Comparisons of somatic action potentials from dispersed and intact rat nodose ganglia using patch-clamp technique

To differentiate the electrophysiological characteristics of somatic action potentials (AP) from isolated Neo and Juv nodose sensory neurons (NSN) and those from slices of intact Juv and adult rat nodose ganglia.

For isolated cell recordings nodose ganglia from 3-8 d old Neo and 4 weeks old Juv rats were dissociated using trypsin and collagenase, respectively. Nodose ganglia slices with attached vagus were prepared using a sequential treatment of collagenase and trypsin for both Juv and adult rats. Conduction velocity (CV) was collected by vagal stimulation. Whole-cell patch was applied for somatic AP recordings.

(1) 281 NSN from both isolated cells and nodose slices were studied. Across all age groups, there was no difference observed among either C- or A-types. The difference between C- and A-type was significant. (2) Neurons exhibiting AP with prominent repolarization hump, broader APD50 (>2.0 ms), upstroke velocity at the point of APD50 (UV(APD50)) and downstroke velocity at the point of APD50 (DV(APD50)) below 100 V . s-1 and 50 V . s-1 were classified as C-type (n = 222). Those without a hump, brief APD50 (<1.0 ms), and UV(APD50) and DV(APD50) greater than 200 V . s-1 and 100 V . s-1 were classified as A-type (n = 59). (3) With slices, except for hump, APD, UV, and DV, significant differences were also observed (C- vs A-type) in CV from both Juv (0.56 +/- 0.15 vs 15.6 m.s-1) and adult (0.9 +/- 0.4 vs 14.5 +/- 1.0 m . s-1) nodose slices, discharge rate (single or burst vs repetitive), and frequency follow (<20 Hz vs >100 Hz). (4) Phase analysis showed that C-type had higher AP firing threshold, and lower total in- and outward peak currents than A-type.

C- and A-type AP from isolated NSN of Neo or Juv rats exhibited electrophysiological characteristics that closely followed those of AP recorded in nodose slices. Therefore, isolated NSN can effectively serve as an experimental surrogate for electrophysiological studies of NSN requiring prior identification of afferent fiber type. Features of the AP wave-form such as the repolarization hump, APD50), and UV are strongly correlated with CV and are therefore reliable measures for classifying isolated NSN as either C- or A-type. It is most important that the nodose slice enables us to study the AP and ion channel characteristics on identified NSN by afferent fiber CV with adult animals.