DROSOPHILA - a model for drug addiction Flashcards
Most harmful drug? No of deaths?
Alcohol - 8416 alcohol related deaths in the UK in 2013
Contributing factors to addiction? How?
- Genetic - may impact drug sensitivity and development of tolerance
- Social environment - past and present
- Personality and personal history - eg trauma
Are flies a good model for drug addiction? Advs
- Their life cycles are around 10 days so they are a quick and cost efficient model to use
- 50% of their genes are present in humans and 75% of the genes known to be implicated in human disease are also present and implicated in drosophila
- Flies do exhibit SOME complex behaviours
- Cannot model personalities or environment but can model genetics
Diff drugs in humans and their primary targets?
How about secondary
-OPIATES - opiate receptors
-NICOTINE - Ach receptors
-CANNABIS - cannaboid receptors
-ALCOHOL - NMDA and GABBA receptors
Most drugs act secondarily via dopamine and mesolimbic reward system
BOOZE-O-MAT - an experimental approach
How does it work?
WHat is generated to measure changes in behaviour?
- Chamber which contains flies and ethanol is pumped in
- Changes in behaviour are analysed by producing a locomotor velocity profile
What is the locomotor velocity profile and what was shown for that of flies compared with humans?
- Showed the dynamic
- Concentrations at which flies show increased locomotion and sedation are similar to the concentrations that elicit these responses in mammals including humans.
What movement profiles do the flies display (in order)?
Startled response –> Sedation –> Drunk coma
INEBRIOMETER - an experimental approach
What do wild type and more sensitive flies show?
The Inebriometer measures ‘elution’ time for flies - mean amount of time the flies stay in the chamber before they have to leave
WT flies remain in the chamber for around 20 mins
More sensitive flies remain in the chamber for less time (and the reverse for less sensitive flies)
2 independant genetic factors that impact alcohol addiction?
- DEVELOPMENT OF TOLERANCE - drug sensitivity is reduced when the drug is used repeatedly over time
- SENSITIVITY - the inability to tolerate adverse effects of a drug - low sensitivities to moderate doses are associated with the risk of future alcoholism
Investigating genetic links to sensitivity and tolerance in flies – how is this done in flies? (using inebriometer)
1) irridate flies to induce genetic mutations
2) test flies in the inebriometer and screen for flies who are v tolerant and v sensitive
3) IDENTIFY MUTATIONS!
Cheap date mutant – what was the phenotype seen in cheap date? What does the gene code for?
- Cheap date mutants are much much more sensitive to ethanol so elute the booze-o-mat chamber more quickly and enter the sedation and coma state more quickly.
- Cheap date codes for an AMNESIAC GENE allele – this is a neuropeptide which activates cAMP
Why is this the phenotype seen in cheap date mutant?
What does this suggest about the relevance of an activated cAMP pathway in relation to the build up of alcohol tolerance?
Neuropeptide which activates cAMP, that results in the change in expression of a subset of genes in the nucleus.
This sub set of genes in the nucleus cause a DECREASE in SENSITIVITY TO ETHANOL (hence the cheap date mutants being more sensitive)
This also suggests the cAMP pathway needs to be activated to BUILD TOLERANCE
ETHANOL RESPONSE cAMP pathway mutants
D.C.O - pka catalytic sub unit
tutabaga - adenylyl cyclase enzyme
dunce - cAMP phosphodiesterase
How can flies be tested and increased for tolerance levels?
Repeatedly add flies to the inebriometer causing tolerance to build up in flies
SCREEN FOR MUTATIONS
Hangover mutants - what phenotype was seen and what does the protein code for?
Hangover mutants show reduced tolerance - every time they are exposed they get a ‘hangover’
The hangover gene codes for a gene that is part of a pathway that is required to build up tolerance. Encodes a Zn finger protein which BINDS RNA
