Trender i cannabisanvändningen bland unga – Isabella Gripes, utredare
Belöningssystemet
1. Belöningssystemet Mia Ericson Beroendemedicin, Sektionen för psykiatri och neurokemi, Institutionen för neurovetenskap och fysiologi, Sahlgrenska akademin, Göteborgs universitet
10. Kommunikation mellan nervercellerna sker med hjälp av neurotransmittorer: Exv.: dopamin, serotonin, glutamat, GABA, noradrenalin, acetylkolin synapsklyfta synaps nervsignal lagringsblåsa : är fylld med transmittorer som vid nervsignal töms i synapsklyftan mottagarcellens receptorer
11. Dopamin nervsignal BELÖNINGSSYSTEMET Höjda nivåer dopamin framkallar belöning, men kan senare ge ett sug efter mer. Mat Dryck Nikotin Alkohol Droger
12. Det mesokortikolimbiska dopamin-systemet • förmedlar motiverande signaler för beteenden betydelsefulla för konsumtion, tex födo- och vattenintag, samt sexuell aktivitet • inblandat i inlärning/minne av belöning människa gnagare Det mesolimbiska dopamin-systemet (VTA till ventrala striatum) VTA Ventrala striatum VTA nAc
13. Hur mäter man neurotransmittorer utanför cellen? Dialysprob med semipermiabelt membran Mikrodialys
20. Snabbare kick efter drogintag medför inte bara högre koncentrationer av drogen i hjärnan utan det verkar även som att fler hjärnområden aktiveras starkare
34. Elektrofysiologiska mätningar har visat att nervceller i belöningssystemet reagerar på ny stimuli, oväntade belöningar, och reward predictive sensory cues.
35. DA systemet blir hyperreaktivt på stimuli som tidigare associerats med drogintag och på drogen som sådan
36. Kokain bygger om delar av hjärnan och får den att ignorera naturliga belöningar
37. Natur Video Kokain Video Främre delen av hjärnan Bakre delen av hjärnan Amygdala inaktivt Amygdala aktiverat
38. Är det ökade nivåer av dopamin som gör att man bli beroende?
47. Tid Effekt Tolerans Sensitisering Tolerans Sensitisering Minskad drogeffekt av en given dos efter upprepad administrering, eller, större dos krävs för att uppnå samma effekt. Exempel: Heroin, alkohol (sensibilisering, omvänd tolerans) ökad drogeffekt av en given dos efter upprepad administration, eller, samma effekt av en lägre dos. Exempel: Heroin, nikotin Intermittent administrering viktig faktor 0% 100% 50% Tid rökning Nikotinnivåer Dopaminsvar rökning rökning
56. Volkow et al., Neuropharmacology, 2004. Drift Belöning Minnen kontroll Icke-beroende hjärna NOT GO Beroende hjärna Drift Minnen GO Belöning Beroende förändrar hur hjärnan fungerar kontroll
73. Samband mellan nikotinets disinhiberande effekt och etanolpreferens; korrelation Peter Olausson et al. 2001
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75. Hypotes - baserad på djur- och humanstudier Nikotinexponering in utero och/eller senare i livet ger upphov till avhämning som ökar risken att drabbas av ADHD-symtom, substansmissbruk och ”kriminalitet”. Antal individer Avhämning/”impulsivitet” dysfunktionell
76. Ökad risk för nikotinberoende hos barn till rökande mammor
81. Är alkohol och nikotin verkligen en inkörsport till tyngre droger?
82. Nikotin är ofta den första drogen och den som är mest sammissbrukad NICOTINE age 1 0 -15 ETHANOL age 14-18 CANNABIS age 14-18 AMPHETAMINE/COCAINE OPIATES
83. Kokain Vägen till att använda kokain (baserat på 32 594 människor i USA) Tobak Cannabis Alkohol Tobak Tobak Tobak Cannabis Cannabis Cannabis Alkohol Alkohol Alkohol 1 eller 2 av ovanstående 52% 13% 17% 5% 13% 0%
84.
85.
86. Vi har funnit att taurin fungerar på liknande sätt som alkohol i hjärnans belöningssystem….. och…..det ser ut som att taurin förstärker effekterna av alkohol
88. Spelmissbruk Spelmissbrukare får en större dopamin frisättning i hjärnans belöningssystem än icke spelmissbrukande individer. I en studie på 43 093 individer i USA fann man att spelmissbrukare har en livstidsprevalens för alkoholmissbruk på 73,2%, drogmissbruk 38,1%, förstämningssyndrom 49,6%, ångest 41,3% och 60,8% hade någon form av personlighetsstörning. Läkemedel som hjälper mot alkoholism har även effekt mot spelmissbruk. Många biologiska och genetiska likheter med drogmissbrukare.
