Addiction

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  • Created by: Lauren
  • Created on: 29-04-15 14:11

Medial Forebrain Bundle and Mesolimbic System

Located within the lateral hypothalamus - a system of fibres connecting structures of limbic system to other regions of brain stem

Incorporates the midbrain's dopamine systems including the mesolimbic system:

  • Two midbrain nuclei - substantia niagra and VTA. These are rich in dopamine and project to forebrain including the lateral hypothalamus, preoptic area and NA (forebrain reward centre)
  • Activating is rewarding and stimulation of MFB stimulates dopamine systems
  • Dopamine antagonists in NA reduces effect of MFB stimulation
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Addictive Drugs and Tolerance

Many affect dopamineric neurones including opiates, cocaine, amphetamine, nicotine and alcohol

Addiction => Behaviour pattern of drug use. An overwhelming involvement with high tendency to relapse.

Physical dependence => Reduced drug action (tolerance) and cessation of drug taking leads to physiological disturbances (withdrawal)

Psychological dependence => Produces pleasurable state which motivates further use through negative reinforcement

Tolerance => downregulation caused by desensitisation of receptors or decreased dendritic branching as well as pavlovian conditioning and instrumental behaviour e.g. habituation

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Withdrawal

  • Opiates cause emotional changes in mood and functions of CNS by stimulating opiate receptors (which affects dopaminergic neruones) however stimulation alone is enough to reinforce
  • Cocaine and amphetamine are CNS stimulants and addicting effects occur when altering activity of mesolimbic dopamine system as cocaine blocks dopamine reuptake and amphetamine does this plus increase release of dopamine
  • Nicotine stimulates dopamine neurones of mesolimbic system however injections of nicotinic agonist in NA has no reinforcing effects
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