Preclinical assessment ofpotential therapeutic targets

for alcohol & drug abuse

Andrew J Lawrence

Drug Use Is Prevalent

• Alcohol & Tobacco use (ONS, UK):• more 13-year-olds have drunk alcohol than notthat’s 350,000 13-year-old drinkers in England and Wales alone

• 55% in England 16+ smoked daily, or ex-regular smoker (2001-02)

• Illicit drug use (AIHW):• cannabis: 34% aged 14+ have used in lifetime• opioids (inc. heroin): 2.3%, or 384,800 people• amphetamines: 9.1% (or, 1 in 5 of those aged 20-29)

Drug Use Is Protracted“many aging baby

boomers…will carrytheir love affair withdrugs into old age”

SciAm, May 08

estimates those aged 50+seeking drug abuse help willrise from 1.7m in 2000/01 to4.4m by 2020

Seattle Hempfest

Components of the Addicted HumanState

• Relapse – inability to cease drug taking• Underscored by:

– persistent neuroplasticity in motivationalcircuitry

– incubation of craving (drug ‘wanting’) duringabstinence

Grüsser et al., 2004

Cue-induced activation in theanterior cingulate (BA32) and medialprefrontal cortex (BA10)

Cue-induced activation of the putamen

Imaging substrates for relapse propensity

Operant responding in rats

Extinction Reinstatement

Leve

r Pr

esse

s

Cue, stress, prime

Note in the case ofpriming there iscrossover betweenthe ability of one drugto precipitate respondingfor another. In this case,nicotine priming isreinstating extinguishedresponding foralcohol

Le et al., 2003

Cross-sensitization?

Circuitry Model of Drug-seeking

Kalivas & Volkow 2005

Kasanetz et al 2010

In rats, cocaine self-administration leads to deficits in NMDA receptor-mediatedcorticoaccumbal LTD.

This recovers in addiction resistant rats, but remains impaired in addictionvulnerable rats.

Suggests transition to addiction related to persistent corticostriatal dysfunction.

After withdrawal from chronic cocaine administration: GLT1 synaptic GLU & CYS-GLU exchange extrasynaptic GLU.In the postsynaptic neuron, filamentous (F) actin, AMPA receptors and PSD95

During relapse: Release & GLT1 synaptic GLUAMPA receptors & size of spine head

Drug-induced alterations in glutamatergic signalling to basal ganglia

Kalivas 09

Restoration of Glutamate homeostasis by N-acetylcysteine

Kalivas 09

NAC is deacetylated after administration and dimerizes to cystine, which is transportedinto cells by cystine–glutamate exchange (xc-). Restoration of tone might re-establishthe homeostatic influence of mGluR2/3 on synaptic glutamate release and mGluR5 onsynaptic grading. It is possible that some of the benefits of NAC in treating addictionmight be related to elevating glutathione (balancing redox potential of cells)

“For the 16 subjects who completed the study, 9 subjects terminated use ofcocaine completely during the medication phase, 5 subjects substantiallydecreased their use, and 2 demonstrated no change in cocaine use.”

Kalivas 2009

Circuitry for dysregulation of reward-seeking / goal directed behaviour

In the addicted state it is proposedthat the PFC regulation of accumbaloutlfow is diminished

Note differential role of prelimbicvs infralimbic cortex in relapse

Layer V cells in prelimbic cortex express Orexin1 receptors that arepostsynaptic to OxA input

Li B et al. Cereb. Cortex 2010

SB334867 Prevents cue-induced reinstatement

Dayas et al 2007

Orexin-containing neurons are activated duringcue-induced reinstatement to alcohol-seeking

Leve

r pre

sses

extinction reinstatement

extinction reinstatementabstinence

Will animals reinstate drug-seeking followingextinction & protracted abstinence?

(i) Early reinstatement straight after extinction(ii) Late reinstatement, 5 months withdrawal after extinction

Active lever Inactive lever

Yes, they do & orexin1 receptorsimplicated at both time points

British Journal of Pharmacology(2011) 162: 880–889

% change in Fos positive cells due to the effect of protractedabstinence or SB-334867 treatment

Effect of Protracted Abstinence Effect of SB-334867 Treatment

Vehicle Immediate Delayed

PrL +75%* -42%* -26%*

IL +90%* -7% -22%

Piriform +54%* -29% -30%*

OFC +38%* -47%* -34%*

NAc Core +18% -48%* -5%

Identification of putative loci for orexin1 receptor antagonism to regulatealcohol-seeking

Prefrontal Cortex in Addiction

• Cortico-accumbal EPSCs are modified following cocainesensitization

• PFC inactivation prevents reinstatement of drug-seeking

• Persistent deficits in corticostriatal LTD in “addicted” rats

• Ascending peptidergic inputs onto PFC may play a role in theintegration of the salience of drug-related cues

Thomas et al 2001

Kalivas & Volkow 2005

Kasanetz et al 2010

Jupp et al 2010

Acknowledgements

• Bianca Jupp• Elena Krstew• Gabi Dezsi• NHMRC

Identification of putative loci for orexin1 receptor antagonism to regulatealcohol-seeking