Background and purpose: Lithium's antidepressant action may be mediated by inhibition of inositol monophosphatase (IMPase), a key enzyme in Gq -protein coupled receptor signalling. Recently, the antioxidant agent ebselen was identified as an IMPase inhibitor. Here, we investigated both ebselen and lithium in models of the 5-HT2A receptor, a Gq -protein coupled receptor involved in lithium's actions.
Experimental approach: 5-HT2A receptor function was assessed in mice by measuring the behavioural (head-twitches, ear scratches) and molecular (cortical immediate early gene [IEG] mRNA; Arc, c-fos, Egr2) responses to 5-HT2A receptor agonists. Ebselen and lithium were administered either acutely or repeatedly prior to assessment of 5-HT2A receptor function. Because lithium and 5-HT2A receptor antagonists augment the action of selective serotonin reuptake inhibitors (SSRIs), ebselen was tested for this activity by co-administration with the SSRI citalopram in microdialysis (extracellular 5-HT) experiments.
Key results: Acute and repeated administration of ebselen inhibited behavioural and IEG responses to the 5-HT2A receptor agonist DOI. Repeated lithium also inhibited DOI-evoked behavioural and IEG responses. In comparison, a selective IMPase inhibitor (L-690330) attenuated the behavioural response to DOI whereas glycogen synthase kinase inhibitor (AR-A014418) did not. Finally, ebselen enhanced the increase in extracellular 5-HT induced by citalopram, and also increased regional brain 5-HT synthesis.
Conclusions and implications: Our data demonstrated lithium-mimetic effects of ebselen in different experimental models of 5-HT2A receptor function, probably mediated by IMPase inhibition. This evidence of lithium-like neuropharmacological effects of ebselen adds further support for the clinical testing of ebselen in mood disorders, including as an antidepressant augmenting agent.
© 2018 The British Pharmacological Society.