Nicotine phase shifts the 6-sulphatoxymelatonin rhythm and induces c-Fos in the SCN of rats

Human circadian rhythm studies: Practical guidelines for inclusion/exclusion criteria and protocol

As interest in circadian rhythms and their effects continues to grow, there is an increasing need to perform circadian studies in humans. Although the constant routine is the gold standard for these studies, there are advantages to performing more naturalistic studies. Here, a review of protocols for such studies is provided along with sample inclusion and exclusion criteria. Sleep routines, drug use, shift work, and menstrual cycle are addressed as screening considerations. Regarding protocol, best practices for measuring melatonin, including light settings, posture, exercise, and dietary habits are described. The inclusion/exclusion recommendations and protocol guidelines are intended to reduce confounding variables in studies that do not involve the constant routine. Given practical limitations, a range of recommendations is provided from stringent to lenient. The scientific rationale behind these recommendations is discussed. However, where the science is equivocal, recommendations are based on empirical decisions made in previous studies. While not all of the recommendations listed may be practical in all research settings and with limited potential participants, the goal is to allow investigators to make well informed decisions about their screening procedures and protocol techniques and to improve rigor and reproducibility, in line with the objectives of the National Institutes of Health.

Systematic review of drugs that modify the circadian system's phase-shifting responses to light exposure

We searched PubMed for primary research quantifying drug modification of light-induced circadian phase-shifting in rodents. This search, conducted for work published between 1960 and 2018, yielded a total of 146 papers reporting results from 901 studies. Relevant articles were those with any extractable data on phase resetting in wildtype (non-trait selected) rodents administered a drug, alongside a vehicle/control group, near or at the time of exposure. Most circadian pharmacology experiments were done using drugs thought to act directly on either the brain's central pacemaker, the suprachiasmatic nucleus (SCN), the SCN's primary relay, the retinohypothalamic tract, secondary pathways originating from the medial/dorsal raphe nuclei and intergeniculate leaflet, or the brain's sleep-arousal centers. While the neurotransmitter systems underlying these circuits were of particular interest, including those involving glutamate, gamma-aminobutyric acid, serotonin, and acetylcholine, other signaling modalities have also been assessed, including agonists and antagonists of receptors linked to dopamine, histamine, endocannabinoids, adenosine, opioids, and second-messenger pathways downstream of glutamate receptor activation. In an effort to identify drugs that unduly influence circadian responses to light, we quantified the net effects of each drug class by ratioing the size of the phase-shift observed after administration to that observed with vehicle in a given experiment. This allowed us to organize data across the literature, compare the relative efficacy of one mechanism versus another, and clarify which drugs might best suppress or potentiate phase resetting. Aggregation of the available data in this manner suggested that several candidates might be clinically relevant as auxiliary treatments to suppress ectopic light responses during shiftwork or amplify the circadian effects of timed bright light therapy. Future empirical research will be necessary to validate these possibilities.

Perinatal exposure to nicotine disrupts circadian locomotor and learning efficiency rhythms in juvenile mice

The increased rates of nicotine exposure by electronic nicotine delivery systems (vaping), ingestion, or patches during pregnancy as an alternative to the smoking of tobacco arise concerns about the neurodevelopmental, cognitive, and behavioral long-term consequences in the juvenile offspring. Nowadays, the use of electronic cigarettes as supposed a safer smoking alternative has been increased mainly in young females at reproductive age, due to the "safety" misconception. However, previous studies suggest that exposure to nicotine during pregnancy and prenatal development may lead to detrimental effects in the postnatal lifespan. Nicotine, as an alkaloid, alters the reward system acting as acetylcholine (ACh) agonist on nicotinic cholinergic receptors (nAChRs). In early brain development, the cholinergic system is also involved in neurite outgrowth, cell survival, proliferation, differentiation, neurogenesis, and many other critical processes being considered as a developmental signal marker. The nicotine noxious effect at those early stages may impact the system programming and plasticity in the long-term postnatal life. In this study, we analyze the circadian locomotor activity and learning efficiency rhythms in the juvenile male offspring of mice exposed to nicotine through pregnancy and lactation. Attenuated rhythm amplitude and relative power of the circadian component were found in the nicotine exposed offspring (pN). The acrophase (the best performance during a 24-h cycle) of learning efficiency was delayed and the long-term memory consolidation task failed after 8 days of learning experience. The aforementioned results suggest nicotine exposure in uterus modifies the circadian modulation related to the memory consolidation and locomotor systems as well as its environmental temporal synchronization.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.

