Modyfing the Message

Question 0

Agonism

agonist?

Answer 0

Agonist = chemical that increases effect of a NT

• can result in excitation or inhibition, depending on the type of NT

Question 1

Besides summation, info transmitted by Neurons can be modified in various ways

Answer 1

That is, variations in any of the functions of NTs and Synapse can affect the message sent

Question 2

Antagonism

antagonist?

Answer 2

antagonist = chemical that DECREASES EFFECT of a NT

• can result in excitation or inhibition, depending on the type of NT

Question 3

EX of agonist and antagonist with ACh

Answer 3

ACh broken down in cleft by enzyme Acetylcholinesterase (AChE) into Choline (re-uptaken) & Acetate

  - in patients with ACh deficit, can block enzyme so little available ACh repeatedly stimulates Postsyn cell
  - so such an AChE blocker is an ACh-Agonist 

In contrast, a Choline Reuptake-Blocker would prevent re-synthesis of ACh and so is a ACh-Antagonist

Question 4

EX Agonist vs. Antagonist with Serotonin

Answer 4

• Serotonin typically remains intact, reuptaken whole into Presynaptic cell by Transporter Proteins
• 5-HT - Agonist drugs like Prosac block reuptake of Serotonin, prolonging its effects on Postsynaptic Cell
• 5-HT Antagonist like enzyme MAO converts Serotonin into inactive form that won’t affect Postsyn Cell

Question 5

Antagonists and Agonist can also operate inside ____________ cell to affect NT release

Answer 5

• Some antagonistic drugs (Reserpine) prevent NTs (Monoamines) from being packaged into vesicles
• some agonists (Black widow spider venom) cause massive release of NT (ACh)

Question 6

Receptivity Changes

Answer 6

• receptor sites can be BLOCKED BY NT MIMICS that do not readily detach
  - e.g. LSD binds to Serotonin sites
• Activation of DNA sequences initiated the production of proteins for structural and chemical changes within cell
• receptor sites can increase/decrease in number
  - e.g. repeated activity -> more DENDRIDIC SPINES, more receptor sites

Question 7

availability of NT components

Answer 7

• some NT’s, like Substanc P, are produced in the Neuron’s soma
• others, like ACh, are produce in Terminal and are efficiently recycled from cleft
• can depend on diet for availability of precursors
• a few precursors will pass blood-brain barrier, so can be administered as drugs

Question 8

Some NTs, like Substance P (PAIN), are produced in Neuron’s soma, and may require hours/days to replenish

Answer 8

• carried by Kinesin molecules (proteins) that ‘walk’ along micro-tubules from soma to terminal

Question 9

NTs that depend on diet for availability

Answer 9

• Tryptophan in turkey&raquo_space; serotonin

- Choline from milk or synthesized from lecithin&raquo_space; ACh

Question 10

Examples of precursors that will pass the blood-brain barrier

Answer 10

L-DOPA for Dopamine

Question 11

Receptors on PRE-synaptic terminal

Answer 11

Auto Receptors

Axoaxonic Synapses

Question 12

Auto-Receptors

Answer 12

Some AXONS have Receptor Sites for their OWN (usually inhibitory) NT

NT binding with these sites&raquo_space; Negative Feedback Loop via Second Messengers within PRE-synaptic cell
- that is, their own NT prevents them from releasing more NT

EX: by closing own Ca++ gates or blocking reset of Resting Potential by interfering with Na+/K+ Pump

Question 13

Axoaxonic Synapses

Answer 13

Axon to Axon

Presynaptic Terminal may have Receptor Sites for Inhibitory or Excitatory NT from ANOTHER CELL

Ex: Brain Endorphins stimulate opiate receptors on terminal of pain cell, inhibiting release of Substance P