Differential Effects of Delta9THC on Learning in Adolescent and Adult rats

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Differential Effects of Delta9-THC on Learning in
Adolescent and Adult rats

• Young May Cha, Aaron M. White , Cynthia M. Kuhn ,
  Wilkie A. Wilson,H.S. Swartzwelder

Pharmacology, Biochemistry and Behavior 83 (2006)
pgs. 448455
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Introduction

• Studied the effects of delta9-tetrahydrocannabinol
  (THC) in both adolescent and adult rats.
• THC is the main psychoactive substance found in
  the Cannabis plant
• Used high and low doses of THC

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Hypothesis

• They hypothesized that THC would impair learning
  more potently in male adolescent animals compared
  to male adults.

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Methods

• 96 male adolescent rats 96 male adult rats
• Injected with either a high dose or low dose of
  THC
• High Dose 10.0 mg/kg
• Low Dose 2.5 mg/kg
• Used the Morris water maze (MWM) as a tool to
  measure learning.

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MethodsAcute

• Experiment 1
• Assess the acute effects of THC on spatial
  learning.
• Adolescent and adult rats received injections of
  THC (5mg/kg) or the control vehicle solution.
• Thirty minutes after the injection, animals began
  training on the spatial task in the MWM.
• Experiment 2
• Assess the effects of a lower dose and a higher
  dose on spatial and non-spatial learning in the
  MWM.
• Low dose-2.5mg/kg
• High dose-10mg/kg.

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MethodsChronic

• Experiment 3-Assessed the long-lasting effects of
  chronic THC treatment on spatial learning.
• Adolescent and adult rats were given injections
  of a control solution or a THC solution
  (5.0mg/kg) once daily for 21 days.
• Twenty-eight days after the last injection, the
  rats were trained, drug-free, on the spatial task
  in the MWM.
• 48 hours after the completion of the spatial
  task, the same rats were also trained on the
  non-spatial version of the water maze task.

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Results Acute-Experiment 1

• Although the performance of adolescent rats
  treated with THC improved, they never reached the
  level of performance of the controls (Fig. 1a).
• There was no significant effect of THC on adults
  in spatial learning
• (Fig. 1b).

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ResultsAcute-Experiment 2
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ResultsAcute

• Spatial Learning
• Overall, THC impaired spatial learning across the
  five day testing period.
• THC also impaired learning more in adolescent
  rats than in adult rats at both the low and high
  doses.
• Non-Spatial Learning
• THC also impaired non-spatial learning across the
  five-day testing period.
• At both doses, THC impaired non-spatial learning
  more powerfully in adolescent rats

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ResultsChronic

• There were no overall effects of chronic
  pre-exposure to THC during either adolescence or
  adulthood, in both the spatial or non-spatial
  task.

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Conclusion

• Acute treatment with THC inhibited both spatial
  and non-spatial learning in the water maze more
  powerfully in male adolescent rats than in male
  adults.
• Chronic THC treatment, either during adolescence
  or adulthood, had no effect on subsequent
  learning four weeks after the last exposure to
  THC.
• More research will be needed to determine which
  periods of development, and which cognitive and
  behavioral functions are most susceptible to the
  effects of THC.

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• Questions?