Synaptic facilitation between tail SNs and MNs following sensitizing tail shocks declined during aging.

<p>A) Representative responses during depolarizing current injection in tail SNs before and 5 min after sensitizing tail shocks in mature and aged II animals. B) In mature tail SNs, the same depolarizing current injection that yielded a single AP in baseline conditions evoked significantly more AP 5, 15, and 30 min after sensitizing tail shocks. * denotes significant increase compared to baseline at p≤0.05, Tukey’s posthoc tests (n = 16). No change in AP number was observed following sensitizing tail shocks in aged II tail SNs (n = 20). C) Monosynaptic facilitation between tail SNs and MNs following sensitizing tail shocks decreased during aging. A single AP evoked in tail SNs by 50 ms injected current resulted in a monosynaptic EPSP in tail MNs in mature (n = 14) and aged II (n = 13) preparations. Tail MNs were hyperpolarized to -90 mV. D) Baseline EPSP amplitude was significantly decreased in MNs of aged II preparations. * denotes significant decrease compared to mature at p≤0.05, 2-sample t-test. E) Baseline EPSP latency did not change during aging. F) Following sensitizing tail shocks, EPSP amplitude increased significantly in mature but not in aged II tail MNs. * denotes significant increase compared to baseline at p≤0.05, Tukey’s posthoc tests.