The action of synthetic cannabinoids on the induction of long-term potentiation in the rat hippocampal slice

Incubation of rat hippocampal slices with the synthetic cannabinoid (-)-11-OH-delta 8-dimethylheptyl tetrahydrocannabinol (HU-210) (100 nM) prevented the induction of long-term potentiation of field excitatory postsynaptic potentials recorded in the CA1 region. However, in slices incubated with its non-psychoactive (+)-isomer HU-211 (100 nM), which is reported to be an NMDA receptor antagonist, high frequency stimulation evoked a long-lasting potentiation, comparable to control slices.

(R)-methanandamide: a chiral novel anandamide possessing higher potency and metabolic stability

Four chiral congeners of arachidonylethanolamide (anandamide) have been synthesized and evaluated for (a) their ability to bind to the cannabinoid receptor in rat forebrain membranes and (b) their pharmacological potency as measured by the compounds' ability to inhibit electrically-evoked contractions of the mouse vas deferens. The lead analog was also tested for its potency in vivo. Of the analogs tested, (R)-(+)-arachidonyl-1'-hydroxy-2'-propylamide [(R)-methanandamide] exhibited the highest affinity for the cannabinoid receptor with a Ki of 20 +/- 1.6 nM, 4-fold lower than that of anandamide (Ki = 78 +/- 2 nM). Moreover, determination of the cannabinoid binding affinity in the presence and absence of the protease inhibitor phenylmethanesulfonyl fluoride (PMSF) revealed that (R)-methanandamide possesses a remarkable stability to aminopeptidase hydrolysis. Pharmacological studies on mouse isolated vasa deferentia demonstrated that all four analogs produce concentration-related inhibition of the twitch response and the order of potency is the same as the rank order of the affinities of these agonists for cannabinoid binding sites. Furthermore, experiments with mice have demonstrated that (R)-methanandamide also possesses cannabimimetric properties in vivo, as established by the four tests of hypothermia, hypokinesia, ring immobility, and antinociception.

Cross-tolerance between delta-9-tetrahydrocannabinol and the cannabimimetic agents, CP 55,940, WIN 55,212-2 and anandamide

1. Mice pretreated intraperitoneally for 2 days with delta-9-tetrahydrocannabinol (delta-9-THC) at a dose of 20 mg kg-1 day-1 and then challenged intravenously with this drug, 24 h after the second pretreatment, showed a 6 fold tolerance to the hypothermic effect of delta-9-THC. This pretreatment also induced tolerance to the hypothermic effects of the cannabimimetic agents, CP 55,940 (4.6 fold) and WIN 55,212-2 (4.9 fold), but not to the hypothermic effect of the putative endogenous cannabinoid, anandamide. 2. Vasa deferentia removed from mice pretreated intraperitoneally with delta-9-THC twice at a dose of 20 mg kg-1 day-1 were less sensitive to its inhibitory effect on electrically-evoked contractions than vasa deferentia obtained from control animals. The cannabinoid pretreatment induced a 30 fold parallel rightward shift in the lower part of the concentration-response curve of delta-9-THC and a marked reduction in the maximal inhibitory effect of the drug. It also induced tolerance to the inhibitory effects on the twitch response of CP 55,940 (8.7 fold), WIN 55,212-2 (9.6 fold) and anandamide (12.3 fold). 3. The results confirm that cannabinoid tolerance can be rapid in onset and support the hypothesis that it is mainly pharmacodynamic in nature. The finding that in vivo pretreatment with delta-9-THC can produce tolerance not only to its own inhibitory effect on the vas deferens but also to that of three other cannabimimetic agents, suggests that this tissue would be suitable as an experimental model for investigating the mechanisms responsible for cannabinoid tolerance. 4. Further experiments are required to establish why tolerance to anandamide-induced hypothermia was not produced by a pretreatment with delta-9-THC that did induce tolerance to the hypothermic effects of delta-9-THC, CP 55,940 and WIN 55,212-2 and to the inhibitory effects of delta-9-THC,CP 55,940, WIN 55,212-2 and anandamide on the twitch response of the vas deferens.

