Delta(9)-THC administered into the medial prefrontal cortex disrupts the spatial working memory.
BACKGROUND
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.
Silva de Melo
Lívia Carla
LC
Department of Physiological Sciences, Federal University of Espírito Santo, Av. Marechal Campos, 1468, B. Maruípe, 29042-755 Vitória, ES, Brazil.
Cruz
Ariane Pinheiro
AP
Rios Valentim
Saavedra José
SJ
Marinho
Andresa Rosane
AR
Mendonça
Josidéia Barreto
JB
Nakamura-Palacios
Ester Miyuki
EM
D000818:Animals; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000008:administration & dosage / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008568:Memory / Q000187:drug effects*; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000502:physiology; D011619:Psychotropic Drugs / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D011619:Psychotropic Drugs; D013759:Dronabinol