Dissociation of learning in marihuana tolerant rats

Creation and first 20 years of the society for the stimulus properties of drugs (SSPD)

Clinical observations and novels in the 19th century recognized that memory of some events can be retrieved only under the influence of the same drug condition that was present during the event. This dissociative effect of drugs probably reflects the same drug effects that were later called the discriminative stimulus effects of drugs. The Society for Stimulus Properties of Drugs (SSPD) was founded in 1978 as a forum for communications and periodic meetings on this drug effect. During its early years many of its members were psychologists, but subsequent to that time the most frequent research application has been for the pharmacological purpose of identifying new drugs that have the same discriminative stimulus attributes as a prototype training drug. The majority of members have been in the United States, but several major international meetings have been in Europe. The methods used by the society's members involve both neuropharmacological and psychological processes, allowing them to make unique contributions to the study of both mind and brain.

Reversible effects of acute and long-term administration of delta-9-tetrahydrocannabinol (THC) on memory in the rat

A study was designed to develop a measure of both acute and chronic effects of THC administration on memory in the rat. Errors in an 8-arm radial maze, before and after two delay intervals (5 s and 1 h, introduced between the fourth and the fifth arm choice), constituted the principal dependent measures. The first experiment involved testing the animals shortly after administration of 1.25 mg/kg THC. The drug did not affect performance in the pre-delay tests, although a significant effect was observed after the 5-s delay but not after 1-h delay. In the second experiment, 5 mg/kg THC or saline were administered 6 days/week for 90 days. Testing was conducted 18 h after each drug administration. During chronic administration the pre-delay performance did not differ between groups but the post-delay performance of the THC group deteriorated in a gradual manner, relative to their controls, in both the 5-s and 1-h delay conditions. After discontinuation of drug administration, the differences between groups reversed only after 30 days. The results provided evidence that both acute and chronic administration of THC affected working-memory in the radial arm maze test, although it did not interfere with the general cues of the task (reference memory). Chronic drug effects on memory were reversible after prolonged abstinence. Thus, the 8-arm radial maze task proved to be a useful measure of THC effects on memory and could be further used to investigate more thoroughly the mechanisms involved in such drug effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of tolerance to kava in mice

1. The development of tolerance to the aqueous extract of kava, and to the lipid soluble extract (kava resin) was tested in mice. 2. Tolerance to the unknown pharmacologically active ingredient(s) developed very rapidly, given parenterally, in the aqueous extract. A minimally effective daily dose (50 mg/kg) of the aqueous extract for 3 days was sufficient to produce tolerance to a test dose of 150 mg/kg, which is close to the ED50. As tolerance was evident at the first test period it can be assumed to be physiological tolerance. 3. Kava resin decreased spontaneous motility and caused a loss of muscle control. A minimally effective daily dose of kava resin (100 mg/kg) did not produce tolerance to the above effects of a weekly test dose of kava resin (166 mg/kg) within 7 weeks. In a further experiment the dose was raised to 150 mg/kg twice daily and this schedule caused partial tolerance to occur within 3 weeks, but very little further tolerance developed over the ensuing 2-week period. 4. To try to induce learned (behaviourally acquired) tolerance a dose of 166 mg/kg kava resin was injected daily and animals were tested each day while under the influence of the drug. However, even under these conditions, there was no tolerance evident within 3 weeks, when the experiment was terminated. 5. It appears difficult to induce the development of physiological or learned tolerance to kava resin in mice.

Hashish extract impairs retention of defeat-induced submissive behavior in mice

The effects of hashish extract on adaptive behavior of male mice were studied in a paradigm which allows the investigation of learning mechanisms in a social context. Mice of the C3H strain, which were not submissive in a confrontation with a nonaggressive DBA mouse on day 1, were defeated on day 2 over 3 min by aggressive, isolated DBA mice, and showed conditioned submissive behavior upon mere contact with a nonaggressive DBA mouse on day 3. A hashish extract containing 38.6-39.4% delta 9-tetrahydrocannabinol (delta 9-THC), 11.6-12.0% cannabinol and 47.7-48.5% cannabidiol was administered orally in all experiments. Hashish extract given 90 min before defeat on day 2, in dosages corresponding to 1, 5, and 10 mg delta 9-THC/kg, impaired retention of defensive upright, defensive sideways and immobility on day 3 (experiment 1). Experiment 2 showed that the drug (5, and 10 mg delta 9-THC/kg) had no antinociceptive potency in mice and did not modify defeat-induced analgesia. Experiment 3, with drug (5 mg delta 9-THC/kg) or solvent administration on day 2 and day 3, showed that the retention deficit was neither due to state-dependent learning, nor to impaired retrieval. It is suggested that hashish extract administered before learning may interfere with memory processing.

