[Sleep and biological rhythms in depression. Changes caused by antidepressants]

Oscillatory serotonin function in depression

Oscillations in brain activities with periods of minutes to hours may be critical for normal mood behaviors. Ultradian (faster than circadian) rhythms of mood behaviors and associated central nervous system activities are altered in depression. Recent data suggest that ultradian rhythms in serotonin (5HT) function also change in depression. In two separate studies, 5HT metabolites in cerebrospinal fluid (CSF) were measured every 10 min for 24 h before and after chronic antidepressant treatment. Antidepressant treatments were associated with enhanced ultradian amplitudes of CSF metabolite levels. Another study used resting-state functional magnetic resonance imaging (fMRI) to measure amplitudes of dorsal raphé activation cycles following sham or active dietary depletions of the 5HT precursor (tryptophan). During depletion, amplitudes of dorsal raphé activation cycles increased with rapid 6 s periods (about 0.18 Hz) while functional connectivity weakened between dorsal raphé and thalamus at slower periods of 20 s (0.05 Hz). A third approach studied MDMA (ecstasy, 3,4-methylenedioxy-N-methylamphetamine) users because of their chronically diminished 5HT function compared with non-MDMA polysubstance users (Karageorgiou et al., 2009). Compared with a non-MDMA using cohort, MDMA users showed diminished fMRI intra-regional coherence in motor regions along with altered functional connectivity, again suggesting effects of altered 5HT oscillatory function. These data support a hypothesis that qualities of ultradian oscillations in 5HT function may critically influence moods and behaviors. Dysfunctional 5HT rhythms in depression may be a common endpoint and biomarker for depression, linking dysfunction of slow brain network oscillators to 5HT mechanisms affected by commonly available treatments. 5HT oscillatory dysfunction may define illness subtypes and predict responses to serotonergic agents. Further studies of 5HT oscillations in depression are indicated.

Differential effects of acute cold and footshock on the sleep of rats

Several studies have shown that 1 h of immobilisation stress during the rat's active period results in rebound of paradoxical (PS) and slow wave sleep (SWS). Since the effects of stress on behaviour and physiological parameters vary according to the stimulus, the present study sought to examine the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sleep pattern of rats submitted to 1 h of footshock, immobilisation or cold, or 18 h of PS deprivation (PSD). Stress sessions began between 0900 and 0930 h. Immediately after the end of the stress session, or at the corresponding time for controls, animals were blood sampled for determination of ACTH and corticosterone (CORT) plasma levels. In Experiment 2, animals were implanted with electrodes for basal and post-stress polysomnographic recording (6 h long). The results showed that all stressors produced an activation of the HPA axis; however, footshock induced the largest ACTH levels, whereas cold resulted in the highest CORT levels. In regard to the sleep data, immobilisation and PSD led to a rebound of SWS (+16.87% and +9.37%, respectively) and PS (+42.45% and +55.25%, respectively). Immobilisation, however, induced an increased number of PS episodes, whereas PSD resulted in longer PS episodes. Cold stress produced an exclusive rebound of SWS (+14.23%) and footshock promoted sustained alertness during the animal's resting period (+47.18%). These results indicate that different stimuli altered the sleep pattern in a distinct manner; and these alterations might be related to the state of the HPA axis activation.

Influence of a 1-h immobilization stress on sleep and CLIP (ACTH(18-39)) brain contents in adrenalectomized rats

Basal sleep amounts in adrenalectomized rats (AdX), as compared to intact animals, exhibit a significant increase in slow-wave sleep (SWS), a tendency towards an increase in paradoxical sleep (PS), and circadian rhythms (SWS and PS) flattened in amplitude. An immobilization stress (IS) of 1 h, imposed on AdX rats at the beginning of the dark period, is accompanied by an intense polygraphic waking. Just after the IS, SWS amount become significantly higher than in control rats (+44%/11 h of darkness) whereas significant increases of PS occur only 5-10 h after the IS (+24%/11 h of darkness). A specific radioimmunoassay for CLIP (corticotropin-like intermediate lobe peptide or ACTH(18-39)) was performed in biopsies taken either from the nucleus raphe dorsalis (nRD) or the arcuate nucleus (AN). In the nRD, just after the IS, phosphorylated CLIP (Ph-CLIP) concentration exhibits a decreasing tendency, but 4 h later, it increases significantly (+22%, p<0.05). In the AN, Ph-CLIP concentration remains unchanged after the IS as well as 4 h later. These results differ from those previously reported in intact animals also submitted to a 1-h IS, that is, a SWS rebound less marked (+27%/11 h of darkness), a PS rebound more important starting immediately after the IS (+46%/11 h of darkness) and a significant increase in Ph-CLIP occurring just after the end of the restraint. In conclusion, data obtained after a restraint stress either in AdX or in control rats point out the dependence of the PS rebound on the nRD Ph-CLIP concentration.

