G. B. Chesher

Physical dependence on physiologically released endogenous opiates

Mice which had been submitted to a chronic schedule of warm water swimming exhibited a naloxone precipitated withdrawal behaviour which was remarkably similar to that produced in mice following chronic morphine treatment. These results are consistent with the activation of endogenous opiates during swim stress in mice and present the possibility that opiate receptors are activated in a manner analogous to the repeated application of exogenous opiates, producing both tolerance and withdrawal-like behaviour.

The correlation between swim-stress induced antinociception and [3H] leu-enkephalin binding to brain homogenates in mice

Mice which had been made to swim for 3 minutes showed a tail flick latency which was significantly longer than that of unswum controls. The [3H] leu-enkephalin [LE] binding to brain homogenates from swum mice was significantly reduced when compared with that form unswum controls. Scatchard analysis revealed that the reduction in binding occurred at the LE low affinity site. However, when homogenates were allowed a preincubation period of 20 min at 37 degree C, the difference in LE binding between swum and unswum mice was no longer apparent. These data are interpreted to suggest that the reduced LE binding may be due to the occupation of a proportion of the opiate receptor population by an endogenous ligand. A correlation between the duration of the swim induced antinociceptive response and the changes in LE binding is described which although non-significant, is consistent with the interpretation for the involvement of endogenous opiates in the observed increases in tail flick latency.

α-Noradrenergic modulation of hypothalamic self-stimulation: Studies employing clonidine, 1-phenylephrine and α-methyl-p-tyrosine

Abstract An α-noradrenergic substrate of rewarding intracranial stimulation (ICS) has been hypothesized based on the observation that the α-antagonist phentolamine produced an inhibition of self-stimulation. The present experiment investigated the effects on hypothalamic self-stimulation of the alpha agonist clonidine in normal and in catecholamine-depleted rats. Using a shuttle-box technique that provides a rate-independent index of the rewarding and aversive components of ICS, it was demonstrated that clonidine produces a dose-dependent inhibition of reward that is clearly dissociable from any non-specific effects of the drug. The ineffectiveness of the peripheral α-agonist 1-phenylephrine indicates that the inhibition of reward produced by clonidine is mediated centrally. Clonidine and the catecholamine synthesis inhibitor α-methyl-p-tyrosine act together in a synergistic manner to greatly increase the magnitude and prolong the duration of the inhibition of reward while leaving the aversive component unaffected. These data are interpreted as supporting an α-noradrenergic basis of ICS reward while indicating that the aversive component of ICS is essentially independent of noradrenergic transmission.

An analysis of some effects of ethanol on performance in a passive avoidance task.

In a one-trial step-through passive avoidance task, pretraining administration of ethanol was shown to decrease the latencies to step through at both training (day 1) and testing (day 2) for both rats and mice. A detailed analysis of these effects showed that they differed from those reported previously by others. The mechanisms underlying these effects of ethanol were also examined. The decreased day 1 latency to step through seen in rats may have been caused by an ethanol-induced hypermotility. However, ethanol did not increase the locomotor activity of mice, although it also reduced the day 1 latency to step through of this species. In addition, it was found that the ethanol-induced impairment of passive avoidance responding (i.e. the decreased day 2 latency to step through) was not state-dependent and that it was unlikely that it could be explained by a drug-induced impairment of task acquisition, long-term memory formation or memory recall. It also seemed unlikely that the impairment could be explained by an ethanol-induced decrease in shock sensitivity. Other mechanisms which may be involved are discussed.

Tolerance and cross tolerance with morphine resulting from physiological release of endogenous opiates

Mice which had been exposed to a chronic schedule of warm water swimming showed the development of a significant tolerance to the antinociceptive response (tail-flick latency) and a significant, two-fold increase in the ED50 of morphine (tail-flick latency and abdominal constriction response). These results suggest the involvement of endogenous opiates during swim stress in mice and are consistent with the hypothesis that during chronic stress the opiate receptors are activated in a manner analogous to the repeated application of exogenous opiates producing tolerance, morphine cross tolerance and (as previously reported) withdrawal-like behaviour.

Release of adrenergic transmitter from terminal nerve plexus in artery.

Studies of the release of the adrenergic transmitter in the rabbit pulmonary artery have been carried out in vitro. At a stimulation frequency of 10 per second, the release was 52.9 pg per gram wet weight per pulse. The mean number of nodes or varicosities per gram wet weight of artery was 9.3×107. If 80% of the released transmitter is taken up by tissues in the artery wall, these values correspond to the average release of approximately 400 molecules ofl-norepinephrine per node per pulse. The transmitter concentrations in the region of the muscle in the outermost lamina of the vessel during sympathetic activity are discussed in relation to the spatial dimensions of the neuroeffector cleft. The release of the total contents of a vesicle on the average every 7 or 8 pulses from each node is consistent with these requirements.