delta 9-Tetrahydrocannabinol and anandamide enhance the ability of muscimol to induce catalepsy in the globus pallidus of rats

Doses of 3 or 30 micrograms of delta 9-tetrahydrocannabinol markedly increased the ability of 25 ng of muscimol to delay the descent of rats from a horizontal bar (descent latency) when these drugs were coadministered bilaterally into the globus pallidus. Intrapallidal injections of 30 micrograms of the putative endogenous cannabinoid, anandamide, also increased the effect of muscimol on descent latency. These data indicate that the production of catalepsy by cannabinoids may depend at least in part on an ability to enhance GABAergic transmission in the globus pallidus and support the hypothesis that anandamide is indeed an endogenous ligand for the cannabinoid receptor.

Isolation and structure of a brain constituent that binds to the cannabinoid receptor

Arachidonylethanolamide, an arachidonic acid derivative in porcine brain, was identified in a screen for endogenous ligands for the cannabinoid receptor. The structure of this compound, which has been named "anandamide," was determined by mass spectrometry and nuclear magnetic resonance spectroscopy and was confirmed by synthesis. Anandamide inhibited the specific binding of a radiolabeled cannabinoid probe to synaptosomal membranes in a manner typical of competitive ligands and produced a concentration-dependent inhibition of the electrically evoked twitch response to the mouse vas deferens, a characteristic effect of psychotropic cannabinoids. These properties suggest that anandamide may function as a natural ligand for the cannabinoid receptor.

Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine

1. The psychoactive cannabinoids (-)-delta 9-tetrahydrocannabinol ((-)-delta 9-THC) and the 1,1-dimethyl-heptyl homologue of (-)-11-hydroxy-delta 8-tetrahydrocannabinol ((-)-DMH) both inhibited electrically-evoked contractions of the mouse isolated vas deferens and the myenteric plexus-longitudinal muscle preparation of the guinea-pig small intestine. 2. Concentrations of (-)-delta 9-THC and (-)-DMH that decreased twitch heights by 50% were 6.3 and 0.15 nM respectively in the mouse vas deferens and 60 nM and 1.4 nM respectively in the myenteric plexus preparation. (-)-DMH was about 40 times more potent than (-)-delta 9-THC in both preparations, supporting the notion that their mode of action in each tissue is the same. 3. The psychically inactive cannabinoid, (+)-DMH, had no inhibitory effect in the mouse vas deferens at a concentration of 30 nM, showing it to be at least 1000 times less potent than (-)-DMH. In the myenteric plexus preparation, (+)-DMH was about 500 times less potent than its (-)-enantiomer. 4. The inhibitory effects of sub-maximal concentrations of (-)-delta 9-THC were not attenuated by 300 nM naloxone. 5. The findings that (-)-delta 9-THC and (-)-DMH are highly potent as inhibitors of the twitch response of the mouse vas deferens and guinea-pig myenteric plexus preparation and that DMH shows considerable stereoselectivity suggest that the inhibitory effects of cannabinoids in these preparations are mediated by cannabinoid receptors.

An investigation of the involvement of GABA in certain pharmacological effects of delta-9-tetrahydrocannabinol

Experiments were performed with mice to determine whether doses of the benzodiazepine, flurazepam, or the GABA uptake inhibitor, NO-328, known to potentiate catalepsy induced by delta-9-tetrahydrocannabinol (THC), would also interact synergistically with THC in the production of certain other effects. No synergism was detected either in the production of antinociception (tail flick test) or in a test in which the ability of flurazepam to delay onset of clonic convulsions induced by intravenous infusion of pentylenetetrazole was compared in the presence and absence of THC or cannabidiol. The hypothermic effect of THC was unaffected by NO-328 but enhanced by flurazepam, albeit only at doses higher than those needed to potentiate THC-induced catalepsy. In vitro experiments with guinea pig ileum showed that the ability of THC to inhibit electrically evoked contractions was unaffected by delta-amino-n-valeric acid, a GABA(B) receptor antagonist, and that preparations rendered tolerant to GABA responded normally to THC. Contractions induced by GABA in unstimulated ileal longitudinal muscle were attenuated by THC. We conclude that there is little evidence from our data that any of the THC effects studied were GABA mediated.

