Physostigmine is a highly toxic parasympathomimetic alkaloid, specifically, a reversible cholinesterase inhibitor. It occurs naturally in the Calabar bean and the fruit of the Manchineel tree.
The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP for its ligand ketazocine, is a G protein-coupled receptor that in humans is encoded by the OPRK1 gene. The KOR is coupled to the G protein Gi/G0 and is one of four related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds. These effects include altering nociception, consciousness, motor control, and mood. Dysregulation of this receptor system has been implicated in alcohol and drug addiction.
BIMU-8 is a drug which acts as a 5-HT4 receptor selective agonist. BIMU-8 was one of the first compounds of this class. The main action of BIMU-8 is to increase the rate of respiration by activating an area of the brain stem known as the pre-Botzinger complex.
The nociceptin opioid peptide receptor (NOP), also known as the nociceptin/orphanin FQ (N/OFQ) receptor or kappa-type 3 opioid receptor, is a protein that in humans is encoded by the OPRL1 gene. The nociceptin receptor is a member of the opioid subfamily of G protein-coupled receptors whose natural ligand is the 17 amino acid neuropeptide known as nociceptin (N/OFQ). This receptor is involved in the regulation of numerous brain activities, particularly instinctive and emotional behaviors. Antagonists targeting NOP are under investigation for their role as treatments for depression and Parkinson's disease, whereas NOP agonists have been shown to act as powerful, non-addictive painkillers in non-human primates.
Desmetramadol, also known as O-desmethyltramadol (O-DSMT), is an opioid analgesic and the main active metabolite of tramadol. Tramadol is demethylated by the liver enzyme CYP2D6 to desmetramadol in the same way as codeine, and so similarly to the variation in effects seen with codeine, individuals who have a less active form of CYP2D6 will tend to have reduced analgesic effects from tramadol. Because desmetramadol itself does not need to be metabolized to induce an analgesic effect, it can be used in individuals with low CYP2D6 activity unlike tramadol.
8-OH-DPAT is a research chemical of the aminotetralin chemical class which was developed in the 1980s and has been widely used to study the function of the 5-HT1A receptor. It was one of the first major 5-HT1A receptor full agonists to have been discovered.
RB-101 is a drug that acts as an enkephalinase inhibitor, which is used in scientific research.
N-n-Propylnorapomorphine (NPA) is an aporphine derivative dopamine agonist closely related to apomorphine. In rodents it has been shown to produce hyperactivity, stereotypy, hypothermia, antinociception, and penile erection, among other effects. Notably, its effects on locomotion are biphasic, with low doses producing inhibition and catalepsy and high doses resulting in enhancement of activity. This is likely due to preferential activation of D2/D3 autoreceptors versus postsynaptic receptors, the latter of which overcomes the former to increase postsynaptic dopaminergic signaling only with high doses.
SC-17599 is a steroid derivative drug discovered in 1968 which acts as a selective μ-opioid receptor agonist, with little or no affinity for the δ-opioid or κ-opioid receptors. It is an active analgesic in vivo, more potent than codeine or pethidine but slightly less potent than morphine, and produces similar effects to morphine in animals but with less sedation
Spiradoline (U-62066) is a drug which acts as a highly selective κ-opioid agonist. It has analgesic, diuretic, and antitussive effects, and produces subjective effects in animals similar to those of ketazocine and alazocine. The main effect in humans is sedation, along with analgesic and diuretic effects, but significant side effects such as dysphoria and hallucinations have stopped it from being used clinically.
Ro64-6198 is an opioid drug used in scientific research. It acts as a potent and selective agonist for the nociceptin receptor, also known as the ORL-1 receptor, with over 100x selectivity over the other opioid receptors. It produces anxiolytic effects in animal studies equivalent to those of benzodiazepine drugs, but has no anticonvulsant effects and does not produce any overt effects on behaviour. However it does impair short-term memory, and counteracts stress-induced anorexia. It also has antitussive effects, and reduces the rewarding and analgesic effects of morphine, although it did not prevent the development of dependence. It has been shown to reduce alcohol self-administration in animals and suppressed relapses in animal models of alcoholism, and ORL-1 agonists may have application in the treatment of alcoholism.
