Effect of p-chlorophenylalanine and tryptophan on sleep, EEG and motor activity in the rat

Periostracum Cicadae Extract and N-Acetyldopamine Regulate the Sleep-Related Neurotransmitters in PCPA-Induced Insomnia Rats

Insomnia is the second most prevalent mental illness worldwide. Periostracum cicadae (PC), as an animal traditional Chinese medicine with rich pharmacological effects, has been documented as a treatment for children's night cries, and later extended to treat insomnia. This study aimed to investigate the effects of PC extract and N-acetyldopamine compounds in ameliorating insomnia. The UPLC-ESI-QTOF-MS analysis determined that PC extract mainly contained N-acetyldopamine components. Previously, we also isolated some acetyldopamine polymers from PC extract, among which acetyldopamine dimer A (NADA) was present in high content. Molecular docking and molecular dynamic simulations demonstrated that NADA could form stable complexes with 5-HT1A, BDNF, and D2R proteins, respectively. The effects of PC extract and NADA on insomnia were evaluated in the PCPA-induced insomnia model. The results indicated that PC extract and NADA could effectively ameliorate hypothalamic pathology of insomnia rats, increase the levels of 5-HT, GABA, and BDNF, and decrease the levels of DA, DOPAC, and HVA. Meanwhile, the PC extract and NADA also could significantly affect the expression of 5-HT1A, BDNF, and DARPP-32 proteins. This study proved that PC extract and acetyldopamine dimer A could effectively improve PCPA-induced insomnia in rats. It is speculated that the main pharmacological substances of PC were acetyldopamine components.

Zhumian Granules improves PCPA-induced insomnia by regulating the expression level of neurotransmitters and reducing neuronal apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Sleep problems, according to Traditional Chinese medicine (TCM) philosophy, are attributed to the imbalance between yin and yang. Zhumian Granules, also known as Sleep-aid Granules or ZG, are a traditional Chinese herbal remedy specifically designed to alleviate insomnia. This formula consists of many components, including Wu Wei Zi (Schisandrae Chinensis Fructus), Suan Zao Ren (Ziziphi Spinosae Semen), and other medicinal plants. According to the pharmacology of Traditional Chinese Medicine (TCM), Wu Wei Zi and Suan Zao Ren have the ability to relax the mind and promote sleep. When taken together, they may balance the opposing forces of yin and yang. Therefore, ZG may potentially be used as a therapeutic treatment for insomnia.

AIM OF THE STUDY

This research was specifically developed to establish a strong empirical basis for the subsequent advancement and utilization of ZG in the management of insomnia. This research aimed to gather empirical data to support the effectiveness of ZG, thereby providing useful insights into its potential therapeutic advantages for persons with insomnia.

MATERIALS AND METHODS

This study utilized Zhumian Granules (ZG), a traditional Chinese herbal decoction, to examine its sedative and hypnotic effects on mice with PCPA-induced insomnia. The effects were assessed using the pentobarbital-induced sleep test (PIST), Morris water maze test (MWM), and autonomic activity test. The levels of neurotransmitters in each group of mice were evaluated using UPLC-QQQ-MS. The impact of ZG on the quantity and structure of hippocampal neurons was seen in brain tissue slices using immunofluorescence labeling.

RESULTS

ZG was shown to possess active sedative properties, effectively lowering the distance of movement and lengthening the duration of sleep. ZG mitigated the sleeplessness effects of PCPA by elevating the levels of 5-hydroxytryptamine (5-HT), 4-aminobutyric acid (GABA), and 5-hydroxyindoleacetic acid (5-HIAA), while reducing the levels of dopamine (DA) and norepinephrine (NE), as well as decreasing neuronal death.

CONCLUSIONS

This research confirmed the sedative and hypnotic properties of ZG and elucidated its probable mechanism involving neurotransmitters.

Anti-insomnia Effect of a Polyherbal Formulation on P-chlorophenyalanine Induced Experimental Animal Model

Sleep is a dynamic and controlled set of physiological and behavioural practices during which the stabilisation and restoration processes of the body take place properly. Therefore, sleep disorders, especially chronic insomnia, can harm an individual's physical and mental health. However, the therapeutic alternatives are limited and possess severe side effects. Thus, in this study, we aimed to investigate the anti-insomnia effect of a polyherbal formulation (Sleep) (SLP) on p-chlorophenyalanine (PCPA) induced insomnia in rats. Intraperitoneal injection of PCPA induced the experimental condition, and the therapeutic effect of SLP was evaluated by studying the sleep pattern and expression of various neurotransmitters and receptors, along with neurotrophins. Moreover, insomnia-associated oxidative stress and inflammation were also studied. From the findings, we found that the SLP-supplemented animals improved their sleeping behaviour and that the major neurotransmitters, hormones, and receptors were maintained at an equilibrium level. Furthermore, the neurotrophin level was increased and pro-inflammatory cytokines were reduced. The evaluation of oxidative stress markers shows that the antioxidants were significantly boosted, and as a result, lipid peroxidation was prevented. The overall findings suggest that SLP can be used as an effective medication for the treatment of sleep disorders like insomnia as it triggers the major neurotransmitter system.

Highly Activated Neuronal Firings Monitored by Implantable Microelectrode Array in the Paraventricular Thalamus of Insomnia Rats

Insomnia is a common sleep disorder around the world, which is harmful to people's health, daily life, and work. The paraventricular thalamus (PVT) plays an essential role in the sleep-wake transition. However, high temporal-spatial resolution microdevice technology is lacking for accurate detection and regulation of deep brain nuclei. The means for analyzing sleep-wake mechanisms and treating sleep disorders are limited. To detect the relationship between the PVT and insomnia, we designed and fabricated a special microelectrode array (MEA) to record electrophysiological signals of the PVT for insomnia and control rats. Platinum nanoparticles (PtNPs) were modified onto an MEA, which caused the impedance to decrease and improved the signal-to-noise ratio. We established the model of insomnia in rats and analyzed and compared the neural signals in detail before and after insomnia. In insomnia, the spike firing rate was increased from 5.48 ± 0.28 spike/s to 7.39 ± 0.65 spike/s, and the power of local field potential (LFP) decreased in the delta frequency band and increased in the beta frequency band. Furthermore, the synchronicity between PVT neurons declined, and burst-like firing was observed. Our study found neurons of the PVT were more activated in the insomnia state than in the control state. It also provided an effective MEA to detect the deep brain signals at the cellular level, which conformed with macroscopical LFP and insomnia symptoms. These results laid the foundation for studying PVT and the sleep-wake mechanism and were also helpful for treating sleep disorders.