Characterization of the 3xTg-AD mouse model of Alzheimer's disease: part 1. Circadian changes

Circadian disturbances, including a fragmented sleep-wake pattern and sundowning, are commonly reported early in the progression of Alzheimer's disease (AD). These changes are distinctly different from those observed in non-pathological aging. Transgenic models of AD are a promising tool in understanding the underlying mechanisms and cause of disease. A novel triple-transgenic model of AD, 3xTg-AD, is the only model to exhibit both Abeta and tau pathology, and mimic human AD. The present study characterized changes pertaining to circadian rhythmicity that occur prior to and post-AD pathology. Both male and female 3xTg-AD mice demonstrated alterations to their circadian pacemaker with decreased nocturnal behavior when compared to controls. Specifically, males showed greater locomotor activity during the day and shorter freerunning periods prior to the onset of AD-pathology, and females had a decrease in activity levels during their typical active phase. Both sexes did not differ in terms of their freerunning periods or photic phase shifting ability. A decrease in vasoactive intestinal polypeptide-containing and vasopressin-containing cells was observed in the suprachiasmatic nucleus of 3xTg-AD mice relative to controls. This study demonstrates that abnormalities in circadian rhythmicity in 3xTg-AD mice precede expected AD pathology. This suggests that human studies may wish to determine if similar circadian dysfunction is predictive of early-onset AD.

Pre- and post-nicotine circadian activity rhythms can be differentiated by a paired environmental cue

Previous studies have shown that addictive drugs presented daily at fixed times produce circadian (oscillator-driven) anticipatory and evoked activity rhythms in rats. Other studies have shown that environmental cues paired with addictive drugs produce tolerance to drug effects and elicit craving behavior when presented without the drug. The present study tested these circadian entrainment and paired-cue conditioning effects together. This study compared the ability of daily nicotine and saline injections at different fixed times to entrain pre-injection (anticipatory) and post-injection (evoked) circadian activity rhythms in two groups of female Sprague-Dawley rats. One group (Paired) had an environmental cue (a tone) paired with the effects of the nicotine injection, and the second group (Unpaired) had the tone paired with the effects of the saline injection. The rats were housed singly for 56 days in chambers with attached wheels under constant dim light and rate-limited food access. During three separate injection phases, nicotine and saline were administered daily at different fixed times, and the tone was presented at the second injection time. Three multi-day test phases examined circadian activity (a) without injections or tone, (b) with the tone alone at normal and novel times, and (c) with the tone absent and with injections occurring at normal and at novel times. The results showed that nicotine entrained both pre- and post-injection circadian oscillators, and the nicotine-paired tone interfered with pre-injection anticipatory activity.

Chronobiometry of Behavioral Activity in the Ts65Dn Model of Down Syndrome

Disruption of the sleep-wake cycle has been reported among individuals with Down syndrome (DS). Here we studied behavioral rhythms in adult male and female Ts65Dn mice, a model of DS. The overall behavioral activity of Ts65Dn and diploid (2N) littermates as defined by total movements (TM), movement time (MT), ambulatory movement time (AMT), time spent in center of arena (CT), jumps (JFP), rotational behavior (TURNS), and wheel-running activity (WRA) was recorded under a 12 h:12 h light-dark photocycle. During the light phase, Ts65Dn mice exhibited higher TM, MT, CT, JFP, and WRA compared to 2N littermates. During the dark phase, Ts65Dn and 2N mice differed only in CT and WRA, with the Ts65Dn group engaging in higher levels of both. There were no gender differences for any of the behavioral variables studied. Non-linear least-squares (Cosinor) analysis of the distribution of total behavioral activity (TM) indicated that Ts65Dn mice exhibited a slightly higher mean oscillation (i.e., mesor), but significantly lower amplitude in comparison to 2N mice, suggesting that levels of TM were elevated in trisomic mice but were relatively constant throughout the photocycle. The peak of the Ts65Dn TM rhythm was significantly phase-advanced, occurring approximately 4 h earlier than 2N mice. Overall, Ts65Dn mice were hyperactive and differed significantly in daily patterns of specific behaviors from those of 2N littermates. To control for the potential confound of retinal degeneration in Ts65Dn and 2N mice, we compared and found no difference between the TM rhythm parameters of 2N and non-retinally degenerate C57/129Sv mice, suggesting that abnormal behavioral rhythmicity in Ts65Dn mice may not due to the absence of rod and cone photoreceptors. These results serve as a starting point for further investigations into the physiological basis of sleep-wake disturbances in DS patients.

