Maternal melatonin effects on clock gene expression in a nonhuman primate fetus.

In the adult mammal the circadian system, which allows predictive adaptation to daily environmental changes, comprises peripheral oscillators in most tissues, commanded by the suprachiasmatic nucleus (SCN) of the hypothalamus. The external environment of the fetus is provided by its mother. In primates, maternal melatonin is a candidate to entrain fetal circadian rhythms, including the SCN rhythms of metabolic activity. We found in the 90% of gestation capuchin monkey fetus expression of the clock genes Bmal-1, Per-2, Cry-2, and Clock in the SCN, adrenal, pituitary, brown fat, and pineal. Bmal-1, Per-2, and the melatonin 1 receptor (MT1) showed a robust oscillatory expression in SCN and adrenal gland, whereas a circadian rhythm of dehydroepiandrosterone sulphate was found in plasma. Maternal melatonin suppression changed the expression of Bmal-1, Per-2, and MT1 in the fetal SCN. These effects were reversed by maternal melatonin replacement. In contrast, neither maternal melatonin suppression nor its replacement had effects on the expression of Per-2 and Bmal-1 or MT1 in the fetal adrenal gland or the circadian rhythm of fetal plasma dehydroepiandrosterone sulphate. Our data suggest that maternal melatonin is a Zeitgeber for the fetal SCN but probably not for the adrenal gland.

Arousal and differential Fos expression in histaminergic neurons of the ascending arousal system during a feeding-related motivated behaviour.

Arousal depends on the concerted activity of the ascending arousal system (AAS) but specific stimuli may primarily activate some nuclei of this system. Motivated behaviours are characterized by behavioural arousal, although it is not known which AAS nuclei are active during a motivated behaviour. To address this issue, rats were rendered motivated for food by fasting them for 1 day and then were enticed with food that they could not obtain for varying periods of time. We studied the level of arousal by polysomnography or radiotelemetry, and Fos-ir in the AAS, during food enticing. We found a strong arousal and an early increase in Fos-ir in the histaminergic neurons from the tuberomammillary nucleus, after 30 min of enticing, followed by increased Fos-ir in the whole AAS if food enticing was prolonged to 1 or 2 hours. In contrast, food presentation to non-motivated rats did not increase arousal or Fos-ir in the tuberomammillary nucleus. As opposed to the active arousal of the motivated rats, passive arousal induced by sensory stimulation was associated with increased Fos-ir in the locus coeruleus and the orexin neurons, but not with increased Fos-ir in the tuberomammillary nucleus or in the other nuclei of the AAS. We conclude that the arousal during feeding-related motivated behaviour is associated primarily with the activation of the tuberomammillary nucleus, while the other arousal-related nuclei become active later on.

Prenatal development of the retinohypothalamic pathway and the suprachiasmatic nucleus in the sheep.

Circadian rhythms are present during fetal life in several mammalian species. To characterize the ontogeny of the neural mechanisms that account for circadian rhythmicity in a precocious species, we studied the prenatal development of the retinohypothalamic pathway in lambs (gestation period of 147 days), using horseradish peroxidase and wheat germ agglutinin as anterograde tracers. The suprachiasmatic nucleus was present as early as embryonic day 52 (E52). After E58, the suprachiasmatic nucleus reached its full number of neurons, estimated by the disector method in about 160,000 cells per nucleus at E62. The retinohypothalamic axons invaded the suprachiasmatic nucleus from E58, while neuroblasts were still migrating to the nucleus. At E62, there was a strong retinal projection that evolved until E121, when the retinal afferents established their definitive pattern of distribution in the ventral and central regions of the suprachiasmatic nucleus, and adjacent hypothalamic structures. The development of the retinohypothalamic pathway was delayed by about a week relative to the innervation of other subcortical visual centers. The present findings demonstrated an early prenatal development of the visual pathways in lambs, including the retinohypothalamic pathway, suggesting that the mechanisms for the visual entrainment of circadian rhythms in lambs may be functioning several weeks before birth.