Serotonin in the spotlight

Use of "Lights" for Bipolar Depression

PURPOSE

In this review, we will review the background and diagnosis of bipolar disorder (BD); describe the efficacy data and potential circadian and neural mechanisms underlying the effects of bright light for bipolar depression; and discuss the implementation of light therapy in clinical practice.

RECENT FINDINGS

To date, morning bright light is the most widely tested form of light therapy for all mood disorders. Clinical trial reports suggest that midday or morning bright light treatment and novel chronotherapeutic interventions are effective for bipolar depression. Mechanisms of response may relate to effects on the circadian system and other changes in neural functioning. Using bright light to manage depressive symptoms in BD is reasonable but also requires concurrent antimanic treatment and careful clinical monitoring for response, safety, and mood polarity switch.

Non-Photic Modulation of Phase Shifts to Long Light Pulses

Circadian rhythms can be reset by both photic and non-photic stimuli. Recent studies have used long light exposure to produce photic phase shifts or to enhance non-photic phase shifts. The presence or absence of light can also influence the expression of locomotor rhythms through masking; light during the night attenuates locomotor activity, while darkness during the day induces locomotor activity in nocturnal animals. Given this dual role of light, the current study was designed to examine the relative contributions of photic and non-photic components present in a long light pulse paradigm. Mice entrained to a light/dark cycle were exposed to light pulses of various durations (0, 3, 6, 9, or 12 h) starting at the time of lights-off. After the light exposure, animals were placed in DD and were either left undisturbed in their home cages or had their wheels locked for the remainder of the subjective night and subsequent subjective day. Light treatments of 6, 9, and 12 h produced large phase delays. These treatments were associated with decreased activity during the nocturnal light and increased activity during the initial hours of darkness following light exposure. When the wheels were locked to prevent high-amplitude activity, the resulting phase delays to the light were significantly attenuated, suggesting that the activity following the light exposure may have contributed to the overall phase shift. In a second experiment, telemetry probes were used to assess what effect permanently locking the wheels had on the phase shift to the long light pulses. These animals had phase shifts fully as large as animals without any form of wheel lock, suggesting that while non-photic events can modulate photic phase shifts, they do not play a role in the full phase-shift response observed in animals exposed to long light pulses. This paradigm will facilitate investigations into non-photic responses of the mouse circadian system.

Cocaine modulates pathways for photic and nonphotic entrainment of the mammalian SCN circadian clock

Cocaine abuse is highly disruptive to circadian physiological and behavioral rhythms. The present study was undertaken to determine whether such effects are manifest through actions on critical photic and nonphotic regulatory pathways in the master circadian clock of the mouse suprachiasmatic nucleus (SCN). Impairment of SCN photic signaling by systemic (intraperitoneal) cocaine injection was evidenced by strong (60%) attenuation of light-induced phase-delay shifts of circadian locomotor activity during the early night. A nonphotic action of cocaine was apparent from its induction of 1-h circadian phase-advance shifts at midday. The serotonin receptor antagonist, metergoline, blocked shifting by 80%, implicating a serotonergic mechanism. Reverse microdialysis perfusion of the SCN with cocaine at midday induced 3.7 h phase-advance shifts. Control perfusions with lidocaine and artificial cerebrospinal fluid had little shifting effect. In complementary in vitro experiments, photic-like phase-delay shifts of the SCN circadian neuronal activity rhythm induced by glutamate application to the SCN were completely blocked by cocaine. Cocaine treatment of SCN slices alone at subjective midday, but not the subjective night, induced 3-h phase-advance shifts. Lidocaine had no shifting effect. Cocaine-induced phase shifts were completely blocked by metergoline, but not by the dopamine receptor antagonist, fluphenazine. Finally, pretreatment of SCN slices for 2 h with a low concentration of serotonin agonist (to block subsequent serotonergic phase resetting) abolished cocaine-induced phase shifts at subjective midday. These results reveal multiple effects of cocaine on adult circadian clock regulation that are registered within the SCN and involve enhanced serotonergic transmission.

Bright-light therapy in the treatment of mood disorders

Bright-light therapy (BLT) is established as the treatment of choice for seasonal affective disorder/winter type (SAD). In the last two decades, the use of BLT has expanded beyond SAD: there is evidence for efficacy in chronic depression, antepartum depression, premenstrual depression, bipolar depression and disturbances of the sleep-wake cycle. Data on the usefulness of BLT in non-seasonal depression are promising; however, further systematic studies are still warranted. In this review, the authors present a comprehensive overview of the literature on BLT in mood disorders. The first part elucidates the neurobiology of circadian and seasonal adaptive mechanisms focusing on the suprachiasmatic nucleus (SCN), the indolamines melatonin and serotonin, and the chronobiology of mood disorders. The SCN is the primary oscillator in humans. Indolamines are known to transduce light signals into cells and organisms since early in evolution, and their role in signalling change of season is still preserved in humans: melatonin is synthesized primarily in the pineal gland and is the central hormone for internal clock circuitries. The melatonin precursor serotonin is known to modulate many behaviours that vary with season. The second part discusses the pathophysiology and clinical specifiers of SAD, which can be seen as a model disorder for chronobiological disturbances and the mechanism of action of BLT. In the third part, the mode of action, application, efficacy, tolerability and safety of BLT in SAD and other mood disorders are explored.

