Brain serotonin metabolism and delta9-tetrahydrocannabinol-induced muricide behavior in rats

Potentialisation des effets du Δ9-tétrahydrocannabinol (THC) par la carence magnésique chez le rat

Aggressive behavior can be classified into three major categories: defense, social attack and predatory behavior. The predatory behavior of rats, which prompts them to prey on mice (muricidal behavior) may be induced by injection of high doses (11 mg/kg) of Delta9-tetrahydrocannabinol (THC) or by acute magnesium deficiency. We have studied the effect of a single injection of low doses of THC (2, 4 or 8 mg/kg) in rats with a severe (50 ppm magnesium diet) or moderate (150 ppm) magnesium deficiency. The combination of moderate magnesium deficiency with low doses of THC induced muricidal behavior in all the rats and an increase in aggressiveness at the doses of 4 or 8 mg/kg of THC. Hyperaggressiveness increased with magnesium deficiency severity. Serotonin is probably involved in aggressiveness induced by both moderate magnesium deficiency and low doses of THC, but implication of other neurotransmitters and magnesium deficiency-induced alterations of CB1-and/or CB2-receptor expression are not excluded.

THC aggravates rat muricide behavior induced by two levels of magnesium deficiency

A severe magnesium deprivation induces an interspecific aggressive behavior (muricidal behavior, MB) in different strains of rats. Delta9-tetrahydrocannabinol (THC) is also known to induce MB even after a single injection (11 mg/kg) in starving, isolated rats. In the present work, we investigated the MB behavior, for six successive assays 1 h delayed, of two groups of male Long-Evans rats fed 50- or 150-ppm Mg(2+)-deficient diets, for 42 days after a single injection of THC at doses (2, 4 or 8 mg/kg) that did not induce aggressiveness in control rats. This treatment led to Mg(2+) plasma levels of 5+/-0.3 and 12.3+/-0.9 mg/ml vs. 21+/-1.5 mg/ml initially. In the 50-ppm Mg-deficient rat group, all the rats were muricidal but the MB pattern was severely aggravated by THC. In the 150-ppm Mg-deficient rat group, no rat was muricidal but all doses of THC induced a 100% MB. In addition, by quantifying the three phases of MB, we showed through six consecutive hourly muricidal assays, that the two first phases (attack latency and attack on the living mouse) decreased progressively, whereas the third phase (attack on the dead mouse) increased dramatically. This indicates firstly that Mg-deprivation decreases the responsiveness threshold of rats to THC. Secondly, these very low doses of THC induced an aggravation of MB and an acquired hyper-aggressiveness in both 50- and 150-ppm Mg-deficient rats, probably involving different neurotransmitters, mainly serotonin, which is decreased by both treatments.

Measurement of the three phases of muricidal behavior induced by delta9-tetrahydrocannabinol in isolated, fasting rats

Delta9-Tetrahydrocannabinol (THC) has long been recognized as inducing mouse-killing behavior (muricidal behavior) in starving, isolated rats after a single injection. We showed that when the killing tendency was increased by THC, a preliminary contact with a mouse decreased the probability of muricidal behavior. By quantifying the three phases of the muricidal behavior in either nonkiller or naive THC-treated rats, we showed that the duration of each step was notably increased as compared to untreated natural killer rats, mainly the attack on the dead mouse, indicating increased aggressiveness. Finally, no significant changes were observed in the duration of the three phases in natural killer rats when the muricide assays were repeated every hour. In contrast, in THC-treated rats--either naive or nonkiller--all three phases decreased with the assay repetition to levels comparable to those of natural killer rats, suggesting that the killer behavior was progressively acquired for the six assays. These changes could be a useful model to study the central effects of THC and either its agonists or antagonists.

Effects of acute and chronic toluene inhalation on behavior and (3H)-serotonin binding in rat

Toluene inhalation (0.7% in air) induced in rats abnormal neurological states resembling the serotonin syndrome, such as hindlimb abduction, resting tremor and head weaving. The frequency and intensity of these responses were unchanged after two weeks of exposure (0.7% in air, 15 min/day for 14 days), indicating an absence of tolerance development. An examination of specific serotonin (3H-5HT) binding to crude synaptic membranes prepared from brains of rats subjected to acute and chronic toluene exposure revealed that while no changes in either apparent Kd or apparent Bmax occurred in acutely exposed animals, in chronically treated animals specific (3H)-5HT binding decreased in hippocampus and pons + medulla oblongata. These results indicate that serotonergic mechanisms may play a role in some of the effects of toluene inhalation in rats, but cannot explain the absence of tolerance development after chronic exposure to toluene.

Effects of psychotropic drugs on delta 9-tetrahydrocannabinol-induced long-lasting muricide

The effects of psychotropic drugs on THC-induced long-lasting muricide were investigated in rats. Changes in open field activity (ambulation and rearing) of the rat were concurrently assessed as an index of behavioral toxicity. Imipramine-like antidepressants, atropine, and antiparkinsonism drugs exhibited a selective inhibitory activity on muricide, whereas the effects of neuroleptics, pentobarbital, diazepam, and methamphetamine were nonspecific. It is also suggested that cholinergic, catecholaminergic, and serotonergic mechanisms are involved in THC-induced muricide. This type of induced muricide appears to be a useful experimental model particularly suitable for the evaluation of antidepressants in correlation with brain amine dynamics.

The effect of delta 9-tetrahydrocannabinol (delta 9-THC) on the turnover rate of brain serotonin of the rat

1. One isotopic and three non-isotopic methods were used to determine the effect of an acute intravenous dose of delta 9-tetrahydrocannabinol (delta 9-THC, 2 mg/kg) on the rat brain turnover rate of serotonin. 2. In control animals the turnover rate of serotonin was about 2 nmol/g per h. This rate was not altered by delta 9-THC when it was calculated from the rise of 5-hydroxyindoleacetic acid following probenecid from the rise of serotonin following pargyline. 3. delta 9-THC did not alter serotonin turnover rate when it was calculated from the conversion of 3H-tryptophan to 3H-serotonin. 4. The serotonin turnover rate was significantly increased by delta 9-THC when the rate was calculated from the decline of 5-hydroxyindoleacetic acid following pargyline. 5. These results suggest that delta 9-THC does not alter the turnover of rat brain serotonin. The previously reported delta 9-THC-induced changes in body temperature and increased brain levels of 5-hydroxyindoleacetic acid may be mediated by some other mechanism such as interference by delta 9-THC of the vesicular binding of serotonin.