Wj. Drijfhout et al., NOREPINEPHRINE RELEASE IN THE RAT PINEAL-GLAND - THE INPUT FROM THE BIOLOGICAL CLOCK MEASURED BY IN-VIVO MICRODIALYSIS, Journal of neurochemistry, 66(2), 1996, pp. 748-755
The sympathetic innervation of the rat pineal gland was investigated,
measuring the norepinephrine (NE) release by on-line in vivo microdial
ysis, NE was assayed using an HPLC method with precolumn derivatizatio
n and fluorescence detection. Its high sensitivity and reliability mad
e it very suitable to monitor the low levels of NE in the dialysates (
12.5 fmol during nighttime, 3 fmol during daytime). To increase NE lev
els, the monoamine reuptake inhibitor cocaine was added to Ringer's so
lution at concentrations of 10(-6) and 10(-5) M. This resulted in incr
eases of neurotransmitter output of 167 and 219%, respectively, but di
d not change the qualitative and/or quantitative outcome of other expe
riments, Perfusion with 10(-6) M tetrodotoxin for 1 h resulted in a de
crease of the NE release by >80%, whereas perfusion with the alpha(2)-
receptor antagonist yohimbine caused a twofold increase. These results
indicate that the NE release in the rat pineal was of neuronal origin
and regulated by a negative feedback mechanism involving inhibitory p
resynaptic alpha(2)-receptors. Long-term (i.e., 16 h) measurements are
described, showing the circadian properties of NE release. A pronounc
ed rhythm is reported, showing extremely sharp transitions between low
daytime and high nighttime values. Increases and decreases are report
ed to occur within the duration of collecting one sample (20 min). For
comparison, the rhythm of melatonin release was also recorded. The on
and off switches of the sympathetic input correlated well with the ci
rcadian rhythm of melatonin release and can thus be considered as the
primary clock signal, inducing the nightly production of melatonin.