Reduced phase-advance of plasma melatonin after bright morning light in the luteal, but not follicular, menstrual cycle phase in premenstrual dysphoric disorder: an extended study

The authors previously observed blunted phase-shift responses to morning bright light in women with premenstrual dysphoric disorder (PMDD). The aim of this study was to determine if these findings could be replicated using a higher-intensity, shorter-duration light pulse and to compare these results with the effects of an evening bright-light pulse. In 17 PMDD patients and 14 normal control (NC) subjects, the authors measured plasma melatonin at 30-min intervals from 18:00 to 10:00 h in dim (<30 lux) or dark conditions the night before (Night 1) and after (Night 3) a bright-light pulse (administered on Night 2) in both follicular and luteal menstrual cycle phases. The bright light (either 3000 lux for 6 h or 6000 lux for 3 h) was given either in the morning (AM light), 7 h after the dim light melatonin onset (DLMO) measured the previous month, or in the evening (PM light), 3 h after the DLMO. In the luteal, but not in the follicular, phase, AM light advanced melatonin offset between Night 1 and Night 3 significantly less in PMDD than in NC subjects. The effects of PM light were not significant, nor were there significant effects of the light pulse on melatonin measures of onset, duration, peak, or area under the curve. These findings replicated the authors' previous finding of a blunted phase-shift response to morning bright light in the luteal, but not the follicular, menstrual cycle phase in PMDD compared with NC women, using a brighter (6000 vs. 3000 lux) light pulse for a shorter duration (3 vs. 6 h). As the effect of PM bright light on melatonin phase-shift responses did not differ between groups or significantly alter other melatonin measures, these results suggest that in PMDD there is a luteal-phase subsensitivity or an increased resistance to morning bright-light cues that are critical in synchronizing human biological rhythms. The resulting circadian rhythm malsynchonization may contribute to the occurrence of luteal phase depressive symptoms in women with PMDD.

Effects of different light intensities in the morning on dim light melatonin onset

The present study evaluated the effects of exposure to light intensity in the morning on dim light melatonin onset (DLMO). The tested light intensities were 750 lux, 150 lux, 3000 lux, 6000 lux and 12,000 lux (horizontal illuminance at cornea), using commercial 5000 K fluorescent lamps. Eleven healthy males aged 21-31 participated in 2-day experiments for each light condition. On the first experimental day (day 1), subjects were exposed to dim light (<30 lux) for 3 h in the morning (09:00-12:00). On the same day, saliva samples were taken in dim light (<30 lux) every 30 min from 21:00 to 01:00 to determine the DLMO phase. The subjects were allowed to sleep from 01:00 to 08:00. On the second experimental day (day 2), the subjects were exposed to experimental light conditions for 3 h in the morning. The experimental schedule after light exposure was the same as on day 1. On comparing day 2 with day 1, significant phase advances of DLMO were obtained at 3000 lux, 6000 lux and 12,000 lux. These findings indicate that exposure to a necessary intensity from an ordinary light source, such as a fluorescent lamp, in the morning within one day affects melatonin secretion.

Bright light exposure during acute tryptophan depletion prevents a lowering of mood in mildly seasonal women

We investigated the influence of bright light exposure on the mood-lowering effect of acute tryptophan depletion (ATD). Mildly seasonal healthy young women without a personal or family history of psychiatric disorders remained in either dim or bright light during two test days. Tryptophan-deficient and nutritionally balanced amino acid mixtures were administered in counterbalanced order. Mood state was assessed using the Profile of Mood States (POMS) and Visual Analogue Scales (VAS). In dim light, ATD decreased POMS scores across most subscales, indicating a worsening of mood. In bright light, mood was unaffected by ATD. Thus, bright light blocked the worsening of mood caused by ATD. This was also observed on the positive mood VAS. These results indicate a direct, immediate interaction between bright light and serotonin function. Bright light might help protect against ATD-induced mood change by increasing serotonin above the threshold level below which there is a lowering of mood.

Moderate exercise and bright light treatment in overweight and obese individuals

OBJECTIVE

Increased physical activity is important given the concern over the growing rates of obesity. The aim of this study is to conduct a controlled investigation of the effects of bright light therapy and exercise on weight loss and body composition in overweight and obese individuals.

RESEARCH METHODS AND PROCEDURES

Twenty-five overweight and obese subjects were assigned to 6 weeks of moderate exercise with or without bright light treatment. Outcome measure included changes in body mass and body composition and ratings of mood, seasonality, and sleep.

RESULTS

Body weight decreased significantly with exercise in subjects in the light and non-light treatment groups, but the change was not significantly different between the groups. Similar results were found for BMI. With exercise, body fat decreased significantly only in the light treatment group. There was a significant effect of the interaction of group by time on body fat composition, but the group by time interaction failed to reach statistical significance for body weight and BMI. Mood scores improved significantly with exercise in the light group, but no significant changes were noted regarding sleep.

