Here's a Journal Club Presentation I'd made on 'Repeated Δ9-THC Exposure in Adolescent Monkeys: Persistent Effects Selective for Spatial Working Memory'. It was taken from the April 14 issue of the American Journal of Psychiatry. It examined the long-term effects than THC exposure had on the working memory efficiency of adolescent monkeys, thereby providing some evidence to the near permanent effects cannabis use might have on the developing brain.

1. 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 D
David A Lewis, MD
1

2. Overview• Introduction
• Cannabis & Adolescence overview
• Demarcation of Spatial/Object Working Memory
• Related studies
• Article
Aim
Material and Methods
Results
Discussion
Limitations 2

3. 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)
3

4. 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
4

5. Introduction - Cannabis
5

6. 6

7. 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
7

8. 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
8

9. 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
9

10. Related studies -1
• The Influence of Marijuana Use on Neurocognitive
Functioning in Adolescents
• Objective
1. 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.
10

11. 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

12. Related Studies – 1 (Q2)
• Adults who initiated regular MJ use earlier in adolescence
demonstrated greater abnormalities than those who began use
later
12
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

13. 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

14. Related studies -2
Delay- 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 maturing
2.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
Sample
Christopher D Verrico,Shijing Liu,et al Neuropsychopharmacology (2012) 37, 1357–1366 14

15. 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

16. 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 D
David A Lewis, MD
•Am J Psychiatry Vol 171 (No.4) Apr 2014
16

17. 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
17

18. Introduction
AIM
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
18

19. 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

20. Materials & methods – Spatial WM Task
20

21. Materials & methods – Object WM Task
21

22. 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
22

23. Materials and Methods – WM Tasks
• Order effect
1.Practice effects
• Improvement due to repeated practice with tasks
1.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 23

24. 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
24

25. • 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
25

26. • 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
26

27. 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
27

28. 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)
28

29. Materials and Methods – Statistical Analysis
• Segmented Linear Regression
29

30. 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

31. 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)
31

32. 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

33. 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
33

34. 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
34

35. 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
35

36. 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
36

37. Limitations
1. IV THC distinct from smoking cannabis
– Other cannabinoids / flavonoids etc
• ??? Enhance/Offset effects of THC
1. 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
WM
37

38. 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
38

39. 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
39

40. Limitations
• Statistics could have been better described
• No blinding
40

41. 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

42. 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
√
42

43. 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? √
43

44. 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 2002
44

45. 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?
45

46. Thank you
46