Fernando Varela de Carvalho

The effects of chronic cannabis treatment on the aggressive behavior and brain 5-hydroxytryptamine levels of rats with different temperaments.

The effects of cannabis extract on aggressive behavior and whole and regional brain 5-HT levels were studied in rats selected for differences in temperament. The results indicated that rats with a high index of defection (HI) appeared to be more susceptible to the cannabis elicited aggressive behavior than the animals with a low index of defecation (LI). The defecation score expressed by the number of boluses and the ambulation score were counted in a series of open-field experiments. After chronic treatment with cannabis the 5-HT whole brain levels remained unchanged in the non-aggressive rats of both LI and HI group whereas the 5-HT levels fell down to about 50% of normal levels in the whole brain of aggressive animals. The greatest regional reductions in 5-HT were found in the cerebral hemispheres, midbrain and hypothalamus, although 5-HT levels remained unchanged in cerebellum and medula oblongata. This paper presents evidence suggesting that temperament may be an important factor involved in the ability of cannabis to induce aggressive behavior in starved rats, and that some basic brain mechanism probably differs in HI and LI rats. This difference could be responsible for the small aggressive response observed in LI rats after chronic treatment with cannabis.

The effects of chronic cannabis treatment upon brain 5-hydroxytryptamine, plasma corticosterone and aggressive behavior in female rats with different hormonal status

Ovariectomized rats, chronically treated with cannabis extract or control solution, were given different hormonal treatments. Results indicated that both cannabistreated and estrogen-treated animals were more aggressive than controls. Furthermore, aggressiveness was virtually abolished when cannabis-treated females were made sexually receptive by estrogen and progesterone treatments. After 25 days of cannabis or control solution treatment, all subjects were sacrificed. The levels and turnover rate of brain 5-HT and peripheral plasma corticosterone were then assayed. Data indicated both a significant inverse relationship between plasma corticosterone and whole brain levels of 5-HT (r=−0.742 to −0.985) for all groups and a significant positive relationship between aggressive behavior and plasma corticosterone (r=+0.675 to +0.946) in all groups that were fighting prior to decapitation. Results are tentatively explained, suggesting that the variability of the female response to stress during the different phases of the estrus cycle, permitted them to perform differently after chronic cannabis treatment. 5-HT is apparently involved, either directly in its effects on aggressive behavior or indirectly through the pituitary-adrenocortical axis activation.