5-HT1A and 5-HT1B receptors control the firing of serotoninergic neurons in the dorsal raphe nucleus of the mouse: studies in 5-HT1B knock-out mice

The characteristics of the spontaneous firing of serotoninergic neurons in the dorsal raphe nucleus and its control by serotonin (5‐hydroxytryptamine, 5‐HT) receptors were investigated in wild‐type and 5‐HT1B knock‐out (5‐HT1B–/–) mice of the 129/Sv strain, anaesthetized with chloral hydrate. In both groups of mice, 5‐HT neurons exhibited a regular activity with an identical firing rate of 0.5–4.5 spikes/s. Intravenous administration of the 5‐HT reuptake inhibitor citalopram or the 5‐HT1A agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) induced a dose‐dependent inhibition of 5‐HT neuronal firing which could be reversed by the selective 5‐HT1A antagonist N‐[2‐[4‐(2‐methoxyphenyl)‐1‐piperazinyl]ethyl]‐N‐(2‐pyridinyl)cyclohexane carboxamide (WAY 100635). Both strains were equally sensitive to 8‐OH‐DPAT (ED50 ∼ 6.3 μg/kg i.v.), but the mutants were less sensitive than wild‐type animals to citalopram (ED50 = 0.49 ± 0.02 and 0.28 ± 0.01 mg/kg i.v., respectively, P