# Presentation: 534673

## EFFFECTS OF CHRONIC MARIJUANA USE AND 

- THC ON BRAIN FUNCTION IN HUMANS:
- AN FMRI STUDY

- APA 2004

- Alan S. Bloom, Ph.D.
- Medical College of Wisconsin

## PROBLEM

- The frequent use of marijuana by young people in our society continues to be a problem.  It is the illicit drug that is most commonly used by youths today.
- Anatomically, the distribution of CB1 cannabinoid receptors in the animal and human brain is well described. High densities of receptors are located in hippocampus, cerebellum, cortex, substantia nigra, globus pallidus and other striatal regions.  Receptor density is low in hypothalamus and lower brainstem.
-   In general, the distribution of receptors in the brain is reasonable, if we take into account the known pharmacological actions of marijuana.  They are found in areas associated with memory, coordination, attention and endocrine regulation.
-   The goal of this research is to elucidate sites of action of ∆9-tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana, in the human brain and to determine those sites that are related to the drug’s psychoactive properties and cognitive effects.

## MARIJUANA (THC) EFFECTS

- Euphoria
- Memory Impairment
- Perceptual-Motor alterations
- Cardiovascular
- Pulmonary
- Reproductive
- Psychopathological Effects

## CB1 Receptor Distribution and Functional Areas

- 	High density in brain areas concerned with memory, cognition, motor coordination and reward

## CANNABIS AND HUMAN BRAIN IMAGING

- Volkow et al. (1996)- PET - iv THC -brain glucose metabolism in chronic marijuana users.  Prior to drug administration, chronic users showed lower relative cerebellar metabolism than normal control subjects.  THC iv (2 mg) increased relative cerebellar metabolism in both chronic users and controls, but only chronic users showed increases in orbitofrontal cortex, prefrontal cortex and basal ganglia.
- Mathew - effects of THC on CBF - 15O-PET - THC (3 to 5 mg iv, over 20 min) increased CBF in the frontal regions bilaterally, insula and cingulate gyrus and subcortical regions -somewhat greater effects in the right hemisphere.  The increase in blood flow correlated with the subjective sense of intoxication.
- 	O’Leary (2000, 2002, 2003) examined the effects of smoked marijuana on task activation measured using 15O-PET.  They reported that smoked marijuana produced no change in whole brain blood flow.  However, significantly altered activation by a dichotic listening task in multiple brain regions was observed after smoking marijuana.  In general, this occurred in the absence of significant decreases in task performance.  Overall, they reported increased rCBF  in anterior brain paralimbic regions and cerebellum that may be related to marijuana effects on mood and reduced  rCBF in auditory and visual sensory regions and other regions that may be involved in attention.  They proposed that decreases in these regions may be involved in the perceptual and cognitive effects of marijuana.

## AIMS

- To quantify ∆9-THC action  using BOLD imaging to determine its pharmacodynamic properties within the human brain and to relate them in time and intensity to observed physiological and behavioral actions of  intravenous ∆9-THC.
- To determine the ability of ∆9-THC and frequent marijuana use to alter functional brain activity using perceptual-motor and cognitive tasks that activate specific brain regions containing cannabinoid receptors as experimental probes.

## METHODS

_**SUBJECTS:**_  Right-handed subjects, ages 19 to 45 years, were recruited using newspaper, radio and television advertisements and gave informed consent to this IRB-approved study prior to participation.  Handedness was assessed using the Edinburgh Inventory (Oldfield, 1971).  THC-using subjects were experienced heavy marijuana users with at least one year of current use (average use > 15 times/month).  They were all generally healthy based upon history and physical examination and were not currently symptomatic of any major psychiatric disorder nor currently using any abuse substance other than cigarettes, alcohol or marijuana.  Subjects in the control group were not current or recent marijuana users and met all other inclusion criteria.
- Subjects presented to the General Clinical Research Center at the Medical College of Wisconsin, received a physical examination, a urine screen for drugs of abuse (Triage®) and blood tests for pregnancy, HIV, hepatitis, liver function and CBC.  All subjects that met the inclusion criteria agreed to receive up to 3 doses (O.5, 1.0 3.0 mg.) of THC or ethanol vehicle as described by Volkow (1996) while undergoing functional MR imaging.  Each injection was given on a separate day.

## Slide 8

## Slide 9

## Behavioral Ratings

- <date/time>

- Administered doses are rated behaviorally effective by experienced marijuana users similar to those used in a social setting and produce a dose-related increase in HR.
- Data obtained during scanning should reflect changes similar to those experienced socially.