Evidence that the hypothermic response of mice to delta-9-tetrahydrocannabinol is not mediated by changes in thermogenesis in brown adipose tissue

Delta 9-Tetrahydrocannabinol (20 mg/kg i.p.) and propranolol (20 and 50 mg/kg i.p.) produced marked falls in the rectal temperatures of mice kept at an ambient temperature of 22 degrees C. Propranolol (50 mg/kg i.p.) also decreased the thermogenic activity of brown fat, as measured by a decrease in the level of [3H]GDP binding to mitochondria obtained from mouse interscapular brown adipose tissue. In contrast, delta 9-tetrahydrocannabinol (20 mg/kg i.p.) did not affect mitochondrial GDP binding even though the dose used was one shown previously to depress heat production. GDP binding was also unaffected by this cannabinoid in brown adipose tissue taken from mice that had been kept at 13 degrees C instead of 22 degrees C. In mice kept at 34 degrees C, isoprenaline (0.25 and 1.0 mg/kg s.c.) induced a marked rise in rectal temperature and increased the level of GDP binding to brown fat mitochondria. Propranolol (50 mg/kg i.p.) prevented the hyperthermic response to isoprenaline, the mice becoming hypothermic instead. Delta 9-Tetrahydrocannabinol (20 mg/kg i.p.) had no effect on isoprenaline-induced hyperthermia. We conclude from these data that there is no significant involvement of brown adipose tissue in the hypothermic response of mice to delta 9-tetrahydrocannabinol.

Enhancement by chlordiazepoxide of catalepsy induced in rats by intravenous or intrapallidal injections of enantiomeric cannabinoids

The cataleptic response of rats to (-)-delta-9-tetrahydrocannabinol (delta-9-THC), measured using a bar test, was enhanced by subcutaneous pretreatment with chlordiazepoxide (10 mg/kg). Significant potentiation was observed when the cannabinoid was administered peripherally (0.1-1.0 mg/kg i.v.) and when it was injected bilaterally into sites in or very near the posterior medial region of the globus pallidus (30 micrograms). Similar results were obtained with (-)-11-hydroxy-delta-8-dimethylheptyl-THC (0.005 to 0.02 mg/kg i.v. and 3, 10 or 30 micrograms intracerebrally). However, the (+) isomer of the 11-hydroxy compound was inactive in the presence and absence of chlordiazepoxide. It was also found that chlordiazepoxide (10 mg/kg s.c.) enhanced the cataleptic response to the GABA agonist, THIP (0.25 microgram), injected bilaterally into sites located in or very near the globus pallidus and that the cataleptic response to delta-9-THC (1 mg/kg i.v.) could be potentiated by chlordiazepoxide (50 micrograms), when this was injected into similar sites in the brain. The results support the hypothesis that the cataleptic response to cannabinoids is mediated by gamma-aminobutyric acid. They also provide evidence that cannabinoids can produce catalepsy by interacting with tissue in the vicinity of the globus pallidus and that the ability to interact in this way depends on the conformation of the cannabinoid molecule.

Drugs which stimulate or facilitate central cholinergic transmission interact synergistically with delta-9-tetrahydrocannabinol to produce marked catalepsy in mice

In experiments in which mice were placed with their forepaws over a 4 cm high horizontal bar, delta-9-tetrahydrocannabinol (THC; 10 mg/kg i.p.) delayed descent from the bar. This effect on descent latency was markedly enhanced by physostigmine (0.05 or 0.25 mg/kg s.c.) and oxotremorine (0.04 or 0.08 mg/kg s.c.), administered immediately before THC. These interactions were attenuated by atropine (2.0 mg/kg s.c.) and (-)-scopolamine (1.9 mg/kg s.c.) but not by atropine methyl nitrate (2.11 mg/kg s.c.), which does not readily cross the blood-brain barrier. However, atropine methyl nitrate did prevent salivation induced by oxotremorine in the presence of THC. No synergism was detected between THC and neostigmine (0.047 mg/kg s.c.). Atropine and (-)-scopolamine also decreased the ability of chlordiazepoxide (10 mg/kg s.c.) to enhance the effect of THC on descent latency. The interaction was not antagonized by atropine methyl nitrate or mecamylamine (1.17 or 2.34 mg/kg s.c.). These results point to an involvement of central acetylcholine-releasing pathways in the cataleptic response of mice to THC.

