Abstract
Baroreceptor inputs to nucleus of the tractus solitarius medialis (mNTS) neurons can be differentiated, among other features, by their response to vanilloid or purinergic agonists, active only on C- or A-fibers, respectively. A major aim of this study was to examine whether neurons of NTS centralis (cNTS), a subnucleus dominated by esophageal inputs, exhibit a similar dichotomy. Since it has been suggested that cholecystokinin (CCK), exerts its gastrointestinal (GI)-related effects via paracrine activation of vagal afferent C-fibers, we tested whether CCK-sensitive fibers impinging upon cNTS neurons are responsive to vanilloid but not purinergic agonists. Using whole cell patch-clamp recordings from cNTS, we recorded miniature excitatory postsynaptic currents (mEPSCs) to test the effects of the vanilloid agonist capsaicin, the purinergic agonist α,β-methylene-ATP (α,β-Met-ATP), and/or CCK-octapeptide (CCK-8s). α,β-Met-ATP, capsaicin; and CCK-8s increased EPSC frequency in 37, 71, and 46% of cNTS neurons, respectively. Approximately 30% of cNTS neurons were responsive to both CCK-8s and α,β-Met-ATP, to CCK-8s and capsaicin, or to α,β-Met-ATP and capsaicin, while 32% of neurons were responsive to all three agonists. All neurons responding to either α,β-Met-ATP or CCK-8s were also responsive to capsaicin. Perivagal capsaicin, which is supposed to induce a selective degeneration of C-fibers, decreased the number of cNTS neurons responding to capsaicin or CCK-8s but not those responding to α,β-Met-ATP. In summary, GI inputs to cNTS neurons cannot be distinguished on the basis of their selective responses to α,β-Met-ATP or capsaicin. Our data also indicate that CCK-8s increases glutamate release from purinergic and vanilloid responsive fibers impinging on cNTS neurons.