Effect of ebselen, a putative lithium-mimetic on central 5HT2A receptor function in the mouse

Ivi Antoniadou, Tasneem Ariswala, Florence Serres, Nisha Singh, Sri Vasudevan, Amy Halliday, Grant Churchill, Trevor Sharp. University Department of Pharmacology, Oxford, UK.

Inhibition of inositol monophosphatase (IMPase) and phosphoinositide signalling is a putative mechanism underlying the mood stabilizing effects of lithium (Berridge et al., 1989). We have recently found that an antioxidant, ebselen, is a potent IMPase inhibitor (Singh et al, 2010). Here we report the effect of ebselen on behavioural (head twitch) and molecular (immediate early gene; IEG) responses to activation of the 5HT2A receptor, which is Gq linked to the phosphoinositide cycle.

Adult male C57BL/6 mice (20-25 g) were injected with vehicle (4% w/v cyclodextrin) or ebselen (1, 5 or 10 mg/kg) followed 1 h later by the non-selective 5HT2A agonists DOI (2 mg/kg) or psilocin (2 mg/kg). Additionally, lithium (first dose 10 mmol/kg then 3 mmol/kg twice daily) or vehicle (0.9% saline) were injected for 3 days followed by DOI (2 mg/kg) 18 h after the last injection. All drugs were given i.p.. Head twitches were scored 5 min after agonist injection for 15 min. For IEG measurements, brains were removed 1 h after agonist injection and snap frozen. In situ hybridization was performed on brain sections using 35S-dATP labelled oligonucleotides complimentary to c-fos and egr2 mRNA. Data were analysed statistically using Student’s unpaired t-test or one way ANOVA with post hoc LSD as appropriate (n = 6/group, mean ± SEM values shown).

Ebselen reduced the number of head twitches induced by DOI in a dose-dependent manner (vehicle 4±1; DOI 51±2; ebselen 1 mg/kg 56±5; ebselen 5 mg/kg 41±4; ebselen 10 mg/kg 28±5; p<0.05). Similarly, ebselen reduced head twitches induced by psilocin (vehicle 5±1; psilocin 17±2; ebselen 10 mg/kg 11±1; p<0.05). As with ebselen, lithium also inhibited DOI-induced head twitches (DOI 59±5; lithium 45±1; p<0.05). The increase in IEG mRNA evoked by DOI was also attenuated by ebselen in some brain regions. For example, ebselen reduced the c-fos response to DOI in the cingulate cortex (vehicle 133±11; DOI: 203±19; ebselen 10 mg/kg 151±5; nCi/g, p<0.05), and somatosensory cortex (vehicle 95±3; DOI 181±20; ebselen 10 mg/kg 123±11; nCi/g, p<0.05) but not orbital cortex (vehicle 108±6; DOI 248±17; ebselen 10 mg/kg 281±21). Also ebselen reduced the egr2 response to DOI in the endopiriform cortex (vehicle 47±3; DOI 68±4; ebselen 10 mg/kg 52±2; nCi/g, p<0.05) and caudate putamen (vehicle 49±2; DOI 69±5; ebselen 10 mg/kg 55±2; nCi/g, p<0.05) but not prelimbic cortex (vehicle 55±2; DOI 76±5; ebselen 10 mg/kg 70±2; nCi/g, p<0.05).

The current data show that ebselen attenuates behavioural and molecular responses to 5HT2A receptor agonist administration in the mouse. These findings are consistent with the hypothesis that ebselen reduces central 5HT2A receptor function by IMPase inhibition.

Berridge, MJ, Downes, CP & Hanley, MR 1989, Neural and developmental actions of lithium: a unifying hypothesis. Cell, 59, 411-419.

Singh, N, Vasudevan, S, Thomas, J, et al 2010, Inositol monophosphatase: drug target or false.

This work was supported by a BBSRC project grant and a Greek state foundation scholarship.