Behavioural thermoregulation in mice: effects of low doses of general anaesthetics of different potency

Chloroform, monochlorodifluoromethane and nitrous oxide produced dose-related decreases in the rectal temperatures of mice allowed to choose between a warm and a cool environment. The doses used were subanaesthetic, respectively 0.0013-0.004, 0.028-0.085 and 0.25-0.5 atm. The hypothermia (up to 3.6 degrees C) was usually associated with significant reductions in time spent in the warm. The log dose-hypothermic response plots were approximately parallel and there was a marked correlation between anaesthetic potency, as measured by the abolition of the righting response, and hypothermic potency.

Behavioral thermoregulation in mice subjected to high pressure

Mice exposed to normoxic He and Ne at increased pressure and allowed to choose between a neutral and a cool environment showed a preference for the cooler environment. This behavior was apparent at 5.7 but not at 2.5 atm He. At 11.3 atm He and Ne, the behavior was associated with a similar reduction in the deep body temperature to a new steady level. The reduction in body temperature increased with pressure, up to 35 atm He, the maximum studied. Since the heat transfer of the He and Ne gas mixtures is different and both gases exert negligible anesthetic effects, the hydrostatic pressure most likely affects behavioral thermoregulation by affecting neuronal function.

Drugs which stimulate or facilitate central GABAergic transmission interact synergistically with delta-9-tetrahydrocannabinol to produce marked catalepsy in mice

In experiments in which mice were placed with their forelegs over a 4 cm high horizontal bar, pretreatment with delta-9-tetrahydrocannabinol (THC; 10 mg/kg i.p.) significantly delayed descent from the bar. This response to THC was markedly enhanced by doses of amino-oxyacetic acid, flurazepam, cis(Z)-flupentixol, muscimol, (-)-baclofen and NO-328 having little or no effect when given alone. No synergism was detected between THC and (+)-baclofen or trans(E)-flupentixol. The interactions between THC and flurazepam, amino-oxyacetic acid and NO-328 were attenuated by (+)-bicuculline and by homotaurine, but not by strychnine. The interaction between THC and (-)-baclofen was prevented by homotaurine but not by (+)-bicuculline whereas only (+)-bicuculline reduced the interactions of THC with muscimol and cis(Z)-flupentixol. Flumazenil prevented the interaction between THC and flurazepam but not that between THC and NO-328. The results suggest that the synergistic interactions observed in this study depended on the activation of GABAA and/or GABAB receptors, probably located in extrapyramidal GABAergic pathways.

Delta-9-tetrahydrocannabinol-induced catalepsy in mice is enhanced by pretreatment with flurazepam or chlordiazepoxide

Pretreatment with flurazepam (3 mg/kg s.c.) or chlordiazepoxide (5.5-30 mg/kg s.c.) at an ambient temperature of 34 degrees C, markedly enhanced the cataleptic response of mice to delta-9-tetrahydrocannabinol (THC; 5-20 mg/kg i.p.) as measured in a bar test. Also, the incidence of loss of the righting response was significantly greater in mice receiving a subhypnotic dose of flurazepam (0.3-3 mg/kg s.c.), followed by THC (5-20 mg/kg i.p.), than in animals receiving THC preceded by saline. Loss of the righting response was not associated with any gross reduction in skeletal muscle tone (inclined screen and wire grip tests) and it was proposed that the animals were not anaesthetized but instead could be placed on their backs because flurazepam had enhanced the cataleptic effect of THC. Loss of the righting response produced in mice by pentobarbitone (60 mg/kg i.p.) or by a large dose of flurazepam (300 mg/kg s.c.) was associated with a marked loss of muscle tone and probably indicated the induction of anaesthesia. It is possible that THC interacts with benzodiazepines by increasing synaptic concentrations of gamma-aminobutyric acid (GABA). However, many other possible mechanisms exist and these cannot yet be excluded.

