Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word choline refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitteracetylcholine and functions with inositol as a basic constituent of lecithin.
The parasympathetic nervous system, which uses acetylcholine almost exclusively to send its messages, is said to be almost entirely cholinergic. Neuromuscular junctions, preganglionic neurons of the sympathetic nervous system, the basal forebrain, and brain stem complexes are also cholinergic. In addition, the receptor for the merocrine sweat glands are also cholinergic, since acetylcholine is released from postganglionic sympathetic neurons.
In neuroscience and related fields, the term cholinergic is used in these related contexts:
- A substance (or ligand) is cholinergic if it is capable of producing, altering, or releasing acetylcholine, or butyrylcholine (“indirect-acting”), or mimicking their behaviours at one or more of the body’s acetylcholine receptor (“direct-acting”) or butyrylcholine receptor types (“direct-acting”).
- A receptor is cholinergic if it uses acetylcholine as its neurotransmitter.
- A synapse is cholinergic if it uses acetylcholine as its neurotransmitter.
- Some dementias are currently treated by increasing acetylcholine concentration by using acetylcholinesterase inhibitors to inhibit acetylcholinesterase from breaking down acetylcholine.
An anticholinergic agent is a substance that blocks the action of the neurotransmitter acetylcholine at synapses in the central and the peripheral nervous system.These agents inhibit parasympatheticnerve impulses by selectively blocking the binding of the neurotransmitter acetylcholine to its receptor in nerve cells. The nerve fibers of the parasympathetic system are responsible for the involuntary movement of smooth muscles present in the gastrointestinal tract, urinary tract, lungs, and many other parts of the body. Anticholinergics are divided into three categories in accordance with their specific targets in the central and peripheral nervous system: antimuscarinic agents, ganglionic blockers, and neuromuscular blockers.
Anticholinergics are classified according to the receptors that are affected:
- Antimuscarinic agents operate on the muscarinic acetylcholine receptors. The majority of anticholinergic drugs are antimuscarinics.
- Antinicotinic agents operate on the nicotinic acetylcholine receptors. The majority of these are non-depolarising skeletal muscle relaxants for surgical use that are structurally related to curare. Several are depolarizing agents.
Examples of common anticholinergics:
- Antimuscarinic agents
- Antipsychotics (clozapine, quetiapine)
- Certain SSRIs (citalopram)
- Dicyclomine (Dicycloverine)
- Propantheline bromide
- Butriptyline† (Evadyne) (relatively weak serotonin reuptake inhibitor)
- Clomipramine (Anafranil)
- Imipramine (Tofranil, Janimine, Praminil)
- Trimipramine (Surmontil) (relatively weak serotonin reuptake inhibitor)
Those that preferentially inhibit the reuptake of norepinephrine (by at least 10-fold over serotonin) include:
- Desipramine (Norpramin, Pertofrane)
- Dibenzepin‡ (Noveril, Victoril)
- Lofepramine§ (Lomont, Gamanil)
- Maprotiline (Ludiomil) – can be classed with the TCAs though more frequently classed with the TeCAs
- Nortriptyline (Pamelor, Aventyl, Norpress)
- Protriptyline (Vivactil)
Whereas either fairly balanced reuptake inhibitors of serotonin and norepinephrine or unspecified inhibitors include:
- Amitriptyline (Elavil, Endep)
- Amitriptylinoxide (Amioxid, Ambivalon, Equilibrin)
- Amoxapine (Asendin) – can be classed with the TeCAs but more frequently classed with the TCAs
- Demexiptiline† (Deparon, Tinoran)
- Dimetacrine† (Istonil, Istonyl, Miroistonil)
- Dosulepin§ (Prothiaden)
- Doxepin (Adapin, Sinequan)
- Fluacizine† (Phtorazisin)
- Imipraminoxide† (Imiprex, Elepsin)
- Melitracen§ (Deanxit, Dixeran, Melixeran, Trausabun)
- Metapramine† (Timaxel)
- Nitroxazepine‡ (Sintamil)
- Noxiptiline‡ (Agedal, Elronon, Nogedal)
- Pipofezine‡ (Azafen/Azaphen)
- Propizepine† (Depressin, Vagran)
- Quinupramine† (Kevopril, Kinupril, Adeprim, Quinuprine)
And the following are TCAs that act via main mechanisms other than serotonin or norepinephrine reuptake inhibition:
- Amineptine‡ (Survector, Maneon, Directim) – norepinephrine–dopamine reuptake inhibitor
- Iprindole† (Prondol, Galatur, Tetran) – 5-HT2 receptor antagonist
- Opipramol‡ (Insidon, Pramolan, Ensidon, Oprimol) – σ receptor agonist
- Tianeptine § (Stablon, Coaxil, Tatinol) – atypical μ-opioid receptor agonist
Many of the agents proposed to remyelinate are anti-cholinergics.
ProfG has said he is not a fan of these.
Read this as homework for the weekend