PSYC 2: Biological Foundations - Fall 2012 - Professor Claffey

Notes: Synapse

History:
10/26/12 - changed formatting
10/4/12 - original version

Structure & Function

(This content is covered in Sinjin's presentation, see link in calendar)
Neurotransmitters
Synaptic cleft
Post-synaptic potential
    Excitation
    Inhibition
Receptors
    Ionotropic
    Metabotropic

Neurotransmitter Sequence

(This content is covered in Sinjin's presentation, see link in calendar)

1. Neurotransmitter synthesis
    Small neurotransmitters
    Large neurotransmitters

2. Exocytosis (neurotransmitter release)

3. Receptor interaction
    Ionotropic receptors
    Metabotropic receptors

4. Removal from synapse
    Diffusion
    Reuptake
    Enzymatic degradation (breakdown)

Integration

A depolarization from one neuron is typically not enough to trigger an action potential
Each neuron can receive signals from 1000s of synapses
Integration - combining many different signals to determine if an action potential occurs

Temporal Integration
depolarizations that _________________________ may combine to cause ________________

Spatial Integration
depolarizations that __________________________ may combine...

Types of neurotransmitters

More than 100 identified neurotransmitter substances

________________ (small NT)
    Molecules that make up proteins, found in our diet
    Most common neurotransmitters for fast acting, directed synapses

    ________________ - main excitatory transmitter, sensory & learning systems

    ________________ - main inhibitory transmitter

________________ (small NT)
    Not a typical synapse NT
    Release NT broadly throughout brain
    Produced by cells in the brain stem
    More likely to modify "global" function/state of the brain

    ________________ - motor function and reward

    ________________ - (adrenaline, adrenergic)

    ________________- (nor-adrenaline, nor-adrenergic) - brain arousal, mood, hunger, sleep

    ________________ - mood, temperature, aggression, sleep

________________ (small NT)
    Neurons are called cholinergic
    Location
        Neuromuscular junction
        Throughout autonomic system (parts of our nervous system NOT under voluntary control)
        In parts of central nervous system - cortical arousal, memory

Unconventional NTs (small NT)
    Don't have to know

________________ (large NT)
    Full proteins made up of many amino acids
    >100 neuropeptides
    Many have role as both neurotransmitter and hormone

Drug action

Antagonist - decrease the effect of a neurotransmitter
Agonist - increase the effect of a neurotransmitter

Receptor agonists
Nicotine - stimulates acetylcholine receptors

Receptor blockers
Botox - nicotinic receptor antagonist

Reuptake blockers
Cocaine, amphetamines - impairs dopamine transporter

Source: http://www-scf.usc.edu/~uscience/adderall_abuse.html

Gap Junctions

A direct connection between the cytosol (internal fluid) of two cells
Faster than a chemical synapse
Doesn't require neurotransmitters
Not common in the brain

gap junction

Synaptic Plasticity

Changes in connections between neurons can produce changes in behavior

"Neurons that fire together, wire together"
- paraphrasing Donald Hebb's 1949 theory of memory

Long Term Potentiation (LTP)

Typically studied in hippocampus

Process

Put a STIMULATING electrode in the upstream (presynaptic) neuron
Put a RECORDING electrode in the downstream (post-synaptic) neuron
Record the reaction of the downstream neuron to a single upstream stimulation
Provide high-frequency, high-intensity stimulation to upstream neuron (no measurement)
Record the reaction of the downstream neuron to a single upstream stimulation

Increased response in downstream neuron
Can be measured months later
Requires pre- and post- synaptic neurons to both have action potentials

Induction

Source: http://employees.csbsju.edu/ltennison/PSYC340/learning.htm

LTP Requires ________ receptors
    NMDA receptors allow Ca++ to enter
        Ca++ causes changes in cell functioning, such as creating new receptors

    NMDA receptors are excited by _____________
        and require post-synaptic neuron to already be partially ______________

NMDA are able to detect the co-occurrence of

______________________ and ______________________ depolarization

Maintenance/Expression

The post-synaptic neuron does not strengthen connections with all pre-synaptic neurons,
only across synpases that were depolarized

LTP requires protein synthesis

Neuron is making new ____________ to "build" or strengthen the synapse

Relation to behavior

LTP is a model for memory, and memory is probably "like" LTP,
but LTP is an artificial technique done in a laboratory setting

Rats learning a maze task fail to learn if NMDA receptors are blocked (Morris et al 1986)

Rats learning an avoidance task produce new AMPA receptors, the same receptors produced by LTP. Also, in vitro synapse that were potentiated during training could not be further induced by LTP. (Whitlock et al, 2006)

Animals undergoing fear conditioning show evidence of LTP-like processes (Rogan et al, 1997)

Learning in a Sea Slug

Aplysia

A sea slug with 200 neurons studied by Eric Kandel
Has a gill which it will withdraw if its siphon is touched

These are two examples of synaptic changes that explain an animal's behavior

Habituation

Source: http://michaeldmann.net/mann18.html

If the siphon is repeatedly touched, the gill withdrawal reflex disappears
With repeated activation, the neurons contain less dopamine and release less dopamine each time
Eventually gill withdrawal stops

A "short term" change in synaptic activity that does NOT require building new proteins

Sensitization

Source: http://michaeldmann.net/mann18.html

If the tail is shocked at the same time the siphon is touched:
    Gill is more vigorously withdrawn to a siphon touch
     Siphon has become "more sensitive"

Facilitating interneuron releases serotonin onto sensory neuron
    Causes the sensory neuron to release more neurotransmitter when the siphon is stimulated
    Causes motor neuron to react more vigorously

A "short term" change in synaptic activity that does NOT require building new proteins
    (can be made "long term" with more training)