Delta(9)-THC administered into the medial prefrontal cortex disrupts the spatial working memory

Psychopharmacology (Berl). 2005 Nov;183(1):54-64. doi: 10.1007/s00213-005-0141-1. Epub 2005 Oct 22.

Abstract

Rationale: Delta(9)-Tetrahydrocannabinol (Delta(9)-THC) disrupts working memory. The prefrontal cortex (PFC) is involved in the processing of working memory, and its medial portion (mPFC) is part of a brain reward circuit as constituted by the mesocorticolimbic dopaminergic system.

Objective: This study examined the involvement of the mPFC in the effects of Delta(9)-THC on spatial working memory.

Methods: Ten male Wistar rats well-trained in a radial arm maze and with bilateral cannula implanted in the mPFC received Delta(9)-THC intra-cortically (Delta(9)-THC IC) at doses of 0 (VEH), 32, 100 or 180 microg, 5 min before a 5-s or a 1-h delayed task in order to measure a short- or long-term spatial working memory, respectively. By contrast, 11 other animals received Delta(9)-THC intraperitoneally (Delta(9)-THC IP) at doses of 0 (VEH), 0.32, 1 or 1.8 mg/kg, 30 min before a 5-s or a 1-h delayed task. Additionally, after a 15-day washout, the effect of an IP or IC pre-exposure of Delta(9)-THC was examined by repeating both dose-effect curves in a crossover order for the routes of administration.

Results: Delta(9)-THC IP produced significantly larger number of errors at doses of 0.32 or 1 mg/kg as compared to VEH in the 1-h post-delay performance. Delta(9)-THC 100 microg IC also produced significantly larger number of errors as compared to VEH and also to the other doses (32 or 180 microg) IC in the 1-h post-delay performance. Previous exposure to Delta(9)-THC IP or IC did not significantly affect the disruptive effect of this cannabinoid.

Conclusions: Delta(9)-THC administered directly in the mPFC impaired 1-h delayed task in the radial arm maze in a manner similar to that observed for its systemic administration, suggesting that the mPFC is involved in the disruptive effects of Delta(9)-THC on spatial working memory.

MeSH terms

  • Animals
  • Dose-Response Relationship, Drug
  • Dronabinol / administration & dosage
  • Dronabinol / pharmacology*
  • Injections, Intraventricular
  • Male
  • Maze Learning / drug effects
  • Memory / drug effects*
  • Prefrontal Cortex / drug effects*
  • Prefrontal Cortex / physiology
  • Psychotropic Drugs / administration & dosage
  • Psychotropic Drugs / pharmacology*
  • Rats
  • Rats, Wistar
  • Time Factors

Substances

  • Psychotropic Drugs
  • Dronabinol