Abstract

The many studies that have been included in this review suggest that cannabinoids have ubiquitous effects on biological systems. These results also underscore the intensity to which cannabinoids have been studied. While there are numerous reasons for the prodigious amount of cannabinoid research, a major stimulus has been the desire to identify a specific biochemical event or pathway that is responsible for the expression of delta 9-THC's unique psychoactivity. It is the hope that delta 9-THC, as with all centrally acting drugs, might serve as an important tool for achieving a better understanding of the central nervous system. As discussed in this review, the psychoactivity of cannabinoids might best be described as a composite of numerous effects. If that is indeed the case, then it would seem logical that these centrally mediated effects do not arise from a single biochemical alteration, but rather from multiple actions. Of course, a major problem arises when one attempts to establish a relationship between cause and effect when multiple mechanisms and effects are involved. An initial approach to reducing the complexity of elucidation of mechanism of action should involve attempts to distinguish those cannabinoid actions which result in specific effects (psychoactivity) from those which produce non-psychoactive effects (such as general depression). There are several fundamental principles that can be used to assess specificity, including concentration or dose of the drug that is required to produce a given effect. Low doses of delta 9-THC are capable of producing the psychoactivity that is unique to cannabinoids, whereas higher doses may produce effects that are both specific and nonspecific for cannabinoids. Unfortunately, establishing this basic tenet for delta 9-THC has proven to be difficult. It has not been possible to establish the concentration of delta 9-THC at its site of action that is necessary to produce a given pharmacological effect. While it is a simple matter to measure the concentration of cannabinoids in either a whole tissue or an incubation medium, the hydrophobicity of cannabinoids dramatically affects their affinity for, and hence concentration in, the biochemical components of the tissue. If the concentration of delta 9-THC could be measured at its site of action, then the relevance of many of its pharmacological effects could be adequately determined. Two possible mechanisms by which cannabinoids might produce psychoactivity are membrane perturbation and receptor interactions, and indeed, both mechanisms have received considerable attention.(ABSTRACT TRUNCATED AT 400 WORDS)