A Century Searching for the Neurons Necessary for Wakefulness

Wakefulness is necessary for consciousness, and impaired wakefulness is a symptom of many diseases. The neural circuits that maintain wakefulness remain incompletely understood, as do the mechanisms of impaired consciousness in many patients. In contrast to the influential concept of a diffuse "reticular activating system," the past century of neuroscience research has identified a focal region of the upper brainstem that, when damaged, causes coma. This region contains diverse neuronal populations with different axonal projections, neurotransmitters, and genetic identities. Activating some of these populations promotes wakefulness, but it remains unclear which specific neurons are necessary for sustaining consciousness. In parallel, pharmacological evidence has indicated a role for special neurotransmitters, including hypocretin/orexin, histamine, norepinephrine, serotonin, dopamine, adenosine and acetylcholine. However, genetically targeted experiments have indicated that none of these neurotransmitters or the neurons producing them are individually necessary for maintaining wakefulness. In this review, we emphasize the need to determine the specific subset of brainstem neurons necessary for maintaining arousal. Accomplishing this will enable more precise mapping of wakefulness circuitry, which will be useful in developing therapies for patients with coma and other disorders of arousal.

Modulating role of serotonergic signaling in sleep and memory

Serotonin is an important neurotransmitter with various receptors and wide-range effects on physiological processes and cognitive functions including sleep, learning, and memory. In this review study, we aimed to discuss the role of serotonergic receptors in modulating sleep-wake cycle, and learning and memory function. Furthermore, we mentioned to sleep deprivation, its effects on memory function, and the potential interaction with serotonin. Although there are thousands of research articles focusing on the relationship between sleep and serotonin; however, the pattern of serotonergic function in sleep deprivation is inconsistent and it seems that serotonin has not a certain role in the effects of sleep deprivation on memory function. Also, we found that the injection type of serotonergic agents (systemic or local), the doses of these drugs (dose-dependent effects), and up- or down-regulation of serotonergic receptors during training with various memory tasks are important issues that can be involved in the effects of serotonergic signaling on sleep-wake cycle, memory function, and sleep deprivation-induced memory impairments. This comprehensive review was conducted in the PubMed, Scopus, and ScienceDirect databases in June and July 2021, by searching keywords sleep, sleep deprivation, memory, and serotonin.

Enzymolysis peptides from Mauremys mutica plastron improve the disorder of neurotransmitter system and facilitate sleep-promoting in the PCPA-induced insomnia mice

ETHNOPHARMACOLOGY RELEVANCY

For many centuries, Mauremys mutica is highly valued as a food homologous Chinese herbal medicine. It has been considered useful to sedate, nourish brain and promote sleep. However, the animal experimental evidence of its sleep-promoting activity is missing in literature.

AIM OF THE STUDY

In this study, PCPA-induced insomnia model was used to explore the sleep-promoting mechanism of enzymolysis peptides from PMM, and its main composition and chemical structure were analyzed.

MATERIALS AND METHODS

Experiments were performed using PCPA-induced insomnia model, all animals were intraperitoneally injected with PCPA (350 mg/kg·d) for two days. The sleep-promoting effect evaluated using measuring content of 5-HT, GABA, DA, IL-1, BDNF and expression of 5-HT1A receptor and GABAA receptor α1-subunit in mice brain. Primary structure of peptides was identified by HPLC-ESI-QqTOF-MS/MS.

RESULTS

Compared with the model group, the content of 5-HT, GABA, IL-1, BDNF in mice brain of PMM peptide groups was increased to varying degrees, the content of DA was decreased, and the gene transcription and protein expression of 5-HT1A receptor and GABAA receptor α1-subunit were almost all returned to normal levels. In addition, the primary structures of most abundant nine typical peptides in PMM peptides were identified.

CONCLUSIONS

The results showed that PMM peptides could improve the disorder of neurotransmitter system, restore compensatory over-expression 5-HT1A receptor and GABAA receptor α1-subunit, and have a good sleep-promoting effect. The specific amino acid composition, sequence and glycosylation modification of PMM peptides may be the key reason for their activity, which lays a foundation for the subsequent development of sleep-promoting peptide products.

The serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the sleep-promoting effects of tryptophan: A randomized placebo-controlled crossover study

BACKGROUND

The low-expressive short (S) allele of a functional polymorphism (5-HTTLPR) within the serotonin (5-hydroxytriptamine; 5-HT) transporter gene (SLC6A4) has been associated with a reduced functioning of the brain 5-HT system relative to the long (L) allele. As a consequence, the S-allele is found to predispose individuals to a higher risk of sleep quality reduction and clinical insomnia.

AIMS

The present study investigated whether subchronic pre-sleep tryptophan administration could compensate for this predisposition by improving sleep in 5-HTTLPR S-allele carriers.

METHODS

In a double-blind placebo-controlled crossover design a sample of homozygous 5-HTTLPR S-allele (n = 47) and L-allele (n = 51) carriers were assessed for subjective (sleep diary) and objective (actigraphy) sleep during a treatment protocol consisting of 1 week of placebo (1000 mg/day) and 1 week of tryptophan administration (1000 mg/day).

RESULTS

The results support the sleep-promoting effects of tryptophan. Tryptophan improved objective sleep efficiency and objective wake after sleep onset irrespective of allelic variation. There was a marginally significant improvement of subjective sleep quality in the 5-HTTLPR S-allele group but not in the L-allele group following tryptophan relative to placebo intake. In contrast, a significantly poorer sleep quality in the S-allele as opposed to the L-allele group in the placebo condition was not observed in the tryptophan condition.

CONCLUSIONS

Tryptophan augmentation promises to be a valuable treatment strategy for sleep impairments related to genetic deficiencies in 5-HT functioning.

Loganin Exerts Sedative and Hypnotic Effects via Modulation of the Serotonergic System and GABAergic Neurons

Corni fructus, the fruit of Cornus officinalis Sieb. et Zucc., has been used as a tonic for the kidney in China for thousands of years. Loganin is one of the major constituents derived from Corni fructus. In this study, we revealed the sedative and hypnotic activity of loganin and investigated its mechanisms for the first time. Pentobarbital-induced sleep test and insomnia mice models [induced by caffeine and p-chlorophenylalanine (PCPA)] were used for the assessment of sedative and hypnotic effects of loganin. It was found that loganin (20–50 mg/kg) exerted sedative effect in normal mice. Loganin exhibited hypnotic effect by increasing sleep onset and sleep duration in pentobarbital-treated mice, recovering PCPA-induced insomnia and exerting synergistic hypnosis effect with 5-HTP. In addition, electroencephalograph (EEG) and electromyography (EMG) recordings of rats showed that loganin (35 mg/kg) prolonged the ratio of non-rapid eye movement (NREM) sleep and shortened wakefulness significantly, further immunohistochemistry showed that loganin (35 mg/kg) increased c-Fos expression in GABAergic neurons of rats in the ventrolateral preoptic nucleus (VLPO). The levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite were measured in the hippocampus, prefrontal cortex and striatum of mice, 1 h after loganin (35 mg/kg) treatment. 5-HT, 5-HIAA/5-HT, DA, and DOPAC were decreased significantly in the prefrontal cortex. In conclusion, these results indicated that loganin produced beneficial sedative and hypnotic activity, which might be mainly mediated by modification of the serotonergic system and GABAergic neurons.