DISCUSSION

This preliminary study is the first to show that addition of bright light treatment to a 6-week moderate exercise program can alter body composition by significantly reducing body fat. The reduction in body fat mass is of particular importance, because visceral fat has been particularly implicated as a major factor in the development of the metabolic syndrome. This study is an important step toward finding ways to maximize the effects of exercise.

A molecular explanation of interactions between photic and non-photic circadian clock-resetting stimuli

Non-photic clock-resetting events (arousal and locomotor activity) in the subjective day reduced expression of Period genes in the suprachiasmatic nucleus of hamsters. This decrease was attenuated by a 30-min light pulse occurring during the last 0.5 h of 3.5 h of confinement to a novel running wheel. This provides an example at the molecular level of an interaction between different modalities of synchronizing agents.

Behavioral arousal blocks light-induced phase advances in locomotor rhythmicity but not light-induced Per1 and Fos expression in the hamster suprachiasmatic nucleus

Both photic and nonphotic stimuli entrain circadian rhythms. Although the adaptive significance of nonphotic clock resetting is unknown, one possibility is that nonphotic cues modulate circadian responses to light. Results of studies on the interaction between photic and nonphotic stimuli support this idea. During the day, light blocks the effects of nonphotic stimuli on the phase of locomotor rhythms and on expression of clock genes in suprachiasmatic nucleus (SCN) neurons. At night, novelty-induced activity prior to and during exposure to light attenuates the phase-shifting response to that light, but the effects of this manipulation on clock gene expression are unknown. The present experiments explore the interaction between behavioral state and response to light at the molecular level. We show that confining hamsters to novel wheels immediately after a light pulse during the late subjective night attenuates light-induced phase advances of wheel-running rhythms and the transient effects on circadian period. In contrast to the striking effect of novelty-induced activity on behavioral responses to light, Fos protein and Per1 mRNA were robustly expressed in the SCN of all light-pulsed animals, regardless of behavioral treatment. Our results are inconsistent with the idea that light and nonphotic stimuli block each other's effects on phase shifts by inducing or attenuating transcription of Per1. Photic regulation of clock genes and spontaneous rhythmic expression of clock genes are probably mediated by different mechanisms.

Melatonin enhances the sensitivity of circadian pacemakers to light in the nocturnal field mouse Mus booduga

The effect of exogenous melatonin (1 mg/kg) on light pulse (LP) induced phase shifts of the circadian locomotor activity rhythm was studied in the nocturnal field mouse Mus booduga. Three phase response curves (PRCs: LP, control, and experimental) were constructed to study the effect of co-administration of light and melatonin at various circadian times (CTs). The LP PRC was constructed by exposing animals free-running in constant darkness (DD) to LPs of 100-lux intensity and 15-min duration, at various CTs. The control and experimental PRCs were constructed by using a single injection of either 50% DMSO or melatonin (1 mg/kg dissolved in 50% DMSO), respectively, administered 5 min before LPs, to animals free-running in DD. A single dose of melatonin significantly modified the waveform of the LP PRC. The experimental PRC had significantly larger areas under advance and delay regions of the PRC compared to the control PRC. This was also confirmed when the phase shifts obtained at various CTs were compared between the three PRCs. The phase delays at three phases (CT12, CT14, and CT16) of the experimental PRCs were significantly greater than those of the control and the LP PRCs. Based on these results we conclude that phase shifting effects of melatonin and light add up to produce larger responses.

Light exposure during daytime modulates expression of Per1 and Per2 clock genes in the suprachiasmatic nuclei of mice

The suprachiasmatic nuclei (SCN) of the hypothalamus contain the master circadian clock in mammals. Nocturnal light pulses that reset the circadian clock also lead to rapid increases in levels of Per1 and Per2 mRNA in the SCN, suggesting that these genes are involved in the synchronization to light. During the day, when light has no phase-shifting effects in nocturnal rodents, the consequences of light exposure for Per expression have been less thoroughly studied. Therefore, the effects of light exposure during the day were assessed on Per1 and Per2 mRNA in the SCN of mice. Expression of Per1 and Per2 was generally increased by 30-min light pulses during the subjective day, with more pronounced effects in the morning. One exception was noted for a transient decrease in Per2 expression after a short light pulse applied at midday. Prolonged light exposure (up to 3 hr) starting at midday markedly increased Per2 expression but not that of Per1. Moreover, the amplitude of the daily variations of both Per and the duration of Per1 peak was increased in mice exposed to a light-dark cycle compared with those transferred to constant darkness. Finally, the amplitude of the daily variations of both Per and the basal level of Per1 were increased in mice under a light-dark cycle compared with animals synchronized to a skeleton photoperiod (i.e., with daily dawn and dusk 1-hr exposures to light). Taken together, the results indicate that prolonged light exposure during daytime positively modulates daily levels of Per1 and Per2 mRNA in the SCN of mice.