The hypothermic response of mice to delta-9-tetrahydrocannabinol is enhanced by chlorpromazine, thioxanthenes, alpha-adrenoceptor antagonists and pentolinium but not by SCH 23390 or sulpiride

Chlorpromazine, given either subcutaneously (0.375 mg/kg) or unilaterally into the preoptic/anterior hypothalamic area through a chronically implanted cannula (20 micrograms), was found to enhance the hypothermic response to delta-9-tetrahydrocannabinol (THC; 5 mg/kg i.p.) in unrestrained adult male MF1 mice, kept at 22 degrees C. In mg/kg terms, chlorpromazine was no more potent when injected into the preoptic/anterior hypothalamic area than when given subcutaneously. Phentolamine (54 micrograms) had no significant effect on hypothermia induced by THC when injected into the hypothalamus although it did enhance this response when given subcutaneously (15 mg/kg). Hypothermia induced by THC was also enhanced by flupentixol (0.375 mg/kg s.c.), piflutixol (23.4 micrograms/kg s.c.), pentolinium (5 mg/kg s.c.), prazosin (0.1875 mg/kg s.c.) and indoramin (6 mg/kg s.c.) but not by SCH 23390 (6 mg/kg s.c.) or sulpiride (40 mg/kg s.c.). When taken together with the results from a previous study, these data support the hypothesis that chlorpromazine enhances hypothermia induced in mice by THC by antagonizing alpha-adrenoceptors so as to decrease the capacity of the animals to minimise peripheral blood flow by vasoconstriction. The present data also support the hypothesis that flupentixol and piflutixol interacted with THC not by antagonizing dopamine at D1 or D2 receptors but rather by blocking alpha-adrenoceptors.

Enhancement of the hypothermic response of mice to delta-9-tetrahydrocannabinol by subhypothermic doses of chlorpromazine and phentolamine

Pretreatment with subhypothermic doses of chlorpromazine, given directly into the IIIrd cerebral ventricle via a chronically implanted cannula (50 micrograms) or subcutaneously (0.75 mg/kg), was found to enhance the hypothermic response to delta-9-tetrahydrocannabinol (THC: 5 20 mg/kg i.p.) in unrestrained adult male MF1 mice, kept at 22 degrees C. Subcutaneous pretreatment with a subhypothermic dose of phentolamine (30 mg/kg) had a similar effect, whereas pretreatment with desipramine (10 mg/kg s.c.), mepyramine (2.3 and 11.5 mg/kg s.c.), methysergide (2 mg/kg s.c.), pimozide (1 and 5 mg/kg s.c.) or lignocaine (50 mg/kg s.c.), had no effect. Intracerebroventricular pretreatment with phentolamine was also without effect and it is concluded that this drug interacts with THC at some site located outside the brain. Since, in mg/kg terms, chlorpromazine was more potent in enhancing THC-induced hypothermia when given subcutaneously than when injected into the IIIrd ventricle, it too may interact with THC at a peripheral site. Indeed, chlorpromazine and phentolamine may both increase the hypothermic response to THC by antagonizing alpha-adrenoceptors on cutaneous blood vessels, thereby decreasing the capacity of animals to minimise peripheral blood flow by vasoconstriction. Alternatively, since the distribution of chlorpromazine within the brain may well have been less efficient after intraventricular than after subcutaneous injection, the possibility remains that chlorpromazine interacted centrally with THC.