The circadian visual system, 2005

The primary mammalian circadian clock resides in the suprachiasmatic nucleus (SCN), a recipient of dense retinohypothalamic innervation. In its most basic form, the circadian rhythm system is part of the greater visual system. A secondary component of the circadian visual system is the retinorecipient intergeniculate leaflet (IGL) which has connections to many parts of the brain, including efferents converging on targets of the SCN. The IGL also provides a major input to the SCN, with a third major SCN afferent projection arriving from the median raphe nucleus. The last decade has seen a blossoming of research into the anatomy and function of the visual, geniculohypothalamic and midbrain serotonergic systems modulating circadian rhythmicity in a variety of species. There has also been a substantial and simultaneous elaboration of knowledge about the intrinsic structure of the SCN. Many of the developments have been driven by molecular biological investigation of the circadian clock and the molecular tools are enabling novel understanding of regional function within the SCN. The present discussion is an extension of the material covered by the 1994 review, "The Circadian Visual System."

[Stress, cancer and circadian rhythm of melatonin]

Influence of stress on immunity and pathogenesis relates to corticotropic axis: hypothalamus-hypophysis-surrenals (HHS). Its over-stimulation due to traumas during early childhood or before birth seems to generate brain abnormalities such as reduction of hippocampus volume. More typical of adult age, hypothalamus-pineal gland axis (HP), responsible for melatonin production, may be impaired because of chronic stress, mainly through sleep disturbances or addictive behaviours. Old age has been reported to produce same impairments. Circadian cycle of melatonin is closely related to immune functions and its disturbance seems to induce, among populations undergoing frequent changes of life rhythm, a significant raise of cancer incidence: night shift workers, air pilots... Stress then seems enable to increase cancer risk through its negative impact on HHS and HP axis and therefore on immunity. Immunotherapy, which was an interesting solution considering this, has not yield yet expected results. Upstream, other ways have been successfully investigated in prospective randomised trials, such as psychotherapeutic treatments, with positive effects on cellular immunity and survival. The ability to condition immune responses in animals allows thinking that hypnotherapy could also be used along with standard treatments.

Transcription factor gene expression profiling after acute intermittent nicotine treatment in the rat cerebral cortex

Several studies in different in vitro and in vivo models have demonstrated neuroprotective effects of nicotinic receptor agonists and indirect trophic actions of nicotine on brain are suggested from observations describing nicotine as a cognitive enhancer by increasing vigilance and improving learning and memory. While an increasing number of studies have given evidence of neuroprotective and neurotrophic effects of nicotine treatment, the molecular mechanism mediating the neurotrophic effects of nicotine are not fully understood. Previously in an analysis of several neurotrophic factors as possible mediators of nicotine-induced neuroprotection and/or neurotrophic effects we could reveal that an acute intermittent nicotine treatment increases fibroblast growth factor-2 mRNA and protein in several brain regions of rat brain. Even if other studies have demonstrated in different paradigms that nicotine administration modulates expression level of a variety of genes, there is still a lack of indication which candidate genes, involved in neuroprotective responses are modulated by nicotine. In the present work we have used a microarray assay to further find and characterize new genes responsive to acute intermittent nicotine treatment and linked to neuroprotection. Therefore, we used Rat Genome U34A Affymetrix GeneChip arrays containing about 8800 probe sets to characterize transcriptional responses in the rat parietal cortex after acute intermittent nicotine treatment. We focused our attention to expression of transcription factors and several of them were up- or down-regulated by nicotine, among these Nr4a1 (Nurr77), Egr-1 and Egr-2. In situ hybridization was used to corroborate the microarray data and to reveal further spatial and temporal patterns of these nicotine induced genes. Taken together the present results identified several novel candidate genes modified by acute intermittent nicotine exposure and as such potentially involved in neuroprotective-neurotrophic actions.

