Repeated Δ9-THC Exposure in Adolescent Monkeys: Persistent Effects Selective for Spatial Working Memory

Christopher D Verrico, Ph D Hong Gu, M.S. Melanie L Peterson, B.S. Allan R Sampson, Ph DDavid A Lewis, MD

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Overview• Introduction• Cannabis & Adolescence overview

• Demarcation of Spatial/Object Working Memory

• Related studies

• ArticleAimMaterial and MethodsResultsDiscussionLimitations

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Introduction - Cannabis• Δ9-Tetrahydrocannabinol – THC

• Concentration varies from 0.5 to 5 % • Potency

– 3.3% (1983) to 7.8% in 2005

• Interaction with endogenous cannabinoid signaling system 1. CB1 – brain 2. CB2 – Immune system • Naturally produced substrates

– Anandamide – 2AG (2-arachidonyl glycerol)

Comprehensive Textbook of Psychiatry, 9th Ed Kaplan & Sadhock 3

Introduction - Cannabis• ↑ Postsynaptic Ca+2 • Cannabinoids released • CB1 coupled with – Inhibition of Ca+2 channels– Activation of K+ channels

• Blunting of onward depolarisation

• ↓ release of onward NT – Glutamate– Dopamine– GABA

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Introduction - Cannabis

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Introduction – Adolescent Brain Development• Gray matter volumes ↓– Elimination of unnecessary connections by pruning

• White matter volumes ↑– Incr myelination esp in Frontal Cortex to speed transmission

• Region specific rates of maturation – Late development of higher order association areas assoc with

Visuo-spatial ability/ Attention/ Memory/ Executive Function

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Introduction – Cannabis & the Adolescent Brain

• The adolescent brain may be esp susceptible to damage – On-going Neuro-maturation – Peak sensitivity to Cannabinoid Receptor interactions

• Receptor densities peak during adolescence Curr Drug Abuse Rev. 2008 Jan;1(1):99-111.The influence of marijuana use on neurocognitive functioning in adolescents.

Schweinsburg AD1, Brown SA, Tapert SF

• Cannabis use and age – First use begins in mid to late teenage years – Heaviest use by early 20s Comprehensive Textbook of Psychiatry, 9th Ed Kaplan & Sadock

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Working Memory Central Executive Phonographical Loop

• Directing Attention to Relevant Information

• Suppressing Irrelevant Information & Inappropriate Actions

• Coordinating Cognitive Processes when >1 task is to be done simultaneously

• Stores Phonological Information • Prevents decay by continuous

Articulation

Visuo-spatial Sketchpad

Visual = Shape/Colour/ Texture

Spatial = Location

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Related studies -1• The Influence of Marijuana Use on Neurocognitive

Functioning in Adolescents• Objective1. Is adolescent marijuana use associated with persistent effects

on Neurocognitive functioning? 2. Are adolescents more vulnerable to the neural influences of MJ

use than adolescents?

Schweinsburg AD1, Brown SA, Tapert SF Curr Drug Abuse Rev. 2008 Jan;1(1):99-111.

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Related Studies – 1 • Results Q1 - MJ Use in adults

– Adults who use MJ chronically did/did not perform poorer on tests of learning / memory / attention / visuospatial skills / Executive function

– By 28 days, heavy users were indistinguishable from former users and non-users

– fMRI – altered brain response patterns despite similar task performance (absent practice related ↓ parietal activation)

• Results Q1 - MJ Use in adolescents – MJ users failed to show significant improvement in STM following 6 wks

of abstinence – After 6 weeks of abstinence, MJ users showed deficits in Attention /

Visuomotor ability / fMRI abnormalities

Schweinsburg AD1, Brown SA, Tapert SF Curr Drug Abuse Rev. 2008 Jan;1(1):99-111. 11

