Lecture 5 Flashcards
Neurotransmitter types
- Aminoacids (small and a lot)
- Amines (medium size and concentration)
- Peptides (large and low concentration)
Production of Amines and Aminoacids
Enzymes are synthesized in the cell body. In the synapse the enzymes are used to synthesize aminoacids and amins.
Inactivation largely through reuptake
Production of Peptides
Enzymes synthesized in the cell body. Enzymes and pre-peptide precursors go down microtubule tracks. Enzymes modify pre-peptidess to produce peptide neurotransmitters.
Inactivation through breakdown and diffusion
The prototypical neuron
- Cytoskeleton: internal scaffolding within the neuronal membrane
- Tubulin: cell body, dendrites, proximal axon
- Tau: axons
- Actin: in the growth cone, in the heads of the spines
Anterograde tracing
From soma to synapse.
Horse radish Peroxidase (HRP)
Phaseolus vulgaris-leuocoagglutinin (PHA-L)
Retrograde tracing
From synapse to soma.
Fluoro-Gold (FG)
Cholera Toxin (CT)
Fast Blue (FB)
Immunohistochemistry
Method to identify location of molecules within cells using antibodies
- Neurotransmitter candidate is injected into organism and this creates antibodies that bind to it
- Blood is withdrawn and antibodies are isolated
- Antibodies are tagged with a visible marker and are applied to sections of brain tissue.
When using different antibodies you can identify several types of neurons within the same brain region
In situ hybridization
Method to identify cells that synthesize a particular protein or peptide.
This method uses a complementary strand of mRNA (probe) that was constructed in a lab that will stick to a specific sequence of nucleic acids in a strand of mRNA.
The binding is called hybridization.
Over time the probes stick to any complementary strands of mRNA and then you can search for the neurons containing the label.
One way of labeling is by way of fluorescence, also known is FISH.
Acetylcholine general information
- Nicotinic and Muscarinic receptors
- Mediumsized transmitter
- Part of diffuse modulatory systems of the brain
- Production depends on two enzymes: Choline acetyltransferase (making Ach) and Acetylcholine esterase (recycling Ach)
- No reuptake (Ach esterase)
Novichok
- Organophosphates
- Block acetylcholine esterase
- Used in Navalny poisoning
- Neuromuscular paralysis
Vesicle packing and recycling
- Synapsin: connects pool of vesicles
- CaMKII: dissociates synapsin from vesicles
- SNAPS and SNARES: priming and docking
Vesicle fusing with membrane
- Synaptobrevin: vesicle membrane
- Syntaxin: synaps membrane
- Cleave SNARE: block transmitter release
- Ca2: brings membranes together which leads to fusion
Vesicle recovery
- Clathrin: connects to vesicular membrane and coat around it
- Dynamin: pinches vesicle from the synaptic membrane
- Actin: transport from the membrane
- Auxilin: removal of clathrin coat
Acetylcholine projections
Basal forebrain complex: Medial septal nuclei (-> hippocampus) and basal nucleus of Meynert (-> neocortex)
Pontomesencephalotegmental complex: Pons and tegmentum -> dorsal thalamus
Acetylcholine nicotinic receptor
- 5 subunits
- Fast and shortlasting action
- Gate flips open when Ach binds
Acetylcholine Muscarinic receptor
- 7 membrane sections
- Slow and longlasting action
- No pore, G-protein coupled to 2nd messenger system
2 types of neurotransmitter receptors
- Ionotropic: allows ions to flow in after transmitter binds
- Metabotropic: needs G-protein and second messengers to indirectly modulate ionic activity
Acetylcholine function
- Central Ach from basal forebrain:
1. Enhance LTP and learning
2. Enhance selective attention
3. Are involved in the generation of neuronal oscillations - Transmitter at neuromuscular function
- Transmitter at parasympathetic NS
Acetylcholine system diseases
- Alzheimers (CNS): degeneration of Ach nuclei in basal forebrain
- Myasthenia gravis (PNS): antibodies against nAch receptors at neuromuscular junctions
Alzheimers medication
- Ach esterase blockers: temporarily beneficial on attention, concentration and speech performance.
- NDMA blockade: prevents overexcitation of glutamate by which cells can die
Myasthenia gravis medication
- Cholinesterase inhibitors: enhance communication between nerves and muscles
- Corticosteroids: limit antibody production
- Immunosuppressants
Glutamate reuptake
Via excitatory amino acid transporters
Also via astrocytes
Glutamate receptors
- AMPA receptor (Amino terminal and Ligand binding) (Na and K)
- Kaniate receptor
- NMDA receptor (Na, K and Ca)
Glutamate system
- Mediates fast excitatory transmission in CNS
- NMDA receptors play important role in feedback processing, short term memory, and plasticity
- Blockade of NMDA receptors produces dissociative anaesthesia
Long term potentiation (glutamate)
Low frequency synaptic transmission: AMPA activates, NMDA blocked, EPSP mediated by AMPA
High frequency transmission: strong depolarization -> Ca2 enters cell -> increase of AMPA receptors channel conductance -> long lasting increase in EPSP amplitude
Early and late LTP
- Early: dynamic changes in AMPA receptors
Adding postsynaptic AMPA receptors after LTP
Late: PKA activating CREB
New spines
Long term depression
- Prolonged low frequency stimulation
- Activation of phosphatases
- Loss of synaptic AMPA receptors
- Clathrin dependent endocytosis
Long term depression
- Prolonged low frequency stimulation
- Activation of phosphatases
- Loss of synaptic AMPA receptors
- Clathrin dependent endocytosis
Learning by doing
- Neurogenesis: growth of new neurons and contacts from stem cells (hours-days-weeks)
- Synaptic plasticity: more efficient communication between neurons. Neurons that fire together, wire together.
- Learning and memory
Enriched environment epigenetics
Rats raised in an enriched environment have brigger brains and more connections
Cells also have bigger dendritic trees
Better cognition and motor skills
GABA receptor
- Inhibitory receptors
- Chloride channels
- Reuptake by GAT cotransporters
- GAD enzyme: Glutamate to GABA
Ionotropic GABA receptors
- Shunting inhibition: leak preventing EPSP’s from triggering action potentials
- Agonists act as sedatives
- Antagonists acts as convulsants
GABA system
- Local balance of excitation through GABAergic inhibition
- Inhibition prevents excessive activity (epilepsy)
- Pulsed inhibition generates neuronal oscillations
- Excessive GABAergic inhibition leads to sedation
- Benzo’s are GABA agonists and are used as tranquilizers
