- Email: [email protected]
5-HT2 receptors could be primarily involved in the regulation of slow-wabe sleep in the rat
European Journal of Pharmacology, 137 (1987) 145-146
145
Elsevier EJP 063RC
Rapid communication
5-HT 2 receptors could be primarily involved in the regulation of slow-wave sleep in the rat Christine D u g o v i c * a n d A l b e r t W a u q u i e r Department of Neuropharmaeology, Janssen Pharmaceutiea, B-2340 Beerse, Belgium Received 10 April 1987, accepted 13 April 1987
Numerous experiments have demonstrated the existence of a positive relationship between brain serotonergic (5-HT) transmission and the amount of sleep. However, studies of unit activity of raphe neurons and of 5-HT release during the sleepwakefulness cycle have produced results which are inconsistent with this model (Jouvet, 1983). In addition, both 5-HT agonists and antagonists are known to decrease sleep, making it difficult to interpret the results of pharmacological manipulations of 5-HT receptors. Recently, it has been shown that ritanserin, a selective antagonist at central 5-HT2 receptors (Leysen et al., 1985), increased slow-wave sleep (SWS) (stages 3 and 4) in human volunteers (Idzikowski et al., 1986; Declerck et al., in press). This finding might suggest that 5-HT2 receptors exert an inhibitory control on SWS. Therefore, it is of interest to further investigate the role of 5-HT2 receptors in sleep regulation. For this purpose, sleep patterns were analyzed after pharmacological blockade a n d / o r stimulation of these receptors in the rat. A first experiment served to test the effects of ritanserin during the light period. In a second experiment, the preferential 5-HT2 agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-amipropane (DOM) (Shannon et al., 1984) was injected into animals pretreated with ritanserin. * To whom all correspondence should be addressed: Department of Neuropharmacology, Janssen Pharmaceutica, B2340 Beerse, Belgium.
Pharmacological treatments were performed in adult Wistar rats which were chronically implanted for standard sleep monitoring and were maintained on a 12 h light-dark schedule. The rats were divided into two groups and submitted to the following pharmacological protocol: group I (n = 6) received at the onset of the light period (9:30 a.m.) 0, 0.16, 0.63 or 2.5 m g / k g of ritanserin injected intraperitoneally (i.p.); group II (n = 6) received at 9:00 a.m. 0, 0.16, 0.63 or 2.5 m g / k g of ritanserin i.p., and 30 min later DOM at the dose of 0.63 m g / k g i.p. The animals were allowed to recover for 3 days between two treatments. Sleep patterns were analyzed for each of the two 4 h periods following the last injection and compared to baseline (saline injection under the same conditions). Statistical tests were performed by means of the two-tailed Student's t-test. Ritanserin injected alone at the beginning of the light period, induced a significant increase of deep SWS at the doses of 0.63 m g / k g (+19%, P < 0 . 0 1 ) and 2.5 m g / k g (+13%, P < 0 . 0 5 ) . The amounts of paradoxical sleep (PS) were reduced dose dependently from the dose of 0.16 m g / k g onwards ( - 4 2 % , P < 0.05 to - 6 7 % , P < 0.001). These effects occurred mainly during the first 4 h period following the injection. They persisted into the second 4 h period but were less pronounced. Deep SWS latency was not modified while PS latency was progressively prolonged with increasing doses of ritanserin. DOM injection (0.63 mg/kg) induced a significant decrease of deep SWS ( - 4 3 % , P < 0.001)
0014-2999/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
146 TABLE 1 Dose-response effects of ritanserin on deep SWS and PS in DOM-treated rats (0.63 m g / k g i.p.). Sleep amounts (mean + S.E.M. for 6 animals) were calculated for the 4 h period following the treatment and are expressed in percent of baseline (saline injection under the same conditions). The 5-HT 2 antagonist prevented the deep SWS insomnia in a dosedependent manner, whereas the PS insomnia was not modified. a p < 0.05, b p < 0.01, c p < 0.001 (two-tailed Student's t-test) as compared to baseline. Ritanserin ( m g / k g i.p.)
+ DOM ( m g / k g i.p.)