Acute tolerance to the discriminative stimulus properties of morphine

Two pigeons were trained to discriminate intramuscular injections of 1.0 mg/kg morphine from water by presenting food after keypeck responses on one key when morphine was administered and after responses on a second key when water was administered. Following training, close to 100% of responses occurred on the appropriate key following administration of 1.0 mg/kg morphine or water. Morphine (0.1-5.6 mg/kg) produced dose-dependent increases in the percentage of morphine-appropriate responses (discriminative stimulus properties) and decreases in the rate of responding. A shift to the right of the morphine dose-effect curve for the discriminative stimulus properties of morphine resulted from a single injection of morphine (10.0 mg/kg) 24 hrs prior to testing (i.e., acute tolerance) but not from a single injection of pentobarbital (17.0 mg/kg). Tolerance to the discriminative stimulus properties of morphine was reversible within five days of the single injection. Tolerance did not develop to the effects of morphine on response rate. Naloxone antagonized both the discriminative stimulus properties and the response rate-decreasing effects of morphine. Thus, a single administration of morphine can alter morphine discriminability without affecting other aspects of behavior.

Discriminative properties of pentobarbital after repeated noncontingent exposure in gerbils

Two groups of gerbils were pretreated with pentobarbital (P-barb.) (10 and 20 mg/kg) for 20 days before being subjected to drug discrimination training in a (T-shaped shock-escape maze. The rapidity with which these gerbils acquired the discrimination was compared to that of gerbils that were drug naive until beginning the P-barb.-discrimination training. The acquisition rates of the respective groups did not differ substantially within each dose level (10 and 20 mg/kg), although open-field activity (primarily the rearing scores) differentiated the P-barb.- and vehicle-pretreated animals at both dose levels. The peak effect in rectal temperature, however, was not markedly different after the first and 20th drug exposures, although the temperature effects leveled off earlier during the second recording session. In conclusion, certain parameters (open-field activity) may be changed as a consequence of repeated administrations of P-barb. without a significant parallel loss of the cue or stimulus properties of the drug.

Tolerance to the effects of delta9-THC on shuttle-box performance and body temperature

Two groups of rats were trained in a shuttle-box and received delta9-tetrahydrocannabinol (delta9-THC), either before or after being tested. The drug-before group showed tolerance--within 3-6 sessions--to the response-inhibiting effect of THC. The drug-after animals appeared also to be tolerant when they received delta9-THC before being tested. It is concluded that the tolerance to this effect probably is not learned, but has a physiological base. This is corroborated by the finding that during the same study all the animals developed tolerance to the hypothermic effect of delta9-THC.

Aspects of tolerance to and dependence on cannabis

Tolerance at all levels of complexity in the brain involves "learning" in the sense of the acquisition of compensatory adaptations to the consequences of the presence of a drug-produced disturbance in function. Depending on the function, species, and dose of cannabis, "tissue tolerance," behaviorally augmented (to provide the presence of the disturbed function) or not, develops at different rates or not all (e.g., to impairment of the logical sequence of thoughts, to which no tolerance has yet been demonstrated). "Dispositional tolerance" (increased rate of metabolism of delta 9-THC due to enzyme induction) may play a role in the development of tolerance or "reverse tolerance" to cannabis in man. There is evidence that for the label "high," placebo effects may account for the "reverse tolerance" seen in experienced users on smoking (but not on ingestion of delta 9-THC or placebo) along with evidence of residual tolerance to other not-so-labeled effects of the drug. Dependence on cannabis, in the sense of abstinence phenomena on abrupt withdrawal of delta 9-THC, has been demonstrated in monkeys made tolerant to delta 9-THC given four times daily for about 1 month. In man, physiologic marijuana abstinence signs have not been demonstrated, but behavioral (and some physiologic) abstinence phenomena have been reported in heavy users of hashish or ganja. The between-dose hyperirritability and dysphoria reported to occur in experimental studies on chronic marijuana intoxication may actually be early and short-lived abstinence changes. In the West, where marijuana with relatively low delta 9-THC content is widely smoked, dependence in the sense of drug-seeking behavior appears to be less a function of any pharmacologic reinforcing properties the drug may have than of secondary (conditioned) reinforcement derived from the social milieu in which the marijuana is smoked. In cultures where marijuana of higher delta 9-THC content, hashish, or ganja is used, pharmacologic reinforcement (through suppression of abstinence changes) may play a greater role in maintaining drug-seeking behavior.

Role of experience in acquisition and loss of tolerance to the effect of delta-9-THC on spaced responding

Albino rats were given extensive training in spaced responding, using a DRL 30 sec schedule of food reinforcement (only lever presses more than 30 sec apart were reinforced). All rats then went 12 days without behavioral testing. During this period half the rats received daily intragastric doses of delta-9-tetrahydrocannabinol (THC) and the rest equal volumes of the THC vehicle. On day 13, some rats received THC 3 hr before behavioral testing while others received only vehicle. The former showed a sharp increase in lever press rate over baseline levels, but the vehicle control rats were unaffected. The rats with 12 prior THC doses were no less affected than those with no previous drug history. Continued testing resulted in recovery of baseline performance within 5 sessions, again with no effect of previous drug history. Similar results were obtained with doses of 4 mg/kg and 16 mg/kg, though the drug's effects were more pronounced at the higher dose. These results demonstrate that performance in the drug state can be a far more important determinant of tolerance than mere exposure to THC. Drug administration was then suspended for 1 week. Rats that had become tolerant to 4 mg/kg THC were then redivided into 3 new groups. One group received daily doses of vehicle and DRL sessions, a second received DRL sessions without vehicle, and 1 group received neither vehicle nor DRL sessions for this week. Subsequent DRL testing after THC administration showed that only the groups receiving DRL sessions in the intervening week lost their previously acquired tolerance. Experience thus appears to play an important role in loss of tolerance to THC as well as in acquisition of tolerance.