Possible Molecular Mediators Involved and Mechanistic Insight into Fibromyalgia and Associated Co-morbidities

Fibromyalgia is a chronic complex syndrome of non-articulate origin characterized by musculoskeletal pain, painful tender points, sleep problems and co-morbidities including depression, migraine. The etiopathogenesis of fibromyalgia is complex, variable and remains inconclusive. The etiological factors that have been defined include stress, genetic predisposition and environmental components. As per the reports of the American College of Rheumatology (ACR) the prevalence of fibromyalgia varies from 2 to 22% among the general population with poor diagnostic features primarily pain. Fibromyalgia encompasses a spectrum of co-morbid conditions with multifarious pathogenesis. The highly prevalent manifestations of fibromyalgia include heterogeneous pain and aches. Biochemical and neurobiological elements of fibromyalgia include neurotransmitters, hypothalamic pituitary adrenal axis (HPA axis), inflammatory cytokines, monoaminergic pathway, opioid peptides, sex hormones, nerve growth factor (NGF) and local free radical insult. An imbalance in the serotonergic system is the major underlying etiological factor that has been explored most widely. Owing to complex interplay of diverse pathophysiological pathways, overlapping co-morbidities such as depression have been clinically observed. Therapeutic management of fibromyalgia involves both non pharmacological and pharmacological measures. The current review presents various dysregulations and their association with symptoms of fibromyalgia along with their underlying neurobiological aspects.

Study on the hypnotic effect of rare protopanaxadiol-type and protopanaxatriol-type ginsenosides

Ginsenosides, as major active components of ginseng, possess various pharmacological activities, including anti-tumor, anti-diabetic and hypotensive effects. However, the sedative and hypnotic effect of ginsenosides and the involved mechanism remain unclear. In the present study, the hypnotic effect of rare protopanaxadiol-type (PD) ginsenosides, consisting of Rg3, Rk1, Rg5, and protopanaxatriol-type (PT) ginsenosides, consisting of Rh1, Rk3, Rh4, was investigated and compared in rodent models through behavioral pharmacology methods. Both rare PD and PT ginsenosides decreased spontaneous locomotion activity in normal mice and reduced sleep latency, and extended sleep duration in pentobarbital-treated mice. Moreover, PD and PT ginsenosides attenuated the insomnia induced by caffeine in mice. These hypnotic effects of PD and PT ginsenosides were potentiated by 5-hydroxytryptophan (5-HTP), a precursor of serotonin, and inhibited by p-chlorophenylalanine (PCPA), a 5-HT synthesis inhibitor. Flumazenil (FLU, a specific gamma aminobutyric acid (GABA) antagonist) also impaired the hypnotic effect of both PD and PT ginsenosides. The aforementioned results indicated that PD and PT ginsenosides exhibit sedative and hypnotic activity, and PT ginsenosides show higher activity than PD ginsenosides at high doses (96 mg kg⁻¹). Furthermore, the bioactivity of these two types of ginsenosides might be mediated via the serotonergic and GABAergic systems.

Ginsenosides, as major active components of ginseng, possess various pharmacological activities, including anti-tumor, anti-diabetic and hypotensive effects.

Targeted Neurotransmitters Profiling Identifies Metabolic Signatures in Rat Brain by LC-MS/MS: Application in Insomnia, Depression and Alzheimer's Disease

Epidemiological, cross-sectional, and prospective studies have suggested that insomnia, Alzheimer’s disease (AD) and depression are mutually interacting conditions and frequently co-occur. The monoamine and amino acid neurotransmitter systems in central nervous system were involved in the examination of neurobiological processes of this symptom complex. However, few studies have reported systematic and contrastive discussion of different neurotransmitters (NTs) changing in these neurological diseases. Thus, it is necessary to establish a reliable analytical method to monitoring NTs and their metabolite levels in rat brain tissues for elucidating the differences in pathophysiology of these neurological diseases. A rapid, sensitive and reliable LC-MS/MS method was established for simultaneous determination of the NTs and their metabolites, including tryptophan (Trp), tyrosine (Tyr), serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), dopamine (DA), acetylcholine (ACh), norepinephrine (NE), glutamic acid (Glu), and γ-aminobutyric acid (GABA) in rat brain tissues. The mobile phase consisting of methanol and 0.01% formic acid in water was performed on an Inertsil EP C18 column, and the developed method was validated well. Results demonstrated that there were significant differences for 5-HT, DA, NE, Trp, Tyr and ACh between model and control group in all three models, and a Bayes linear discriminant function was established to distinguish these three kinds of nervous system diseases by DA, Tyr and ACh for their significant differences among control and three model groups. It could be an excellent strategy to provide perceptions into the similarity and differentia of mechanisms from the point of NTs’ changing in brain directly and a new method to distinguish insomnia, depression and AD from view of essence.

Gan-Dan-Liang-Yi-Tang alleviates p-chlorophenylalanine-induced insomnia through modification of the serotonergic and immune system

Gan-Dan-Liang-Yi-Tang (GDLYT) is a Traditional Chinese Medicine that has been historically used for the treatment of insomnia. However, investigations into its pharmacological ingredients and the mechanism underlying its sedative and hypnotic effects remain limited. The present study reported the detailed mechanisms underlying the sedative and hypnotic effects of GDLYT. Kunming mice were administered GDLYT at various sub-hypnotic doses, which underwent sodium pentobarbital treatment test, pentetrazole induced convulsant studies and p-chlorophenylalanine (PCPA) induced insomnia model. Potentiated hypnotic and sedative effects in mice was studied, and also the changes in related neurotransmitter and immune factors were evaluated. The results suggested that GDLYT possessed weak sedative effects on pentetrazole-induced convulsive activity in normal mice at a dose of 1.3 mg/kg, with an increase in sleep onset in subhypnotic dose of sodium pentobarbital-treated mice. GDLYT was also able to alleviate insomnia induced by PCPA in the rodent models, and increased 5-hydroxytryptamine levels in the prefrontal cortex, hippocampus, hypothalamus and corpus striatum of PCPA-treated rats. Furthermore, the hypnotic effects of GDLYT were modified, which allowed for PCPA-induced immune system changes, including increased interleukin (IL)-1β, tumor necrosis factor-α and IL-2 expression levels. The results of the present study indicated that GDLYT induced sedative and hypnotic bioactivity by regulating serotonergic activity in the central nervous system and immune system.

Insomnia Caused by Serotonin Depletion is Due to Hypothermia

STUDY OBJECTIVE

Serotonin (5-hydroxytryptamine, 5-HT) neurons are now thought to promote wakefulness. Early experiments using the tryptophan hydroxylase inhibitor para-chlorophenylalanine (PCPA) had led to the opposite conclusion, that 5-HT causes sleep, but those studies were subsequently contradicted by electrophysiological and behavioral data. Here we tested the hypothesis that the difference in conclusions was due to failure of early PCPA experiments to control for the recently recognized role of 5-HT in thermoregulation.

