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  • 1
    Electronic Resource
    Electronic Resource
    Norepinephrine Release in the Rat Pineal Gland: The Input from the Biological Clock Measured by In Vivo Microdialysis (1996)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 66 (1996), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The sympathetic innervation of the rat pineal gland was investigated, measuring the norepinephrine (NE) release by on-line in vivo microdialysis. NE was assayed using an HPLC method with precolumn derivatization and fluorescence detection. Its high sensitivity and reliability made 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 levels, the monoamine reuptake inhibitor cocaine was added to Ringer's solution at concentrations of 10−6 and 10−5M. This resulted in increases of neurotransmitter output of 167 and 219%, respectively, but did not change the qualitative and/or quantitative outcome of other experiments. Perfusion with 10−6M tetrodotoxin for 1 h resulted in a decrease of the NE release by 〉80%, whereas perfusion with the α2-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 presynaptic α2-receptors. Long-term (i.e., 16 h) measurements are described, showing the circadian properties of NE release. A pronounced rhythm is reported, showing extremely sharp transitions between low daytime and high nighttime values. Increases and decreases are reported 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 circadian rhythm of melatonin release and can thus be considered as the primary clock signal, inducing the nightly production of melatonin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1996.66020748.x
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  • 2
    Electronic Resource
    Electronic Resource
    Microdialysis of Melatonin in the Rat Pineal Gland: Methodology and Pharmacological Applications (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The present study describes the development of a new technique to measure melatonin contents in the pineal gland of freely moving rats, by means of on-line microdialysis. The transcerebral cannula was modified, and a sensitive assay of melatonin, using HPLC with fluori-metric detection, was set up. With this system it is possible to monitor the melatonin levels on-line in the pineal gland during day-and nighttime. The nightly increase in melatonin release was recorded. Tetrodotoxin had an inhibitory effect on nighttime levels, whereas even high concentrations did not alter the daytime level. From this we conclude that neuronal activity is necessary to synthesize melatonin and that during daytime no net neuronal activity is present. Melatonin levels could be greatly enhanced by systemic administration of the β-agonist isoprenaline (ISO). Also, local infusion of ISO or 8-bromoadenosine 3′,5′-cyclic monophosphate, an analogue of the second messenger cyclic AMP, resulted in increased melatonin levels, demonstrating the presence of β-adrenergic receptors, coupled to a cyclic AMP-based second messenger system, on the pineal gland. Injection of phenylephrine had no effect on daytime levels. Only when administered during ISO-induced stimulation of melatonin release did it enhance this stimulated release. This proved the regulatory role of α1-receptors on pinealocytes. The method presented is of special interest for investigating the innervation of the pineal gland and the biochemical processes that regulate the biosynthesis of melatonin. Also, for studies on the diurnal rhythms of melatonin release and factors that influence these rhythms in freely moving animals, this model will be of great value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03605.x
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  • 3
    Electronic Resource
    Electronic Resource
    Exogenous melatonin entrains rhythm and reduces amplitude of endogenous melatonin: An in vivo microdialysis study (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 20 (1996), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The circadian rhythm of melatonin production was studied using on-line, in vivo microdialysis in the rat pineal gland. With this technique it was possible to record a pronounced melatonin rhythm with very high time resolution. Three phase-markers of the rhythm were calculated from the data, indicating increase (IT50), decrease (DT50) and amplitude of the rhythm. Comparing these phase markers led to several conclusions. Entrainment of the rhythm under constant darkness was performed with melatonin administration at different circadian stages [circadian time (CT) 8 and CT12] and for different periods of time (2 weeks and 4 weeks). Also, entrainment was established by applying 15 min light pulses at CTO. Entrainment of IT50 with melatonin partially uncoupled it from DT50. Four weeks entrainment in constant darkness (DD) caused a phase-delay in DT50 of 2.2 hr. Entrainment of IT50 with light at CTO for 2 weeks in DD caused a phase-advance in DT50 of 1.3 hr. The entrainment with melatonin was restricted to a narrow window for melatonin to be applied, since injections at CT8 did not result in entrainment. Exogenous melatonin reduced the amplitude of the rhythm of endogenous melatonin. This effect was not circadian time dependent, since administration at CT8 for 2 weeks and at CT12 for 4 weeks resulted in a highly significant decrease. Light did not seem to have an effect on the amplitude. The data presented here provide us with new information about the nature of entrainment by melatonin. Since the present development of melatonergic agents for clinical use focuses on the entrainment capacity, effects of these compounds on amplitude of circadian rhythms needs to be addressed. In vivo microdialysis seems to be a good technique for that.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1996.tb00235.x
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    Paper (German National Licenses)
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