Drugs acting on neurons Flashcards
where do Dopaminergic inputs start and where do they end?
- start at VTA
- go to nucleus accumbens and frontal cortex
what was nicotine used for historically?
as a botanical insecticide (natural insecticide in tobacco)
what is the number 1 avoidable killer in the world?
smoking
how long does it take for nicotine to reach the brain? how is that possible?
- 7 seconds
- high lung surface area and when gets into blood, goes right back to heart, which pumps it everywhere in the body
what are types of toxins that can be found in cigarettes?
carcinogens and ciliotoxins
what are ciliotoxins?
chemicals that impair the ability of the lung to get rid of all particles and pollutants that are inhaled – affects the mucociliary system in lungs
what can smoking cause?
- lung and bladder cancer
- coronary heart disease
- strokes
- peripheral vascular disease (impaired blood flow to legs making i harder for people to walk)
- chronic lung disease
- increase rate of influenza, diabetes, pneumonia, tuberculosis
what is the effect of smoking on blood vessels?
constricts blood flow to all the fine vessels in the periphery (effect on appearance – wrinkles, cataracts)
what is mainstream smoke vs sidestream smoke?
- main: what person exhales
- side: what comes off the burning end
explain the absorption of nicotine.
- lipid-soluble
- weak base: so ionized/more soluble at high pH, but cigarette companies will add chemicals to make it more alkaline so that it can be more readily absorbed, so will reach brain faster (more addictive)
- bypasses first-pass
- can easily diffuse into capillaries
are lower-nicotine cigarettes safer?
no since people will simply adjust the dose by smoking more/holding the smoke (smoker controls the bioavailability)
explain the distribution of nicotine.
- goes everywhere (including fetus and breastmilk)
- reaches Chemoreceptor trigger zone (CTZ), which is connected to vomiting center
- will induce vomiting the first couple times, but will develop tolerance for that
explain the metabolism of nicotine.
- mostly in liver by CYP2A6
- that enzyme converts it to less active metabolite cotinine
- half-life of 2 hours
- takes about 4 cigarettes to get to steady state (about 4 half-lives)
what is the effect of having underactive CYP2A6 enzyme (it is a genetic variation)?
- need to smoke fewer cigarettes, so less at risk of exposure to all the other chemicals in cigarettes
- also responsible to convert some procarcinogens into carcinogens so more protected from those
explain the excretion of nicotine.
- nicotine, cotinine, and carcinogens excreted in kidney, so makes urine carcinogenic (why risk of bladder disease)
- alkaline urine: will decrease excretion since will be in unionized form so will tend to be reabsorbed in tubules
which receptor does nicotine act on? what type of receptor is it?
nicotinic cholinergic receptor, which is a ligand-gated ion channel selective to sodium and calcium
is nicotine an agonist or antagonist?
both
where are nicotinic receptors found?
- found on postsynaptic side (but also act on presynaptic side to modulate amount of neurotransmitter release)
- in ganglia of sympathetic and parasympathetic nervous systems in addition to brain
- also found at innervation of skeletal muscle and in adrenal gland
what is the most common nicotinic receptor in the brain?
alpha-4, beta-2
what happens when nicotine binds to the receptor?
first stimulates then blocks the receptor
how many molecules does it take to activate the nicotinic receptor? which molecules can activate it?
2 molecules
- can be nicotine or/and acetylcholine
what is the difference between acetylcholine and nicotine binding to the nicotinic receptor?
- acetylcholine: binds, and activation causes sodium to flow in, then the channel becomes desensitized and the agonist cannot bind but eventually goes back to standby state
- nicotine: the desensitization phase is much longer so stimulates synthesis of more receptors and recruitment to the membrane (contributes to tolerance)
what is the effect of nicotine in the periphery?
- blocks/stimulates the autonomic nervous system (can contribute to side effects)
- stimulates receptors then blocks then from acetylcholine due to high affinity
- leads to release of norepinephrine and adrenaline/epinephrine which contributes to increased HR, vasoconstriction, increase BP, and vessel damages caused by other toxic compounds
what is another psychoactive compound in cigarettes? what does it do?
