Drugs and Behavior ch 11: Caffeine

methylxanthines

include caffeine, theophylline and theobromine. they are consumed in beverages, foods, and medications/street drugs

history of caffeine

ancient use (coffee and tea) in Arabia and Egypt, introduced to Europe in the 15th century

280 mg/day

level of US consumption

caffeine and kids

lower body weights mean higher concentrations, the sensitivity is the same as in adults. children may experience a caffeine withdrawal syndrome

90%

how much of the world population consume it regularly

most common sources of caffeine

coffee, tea, and soft drinks

leading countries in caffeine consumption

netherlands (2.414 cups/day), finland, sweden, and denmark

US consumption rate

0.931 cups/day

caffeine has the highest affinity for

A2a, A1, A2b

4 adenosine receptors

A1, A2a, A2b, A3

A2a

knock-out mice show no effects on caffeine

phosphodiesterase inhibition

enzymes that cause blood vessels to relax and widen, improving circulation and lowering blood pressure. dose required in extremely high

adenosine NT and receptor activation

causes behavioral sedation, dilation of blood vessels, and production of asthma, caffeine blocks adenosine receptors (adenosine antagonist)

dopamine

enhanced activity by caffeine antagonism of A2a receptors in the caudate/putamen, NAcc

A2a antagonism

decreases Da binding affinity fort the D2 autoreceptors

pharmacokinetics

oral administration, rapid absorption and distribution. crosses the blood-brain barrier and placenta

half-life

2.5 hrs to 7.5 hours

peak levels

in 15-45 mins (coffee 30 mins, soda 2 hrs)

metabolism

lever enzymes, kidney excretion. it is slowed by liver disease, pregnancy, and oral contraceptives. enhanced by cigarette smoking. therapeutic drugs interact.

tolerance

occurs to sleep and physiological functions, not so much to stimulant effects

WHO ICD-10

has caffeine dependence

caffeine withdrawal in DSM-V

headache and fatigue, depression, lower alertness and energy, sleepiness and irritability

CNS stimulation (acute)

antagonist at adenosine recpetors

PNS effects (acute)

• contraction of heart muscle

• relaxation of smooth muscle

• elevation of basal metabolism

behavioral effects

• elevation of mood

• maintenance of normal performance/decrease fatigue

• impairment of decision-making in reaction time studies

• dependent on dose, setting, and personality

performance effects

• motor speed and accuracy are increased by low doses

• decreased eye-hand coordination

• improved night driving vigilance

• speeds reaction time in simple tasks

coffee and smoking

smokers excrete caffeine faster, coffee decreases smoking

alcohol energy drinks

decreases the sensations of sleepiness and tiredness (perception of intoxication). it doesn’t decrease the motor deficits form alcohol or cognitive impairment

caffeinism

caffeine intoxication; intake of 600 mg/day

1000mg/day toxic effects

• muscle twitching

• rambling thought and speech

• cardiac arrhythmia

• psychomotor agitation

lethal dose of caffeine

10 grams for an adult (62.5 monsters)

chronic effects

no relationship with cancer or heart attack, unless slow to metabolize. increased osteoporosis in post-menopausal women. increased serum cholesterol, indigestion, palitations and tremor, headache and insomnia.

beneficial effects

may protect against liver cirrhosis. heavy coffee use may protect against hypertension

recommendations

the american medical association says moderate consumption, pregnant women should keep consumption low, and anxiety disorders may be aggravated by caffeine.

therapeitic uses

• part of cold and headache remedies

• part of weight-loss medications

• caffeine stimulates breathing in premature infants

• theophylline (tea) dilates coronary and bronchial arteries