Modulation of photic resetting in rats by lesions of projections to the suprachiasmatic nuclei expressing p75 neurotrophin receptor

The suprachiasmatic nuclei of the hypothalamus (SCN) are the site of the master circadian clock in mammals. The SCN clock is mainly entrained by the light-dark cycle. Light information is conveyed from the retina to the SCN through direct, retinohypothalamic fibres. The SCN also receive other projections, like cholinergic fibres from basal forebrain. To test whether cholinergic afferents are involved in photic resetting, lesions of cholinergic projections were performed in rats with intracerebroventricular (i.c.v.) injections or intra-SCN microinjections of 192 IgG-saporin. When injected in the SCN, this immunotoxin destroys the cholinergic projections and retinohypothalamic afferents that express p75 low-affinity nerve growth factor (p75(NGF)) receptors. The extent of lesions in the basal forebrain and SCN was assessed by acetylcholinesterase histochemistry, p75(NGF) receptor, choline acetyl-transferase, calbindin-D28K and VIP immunocytochemistry. The intra-SCN treatment reduced light-induced phase advances by 30%, and induced a complete loss of forebrain and retinal afferents expressing p75(NGF) receptors within the SCN and a decrease of forebrain cholinergic neurons, most likely those projecting to the SCN. The i.c.v. treatment reduced light-induced phase advances by 40%, increased phase delays and led to extensive damage of forebrain p75(NGF)-expressing neurons, while sparing half of the fibres expressing p75(NGF) receptors (retinal afferents?) in the SCN. Because the integrity of forebrain p75(NGF)-expressing neurons appears to be critical in mediating the effects on light-induced phase advances, we therefore suggest that anterior cholinergic projections expressing p75(NGF) receptors modulate the sensitivity of the SCN clock to the phase advancing effects of light.

Basal forebrain neurons modulate the synthesis and expression of neuropeptides in the rat suprachiasmatic nucleus

We tested the hypothesis that efferents from the nucleus basalis magnocellularis (NBM) play a direct role in the regulation of neuropeptide synthesis and expression by neurons of the rat suprachiasmatic nucleus (SCN). Adult male rats in which the NBM was destroyed with quinolinic acid, either unilaterally or bilaterally, were compared with rats injected with physiological saline and with control rats. The estimators used to assess the effects of cholinergic deafferentation on the neuroanatomy and neurochemistry of the SCN were the total number of SCN neurons, the total number and somatic size of SCN neurons producing vasopressin (VP) and vasoactive intestinal polypeptide (VIP), and the respective mRNA levels. Bilateral destruction of the NBM did not produce cell death in the SCN, but caused a marked reduction in the number and somatic size of SCN neurons expressing VP and VIP, and in the mRNA levels of these peptides. The decrease in the number of VP- and VIP-producing neurons provoked by unilateral lesions was less striking than that resulting from bilateral lesions. It was, however, statistically significant in the ipsilateral hemisphere, but not in the contralateral hemisphere. The results show that the reduction of cholinergic inputs to the SCN impairs the synthesis, and thereby decreases the expression of neuropeptides by SCN neurons, and that the extent of the decline correlates with the amount of cholinergic afferents destroyed. This supports the notion that acetylcholine plays an important, and direct role in the regulation of the metabolic activity of SCN neurons.

Pineal melatonin and brain transmitter monoamines in CBA mice during chronic oral nicotine administration

The effects of chronic oral nicotine administration on the pineal melatonin and brain transmitter monoamines were studied in male CBA mice, which possess a clear daily rhythm of melatonin secretion. On the 50th day of nicotine administration, pineal melatonin as well as cerebral dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined at various times. The chronic nicotine treatment did not alter the timing of the pineal melatonin peak, which occurred at 10 h after the light offset. However, in mice drinking nicotine solution, the nocturnal pineal melatonin levels were lower than in control mice drinking tap water. The chronic nicotine treatment increased the striatal DA, DOPAC, HVA and 5-HIAA levels, the hypothalamic NE, MHPG and 5-HIAA and the cortical MHPG. Most prominent effects of nicotine were found at 8 h after the light offset, when the striatal levels of DA and HVA, hypothalamic NE and MHPG as well as cortical MHPG were significantly elevated in the nicotine-treated mice compared with the control mice. No direct correlation between nicotine's effects on brain transmitter monoamines and on pineal melatonin levels was apparent. The results suggest that chronic nicotine treatment slightly suppresses the melatonin production but does not alter the daily rhythm of pineal melatonin in mice maintained on a light-dark cycle. However, the results indicate that nicotinic receptors might be involved in the regulation of pineal function.