- monoamine oxidase inhibitor
- blocks monoamine oxidase, which usually breaks down norepinephrine and dopamine in the presynaptic terminal
what is methanol?
used to be added to cigarettes
- gives minty flavour
- is a bioactive drug that modulates cholinergic receptors, making nicotine more addictive
what is the mechanism that leads to nicotine addiction?
- nicotine can stimulates nicotinic receptors at GABA neurons to then inhibit the dopaminergic pathway
- but, these desensitize very quickly (and for a long time), so leads to less GABA neurotransmitter inhibiting dopaminergic neurons
- nicotine also stimulates release of glutamate that stimulate dopaminergic neurons to release even more dopamine
- so, increase excitation and decrease inhibition
what are ways to treat nicotine addiction?
- replacement therapy: substitute to get only nicotine without all the other chemicals in cigarettes (does get “high”)
- bupropion: blocks nicotinic receptors on dopaminergic neurons in the VTA
- varenicline: partial agonist at the a4b2 nicotinic receptor in the VTA
- block CYO2A6 with methoxsalen (can help decrease blood levels of all the other toxic compounds)
- topiramate: blocks the ability of nicotine to give high (decreased DA function(
what are the general effects of ethanol?
- general CNS depressant
- relief from anxiety
- disinhibition (brief excitation)
- sedation
- hypnosis
- general anesthesia
- coma
- death
what are the 5 concepts of CNS depressants?
- have additive effects when combines
- can’t reverse effect with stimulant
- general depressant aren’t that general
- chronic use leads to rebound excitation when stopping
- all CNS depressants result in some degree of tolerance (frequent cross-tolerance)
what are 2 types of amnesia tat can be seen with alcohol consumption?
- partial: fragmentary loss of memory (universal and dose-related)
- total (blackout): total loss of memory, susceptibility varies with person (don’t need to be comatose to blackout)
which parts of the brain does ethanol act on? what effect does this have?
- cortex: affects judgment
- hippocampus: affects memory
- cerebellum: coordination
- other: vision, movement, sensation, reward pathway
on which receptors does ethanol act on?
- sodium, potassium, and calcium channels
- 5HT and ACh receptors
- inhibitory: GABA, glycine
- excitation: glutamate
what are GABAa receptors? where are they located/where do they act? what is the effect of ethanol on them?
- inhibitory receptor and chloride ion channel
- there are synaptic and extra-synaptic receptors that are both inducible by ethanol
- ethanol increases inhibition of inhibitory pathways
how does ethanol affect glycine release? what is the effect of this?
- causes release of glycine
- acts pre-synaptically to release glycine which acts on post-synaptic glycine receptors to cause inhibition
what is the effect of ethanol of NMDA receptors? what is the effect?
- blocks NMDA receptors (they excite cells via glutamate release)
- chronic use leads to increase NMDA receptors – causes increase excitation when no ethanol
what is the effect of ethanol of serotonin, acetylcholine, and opiate receptors?
- decreases serotonin and acetylcholine release
- endorphins released by ethanol act on opiate receptors (linked to dependance)
explain the absorption of ethanol. (how easily it is absorbed, when is peak, site of absorption)
- is small, lipid-soluble so absorbed easily
- in brain after 5 mins
- peak at 30-90 mins (high on empty stomach)
- 20% absorbed in stomach (especially on empty stomach)
- rate increases with presence of carbonation
- some is broken down in stomach by alcohol dehydrogenase
- side effect: gastritis
- most absorption in small intestine
explain the distribution of ethanol.
- goes everywhere
- distributed in total body water
- so, AVD is equal to Total body water (which is why females need less alcohol for same effect – have less body water)
can ethanol cross the BBB? what does this cause?
- yes
- means that passes through chemoreceptor trigger zone, so causes nausea and vomiting