responded to microinjection of monosodium glutamate (Glu, 0.25 M, 100 nl) resulting in changes of systemic arterial pressure (SAP). Brain sites under exploration included gigantocellular tegmental field and lateral tegmental field (FTG-FTL), the dorsomedial (DM) and ventrolateral (VLM) medulla which produced pressor responses; caudal VLM (CVLM) and paramedian reticular nucleus (PRN) which produced depressor responses. It was found that CCh produced significant fall of SAP in DM and VLM while the rise of SAP in the same site by Glu. CCh produced SAP decrease in CVLM similar to Glu. GABA significantly caused a slight to moderate increase of SAP in FTG-FTL, DM and VLM, and decrease of SAP in CVLM, all in direction similar to that of Glu. Gly produced significant and marked increase of SAP in DM and VLM similar to Glu both in magnitude and duration. Gly produced increase of SAP in CVLM but the fall of SAP by Glu. PRN was relatively non-reactive except a few microinjections of CCh which produced hypotension. In conclusion, the cardiovascular-reactive sites in the pontomedulla that respond to Glu may also react to other chemicals or neurotransmitters. It is highly possible that multiple receptors of different nature co-exist in neurons of some cardiovascular regions in the pontomedulla.