Deep SWS (%)
PS (%)
0 0.16 0.63 2.5
0.63 0.63 0.63 0.63
57_+4 c 83_+6 a 96-+6 113_+3 a
22_+11 c 35-+14 b 10-+ 5 c 35_+16 b
and a pronounced reduction of PS ( - 7 8 % , P < 0.001) during the first 4 h. As shown in table 1, pretreatment with ritanserin prevented the D O M induced deep SWS insomnia in a dose-dependent manner. PS amounts remained low after all the doses of ritanserin. This result indicates that 5-HT 2 receptors might be involved in the regulation of deep SWS. In order to confirm this hypothesis we carried out a further series of experiments with putative 5-HT~ agonists: 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methoxy3-(1,2,3,6-tetrahydro-4-pyridinyl)- 1H-indole (RU 24969). In these preliminary experiments 8-OHD P A T and R U 24969 at the dose of 0.63 m g / k g i.p. reduced the amounts of deep SWS to 44% (n = 4) and 51% (n = 3) respectively as compared to baseline during the first 4 h. Ritanserin at the doses of 0.16, 0.63 or 2.5 m g / k g i.p. did not reverse these effects. Our data show that the 5-HT 2 receptor antagonist ritanserin induces an increase of deep
SWS in the rat. These results agree with those obtained in humans (Idzikowski et al., 1986; Declerck et al., in press). Furthermore, we demonstrated that ritanserin produces a dose-related antagonism of the reduction in SWS induced by D O M . The fact that ritanserin is able to prevent the deep SWS insomnia after DOM, a preferential 5-HT 2 agonist, but not after 8 - O H - D P A T or RU 24969, both putative 5-HT 1 agonists, lends support to the hypothesis that 5-HT 2 receptors are primarily involved in the regulation of SWS. Hypotheses relating serotonergic transmission to sleep must take into account the different possible roles of 5-HT 1 and 5-HT 2 receptors. Further work with specific agonists and antagonists could resolve previous controversies on the role of serotonin in sleep.
References Declerck, A.C., A. Wauquier, P.H.M. Van der Ham-Veltman and Y. Gelders, Increase of slow wave sleep in h u m a n volunteers by the serotonin S2 antagonist ritanserin (the first exploratory polygraphic sleep study), Curr. Ther. Res. (in press). Idzikowski, C., F.J. Mills and R. Glennard, 1986, 5-Hydroxytryptamine-2 antagonist increases h u m a n slow wave sleep, Brain Res. 378, 164. Jouvet, M., 1983, Hypnogenic indolamine-dependent factors and paradoxical sleep rebound, in: Sleep 1982 (Karger, Basel) p. 2. Leysen, J.E., W. Gommeren, P. Van Gompel, J. Wynants, P.F.M. Janssen and P.M. Laduron, 1985, Receptor-binding properties in vitro and in vivo of ritanserin, a very potent and long acting serotonin-S 2 antagonist, Mol. Pharmacol. 27, 600. Shannon, M., G. Battaglia, R.A. (31ennon and M. Titeler, 1984, 5-HT 1 and 5-HT 2 binding properties of derivatives of the hallucinogen 1-(2,5-dimethoxyphenyl)-2-amipropane (2,5DMA), European J. Pharmacol. 102, 23.
145
Elsevier EJP 063RC
Rapid communication
5-HT 2 receptors could be primarily involved in the regulation of slow-wave sleep in the rat Christine D u g o v i c * a n d A l b e r t W a u q u i e r Department of Neuropharmaeology, Janssen Pharmaceutiea, B-2340 Beerse, Belgium Received 10 April 1987, accepted 13 April 1987
Numerous experiments have demonstrated the existence of a positive relationship between brain serotonergic (5-HT) transmission and the amount of sleep. However, studies of unit activity of raphe neurons and of 5-HT release during the sleepwakefulness cycle have produced results which are inconsistent with this model (Jouvet, 1983). In addition, both 5-HT agonists and antagonists are known to decrease sleep, making it difficult to interpret the results of pharmacological manipulations of 5-HT receptors. Recently, it has been shown that ritanserin, a selective antagonist at central 5-HT2 receptors (Leysen et al., 1985), increased slow-wave sleep (SWS) (stages 3 and 4) in human volunteers (Idzikowski et al., 1986; Declerck et al., in press). This finding might suggest that 5-HT2 receptors exert an inhibitory control on SWS. Therefore, it is of interest to further investigate the role of 5-HT2 receptors in sleep regulation. For this purpose, sleep patterns were analyzed after pharmacological blockade a n d / o r stimulation of these receptors in the rat. A first experiment served to test the effects of ritanserin during the light period. In a second experiment, the preferential 5-HT2 agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-amipropane (DOM) (Shannon et al., 1984) was injected into animals pretreated with ritanserin. * To whom all correspondence should be addressed: Department of Neuropharmacology, Janssen Pharmaceutica, B2340 Beerse, Belgium.