A-68930 is a synthetic compound that acts as a selective dopamine receptor D1 agonist. It is orally active and has antidepressant and anorectic effects in animals, producing wakefulness and tachycardia, but without stimulant effects, instead producing sedation. The difference in effects between A-68930 and other D1 agonists such as SKF-82958 may be due to their differing effects on the related D5 receptor.
U-69,593 is a drug which acts as a potent and selective κ1-opioid receptor agonist. In animal studies it has been shown to produce antinociception, anti-inflammation, anxiolysis, respiratory depression, and diuresis, while having little effect on gastrointestinal motility. It also inhibits the peripheral, though not central secretion of oxytocin and vasopressin in rats.
ICI-199,441 is a drug which acts as a potent and selective κ-opioid agonist, and has analgesic effects. It is a biased agonist of the KOR, and is one of relatively few KOR ligands that is G protein-biased rather than β-arrestin-biased.
S-14671 is a naphthylpiperazine derivative which acts as a 5-HT1A receptor agonist (pKi = 9.3) with high efficacy and exceptional in vivo potency, and also as a 5-HT2A and 5-HT2C receptor antagonist (both are pKi = 7.8). It displays only low and non-significant affinity for 5-HT1B and 5-HT3 sites.
The hot plate test is a test of the pain response in animals, similar to the tail flick test. Both hot plate and tail-flick methods are used generally for centrally acting analgesic, while peripherally acting drugs are ineffective in these tests but sensitive to acetic acid-induced writhing test.
(+)-Naloxone (dextro-naloxone) is a drug which is the opposite enantiomer of the opioid antagonist drug (−)-naloxone. Unlike (−)-naloxone, (+)-naloxone has no significant affinity for opioid receptors, but instead has been discovered to act as a selective antagonist of Toll-like receptor 4. This receptor is involved in immune system responses, and activation of TLR4 induces glial activation and release of inflammatory mediators such as TNF-α and Interleukin-1.
Cymserine is a drug related to physostigmine, which acts as a reversible cholinesterase inhibitor, with moderate selectivity (15×) for the plasma cholinesterase enzyme butyrylcholinesterase, and relatively weaker inhibition of the better-known acetylcholinesterase enzyme. This gives it a much more specific profile of effects that may be useful for treating Alzheimer's disease without producing side effects such as tremors, lacrimation, and salivation that are seen with the older nonselective cholinesterase inhibitors currently used for this application, such as donepezil. A number of cymserine derivatives have been developed with much greater selectivity for butyrylcholinesterase, and both cymserine and several of its analogues have been tested in animals, and found to increase brain acetylcholine levels and produce nootropic effects, as well as reducing levels of amyloid precursor protein and amyloid beta, which are commonly used biomarkers for the development of Alzheimer's disease.
Hemorphin-4 is an endogenous opioid peptide of the hemorphin family which possesses antinociceptive properties and is derived from the β-chain of hemoglobin in the bloodstream. It is a tetrapeptide with the amino acid sequence Tyr-Pro-Trp-Thr. Hemorphin-4 has affinities for the μ-, δ-, and κ-opioid receptors that are in the same range as the structurally related β-casomorphins, although affinity to the κ-opioid receptor is markedly higher in comparison. It acts as an agonist at these sites. Hemorphin-4 also has inhibitory effects on angiotensin-converting enzyme (ACE), and as a result, may play a role in the regulation of blood pressure. Notably, inhibition of ACE also reduces enkephalin catabolism.
Hemorphins are a class of naturally occurring, endogenous opioid peptides which are found in the bloodstream, and are derived from the β-chain of hemoglobin. They have antinociceptive effects via activation of the opioid receptors, and some may also play a role in blood pressure through inhibition of the angiotensin-converting enzyme (ACE), as well as cause an elevation of endogenous enkephalin levels. Some examples of hemorphins include hemorphin-4, spinorphin, and valorphin.
