Effects of acute and chronic treatment with amitryptyline on the sleep-wake activity of rats

A single dose of hypnotic corrects sleep and EEG abnormalities in symptomatic Huntington's disease mice

Sleep and electroencephalogram abnormalities are prominent early features of Huntington's disease (HD) that typically appear before the onset of characteristic motor symptoms. The changes in sleep and electroencephalogram seen in HD patients are largely recapitulated in mouse models of HD such as transgenic R6/2 lines. To test whether or not drugs with hypnotic properties can correct the sleep and electroencephalogram abnormalities seen in HD mice, we treated male wild-type (WT; N = 7) and R6/2 mice (N = 9) acutely with intraperitoneal injections of vehicle, zolpidem (5, 10 or 20 mg/kg) or amitriptyline (5, 10 or 20 mg/kg), and then monitored their sleep-wake behavior. In R6/2 mice, both zolpidem and amitriptyline suppressed the abnormally high REM sleep amount and electroencephalographic gamma (30-46 Hz) oscillations in a dose-dependent manner. Amitriptyline's effect on sleep was similar in both genotypes, whereas zolpidem showed significant genotype differences. Zolpidem exerted a strong hypnotic effect in WT mice by increasing electroencephalographic delta power, doubling the mean bout duration and the total amount of non-rapid eye movement sleep. However, no such effect was seen in R6/2 mice. Our study demonstrates that the pathophysiological changes seen in sleep and electroencephalogram are not 'hard-wired' in HD brain and can be reversed even at late stages of the disease. The diminished hypnotic effect of zolpidem suggests that the GABAergic control of sleep-wake states is impaired in HD mice. A better understanding of the neurochemical basis underlying these abnormalities should lead to more effective and rational therapies for HD.

Acute administration of the novel serotonin and noradrenaline reuptake inhibitor, S33005, markedly modifies sleep-wake cycle architecture in the rat

RATIONALE

The interrelationship between depressive states and sleep-wake cycle architecture is characterised by a decreased latency to the first paradoxical sleep (PS) episode, together with an enhancement of PS during the first part of the night. Conversely, slow-wave sleep (SWS) is decreased and intermittent awakenings increased. Notably, antidepressant treatment is generally associated with a diminution of PS.

OBJECTIVES

In light of these observations, we examined the influence of acute administration of the novel mixed serotonin-noradrenaline reuptake blocker, (-)1-(1-dimethylaminomethyl 5-methoxybenzocyclobutan-1-yl)-cyclohexanol HCl (S33005), upon sleep-wake architecture in rats.

METHODS

Animals were injected with vehicle or incremental doses of S33005 at the onset of either the dark or light periods. Digitised polygraphic recordings were performed, and changes evoked by S33005 were determined over 24-h recording periods, i.e., number and duration of sleep-wake episodes, latencies to PS and SWS, power band spectra of the electroencephalogram (EEG) and circadian changes.

RESULTS

At 0.04 mg/kg, S33005 was inactive, whereas at 0.63 mg/kg, it modestly increased PS latencies and diminished PS duration during the light period. At 10 mg/kg, S33005 reduced markedly PS duration for about 4-h when injected prior to both light and dark periods. Latency to PS was prolonged, and the circadian acrophase was delayed. These effects are in keeping with previous studies of monoamine reuptake inhibitors, but, notably, SWS duration was increased when S33005 was injected at the onset of the light phase (+4%). These changes occurred without marked modifications in circadian rhythmicity or EEG spectral band power. Finally, even at the highest dose of S33005, only a limited rebound of SWS (+5%) and PS (+10%) was apparent. Amongst antidepressant to date examined, this is an original profile of influence upon sleep patterns.

CONCLUSIONS

These results demonstrate a pattern of influence of S33005 upon sleep-wake architecture in rats which is globally consistent with antidepressant properties, but with a distinctive enhancement of restorative slow-wave sleep.

REM sleep - by default?

