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The Journal of Neuroscience, June 13, 2007, 27(24):6412-6416; doi:10.1523/JNEUROSCI.1432-07.2007

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Brief Communications
Suprachiasmatic Modulation of Noradrenaline Release in the Ventrolateral Preoptic Nucleus

Benoît Saint-Mleux,¹ Laurence Bayer,¹ Emmanuel Eggermann,¹ Barbara E. Jones,² Michel Mühlethaler,¹ and Mauro Serafin¹

¹Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and ²Department of Neurology and Neurosurgery, McGill University, Montreal Neurological Institute, Montreal, Quebec, Canada H3A 2B4

Correspondence should be addressed to Dr. Mauro Serafin, Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1 Rue Michel-Servet, 1211 Genève 4, Switzerland. Email: mauro.serafin{at}medecine.unige.ch

As the major brain circadian pacemaker, the suprachiasmatic nucleus (SCN) is known to influence the timing of sleep and waking. We thus investigated here the effect of SCN stimulation on neurons of the ventrolateral preoptic nucleus (VLPO) thought to be involved in promoting sleep. Using an acute in vitro preparation of the rat anterior hypothalamus/preoptic area, we found that whereas single-pulse stimulations of the SCN evoked standard fast ionotropic IPSPs and EPSPs, train stimulations unexpectedly evoked a long-lasting inhibition (LLI). Such LLIs could also be evoked in VLPO neurons by pressure application of NMDA within the SCN, indicating the specific activation of SCN neurons. This LLI was shown to result from the presynaptic facilitation of noradrenaline release, because it was suppressed in presence of yohimbine, a selective antagonist of ₂-adrenoreceptors. The LLI depended on the opening of a potassium conductance, because it was annulled at E_K and could be reversed below E_K. These results show that the SCN can provide an LLI of the sleep-promoting VLPO neurons that could play a role in the circadian organization of the sleep–waking cycle.

Key words: arousal; circadian; noradrenaline; presynaptic mechanism; rat; sleep; wakefulness

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Received Aug. 7, 2006; revised May 8, 2007; accepted May 8, 2007.

Correspondence should be addressed to Dr. Mauro Serafin, Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1 Rue Michel-Servet, 1211 Genève 4, Switzerland. Email: mauro.serafin{at}medecine.unige.ch

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