DESIGN

Adult male C57BL/6N mice were treated with PCPA (800 mg/kg intraperitoneally for 5 d; n = 15) or saline (n = 15), and housed at 20 °C (normal room temperature) or at 33 °C (thermoneutral for mice) for 24 h. In a separate set of experiments, mice were exposed to 4 °C for 4 h to characterize their ability to thermoregulate.

MEASUREMENTS AND RESULTS

PCPA treatment reduced brain 5-HT to less than 12% of that of controls. PCPA-treated mice housed at 20 °C spent significantly more time awake than controls. However, core body temperature decreased from 36.5 °C to 35.1 °C. When housed at 33 °C, body temperature remained normal, and total sleep duration, sleep architecture, and time in each vigilance state were the same as controls. When challenged with 4 °C, PCPA-treated mice experienced a precipitous drop in body temperature, whereas control mice maintained a normal body temperature.

CONCLUSIONS

These results indicate that early experiments using para-chlorophenylalanine that led to the conclusion that 5-hydroxytryptamine (5-HT) causes sleep were likely confounded by hypothermia. Temperature controls should be considered in experiments using 5-HT depletion.

A UFLC-MS/MS method for simultaneous quantitation of spinosin, mangiferin and ferulic acid in rat plasma: application to a comparative pharmacokinetic study in normal and insomnic rats

Suan-Zao-Ren (SZR) decoction, consisting of Ziziphi Spinosae Semen, Poria, Chuanxiong Rhizoma, Anemarrhenae Rhizoma and Glycyrrhizae Radix Et Rhizoma, is a Traditional Chinese Medicine prescription, clinically used for the treatment of insomnia. The objective of this study was to develop a sensitive and reliable UFLC-MS/MS method for simultaneous quantitation of spinosin, mangiferin and ferulic acid, the main active ingredients in SZR decoction, and to compare the pharmacokinetics of these active ingredients in normal and insomnic rats orally administrated with the prescription. Analytes and IS were separated on a Shim-pack XR-ODS column (75 mm × 3.0 mm, 2.2 µm particles) using gradient elution with the mobile phase consisting of methanol and 0.1% formic acid in water at a flow rate of 0.4 mL/min. The detection of the analytes was performed on 4000Q UFLC-MS/MS system with turbo ion spray source in the negative ion and multiple reaction-monitoring mode. The lower limits of quantification were 1, 6 and 1 ng/mL for spinosin, mangiferin and ferulic acid, respectively. Intra- and inter-day precision and accuracy of analytes were well within acceptance criteria (15%). The mean extraction recoveries of analytes and IS from rats plasma were all more than 85.0%. The validated method has been successfully applied to comparing pharmacokinetic profiles of analytes in rat plasma. The results indicated that no significant difference in pharmacokinetic parameters of ferulic acid was observed between two groups, while absorptions of spinosin and mangiferin in insomnic group were significantly lower than those in normal group.

Ferulic acid potentiates pentobarbital-induced sleep via the serotonergic system

Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) is a widely distributed natural phenolic compound that is abundant in many plant tissues and foods. This study investigated possible mechanisms underlying the sedative-hypnotic effect of FA through behavioral pharmacology methods. FA showed dose-dependent sedative effects on locomotion activity in normal mice. FA also significantly potentiated pentobarbital-induced (45 mg/kg, i.p.) sleep by prolonging sleeping time and shortening sleep latency in a dose-dependent manner. These effects were augmented by the administration of 5-hydroxytryptophan (5-HTP), a precursor of 5-hydroxytryptamine (5-HT). With a sub-hypnotic dose of pentobarbital (25 mg/kg, i.p.), FA significantly increased the rate of sleep onset and exhibited a synergistic effect with 5-HTP (2.5 mg/kg, i.p.). Pretreatment with p-chlorophenylalanine (PCPA, an inhibitor of tryptophan hydroxylase) significantly decreased the duration of pentobarbital-induced sleep, whereas FA significantly reversed this effect. These results suggest that FA has sedative-hypnotic activity, possibly mediated by the serotonergic system.

Neural circuitry of stress-induced insomnia in rats

Sleep architecture is often disturbed after a stressful event; nevertheless, little is known about the brain circuitry responsible for the sleep perturbations induced by stress. We exposed rats to a psychological stressor (cage exchange) that initially causes an acute stress response, but several hours later generates a pattern of sleep disturbances similar to that observed in stress-induced insomnia in humans: increased sleep latency, decreased non-REM (nREM) and REM sleep, increased fragmentation, and high-frequency EEG activity during nREM sleep. We examined the pattern of Fos expression to identify the brain circuitry activated, and found increased Fos in the cerebral cortex, limbic system, and parts of the arousal and autonomic systems. Surprisingly, there was simultaneous activation of the sleep-promoting areas, most likely driven by ongoing circadian and homeostatic pressure. The activity in the cerebral cortex and arousal system while sleeping generates a novel intermediate state characterized by EEG high-frequency activity, distinctive of waking, during nREM sleep. Inactivation of discrete limbic and arousal regions allowed the recovery of specific sleep components and altered the Fos pattern, suggesting a hierarchical organization of limbic areas that in turn activate the arousal system and subsequently the cerebral cortex, generating the high-frequency activity. This high-frequency activity during nREM was eliminated in the stressed rats after inactivating parts of the arousal system. These results suggest that shutting down the residual activity of the limbic-arousal system might be a better approach to treat stress-induced insomnia, rather than potentiation of the sleep system, which remains fully active.

Potentiating effects of L-type Ca2+ channel blockers on pentobarbital-induced hypnosis are influenced by serotonergic system

In order to elucidate the mechanism(s) behind the interactions between barbiturates and Ca(2+) antagonists, the effects of three structurally diverse types of Ca(2+) antagonists combined or not with 5-HT on pentobarbital-induced hypnosis in mice were investigated. The results showed that dihydropyridine derivative nifedipine (10.0 and 20.0 mg/kg, p.o.) and other types of Ca(2+) antagonist, verapamil (5.0 and 10.0 mg/kg, p.o.) and diltiazem (2.5, 5.0 and 10.0 mg/kg, p.o.) increased both the sleeping time in hypnotic dosage of pentobarbital (45 mg/kg, i.p.) treated mice and the rate of sleep onset in the sub-hypnotic dosage of pentobarbital (28 mg/kg, i.p.) treated mice in a dose-dependent manner, respectively, and these effects were significantly augmented by 5-hydroxytryptophan (5-HTP), the immediate precursor of 5-hydroxytryptamine (5-HT). Pretreatment with p-chlorophenylalanine (PCPA, 300 mg/kg, s.c.), an inhibitor of tryptophan hydroxylase, significantly decreased pentobarbital-induced sleeping time and nifedipine (10.0 mg/kg, p.o.), verapamil (5.0 mg/kg, p.o.) and diltiazem (2.5 mg/kg, p.o.) abolished this effect. From these results, it should be presumed that the augmentative effect of L-type Ca(2+) channel blockers on pentobarbital-induced sleep may be influenced by serotonergic system.