**Notes:**
Important results from the behavioral ratings, especially for high.

Range of administered doses are perceived as behaviorally effective by experienced users, similar to their experience in a social setting.

Each of doses receive increased ratings with increasing dose.  Doses are perceived as quantifiably different by subjects, who are unaware of the dose they will be administered.

Conclusion/Importance:
Study doses should be representative to those used in a social setting.  Therefore, data obtained during scanning should represent changes in perfusion and neural activity similar to those experienced in a social setting.

Now lets see how these behaviorally effective doses effect perfusion.

## Pharmacokinetic Principles

**There are time-related changes in drug concentration within the circulation and body compartments. They are measurable, predictable and well known for most drugs.**
**Plasma pharmacokinetics consist of a distribution phase (absorption) and an elimination phase (redistribution/metabolism) that follows first order kinetics and can be modeled as the difference of 2 exponentials,  one rate constant for the absorption phase and another for the elimination phase.**

## Non-linear curve fitting model used to determine drug effects and representative voxel time courses for positive and negative change in BOLD signal (kin - 2 to 10 min; kout - 30 to 120 min)

**INJECTION**

**40 MIN**

**INJECTION**

- Non-linear curve fitting model used to determine drug effects and representative voxel time courses for positive and negative change in BOLD signal (kin - 2 to 10 min; kout - 30 to 120 min)

## Slide 13

## Effects of THC on Brain Activity

_**0.5 and 1.0 mg. THC**_**	****	**_**3.0 mg THC**_
_**Negative changes in AUC**_**	****	**_**Positive changes in AUC**_
- Superior temporal gyrus			right anterior cingulate
- middle frontal and precentral gyrus		superior middle and inferior
- anterior cingulate				frontal gyrus
- insula 					bilateral posterior cingulate
- Cerebellum				caudate
- 					N. Accumbens
_**Positive changes in AUC**_
- middle frontal gyrus			_**Negative changes in AUC**_
- posterior cingulate			superior temporal cortex
- globus pallidus				insula
- left caudate 				cerebellum
- N. Accumbens

## 3 MG. THC

## NUCLEUS ACCUMBENS

- The reinforcing (rewarding) properties of THC are controversial.
- Although it is readily self-administered by humans, this is not always the case in other species including primates and rodents.
- A body of work by Gardner has demonstrated clear reinforcing properties of THC in an appropriate rat strain.
- We focused down on THC’s effects in the n. accumbens due to this region’s association with the reinforcing properties of abuse substances.

## 0.5 mg

**0.5 mg**

**1.0 mg**

**3.0 mg**

- EFFECTS OF THC ON ACTIVITY WITHIN N. ACCUMBENS
- Subjects were injected with 0.5, 1, or 3 mg of THC. Colorized areas represent those voxels in which mean percent area under the curve was greater than the null hypothesis at p<.01 level.

## *

- <date/time>

- **

- **

- Effects of THC on activation in the n. accumbens.  Activation was determined by making a combined (OR) mask of the activations produced by all three doses in the accumbens.  That mask was then used to to describe a functional region in which the mean percent area under the time-effect curve was calculated for each subject.  Values shown are the mean ± the SEM. ** P≤0.05 compared to vehicle, * p≤0.05 compared to other doses.

**Notes:**
The inserted images on the graph display the orange colorized areas of increased signal activity in the nucleus accumbens. 

The Y axis represents BOLD signal activity in percent activation calculated from area under the curve in comparison to pre-injection measurement.

The bar graph quantitates the BOLD signal activation shown by the colorized areas.  As you can see the 0.5 mg and 1.0 mg group had a significant BOLD signal response compared to injection of the vehicle represented by the 0.0mg group.  Further more the 3.0 mg group had a significant BOLD signal response greater than all other groups.

The X axis is the dose in mgs of IV THC each subject received.  Subjects receiving 0.0mg received an injection free of THC and only the ethanol suspension vehicle.

The bar graph quantitates the BOLD signal activation in response to IV THC.  As you can see the 0.5 mg and 1.0 mg group had a significant BOLD signal response compared to injection of the vehicle represented by the 0.0mg group.  Further more the 3.0 mg group had a significant BOLD signal response greater than all other groups.  

## Slide 19

## Task Activation Data Analysis

- Activation intensity was calculated for each pixel by dividing the mean signal intensity during the active periods by the mean intensity during the "rest" periods.
- The resultant functional images were averaged across all subjects for each task to produce mean activation maps for each condition.
- Areas of significant activation were determined for the group on a voxel by voxel basis using a one sample, 3-D t-test against the null hypothesis of no change and a minimum cluster size of 300μ1.
- Comparisons between pre- and post-drug activation were made by determining the mean task activation within functional and standard brain region masks (AFNI).

