Animal experiment:

Rats[2] Male Wistar rats weighing 270-300 g, are used. Lesopitron is administered either through the dialysis probe (dissolved in artificial CSF) or i.p. (dissolved in 0.9% saline, 2 mL/kg body weight).

Lesopitron dihydrochloride is a full and selective 5-HT1A receptor agonist with IC50 of 125 nM in rat hippocampal membranes.

In vitro binding and autoradiographic studies with [3H]8-OH-DPAT and [3H]Lesopitron as radioligands confirm that Lesopitron binds to 5-HT1A receptors in the rat brain with a relatively high affinity (pKi=7.35). As expected of a full agonist at postsynaptic 5-HT1A receptors, Lesopitron (IC50=125 nM) inhibits forskolin-stimulated adenylate cyclase activity in rat hippocampal membranes to the same extent as 5-HT. Lesopitron inhibits the firing of serotoninergic neurons both in vitro (in brainstem slices, IC50=120 nM)[1].

Lesopitron inhibits the firing of serotoninergic neurons both in vivo (in chloral hydrate-anaesthetized rats, ID50=35 μg/kg i.v.)[1]. Lesopitron administered at a dose which induces anxiolytic behaviour in rats (30 μg/kg, i.p.) markedly reduces 5-HT levels (to 45% of the basal value) in cortical perfusates[2].

[1]. Haj-Dahmane S, et al. Interactions of Lesopitron (E-4424) with central 5-HT1A receptors: in vitro and in vivo studies in the rat. Eur J Pharmacol. 1994 Apr 1;255(1-3):185-96. [2]. Ballarín M, et al. Effect of acute administration of the 5-HT1A receptor ligand, Lesopitron, on rat cortical 5-HT and dopamine turnover. Br J Pharmacol. 1994 Oct;113(2):425-30.