Vessels in the ANS

Question 1

the main inhibitory neurotransmitter in the CNS

Answer 1

GABA

Question 2

In addition to acetylcholine and norepinephrine it is common for the vesicles in the autonomic neuron to contain transmitters

Answer 2

In addition to acetylcholine and norepinephrine it is common for the vesicles in the autonomic neuron to contain transmitters in addition to acetylcholine and norepinephrine (co-transmission) which fine tune the effects of autonomic activity on the particular tissue.

Question 3

ATP is commonly stored

Answer 3

ATP is commonly stored in vesicles containing norepinephrine and may be responsible for the fast component of some sympathetic responses with NE having similar but slower effects.

Question 4

Other co- transmitter

Answer 4

Other co- transmitters include VIP (vasoactive intestinal peptide), GnRH (gonadotrophin releasing hormone), GABA (gamma-aminobutyric acid), 5-HT (serotonin), and dopamine.

Question 5

Non-adrenergic, non-cholinergic (NANC) transmission

Answer 5

Non-adrenergic, non-cholinergic (NANC) transmission also can occur in which there is no acetylcholine or epinephrine needed. There are numerous of these, but the most important to remember is nitric oxide (NO) which is a potent smooth muscle relaxant that causes vasodilation. Organic nitrates (such as nitroglycerin) are converted to NO to exert their vasodilatory effect. This is an area of current study in pharmacology.

Question 6

Peripherally acting muscle relaxants:

Answer 6

Muscle relaxants that work outside of the CNS can act on the motor neuron, the neuromuscular junction, or the muscle.

Question 7

Peripherally acting muscle relaxant act on the

Answer 7

Those acting on the motor neuron include local anesthetics (refer to later section on local anesthetic drugs) and certain toxins (tetrodotoxin (pufferfish), saxitoxin).

Question 8

The peripherally acting muscle relaxants that acting on the neuromuscular junction

Answer 8

Those acting on the neuromuscular junction can be further subdivided into presynaptic and post- synaptic. For a nice review of neuromuscular junction function check this out:

Question 9

Pre-synaptic periphearlly acting muscle relaxants

Answer 9

Interfere with the synthesis, transport and/or release of acetylcholine from vesicles in the terminal neuron, for example hemicholinium decreases synthesis of acetylcholine by blocking re- uptake of choline at the presynaptic neuron. Vesamicol blocks the intracellular transporter responsible for putting the acetylcholine into vesicles. Botulinum toxin, low calcium and high magnesium decrease release of acetylcholine from the nerve terminal. Drugs in this category are not generally used in veterinary medicine.

Question 10

Post-synaptic peripherally acting muscle relaxant

Answer 10

The neuromuscular blocking agents interfere with function on the post-synaptic membrane through stimulation or alteration of the nicotinic acetylcholine receptor, or acting on the muscle itself (e.g. Dantrolene – which will be covered later). These agents produce profound muscle relaxation and thus are considered differently from the rest of the muscle relaxing agents and will be discussed further below.