## CONCEPT FORMATION TASK

**CONCEPT FORMATION TASK**

## This task is modeled after a task that was described by Cohen (1993). The 2-back VSWM task presents fifteen outline squares, arranged in a pseudorandom fashion on the screen. During each 30 sec task block, one of the squares turns black sequentially every 1.5 sec in a random order. The subject is instructed to press a button if the same square is filled in black twice, separated by any other one square (i.e. a two-back working memory task).  A 30 sec 'rest' period where only a central fixation cross was presented alternates with each 30 second active period.

## PARTICIPANT DEMOGRAPHICS

| Gender | 10 Males, 3 Females |
| --- | --- |
| Age | Mean - 23.6, S.D. - 7.0
Range - 19 to 45 |
| Years of Use | Mean - 6.6, S.D. - 3.2
Range - 3 to 12 |

##  Effects of 1 mg of ∆9-THC on task performance

-  Effects of 1 mg of ∆9-THC on task performance

## CF TASK

- Effects of iv THC (1 mg) on activation by a concept formation task.  Colorized areas represent those voxels in which the mean task activation was greater than 0.5% and was significantly different from the null hypothesis of no activation (p≤0.01). Oranges represent positive and blues negative activation.

- Pre-Drug

- Post-Drug

## Slide 26

## CONCEPT FORMATION TASK

_**Re-Drug Activations**__**	**_**	****	**_**Post Drug Decreases or  **_L & R post parietal cortex**	****	****	**_**lack of significant**_**                   **SMA**	****	****	****	****	**_**activation**_
- Cingulate (BA 32)			middle front gyrus/DEPFC
- L&R premotor (BA6) cortex		post-parietal
- L & R premotor (BA6) cortex		SMA
- R MFG including DLPFC (BA 46, 10)	cingulate
- L MFG 					thalamus
- R & L lateral occipital cortex (BA 18, 19)	pons
- R. Thalamus				cerebellum
- L & R cerebellum including
-  declive, culmen and vermis		_**New area – negative activation**_
- pons					posterior cingulate
_**Negative activation**_
- ant. cingulate (BA 32)

## VSWM TASK

- Pre-Drug

- Post-Drug

- Effects of iv THC (1 mg) on activation by a visuospatial working memory task.  Colorized areas represent those voxels in which the mean task activation was greater than 0.5% and was significantly different from the null hypothesis of no activation (p≤0.01). Oranges represent positive and blues negative activation.

## VISUOSPATIAL WORKING MEMORY TASK

## MOTOR TASK

**MOTOR TASK**
**Bilateral Finger Tapping**

## RESULTS AND CONCLUSIONS

- The 1 mg dose of THC produced a moderate marijuana-like high. Performance (accuracy and reaction time) on the CF AND VSWM task was not affected by this dose of THC.
- THC administration decreased brain activation induced by each of the tasks.  The effect was greater on the CF task than the VSWM task. The effects of THC on the finger tapping task were time-dependent.  Both motor and visual cortex activations were significantly decreased at 15 minutes after drug administration.  There was a significant return of activation at 35 minutes.
- Overall, these data suggest that THC can decrease brain activation induced by cognitive and simple motor tasks and the effect is greater on a task with higher cognitive demands.  The decreases in activation were not associated with decreased task performance.  However, it is possible that this could change with higher doses of THC or tasks of greater difficulty.  Possible explanations for the observed decreases in task activation include receptor mediated drug-induced alterations in neurovascular coupling or drug related behavioral mechanisms.

## SUMMARY

- We have detected THC-induced changes in both fMRI signal (neuronal activity) and brain activation by a cognitive task.  Furthermore, the fact that we observed both increases and decreases in fMRI signal as a result of THC injection and regionally specific changes in task activation strongly suggests that they are not due to either global vascular or peripheral cardiovascular drug effects. Taken as a whole, these studies demonstrate  that THC produces significant effects on regional brain activity and cognitive task-induced activation at a dose that produces effects that are similar to those produced by marijuana in a social situation; and that this dose range does not produce significant global effects on brain blood flow.

## Acknowledgements

- Research supported by
- NIDA grants DA11326 and  DA09465
- GCRC grant 5M01RR00058

- Robert Risinger, M.D.
- Jeffrey Benson, M.D.
- S. J. Li, Ph.D.
- Kathleen LaGrave
- Linda Piacentine, M.S., ACNP
- Raymond Hoffman, Ph.D.
- Elliot Stein, Ph.D.