The effect of (-) ? 9-tetrahydrocannabinol, alone and in combination with ethanol, on human performance

Twenty five volunteers received (-) Δ9-tetrahydrocannabinol (THC) (320 μg/kg) or placebo (both orally, T0), and, 60 min later, they consumed an ethanolic beverage (0.54 g/kg) or placebo. The effects of this medication were measured at T1 (100 min after THC ingestion), T2 (160 min), T3 (220 min) and T4 (280 min) using a battery of cognitive, perceptual and motor function tests. Factorial analysis indicated that the test procedures could be adequately expressed by four rotated factors: a reaction speed factor (I′), a cognitive factor (II′), a standing steadiness factor (III′) and a psychomotor coordination factor (IV′), The first principal component (I) was used as a measure of general performance across the whole test battery.Both THC and ethanol produced significant decrements in the general performance factor. Ethanol produced significant decrements in standing steadiness and psychomotor coordination, while THC caused a significant deterioration in performance on all the four rotated factors. In all cases the peak effect of ethanol occurred at T1 and by T4 the effect had worn off. The performance decrements induced by THC were slower in onset and lasted longer than those induced by ethanol. In general, the peak effect of THC occurred at T1 and T2. There was no evidence of any interaction between THC and ethanol, and the effects of a combination of THC and ethanol were no more than additive. THC (but not ethanol) produced a significant rise in pulse rate. Prior administration of THC did not significantly affect the blood ethanol levels obtained. The subjects were able to identify correctly which of the treatments they had received.

The effects of orally administered Δ9-tetrahydrocannabinol in man on mood and performance measures : a dose-response study

Abstract A dose-response study of the effect of orally administered Δ9-tetrahydrocannabinol (THC) on human mood and skills performance was conducted. Using five dose levels of THC (0, 5, 10, 15, 20 mg) with 16 volunteers per dosage group, mood and performance measures were recorded at five testing occasions, one before and four after drug administration. The slope of the linear regression of performance on the test battery was significant for up to 200 minutes after dosage. That is to say, oral THC, at the doses used, produced significant dose-dependent impairment of performance for a period in excess of three hours. A similar time course for the effect of THC on the subjective assessment of intoxication (‘stone’) suggested a correlation between drug-induced impairment skills and the effects on mood.

The effect of cannabidiol, alone and in combination with ethanol, on human performance

Fifteen volunteers received cannabidiol (CBD) (320 μg/kg) or placebo (both orally, T0), and 60 min later they consumed an ethanolic beverage (0.54 g/kg) or placebo. The effects were measured at T1 (100 min after CBD ingestion), T2 (160 min) and T3 (220 min) using cognitive, perceptual and motor function tests. Factorial analysis indicated that test procedures could be adequately expressed by three rotated factors: A reaction speed factor (I), a standing steadiness factor (II) and a psychomotor coordination/cognitive factor (III). Ethanol produced a significant decrement in factor III. There was no demonstrable effect of CBD, either alone or in combination with ethanol. Neither CBD nor ethanol produced any significant effect on pulse rate. Prior administration of CBD did not significantly affect the blood ethanol levels. Whilst the subjects were able to identify correctly when they were given ethanol, they did not report any subjective effects of CBD.

Interaction of Δ9-tetrahydrocannabinol and cannabidiol with phenobarbitone in protecting mice from electrically induced convulsions

In a previous study (Chesher & Jackson, 1974) we reported that the protection against electrically-induced seizures afforded mice by phenytoin, was potentiated significantly by Ag-tetrahydrocannabinol (THC) and cannabidiol (CBD). In contrast, these cannabinoids failed to alter the effect of phenobarbitone on the convulsive threshold to leptazol induced seizures. Although TMC itself showed a weak anticonvulsant activity against electrically induced seizures, it failed to affect the convulsive threshold to leptazol. These findings suggested that the interaction between the cannabinoids and phenytoin possibly involved activity in the central nervous system rather than a metabolic interaction. This hypothesis is supported by the results of the present study which reports the potentiation by the cannabinoids of the effect of phenobarbitone on electrically-induced seizures. Random bred male mice (QS strain, 18-30 g) were used and allowed free access to food and water up to the time of the experiment. Maximum electroshock seizures (MES) were induced using a current of 50 mA, 50 Hz and 0.3 s duration applied by corneal electrodes moistened with 0.9 % saline (Swinyard, 1949; Swinyard, Brown & Goodman, 1952). Two endpoints were recorded; the abolition of the hind limb extensor component of the seizure was taken to represent protection and, in those animals where hind limb extension occurred, its duration was recorded by means of a stop-watch. Cannabinoids were prepared in a suspension in propylene glycol and Lissapol-Dispersol (Whittle, 1964) as described previously (Chesher, Dahl & others, 1973) and administered by gavage (1 ml100 g-1 body wt) 1 h before phenobarbitone (i.p.) and 2 h before MES. The data were analysed by probit analysis. The results (Table 1) show that THC (50 mg kg-l) significantly potentiated the protection afforded mice by phenobarbitone when determined both by protection from seizures and by the shortening of the duration of hind limb extension. CBD (50 mg kg-l) was much less active and whilst it significantly reduced the ED50 of phenobarbitone when assessed as protection from convulsions, it produced no significant change when effectiveness was assessed by the duration of hind limb extension.