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addiction Nicotine ch7

addiction Nicotine ch7 - Nicotine Nicotinic/cholinergic...

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Nicotine Nicotinic/cholinergic receptors (nAChRs): One of two subtypes of Ach The other is muscarinic Ionotropic Five protein subunits(alpha4 and beta2 ); these subunits vary depending on location (neurons, muscles) Locations include CNS, neuromuscular junction, ANS (PNS & SNS) High affinity nAChRs bind nicotine more than low affinity nAChRs. High affinity AChRs located in brain- cortex, hippocampus, monoamine containing nuclei like VTA and substantia nigra, PNS & SNS Low affinity nAChRs are located in the neuromuscular junction Mesolimbic dopaminergic pathway (VTA----NA plays a key role in nicotine’s reinforcing effects due to high affinity receptors and DA release. Nicotine binds to nicotinic receptors (ionotropic), opening Na+ channels, depolarizing cell membrane, creating action potential, leading to a fast excitatory response. Some nicotinic receptors allow Ca++ to enter, triggering other slower actions within the cell membrane and the cell body. Some nAChRs are located on nerve terminals (axons) of presynaptic neurons; when these receive nicotine, they cause the release of neurotransmitters (NTs). High doses of nicotine lead to excessive firing of affected neurons (receptors are continuously activated) which leads to continuous depolarization (firing) of post synaptic cell causing, eventually, depolarization block- the cell can not fire again until nicotine is removed; this explains biphasic nature of nicotine. If nicotine remains and blocks
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  • Spring '11
  • ceasar
  • nicotine binds, Nicotine Nicotinic/cholinergic receptors, nicotine causes nausea, nicotine physical dependence, Nicotine Effects

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