CLONING EXPERIMENTS AND DEVELOPMENTAL EXPRESSION OF BOTH MELATONIN RECEPTOR ME1(1A) MESSENGER-RNA AND MELATONIN BINDING-SITES IN THE SYRIAN-HAMSTER SUPRACHIASMATIC NUCLEI
F. Gauer et al., CLONING EXPERIMENTS AND DEVELOPMENTAL EXPRESSION OF BOTH MELATONIN RECEPTOR ME1(1A) MESSENGER-RNA AND MELATONIN BINDING-SITES IN THE SYRIAN-HAMSTER SUPRACHIASMATIC NUCLEI, Molecular brain research, 60(2), 1998, pp. 193-202
The suprachiasmatic nuclei (SCN) are implicated in the control of circ
adian biological rhythms, and especially the melatonin nocturnal synth
esis. In numerous rodents, melatonin has been shown to feed back on th
e SCN activity through high affinity receptors. In contrast, Syrian ha
mster SCN activity is unresponsive to melatonin injections. As this la
ck of effect could be linked to a developmental loss of SCN melatonin
receptors, the goals of the present study were 1) to report in Syrian
hamster SCN, and pars tuberalis (PT) as a control, a complete pattern
of the postnatal (PN) development of the melatonin receptor density an
d 2) to investigate whether the regulation of the Mel(1a) mRNA express
ion could be implicated in the post natal variations of the melatonin
binding capacities. We first subcloned by PCR a partial cDNA encoding
the Mel(1a) receptor from Syrian hamster SCN. Subsequent quantificatio
n of Mel(1a) mRNA. expression and melatonin receptor density revealed
that in the PT and SCN, both Mel(1a) mRNA expression and melatonin bin
ding capacities declined abruptly between PN 0 and PN 8. Afterwards, i
n the PT, both parameters went up until they got stabilized in adultho
od. Therefore, in the PT, post natal melatonin receptor density variat
ions were highly correlated with post natal variations of the Mel(1a)
mRNA expression. In the SCN, after PN 8, the melatonin receptor densit
y followed its drop and then declined by more than 92% between post na
tal day 0 (PN 0) and PN 60 (12.11 +/- 0.27 vs. 0.94 +/- 0.08 fmol/mg p
rotein at PN 0 and PN 60 respectively). In contrast, Mel(1a) mRNA expr
ession only slightly went down after PN 8 and got stabilized in adult
age at 42% of the birth day expression level. These results show that
Syrian hamster SCN undergo a dramatic post natal loss of their melaton
in receptors that could explain the lack of effect of melatonin inject
ions on SCN circadian activity. Furthermore, this SCN binding capaciti
es decline could not be attributed to an inhibition of the mRNA expres
sion, but rather to a post transcriptional blockade of the Mel(1a), re
ceptor expression. (C) 1998 Elsevier Science B.V. All rights reserved.