Pharmacological treatments were performed in adult Wistar rats which were chronically implanted for standard sleep monitoring and were maintained on a 12 h light-dark schedule. The rats were divided into two groups and submitted to the following pharmacological protocol: group I (n = 6) received at the onset of the light period (9:30 a.m.) 0, 0.16, 0.63 or 2.5 m g / k g of ritanserin injected intraperitoneally (i.p.); group II (n = 6) received at 9:00 a.m. 0, 0.16, 0.63 or 2.5 m g / k g of ritanserin i.p., and 30 min later DOM at the dose of 0.63 m g / k g i.p. The animals were allowed to recover for 3 days between two treatments. Sleep patterns were analyzed for each of the two 4 h periods following the last injection and compared to baseline (saline injection under the same conditions). Statistical tests were performed by means of the two-tailed Student's t-test. Ritanserin injected alone at the beginning of the light period, induced a significant increase of deep SWS at the doses of 0.63 m g / k g (+19%, P < 0 . 0 1 ) and 2.5 m g / k g (+13%, P < 0 . 0 5 ) . The amounts of paradoxical sleep (PS) were reduced dose dependently from the dose of 0.16 m g / k g onwards ( - 4 2 % , P < 0.05 to - 6 7 % , P < 0.001). These effects occurred mainly during the first 4 h period following the injection. They persisted into the second 4 h period but were less pronounced. Deep SWS latency was not modified while PS latency was progressively prolonged with increasing doses of ritanserin. DOM injection (0.63 mg/kg) induced a significant decrease of deep SWS ( - 4 3 % , P < 0.001)
0014-2999/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
146 TABLE 1 Dose-response effects of ritanserin on deep SWS and PS in DOM-treated rats (0.63 m g / k g i.p.). Sleep amounts (mean + S.E.M. for 6 animals) were calculated for the 4 h period following the treatment and are expressed in percent of baseline (saline injection under the same conditions). The 5-HT 2 antagonist prevented the deep SWS insomnia in a dosedependent manner, whereas the PS insomnia was not modified. a p < 0.05, b p < 0.01, c p < 0.001 (two-tailed Student's t-test) as compared to baseline. Ritanserin ( m g / k g i.p.)
+ DOM ( m g / k g i.p.)
Deep SWS (%)
PS (%)
0 0.16 0.63 2.5
0.63 0.63 0.63 0.63
57_+4 c 83_+6 a 96-+6 113_+3 a
22_+11 c 35-+14 b 10-+ 5 c 35_+16 b
and a pronounced reduction of PS ( - 7 8 % , P < 0.001) during the first 4 h. As shown in table 1, pretreatment with ritanserin prevented the D O M induced deep SWS insomnia in a dose-dependent manner. PS amounts remained low after all the doses of ritanserin. This result indicates that 5-HT 2 receptors might be involved in the regulation of deep SWS. In order to confirm this hypothesis we carried out a further series of experiments with putative 5-HT~ agonists: 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methoxy3-(1,2,3,6-tetrahydro-4-pyridinyl)- 1H-indole (RU 24969). In these preliminary experiments 8-OHD P A T and R U 24969 at the dose of 0.63 m g / k g i.p. reduced the amounts of deep SWS to 44% (n = 4) and 51% (n = 3) respectively as compared to baseline during the first 4 h. Ritanserin at the doses of 0.16, 0.63 or 2.5 m g / k g i.p. did not reverse these effects. Our data show that the 5-HT 2 receptor antagonist ritanserin induces an increase of deep
SWS in the rat. These results agree with those obtained in humans (Idzikowski et al., 1986; Declerck et al., in press). Furthermore, we demonstrated that ritanserin produces a dose-related antagonism of the reduction in SWS induced by D O M . The fact that ritanserin is able to prevent the deep SWS insomnia after DOM, a preferential 5-HT 2 agonist, but not after 8 - O H - D P A T or RU 24969, both putative 5-HT 1 agonists, lends support to the hypothesis that 5-HT 2 receptors are primarily involved in the regulation of SWS. Hypotheses relating serotonergic transmission to sleep must take into account the different possible roles of 5-HT 1 and 5-HT 2 receptors. Further work with specific agonists and antagonists could resolve previous controversies on the role of serotonin in sleep.
References Declerck, A.C., A. Wauquier, P.H.M. Van der Ham-Veltman and Y. Gelders, Increase of slow wave sleep in h u m a n volunteers by the serotonin S2 antagonist ritanserin (the first exploratory polygraphic sleep study), Curr. Ther. Res. (in press). Idzikowski, C., F.J. Mills and R. Glennard, 1986, 5-Hydroxytryptamine-2 antagonist increases h u m a n slow wave sleep, Brain Res. 378, 164. Jouvet, M., 1983, Hypnogenic indolamine-dependent factors and paradoxical sleep rebound, in: Sleep 1982 (Karger, Basel) p. 2. Leysen, J.E., W. Gommeren, P. Van Gompel, J. Wynants, P.F.M. Janssen and P.M. Laduron, 1985, Receptor-binding properties in vitro and in vivo of ritanserin, a very potent and long acting serotonin-S 2 antagonist, Mol. Pharmacol. 27, 600. Shannon, M., G. Battaglia, R.A. (31ennon and M. Titeler, 1984, 5-HT 1 and 5-HT 2 binding properties of derivatives of the hallucinogen 1-(2,5-dimethoxyphenyl)-2-amipropane (2,5DMA), European J. Pharmacol. 102, 23.