Effect of serotonin and serotonin analogues on passive membrane properties of lateral septal neurons in vitro.

In this study we have tested the effect of serotonin (5-HT) and serotonin-analogues on passive membrane properties of septal neurons in a rat brain slice. Superfusion with 5-HT hyperpolarized the membrane potential and decreased the membrane resistance of lateral septal neurons in a concentration dependent manner. The lowest effective concentration was 1 microM while maximal effects were observed with 30 microM. Hyperpolarizing responses to 5-HT persisted in the presence of haloperidol, phentolamine or ritanserin. The 5-HTIa agonist 8-hydroxy-2-[n-dipropylamino]tetralin (8OHDPAT) hyperpolarized septal neurons like 5-HT though the agonist was active at a lower concentration than 5-HT and induced longer-lasting effects. Two other 5-HT1a analogues, TVX Q 7821 and buspirone, could also mimick the effect of 5-HT. The 5-HT1b agonist 1-(m-trifluoromethylphenyl)piperazine (TFMPP) did not appreciably affect the membrane potential or resistance of septal neurons. The present results are consistent with data from binding studies and suggest that the effect of 5-HT on lateral septal neurons is at least partly mediated through 5-HT1a-like receptors.