ABSTRACT
This chapter utilizes cardiovascular afferents as a focus for discussion of the issue of excitatory amino acid neurotransmission of visceral afferents in general. The pharmacology of excitatory amino acid receptors has exploded with the development of dozens of new agonists and antagonists. This new armory of tools has given rise to recognition of an ever more complex scheme of receptor classes and subtypes coupled to ion channels and to second-messenger systems. The evidence is quite strong that glutamate (Glu) is the major neurotransmitter at nucleus tractus solitarii (NTS) neurons. Sensory afferents impinging upon NTS neurons appear to release Glu which, as in the spinal cord, binds to non-N-methyl-d-aspartate receptors to mediate primary, monosynaptic, fast afferent synaptic transmission. For intact reflexes, investigators have microinjected agonists and antagonists into mNTS and followed changes in blood pressure and heart rate in anesthetized animals, primarily rats.
