Kenneth M. Johnson

Cannabinoid effects on plasma corticosterone and uptake of 3H-corticosterone by mouse brain.

The effects of three cannabinoids, 11-hydroxy-delta9-tetrahydrocannabinol (11-HO-delta9-THC), delta9-THC and cannabinol (CBN), ranging in behavioral activity from high to low, were studied on two aspects of pituitary--adrenal function. Plasma corticosterone levels were used as an index of adrenocorticotropic hormone (ACTH) release. All three cannabinoids elicited an increase in plasma corticosterone elvels in a manner similar to their behavioral potency. These cannabinoids also elicited an increase in the concentration of 3H-corticosterone taken up by the brains of adrenalectomized mice in a manner similar to their potency in elevating plasma corticosterone levels. The significance and possible underlying mechanism of the apparent correlation resulting between these effects and the behavioral effects of cannabinoids are discussed.

Effects of Δ9-THC on the Synaptosomal Uptake of 3H-Tryptophan and 3H-Choline

The in vitro addition of (–)-Δ9-tetrahydrocannabinol (Δ9-THC) resulted in a dose-responsive inhibition of the high-affinity specific synaptosomal uptake of both 3H-tryptophan and 3H-choline in mouse forebrain crude synaptosomal preparations. The approximate concentrations of Δ9-THC required to cause a 50% inhibition of the uptake of 3H-tryptophan and 3H-choline were 33 and 16 μM, respectively. Kinetic analysis showed that inhibition of both compounds were consistent with a noncompetitive mechanism. The pretreatment of mice with doses of 10, 30 or 100 mg/kg Δ9-THC had no effect on the subsequent in vitro synaptosomal uptake of either 3H-tryptophan or 3H-choline into forebrain synaptosomes.

INTERACTIONS OF ACTIVE CONSTITUENTS OF MARIHUANA WITH OTHER DRUGS IN THE NEURON

A number of papers have appeared in recent years that describe the interaction of other drugs with marihuana or one of its active constituents. These drug interaction studies can be divided into three groups: Some investigators have studied the effects of one other constituent of marihuana on the pharmacological effects of delta-9-tetrahydrocannabinol ( Ag-THC), which has been shown to be the major active constituent of marihuana.l- In some reports the investigators have studied the interaction of one of the other drugs of abuse with marihuana or its active constituent.+1° In the third group of experiments, the interaction of various therapeutic agents with marihuana o r one of its active constituents has been investigated.l- * The majority of the experiments referred to above have been involved with an in vivo interaction of a drug with a cannabinoid. Although the majority of these experiments have been carried out in laboratory animals, some work in human volunteers has been reported. The majority of these papers have been referred to by other speakers in this conference. There are few reports of the interaction of other drugs on the in vitro or biochemical effects of the cannabinoids. In the present communication, it is our intent to discuss two different drug interactions with Ag-THC that occur within the neuron. The first of these interactions is concerned with the effect of reserpine and Ag-THC on the subcellular distribution of each other in brain tissue. Other investigators have reported on the effects of drugs on the distribution of AO-THC in the whole animal. However, n o previous attention has been given to the effect of drugs on the subcellular .distribution of A9-THC. In the second portion of this report, we describe the results of our experiments into the effects of the narcotic antagonist, naloxone, on some of the pharmacological effects of an interesting new cannabinoid. Again, we have examined this interaction at a neurochemical level. It is our intent to describe drug interactions of a pharmacodynamic or distributional nature and relate these interactions to alterations in the pharmacological effect of the cannabinoids produced by these other drugs.

THE EFFECTS OF CANNABINOIDS ON RAT BRAIN SYNAPTOSOMES

Summary The effect of cannabinoids was studied on uptake and release of 3[H]-labelled serotonin, dopamine (DA) and norepinephrine (NE) by synaptosomes prepared from rat whole forebrain, hypothalamus or corpus striatum. Δ9-THC inhibited uptake and facilitated release of 3[H]-serotonin by forebrain synaptosomes, the release being accompanied by increase of 3[H]-indoleacetic acid in the medium. Over a series of cannabinoids, there was no correlation between inhibition of uptake and behavioral effect. Δ9-THC also inhibited tryptophan and choline uptake. Δ9 and Δ8-THC at low concentrations stimulated uptake of 3[H]-DA and NE by hypothalamic and striated synaptosomes, and inhibited at high concentrations. Cannabinol and cannabidiol displayed only inhibitory effects at higher concentrations. In tests on release of these amines, Δ9-THC had a biphasic effect, but cannabinol and cannabidiol only facilitated. The biphasic effects of Δ9- and Δ8-THC may therefore provide a molecular basis for biphasic behavioral effects. The metabolite 11-OH-Δ9-THC differed in its action from Δ9-THC both on hypothalamic and striated synaptosomes.

Adrenalectomy Reverses the Effects of Delta-9-THC on Mouse Brain 5-Hydroxytryptamine Turnover

Acute administration of certain cannabinoids, including delta 9-tetrahydrocannabinol (delta 9- THC), resulted in elevated levels of plasma corticosterone in mice. The rank order potency of these cannabinoids is the same as others have reported using behavioral tests. The maximally effective dose of delta 9-THC (30 mg/kg) in this test also increased the amount of 3H-tryptophan found in the brains of mice given an intravenous injection of 3H-tryptophan 10 min prior to decapitation. This effect was associated with an increase in the amount of 3H-5-hydroxytryptamine synthesized during the pulse period. Adrenalectomy was found to inhibit these effects of delta 9-THC. The possibility that corticosterone may mediate the effects of delta 9-THC on tryptophan disposition and metabolism is discussed.