Related Studies – 1 (Q2) • Adults who initiated regular MJ use earlier in adolescence

demonstrated greater abnormalities than those who began use later

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Study Early Onset, n=

Late onset, n=

Max abstinence length

Result of EO : LO

Ehenrich et al 1999

<16yrs, 48 ≥16yrs, 51 2hrs ↓ visual scanning

Kempel et al 2003

< 16yrs , 10 ≥ 16yrs, 11 24hrs ↓ selective attention brainwaves

Skosnik et al 2005

<15.9yrs ≥ 16yrs 24hrs ↓ visual processing brainwaves

Wilson et al 2000

<17yrs, 29 ≥ 17yrs, 28 2wks ↓ grey matter, ↑white matter, ↓ blood flow

Pope et al <17yrs, 69 ≥ 17yrs, 53 28days ↓ Verbal IQ, ↓Verbal Recall, ↓Semantic categories

Related Studies – 1 • Conclusion– There is preliminary evidence of persisting NC

abnormalities among adolescent MJ users – It appears adolescents are more vulnerable to neural

impact of MJ – Adolescent MJ users show working memory, attention

and learning abnormalities which persist at least 6 months following cessation of use • (The deficits may resolve with longer term abstinence)

Schweinsburg AD1, Brown SA, Tapert SF Curr Drug Abuse Rev. 2008 Jan;1(1):99-111. 13

Related studies -2Delay- and Dose-Dependent Effects of D9-THC

Administration on Spatial and Object Working Memory Tasks in Adolescent Rhesus Monkeys

AIM : To determine if acute THC administration 1.differentially affects performance accuracy on spatial relative to object WM tasks during a developmental stage when only spatial WM performance accuracy is still maturing2.similarly affects non-mnemonic measures of task performance that are shared by spatial and object WM tasks.•METHOD– (7 + 7) Rhesus monkeys administered THC/Placebo – Assessed for Spatial Delayed Response & Delayed Match to

SampleChristopher D Verrico,Shijing Liu,et al Neuropsychopharmacology (2012) 37, 1357–1366 14

Related studies - 2 (contd…)• Results– THC to adolescent rhesus monkeys

• impairs spatial WM accuracy in a delay- and dose dependent manner

• marginally affects object WM accuracy only at the highest dose (240 mg/kg) and longest delay interval (16 s) at the double reinforcement level

• shows similar dose-response effects on completion rates and initiation latencies on both tasks (non-mnemonic measures)

• Conclusion • THC exposure during adolescence is more likely to impair the still

immature dorsal PFC circuits subserving spatial WM than the mature ventral PFC circuits subserving object WM.

• Data supports the hypothesis that immature cognitive abilities are particularly sensitive to the acute effects of THC. 15

Repeated Δ9-THC Exposure in Adolescent Monkeys: Persistent

Effects Selective for Spatial Working Memory

•Christopher D Verrico, Ph D •Hong Gu, M.S. •Melanie L Peterson, B.S. •Allan R Sampson, Ph DDavid A Lewis, MD

•Am J Psychiatry Vol 171 (No.4) Apr 2014

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Introduction• DLPFC circuitry/Spatial WM

matures later

• Spatial WM – Increasingly depends on

DLPFC in RhMonkeys during ‘adolescence’

– %age of DLPFC neurons active during SWM task doubles betn ages of 12-36mths

– SM task impairment by selective cooling of DLPFC not significant till 30mths

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IntroductionAIM

To examine whether 6mths of repeated iv THC administration (chronic use) in adolescent monkeys would:

1.Result in persistent adverse effects on performance improvements of spatial vs object working memory tasks 2.Alter sensitivity to acute effects of THC on these tasks

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Materials & methods – Subjects• N=14 Chinese-origin Rhesus monkeys – Only males taken, mean age 23.9 (SD=0.6) mths – Water regulation regimen – Trained to respond to cues on a touch-screen monitor

– Absence of human confounders • Premorbid differences in cognitive ability • Type, dosage, pattern and duration of cannabis use • Co-morbid use of other drugs

– Suitability • extended period of cognitive development (Watts and Gavan,

1982) characterized by – protracted refinements in PFC circuitry (Lewis, 1997)– increasing engagement of dorsal PFC circuitry in the mediation of

spatial WM task performance (Goldman & Alexander, 1977) 19

Materials & methods – Spatial WM Task

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Materials & methods – Object WM Task