The circadian Clock mutation increases exploratory activity and escape-seeking behavior

Disturbances of circadian rhythms are associated with many types of mood disorders; however, it is unknown whether a dysfunctional circadian pacemaker can be the primary cause of altered emotional behavior. To test this hypothesis, male and female mice carrying a mutation of the circadian gene, Clock, were compared to wild-type mice in an array of behavioral tests used to measure exploratory activity, anxiety, and behavioral despair. Female Clock mutant mice exhibited significantly greater activity and rearing in an open field and a greater number of total arm entries in the elevated plus maze. In addition, female Clock mutant mice spent significantly more time swimming in the forced swim test than wild-type mice on both days of a 2-day test. Male Clock mutant mice also exhibited increased exploration of the open field and increased swimming in the forced swim test; however, behavioral changes were less robust in Clock mutant males compared to Clock mutant females. These changes in behavior were not dependent on the expression of a lengthened free-running period but were more or less striking depending on the testing conditions. These data indicate that the Clock mutation leads to increased exploratory behavior and increased escape-seeking behavior, and, conversely, does not result in increased anxiety or depressive-like behavior. These results suggest that the Clock gene is involved in regulating behavioral arousal, and that Clock may interact with sex hormones to produce these behavioral changes.

Effects of season and climate on the first manic episode of bipolar affective disorder in Korea

The purpose of this study was to determine if a seasonal pattern existed for the first manic episodes in Korea. The first manic episodes out of 152 bipolar disorder patients were investigated, in subjects who were admitted in two hospitals in Seoul between 1996 and 1999. Correlations between the monthly climate variables and the first monthly manic episodes indicated that the first manic episodes peaked in 25 cases during March. The mean monthly hours of sunshine and sunlight radiation correlated significantly with manic episodes. Separating the patients into two groups, namely, with and without major depressive episode, only the occurrence of manic episodes with major depressive episode was significantly correlated with mean monthly hours of sunshine. Separating the subjects by gender, the monthly first manic episodes was significantly correlated with the intensity of sunlight radiation in female patients only. These findings suggested that increasing the duration and intensity of sunlight could facilitate breakdown into the manic episodes.

Removal of polysialic acid from the SCN potentiates nonphotic circadian phase resetting

The adult suprachiasmatic nucleus (SCN) expresses a polysialylated form of neural cell adhesion molecule (PSA-NCAM) that modulates cell interactions. Previous studies have shown that PSA is important for photic entrainment of the SCN circadian clock, suggesting that changes in cell-cell interactions may contribute to the phase-resetting capacity of this system. A possible role for PSA in nonphotic circadian phase resetting was evaluated using the enzyme endoneuraminidase (endo N) to selectively remove PSA from the SCN. Pretreatment of rat brain slices containing the SCN with endo N enhanced the daytime phase-advancing effects of the serotonin agonist, 8-hydroxy-2-dipropylaminotetralin [8-OH-DPAT] (41% greater than inactivated enzyme controls; P<.05). Similarly, removal of PSA from the Syrian hamster SCN in vivo potentiated the daytime phase-advancing effects of behavioral arousal (sleep deprivation) and of systemic application of 8-OH-DPAT (61% and 220% greater, respectively, than inactivated enzyme controls; both P<.05). While endo N perturbation of both photic and nonphotic phase resetting suggests that PSA plays a central role in clock regulation, it is striking that the effects on the two inputs are opposite in direction. This difference could reflect the antagonistic relationship between photic and nonphotic signaling pathways. It could also be explained by a permissive role of PSA common to both inputs, which in and of itself would not specify direction of response. Such a bidirectional control mechanism, based on PSA's attenuation of cell-cell interactions, is well documented in the developing nervous system, and may be retained in plastic regions of the adult brain.

Bright-light exposure combined with physical exercise elevates mood

BACKGROUND

Physical exercise alleviates depressive symptoms, as does exposure to bright light, especially in those with seasonal variation. Our objective was to compare the effect of exercise alone or combined with morning bright light on mood and the health-related quality of life in healthy subjects.

METHODS

Study subjects were working-age adults, randomized in two groups (n=80): exercise in bright light (group A), or exercise in normal indoor illumination (group B). Intervention lasted for 8 weeks and questionnaire data on mood and the health-related quality of life were collected at study entry, and at weeks 4 and 8.

RESULTS

Physical exercise both in normal indoor illumination and in bright light was effective at alleviating depressive symptoms. The exercise was significantly more effective at alleviating so-called atypical depressive symptoms when combined with bright-light exposure.

LIMITATIONS

There was no active placebo condition, but a comparative, randomized trial was executed.

CONCLUSIONS

Physical exercise in bright light had a positive effect on mood and health-related quality of life in a sample of healthy, working-age people. Further research is needed to explore the mechanisms of the apparent additive effect of exercise and light.