Circadian adaptation to night-shift work by judicious light and darkness exposure

In this combined field and laboratory investigation, the authors tested the efficacy of an intervention designed to promote circadian adaptation to night-shift work. Fifteen nurses working permanent night schedules (> or = 8 shifts/ 15 days) were recruited from area hospitals. Following avacation period of > or = 10 days on a regular daytime schedule, workers were admitted to the laboratory for the assessment of circadian phase via a 36-h constant routine. They returned to work approximately 12 night shifts on their regular schedules under one of two conditions. Treatment group workers (n = 10, mean age +/- SD = 41.7 +/- 8.8 years) received an intervention including 6 h of intermittent bright-light exposure in the workplace (approximately 3,243 lux) and shielding from bright morning outdoor light with tinted goggles (15% visual light transmission). Control group workers (n = 9, mean age +/- SD = 42.0 +/- 7.2 years) were observed in their habitual work environments. On work days, participants maintained regular sleep/wake schedules including a single 8-h sleep/darkness episode beginning 2 h after the end of the night shift. A second 36-h constant routine was performed following the series of night shifts. In the presence of the intervention, circadian rhythms of core body temperature and salivary melatonin cycles were delayed by an average (+/- SEM) of -9.32 +/- 1.06 h and -11.31 +/- 1.13 h, respectively. These were significantly greater than the phase delays of -4.09 +/- 1.94 h and -5.08 +/- 2.32 h displayed by the control group (p = 0.03 and p = 0.02, respectively). The phase angle between circadian markers and the shifted schedule was reestablished to its baseline position only in the treatment group of workers. These results support the efficacy of a practical intervention for promoting circadian adaptation to night-shift work under field conditions. They also underline the importance of controlling the overall pattern of exposure to light and darkness in circadian adaptation to shifted sleep/wake schedules.

Distinct pharmacological mechanisms leading to c-fos gene expression in the fetal suprachiasmatic nucleus

Maternal treatment with cocaine or a D1-dopamine receptor agonist induces c-fos gene expression in the fetal suprachiasmatic nuclei (SCN). Other treatments that induce c-fos expression in the fetal SCN include caffeine and nicotine. In the current article, the authors assessed whether these different pharmacological treatments activate c-fos expression by a common neurochemical mechanism. The results indicate the presence of at least two distinct pharmacological pathways to c-fos expression in the fetal rat SCN. Previous studies demonstrate that prenatal activation of dopamine receptors affects the developing circadian system. The present work shows that stimulant drugs influence the fetal brain through multiple transmitter systems and further suggests that there may be multiple pathways leading to entrainment of the fetal biological clock.

Influences of cholinergic neurotoxin ethylcholine aziridinium ion on circadian rhythms in rats

To investigate whether damages of cholinergic neurons in the brain produce aging-like changes in circadian rhythms, we examined the influences of intracerebroventricular injection of cholinergic neurotoxin ethylcholine aziridinium ion (AF64A, 5 nmol/5 microl) on circadian rhythms in rats, by measuring locomotor activity and body temperature with the automatic behavioral measurement system combined with the telemetry. Daily rhythms in locomotor activity and body temperature were observed in AF64A-treated rats under a 12:12 h light:dark (LD) cycle, however, in AF64A-treated rats, the amplitude of activity and temperature rhythms was significantly decreased, the phase of the both rhythms was advanced and the amount of activity was decreased, compared with control rats. Locomotor activity and body temperature also showed a circadian rhythm in AF64A-treated rats under the constant dark condition with the period similar to that in the control rats. The present findings are in accordance with the observation in aged animals in which cholinergic hypofunction are often observed, suggesting that hypofunctions of the cholinergic systems in the brain might be involved in aging-like changes in the circadian rhythms.

Phase response relationships between light pulses and the melatonin rhythm in rats

There is some controversy whether phase response curves constructed from studies conducted after acute release into constant darkness (Type II) or after prolonged constant darkness are comparable. This study investigated the effects of brief low-intensity light pulses on the onset of 6-sulphatoxymelatonin excretion in rats 48 to 60 h after lights-off and after 14 days of continuous darkness. In the former condition, maximum phase delays occurred between 4 and 6 h after expected lights-off, but no phase advances were observed within 2 days of the presentation of the stimulus. When the times of the pulses were plotted in relation to the individual onsets, peak light-induced phase delays occurred 0 to 2 h after melatonin onset. After 14 days in continuous darkness, the peak phase delays also occurred 0 to 2 h after melatonin onset and were slightly but significantly smaller. No significant phase advances were observed. In a separate small series of experiments, the temperature rhythm of rats was shown to be delayed by a comparable degree to that of melatonin by light pulses 2 and 4 h after expected lights-off under the Type II conditions. It is concluded that phase response curves conducted under Type I and Type II conditions are comparable.

