NT’s, Receptors and their actions
•Cholinergic Receptors (receptors that respond to Ach)
–Nicotinic
–Muscarinic
•Adrenergic Receptors (receptors that respond to NE)
–Alpha
–Beta
Other NT
Dopamine, serotonin, GABA, Glutimate
•Binding of NT to receptors on post synapticmembrane can cause EPSPs or IPSPs depending onthe combination of NT and receptor at any givensynapse.
Acetylcholine (ACh)
Used extensively in PNS and in restricted areas of CNS
Broken down by Achase
Two types of receptors
1.Nicotinic
2.muscarinic
•Autonomic ganglia,
•Neuromuscular junctions
•Post ganglionic Parasympatheticneurons
Nicotinic (Cholinergic) Receptors — Activated by ACh:
• Ionotropic: activation directly leads to movement of ions across membrane
• Chemical (ligand) gated channels
ACh bind receptors/gated channel channel opens Na+ flows in depolarization
• Excitation (EPSP)
Fig. 7.27
Muscarinic (Cholinergic) Receptors—Activated by ACh:
• Metabotropic: binding of receptors directly leads to chemical reactions (metabolism)
• Activates a second-messenger; G-protiens
ACh binds receptor G protien is activated G protien signals gated channel next step varies
• If G protien opens K+ channels: ↑ K+ outflow hyperpolarization IPSP
• If G protein closes Ca+ or Na+ channels: ↓ Ca+/Na+ flow into cell hyperpolarization IPSP
• if G protein closes (blocks) K+ channels: ↓ K+ leaking depolarization EPSP
Can alsoclose K+channel inother cases
Fig. 9.11
Or reduce Ca+inflow
Norepinephrine (NE) and Epinephrine (E)
• Monoamine > catecholamine
• broken down by monoamine oxidases (MOA)
• Used in sympathetic post-ganglionic neurons and insome CNS areas.
Fig. 7.31
Adrenergic Receptors (NE, E)
•Metabotropic; binding of receptor initiates metabolic reactions
NE binds receptor G-protein activates adenylate cyclase cAMP kinase open/closes channel (and/or intracellular effects) IPSP or EPSP
or epinephrine
And/or activates proteinswithin the cytoplasm,and/or initiates events inthe nucleus
Changesin nucleus
Fig. 9.1
Fig. 9.7
Fig. 9.10
muscarinic
e.g., smooth muscleeffects, increases digestiveactivity, slow heart rate ,gland secretion
Receptor Type
NeurotransmitterSensativity
Effector
Effect on Effector
Nicotinic
Ach
Skeletal muscle,adrenal medulla,post-gangioloicneurons of ANS
Excitatory
Muscarinic
Ach in PD-ANS
Cardiac muscle,smooth muscle,exocrine glands,some endocrineglands
Excitatory orinhibitory
Alpha-1
Norepinephrine >epinephrine
Most sympathetictarget tissues
excitatory
Alpha-2
Norepinephrine >epinephrine
Digestive organs
inhibitory
Beta-1
Norepinephrine =epinephrine
Heart
excitatory
Beta-2
Epinephrine only
Smooth muscle ofarterioles andbronchioles
Inhibitory (i.e., leadsto dilation)
Table 7.5
CASTOR BEANS
CASTOR BEANS
MM
How various substances influence neuron and synaptic function
•Review of ANS neurons and NT’s
Dopamine
•In CNS
•Can be excitatory or inhibitory
•2 major dopamine systems in brain
–Involved with motor control (involved with inhibitingmuscles that should be relaxed/preventing overstimulationof skeletal muscle)
•Basal Nuclei (nigrostriatal system)
–involved in behavior and emotional reward (“feel good” NT)
•Part of reward system that influences behavior (“is it worth it tochoose a course of action)
•Most addictions activate this system, also risk taking behaviors
•Overactivity contributes to schizophrenia
–Which is treated by anti-dopamine drugs
•Mesolimbic dopamine system
7-67
Serotonin
•In CNS (and enteric system/GI tract)
•Excitatory and inhibitory
•Involved in regulation of mood, behavior, appetite and cerebralcirculation, muscle control, bone remodelling, reproductivebehavior.
•Effects mood, perception, and behavior
–Linked to depression
•LSD is structurally similar
•Ecstasy targets serotonin receptors
•SSRIs (serotonin-specific reuptake inhibitors) areantidepressants
–e.g., Prozac, Zoloft, Paxil, Luvox
–Block reuptake of serotonin, prolonging its action
7-66
GABA (gamma-aminobutyric acid)
•Inhibitory (opens Cl- channels)
•is most common NT in brain
•Inhibits neural pathways (so they are not over-active)
•Linked to anxiety levels (increased GABAreduces axiety)
•Barbituates & Benzodiazepines (Xanax andvalium) are agonists of GABA receptors
•Alcohol also targets GABA receptors
7-69
Glutamate
•Glutamate most important excitatory NT in CNS
•Important in memory formation and learning
•Involved with excitotoxicity
7-69
Glycine
•Inhibitory (mostly within brainstem and spinalcord)
•Important in maintiaing proper balance ofinhibition and excitation that controls skeletalmuscle contraction
–Opens Cl- channels which hyperpolarize
–Strychnine blocks glycine receptors
•Causes spastic paralysis (over activestimulation/excitation of skeletal muscle)
7-69
•Interesting concept—NOT fact checked