Effects of subanesthetic doses of inert gases on behavioral thermoregulation in mice

Mice exposed to subanesthetic partial pressures of N2O (0.25 to 0.75 atm) or N2 (5.7 or 11.33 atm) and allowed to choose between a warm and a cool environment showed a marked preference for the cooler environment. This behavior was associated with the onset of hypothermia, with deep body temperature falling by up to about 3 degrees C, usually to a new, steady level. Both the length of time spent in the cooler environment and the degree of the hypothermia produced increased with the partial pressure of N2O or N2 used. The effects of N2O on behavioral thermoregulation and body temperature were reversible. There was a correlation between anesthetic potency and the ability of both gases to alter thermoregulation, suggesting that the effect of these agents on thermoregulation was caused by the same molecular interactions as those which underlie anesthesia. Since both gases elicited changes in behavioral thermoregulation promoting rather than opposing the onset of hypothermia, it is concluded that they may have acted to lower the level at which deep body temperature was being regulated.

Changes in body temperature and oxygen consumption rate of conscious mice produced by intrahypothalamic and intracerebroventricular injections of delta 9-tetrahydrocannabinol

delta 9-Tetrahydrocannabinol (delta 9-THC) was injected into the preoptic area of the anterior hypothalamus or into the third or fourth cerebral ventricle of the conscious mouse through a chronically implanted cannula and the effects on body temperature and oxygen consumption rate were measured. At an ambient temperature of 22 degrees C, injections of delta 9-THC into the fourth ventricle (5 and 10 microgram) produced dose-dependent falls in rectal temperature. Hypothermia was also observed after injections of the drug into the hypothalamus (5 and 10 microgram) or into the third ventricle (10 microgram). The hypothermia produced by delta 9-THC was associated with a fall in oxygen consumption rate. Falls in rectal temperature and in oxygen consumption rate were significantly greater after injection of delta 9-THC than after injection of the drug vehicle, Tween 80. The falls in rectal temperature and oxygen consumption rate produced by injection of delta 9-THC into the fourth ventricle were abolished by elevation of the ambient temperature from 22 to 32 degrees C. A pretreatment that consisted of subcutaneous injections of delta 9-THC (20 mg/kg) given once daily for three days produced tolerance to the hypothermic effect of the drug when injected on day 4 either into the fourth ventricle (10 microgram) or into a lateral tail vein (2.0 mg/kg). The results suggest that delta 9-THC acts centrally to alter thermoregulation in mice not only when it is injected directly into the hypothalamus or cerebral ventricles but also when it is given intravenously. After intraventricular or intravenous administration the drug may act at extrahypothalamic as well as at hypothalamic sites. The data also support the hypothesis that in mice, tolerance to the hypothermic effect of A9-THC is pharmacodynamic and does not depend on changes in metabolism or distribution of the drug.

Thermoregulatory effects of N6-2'-Q-dibutyryl adenosine 3',5'-monophosphate in the restrained mouse

1 The N6-2-O-dibutyryl derivative of adenosine 3',5'-monophosphate (db cyclic AMP) has been micro-injected into the third cerebral ventricle of the unanaesthetized, restrained mouse and the effects on body temperature and thermoregulatory activities observed. 2 Db cyclic AMP (4, 16 and 32 micrograms) injected intracerebroventricularly produced hypothermia when compared with temperature responses to sodium n-butyrate (6.8 micrograms). 3 Hypothermia induced by db cyclic AMP in mice was associated with a fall in oxygen consumption together with behavioural and autonomic heat loss activities but not cutaneous vasodilatation. The effects on rectal temperature and oxygen consumption were dose-dependent. 4 The falls in rectal temperature and oxygen consumption induced by db cyclic AMP (4 micrograms) were decreased by elevation of the environmental temperature from 22 to 32 degrees C and abolished at 36 degrees C. 5 It is concluded db cyclic AMP may inhibit central events mediating the rise in metabolic heat production in mice upon exposure to cold environments.