Serotonin Depletion Attenuates AY-9944-Mediated Atypical Absence Seizures

PURPOSE

To test the hypothesis that serotonin (5-HT) plays a role in the modulation of experimental atypical absence seizures.

METHODS

Male Long-Evans hooded rats were treated from postnatal day (P) 2 to P20 with the cholesterol inhibitor AY-9944 (AY). Epidural electrodes were implanted for electrocorticography (ECoG) followed by serotonin depletion by using para-cholorophenylalanine (PCPA). High-performance liquid chromatography (HPLC) was used to measure the levels of serotonin and its metabolite (5-HIAA) in various brain regions. Serotonin metabolism was computed by using the 5-HIAA/5-HT ratio and used to ascertain differences between groups.

RESULTS

PCPA treatment was associated with a significant decrease in the total slow spike-and-wave discharge (SSWD) duration in AY-treated rats compared with controls (p < 0.01). HPLC data confirmed the PCPA depletion of 5-HT and 5-HIAA in cortex, thalamus, hippocampus, and brainstem compared with naïve rats. AY-treated rats showed higher levels of 5-HIAA and 5-HT in the same brain regions, with a concomitant decrease in rates of serotonin turnover.

CONCLUSIONS

The data indicate that serotonin depletion protects against experimental atypical absence seizures. The increased levels of 5-HIAA and 5-HT and altered rates of serotonin turnover suggest that the serotonergic neurotransmission may be perturbed in the AY rat.

Tetrandrine, a bisbenzylisoquinoline alkaloid from Chinese herb Radix, augmented the hypnotic effect of pentobarbital through serotonergic system

This is the first study of hypnotic activity of tetrandrine (a major component of Stephania tetrandrae) in mice by using synergism with pentobarbital as an index for the hypnotic effect. The results showed that tetrandrine potentiated pentobarbital (45 mg/kg, i.p.)-induced hypnosis significantly by reducing sleep latency and increasing sleeping time in a dose-dependent manner, and this effect was potentiated by 5-hydroxytryptophan (5-HTP). In the subhypnotic dosage of pentobarbital (28 mg/kg, i.p.)-treated mice, tetrandrine (60 and 30 mg/kg, p.o.) significantly increased the rate of sleep onset and also showed synergic effect with 5-HTP. Pretreatment of p-chlorophenylalanine (PCPA, 300 mg/kg, s.c.), an inhibitor of tryptophan hydroxylase, significantly decreased pentobarbital-induced sleeping time and tetrandrine abolished this effect. From these results, it should be presumed that serotonergic system may be involved in the augmentative effect of tetrandrine on pentobarbital-induced sleep.

A subpopulation of rats show social and sleep-waking changes typical of chronic neuropathic pain following peripheral nerve injury

Neuropathic conditions for which treatment is sought, the so-called chronic pain syndrome, are characterized usually by complex behavioural disturbances as well as pain. In this study we evaluated whether social behavioural and sleep disruptions occurred after nerve injury. Before and after chronic constriction of the sciatic nerve, resident-intruder and sleep-wake cycles, as well as mechanical and thermal allodynia/hyperalgesia, were quantified. Sciatic nerve injury in all animals reduced withdrawal thresholds to tactile and thermal (cold) stimuli. Resident-intruder and sleep-waking behaviours were altered in some but not all animals. One group (30%, 'persistent change') had enduring reductions in dominant behaviour to an intruder and decreased slow-wave sleep and increased wakefulness during both light and dark cycles. Another group (25%, 'recovery') had a transient reduction in dominant behaviours and decreased slow-wave sleep and increased wakefulness during only the light cycle. In a third group (45%, 'no effect') resident-intruder and sleep-waking behaviours remained normal. Our finding that the degree of 'pain' as inferred from the allodynia/hyperalgesia was identical in all animals suggests that the alterations to resident-intruder and sleep-wake cycles were independent of the level of sensory disturbance. An absence of correlation between intensity of sensory disturbances and measures of disability (loss of sleep, familial/social problems) is also characteristic of human neuropathic pain. These data indicate that: (i) in a subpopulation of animals sciatic injury results in two of the major complex behavioural changes which are characteristic of neuropathic pain in humans; (ii) testing only for allodynia and hyperalgesia is not sufficient to detect this subpopulation.

Modulation of serotonergic projection from dorsal raphe nucleus to basolateral amygdala on sleep-waking cycle of rats

Putative serotonergic dorsal raphe nucleus (DRN) neurons display a dramatic role in the modulation of behavior. However, it is not clear how this modulation is mediated. The present study investigated the modulatory effects of serotonergic projection of the DRN to the basolateral amygdala (BLA) on the sleep-waking cycle using polysomnograph (PSG) in rats. DRN microinjection of kainic acid (KA) caused insomnia immediately. From the third day, however, slow wave sleep (SWS) and paradoxical sleep (PS) increased markedly. DRN microinjection of p-chlorophenylalanine (PCPA, once a day for 2 days), which inhibits the synthesis of serotonin (5-HT), led to similar effect to KA administration. The percent of sleep-wakefulness began to change on the third day after PCPA microinjection into the DRN, and the effect was most significant on the sixth day. The percent of sleep-wakefulness started to resume on the seventh day. SWS and PS were reduced after excitation of DRN neurons by microinjection of L-glutamate (L-Glu) into the DRN. Preapplication of the nonselective 5-HT receptor antagonist methysergide (MS) into bilateral BLA blocked the effect of DRN microinjection of L-Glu. Furthermore, bilateral BLA microinjection of 5-hydroxytryptophan (5-HTP), the precursor of 5-HT, on the sixth day after microinjection of PCPA into the DRN, could reverse the effect of PCPA microinjection. These results indicate that the modulation of the DRN on sleep is partially mediated by the serotonergic projection of the DRN to the BLA.

Serotonin and sleep

For 50 years, serotonin has been in the centre of the search for the mechanisms and control of sleep. Serotonergic neurotransmission is related to the behavioural state of the animal and plays an important role in modulation of the behavioural state, by interacting with other brain areas modulating circadian rhythm, sleep and waking. Serotonergic activity may be accompanied by waking or sleep depending on the brain area and receptor type involved in the response, on the current behavioural state and on the concomitant agonism/antagonism of other neurotransmitter systems.

