Instruct: Given a question, retrieve relevant documents that answer the question.
Query: What is the most abundant neurotransmitter in the human brain?
The most prevalent transmitter is glutamate, which is excitatory at well over 90% of the synapses in the human brain.[6] The next most prevalent is Gamma-Aminobutyric Acid, or GABA, which is inhibitory at more than 90% of the synapses that do not use glutamate. Although other transmitters are used in fewer synapses, they may be very important functionally: the great majority of psychoactive drugs exert their effects by altering the actions of some neurotransmitter systems, often acting through transmitters other than glutamate or GABA. Addictive drugs such as cocaine and amphetamines exert their effects primarily on the dopamine system. The addictive opiate drugs exert their effects primarily as functional analogs of opioid peptides, which, in turn, regulate dopamine levels.
Calcium is the most abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger; in neurotransmitter release from neurons; in contraction of all muscle cell types; as cofactors in many enzymes; and in fertilization. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation.
Kaitocephalin acts by inhibiting glutamate receptors. Glutamate is the most abundant neurotransmitter in the vertebrate nervous system and is involved in learning, memory, and neuroplasticity. It is an excitatory neurotransmitter, so binding of glutamate to its receptors increases ion flow through the postsynaptic membrane. Excess glutamate can lead to cell death and neurological damage through a phenomenon called excitotoxicity. Excitotoxicity occurs when calcium ion influx creates a positive feedback loop, leading to breakdown of the cell membrane and apoptosis. This process is part of the ischemic cascade, when low blood supply (ischemia) causes a series of events leading to cell death; this is the mechanism by which strokes cause brain damage. High levels of glutamate have also been linked to the neuronal degeneration observed in Alzheimer's disease, Parkinson's disease, and epilepsy.
Comparisons of primate species show that what appears to be a link between group size and brain size, and also what species do not fit such a correlation, is explainable by diet. Many primates that eat specialized diets that rely on scarce food have evolved small brains to conserve nutrients and are limited to living in small groups or even alone, and they lower average brain size for solitary or small group primates. Small-brained species of primate that are living in large groups are successfully predicted by diet theory to be the species that eat food that is abundant but not very nutritious. Along with the existence of complex deception in small-brained primates in large groups with the opportunity (both abundant food eaters in their natural environments and originally solitary species that adopted social lifestyles under artificial food abundances), this is cited as evidence against the model of social groups selecting for large brains and/or intelligence.
In Hans Moravec's "Mind Children", an example of mind uploading is given - a human brain is replaced a single neuron at a time by a nanorobot and computer that perfectly simulates the behaviour of the neuron and its neurotransmitters. The end result is a completely digital copy of brain in simulation. However, there are other factors such as the fact that the intricate structure of the brain is changing as the brain learns, so a simulated brain may not learn the same way.
Since glutamate is the most abundant and major excitatory neurotransmitter in the brain, pathophysiological changes in glutamatergic signaling are likely to affect neurobehavioral plasticity, information processing and large-scales changes in functional brain connectivity.Ketamine, a fast-acting general anesthetic derived from phencyclidine and use as a pediatric inductor, plays a non-well known role in the neural network dynamics at the healthy brain . The administration of ketamine in abnormal brain has the potential of reduce the increased function of the networks that are seen in depression. The therapeutic potential of ketamine may be explained by reversing disturbances in the glutamatergic system and restoring parts of a disrupted neurobehavioral homeostasis where several structural, metabolic, and functional abnormalities have taken place. Long term ketamine treatments lead to cognitive impairment including problems of short-term memory, visual and verbal memory. On the other hand, short term treatments are generally well tolerated and any damage may be reversible.
The Female Brain is a book written by the American neuropsychiatrist Louann Brizendine in 2006. The main thesis of the book is that women's behavior is different from that of men due, in large measure, to hormonal differences. Brizendine says that the human female brain is affected by the following hormones: estrogen, progesterone, testosterone, (oxytocin), neurotransmitters (dopamine, serotonin), and that there are differences in the architecture of the brain (prefrontal cortex, hypothalamus, amygdala) that regulates such hormones and neurotransmitters.
The MAOIs work by inhibiting the monoamine oxidase enzymes that, as the name suggests, break down the monoamine neurotransmitters. This leads to increased concentrations of most of the monoamine neurotransmitters in the human brain, serotonin, norepinephrine, dopamine and melatonin. The fact that they are more efficacious than the newer generation antidepressants is what leads scientists to develop newer antidepressants that target a greater range of neurotransmitters. The problem with MAOIs is that they have many potentially dangerous side-effects such as hypotension, and there is a risk of food and drug interactions that can result in potentially fatal serotonin syndrome or a hypertensive crisis. Although selective MAOIs can reduce, if not eliminate these risks, their efficacy tends to be lower.