89.
90. Adaptiva processer i belöningssystemet relaterade till konsumtion av farmakologiskt aktiva substanser eller beteenden lägger grunden för ett beroende
96. 100 miljarder nervceller är bildade vid 2-års ålder Varje nervcell har runt 7 000-10 000 synapser En 3-åring har runt 10 15 synapser (en kvadriljon) That's it?
99. Brain Development Vid sen barndom (ca 11 år hos flickor och 12,5 hos pojkar) blir nerverna ”buskigare” och får en mängd nya synapser (ställen där cellen kan kommunicera med andra celler) Vid denna tid förtjockas lagret av myelin runt nervcellerna Myelin är som isolering som gör att cellerna kommunicerar mer effektivt med varandra
101. Deborha Yurgelon-Todd, 2000 Ungdomar skiljer sig från vuxna i deras förmåga att förstå känslor. Deras framhjärna, som kontrollerar rationellt tänkande är mindre aktivt än amygdala (involverat i känslomässigt tänkande)
102. National Epidemiologic Survey on Alcohol and Related Conditions, 2003. % in each age group who develop first-time dependence Beroende är en utvecklingssjukdom som ofta börjar i tonåren Age 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 1.2% 1.4% 1.6% 1.8% 5 10 15 21 25 30 35 40 45 50 55 60 65 CANNABIS ALCOHOL TOBACCO Age at tobacco , alcohol , and cannabis dependence per DSM IV
105. ≈ 25 år Ungdom Ålderdom Utvecklingsmognad av cortex Individens förmåga Impulskontroll Resonemang Planering Utförande Beslutsfattande Riskbedömning Inverkan av alkohol på hjärnans utveckling Crews et al., 2007
106. Source: Spear, 2002 Ungdomar ÄR känsligare för alkohol Av etiska skäl kan man inte studera människor Djurstudier visar att ungdomar är mindre känsliga för alkoholens sederande effekter. Man behöver konsumera större mängder innan signalen att sluta sätts igång
107. Source: Spear, 2002 Minskad hämning Ungdomar som dricker alkohol är mer känsliga för den socialt smörjande effekten som alkohol har.
108. Left hippocampal smaller in AUD (alcohol use disordered) teens compared to healthy teens by about 10%. Source: Nagel et al., 2005 Alkoholkonsumtion ger ett minskat minnescentrum MRI: Hippocampal Size
109. Berusningsdrickande hos unga jämfört med vuxna Större skador på hjärnan Förändrar utvecklingen av nätverk av nervceller Ändrar beteendet i större utsträckning Ökar risk för beroende
Slide 9: The serotonin neuron: the major target of ecstasy In order to help students understand how Ecstasy affects the function of serotonin neurons, it will be useful to review how neurotransmission takes place in a little more detail. You can explain serotonin neurotransmission as an example (serotonin is one of many neurotransmitters). This slide shows the connection between two neurons (the “synapse”). Serotonin is stored in small vesicles within the nerve terminal of a neuron. Electrical impulses (arising in the Raphe nucleus, for example) traveling down the axon toward the terminal cause the release of serotonin from small vesicles into the synaptic space. Point to the space between the terminal and the neighboring neuron. When in the synaptic space, the serotonin binds to special proteins, called receptors, on the membrane of a neighboring neuron (this is usually at a dendrite or cell body). When serotonin binds to serotonin receptors (there are actually at least 14 types of serotonin receptors), it causes a change in the electrical properties of the receiving neuron that generally results in a decrease in its firing rate. Go to the next slide to explain how the action of serotonin is terminated.
Slide 10: Serotonin transporters Serotonin (in pink) is present in the synaptic space only for a limited amount of time. If it is not bound to the serotonin receptor, serotonin is removed from the synaptic space via special proteins called transporters (in green). The serotonin transporters are proteins located on the serotonin neuron terminals and they are in a unique position to transport serotonin from the synaptic space back into the neuron where it can be metabolized by enzymes. Explain to your students that the serotonin transporters are the primary targets for ecstasy.
Slide 11: Ecstasy and serotonin transporters When ecstasy binds to the serotonin transporters, more serotonin ends up in the synaptic space. This occurs for two reasons. First, ecstasy can prevent the transporters from carrying serotonin back into the terminal. Second, ecstasy can cause the transporters to work in reverse mode—they actually bring serotonin from the terminal into the synaptic space. So, more serotonin is present in the synaptic space and more serotonin receptors become activated. This is the major short-term effect of ecstasy that alters brain chemistry. Although the serotonin system is the primary target for ecstasy, ecstasy has similar effects on the dopamine (another neurotranmsitter) system as well. Ecstasy can inhibit dopamine transporters and cause an increase in dopamine levels in the synaptic space (not shown here). To help students understand how the alteration in brain chemistry results in psychological changes, go to the next slide.
