amines and pathways

Norepinephrine (NE)

Catecholamine neurotransmitter that can activate adrenergic receptors, including β adrenergic receptors.

Epinephrine (Epi)

Catecholamine neurotransmitter and hormone that can activate adrenergic receptors.

β adrenergic receptor

Metabotropic GPCR activated by NE or epinephrine. Can activate Gs.

Gs

G protein that activates adenylyl cyclase.

Adenylyl cyclase (AC)

Enzyme that converts ATP into cAMP.

cAMP

Second messenger that activates protein kinase A.

Protein kinase A (PKA)

Protein kinase activated by cAMP. Phosphorylates target proteins.

cAMP pathway

NE or Epi -> β receptor -> Gs -> adenylyl cyclase -> cAMP -> PKA -> protein phosphorylation.

Gq

G protein that activates phospholipase C.

Phospholipase C (PLC)

Enzyme that splits PIP₂ into IP₃ and DAG.

PIP₂

Membrane phospholipid that PLC splits into IP₃ and DAG.

IP₃

Second messenger that binds receptors on the ER and causes stored Ca²⁺ to be released into the cytoplasm.

DAG

Second messenger that remains in the membrane and helps activate PKC.

Protein kinase C (PKC)

Protein kinase activated downstream of DAG and Ca²⁺. Phosphorylates target proteins.

Phosphoinositide pathway

Gq -> PLC -> PIP₂ -> IP₃ + DAG -> Ca²⁺ release -> PKC activation.

Calmodulin (CaM)

Intracellular protein that binds Ca²⁺. The Ca²⁺ and calmodulin complex can activate CaMK.

Ca²⁺/calmodulin complex

Formed when Ca²⁺ binds to calmodulin. Activates proteins including CaMK.

CaMK

Calcium/calmodulin dependent protein kinase. Activated by the Ca²⁺/calmodulin complex and phosphorylates target proteins.

CaMK pathway

Intracellular Ca²⁺ increases -> Ca²⁺ binds calmodulin -> Ca²⁺/calmodulin activates CaMK -> CaMK phosphorylates proteins.

CaMKII

Major CaMK in neurons. Important for synaptic plasticity and changes in synaptic strength.

Protein kinase

Enzyme that adds phosphate groups to proteins and changes their activity.

Protein phosphatase

Enzyme that removes phosphate groups from proteins.

Phosphorylation

Addition of a phosphate group to a protein, which can change that protein's function.

Catecholamines

Family of neurotransmitters containing dopamine, norepinephrine, and epinephrine.

Tyrosine

Amino acid used as the starting material for catecholamine synthesis.

Tyrosine hydroxylase

Enzyme converting tyrosine -> L DOPA. Rate limiting enzyme of catecholamine synthesis.

L DOPA

Precursor converted into dopamine.

DOPA decarboxylase

Enzyme converting L DOPA -> dopamine.

Dopamine (DA)

Catecholamine neurotransmitter and precursor to norepinephrine.

Dopamine β hydroxylase

Enzyme converting dopamine -> norepinephrine.

Norepinephrine (NE) (Synthesis)

Catecholamine made from dopamine and precursor to epinephrine.

PNMT

Enzyme converting norepinephrine -> epinephrine.

Catecholamine synthesis

Tyrosine -> L DOPA -> dopamine -> norepinephrine -> epinephrine.

Serotonin (5 HT)

Monoamine neurotransmitter synthesized from tryptophan.

Tryptophan

Amino acid used as the starting material for serotonin synthesis.

Tryptophan hydroxylase

Enzyme converting tryptophan -> 5 HTP. Rate limiting enzyme in serotonin synthesis.

5 HTP

Intermediate converted into serotonin.

AADC

Enzyme converting 5 HTP -> serotonin.

Serotonin synthesis

Tryptophan -> 5 HTP -> serotonin.

Glutamate

Major excitatory neurotransmitter in the CNS.

AMPA receptor

Ionotropic glutamate receptor responsible for much of fast excitatory transmission. Opening produces a depolarizing current.

NMDA receptor

Ionotropic glutamate receptor that requires glutamate binding and sufficient depolarization to remove its Mg²⁺ block. Allows Ca²⁺ and other cations through.

NMDA Mg²⁺ block

Mg²⁺ blocks the NMDA channel at negative membrane potentials. Depolarization removes the block.

Kainate receptor

Ionotropic glutamate receptor involved in excitatory transmission.

mGluR

Metabotropic glutamate receptor. GPCR that produces slower intracellular signaling.

Acetylcholine (ACh)

Neurotransmitter that acts on nicotinic and muscarinic receptors.

Nicotinic ACh receptor

Ionotropic ACh receptor. ACh binding directly opens a cation channel.

Nicotine

Agonist of nicotinic ACh receptors.

Curare

Antagonist of nicotinic ACh receptors, particularly at the neuromuscular junction.

Muscarinic ACh receptor

Metabotropic ACh receptor that signals through G proteins.

Muscarine

Agonist of muscarinic ACh receptors.

Atropine

Antagonist of muscarinic ACh receptors.

Glycine

Inhibitory neurotransmitter especially important in the spinal cord and brainstem.

Glycine receptor (GlyR)

Ionotropic Cl⁻ channel activated by glycine, producing inhibition.

Glycinergic inhibition

Glycine increases Cl⁻ conductance, making the postsynaptic neuron less likely to fire.

Ionotropic receptor

Receptor that is itself an ion channel and opens directly when neurotransmitter binds.

Metabotropic receptor

Receptor that changes cell activity through intracellular signaling rather than being an ion channel itself.

GPCR

G protein coupled receptor. Metabotropic receptor that activates a G protein.

G protein

Intracellular signaling protein that connects activated GPCRs to effectors.

Effector

Protein controlled by a G protein, such as adenylyl cyclase, PLC, or an ion channel.

First messenger

Extracellular signaling molecule, such as a neurotransmitter, that binds a receptor.

Second messenger

Intracellular signaling molecule that carries and amplifies a signal inside the cell. Examples include cAMP, IP₃, DAG, and Ca²⁺.

Membrane delimited pathway

Pathway where a G protein directly regulates a nearby membrane protein without using a diffusible second messenger.

Agonist

Molecule that binds to and activates a receptor.

Antagonist

Molecule that binds to a receptor and prevents its activation.

PKA Activation

Activated by cAMP.

PKC Activation

Activated downstream of DAG and Ca²⁺.

CaMK Activation

Activated by Ca²⁺ + calmodulin.