By the end of the 20th century, it became clear that the human brain operates with more than a dozen neurotransmitters and a large number of neuropeptides and hormones. The relationships between these different chemical systems are complex as some of them suppress and some of them induce each other’s release during neuronal exchanges. This complexity of relationships devalues the old approach of assigning “inhibitory vs. excitatory” roles to neurotransmitters: the same neurotransmitters can be either inhibitory or excitatory depending on what system they interact with. It became clear that an impressive diversity of neurotransmitters and their receptors is necessary to meet a wide range of behavioural situations, but the links between temperament traits and specific neurotransmitters are still a matter of research. Several attempts were made to assign specific (single) neurotransmitters to specific (single) traits. For example, dopamine was proposed to be a neurotransmitter of the trait of Extraversion, noradrenaline was linked to anxiety, and serotonin was thought to be a neurotransmitter of an inhibition system. These assignments of neurotransmitter functions appeared to be an oversimplification when confronted by the evidence of much more diverse functionality. 
Research groups led by Petra Netter in Germany, Lars Farde in Karolinska Institute in Sweden and Trevor Robbins in Cambridge, UK had most extensive studies of the links between temperament/personality traits or dynamical properties of behavior and groups of neurotransmitters 
Withdrawal symptoms are a normal response in individuals having chronically used benzodiazepines, and an adverse effect and result of drug tolerance. Symptoms typically emerge when dosage of the drug is reduced. GABA is the second-most-common neurotransmitter in the central nervous system (the most common being glutamate) and by far the most abundant inhibitory neurotransmitter; roughly one-quarter to one-third of synapses use GABA. The use of benzodiazepines has a profound effect on almost every aspect of brain and body function, either directly or indirectly.
Alpha-synuclein is a protein that, in humans, is encoded by the "SNCA" gene. It is abundant in the brain while smaller amounts are found in the heart, muscles, and other tissues. In the brain, alpha-synuclein is found mainly at the tips of nerve cells (neurons) in specialized structures called presynaptic terminals. Within these structures, alpha-synuclein interacts with phospholipids and proteins. Presynaptic terminals release chemical messengers, called neurotransmitters, from compartments known as synaptic vesicles. The release of neurotransmitters relays signals between neurons and is critical for normal brain function.
Some mental illnesses have been linked to an imbalance of chemicals in the brain called neurotransmitters. These neurotransmitters help nerve cells in the brain communicate. If these chemicals are out of balance or are not working properly, messages may not properly transmit through the brain, leading to symptoms of mental illness. In addition, defects in or Traumatic Brain Injury (TBI) to areas of the brain have also been linked to some mental conditions.
BK channels oppose vasoconstriction in blood vessels resulting in vasorelaxation. Blocking the channels leads to vasoconstriction and to an increase in blood pressure. The BK channel α subunit is expressed in muscle and nerve tissue and the BK channels are abundant in the brain. The BK channels modulate neurotransmitter release, the form of the action potential and repetitive firing. Inhibition of the channels can explain why there would be an increased release in excitatory neurotransmitters resulting in tremors, ataxia, hypersensitivity, increased smooth muscle contraction in the colon and an increased heart rate.
While the emphasis below is on physical brain structure, functional aspects are also included. Mind concepts (as in mind vs. body), and cognitive and behavioral aspects, are introduced where they have at least a fairly direct connection to physical aspects of the brain, neurons, spinal cord, nerve networks, neurotransmitters, etc.
Epigenetic changes including hypomethylation of glutamatergic genes (i.e., NMDA-receptor-subunit gene NR3B and the promoter of the AMPA-receptor-subunit gene GRIA2) in the post-mortem human brains of schizophrenics are associated with increased levels of the neurotransmitter glutamate. Since glutamate is the most prevalent, fast, excitatory neurotransmitter, increased levels may result in the psychotic episodes related to schizophrenia. Epigenetic changes affecting a greater number of genes have been detected in men with schizophrenia as compared to women with the illness.
Dendritic spikes most commonly propagate backwards from the soma to distal dendritic branches. Backward propagation serves a number of functions in the neuron, and these functions vary based on the type of neuron. In general, backwards propagation serves to communicate output information to the post synaptic membrane. In many neurotransmitter releasing neurons, backward propagation of dendritic spikes signals the release of neurotransmitters. For example, Mitral cells seem to serve both as projection neurons and as local interneurons. If the axonal output of mitral cell is shut down by somatic inhibition, local dendritic action potentials cause the mitral cell to release neurotransmitters into the environment. Backward propagation of dendritic spikes has been demonstrated in various neuronal types in the brain but has rarely been studied outside of the brain. Other than neurons in the brain, dendritic spikes have been observed in the neurons of the spinal cord.
Neuropeptide Y (NPY) is a 36 amino-acid neuropeptide that is involved in various physiological and homeostatic processes in both the central and peripheral nervous systems. NPY has been identified as the most abundant peptide present in the mammalian central nervous system, which consists of the brain and spinal cord. It is secreted alongside other neurotransmitters such as GABA and glutamate. 
