Prevalence of Smoking in Psychiatric Disorders (PD) and Substance Abuse Disorders (SUD) Kalman D, Morrisette SB, and George, TP Am J Addiction, , 2005

Ligand gated ion channel Pentamer α and β subunits Twelve known subunits α 2-10 and β 2-4 Two main types present in brain α 7 nAChR subtype High affinity for α- bungarotoxin α 4 β 2 nAChR subtype High affinity for nicotine Believed to upregulate in response to nicotine Nicotinic Acetylcholine Receptors (nAChR)

 2 *-nAChRs in the Reward Pathway Ventral Tegmental AreaVentral Striatum Nicotine  2 -nAChR Dopamine

High affinity for neuronal nAChRs High selectivity for nAChR with the β2 subunit Low nonspecific binding Dissociates slowly from the receptor Readily crosses the blood brain barrier Low toxicity [ 123 I]5-IA [5-iodo-3-(2(S)-azetidinylmethoxy)pyridine] Musachio 1998, 1999; Fujita 2000; Horti 1999; Mukhin 2000

Subtype Selectivity of nAChR Ligands Ligand K i nM (Ratio to K i(  4  2) ) 4242 3434 77 muscle (–)-Nicotine 0.84 (1) 100 (120) 130 (150) 1000 (1200) (  )-Epibatidine (1) (6) 4.0 (500) 7.5 (900) (  )-IPH (1) 0.11 (4) 30 (1100) 6.5 (240) 2-Fluoro-A (1) 110 (2400) 165 (3600) 360 (7800) 6-Fluoro-A (1) 10.5 (420) 170 (6500) 460 (18000) 5-Iodo-A (1) 51 (5000) 250 (25000) 1400 (140000) Mukhin,… London et al. Mol. Pharmacol. 2000

[ 123 I]5-IA SPECT measurement of  2 *-nAChR in brain (Staley et al., J Nuc Med, 2005)

Evidence nAChRs upregulate Nicotine, the primary addictive chemical in tobacco smoke, upregulates the nicotinic acetylcholine receptor (nAChR). This has been shown postmortem in human tobacco smokers (Breese et al., 1997; Court et al., 1998). Confirmed in animal studies after chronic nicotine exposure (Kassiou et al., 2001, Marks et al., 1992). Due to changes in receptor density, Bmax, as opposed to changes in receptor affinity, K D (Peng et al., 1994; Marks et al., 1983). The changes in receptor density may underlie tobacco smoking tolerance and dependence.

Urine cotinine levels (ng/mL) were measured with NicoMeter™ test strips Nicotine blocks [ 123 I]5-IA binding in nonhuman primates (Staley et al., J Neuroscience 2006)

Never Smoker (Female, 31 yo) Smoker (Female, 32 yo ), Abstinent 7 days (Staley et al., J Neuroscience 2006) Higher cortical  2 *-nAChR in abstinent smokers vs. never smokers

Evidence nAChRs normalize over time Preclinical: nicotine binding returns to control levels between 7 days and 3 weeks abstinence depending on the route of administration and dosing regimen (Marks et al., 1985; Pietila et al., 1998; Ksir et al., 1985). Postmortem: smokers who quit at least 2 months prior to death had nicotine binding levels similar to controls (Breese et al., 1997). In vivo: the upregulation was shown to be temporary, decreasing by 21 days of abstinence (Mamede et al., 2007).

The purpose was to examine  2 *-nAChR availability in tobacco smokers over the course of abstinence. STUDY 1 Smokers were scanned up to 4 times….. 1 day, 1 week, 2 weeks, 4 weeks 1 week, 4 weeks, 6-12 weeks Cosgrove…..Staley, Arch Gen Psych, 2009

Abstinence from smoking Smokers were helped to remain abstinent with contingency management techniques. Abstinence was confirmed twice daily for the first 8 days with carbon monoxide and urine cotinine measurements. Carbon monoxide levels (ppm) Urine Cotinine levels (ng/mL) Measured with NicAlert™

MRISPECT 3. Metabolism & protein binding 1. Radiotracer Synthesis 2. Radiotracer Injection 4. SPECT & STEP Scan MRI & SPECT

[ 123 I]5-IA SPECT regions of interest FC AC PC TIC FC AC Cd Pt Th OC CB FC AC Parietal Cortex Temporal Cortex Frontal Cortex Anterior Cingulate Caudate Putamen Thalamus Occipital Cortex Cerebellum Medial FC

Outcome Measure Receptor “availability” Receptors that are free or available to be bound by the radiotracer. It is not a measure of all receptors, because some could be occupied by acetylcholine or nicotine. V T /f p = radioactivity in brain /blood

Subject Characteristics 1 day~1 wks~2 wks~4 wks6-12 wks N Age Days abstinent # Cigarettes smoked /day # Years Smoked FTND Urine cotinine (ng/mL) Plasma cotinine (ng/mL) < CO on scan day

Cosgrove…..Staley, Arch Gen Psych, 2009  2 *-nAChR availability in smokers normalizes over the course of prolonged abstinence

 2 *-nAChR availability in brain during acute abstinence

 2 *-nAChR availability in brain during prolonged abstinence 20% decrease from 1-12 wk

 2 *-nAChR availability in brain over time in abstinent smokers

It takes up to 6-12 weeks for receptors to “normalize” Nonsmokers Smokers 1 Day Smokers 1 Week Smokers 2 Weeks Smokers 4 Weeks Smokers 6-12 Weeks

Relief of Negative Affect or Withdrawal/Urge to smoke Negative correlation between  2 *- nAChR availability and craving Cosgrove et al., 2009 Staley et al., 2006 CorrelateRegionCluster size T statisticr valuep value CravingParietal Cortex Postcentral Gyrus BA wk 4 wks Cerebellum

Summary Study 1 Normalization of the nAChR…….. – is prolonged in humans – varies between individuals – may be genetically-mediated