Daily variations in serotonin metabolism in the suprachiasmatic nucleus of the rat: influence of oestradiol impregnation

Héry, Micheline; Faudon, M.; Dusticier, G.; Héry, F.

doi:10.1677/joe.0.0940157

Cited by 65 publications

(23 citation statements)

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“…However, they measured only the two points during 24 h. More values need to be observed at different points to characterize 5-HT and NE rhythms. Although we did not find any 5-HT rhythms in the SC, Hery et al (15) found a marked 5-HT rhythm in the SC at the beginning of the dark period.…”

Section: Discussioncontrasting

confidence: 99%

Twenty-Four Hour Rhythms of Norepinephrine and Serotonin in Nucleus Suprachiasmaticus, Raphe Nuclei, and Locus Coeruleus in the Rat

Semba

Toru

Mataga

1984

Sleep

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Summary: Twenty-four hour rhythms, at 4 h intervals, of norepinephrine (NE) and serotonin (5-HT) contents were investigated in the rat brain regions where sleep-wakefulness regulation is believed to occur: Nucleus suprachiasmaticus (SC), n, raphe dorsalis (RD) and medialis (RM), and locus coeruleus, Cosinor method of Halberg was applied to evaluate sinusoidal rhythmicity of the measured values, In the SC only NE showed a significant rhythm with a peak value at the beginning of the light period, which suggests that a NE mechanism may be involved in oscillating biological rhythms in rats, In the RD and RM, 5-HT and 5-hydroxyindoleacetic acid increased significantly during the light period, Moreover, 5-HT rhythm in the RD was maintained even under constant dark conditions, which suggests that 5-HT rhythm in the RD may be endogenous, Key Words: Twentyfour hour rhythm-Norepinephrine-Serotonin-Nucleus suprachiasmaticusRaphe nuclei-Locus coeruleus, Most physiological functions in rodents, such as locomotion, feeding and drinking, thermoregulation, and hormonal secretion, exhibit circadian rhythms. These rhythms are believed to be controlled by a pacemaker located in the nucleus suprachiasmaticus (SC) of the hypothalamus (1). Physiological rhythms may be affected by biochemical changes in the brain. It has been demonstrated that norepinephrine (NE) and serotonin (5-HT) contents in the whole brain or some brain regions change over a 24 h period (2-6). Recently Ibuka et al. (7) found that the sleep-wakefulness cycle is also regulated by the circadian pacemaker in the SC. Although Jouvet has recently modified his monoamine hypothesis of sleep and stressed the importance of the cholinergic mechanisms (8,9), studying the interactions between 5-HT and NE in sleep-wakefulness regulation is still useful.We have studied the 24 h changes in 5-HT and NE contents in the n. raphe dorsalis (RD) and medialis (RM), locus coeruleus (LC), and SC in the rat. To investigate whether a 24 h rhythm in the raphe nuclei is endogenous, an additional experiment was carried out.

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Section: Discussioncontrasting

confidence: 99%

Twenty-Four Hour Rhythms of Norepinephrine and Serotonin in Nucleus Suprachiasmaticus, Raphe Nuclei, and Locus Coeruleus in the Rat

Semba

Toru

Mataga

1984

Sleep

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“…Available data indicate a participation of the se rotoninergic mechanism in the positive feed-back effect of es trogen on LH secretion in prepubertal and adult female rats [7,8,11,12] suggesting that the serotoninergic system has an inhibitory effect on this mechanism [12]. On the other hand, 5-hydroxytryptophan (5-HTP) induces LH release in female prepubertal rats, but not in males [11].…”

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Effect of Serotoninergic System on FSH Secretion in Male and Female Rats: Evidence for Stimulatory and Inhibitory Actions

Justo¹,

Rossano²,

Szwarcfarb³

et al. 1989

Neuroendocrinology

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The present experiments were designed to assess the effect of the serotoninergic system on FSH secretion in prepubertal (16-, 18-, 20-, 26- and 30-day-old) and adult (60-day-old) male and female rats. The intraperitoneal administration of 5-hydroxytryptophan (5-HTP), a serotonin (5-HT) precursor, induced a significant increase of FSH levels in male rats at 16, 26, 30 and 60 days of age (p < 0.01) but not at 18 and 20 days. In the females, no modifications in FSH concentrations in prepubertal and adult rats were observed after 5-HΓP injection. These results indicate that there are sexual differences in the effect of the serotoninergic system on FSH secretion. Orchidectomy performed in prepubertal (30-day-old) and adult rats (60 days) besides increasing FSH levels, reversed the response of this hormone to 5-HTP administration, since in castrated rats the 5-HT precursor induced a significant decrease in serum FSH concentrations. The administration of 5-HTP to 30 day-old castrated rats treated with testosterone induced FSH release as it did in control animals of this age. In the adult castrated rats the administration of testosterone abolished the inhibitory effect of 5-HTP observed in castrated rats but did not invoke the stimulatory action of 5-HTP observed in the controls. This difference between prepubertal and adult rats appears to be related to a decrease in the sensitivity to testosterone of the central mechanism which controls FSH secretion. These results indicate that 5-HΓP stimulates FSH release in normal rats and inhibits FSH release in castrated rats, testosterone concentration being a relevant factor in determining the ‘type’ of effect produced. The hypothalamic concentrations of 5-HT and 5-hydroxy-indoleacetic acid (5-HIAA) are significantly higher at the ages at which 5-HTP induces FSH release than at other ages suggesting that hypothalamic turnover of these substances is related to the releasing effect of 5-HTP on FSH.