[Treatment of sleep disorders in children]

Sleep disorders require careful evaluation, precise diagnosis and a systematic search for a cause before considering treatment. Hypnotics must never be prescribed directly and when necessary it must be used precautionally during a short period of time, as little is known on their long term effects in children. In addition some psychotropic drugs may lead to tolerance and addiction. Educational and behavioural therapy together with sleep hygiene, have proven to be efficient in most situations. Awaking stimulants are indicated in primary hypersomnia.

Influence of a 1 h immobilization stress on sleep states and corticotropin-like intermediate lobe peptide (CLIP or ACTH18-39, Ph-ACTH18-39) brain contents in the rat

A 1 h immobilization stress (IS) was imposed to rats at the beginning of the dark period, i.e., when the animals start to be active. The IS was accompanied by an intense polygraphic waking and followed, over 12 h of the dark period, by a significant rebound of slow-wave sleep (SWS, +17%) and paradoxical sleep (PS, +57%). In order to estimate the IS-related changes in the endogenous concentrations of corticotropin-like intermediate lobe peptide (CLIP, ACTH18-39) and related compounds, a specific radioimmunoassay (RIA) was used. Assays performed in cerebral biopsies taken from arcuate (AN) and raphe dorsalis (nRD) nuclei led to the obtention of 2 main immunoreactive peaks, corresponding to CLIP and its phosphorylated form Ph-CLIP. Just after end of the IS and within the nRD. Ph-CLIP immunoreactivity increased by about 95%. Four hours later, i.e., when PS rebound was maximal, a 37% increase in Ph-CLIP immunoreactivity was measured in the AN. These observations have never been described before. In the blood, at the end of the restraint, CLIP/ACTH1-39 total immunoreactivity was increased by 330%. It returned to baseline level 4 h later. Blood concentration of corticosterone was also increased by 56% at the end of the IS and was close to baseline level 4 h later. Data reported here indicate that the IS first triggers an increase in Ph-CLIP within the nRD. Since the nRD contains sleep permissive components, this increase might be determinant for the SWS and PS rebound induction. The changes observed in the blood as regards CLIP/ACTH1-39 total immunoreactivity and corticosterone concentration testify to the efficacy of the IS and are part of the conventional picture accompanying such a situation. Finally, the increase in Ph-CLIP, occurring in the AN 4 h after the end of the restraint, might be part of the restorative processes necessary to compensate the stress overshoot.

Antimanic drugs stabilize hamster circadian rhythms

The circadian wheel-running rhythm of golden hamsters was monitored during chronic oral treatment with four mood-stabilizing drugs in doses relevant for treatment of manic-depressive disorder. Carbamazepine and verapamil shortened the duration of locomotor activity and improved the stability of the pattern of running activity. At comparable doses, valproate had no clear effect on any rhythm variable tested. None of these drugs consistently altered the phase of light-synchronized running rhythms or the period of the rhythm in constant darkness. The results are compared to data showing that lithium, which delays entrained phase and lengthens circadian period in hamsters, also shortens activity duration and increases the stability of wheel-running rhythms. Stabilization of circadian rhythms may be a key action of clinically effective mood-stabilizing drugs.

Evidence for a sleep-promoting influence of stress

In the present review the data supporting the existence at the central level of a stress-sleep relation are reported and discussed. An immobilization stress of 1 or 2 hour(s) is accompanied by a marked polygraphic waking and followed by a significant sleep rebound concerning mainly paradoxical sleep (PS). During the restraint, an important release of 5-hydroxyindoles [5-OHles, a good index of serotonin (5-HT) release] occurs in the basal hypothalamus (BH). This release, produced by the nerve endings originating from the nucleus raphe dorsalis (nRD), might secondarily influence the release and/or the synthesis of hypnogenic substances directly involved in the sleep rebound production. Corticotropin-like intermediate lobe peptide (CLIP, or ACTH18-39) is a peptide possessing hypnogenic properties and derived from proopiomelanocortin (POMC) whose perikarya are contained within the BH (arcuate nucleus). The POMC nerve endings impinge on the nucleus raphe dorsalis, a structure containing sleep permissive components upon which CLIP acts to trigger sleep. It remains to be defined how the activity of the neuronal loop described above is impaired under chronic stress conditions.