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Materials and Methods – WM Tasks• Floor effects – Occurs when a measure possess a distinct lower limit for

potential responses, and a large conc of participants score near or at this limit • (floor is too high = test is too hard/ participants aren’t trying

hard enough) • Failure to distinguish participants in their response

• Spatial memory task done before Object Memory Task

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Materials and Methods – WM Tasks• Order effect 1.Practice effects

• Improvement due to repeated practice with tasks

2.Fatigue effects • Decline in performance as participant becomes bored with

same sequence of tests

– Double Reinforcement done to prevent order effects • Red/Green stimuli for 3 pairs • Blue/Yellow stimuli for 4 pairs

• Baseline performance better• (easier) Spatial memory task • (more stimulating) Double reinforcement task

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Materials and Methods – Study Design

• Monkeys divided into 7 pairs – Performed in 2 runs, vehicle/THC would be administered

after 1st run, performance measured 30mins after administration

– Each run had random insertion of • All delays (1, 4, 8 & 16 secs) • Both single/double reinforcement • Both WM and control tasks

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• 4-5 weeks of Baseline training • To bring baseline levels of performance of a pair at par on SM,

SR OM, DR OM

• Acute Period 1 • Performance measured before & 30mins after administration

+ 23hrs (Tue-Fri) or 71 hrs (Mon) after admin• Dose calculation

– Each dose given 3-5 days a week – 23 hrs betn drug administration, 71hrs betn dosage change – 120mcg/kg for 3 pairs, 240mcg/kg for 4 pairs

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• Repeated Dosing Period • THC grp given 120mcg (N=3) or 240mcg (N=4) 5 days a week • WM measured at 23 hrs (Tue-Fri) and 71hrs (Mon) after most

recent dose

• Acute Phase 2 • Earlier calculated doses used • Measured before and then 30mins after admininstration

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Materials and Methods – Statistical Analysis• Primary measure of interest = WM Accuracy Rate – Correct trails as % of completed trials

• 7 measures for each delay and task • Primary measure modelled by a binomial

distribution with logit link function • Monkey as normal random effect

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Materials and Methods – Statistical Analysis• Summary measure (AUC) for accuracy rates

calculated across delays • (1.5 x 1sec AR) + (3.5 x 4sec AR) + (6 x 8sec AR) + (4 x 16sec AR)

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Materials and Methods – Statistical Analysis• Segmented Linear Regression

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Materials and Methods – Statistical Analysis

• Phase 1 – linear accuracy improvement

• Change point • Phase 2 – different

slope of accuracy improvement

• 2nd acute phase – Analysed similar to 1st

acute phase 30

Results• Spatial Working Memory – Accuracy rates ↑ significantly in both grps in all delays

during Phase 1 – Improvement during Phase 1 was slower for THC grps on

4, 8 & 16 sec delay (p<.001 in all) – Length of Phase 1 was significantly longer for THC grp in

1sec (3.2wks), 4 sec (9.5wks), 8 sec (8.4wks) (all p<0.03) – THC significantly ↓ accuracy at change point between

phases (p=0.03)

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Results• Double-Reinforcement Object Memory – NO SIGNIFICANT DIFFERENCE in rate of improvement or

Length of phase 1 bet grps – except on 8 sec delay • THC significantly slowed rate of improvement in phase 1• THC significantly extended length of phase 1

– NO SIGNIFICANT EFFECT ON • Accuracy at change point • Phase 2 slope

• Single Reinforcement Object Memory – NO CONSISTENT DIFFERENCES betn grps on ANY

parameter 32

Results • Acute Effects – THC impaired spatial working memory accuracy in a

delay-dependent manner during 1st acute period – No impairment of object working memory – Same nature of impairment observed in 2nd acute period

– Spatial WM memory impairments did not differ significantly betn two acute periods • Grp by period by delay (p=0.97) • Grp by period (p=0.64)

– No tolerance, sensitivity

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Results

1. Repeated THC administration impaired age and practice related improvements in accuracy on SPATIAL WM in a delay dependent manner

