The cannabinoids are a class of drugs that produce diverse pharmacological effects in animals such as antinociception, hypothermia, catalepsy and sedation. Specifically, the objective of the research in this proposal is to determine the mechanisms by which cannabinoids produce antinociception. The profile of the pharmacological activity of the cannabinoids is unlike that of other known antinociceptive drugs. The cannabinoids may thus prove to be unique in the mechanisms by which they block pain. Therefore, our goal is to use the cannabinoids as tools to elucidate what may prove to be a new mechanism for the relief of pain. Our preliminary data indicate that cannabinoids produce antinociceptive effects by interaction at both spinal and supraspinal sites. We hypothesize that the mechanism of action of the drugs may differ at these two sites. In spite of previous research, most of which involved supraspinal effects of the drugs, it remains unclear how these drugs produce antinociceptive effects. Few studies have previously been performed in vivo or in vitro to evaluate the effects of the drugs in the spinal cord. We propose to perform a systematic study of the role of calcium and adenylyl cyclase modulation in the antinociceptive effects of the cannabinoids in order to compare and contrast the mechanism of action of the drugs in the spinal cord versus in the brain. In these studies modulators of calcium and cyclic-AMP will be injected into the brain or the spinal cord region in mice prior to the administration of the cannabinoids at similar sites. The antinociceptive effects of the cannabinoids will then be determined using the tail-flick and the hot-plate tests. If calcium and adenylyl cyclase appear to be implicated in the antinociceptive effects of the cannabinoids in vivo, we will evaluate the role of these second messengers in in vitro studies. We have observed that the antinociceptive effects of spinally administered morphine are greatly enhanced by the co-administration of inactive doses of delta9-THC and 11-OH-delta9-THC. Conversely, the co-administration of morphine and delta9-THC intravenously results in an additive antinociceptive response. These data are intriguing and provide further evidence for a possible dissimilarity in the mechanism of action of the drugs in the brain and in the spinal cord. We hypothesize that the mechanisms of action of the cannabinoids may have similarities to those of the opiates since morphine and delta9-THC are synergistic when co- administered intrathecally. Therefore, studies are proposed for the characterization of the interrelationships between cannabinoid and opiate mechanisms of action in vivo and in vitro. Studies are also proposed to determine the opiate receptor subtype involved in the synergistic effects observed. We hypothesize that this synergism reflects an interaction between the cannabinoids and morphine with specific second messenger systems such as calcium and cyclic-AMP. The evaluation of the opiate/cannabinoid interaction may serve as a tool to gain a better understanding of manipulating the perception of pain.
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