Extracellular serotonin levels in the medullary reticular formation during normal sleep and after REM sleep deprivation

Rapid eye movement (REM) sleep is hypothesized to result from the activity of REM sleep-generating and REM sleep-inhibiting neurons. The serotoninergic (5-HT) neurons of the dorsal raphe nucleus (DRN) represents one such population of REM-sleep inhibiting neurons since they are silent during REM sleep. Consistent with the decrease in activity of 5-HT neurons, the brain extracellular levels of 5-HT are lower during REM sleep compared to wakefulness. It is not known whether serotonin release is also reduced as a consequence of REM sleep rebound. Using microdialysis sampling coupled to HPLC-ECD, we measured the extracellular levels of 5-HT and its metabolite (5-HIAA) in the medial medullary reticular formation (mMRF) of freely behaving rats during normal sleep, REM sleep deprivation as well as during REM sleep rebound. We found that the levels 5-HT and 5-HIAA were significantly decreased by REM sleep deprivation. The reduction of 5-HT release was maintained during REM sleep rebound but the extracellular level of its main metabolite was increased. In addition, even during REM sleep rebound, 5-HT release during sleep was low compared to wakefulness. Taken together these data support the permissive role of 5-HT neurotransmission for REM sleep expression.

Extracellular serotonin variations during vigilance states in the preoptic area of rats: a microdialysis study

Numerous studies have shown that serotonergic transmission decreases from waking (W) to slow wave sleep (SWS) to paradoxical sleep (PS), suggesting an active role of serotonin (5-HT) in W but not in sleep. Conversely, the inhibition of 5-HT activity produces insomnia. This insomnia can be reversed by injections of 5-hydroxytryptophan in the preoptic area (POA), suggesting that 5-HT is necessary in this cerebral structure for sleep. Using microdialysis, we studied, 5-HT variations in the POA of rats in relation to vigilance states. 5-HT levels were higher during W than during during SWS and PS. 5-HT increased just before the rats fell asleep and then decreased during sleep. A decreased 5-HT transmission was also observed from SWS to PS. These data document a positive correlation between 5-HT levels in POA and wakefulness. Moreover, these observations are in favour of a permissive role of 5-HT in the POA during PS. A comparison between the POA and the prefrontal cortex in the sleep-wake cycle is discussed.

Sleep inducing effects of propofol microinjection into the medial preoptic area are blocked by flumazenil

The intravenous anesthetic, propofol, has been shown to increase sleep when microinjected into the medial preoptic area (MPA) of the rat. Similar increases in sleep have also been observed with triazolam, pentobarbital and ethanol microinjection. Together, these findings implicate the MPA as an important anatomic site mediating the effects of sedatives on naturally occurring sleep. Although the molecular mechanism by which propofol in the MPA acts to induce sleep is unclear, potentiating effects on the GABA(A) receptor complex may play a role. To assess this possibility, we microinjected propofol alone, and in combination with the benzodiazepine receptor antagonist flumazenil, into the MPA. At a dose of 0.76 microg, flumazenil had no effect on sleep when given alone, and completely blocked the increase in sleep caused by a 40-ng dose of propofol although it did not affect the increase in sleep caused by an 80-ng dose of propofol. These data suggest that the sleep inducing property of propofol is in part mediated by direct or indirect actions on the GABA(A)-benzodiazepine receptor complex.

Serotonin and the sleep/wake cycle: special emphasis on microdialysis studies

Several areas in the brainstem and forebrain are important for the modulation and expression of the sleep/wake cycle. Even if the first observations of biochemical events in relation to sleep were made only 40 years ago, it is now well established that several neurotransmitters, neuropeptides, and neurohormones are involved in the modulation of the sleep/wake cycle. Serotonin has been known for many years to play a role in the modulation of sleep, however, it is still very controversial how and where serotonin may operate this modulation. Early studies suggested that serotonin is necessary to obtain and maintain behavioral sleep (permissive role on sleep). However, more recent microdialysis experiments provide evidence that the level of serotonin during W is higher in most cortical and subcortical areas receiving serotonergic projections. In this view the level of extracellular serotonin would be consistent with the pattern of discharge of the DRN serotonergic neurons which show the highest firing rate during W, followed by a decrease in slow wave sleep and by virtual electrical silence during REM sleep. This suggests that during waking serotonin may complement the action of noradrenaline and acetylcholine in promoting cortical responsiveness and participate to the inhibition of REM-sleep effector neurons in the brainstem (inhibitory role on REM sleep). The apparent inconsistency between an inhibitory and a facilitatory role played by serotonin on sleep has at least two possible explanations. On the one hand serotonergic modulation on the sleep/wake cycle takes place through a multitude of post-synaptic receptors which mediate different or even opposite responses; on the other hand the achievement of a behavioral state depends on the complex interaction between the serotonergic and other neurotransmitter systems. The main aim of this commentary is to review the role of brain serotonin in relation to the sleep/wake cycle. In particular we highlight the importance of microdialysis for on-line monitoring of the level of serotonin in different areas of the brain across the sleep/wake cycle.

Changes in sleep and wakefulness following 5-HT1A ligands given systemically and locally in different brain regions

Serotonin (5-HT) has been implicated in the regulation of vigilance, but whether 5-HT is important for sleep or waking processes remains controversial. This review addresses the role of 5-HT1A receptors in sleep and wakefulness. Systemic administration of 5-HT1A agonists consistently increases wakefulness, whereas slow wave sleep (SWS) and REM (rapid-eye movement) sleep are reduced. However, systemic 5-HT1A agonists also produce a delayed increase in deep slow wave sleep, or an increase in slow wave activity. Intrathecal administration of a selective 5-HT1A agonist produces an increase in SWS, whereas wakefulness is reduced, presumably by stimulating 5-HT1A receptors located presynaptically on primary afferents in the spinal cord. Microinjection of serotonin into the region of the cholinergic basalis neurons produces an increase in slow wave activity, presumably by stimulating 5-HT1A receptors. Microdialysis perfusion of a selective 5-HT1A agonist into the dorsal Raphe nucleus causes an increase in REM sleep, whereas the other sleep/wake stages are unaltered. The REM sleep increase is likely due to a decrease in 5-HT neuronal activity, and thereby reduced 5-HT neurotransmission in projection areas, e.g. the laterodorsal and pedunculopontine tegmental nuclei. Direct injection of a selective 5-HT1A agonist into the pedunculopontine tegmental nuclei reduces REM sleep, consistent with such a hypothesis. These complex sleep/wake data of 5-HT1A ligands suggest that 5-HT1A receptor activation may increase waking, increase slow wave sleep or increase REM sleep depending on where the 5-HT1A receptors are located within the central nervous system.

Effect of p-chlorophenylalanine (PCPA) on sleep and monoamines content in the brain of a lizard species

Administration of PCPA, a specific inhibitor of serotonin synthesis, induced a significant decrease of total sleep time in the lizard Ctenosaura pectinata. This effect was exerted on both quiet sleep and active sleep, but it was more intense on active sleep. Reduction in the amount of active sleep was due to a decrease in the number of the episodes not in their mean duration, since this parameter increased significantly from 5.97 s, under control conditions, to 11.77 s, 10.66 s and 8.85 s at 24, 48 and 72 h after PCPA injection, respectively. Neurochemical analysis showed a significant decrease in the amount of serotonin in the analyzed brain stem structures 12 h after PCPA administration. The possible participation of serotonergic mechanisms in the regulation of reptilian sleep is discussed.

