Synthesis and release: It is synthesized from choline and acetyl-CoA under the action of choline acetyltransferase (ChAT) and released through vesicles.

Function: Activates muscle contractions involved in attention, memory and learning.

Receptors: There are ionotropic (such as N-type and P/Q-type) and G-protein-coupled (such as M-type) receptors.

Metabolism: Rapidly broken down by acetylcholinesterase (AChE).

Synthesis and release: Synthesized from tyrosine under the action of dopa decarboxylase (DDC) and tyrosine hydroxylase (TH), and released through vesicles.

Role: Regulates movement, reward, mood and cognitive functions.

Receptors: There are five receptors, D1-D5, divided into D1-like (D1 and D5) and D2-like (D2, D3 and D4).

Metabolism: Metabolized by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT).

Synthesis and release: It is synthesized from tryptophan under the action of tryptophan hydroxylase (TPH) and released through vesicles.

Function: Regulates mood, sleep, appetite and pain perception.

Receptors: There are many receptors, divided into 7 subtypes, including 5-HT1 to 5-HT7.

Metabolism: Metabolized by monoamine oxidase (MAO) and serotonin-N-acetyltransferase (NET).

Synthesis and release: It is synthesized from glutamic acid under the action of glutamate decarboxylase (GAD) and released through vesicles.

Function: It is the most important excitatory neurotransmitter in the central nervous system.

Receptors: There are ionic types (such as NMDA, AMPA and Kainate) and G protein-coupled types (such as mGluRs).

Metabolism: Metabolized by glutamate enzyme (GAD) and glutamate aminotransferase (GOT).

Synthesis and release: It is synthesized from glutamate under the action of glutamic acid decarboxylase (GAD) and released through vesicles.

Role: It is the most important inhibitory neurotransmitter in the central nervous system.

Receptors: There are ionic types (such as GABA-A) and G protein-coupled types (such as GABA-B).

Metabolism: Metabolized by GABA transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH).

Synthesis and release: Dopamine is synthesized under the action of dopamine β-hydroxylase (DBH) and released through vesicles.

Role: Involved in arousal, attention, stress response and emotion regulation.

Receptors: There are many receptors such as α1, α2, β1, β2 and β3.

Metabolism: Metabolized by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT).

Synthesis and release: It is a type of peptide substances, including β-endorphin, δ-endorphin and enkephalin.

Function: As a natural analgesic substance, involved in pain perception, emotion and stress response.

Receptor: Binds to opioid receptors (mainly mu, delta and kappa types).

Metabolism: Metabolized by various enzymes such as endorphins and peptidases.