Neurotransmitter sleep

Other studies indicate that sucrose does not cause hyperactivity. Carbohydrate ingestion increases levels of serotonin (5-hydroxytryptamine), a brain neurotransmitter that promotes relaxation and sleep. Dietary sucrose should theoretically have a calming effect and reduce activity, manifestations which have been observed in case studies (63). To date, clinical investigations have failed to show a significant connection between sucrose consumption and aggressive or dismptive behavior (66). 

A medication that causes induction of sleep. The majority of currently available hypnotics (for example benzodiazepine receptor agonists) act via potentiating the brain s inhibitory GABAergic systems, in turn reducing the activity of arousal (i.e. wake promoting) neurotransmitter systems. 

Caffeine binds to adenosine receptors in the brain, preventing adenosine from inducing sleep or opening blood vessels. Caffeine also increases levels of dopamine, the neurotransmitter associated with pleasure. This is the chemical mechanism for addiction. The response to adenosine competition causes increased adrenaline flow. 

How the different neurotransmitters may be involved in the initiation and maintenance of some brain disorders, such as Parkinson s disease, epilepsy, schizophrenia, depression, anxiety and dementia, as well as in the sensation of pain, is then evaluated and an attempt made to see how the drugs which are used in these conditions produce their effect by modifying appropriate neurotransmitter function (section C). The final section (D) deals with how neurotransmitters are involved in sleep and consciousness and in the social problems of drug use and abuse. 

There have been many references in this book to the role of neurotransmitters in the control of CNS excitability. It is therefore appropriate, but possibly foolhardy, to see if the two natural extremes of that excitability, namely sleep and waking, can be explained in terms of neurotransmitter activity. Of course, these states are not constant our sleep can be deep or light and, even when we are awake, our attention and vigilance fluctuate, as the reading of these pages will no doubt demonstrate. Also, the fact that we sleep does not mean that our neurotransmitters are inactive this would imply that sleep is a totally passive state, whereas all the evidence suggests that it is an actively induced process, subject to refined physiological control. 

The more synchronised the activity of the cortical neurons, the greater the summation of currents and the larger and slower the EEG wave, as in the sleep pattern (Fig. 22.4). While there are some dissociations between EEG pattern and behavioural states, the EEG offers one way of determining experimentally the pathways (and neurotransmitters) that control arousal and sleep, and can be regarded as an important objective measurement of the cortical correlates of sleep and waking. 

It is important to emphasise that a lesion of the reticular system disrupts a number of afferent inputs to the cortex. Particularly important in this respect are the mono-aminergic (especially noradrenaline, 5-HT and histamine) and cholinergic pathways. When the ascending inputs from these neurons are destroyed, sleep is passive and not at all like natural sleep which, as detailed above, has distinct phases and depends on brainstem influences on cortical function. How these different neurotransmitters might influence sleep and arousal will be considered next. 

Based on the above aeeount of the neuronal pathways thought to be responsible for the basie sleep-wake cyele, the neurotransmitters that are most likely to be involved in the eyele are those which ... 

This neurotransmitter presents something of a paradox in respect of its role in sleep and waking behaviour, although its importance to both is undoubted. Early experiments... 

Setting aside the general anaesthetics, which do not directly modify the function of any particular neurotransmitter, all the drugs that are used to induce sleep, i.e. the hypnotics , augment the function of GABA and so directly depress neuronal function and probably facilitate cortico-thalamic synchrony. Most of them are benzodiazepines... 

Non-motor symptoms are due to multiple neurotransmitter abnormalities throughout the brain, and some symptoms may be aggravated by PD medications. Sleep disturbance can affect more than 70% of PD patients and includes insomnia, sleep... 

Complicated processes govern wakefulness, sleep, and the transitions leading to sleep initiation and maintenance. Although the neurophysiology of sleep is complex, certain neurotransmitters promote sleep and wakefulness in different areas of the central nervous system (CNS). Serotonin is thought to control non-REM sleep, whereas cholinergic and adrenergic transmitters mediate REM sleep. Dopamine, norepinephrine, hypocretin, substance P, and histamine all play a role in wakefulness. Perturbations of various neurotransmitters are responsible for some sleep disorders and explain why various treatment modalities are beneficial. 

In the vertebrate CNS monoamines have been associated with a number of physiological functions (reviewed in Kandel et al., 1991). Serotonin has functions associated with mood, pain, sleep, learning, and memory. Dopamine has functions associated with schizophrenia, Parkinson s disease, and cocaine addiction. In vertebrates, dopamine is further metabolized into two additional neurotransmitters, norepinephrine and epinephrine. Norepinephrine increases the excitability of cells in response to sudden sensory input such as fear. Epinephrine has been identified in specific neurons of the brain, but the function of these cells is unknown. In addition, AADC has also been found in a class of neurons that do not have any of the four neurotransmitters discussed above (Jaeger et al., 1983). These neurons may use one of the trace amines, tyramine, tryptamine, or phenylethylamine, as a neurotransmitter. 

Hydroxy tryptamine, or serotonin, is a neurotransmitter in the central nervous system (CNS). The nerve-cell bodies of the major serotoninergic neurones are in the midline raphe nuclei of the rostral pons, and ascending fibers innervate the basal ganglia, hypothalamus, thalamus, hippocampus, limbic forebrain, and areas of the cerebral cortex. The serotoninergic system plays an important role in the control of mood and behavior, motor activity, hunger, thermoregulation, sleep, certain hallucinatory states, and some neuro-endocrine mechanisms. 

Some arousal-related neurotransmitters, including noradrenaline, serotonin, and acetylcholine, feed back to inhibit POA sleep-active neurons. This aspect of the system has been reviewed previously (McGinty Szymusiak, 2000 Saper et al., 2001). Therefore, once sleep-active neurons are activated, arousal-related neurons are inhibited, and inhibitory control of sleep-active neurons by arousal systems is reduced. In this way, sleep onset is facilitated. That is, the mutually inhibitory systems can switch more quickly from wake to sleep, and back. These mutually inhibitory interactions also promote stability of both waking and sleep. 

The concept of chemical neurotransmission originated in the 1920s with the classic experiments of Otto Loewi (which were themselves inspired by a dream), who demonstrated that by transferring the ventricular fluid of a stimulated frog heart onto an unstimulated frog heart he could reproduce the effects of a (parasympathetic) nerve stimulus on the unstimulated heart (Loewi Navratil, 1926). Subsequently, it was found that acetylcholine was the neurotransmitter released from these parasympathetic nerve fibers. As well as playing a critical role in synaptic transmission in the autonomic nervous system and at vertebrate neuromuscular junctions (Dale, 1935), acetylcholine plays a central role in the control of wakefulness and REM sleep. Some have even gone as far as to call acetylcholine a neurotransmitter correlate of consciousness (Perry et al., 1999). 

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