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“…The facilitatory effect of 5HT occurs during a 'critical period' [6,10]; therefore, 5HT's influence upon the LH surge, like the surge itself, is linked in some way to the time of day. These quantitative and temporal perculiarities of 5HT's facilitatory effect on LH surges suggest that the daily pattern of 5HT synthesis and degradation, producing regu lar changes in its hypothalamic content [ 13,23], is function ally important.…”

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confidence: 99%

Quantitative and Temporal Aspects of Serotonin’s Facilitatory Action on Phasic Secretion of Luteinizing Hormone in Female Rats

Walker¹

1983

Neuroendocrinology

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The purpose of this study was to determine if the circadian rhythm in hypothalamic serotonin (5HT) contributes to the facilitatory effect of the amine upon estrogen-induced luteinizing hormone (LH) surges in ovariectomized rats. p-Chlorophenylalanine (pCPA; 250 mg/kg) blocked 5HT synthesis, reduced its content and abolished its circadian rhythm in the hypothalamus. 5-Hydroxytryptophan (5HTP; 100 mg/kg) administered with pargyline (75 mg/kg), a monoamine oxidase inhibitor, stimulated 5HT synthesis, increased its levels and also eliminated daily changes in hypothalamic 5HT. Thus, drugs with opposite effects on 5HT synthesis had the same effect on the hypothalamic 5HT circadian rhythm. Besides blocking daily changes in 5HT, pCPA and 5HTP also blocked LH surges in ovariectomized rats receiving estrogen supplements. On the other hand, both circadian rhythms were reinstated when pCPA-treated rats were also given 5HTP, i.e., 5HTP which was initially inhibitory, became facilitatory to LH surges in rats pretreated with pCPA. These findings suggest that the amount of hypothalamic 5HT as well as its metabolic pattern are important to the facilitatory effect of 5HT on phasic LH secretion. To test this hypothesis further, 5HTP was given in lower doses (50 mg/kg) and without pargyline, in order to attenuate rather than obliterate the hypothalamic 5HT rhythm. Injections of 5HTP at 18.00 h and 12 h later at 06.00 h reduced the daily fluctuations in hypothalamic 5HT content and also attenuated estrogen-induced LH surges. When increasing doses of 5HTP were used to enhance hypothalamic 5HT content, an inverse correlation (p < 0.01) with serum LH content was observed over the range 5 kg–100 mg/kg 5HTP. The effect of progesterone upon daily changes in hypothalamic 5HT was also determined. When administered at 10.00 h, progesterone significantly potentiated (p < 0.01) phasic secretion of LH and also increased (p < 0.05) peak, but not baseline, hypothalamic 5HT levels, thus amplifying the neurotransmitter’s circadian rhythm. Furthermore, when 5HTP was given 1 h before progesterone, the onset of phasic LH secretion was advanced. This change in the timing of phasic LH secretion was associated with early accumulation of 5HT in the hypothalamus. Hypothalamic 5HT turnover was increased by 5HTP treatment in rats made supersensitive to 5HT stimulation, and LH surges were also potentiated under these conditions. The results of this study suggest that the daily pattern of hypothalamic 5HT metabolism influences the pattern of LH secretion during the estrogen-positive feedback response. Since the size of LH surges correlates with daily fluctuations in hypothalamic 5HT, then a facilitatory signal whose intensity is related to the magnitude of these daily changes may be generated during the post-acrophase component of the 5HT circadian rhythm.

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Daily variations in serotonin metabolism in the suprachiasmatic nucleus of the rat: influence of oestradiol impregnation

Cited by 65 publications

References 0 publications

Twenty-Four Hour Rhythms of Norepinephrine and Serotonin in Nucleus Suprachiasmaticus, Raphe Nuclei, and Locus Coeruleus in the Rat

Twenty-Four Hour Rhythms of Norepinephrine and Serotonin in Nucleus Suprachiasmaticus, Raphe Nuclei, and Locus Coeruleus in the Rat

Effect of Serotoninergic System on FSH Secretion in Male and Female Rats: Evidence for Stimulatory and Inhibitory Actions

Quantitative and Temporal Aspects of Serotonin’s Facilitatory Action on Phasic Secretion of Luteinizing Hormone in Female Rats

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