Modulation of synaptic transmission

Question 1

Where are chemical transmitters produced & packaged?

Where are neuropeptide transmitters produced & packaged?

Answer 1

In presynaptic terminal
-mediate FAST synaptic transmission

In cell body (conveyed by axonal transport)
-modulate ongoing activity!

Question 2

What are some functions of neuropeptide signalling?

Answer 2

-Mental state
-Cognitive function
etc.

Question 3

What is the function of G-proteins?

Answer 3

Bind & hydrolyse GTP

-trimers are formed of alpha (20), beta (6) and gamma (12) subunits

Question 4

What effect does NA have in sensory fibres?

What is the functional significance of this?

Answer 4

DECREASE neurotransmitter release

The same neurotransmitter (NA) can have opposite effects on target cell function, depending on the signalling pathway to which the R is coupled

In sensory neurons, SENSITIVITY IS DECREASED BY NA VIA IP3 & PKC

NA DECREASES DURATION OF AP IN SENSORY NEURONS BY INHIBITING Ca CURRENT!

Question 5

What effect does NA have in cardiac ventricles?

Answer 5

INCREASES Ca influx thru Cav channels

Phosphorylation leads to an increase in duration of plateau,
corresponding to an INCREASE in amplitude of INWARD CURRENT CARRIED BY Ca

Enhanced ICa current explained by INCREASE in OPEN PROBABLITY (Po) of Ca channels

PHOSPHORYLATION DECREASES Po FOR VOLTAGE-G Ca CHANNEL NA
-Leads to DECREASE IN SENSITIVITY TO PERIPHERAL STIM.

Question 6

What are inward rectifiers?

Answer 6

Channels that carry current inward better than outward!

• active at (-) potentials, & thus are important in setting the RESTING MEM. POTENTIAL
• @ potentials above Ek, Kir channels help bring mem. potential down

Question 7

What do inward rectifier channels do at voltages below Ek?

Answer 7

Enhance current amplitudes!

Question 8

What is Ohm’s law?

Answer 8

V = I R
(where R = 1/G)

CURRENT follow Ohm’s law! (current is proportional to voltage)

V= voltage
I = current
R = resistance
G = conductance

Question 9

Besides probability to determine whether channels are open, what does CURRENT require?

Answer 9

a DRIVING FORCE!

=difference between mem. potential & equilib. potential

Question 10

Kir follows Ohm’s law, but what does a voltage-sensitive block cause?

Answer 10

Creates rectification!

Block of outward Kir current is caused by intracellular Mg2+ (& organic cations (+))

Question 11

How is neuropeptide signalling regulated?

Answer 11

Regulation by Kir

e.g. SUBSTANCE P (SP) induces slow excitation

ACh fibres project throughout cortex, co-releasing SP & other neuropeptides to influence ATTENTION, AROUSAL, MOTIVATION, memory & consciousness

SP INCREASES EXCITABILITY of neurons by DECREASING Kir channel activity!