The effect of delta 9-tetrahydrocannabinol and LSD on the acquisition of an active avoidance response in the rat

The course of active avoidance learning of rats in a symmetrical Y-maze under the influence of 1, 3, and 9 mg/kg of delta 9-THC i.p., and 5, 20, and mug/kg of LSD was investigated. Delta-THC in a dosage of 1 mg/kg had no effect on avoidance learning. Three to a lesser extent 9 mg/kg produced more rapid learning with a significantly better performance. Learning under delta 9-THC proved to be state-dependent. The withdrawal of delta 9-THC caused a decrease in the avoidance rate, which was dependent on the dosage. Upon renewal of the THC doses, the animals reattained their earlier preformance. In the course of the experiment there was rapid tolerance development, especially of the sedative properties of THC. LSD retarded the rate of acquisition of the active avoidance response. Whereas the control animals displayed over 80% successful active avoidance from the 14th session onwards, this was achieved by the LSD groups only after the 20th session. However, in contrast to the control group the LSD animals were able to increase their avoidance rate to over 90%, and this was maintained to the end of the experiment (a total of 24 sessions with LSD). The sudden withdrawal of LSD produced a fall in avoidance rate, which was dependent on the pervious training dosage; as with delta 9-THC state-dependent learning can also be assumed for LSD.

Delta 9-Tetrahydrocannabinol, ethanol, and amphetamine as discriminative stimuli-generalization tests with other drugs

Three groups of rats (A, B, C) were trained in a T-maze discriminate between drug-and control solution-induced internal discriminative stimuli. The drugs used to induce discriminative stimuli were: delta 9-THC, 5.0 mg/kg (Group A); ethanol, 1.2 g/kg (Group B), and amphetamine, 1.0 mg/kg(Group C). After discrimination acquisition several drugs were tested for generalization in each group. Group A was tested with delta 8-THC, CBD, CBN, ethanol, pentobarbital,chlorpromazine, amphetamine, and apomorphine; only delta8-THC and CBN induced delta9-THC-like responses. Group B was tested with delta 9-THC, delta 8-THC, CBD, CBN, pentobarbital, and amphetamine; pentobarbital induced ethanol-like response. Group C was tested with delta 9-THC, apomorphine, and ethanol; delta 9-THC and apomorphine elicited amphetamine-like responses.

A test of state dependency effects in marihuana intoxication for the learning of psychomotor tasks

Cannabis cigarettes calibrated to deliver 7 mg delta9-THC were administered to experienced cannabis users and to novices in a 2 x 2 state-dependency learning design using psychomotor tasks. Subjects given four training sessions under marihuana performed no better on the fifth (test) session with the drug than those subjects who had trained in the non-drug condition and were tested in the drug condition. Cannabis-induced impairment in the performance of these tasks is such that prior training in the non-drug condition appears to confer no advantage to the subject. There was no evidence of state-dependency effects in psychomotor performance between drug and non-drug conditions.

Temporal parameters of d-amphetamine as a discriminative stimulus in the rat

Three groups of rats were trained on a two-lever operant discrimination using d-amphetamine (0.8, 1.6 or 2.4 mg/kg) and saline as cues. Reinforcement of responding on one lever was associated with the drug and reinforcement on the other lever was associated with saline. Following acquisition, behavioral control was evaluated during 10-min extinction tests at 0, 15, 30, 60, 90, 120, 180 or 240 min after injection of drug or saline. Onset of the stimulus properties of d-amphetamine occurred within 10 min and maximal effects were attained by 15-30 min post-injection. Drug effects were minimal or absent 2-4 h after administration. The time course for all doses of d-amphetamine was identical when each group was tested iwth its respective training dose. When subjects were tested with doses other than their training dose, the time course of the drug effect varied as a function of training dose, test dose and time after injection.

Comparison of the discriminative stimulus properties of delta9-THC and psilocybin in rats

Male albino rats were trained to respond differentially on the left or right lever in a 2-lever chamber on the basis of which drug had been given intra-peritoneally (IP) 30 min before experimentation. In 1 group 1.9 mg/kg of delta9-THC and control injections (vehicle) served as the discriminative stimuli associated with each lever and in another group the drug stimuli were 1.0 mg/kg of delta9-THC and 1.0 mg/kg of psilocybin. The results confirmed those of other experiments using different procedures; that delta9-THC can acquire discriminative control over responding. The fact that delta9-THC and psilocybin were also found to differentially control lever choice demonstrates that these 2 drugs probably produce discriminably different states in rats.