CNS STIMULANTS

CNS STIMULANTS stimulate the CNS. Some of those with a predominant effect on mood and behaviour — psychomotor stimulants — have some medical use in treating patients who suffer from narcolepsy. There is a tendency for those who use psychomotor stimulant drugs on a regular basis to become dependent and show a withdrawal syndrome when they stop taking the drug.

Dexamphetamine is one of the most powerful and best known psychomotor stimulants, and other similar agents include dexfenfluramine, diethylpropion and fenfluramine. All these are on the controlled drugs list, and have a limited medical use as appetite suppressants. Such drugs work by interacting with the release of monoamines within the central (and peripheral) nervous system, and can be regarded as indirect SYMPATHOMIMETICS. Recently, there has been some use of the weak amphetamine-like stimulant methylphenidate to treat attention-deficient hyperactivity disorder (ADHD) in children.

Cocaine is a powerful psychomotor stimulant, commonly used as a drug of abuse. Its actions are very like those of the amphetamines. It works by blocking reuptake of catecholamines within the central (and peripheral) nervous systems and is an indirect sympathomimetic.

Caffeine, theobromine and theophyiline, and related methylxanthine compounds, are mild stimulants and have everyday use, e.g. in tea, coffee, chocolate and some soft drinks. Methylxanthines work in part as PHOSPHODIESTERASE inhibitors and in part as antagonists at P1-purinoceptors (see adenosine receptor antagonists).

Convulsant drugs (also called analeptics) are a diverse group of agents, sometimes with poorly understood mechanisms of action. Strychnine, a plant alkaloid present in nux vomica, acts through blocking the actions of the inhibitory amino acid neurotransmitter glycine, mainly at spinal cord level, and is a powerful convulsant (see GLYCINE receptor antagonists). Bicuculline and picrotoxin (active constituent, picrotoxinin) are plant alkaloids that block the action of endogenous GABA at the GABAA receptor chloride Channels (see GABA RECEPTOR ANTAGONISTS; NEUROTOXINS). Tetanus toxin is a protein toxin produced by the anaerobic bacterium Clostridium tetani. It is transported along sensory neurons and within the CNS and blocks the action of glycine and so has a convulsant action. The synthetic agents nikethamide and pentetrazol (leptazol; pentamethylenetetrazole) are convulsants with a poorly understood mechanism of action. They were previously used as respiratory stimulants as they act more to stimulate respiration. Doxapram is similar, but has a greater margin of safety — it is sometimes used by intravenous infusion in patients with acute respiratory failure.