wrong answers from mock exam Flashcards
what are the two main sites of action for glycine and what are its mechanisms at those site ?
- glycine is an agonist at glycine receptors, which are ion channels similar to ionotropic GABA-A receptors
- glycine is a co-agonist at NMDA glutamtae receptors
Spinal cord motor neurons are one of the main target sites of strychnine. Briefly explain the mechanism of strychnine and how it produces its characteristic pathological effects. (6 marks)
Renshaw cells are spinal cord interneurons. They are stimulated by collaterals from alpha motor neurons and release glycine onto motor neurons. This provides a negative feedback loop. Strychnine is a competitive antagonist at the glycine receptors on the motor neurons and thus will cause the motor neurons to fire at a faster rate. This produces a spastic paralysis, with a characteristic arching of the back. The victim will die of asphyxiation as the respiratory muscles are also affected.
what are renshaw cells ?
- inhibitory interneurons
- stimulated from alpha motor neruons and release glycine onto motor neurons
- provide a negative feedback loop
how to strychnine act on motor neurons in the spinal cord ?
- competitive antagonist at glycine receptors on motor neurons, causing them to fire at a faster rate
what does strychnine bindings to glycine receptors on motor neurons cause ?
- spastic paralysis characterised by arching back
- victim dies of asphyxiation as the respiratory muscles are also affected
what is the mechanism of glutamatae reuptake ?
EAATs / excitatory amino acid transporters
how is glutamate release ?
SNARE proteins activated by calcium release glutamate
what is a GABA-A agonist ?
muscimol, psychoactive compound in fly agaric mushrooms
are all glutamate receptors tetramers ?
NO. ionotropic are, metabotropic are not - they act as dimers
what are the drug tragets for GABA-A receptor agonists?
epilepsy, anxiety, sedation
what are 2 antagonists of GABA-A receptor at the GABA binding site?
- bicuculline
- gabazine
what are 2 agonists for GABA-A receptor at teh GABA binding site?
- muscimol
- gabaxadol
what is an agonist for GABA-B receptors ?
baclofen
what is an antagonist for GABA-B receptors ?
- saclofen
- CGP35348
what are 2 agonists at the BDZ binding site in GABA-A receptors ?
- anxiolytics
- benzodiazepines
what are antagonists at the BDZ binding site for GABA-A receptors ?
- flumazenil
- inverse agonists
what are 2 agonists at the extra-synaptic modulatory site on GABA-A receptors ?
- barbiturates
- anaesthetics
what is the mechanism of GABA-A receptors ?
ligand gated chloride channel
what is the mechanism of GABA-B receptors ?
G-protein coupled, acts on Ca++ and K+ channels
what is the difference in location between GABA-A and GABA-B receptors ?
GABA-A: widespread in CNS
GABA-B: pre- and post- synaptic, widespread
what is the function of GABA-A receptors ?
post-synaptic inhibition (fast ipsp and slower tonic)
what is the function of GABA-B receptors ?
pre-synaptic inhibition of Ca++ channels and post-synaptic activation of K+ channels
where are extra-synaptic GABA-A receptors and what is their function?
located out of the synapse (on PSM) and reuptake ambient GABA
what is the structure of GABA-A receptors, what are the drug targets, and why ?
- pentameric ligand-gated ion channels
- 19 different subunit genes (3 subunits for each)
- agonists for GABA-A receptors e.g. benzodiazepines are used as sedatives, anxiolytics and anticonvulsants or for epilepsy or anxiety