Case study of circadian rhythm sleep disorder following haloperidol treatment: reversal by risperidone and melatonin

A patient with Gilles de la Tourette syndrome treated with haloperidol, ingested once daily after awakening from sleep, exhibited an irregular sleep-wake pattern with a free-running component of approximately 48 h. Transfer to risperidone, ingested once daily after awakening from sleep, was beneficial resulting in a sleep-wake cycle more synchronized at the appropriate phase to the external zeitgebers, and fewer nocturnal disturbances. The circadian sleep-wake schedule was fully synchronized when the patient had been subsequently treated with melatonin at 21:00h, before intended nocturnal sleep, in addition to risperidone in the morning. Restoration of the sleep-wake circadian pattern was accompanied by the patient's subjective report of significant improvement in his quality of life, social interactions, and occupational status. This observation suggests that circadian rhythm sleep disorders can be related to the typical neuroleptic haloperidol and restored by the atypical neuroleptic risperidone. Similar findings reported in patients suffering from other disorders support the hypothesis that the described disruption of the sleep-wake schedule is medication rather than illness-related. Therefore, it is very important to realize that circadian rhythm sleep disorders may be a side effect of neuroleptics.

In vivo resetting of the hamster circadian clock by 5-HT7 receptors in the suprachiasmatic nucleus

Serotonin (5-HT) has been strongly implicated in the regulation of the mammalian circadian clock located in the suprachiasmatic nuclei (SCN); however, its role in behavioral (nonphotic) circadian phase resetting remains elusive. Central to this issue are divergent lines of evidence that the SCN may, or may not, be a target for the phase-resetting effects of 5-HT. We have addressed this question using a novel reverse-microdialysis approach for timed perfusions of serotonergic and other agents to the Syrian hamster SCN with durations equivalent to the increases in in vivo 5-HT release during phase-resetting behavioral manipulations. We found that 3 hr perfusions of the SCN with either 5-HT or the 5-HT(1A,7) receptor agonist 2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydro-naphthalene (8-OH-DPAT) at midday advanced the phase of the free-running circadian rhythm of wheel-running assessed using an Aschoff type II procedure. Phase shifts induced by 8-OH-DPAT were enhanced more than threefold by pretreatment with the 5-HT synthesis inhibitor para-chlorophenylalanine. Phase advances induced by SCN 8-OH-DPAT perfusion were significantly inhibited by the 5-HT(2,7) receptor antagonist ritanserin and by the more selective 5-HT(7) receptor antagonist DR4004, implicating the 5-HT(7) receptor in mediating this phase resetting. Concurrent exposure to light during the 8-OH-DPAT perfusion abolished the phase advances. Furthermore, coperfusion of the SCN with TTX, which blocked in vivo 5-HT release, did not suppress intra-SCN 8-OH-DPAT-induced phase advances. These results indicate that 5-HT(7) receptor-mediated phase resetting in the SCN is markedly influenced by the degree of postsynaptic responsiveness to 5-HT and by photic stimulation. Finally, 5-HT may act directly on SCN clock cells to induce in vivo nonphotic phase resetting.

Opposing effects of behavioural activity and light on neurons of the suprachiasmatic nucleus

The mammalian circadian pacemaker is located in the suprachiasmatic nuclei. It can be shifted in phase by photic cues and by the behavioural activity of the animal. When presented together, light and behavioural activity attenuate each others' phase-shifting effect. Still unclear is how behavioural activity affects the suprachiasmatic nuclei and how it interacts with photic information. Previously, we reported the occurrence of behaviourally induced suppressions of neuronal activity. The present study investigates the characteristics of these suppressions as a function of circadian time and, additionally, in the presence of photic cues. We performed long-term multiunit activity recordings of neurons in freely moving rats and found that these suppressions of neuronal firing in the suprachiasmatic nucleus occurred at every phase of the circadian cycle. The magnitude of the suppressions showed a circadian variation, with larger suppressions during subjective day. When a light pulse was applied during a suppression, light and activity appeared to oppose each others' effects within the recorded population of neurons. The resulting discharge level appeared to be the sum of both responses. The opposing effects of light and activity were also found in single unit recordings, indicating that photic and behavioural stimuli interact at the level of a single neuron.

Diminished melatonin secretion in the elderly caused by insufficient environmental illumination

The pineal hormone melatonin has some circadian regulatory effects and is assumed to have a close relation with sleep initiation and maintenance. Many previous reports have described age-related decreases in melatonin levels, especially in elderly insomniacs (EIs), which may act as causal or exacerbating factors in sleep disturbances in the elderly. Ten elderly residents with psychophysiological insomnia (mean age, 74.2 yr), 10 healthy residents of the same home [elderly control (EC) group; mean age, 72.7 yr], and 10 healthy young control subjects (mean age, 20.9 yr) living at home participated in this study. The elderly persons, especially the EIs, were exposed to significantly less environmental light and simultaneously suffered from significantly diminished nocturnal melatonin secretion. Supplementary exposure to 4 h (1000 to 1200 h, 1400 to 1600 h) of midday bright light in the EI group significantly increased melatonin secretion to levels similar to those in the young control group without circadian phase-shifting. There was a tendency for the magnitude of the increase in nocturnal melatonin secretion stimulated by bright light to parallel amelioration of sleep disturbances in these subjects. The present findings suggest that we need to pay attention to elderly individuals who suffer under conditions of poor environmental light resulting in disorganized circadian rhythms, including the sleep-wake cycle.

