Figure 3.

Actions of 5-HT_1B, 5-HT₂ and 5-HT₃ receptor agonists. (A) The 5-HT_1B receptor agonist CGS produces both depression and facilitation of synaptic responses in DDH neurons. (i) Normalized data showing a modest CGS-induced epsp depression in younger animals (black circles; n=6), while facilitating epsps in older animals (grey circles; n=4). (ii). The CGS-induced epsp amplitude increase is associated with a reversible increase in neuronal input resistance (160 MΩ in control; 330 MΩ in CGS) and a decrease in rheobase (70 pA in control; 50 pA in CGS). Responses presented arise from 30 pA depolarizing and hyperpolarizing current steps. (B) The 5-HT₂ receptor agonist DOI modestly facilitates (18%) (i) or depresses (20%) evoked synaptic responses in DDH neurons (ii). (C) The 5-HT₃ receptor agonist CPBG facilitates synaptic responses in the younger animals, but produces both facilitation and depression in neurons obtained from older animals. (i). Normalized data showing the modest facilitatory actions of CPBG on neurons obtained from both younger (n=6) and older (n=2) animals. (ii). Example showing synaptic facilitation (15%) obtained in a neuron obtained from an older animal.