Acetylcholine in the context of "Nicotinic agonist"

In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a receptor and produce physiological responses, such as a change in the electrical activity of a cell. For example, GABA, an inhibitory neurotransmitter, inhibits electrical activity of neurons by binding to GABA_A receptors. There are three main ways the action of the receptor can be classified: relay of signal, amplification, or integration. Relaying sends the signal onward, amplification increases the effect of a single ligand, and integration allows the signal to be incorporated into another biochemical pathway.

Receptor proteins can be classified by their location. Cell surface receptors, also known as transmembrane receptors, include ligand-gated ion channels, G protein-coupled receptors, and enzyme-linked hormone receptors. Intracellular receptors are those found inside the cell, and include cytoplasmic receptors and nuclear receptors. A molecule that binds to a receptor is called a ligand and can be a protein, peptide (short protein), or another small molecule, such as a neurotransmitter, hormone, pharmaceutical drug, toxin, calcium ion or parts of the outside of a virus or microbe. An endogenously produced substance that binds to a particular receptor is referred to as its endogenous ligand. E.g. the endogenous ligand for the nicotinic acetylcholine receptor is acetylcholine, but it can also be activated by nicotine and blocked by curare. Receptors of a particular type are linked to specific cellular biochemical pathways that correspond to the signal. While numerous receptors are found in most cells, each receptor will only bind with ligands of a particular structure. This has been analogously compared to how locks will only accept specifically shaped keys. When a ligand binds to a corresponding receptor, it activates or inhibits the receptor's associated biochemical pathway, which may also be highly specialised.

Phospholipids are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typically have omega-3 fatty acids EPA and DHA integrated as part of the phospholipid molecule. The phosphate group can be modified with simple organic molecules such as choline, ethanolamine or serine.

Phospholipids are essential components of neuronal membranes and play a critical role in maintaining brain structure and function. They are involved in the formation of the blood-brain barrier and support neurotransmitter activity, including the synthesis of acetylcholine.

The enteric nervous system (ENS) is one of the three divisions of the autonomic nervous system (ANS), the others being the sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS). It consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. The ENS is nicknamed the "second brain". It is derived from neural crest cells.

The enteric nervous system is capable of operating independently of the brain and spinal cord, but is thought to rely on innervation from the vagus nerve and prevertebral ganglia in healthy subjects. However, studies have shown that the system is operable with a severed vagus nerve. The neurons of the enteric nervous system control the motor functions of the system, in addition to the secretion of gastrointestinal enzymes. These neurons communicate through many neurotransmitters similar to the CNS, including acetylcholine, dopamine, and serotonin. The large presence of serotonin and dopamine in the intestines are key areas of research for neurogastroenterology.

Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second messenger signaling cascade that induces a broad, long-lasting signal. This modulation can last for hundreds of milliseconds to several minutes. Some of the effects of neuromodulators include altering intrinsic firing activity, increasing or decreasing voltage-dependent currents, altering synaptic efficacy, increasing bursting activity and reconfiguring synaptic connectivity.

Major neuromodulators in the central nervous system include: dopamine, serotonin, acetylcholine, histamine, norepinephrine, nitric oxide, and several neuropeptides. Cannabinoids can also be powerful CNS neuromodulators. Neuromodulators can be packaged into vesicles and released by neurons, secreted as hormones and delivered through the circulatory system. A neuromodulator can be conceptualized as a neurotransmitter that is not reabsorbed by the pre-synaptic neuron or broken down into a metabolite. Some neuromodulators end up spending a significant amount of time in the cerebrospinal fluid (CSF), influencing (or "modulating") the activity of several other neurons in the brain.

Botulinum toxin, botulinum neurotoxin, or botox is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species, and it is the deadliest known substance ever recorded in the chemical literature. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction, thus causing flaccid paralysis. The toxin causes the disease botulism. The toxin is also used commercially for medical and cosmetic purposes. Botulinum toxin is an acetylcholine release inhibitor and a neuromuscular blocking agent.

The seven main types of botulinum toxin are named types A to G (A, B, C1, C2, D, E, F and G). New types are occasionally found. Types A and B are capable of causing disease in humans, and are also used commercially and medically. Types C–G are less common; types E and F can cause disease in humans, while the other types cause disease in other animals.

Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that catalyzes the breakdown of acetylcholine, a neurotransmitter. Nerve agents are irreversible acetylcholinesterase inhibitors used as poison.

