Delta-9-tetrahydrocannabinol (THC) affects forelimb motor map expression but has little effect on skilled and unskilled behavior

- Acute low-dose THC increased motor map size.
- Acute medium- and high-dose THC decreased motor map size.
- Acute medium- and high-dose THC reduced reaching attempts.
- Acute medium- and high-dose THC did not alter skilled reaching.
- Acute high-dose THC did not alter unskilled behaviors, except latency to move.

It has previously been shown in rats that acute administration of delta-9-tetrahydrocannabinol (THC) exerts a dose-dependent effect on simple locomotor activity, with low doses of THC causing hyper-locomotion and high doses causing hypo-locomotion. However the effect of acute THC administration on cortical movement representations (motor maps) and skilled learned movements is completely unknown. It is important to determine the effects of THC on motor maps and skilled learned behaviors because behaviors like driving place people at a heightened risk. Three doses of THC were used in the current study: 0.2 mg/kg, 1.0 mg/kg and 2.5 mg/kg representing the approximate range of the low to high levels of available THC one would consume from recreational use of cannabis. Acute peripheral administration of THC to drug naïve rats resulted in dose-dependent alterations in motor map expression using high resolution short duration intracortical microstimulation (SD-ICMS). THC at 0.2 mg/kg decreased movement thresholds and increased motor map size, while 1.0 mg/kg had the opposite effect, and 2.5 mg/kg had an even more dramatic effect. Deriving complex movement maps using long duration (LD)-ICMS at 1.0 mg/kg resulted in fewer complex movements. Dosages of 1.0 mg/kg and 2.5 mg/kg THC reduced the number of reach attempts but did not affect percentage of success or the kinetics of reaching on the single pellet skilled reaching task. Rats that received 2.5 mg/kg THC did show an increase in latency of forelimb removal on the bar task, while dose-dependent effects of THC on unskilled locomotor activity using the rotorod and horizontal ladder tasks were not observed. Rats may be employing compensatory strategies after receiving THC, which may account for the robust changes in motor map expression but moderate effects on behavior.