S 15535, a benzodioxopiperazine acting as presynaptic agonist and postsynaptic 5-HT1A receptor antagonist, prevents the impairment of spatial learning caused by intrahippocampal scopolamine.
1 The effect of S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine), an agonist at presynaptic and antagonist at postsynaptic 5-HT1A receptors, on the impairment of spatial learning caused by intrahippocampal scopolamine in a two-platform spatial discrimination task was studied. 2 Scopolamine (4.0 microg microl-1), injected bilaterally into the CA1 region of the dorsal hippocampus 10 min before each training session, impaired choice accuracy with no effect on choice latency and errors of omission. 3 Administered subcutaneously 30 min before each training session, S 15535 1.0 (but not 0.3) mg kg-1 did not modify choice accuracy but prevented its impairment by intrahippocampal scopolamine. 4 WAY 100635, a 5-HT1A receptor antagonist, injected into the dorsal raphe at 1.0 microg 0.5 microl-1 5 min before scopolamine, had no effect on choice accuracy and latency or errors of omission and did not modify the effect of scopolamine but completely antagonized the effect of S 15535 (1.0 mg kg-1) on scopolamine-induced impairment of choice accuracy. 5 The results confirm a previous report (Carli et al., 1998) that stimulation of presynaptic 5-HT1A receptors in the dorsal raphe counteracts the deficit caused by intrahippocampal scopolamine, probably by facilitating the transfer of facilitatory information from the entorhinal cortex to the hippocampus. 6 Drugs that stimulate action on presynaptic 5-HT1A receptors, such as S 15535 and other partial 5-HT1A receptors agonists, may be useful in the symptomatic treatment of human memory disturbances associated with loss of cholinergic innervation to the hippocampus.