Intraocular injection of kainic acid does not abolish thecircadian rhythm of arylalkylamine N-acetyltransferase mRNA in ratphotoreceptors

[摘要] Purpose: Melatonin synthesis in mammalian retinal photoreceptors isunder photic and circadian control and regulated by changes in theactivity of arylalkylamine N-acetyltransferase (AANAT). Recentstudies have suggested that retinal dopaminergic neurons contain acircadian pacemaker, and dopamine is the neurotransmitter that drivescircadian rhythmicity in the mammalian retina.Methods: To investigate the role of inner retinal neurons, includingdopamine neurons, in generating the rhythm of melatonin synthesis, ratretinas were lesioned with kainic acid (KA), which was shown previouslyto induce degeneration of neurons in the inner nuclear layer and toeliminate rhythmicity in the dopaminergic system. Aanat, rhodopsin,medium wavelength (mwl) opsin, short wavelength (swl) opsin, and period1(Per1), and period2 (Per2) mRNA levels were measured usingreal-time quantitative RT-PCR in KA injected and control eyes.Results: Our data show that intraocular injections of KA did notabolish the daily and circadian rhythms of Aanat mRNA in thephotoreceptors, but it did shift the phase of the Aanat transcriptrhythm in constant darkness. Surprisingly, KA injections reduced thelevels and eliminated daily rhythms of mwl and swl opsin transcripts,but not of rhodopsin mRNA. Per1 and Per2 mRNA levels wererhythmic in saline injected and in KA-treated retinas, and Per2 mRNAlevels were significantly reduced (20-50%) in KA-treated retinas.Conclusions: These findings demonstrate that the circadian clockgenerating melatonin rhythmicity is largely KA insensitive and likely tobe located in the rod photoreceptors, although KA-sensitive neurons doinfluence its timing. More important, our data demonstrate that dopaminerhythmicity is not necessary for generating the circadian rhythm ofAanat mRNA in the photoreceptors. Our data also indicate thatPer1 and Per2 are rhythmically transcribed in the rat retina andKA treatment has a dramatic effect on the overall levels of Per2mRNA.

[学科分类] 生物化学/生物物理