Fig. 1: Jejunal enteric nervous system intrinsic primary afferent neuron IPAN physiology differs between old and young mice.
a For this and all other bar graphs in the present paper, mean values given at base of bar graphs, open circles represent values measured from individual neurons. Resting membrane potentials (Vm) of aged are more polarized than those of young mice. Cm (membrane capacitance = measure of cell surface membrane area) was not different. Input resistance (Rin), a measure of number of open background channels = reciprocal of cell membrane leakiness)-aged IPANs had lower Rin. Background leak conductance (gleak) was lower for young than for old IPANs. Rheobase (threshold current required to evoke one action potential 50% of the time) was lower for young than old IPANs. The width of the action potential at half height of its positive amplitude (AP1/2 width) was not statistically different for young vs aged IPANs. The number of action potentials evoked at 2 x rheobase intensity (No. APs 2 x rheobase) was greater for young compared to aged IPANs. The area under the curve of the postaction potential slow afterhyperpolarisation (sAHP AUC) was greater for aged than young IPANs. b, d Representative action potential shapes for young and aged IPANs (colour-code: green indicates young, brown indicates aged). c, e First order time derivative of action potential showing that both old and young spikes have a hump (arrowhead) on their descending phase, indicating that calcium influx (which contributes significantly to AP1/2 width) did not differ notably between young and aged IPANs. f, g Example traces of action potentials evoked at 2x rheobase for young and aged IPANs. h, i Traces of post-action potential sAHP from young vs aged IPANs. Positions of truncated action potentials indicated by filled circles. j, k Examples of IPAN shapes revealed after intracellular neurobiotin dye filling. IPANs had smooth oval cell bodies with multiple long axonal processes running circumferentially within the myenteric plexus (Dogiel type II cell morphology). The full extent of these processes are not shown. Statistics: Nyoung = 12 (from 6 mice), Naged = 8 (from 4 mice). All comparisons made using unpaired t tests except for No. APs 2 x rheobase for which a Mann-Whitney test was applied. All tests were two-tailed. All error bars represent the standard error of the mean.