Elements of three old, overlapping theories of REM sleep (REM) function, the Ontogenetic, Homeostatic and Phylogenetic hypotheses, together still provide a plausible framework - that REM (i) is directed towards early cortical development, (ii) "tones up" the sleeping cortex, (iii) can substitute for wakefulness, (iv) has a calming effect. This framework is developed in the light of recent findings. It is argued that the "primitiveness" of REM and its similarity to wakefulness liken it to a default state of "non-wakefulness" or a waking antagonist, anteceding "true" (non-REM) sleep. The "toning up" is reflected by inhibition of motor, sensory and (importantly) emotional systems, together pointing to integrated "flight or fight" activity, that preoccupies/distracts the organism when non-REM is absent and wakefulness unnecessary. Dreaming facilitates this distraction. In rodents, REM can provide stress coping and calming, but REM deprivation procedures incorporating immobility may further enhance stress and confound outcomes. REM "pressure" (e.g. REM rebounds) may be a default from a loss of inhibition of REM by non-REM. REM can be reduced and/or replaced by wakefulness, without adverse effects. REM has little advantage over wakefulness in providing positive cerebral recovery or memory consolidation.

Effects of acute and chronic treatment with trazodone, an antidepressant, on the sleep-wake activity in rats

Rats were treated with trazodone (2.5 or 10 mg kg-1) twice a day (at light and dark onset) for 11 days, after chronic injection of physiological saline. The sleep-wake activity was recorded for 24 h on the baseline day (saline), on trazodone days 1, 5 and 11, and also on day 12, when physiological saline was injected again (withdrawal day). Trazodone administration increased non-REM sleep. The enhancement of non-REM sleep was dose-related and more pronounced during the dark cycle. The promotion of non-REM sleep was enhanced during the chronic treatment. There were no consistent changes in REM sleep. Spectral analysis of the EEG revealed an increase in slow-wave activity after administration of the high dose (10 mg kg-1) of the drug. It is concluded that trazodone, a clinically effective antidepressant, has a non-REM sleep-promoting effect. It is speculated that the promotion of sleep by trazodone may be mediated by serotonergic mechanisms.

Effects of chronic treatment with two selective 5-HT2 antagonists on sleep in the rat

The effect of chronic administration of 2(2-dimethylaminoethylthio)-3-phenylquinoline (ICI-169,369) and 2(2-dimethylamino-2-methylpropylthio)-3-phenylquinoline (ICI-170,809), two selective 5-HT2 antagonists, on sleep was studied in rats. As previously shown, the acute effect of ICI-170,809 was to increase latency to rapid eye movement sleep (REMS), decrease the number of REM periods (REMPs), suppress the cumulative amount of REMS over 12 h, and increase the duration of REMPs in the first 6 h, while having no effect on non-REM sleep (NREMS). Administration of ICI-169,369 had similar effects except no change was seen in the duration of REMPs and cumulative REMS was suppressed for 24 h. When given 2 x daily for 5 days, tolerance to the REMS suppressant effects developed in both drugs. After discontinuation of treatment, a REMS rebound occurred after ICI-170,809, but not ICI-169,369. No significant effect on NREMS was seen after administration of ICI-170,809, whereas ICI-169,369 lowered 24-h cumulative NREMS on the fifth day of administration.

The light-dark cycle modulates the effects of ritanserin on sleep-wakefulness patterns in the rat

The 5-HT2 receptor antagonist ritanserin (0.63 mg/kg IP) produced differential effects on sleep-wakefulness patterns in rats when administered during the light or dark period: an increase in the duration of deep slow wave sleep at the expense of light slow wave sleep, paradoxical sleep and wakefulness when injected during the light period, and no major sleep alteration when given at dark onset. Since circadian variations in serotonin receptor density might modulate the sleep response, we examined the effects of ritanserin on sleep in rats exposed to continuous light for 10 days, and whether 5-HT2 receptors were affected in separate groups of rats exposed to similar conditions. No significant changes in the KD- and Bmax -values of various receptors were found. However, ritanserin produced greater effects in continuous light conditions than when given during the light period in the 12-hr light-dark condition. This suggests a possible role of 5-HT2 receptors in the organization of sleep when the environmental photoperiod is disturbed.