Effects of delta 9-tetrahydrocannabinol, 2.4-dinitrophenol and pentolinium tartrate on behavioural thermoregulation in mice

1 A new apparatus in which mice are allowed to shuttle between the warm and cool parts of a continuous oval tunnel has been designed for the measurement of drug effects on behavioural thermoregulation.2 The length of time that untreated mice spent in the warmer part of the apparatus (tunnel wall temperature 38 degrees C) was found to be inversely related to the temperature of the cooler part (wall temperature 18 degrees , 24 degrees or 30 degrees C).3 Mice treated with 2,4-dinitrophenol at a dose known to be hyperthermic at an ambient temperature of 32 degrees C (20 mg/kg s.c.) spent an increased length of time in the cooler part of the apparatus (wall temperature 18 degrees C) and did not exhibit any change in rectal temperature.4 Mice treated with pentolinium tartrate at a dose known to be hypothermic at room temperature (5.0 mg/kg i.v.) spent a decreased length of time in the cooler part of the apparatus (wall temperature 24 degrees C) and did not exhibit any change in rectal temperature.5 It is concluded from the above results that the apparatus can be used to measure drug effects on behavioural thermoregulation.6 In experiments of 30 min duration, mice treated with Delta(9)-tetrahydrocannabinol (Delta(9)-THC) at doses known to be hypothermic and to lower oxygen consumption at room temperature (20 mg/kg i.p. or 2.0 mg/kg i.v.) spent a longer time in the warmer part of the apparatus between 15 and 30 min after injection. Rectal temperatures measured 30 min after injection were only slightly less than those of control mice. In these experiments the wall temperature of the cool tunnel was 24 degrees C.7 In experiments of 15 min duration, mice treated with Delta(9)-THC (20 mg/kg) and then placed in the apparatus spent more time in the cooler part of the apparatus (wall temperature 24 degrees C) and exhibited a large fall in rectal temperature.8 It is concluded that immediately after injection of Delta(9)-THC the mice do not attempt to oppose drug-induced falls in deep body temperature by moving into a warm environment and that only later do the animals demonstrate a preference for a warm environment.

Effects of delta9-tetrahydrocannabinol on the rates of oxygen consumption of mice

1. Experiments with untreated mice confirmed that at ambient temperatures below 30 degrees C, the oxygen consumption rate of mice normally kept at about 23 degrees C varies inversely with ambient temperature. 2. At given ambient temperatures in the range 20 to 31 degrees C the oxygen consumption rate was 32 to 43% greater for restrained than for unrestrained mice. 3. Hypothermia induced in restrained mice by delta9-tetrahydrocannabinol (delta9-THC) (1.0 to 4.0 mg/kg i.v.) was accompanied by marked falls in the rate of oxygen consumption. The size of these falls parallelled the degree of hypothermia and increased both with increases in dose and with decreases in the ambient temperature. The oxygen consumption rates of unrestrained mice were also lowered by hypothermic doses (10 to 40 mg/kg i.p.) of delta9-THC. 4. The maximum falls in oxygen consumption rate occurred at earlier times after drug administration than the maximum falls in rectal temperature. 5. At none of the ambient temperatures studied did the oxygen consumption rates of delta9-THC-treated mice fall significantly below the basal levels (59 +/- 3 ml 25 g-1 h-1) of unrestrained, resting mice at 30 degrees C. 6. The hypothesis that reduced rates of heat production contribute significantly towards the hypothermia induced by delta9-THC in our experiments is discussed. The possibility that biological processes responsible for increased heat production in response to cold are more sensitive to delta9-THC than those processes governing basal rates of heat production at thermally neutral environmental temperature is also raised.

Effects of delta9-tetrahydrocannabinol and cannabidiol on a Mg2+-ATPase of synaptic vesicles prepared from rat cerebral cortex

1. delta9-Tetrahydrocannabinol and cannabidiol both exhibited a concentration-related inhibition of Mg2+-ATPase of vesicles prepared from synaptosomes isolated from rat cerebral cortex. Cannabidiol was about 3 times more potent than tetrahydrocannabinol. 2. These results were similar to those obtained previously using drugs with well established anticonvulsant activity. 3. Tetrahydrocannabinol at a sub-inhibitory concentration (1 micronM) increased the activity of the Mg2+-ATPase relative to values obtained with vehicle controls.