NMDA receptor antagonist
NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are used as anesthetics for animals and for humans; the state of anesthesia they induce is referred to as dissociative anesthesia. There is evidence that NMDA receptor antagonists can cause a certain type of neurotoxicity or brain damage referred to as Olney's Lesions in rodents, although such damage has never been conclusively observed in primates like humans. Recent research conducted on primates suggests that, while very consistent and long-term ketamine use may be neurotoxic, acute use is not.
Some NMDA receptor antagonists, such as ketamine, dextromethorphan (DXM), phencyclidine (PCP), and nitrous oxide (N2O), are popular recreational drugs used for their dissociative, hallucinogenic, and euphoriant properties. When used recreationally, they are classified as dissociative drugs.
Mechanism of action
The NMDA receptor is a receptor that allows for the transfer of electrical signals between neurons in the brain and in the spinal column. For electrical signals to pass, the NMDA receptor must be open. To remain open, glutamate and glycine must bind to the NMDA receptor. An NMDA receptor that has glycine and glutamate bound to it and has an open ion channel is called "activated."
Chemicals that deactivate the NMDA receptor are called antagonists. NMDAR antagonists fall into four categories:
- Competitive antagonists, which bind to and block the binding site of the neurotransmitter glutamate
- Glycine antagonists, which bind to and block the glycine site
- Noncompetitive antagonists, which inhibit NMDARs by binding to allosteric sites
- Uncompetitive antagonists, which block the ion channel by binding to a site within it.
Once a sufficient amount of NMDA receptors have been deactivated, the result is a dosage dependent decrease in the passing of electrical signals across the brain and a disconnection of neurons. This leads to states of disconnection between conscious parts of the brain, anesthesia and its sensory organs as well as out-of-body experiences and accompanying hallucinations.
- MXE (Methoxetamine)
- PCP (Phencyclidine)
- Deschloroketamine (DCK or DXE)
- 2-Fluorodeschloroketamine (2F-K)
- 2-Oxo-PCE (O-PCE)
- Chronic ketamine exposure induces permanent impairment of brain functions in adolescent cynomolgus monkeys (PubMed.gov / NCBI) | http://www.ncbi.nlm.nih.gov/pubmed/23145560
- Ketamine-Induced Neuronal Cell Death in the Perinatal Rhesus Monkey | http://toxsci.oxfordjournals.org/content/98/1/145
- Kim AH, Kerchner GA, Choi DW (2002). "Blocking Excitotoxicity". In Marcoux FW, Choi DW. CNS Neuroprotection. New York: Springer. pp. 3–36.