Trans-crocetin is involved in the inhibition of the glutamatergic synaptic transmission on rat cortical neurones by saffron extract

Saffron is the dried stigmata of Crocus sativus L. Saffron contains a large quantity of carotenoids, the crocins, glycosides of the C₂₀ apocarotenoid trans-crocetin. It has been shown that ethanolic (80 vol.-%) saffron extract (CSE) and trans-crocetin, interact with the phencyclidine binding site of the NMDA receptor [1]. The aim of the present study was to examine the influence of CSE and trans-crocetin on the glutamatergic synaptic transmission in rat brain slices. Postsynaptic potentials (PSPs) were elicited by focal electrical stimulation in pyramidal cells of the cingulate cortex and recorded using intracellular placed microelectrodes. PSPs were induced by glutamate released from presynaptic terminals which activated postsynaptic NMDA and non-NMDA receptors. In contrast, externally added glutamate induced a depolarisation of the cell membrane of the pyramidal cells. CSE (10–200µg/ml) decreased the glutamate-induced membrane depolarisation and inhibited the evoked PSPs. CSE inhibited the isolated NMDA and non-NMDA component of the PSPs and decreased the NMDA and kainate induced depolarisation. This indicates an antagonistic effect of CSE on NMDA and kainate receptors. Trans-crocetin (1–50µM) investigated under the same conditions as CSE showed comparable inhibitory effects on the glutamate-induced membrane depolarisation and evoked PSPs. Trans-crocetin decreased the NMDA induced membrane depolarisation, but compared to CSE trans-crocetin did not inhibit the isolated non-NMDA component of the PSPs. Therefore, it seems that trans-crocetin did not interact with the non-NMDA type of glutamate receptors. We conclude that trans-crocetin is involved in the antagonistic effect of CSE on NMDA but not on kainate receptors.

References: 1. Lechtenberg, M. et al. 2008, Planta Med 74: 764–772.