Slide 18: Ecstasy causes degeneration of derotonin nerve terminals This slide illustrates the degeneration of serotonin nerve terminals after long-term or repeated use of ecstasy (you can refer back to slide 9 to compare this degenerating terminal to a healthy terminal). Remind students that we have several pieces of evidence that support this effect of ecstasy. Experiments in animals given ecstasy indicate that this kind of degeneration occurs. Moreover, some studies of human ecstasy users report less serotonin and serotonin metabolites in the cerebrospinal fluid (which surrounds and bathes the brain and spinal cord) compared with nonusers. In contrast, the animal studies indicate that the serotonin cell bodies are still intact but the genetic instructions from the nucleus for any regrowth of the terminals may be abnormal. Although scientists do not yet know for certain how ecstasy damages the serotonin terminals in these animal studies, some progress has been made in understanding this process. One mechanism is damage that involves the production of oxygen radicals (unstable forms of oxygen), which are very destructive to proteins, lipids, and DNA. The rich supply of mitochondria (which are a major source of oxygen radical formation) found in the terminals may cause the terminals to be especially sensitive to drugs like ecstasy.
Slide 17 : Long-term effects in monkeys A very important experiment was performed in monkeys to determine if ecstasy can actually damage neurons. Monkeys were given ecstasy twice a day for 4 days (control monkeys were given saline). One group of monkeys’ brains were removed 2 weeks later for analysis and another group of monkeys lived for an additional 7 years before their brains were removed. Scientists examined the brains for the presence of serotonin. This slide shows the presence of serotonin in neurons of the neocortex from three typical monkeys. On the left, the monkey who did not receive any ecstasy had a lot of serotonin (in pink) in the neocortex.Two weeks after a monkey received ecstasy, most of the serotonin was gone (point to the middle panel), suggesting that the serotonin neuron terminals were destroyed (there was no destruction of the serotonin cell bodies arising back in the brainstem). Point to the right-hand panel and show students that this damage appeared to be long-term because 7 years later there was some recovery, but it was not complete. Scientists found similar changes in limbic areas of the brain such as the hippocampus and amygdala. The monkey experiments are an important reminder that humans may suffer the same fate, although this still remains to be demonstrated. Tell the students how difficult it is to do this same kind of experiment in humans, because it requires removing pieces of the brain to look for the loss of the serotonin neurons. An equally important factor that complicates human studies is the virtual impossibility to ascribe any observed deficit or damage to one particular drug in humans.
Slide 10: The memory of drugs. This slide demonstrates something really amazing—how just the mention of items associated with drug use may cause an addict to “crave” or desire drugs. This PET scan is part of a scientific study that compared recovering addicts, who had stopped using cocaine, with people who had no history of cocaine use. The study hoped to determine what parts of the brain are activated when drugs are craved. For this study, brain scans were performed while subjects watched two videos. The first video, a nondrug presentation, showed nature images—mountains, rivers, animals, flowers, trees. The second video showed cocaine and drug paraphernalia, such as pipes, needles, matches, and other items familiar to addicts. This is how the memory of drugs works: The yellow area on the upper part of the second image is the amygdala (a-mig-duh-luh), a part of the brain’s limbic system, which is critical for memory and responsible for evoking emotions. For an addict, when a drug craving occurs, the amygdala becomes active and a craving for cocaine is triggered. So if it’s the middle of the night, raining, snowing, it doesn’t matter. This craving demands the drug immediately. Rational thoughts are dismissed by the uncontrollable desire for drugs. At this point, a basic change has occurred in the brain. The person is no longer in control. This changed brain makes it almost impossible for drug addicts to stay drug-free without professional help. Because addiction is a brain disease. Photo courtesy of Anna Rose Childress, Ph.D.
NA = regulates motivation to seek rewards Amygdala = emotional processing center; evaluates relative pleasure vs aversiveness PFC = planning; setting priorities; organizing thoughts; suppressing impulses; weighing consequences of one’s actions
Adolescents’ brains are “wired” differently than adults. Because the prefrontal cortex is one of the last areas of the brain to mature during development, adolescents tend to use other areas – in this case emotional areas – of the brain in making decisions. For example, brain activity, seen with functional MRI, shows that when judging emotion represented on a face, a teenager’s amygdala (right) is activated, reflecting more of a gut reaction than a reasoned one, while the adult’s (left) brain is activated in an area of the prefrontal cortex involved more in reasoning and reflection.