Inhibitory action of brotizolam on circadian and light-induced per1 and per2 expression in the hamster suprachiasmatic nucleus

Triazolam reportedly causes phase advances in hamster wheel-running rhythm after injection during subjective daytime. However, it is unclear whether benzodiazepine affects the PER: gene expression accompanying a behavioural phase shift. Brotizolam (0.5 - 10 mg kg(-1)) induced large phase advances in hamster rhythm when injected during mid-subjective daytime (circadian time 6 or 9), but not at circadian time 0, 3 or 15. Brotizolam (5 mg kg(-1)) significantly reduced the expression of PER:1 and PER:2 in the suprachiasmatic nucleus 1 and 2 h after injection at circadian time 6, and slightly reduced them at circadian time 20. Injection of 8-OH-DPAT (5 mg kg(-1)) at subjective daytime induced similar phase advances with a reduction of PER:1 and PER:2 expression. Co-administration of brotizolam with 8-OH DPAT failed to potentiate the 8-OH DPAT-induced phase advances and reduced PER: expression. Both phase advance and rapid induction of PER:1 and PER:2 in the suprachiasmatic nucleus after light exposure (5 lux, 15 min) at circadian time 20 was strongly attenuated by co-treatment with brotizolam 5 mg kg(-1). The present results strongly suggest that reduction of PER:1 and/or PER:2 expression during subjective daytime by brotizolam may be an important step in causing a behavioural phase advance. The co-administration experiment suggests that common mechanism(s) are involved in brotizolam- or 8-OH DPAT-induced phase advances and the reduction of PER: gene expression. These results suggest that brotizolam is not only a good drug for insomnia but also a drug capable of facilitating re-entrainment like melatonin.

Circadian binding activity of AP-1, a regulator of the arylalkylamine N-acetyltransferase gene in the rat pineal gland, depends on circadian Fra-2, c-Jun, and Jun-D expression and is regulated by the clock's zeitgebers

The daily rhythm in circulating melatonin is driven by a circadian rhythm in the expression of the arylalkylamine N:-acetyltransferase gene in the rat pineal gland. Turning off expression of this gene at the end of night is believed to involve inhibitory transcription factors, among which Fos-related antigen 2 (Fra-2) appears as a good candidate. Circadian rhythms in the expression of three proteins of activating protein-1 (AP-1) complexes, namely, Fra-2, c-Jun, and Jun-D, are shown here to account for circadian variations in AP-1 binding activity. Quantitative variations in the Fra-2 component over the circadian cycle were associated with qualitative variations in protein isoforms. Destruction of the suprachiasmatic nucleus resulted in decreased nocturnal AP-1 activity, showing that AP-1 circadian rhythm is driven by this nucleus. Exposure to light during subjective night and administration of a serotonin 5-HT(1A)/5-HT(7) receptor agonist during subjective day, respectively, induced a 50% decrease and a 50% increase in both AP-1 and Fra-2 expression. These effects were impaired by suprachiasmatic nucleus lesions. These data show that pineal AP-1 binding activity, which results from Fra-2 expression, can be modulated by light and serotonin through the suprachiasmatic nucleus according to a "phase dependence" that is characteristic of the rhythm of clock sensitivity to both zeitgebers.

Dorsal raphe nuclear stimulation of SCN serotonin release and circadian phase-resetting

Serotonin (5-HT) is strongly implicated in the regulation of mammalian circadian rhythms. However, little is known of the functional relationship between the circadian clock located in the suprachiasmatic nucleus (SCN) and its source of serotonergic innervation, the midbrain raphe nuclei. In previous studies, we reported that electrical stimulation of the dorsal or median raphe nuclei (DRN and MRN, respectively) induced 5-HT release in the SCN. Notably, DRN- but not MRN-stimulated 5-HT release was blocked by the 5-HT(1,2,7) antagonist, metergoline, suggesting that the DRN signals to the SCN indirectly via the activation of a 5-HT-responsive multisynaptic pathway. In the present study, pretreatment with the 5-HT(2,7) antagonist, ritanserin, also significantly inhibited DRN-electrically stimulated SCN 5-HT release. However, pretreatment with the 5-HT(1A) antagonist, NAN-190, or the 5-HT(2) antagonists ketanserin and cinanserin had little suppressive effect on this DRN-stimulated 5-HT release. In complementary behavioral trials, electrical stimulation of the DRN during subjective midday caused a 1.3-h advance in the free-running circadian activity rhythm under constant darkness, which was inhibited by metergoline. Collectively, these results are evidence that: (1) DRN-stimulated 5-HT release in the SCN requires the activation of an intermediate target with receptors having 5-HT(7) pharmacological characteristics; (2) electrical stimulation of the DRN induces phase-resetting of the circadian activity rhythm; and (3) activation of 5-HT receptors is necessary for this DRN-stimulated circadian phase-resetting. In view of the dynamic changes in DRN neuronal activity incumbent with the daily sleep-activity cycle, and its functional linkages to the SCN and intergeniculate leaflet, the DRN could serve to provide behavioral/arousal state information to various sites comprising the brain circadian system.

Effect of bright light on cycling performance

PURPOSE

The purpose of this study was to examine the effect of exposure to three levels of light intensity during cycling on average power output during an all-out 20-min bout of cycle ergometry.

