Synaptic facilitation between tail SNs and MNs following 5-HT treatment declined during aging.

<p>A) Representative responses during 500 ms depolarizing current injection in tail SNs before and 5 min after conclusion of 10 min perfusion of vehicle (ASW; A1) or 5-HT (20 μM; A2) onto the pleural-pedal ganglion. B) In mature tail SNs, the same depolarizing pulse that produced a single AP during baseline conditions evoked significantly more AP when assessed 5 and 15 min after 5-HT treatment. ** denotes significant increase compared to baseline at p≤0.01, Tukey’s posthoc tests (n = 16). No change in AP number was observed in aged II tail SNs following 5-HT treatment (n = 17). C) Monosynaptic facilitation between tail SNs and MNs following 5-HT treatment decreased during aging. A single AP evoked in tail SNs by 50 ms injected current resulted in a monosynaptic EPSP in tail MNs. D) Following 5-HT treatment, tail MN EPSP amplitude increased significantly in mature but not in aged II preparations. * denotes significant increase compared to baseline at p≤0.05, Tukey’s posthoc tests (n = 20 for mature, n = 17 for aged II).