Intraocular injection of kainic acid does not abolish the circadian rhythm of arylalkylamine N-acetyltransferase mRNA in rat photoreceptors.
OBJECTIVE
Melatonin synthesis in mammalian retinal photoreceptors is under photic and circadian control and regulated by changes in the activity of arylalkylamine N-acetyltransferase (AANAT). Recent studies have suggested that retinal dopaminergic neurons contain a circadian pacemaker, and dopamine is the neurotransmitter that drives circadian rhythmicity in the mammalian retina.


METHODS
To investigate the role of inner retinal neurons, including dopamine neurons, in generating the rhythm of melatonin synthesis, rat retinas were lesioned with kainic acid (KA), which was shown previously to induce degeneration of neurons in the inner nuclear layer and to eliminate 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 using real-time quantitative RT-PCR in KA injected and control eyes.


RESULTS
Our data show that intraocular injections of KA did not abolish the daily and circadian rhythms of Aanat mRNA in the photoreceptors, but it did shift the phase of the Aanat transcript rhythm in constant darkness. Surprisingly, KA injections reduced the levels and eliminated daily rhythms of mwl and swl opsin transcripts, but not of rhodopsin mRNA. Per1 and Per2 mRNA levels were rhythmic in saline injected and in KA-treated retinas, and Per2 mRNA levels were significantly reduced (20-50%) in KA-treated retinas.


CONCLUSIONS
These findings demonstrate that the circadian clock generating melatonin rhythmicity is largely KA insensitive and likely to be located in the rod photoreceptors, although KA-sensitive neurons do influence its timing. More important, our data demonstrate that dopamine rhythmicity is not necessary for generating the circadian rhythm of Aanat mRNA in the photoreceptors. Our data also indicate that Per1 and Per2 are rhythmically transcribed in the rat retina and KA treatment has a dramatic effect on the overall levels of Per2 mRNA.
Sakamoto
Katsuhiko
K
Neuroscience Institute and National Science Foundation Center for Behavioral Neuroscience, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA.
Liu
Cuimei
C
Kasamatsu
Manami
M
Iuvone
P Michael
PM
Tosini
Gianluca
G
D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000235:genetics*; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000187:drug effects* / Q000528:radiation effects; D003624:Darkness; D018690:Excitatory Amino Acid Agonists / Q000008:administration & dosage* / Q000494:pharmacology; D005123:Eye; D007267:Injections; D007608:Kainic Acid / Q000008:administration & dosage* / Q000494:pharmacology; D008027:Light; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics; D056950:Period Circadian Proteins; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012243:Rhodopsin / Q000235:genetics; D017299:Rod Opsins / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
D018797:Cell Cycle Proteins; D018690:Excitatory Amino Acid Agonists; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; C539024:Per1 protein, rat; C513312:Per2 protein, mouse; C513311:Per2 protein, rat; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D017299:Rod Opsins; D014157:Transcription Factors; D012243:Rhodopsin; D047068:Arylalkylamine N-Acetyltransferase; D007608:Kainic Acid