Nicotine-induced fos expression in the pedunculopontine mesencephalic tegmentum in the rat

The aim of this study was to assess the effects of a single dose of nicotine (NIC, 0.3 or 1.0 mg/kg, s.c.), after survival times of 30, 60 or 120 min, on immediate early gene expression in the pedunculopontine mesencephalic tegmentum (PMT), using Fos-immunocytochemistry. Either doses of NIC strongly increased Fos-immunoreactivity in both the pedunculopontine tegmental nucleus (PPTg) and the laterodorsal tegmental nucleus (LDTg), as compared to the saline controls, at 30 min and 60 min. In comparison, the effects of NIC-induced Fos expression in the caudate-putamen (CP) were not as strong as the ones observed in the PPTg and LDTg. In fact, at 30 min the 0.3 mg/kg dose of NIC did not induce Fos-expression, unlike the PPTg and LDTg. The CP response was more noticeable in the mediodorsal than in the laterodorsal region. Double-labelling studies using Fos-immunoreactivity and NADPH-diaphorase histochemistry for cholinergic cells in the PPTg and LDTg revealed that, in general, cholinergic neurons had Fos negative nuclei, although double-labelled neurons were occasionally seen in the PPTg. In conclusion, systemically administered NIC activates the neuronal population of the PPTg and the LDTg possibly by directly targeting nicotinic receptors that may be located in non-cholinergic neurons. We postulate that activation of these non-cholinergic neurons modulates the activity of cholinergic cells in the PMT, which in turn may alter dopamine release in the mesolimbic system.

Melatonin treatment attenuates symptoms of acute nicotine withdrawal in humans

Nicotine withdrawal is typically associated with negative changes in mood and performance, which often lead to relapse. We tested whether an oral 0.3-mg dose of melatonin administered 3.5 h after the nicotine withdrawal, and increasing circulating melatonin concentrations within the physiological range, affects the symptoms of acute 10-h (0800-1800 h) nicotine withdrawal in regular smokers. Self-reported ratings of mood, sleepiness, and cigarette craving were assessed hourly, using 17 visual analog scales (VAS). Computerized Four-Choice Reaction Time (FCRT) and Simple Auditory Reaction Time (SART) tests were used to assess performance every 2 h. Saliva samples were collected hourly, and salivary melatonin levels were measured using supersensitive radioimmunoassay. Compared with the placebo, melatonin treatment significantly reduced self-ratings of "anxious," "restless," "tense," "irritable," "angry," "depressed, " "impatient," and "craving for cigarettes." Melatonin treatment did not significantly change the responses on the performance tests used. These data suggest that melatonin can help to counteract the acute effects of smoking cessation on mood.

Emergence of altered circadian timing in a cholinergically supersensitive rat line

Mammalian circadian rhythms are controlled by the suprachiasmatic nuclei (SCN) in concert with light information. Several neurotransmitters and neural pathways modulate light effects on SCN timing. This study used a line of rat with an upregulated cholinergic system to investigate the role of acetylcholine in rhythmicity. With the use of a selective breeding program based on the thermic response to a cholinergic agonist, we developed a supersensitive (S(ox)) and subsensitive (R(ox)) rat line. The S(ox) rats showed an earlier onset time of melatonin rhythm under a 12:12-h light-dark photoperiod from generation 3 (3 +/- 0.5 h after dark) compared with R(ox) rats (4.5 +/- 0.1 h) and an earlier morning decline in temperature (0.9 +/- 0.3 h before lights on) compared with R(ox) animals (0.1 +/- 0.1 h). Furthermore, the S(ox) animals displayed a significantly shorter free-running period of temperature rhythm than R(ox) rats (23.9 +/- 0.04 and 24.3 +/- 0.1 h, respectively, P < 0.05). The results suggest that the altered circadian timing of the S(ox) rats may be related to the cholinergic supersensitivity, intimating a role for acetylcholine in the circadian timing system.