2. THC did not impair improvements in accuracy in OBJECT WM at any delay or reinforcement level

3. Neither tolerance nor sensitivity to the acute effects of THC on WM performance developed after 6mths of exposure

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Discussion

• Relative to cannabis use in adulthood, adolescent use assoc with – Greater neuropsychological deficits– Altered PFC neural activation patterns during WM tasks – ↑ risk of developing Schizophrenia • Characterised by WM impairment

– Own findings support hypothesis that immature cognitive abilities are esp vulnerable to effects of THC

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Discussion

•Earlier human studies on tolerance to acute effects of cannabis inconsistent – Occasional adult users v/s chronic users • Tolerance to acute effects shown by chronic users at equal

– THC blood conc – Levels of subjective high

Raemaekars JG, Kauert G et al Neurocognitive performance during acute THC intoxication in heavy and occasional cannabis users J Psychopharmacol 2009; 23:266-277

– Own finding (no tolerance to acute effects on WM) • Adolescents might remain susceptible to acute cognitive

effects

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Limitations1. IV THC distinct from smoking cannabis – Other cannabinoids / flavonoids etc • ??? Enhance/Offset effects of THC

2. Possibility completing Spatial WM task before Object WM task may confound comparisons

– Selective Spatial WM task impairment surprising as • Object WM task was done later (motivation should have been

impaired due to partial satiation) • Object WM placed greater load on mnemonic processes • THC impairs Spatial WM at doses which don’t affect Object

WM37

Conclusion • Chronic THC exposure can cause persistent

impairments – Specific for spatial WM – Persist during periods of exposure – Does not alter acute cognitive effects – Impairments not caused by motivational process

derangement

• Cannabis use during adolescence may cause poor academic performance even in absence of acute drug use

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Conclusion

• Findings support adolescent cannabis use as risk factor for Schizophrenia as – Certain abnormalities seen prior to psychosis onset in

Schizophrenia are assoc with adolescent cannabis• WM impairment • Altered DLPFC function

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Limitations

• Statistics could have been better described • No blinding

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Checklist for assessing the quality of quantitative studies

Criteria Yes(2) Partial(1) No(0) N/A

1 Question/ objective sufficiently described? √

2 Study design evident & appropriate? √

3 Method of subjective/comparision group selection or source of information/ input variable describe and appropriate?

√

4 Subject ( and comparison group, if applicable) characteristics sufficiently described?

√41

Yes (2) Partial (1) No (0) NA

5 If interventional and random allocation was possible, was it described? √

6 If interventional and blinding of investigators was possible, was it reported?

√

7 If interventional and blinding of subjects was possible, was it reported? √

8 Outcome and (if applicable) exposure measures well-defined and robust to measurement/misclassification bias? Means of assessment reported

√

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Yes (2) Partial (1) No (0) NA

9 Sample size appropriate? √10 Analytic methods

described/justified and appropriate?

√

11 Controlled for confounding? √

12 Results reported in sufficient detail? √

13 Conclusions supported by the results? √

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References • Comprehensive Textbook of Psychiatry, 9th Ed Kaplan & Sadock

• Christopher D Verrico,Shijing Liu,et al Delay- and Dose-Dependent Effects of D9-THC Administration on Spatial and Object Working Memory Tasks in Adolescent Rhesus Monkeys Neuropsychopharmacology (2012) 37, 1357–1366

• Schweinsburg AD1, Brown SA, Tapert SF The Influence of Marijuana Use on Neurocognitive Functioning in Adolescents Curr Drug Abuse Rev. 2008 Jan;1(1):99-111.

• The Oxford Handbook of Memory, Oxford Univ Press 2007

• Onaivi ES, The Biology of Marijuana, Taylor & Francis 200244

CME Qs • 1. Why is studying the effects of THC working memory in

adolescent monkeys particularly relevant for understanding its effects on adolescent humans?

• 2.What brain area do these findings indirectly implicate as underlying the persistent effects of THC on working memory?

• 3.What support do these findings provide for adolescent cannabis use as a risk factor for the appearance of schizophrenia?

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Thank you

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