Bj. Undem et D. Weinreich, ELECTROPHYSIOLOGICAL PROPERTIES AND CHEMOSENSITIVITY OF GUINEA-PIG NODOSE GANGLION NEURONS IN-VITRO, Journal of the autonomic nervous system, 44(1), 1993, pp. 17-34
Conventional intracellular recording techniques were employed to obtai
n information on the electrophysiological and pharmacological characte
ristics of C-type neurons in the guinea pig nodose ganglia. Approximat
ely 90% of the cell bodies gave rise to axons with conduction velociti
es consistent with C-fibers (0.9-1.1 m/s). The average resting membran
e potential and input impedence was about -60 mV and 45 MOMEGA, respec
tively. Orthodromic electrical stimulation of the vagus nerve 20-30 mm
caudal to the ganglion produced overshooting action potentials in the
nodose neurons. The falling phase of the action potential was followe
d by a transient (50-300 ms) fast hyperpolarization (AHP(fast)). In 20
% of C-type neurons the ABP(fast) was followed by a slowly developing,
long-lasting afterhyperpolarization (AHP(slow)) that limited the abil
ity of the neuron to fire action potentials at high frequency. The AHP
(slow) magnitude was dependent on the number of spikes, had a reversal
potential of -87 mV, and was abolished by 100 muM cadmium chloride, s
uggesting that it is produced by a calcium-dependent potassium current
. In about 30% of the nodose neurons, hyperpolarizing current steps fr
om resting potential produced a time- and voltage-dependent anomalous
rectification in the electrotonic potential. External cesium (1 mM), b
ut not barium (100 muM) reversibly blocked this effect. Single-electro
de voltage-clamp measurements revealed a slowly developing inward curr
ent in these neurons that grows in magnitude with step hyperpolarizati
ons from resting potential, and has an estimated reversal potential of
about -44 mV. These properties suggest that this current is analogous
to I(h) observed in many peripheral and central neurons. Autacoids in
cluding serotonin, histamine, several prostanoids, peptidoleukotriene,
and bradykinin, were examined for their ability to affect the excitab
ility of the nodose neurons. Serotonin was the only autacoid capable o
f depolarizing the membrane potential to action potential firing thres
hold. The serotonin-induced membrane depolarization was associated wit
h a significant increase in input conductance. Histamine depolarized t
he membrane potential of the C-type neurons in 28/30 neurons. Bradykin
in, prostacyclin, and leukotriene C4 were found to cause membrane depo
larizations in a subset (73%, 31%, and 50%, respectively) of nodose ne
urons. The AHP(slow) was virtually abolished by bradykinin, prostacyli
n, and in a subset of neurons, leukotriene C4. Inhibition of the AHP(s
low) was accompanied by a change in the accommodative properties of th
e neurons, reflected by the increased frequency at which the neuron co
uld successfully elicit repetitive action potentials. The results demo
nstrate that most autacoids do not overtly evoke action potentials in
the somata of the guinea pig nodose ganglion C-type neurons, rather th
ey influence their excitability by producing subthreshold membrane dep
olarizations and by modulating the rate of neuronal discharge.