Elsevier

Neuroscience

Volume 92, Issue 2, May 1999, Pages 627-639
Neuroscience

Nitric oxide and sleep in the rat: a puzzling relationship

https://doi.org/10.1016/S0306-4522(99)00031-7Get rights and content

Abstract

To date, only a few studies indicate that nitric oxide may play a role in the regulation of the sleep–wake cycle. However, data reported are controversial and the part played by nitric oxide in sleep–wake cycle regulation still remains uncertain. In the present report, we studied the effects on sleep amounts of two different nitric oxide synthase inhibitors: N-nitro-l-arginine methyl ester, a non-selective nitric oxide synthase inhibitor, and 7-nitro-indazole, a specific inhibitor of neuronal nitric oxide synthase. The above compounds were administered via two routes, i.e. intraperitoneally or locally in the dorsal raphe nucleus, a structure involved in sleep regulation. In order to evaluate their efficiency to inhibit nitric oxide synthesis in the rat brain, they were first administered intraperitoneally to a group of animals, and the cortical release of nitric oxide was determined by means of voltammetric measurements. N-Nitro-l-arginine methyl ester (100 mg/kg, i.p.) did not affect the cortical release of nitric oxide, whereas it increased both slow-wave sleep and paradoxical sleep durations. On the contrary, 7-nitro-indazole (40 mg/kg, i.p.) significantly decreased the cortical release of nitric oxide (−25%) and paradoxical sleep duration. Furthermore, following microinjection of either N-nitro-l-arginine methyl ester or 7-nitro-indazole at 100 ng/0.20 μl into the nitric oxidergic cell area of the dorsal raphe nucleus, decreases in paradoxical sleep duration were obtained (−32.8% and −25.3%, respectively).

The results obtained support the existence of a duality in the sleep regulation modalities exerted by nitric oxide, i.e. a peripheral inhibiting influence and a central facilitating role for the nitric oxide–serotoninergic neurons of the dorsal raphe nucleus.

Section snippets

Animals and drugs

The protocol of this study was approved by the French Ministry of Agriculture (no. 03-505), and efforts were made to minimize animal suffering and to reduce the number of animals used. Male Sprague–Dawley (Iffa–Credo, l'Arbresle, France) rats weighing 250–350 g were used in this study. l-NAME (Sigma) was dissolved in 0.9% NaCl and the pH adjusted to 7.2 with NaOH. For i.p. injections, 7-NI (Tocris Cookson) was suspended in peanut oil (Sigma) by sonication, while for local microinjections, it was

Nitric oxide voltammetric measurements

l-NAME administered i.p. did not induce significant variations in the voltammetric NO signal measured in the cortex of anesthetized rats. This lack of effect persisted for at least 80 min, even when the highest dose of the inhibitor (200 mg/kg) was administered (Fig. 1).

Polygraphic recordings

The i.p. administration of l-NAME (100 mg/kg), at the beginning of the dark period, was followed by an important increase in the amounts of SWS and PS. The effects started 1 h after the injection and remained constant over the

Discussion

The main findings obtained in this study indicate the following:

  • 1.

    The i.p. administration of the non-selective NOS inhibitor, l-NAME, at 100 mg/kg, does not influence the cortical release of NO measured by voltammetry, but enhances the durations of both SWS and PS.

  • 2.

    The i.p. administration of the selective nNOS inhibitor, 7-NI, at 40 mg/kg, produces a long-lasting decrease in the cortical release of NO and reduces duration of PS.

  • 3.

    Intra-DRN microinjections of either l-NAME or 7-NI (100 ng in 0.20 ml)

Conclusion

The present findings are in agreement with other studies, which proposed that an intact NO-synthesizing system is required for normal sleep regulation. However, the data reported here underline the existence of a dual role for NO in sleep–wake cycle regulation, i.e. a sleep-inhibiting influence of peripheral origin and a PS-facilitating role at the central level, notably for the NO–5-HT component of the DRN. In view of the great complexity of the anatomical elements of the brain synthesizing

Acknowledgements

This research was supported by INSERM, CNRS, Rône-Alpes region and Fondation pour la Recherche Médicale 98. We also thank C. Limoge for improving the English text and G. Debilly for statistical analysis.

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