METHODS

Twelve male competitive cyclists, with a mean age of 24.3 +/- 3.2 yr, were tested on four separate occasions. During each test session, participants were instructed to produce the highest possible average power output during a 20-min bout of cycle ergometry. Session 1 served as a adaptation trial and was conducted in normal room lighting (approximately 250 lux). In subsequent sessions each participant exercised while sitting in front of a light box. Light intensity was experimentally manipulated through the use of sunglasses that provided high, medium, and low light filtration. Light condition order was counterbalanced. Measurements of heart rate, muscle pain, local perceived exertion, metabolism, and alertness were made during exercise. Mood was assessed before and following exercise with the POMS-BI.

RESULTS

There were no statistically significant differences in the average total power output in the 1,411 lux (274.9 +/- 21.8 W), 2,788 lux (274.4 +/- 20.5 W), and 6,434 lux (270.3 +/- 19.8 W) light conditions. The difference between the average power output in the brightest and least bright condition (4.6 W) was approximately one-fourth of a pooled SD (d = 0.22). There were no significant differences among the conditions in alertness, leg muscle pain, perceived exertion, heart rate, VO2, or mood responses to the exercise.

CONCLUSION

It is concluded that exposure to bright light resulting in estimated retinal exposures ranging from 1,411 to 6,434 lux did not have a large or systematic influence on the performance of 20 min of maximal cycle ergometry.

Interactions between light and melatonin on the circadian clock of mice

Melatonin and light synchronize the biological clock and are used to treat sleep/wake disturbances in humans. However, the two treatments affect circadian rhythms differently when they are combined than when they are administered individually. To elucidate the nature of the interaction between melatonin and light, the present study assessed the effect of melatonin on circadian timing and immediate-early gene expression in the suprachiasmatic nucleus (SCN) when administered in the presence of light. Male C3H/HeN mice, housed in constant dark in cages equipped with running wheels, were treated with either melatonin (90 microg, s.c.) or vehicle (3% ethanol-saline) 5 min prior to exposure to light (15 min, 300 lux) at various times in the circadian cycle. Combined treatment resulted in lower magnitude phase delays of circadian activity rhythms than those obtained with light alone during the early subjective night and advances in phase when melatonin and light were administered during the subjective day (p < .001). The reduction in phase delays with combined treatment at Circadian Time (CT) 14 was significant when light exposure measured 300 lux but not at lower light levels (p < .05). When light preceded melatonin administration, the inhibition of phase delays attained significance only when the light exposure reached 1000 lux (p < .05). Neither basal nor light-induced expression of c-fos mRNA in the SCN was modified by melatonin administration at CT 14 or CT 22. Together, these results suggest that combined administration of melatonin and light affect circadian timing in a manner not predicted by summing the two treatments given individually. Furthermore, the interaction is not likely to be due to inhibition of photic input to the clock by melatonin but might arise from a photically induced enhancement of melatonin's actions on circadian timing.

Platelet [3H]paroxetine and [3H]lysergic acid diethylamide binding in seasonal affective disorder and the effect of bright light therapy

BACKGROUND

Seasonal affective disorder (SAD) has been regarded as a melatonin disorder, but the pathophysiological mechanisms of SAD are to a large extent unclarified. Serotonergic mechanisms have also been studied, but they have shown inconsistent results.

METHODS

We have compared [3H]paroxetine and [3H]lysergic acid diethylamide (LSD) binding in platelets from 23 SAD patients and 23 controls. Then SAD patients had 4 weeks of light therapy. On the last treatment day new blood samples were drawn. Symptoms before and after light treatment were measured by SIGH-SAD.

RESULTS

Bmax for paroxetine binding before light treatment was higher in SAD patients compared to controls and also higher in responders than in nonresponders. Bmax decreased significantly during light treatment. We also found a negative correlation between the two Bmax values before but not after light treatment. There was a negative correlation between Bmax for paroxetine binding before treatment and clinical status after treatment. Patients with reduced Bmax for LSD binding after treatment had a better clinical treatment response.

CONCLUSIONS

The present study indicates that serotonin receptor parameters might be suitable in the prediction of clinical response to light treatment.

Circadian rhythms and depression: effects of exercise in an animal model

There is a clear link between altered circadian rhythms and depressive disorders, although the nature of this relationship is unknown. In addition, exercise affects both mood and alters clock function. To investigate the relationship between circadian rhythms, depression, and exercise, 3-wk-old mice housed on a 12:12-h light-dark cycle were exposed to chronic stress (CS) for 6 wk before being placed into constant darkness (DD). One-half of both the control and stressed mice were given access to a running wheel. Stressed mice consumed significantly less of a 2% sucrose solution during CS and exhibited a significant increase in immobility in the forced swim test 3 wk after the termination of stress relative to control mice. These effects were more pronounced in mice without running wheels. Stressed mice also exhibited altered percent distribution of total activity and increased fragmentation of daily activity rhythms during CS relative to control mice. Alterations in percent distribution were more pronounced in animals without running wheels. No activity rhythm changes were seen in DD, and there were no differences in light-induced phase shifts between stressed and control mice. These results suggest that CS causes long-term depressive-like symptoms but does not have long-lasting effects on activity rhythms. These changes were more pronounced in mice without running wheels, suggesting that exercise may protect against the harmful effects of stress.

