ABSTRACT
The nature of the synaptic transmission between sensory afferent fibers and neurons of the caudal nucleus tractus solitarius is a central question in understanding neural regulation of the cardiovascular system. Methodological difficulties precluded direct electrophysiological and pharmacological analysis of the effects of these two neurotransmitters on individual commissural subnuclei nuclei of the solitary tract (mNTS) neurons. The glutamate responses suggested several different glutamate receptors might be present on the soma of the mNTS neurons. The three glutamate receptor agonists, N-methyl-d-aspartate, quisqualate, and kainic acid, had been implicated as participating in baroreflex transmission by studies introducing antagonists into the mNTS region. Spontaneous synaptic currents were observed in a total of 50 mNTS neurons; 80% of the neurons had either or both excitatory or inhibitory spontaneous synaptic currents. The preparation of adult mammalian mNTS neurons with attached functional synaptic terminals, remnants of the in vivo innervation, has led to the experimental delineation of at least three amino acid-activated ion channels.