Poisoning by a nerve agent leads to constriction of pupils, profuse salivation, convulsions, and involuntary urination and defecation, with the first symptoms appearing in seconds after exposure. Death by asphyxiation or cardiac arrest may follow in minutes due to the loss of the body's control over respiratory and other muscles. Some nerve agents are readily vaporized or aerosolized, and the primary portal of entry into the body is the respiratory system. Nerve agents can also be absorbed through the skin, requiring that those likely to be subjected to such agents wear a full body suit in addition to a respirator.

Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive substance globally. It is mainly used for its eugeroic (wakefulness promoting), ergogenic (physical performance-enhancing), or nootropic (cognitive-enhancing) properties; it is also used recreationally or in social settings. Caffeine acts by blocking the binding of adenosine at a number of adenosine receptor types, inhibiting the centrally depressant effects of adenosine and enhancing the release of acetylcholine. Caffeine has a three-dimensional structure similar to that of adenosine, which allows it to bind and block its receptors. Caffeine also increases cyclic AMP levels through nonselective inhibition of phosphodiesterase, increases calcium release from intracellular stores, and antagonizes GABA receptors, although these mechanisms typically occur at concentrations beyond usual human consumption.

Caffeine is a bitter, white crystalline purine, a methylxanthine alkaloid, and is chemically related to the adenine and guanine bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is found in the seeds, fruits, nuts, or leaves of a number of plants native to Africa, East Asia, and South America and helps to protect them against herbivores and from competition by preventing the germination of nearby seeds, as well as encouraging consumption by select animals such as honey bees. The most common sources of caffeine for human consumption are the tea leaves of the Camellia sinensis plant and the coffee bean, the seed of the Coffea plant. Some people drink beverages containing caffeine to relieve or prevent drowsiness and to improve cognitive performance. To make these drinks, caffeine is extracted by steeping the plant product in water, a process called infusion. Caffeine-containing drinks, such as tea, coffee, and cola, are consumed globally in high volumes. In 2020, almost 10 million tonnes of coffee beans were consumed globally. Caffeine is the world's most widely consumed psychoactive drug. Unlike most other psychoactive substances, caffeine remains largely unregulated and legal in nearly all parts of the world. Caffeine is also an outlier as its use is seen as socially acceptable in most cultures and is encouraged in some.

Nicotine is an alkaloid found primarily in plants of the nightshade family, notably in tobacco and Duboisia hopwoodii. In addition to extraction from tobacco, it is synthesized. Nicotine is used recreationally for its stimulant and anxiolytic effects. In tobacco leaves, nicotine constitutes about 0.6–3.0% of the dry weight, and smaller, trace quantities occur in other Solanaceae crops such as tomatoes, potatoes, and eggplants. In pure form, nicotine is a colorless to yellowish, oily liquid that readily penetrates biological membranes and acts as a potent neurotoxin in insects, where it serves as a antiherbivore toxin. Historically, it was widely used as an insecticide, and its structure provided the basis for synthetic neonicotinoid pesticides.

In humans, nicotine acts primarily as a stimulant by binding to and activating nicotinic acetylcholine receptors (nAChRs) in the central nervous system and peripheral tissues. This results in the release of neurotransmitters such as dopamine, acetylcholine, and norepinephrine, producing effects including increased alertness, reduced anxiety, and mild euphoria. Nicotine is typically consumed through tobacco smoking, vaping, or other nicotine delivery systems. An average cigarette yields about 2 mg of absorbed nicotine, a dose sufficient to produce reinforcement and dependence while remaining far below toxic levels.

Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, the autonomic nervous system, and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, desire, mobility, and reactivity.

Arousal is mediated by several neural systems. Wakefulness is regulated by the ARAS, which is composed of projections from five major neurotransmitter systems that originate in the brainstem and form connections extending throughout the cortex; activity within the ARAS is regulated by neurons that release the neurotransmitters norepinephrine, acetylcholine, dopamine, serotonin and histamine.

Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral nervous system, muscle, and many other tissues of many organisms. At the neuromuscular junction they are the primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction. In the peripheral nervous system: (1) they transmit outgoing signals from the presynaptic to the postsynaptic cells within the sympathetic and parasympathetic nervous system; and (2) they are the receptors found on skeletal muscle that receives acetylcholine released to signal for muscular contraction. In the immune system, nAChRs regulate inflammatory processes and signal through distinct intracellular pathways. In insects, the cholinergic system is limited to the central nervous system.

The nicotinic receptors are considered cholinergic receptors, because they respond to acetylcholine. Nicotinic receptors get their name from nicotine, which selectively binds to nicotinic receptors but not to other acetylcholine receptors. (The other type of acetylcholine receptor, the muscarinic receptor, likewise gets its name from a chemical that selectively attaches to that receptor: muscarine. Acetylcholine itself binds to both muscarinic and nicotinic acetylcholine receptors.)