Serotonin antagonists do not attenuate activity-induced phase shifts of circadian rhythms in the Syrian hamster

A variety of observations from several rodent species suggest that a serotonin (5-HT) input to the suprachiasmatic nucleus (SCN) circadian pacemaker may play a role in resetting or entrainment of circadian rhythms by non-photic stimuli such as scheduled wheel running. If 5-HT activity within the SCN is necessary for activity-induced phase shifting, then it should be possible to block or attenuate these phase shifts by reducing 5-HT release or by blocking post-synaptic 5-HT receptors. Animals received one of four serotonergic drugs and were then locked in a novel wheel for 3 h during the mid-rest phase, when novelty-induced activity produces maximal phase advance shifts. Drugs tested at several doses were metergoline (5-HT1/2 antagonist; i.p.), (+)-WAY100135 (5-HT1A postsynaptic antagonist, which may also reduce 5-HT release by an agonist effect at 5-HT1A raphe autoreceptors; i.p.), NAN-190 (5-HT1A postsynaptic antagonist, which also reduces 5-HT release via an agonist effect at 5-HT1A raphe autoreceptors; i.p.) and ritanserin (5-HT2/7 antagonist; i.p. and i.c.v.). Mean and maximal phase shifts to running in novel wheels were not significantly affected by any drug at any dose. These results do not support a hypothesis that 5-HT release or activity at 5HT1, 2 and 7 receptors in the SCN is necessary for the production of activity-induced phase shifts in hamsters.

Roles of suprachiasmatic nuclei and intergeniculate leaflets in mediating the phase-shifting effects of a serotonergic agonist and their photic modulation during subjective day

Serotonin (5-HT) has been implicated in the phase adjustment of the circadian system during the subjective day in response to nonphotic stimuli. Two components of the circadian system, the suprachiasmatic nucleus (SCN) (site of the circadian clock) and the intergeniculate leaflet (IGL), receive serotonergic projections from the median raphe nucleus and the dorsal raphe nucleus, respectively. Experiment 1, performed in golden hamsters housed in constant darkness, compared the effects of bilateral microinjections of the 5-HT1A/7 receptor agonist, 8-hydroxydipropylaminotetralin (8-OH-DPAT; 0.5 microgram in 0.2 microliter saline per side), into the IGL or the SCN during the mid-subjective day. Bilateral 8-OH-DPAT injections into either the SCN or the IGL led to significant phase advances of the circadian rhythm of wheel-running activity (p < .001). The phase advances following 8-OH-DPAT injections in the IGL were dose department (p < .001). Because a light pulse administered during the middle of the subjective day can attenuate the phase-resetting effect of a systemic injection of 8-OH-DPAT, Experiment 2 was designed to determine whether light could modulate 5-HT agonist activity at the level of the SCN and/or the IGL. Serotonergic receptor activation within the SCN, followed by a pulse of light (300 lux of white light lasting 30 min), still induced phase advances. In contrast, the effect of serotonergic stimulation within the IGL was blocked by a light pulse. These results indicate that the respective 5-HT projections to the SCN and IGL subserve different functions in the circadian responses to photic and nonphotic stimuli.

Dependence of the variation in alertness on the pineal gland

There is a diurnal variation in the pineal serotonin content, with a maximum at 7-8 h after the onset of light and a minimum at 3-4 h after the onset of darkness in rats. The levels of serotonin and melatonin can rapidly be altered by changing the level of ambient light. The diurnal changes in serotonergic activity are hypothesized to counteract two phenomena. First, the increased levels of serotonin would decrease the high propensity to drowsiness in the afternoon. Second, the decreased levels of serotonin would also decrease the high propensity to waking up at night, which occurs because of decreased melatonin secretion.

Behavioral inhibition of light-induced circadian phase resetting is phase and serotonin dependent

Circadian rhythms in Syrian hamsters can be phase shifted by light exposure during the subjective night and by a bout of wheel running induced during the subjective day. Interactions between photic and behavioral stimuli were examined by comparing phase shifts to 15 min, 50 lux light pulses with and without a bout of running induced by confinement to a novel wheel 30 min prior to and extending through light exposure. Light pulses 6 h after dark onset on the first night of constant dark induced phase advance shifts averaging 80 min. Wheel running attenuated these shifts by 45% on average (p<0.01). Light pulses 1 h or 2.25 h after dark onset induced phase delay shifts averaging 50 min and 20 min, respectively, that were not affected by stimulated running. A significant running response to the novel wheel was evident at all 3 time points, but was greater to wheel confinement at both times early in the night. Stimulated running alone early or late in the night did not produce significant phase shifts. Behavioral attenuation of phase advances to light late in the night was prevented by pretreatment with the general 5HT1 antagonist metergoline (2 mg/kg i.p.). Metergoline did not significantly attenuate running in novel wheels. These results indicate that modulation of light-induced phase shifts by behavior is phase dependent and may involve direct or indirect actions of serotonin within the circadian system.