Sleep permissive components within the dorsal raphe nucleus in the rat

Two peptides known for their hypnogenic properties, CLIP (corticotropin-like intermediate lobe peptide or ACTH 18-39) or VIP (vasoactive intestinal polypeptide), were injected locally into the nucleus raphe dorsalis (nRD) of rats pretreated with p-chlorophenylalanine (PCPA). During the dark period, the PCPA insomnia was primarily associated with a reduction in paradoxical sleep (PS), whereas both slow wave sleep (SWS) and PS were decreased during the light period. Immunohistochemistry of serotonin in PCPA-pretreated animals indicated a clear disappearance of 5-HT fibers in the basal hypothalamus and the nRD as compared to control animals. Local injections of CLIP or VIP in the nRD restored PS and SWS. The positive injection sites corresponded to the anatomical distribution of either CLIP or VIP fibers, i.e., the entire nRD for VIP and the antero-dorsal part of this nucleus for CLIP. The sleep effects obtained in PCPA-pretreated rats involve a non-5-HT sleep permissive component within the nRD upon which these injected peptides act.

Diurnal differences in L-tryptophan sleep and temperature effects in the rat

Sleep/waking and EEG power spectra were investigated for 6 h periods in rats following administration of the essential amino acid L-tryptophan (40 mg/kg), the selective serotonin uptake inhibitor zimeldine (20 mg/kg), and following a combination of L-tryptophan and zimeldine. In contrast to earlier studies, L-tryptophan decreased waking and increased total slow wave sleep when administered late in the light phase (8 1/2 h after light onset). No sleep effects were seen after early light phase injections (2 h after lights on). In agreement with earlier studies, zimeldine initially increased wakefulness, followed by an increase in slow wave sleep-2. REM sleep was abolished after zimeldine treatment. Zimeldine increased EEG delta activity and decreased EEG activity above 7 Hz. L-Tryptophan potentiated the zimeldine induced increase in waking only when given early in the light phase. In a separate experiment, body temperature was monitored after L-tryptophan injections in both early and late light phase. A thermogenic effect of L-tryptophan was seen in the early light phase, while the opposite was seen in the late light phase. The data indicate diurnal differences in sleep/waking and temperature effects of a physiological dose of L-tryptophan.

Promotion of sleep by prostaglandin D2 in rats made insomniac by pretreatment with para-chlorophenylalanine

The correlation between the somnogenic effect of prostaglandin (PG) D2 and the serotoninergic system was examined in freely-moving rats (n = 64) by use of a continuous infusion method. Rats pretreated with para-chlorophenylalanine (PCPA: 450 mg/kg body weight, i.p.) or non-PCPA-pretreated rats received infusion of PGD2, serotonin, or its direct precursor, 5-hydroxytryptophan (5HTP), into their third cerebral ventricle at a rate of 100 pmol/0.2 microliter/min between 11:00 and 17:00 h. In the PCPA-pretreated insomniac rats, PGD2 infusion resulted in an immediate increase in slow-wave sleep (SWS) and an increase with a 2-h latency in paradoxical sleep (PS). The total amounts of SWS and PS during the PGD2-infusion period were 151% and 154% of the respective control values. These results indicate that inhibition of the biosynthesis of serotonin and 5HTP by PCPA marginally affects the sleep-promoting effect of PGD2. The transient sleep restoration produced by 5HTP infusion into PCPA-pretreated rats was hardly affected by the simultaneous infusion (200 pmol/0.2 microliter/min; 07:00-17:00 h) of diclofenac sodium, an inhibitor of cyclo-oxygenase, suggesting that PGD2 production is not critically involved in the sleep restoration by 5HTP. The sleep-promoting property of PGD2 is thus probably independent of the serotoninergic modulation of sleep-wake activity.

Re-examination of the effects of raphe lesions on the sleep/wakefulness cycle states in cats

To study the specific effects of central superior raphe nucleus (CeSR) lesions on the different sleep/wakefulness cycle states of the cat, nine animals with implanted electrodes for EOG, EMG and EEG recordings were used. Seven cats received diathermocoagulation lesions that destroyed between 13 and 100 percent of the CeSR; the remaining two cats, which suffered lesions in the paramedial region of the oral pontine reticular nucleus (RPO), were used to determine the effects on sleep/wakefulness states caused by damage to adjacent CeSR structures and/or passage fibres. Three prelesion and five postlesion weekly 24 h recordings were obtained from each cat. Recordings were scored according to the polygraphic criteria for wakefulness (W), drowsiness (D), slow wave sleep (SWS) and paradoxical sleep (PS). Results indicated that insomnia is not produced exclusively by CeSR lesions, since adjacent paramedial RPO lesions also decrease both SWS and PS; however, increased W occurred after the former while increased D occurred after the latter. Correlation coefficient analyses showed that W is the only state that correlates significantly with the volume of CeSR destroyed. The following correlations between different states of the sleep/wakefulness cycle were, however, significant: W-D, W-SWS and SWS-PS. Disinhibition of W, therefore, and not sleep loss seems to be the primary effect of CeSR lesions. Thus, the CeSR nucleus appears to be involved in arousal mechanisms rather than in direct sleep promotion.

Effects of p-chlorophenylalanine on thermoregulation and sleep in rats

Sleep/waking and body temperature (Tb) were recorded in male rats in a 12:12 light-dark photoperiod at one of 3 ambient temperatures (Ta's): 20, 30, or 32 degrees C. After adaptation to the sleep recording chamber for at least 48 h, the rats were injected with saline at the beginning of lights-on (day S1). Twenty-four hours later (day P1), they were injected with PCPA (300 mg/kg, i.p.) and recordings continued for 4 more days (P2-P5). At these Ta's, hypothalamic 5-HT was depleted by 66-75% 30 h post-PCPA. Changes in both amplitude and acrophase of Tb depended on Ta. Compared to S1, amplitude was reduced on P2-P4 at 20 degrees C and on P3-P4 at 30 degrees C. Acrophase was advanced on P1-P3 at Ta 20 degrees C only. Sleep variables were generally independent of Ta and largely unchanged in the dark. In the light, amounts of slow-wave sleep (SWS) were depressed on P2-P4, number of bouts decreased on P3-P5 and percent nocturnality decreased on P2-P5. Bout length was depressed on P2 and lengthened on P4-P5. Acrophase was delayed on P2-P4 at Ta 30 degrees C. Amounts of rapid-eye-movement sleep (REMS) were depressed on P1-P3. REMS bout length decreased on P1-P3. The decreases in number of REMS bouts seen on P1-P3 depended on Ta. Changes in percent nocturnality and acrophase of REMS were minor. Waking----SWS transitions decreased on P3-P5 while SWS----REMS transitions were reduced on P1-P2. These results suggest that PCPA affects circadian aspects of both Tb and sleep, that 5-HT is important in the initiation of SWS bouts, and finally that the mechanisms by which 5-HT depletion affects Tb, SWS and REMS are different.

