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

Effects of 5-hydroxytryptamine on defecation in open-field behavior in rats

An attempt was made to elucidate the role of the serotonergic nervous sytem in defecation resulting from environmental stimulation in rats. The open-field (OF) test and shuttle box method were used to study the defecation. 5-Hydroxytryptophan (5-HTP) significantly decreased the number of fecal boluses excreted in both emotional situations, namely, in both OF and shuttle box. The fecal excretion was significantly reduced compared with the controls after intraventricular injection of 5-hydroxytryptamine (5-HT). Animals pretreated with p-chlorophenylalanine (pCPA) and 5,6-dihydroxytryptamine (5,6-DHT) tended to show a slight increase in the OF defecation. 5-HTP was equally effective in diminishing the OF performance of pCPA-treated rats. The inhibitory effects of 5-HTP on the defecation were also observed after depletion of biogenic amines by reserpine treatment. Home cage defecation was increased after 5-HTP administration, decreased under pretreatment with pCPA and not influenced by intraventricular injection of 5-HTP. These results suggested that the defecation after environmental stimuli was due to a change in 5-HT levels in the brain.

Relationship between body temperature and brain monoamines during the development of tolerance to delat9-tetrahydrocannabinol in the rat

The development of tolerance to delat9-tetrahydrocannabinol (delta9-THC) was examined. Rats with permanently indwelling intravenous catheters were injected daily with delta9-THC, 2 mg/kg, for up to 10 days and on each day subjective behaviour and body weight of each rat were noted. Tolerance appeared to develop to both the excitatory and depressant behavioural effects of delta9-THC, whereas the rate of gain in body weight of delta9-THC treated rats was retarded and tolerance to this phenomenon did not develop over the experimental period. On days 1, 2, 3, 5, 6, and 10 body temperature was recorded continuously for at least 2 h after delta9-THC and in other groups of rats the brain levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured spectrophotofluorimetrically 1 h after delta9-THC. Tolerance developed to the delta9-THC-induced hypothermia by day 3, and on days 6 and 10 hyperthermia was observed. delta9-THC did not markedly affect the brain levels of NA or DA over the experimental period. The brain levels of 5-HT were unchanged on days 1--5 but there was a decrease on days 6 and 10. On days 1, 2, and 3 brain levels of 5-HIAA were raised, whereas on day 6 there was a decrease. These results show that delta9-THC induces tolerance to the hypothermia and elevation of brain 5-HIAA levels in a linear manner. An inverse relationship appears to exist between these two parameters.

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 cannabis-treated 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.