Effects of serotonin and noradrenaline uptake blockers on wakefulness and sleep in cats

The aim of the study was to examine the role of serotonergic (5-HT) and noradrenergic mechanisms in the regulation of wakefulness and sleep. For this purpose, adult cats with implanted electrodes for EEG, EOG and EMG were exposed to the 5-HT uptake blocker citalopram (0.1, 0.5 and 5.0 mg/kg intraperitoneally) and the noradrenaline uptake blocker prindamine (5 mg/kg intraperitoneally) at the start of continuous 16-hour sleep-wake recordings. Citalopram increased deep slow wave sleep and decreased REMS. Also prindamine decreased REMS but initially increased the proportion of time spent in the state of active wakefulness. Furthermore, to examine the interactions between 5-HT-nergic and noradrenergic mechanisms in the regulation of sleep, the administration of citalopram was preceded by intraperitoneal injections of phentolamine (10 mg/kg), an alpha-antagonist, and propranolol (5 mg/kg), a beta-antagonist. Phentolamine was totally ineffective against citalopram whereas propranolol partially counteracted the effects of citalopram on sleep. Prindamine was combined with the alpha-antagonists yohimbine (1 mg/kg), phentolamine (10 mg/kg) and prazosin (1 mg/kg) or with the beta-antagonist propranolol (5 mg/kg). Yohimbine was without any effect on REMS, phentolamine partly antagonized prindamine-induced decrease in the percentage of REMS, and prazosin only prolonged REMS latency and reduced deep SWS as well. Propranolol partially antagonized the prindamine-induced initial increase in active wakefulness time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of age on antidepressant kinetics and memory in Fischer 344 rats

Experiments were conducted in young (3-4 months) and old (24-25 months) male Fischer 344 rats to assess the effects of amitriptyline, scopolamine, and zimelidine on short term memory using an eight arm radial maze paradigm. Kinetic analyses employing serial blood sampling were also conducted for amitriptyline and zimelidine in an attempt to determine if age-related deficits in performance could be related to changes in pharmacokinetics. In the maze, acquisition of performance was significantly decreased in old rats compared to young. Amitriptyline (5 mg/kg) produced a significant decrement in maze performance on day four of a five day testing period in both young and old rats, while scopolamine (1 mg/kg) produced an initial decrement on day one, followed by a return towards pre-treatment levels in these two age groups. Zimelidine (5 mg/kg) produced no performance decrement in either young or old rats. Kinetic analyses revealed an increased half-life, slower plasma clearance, and a larger volume of distribution of amitriptyline and zimelidine in old rats. Although the kinetic parameters in aged rats exhibited a change in the direction of a decreased ability to metabolize both drugs, this change was not of sufficient magnitude to produce an additive detrimental effect on maze performance.

Effects of acute and chronic treatment with an atypical antidepressant drug, nomifensine, on the sleep-wake activity in rats

After the chronic administration of saline, rats were treated with nomifensine (0.1 or 1.0 mg/kg, twice a day, at light and dark onset) for 11 days. The sleep-wake activity was recorded for 24 h on the baseline day (saline), on nomifensine days 1, 5 and 11, and also on day 12, when saline was injected again (withdrawal day). Another group of rats was treated with saline throughout the experiment, without significant effect on the sleep-wake activity. The smaller dose of nomifensine increased non-REM sleep (NREMS) at the expense of wakefulness (W) in the light period. The effect persisted throughout the chronic treatment. A late increase in REM sleep (REMS) was noted on nomifensine days 5 and 11. Nomifensine failed to affect the sleep-wake activity in the dark period. On withdrawal, the baseline percentages of the vigilance states were recovered. As evaluated through spectral analysis of the EEG, the increase in NREMS was accompanied by an increase in slow wave activity. The higher dose of nomifensine elicited an increase in W and a reduction in both sleep states, followed by changes in W and NREMS in the opposite directions. These effects were evident in both the light and the dark periods of the day. Chronic treatment resulted in circadian variations in the effects. Withdrawal of the drug abolished the arousal reaction, but the late increase in NREMS persisted. The dose-dependent biphasic effects of nomifensine on sleep-wake activity can be explained by considering the proposed indirect dopamine and possibly noradrenaline agonist activity of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)