Three neurotransmitters that play important roles in adolescent brain development are glutamate, dopamine and serotonin. Glutamate is an excitatory neurotransmitter. During the synaptic pruning that occurs during adolescence, most of the neural connections that are pruned contain receptors for glutamate or other excitatory neurotransmitters. Because of this, by early adulthood the synaptic balance in the brain is more inhibitory than excitatory.
Most scientists believe that AI research will at some point lead to the creation of machines that are as intelligent, or more intelligent, than human beings in every domain of interest. There is no physical law precluding particles from being organised in ways that perform even more advanced computations than the arrangements of particles in human brains; therefore superintelligence is physically possible. In addition to potential algorithmic improvements over human brains, a digital brain can be many orders of magnitude larger and faster than a human brain, which was constrained in size by evolution to be small enough to fit through a birth canal. While there is no consensus on "when" artificial intelligence will outperform humans, many scholars argue that whenever it does happen, the introduction of a second species of intelligent life onto the planet will have far-reaching implications. Scholars often disagree with one another both about what types of post-AI scenarios are "most likely", and about what types of post-AI scenarios would be "most desirable". Finally, some dissenters argue that AI will never become as intelligent as humans, for example because the human race will already likely have destroyed itself before research has time to advance sufficiently to create artificial general intelligence.
Glutamate is a major constituent of a wide variety of proteins; consequently it is one of the most abundant amino acids in the human body. Under ordinary conditions enough is obtained from the diet that there is no need for any to be synthesized. Nevertheless, glutamate is formally classified as a non-essential amino acid, because it can be synthesized from alpha-Ketoglutaric acid, which is produced as part of the citric acid cycle by a series of reactions whose starting point is citrate. Glutamate cannot cross the blood-brain barrier unassisted, but it is actively transported into the nervous system by a high affinity transport system, which maintains its concentration in brain fluids at a fairly constant level.
Glutamate receptors are synaptic and non synaptic receptors located primarily on the membranes of neuronal and glial cells. Glutamate (the conjugate base of glutamic acid) is abundant in the human body, but particularly in the nervous system and especially prominent in the human brain where it is the body's most prominent neurotransmitter, the brain's main excitatory neurotransmitter, and also the precursor for GABA, the brain's main inhibitory neurotransmitter. Glutamate receptors are responsible for the glutamate-mediated postsynaptic excitation of neural cells, and are important for neural communication, memory formation, learning, and regulation.
Alcohol alters consciousness by shifting levels of neurotransmitters. Neurotransmitters are endogenous chemicals that transmit signals across a synapse from one neuron (nerve cell) to another "target" cell (often another neuron). Neurotransmitters can cause inhibitory or excitatory effects on the "target" cell they are affecting. Alcohol increases the effect of the neurotransmitter GABA (gamma-Aminobutyric acid) in the brain. GABA causes slow actions and inaudible verbal communication that often occur in alcoholics (Berridge, V 2001). Alcohol also decreases the excitatory neurotransmitter glutamate. Suppressing this stimulant results in a similar type of physiological slowdown. In addition to increasing the GABA and decreasing the glutamate in the brain, alcohol increases the amount of the chemical dopamine in the brain, which is one of the addictive causes of alcoholism.
In neuroscience, glutamate refers to the anion of glutamic acid in its role as a neurotransmitter: a chemical that nerve cells use to send signals to other cells. It is by a wide margin the most abundant excitatory neurotransmitter in the vertebrate nervous system. It is used by every major excitatory function in the vertebrate brain, accounting in total for well over 90% of the synaptic connections in the human brain. It also serves as the primary neurotransmitter for some localized brain regions, such as cerebellum granule cells.
The neurotransmitter most often associated with EPSPs is the amino acid glutamate, and is the main excitatory neurotransmitter in the central nervous system of vertebrates. Its ubiquity at excitatory synapses has led to it being called "the" excitatory neurotransmitter. In some invertebrates, glutamate is the main excitatory transmitter at the neuromuscular junction. In the neuromuscular junction of vertebrates, EPP (end-plate potentials) are mediated by the neurotransmitter acetylcholine, which (along with glutamate) is one of the primary transmitters in the central nervous system of invertebrates.
At the same time, GABA is the most common neurotransmitter associated with IPSPs in the brain. a
However, classifying neurotransmitters as such is technically incorrect, as there are several other synaptic factors that help determine a neurotransmitter's excitatory or inhibitory effects.
Glutamate is also a neurotransmitter (see below), which makes it one of the most abundant molecules in the brain. Malignant brain tumors known as glioma or glioblastoma exploit this phenomenon by using glutamate as an energy source, especially when these tumors become more dependent on glutamate due to mutations in the gene "IDH1".