Inhibition of methionine incorporation into brain proteins after the systemic administration of p-chlorophenylalanine and L-5-hydroxytryptophan

The effects of p-chlorophenylalanine (p-CPA) and L-5-hydroxytryptophan (L-5-HTP) on local rates of plasma methionine incorporation into brain proteins were investigated by a quantitative autoradiographic method. The sequential i.v. administration of p-CPA (280 mg/kg, 42 h before the measurement) and L-5-HTP (60 mg/kg, 40 min before the measurement) resulted in an average 82% decrease of plasma methionine incorporation. The two treatments given separately also reduced the rates of plasma methionine incorporation in all the brain areas examined by 33 and 50%, respectively for p-CPA and L-5-HTP. These results indicate that: (1) p-CPA and L-5-HTP, two drugs which affect brain serotonin production in opposite ways, both produce large and general decreases of brain protein synthesis; (2) the administration of L-5-HTP does not restore the p-CPA-induced inhibition of brain protein synthesis but induces further decreases of protein synthesis. These results suggest that the reduction of brain protein synthesis in p-CPA-treated rats is mainly related to high circulating levels of p-CPA and phenylalanine; and that brain serotonin is not the only factor involved in the widespread metabolic changes observed. Such profound alterations of brain metabolism should be considered when interpreting the behavioral and neurochemical effects of p-CPA and L-5-HTP.

Effect of p-chlorophenylalanine on release of 5-hydroxytryptamine from the rat frontal cortex in vivo

1. Rats were given p-chlorophenylalanine (PCPA, 150 mg kg-1, i.p.) to inhibit partially 5-hydroxytryptamine (5-HT) synthesis so that its concentration in the frontal cortex fell by about half. The effects of this treatment on frontal cortex dialysate 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined before and after stimulation by increasing K+ concentration in the perfusion fluid by 100 mM for 20 min. Rates of 5-HT synthesis as indicated by the effects of 3-hydroxybenzylhydrazine (NSD 1015, 150 mg kg-1, i.p.) on frontal cortex tissue and dialysate 5-hydroxytryptophan (5-HTP) and dialysate 5-HIAA were also measured in rats that had not been stimulated with K+. 2. Dialysate 5-HT and 5-HIAA concentrations of both vehicle- and PCPA-treated rats fell into major (group 1) and minor (group 2) populations statistically distinguishable from each other by the high 5-HT and low 5-HIAA values of the latter group. 3. In group 1 animals, PCPA decreased both the dialysate 5-HT concentration and its rise following stimulation by K+ in proportion with the decrease of 5-HT in frontal cortex tissue. 5-HIAA fell more markedly than 5-HT and in similar proportion in both tissue and dialysate. The fall of dialysate 5-HIAA on stimulation by K+ was also attenuated to the same degree. The elevated 5-HT/5-HIAA ratios after PCPA treatment imply increased conservation of the depleted 5-HT stores. 4. PCPA decreased the above 5-HIAA values and the effects of NSD 1015 on tissue 5-HTP or dialysate 5-HIAA concentrations in similar proportion. However, PCPA had little effect on corresponding dialysate 5-HTP values. 5. The results are discussed with respect to relationships between synthesis, storage and release of 5-HT. They indicate that (under the conditions of the present study) the availability of 5-HT to receptors is directly proportional to total vesicular stores under both basal conditions and during neuronal firing.

Chronic zimeldine administration to cats: sustained increase of serotonergic effect as measured with sleep parameters

Sleep effects of oral administration of the serotonin uptake inhibitor zimeldine to cats on 15 consecutive days was measured. On administration days 8 and 15 REM sleep and PGO activity were significantly reduced. The amount of SWS-2 was not changed for the whole group, but a subgroup with low baseline values showed an increase during zimeldine administration. A REM sleep rebound was observed on withdrawal day 2, and NREM sleep PGO activity was increased on withdrawal day 5. The results indicate an increased serotonergic inhibition of PGO wave activity and REM sleep during chronic administration of zimeldine.

Increased waking as well as increased synchronization following administration of selective 5-HT uptake inhibitors to rats

Sleep and waking stages and EEG power spectra were investigated in rats following saline injections and injection of 10 and 20 mg/kg zimeldine or 10 and 20 mg/kg alaproclate, both selective 5-HT reuptake inhibitors. Following zimeldine there was a biphasic effect on sleep and waking, waking being increased during the first 2 1/2 h of recording, while slow wave sleep (SWS), in particular highly synchronized SWS-2 with high slow wave activity, was increased during the second 2 1/2 h recording period. Analysis of EEG power spectra indicated that the amount of synchronized slow wave activity was also increased within the sleep that occurred during the waking-dominated initial 2 1/2 h period. These data suggest simultaneous appearance of increased waking and increased synchronization following general serotonergic stimulation. They are interpreted as due to effects on different regions of the serotonergic system or on different serotonergic receptors. Consistent with earlier findings, zimeldine also suppressed rapid eye movement (REM) sleep. Following alaproclate, a clear waking effect was present, but only a weak synchronizing effect was seen. This is consistent with data on regional differences in uptake inhibition for zimeldine and alaproclate. Alaproclate also reduced REM sleep. Zimeldine or alaproclate was also administered to rats that had reduced sleep following pretreatment with a moderate dose of parachlorophenylalanine (PCPA). None of the drugs increased waking any further, but the PCPA-pretreated animals that received zimeldine had increased SWS-2, indicating that the SWS-2 increase following zimeldine alone was not a rebound effect.

A large scale, high resolution, automated system for rat sleep staging. II. Validation and application

An automated rat sleep staging system was used to describe sleep-waking behaviour in a large number of rats. The computer scorings were validated by visual analysis of a limited set of data by two human raters and the agreement varied between 82 and 100% for homogeneous segments of the different sleep-waking stages. The automated system proved to be very consistent in view of the small variation in placebo values over 110 experiments. The data show that classification of rat sleep waking behaviour into 6 different stages is both advisable and feasible. The experiments further show that rat age (over a range from 0.5 to 2 years) does not greatly affect rat sleep-waking behaviour.

Changes in the rat sleep-wake cycle produced by D,L-beta-(1-naphthyl)alanine, a tryptophan analog

The effects of i.p. injections of D,L-beta-(1-naphthyl)alanine, a synthetic analog of tryptophan were tested on the rat sleep-waking cycle. Administration of 30, 60 and 120 mg/kg resulted in a significant increase in slow-wave sleep (SWS) and a decrease in paradoxical sleep (PS). These modifications were dose-dependent. These results were compared with those previously obtained with L-tryptophan and several analogs and discussed in relation with possible changes in central serotonergic activity.