Effects of cannabidiol and of diphenylhydantoin on the hippocampus and on learning

Cannabidiol as an adjuvant treatment in adults with drug-resistant focal epilepsy

Cannabidiol oil (CBD) has been approved as an anti-seizure medication for the treatment of uncommon types of epilepsy, occurring in children: Dravet syndrome, Lennox-Gastaut syndrome, and Tuberous Sclerosis Complex. There are few publications in relation to use the CBD in adult patients with focal drug-resistant epilepsy. The objective of this study was to evaluate the efficacy, tolerability, safety, and quality of life, of adjuvant treatment with CBD, in adult patients with drug-resistant focal epilepsy for at least 6 months. An open, observational, prospective cohort study was conducted using a before-after design (time series) in adult patients undergoing outpatient follow-up in a public hospital in Buenos Aires, Argentina. From a total of 44 patients, 5% of patients were seizure-free, 32% of patients reduced more than 80% of their seizures and 87% of patients reduced 50% of their monthly seizures. Eleven percent presented a decrease of less than 50% in seizure frequency. The average final dose was 335 mg/d orally administered. Thirty-four percent of patients reported mild adverse events and no patient reported severe adverse effects. At the end of the study, we found in most patients a significant improvement in the quality of life, in all the items evaluated. Adjuvant treatment with CBD in adult patients with drug-resistant focal epilepsy was effective, safe, well tolerated, and associated with a significant improvement in their quality of life.

Fear Memory

Fear memory is the best-studied form of memory. It was thoroughly investigated in the past 60 years mostly using two classical conditioning procedures (contextual fear conditioning and fear conditioning to a tone) and one instrumental procedure (one-trial inhibitory avoidance). Fear memory is formed in the hippocampus (contextual conditioning and inhibitory avoidance), in the basolateral amygdala (inhibitory avoidance), and in the lateral amygdala (conditioning to a tone). The circuitry involves, in addition, the pre- and infralimbic ventromedial prefrontal cortex, the central amygdala subnuclei, and the dentate gyrus. Fear learning models, notably inhibitory avoidance, have also been very useful for the analysis of the biochemical mechanisms of memory consolidation as a whole. These studies have capitalized on in vitro observations on long-term potentiation and other kinds of plasticity. The effect of a very large number of drugs on fear learning has been intensively studied, often as a prelude to the investigation of effects on anxiety. The extinction of fear learning involves to an extent a reversal of the flow of information in the mentioned structures and is used in the therapy of posttraumatic stress disorder and fear memories in general.

Cannabinoid function in learning, memory and plasticity

Marijuana and its psychoactive constituents induce a multitude of effects on brain function. These include deficits in memory formation, but care needs to be exercised since many human studies are flawed by multiple drug abuse, small sample sizes, sample selection and sensitivity of psychological tests for subtle differences. The most robust finding with respect to memory is a deficit in working and short-term memory. This requires intact hippocampus and prefrontal cortex, two brain regions richly expressing CB1 receptors. Animal studies, which enable a more controlled drug regime and more constant behavioural testing, have confirmed human results and suggest, with respect to hippocampus, that exogenous cannabinoid treatment selectively affects encoding processes. This may be different in other brain areas, for instance the amygdala, where a predominant involvement in memory consolidation and forgetting has been firmly established. While cannabinoid receptor agonists impair memory formation, antagonists reverse these deficits or act as memory enhancers. These results are in good agreement with data obtained from electrophysiological recordings, which reveal reduction in neural plasticity following cannabinoid treatment, and increased plasticity following antagonist exposure. The mixed receptor properties of the pharmacological tool, however, make it difficult to define the exact role of any CB1 receptor population in memory processes with any certainty. This makes it all the more important that behavioural studies use selective administration of drugs to specific brain areas, rather than global administration to whole animals. The emerging role of the endogenous cannabinoid system in the hippocampus may be to facilitate the induction of long-term potentiation/the encoding of information. Administration of exogenous selective CB1 agonists may therefore disrupt hippocampus-dependent learning and memory by 'increasing the noise', rather than 'decreasing the signal' at potentiated inputs.

Differential effects of THC- or CBD-rich cannabis extracts on working memory in rats

Cannabinoid receptors in the brain (CB(1)) take part in modulation of learning, and are particularly important for working and short-term memory. Here, we employed a delayed-matching-to-place (DMTP) task in the open-field water maze and examined the effects of cannabis plant extracts rich in either Delta(9)-tetrahydrocannabinol (Delta(9)-THC), or rich in cannabidiol (CBD), on spatial working and short-term memory formation in rats. Delta(9)-THC-rich extracts impaired performance in the memory trial (trial 2) of the DMTP task in a dose-dependent but delay-independent manner. Deficits appeared at doses of 2 or 5 mg/kg (i.p.) at both 30 s and 4 h delays and were similar in severity compared with synthetic Delta(9)-THC. Despite considerable amounts of Delta(9)-THC present, CBD-rich extracts had no effect on spatial working/short-term memory, even at doses of up to 50 mg/kg. When given concomitantly, CBD-rich extracts did not reverse memory deficits of the additional Delta(9)-THC-rich extract. CBD-rich extracts also did not alter Delta(9)-THC-rich extract-induced catalepsy as revealed by the bar test. It appears that spatial working/short-term memory is not sensitive to CBD-rich extracts and that potentiation and antagonism of Delta(9)-THC-induced spatial memory deficits is dependent on the ratio between CBD and Delta(9)-THC.

The effects of phenytoin on instrumental appetitive-to-aversive transfer in rats

Antiepileptic medications are the primary treatment for seizure conditions. Over the past several years, it has become clear that the medications themselves may contribute to the negative cognitive side effects that people with epilepsy often report. In the experiments reported here, the effects of phenytoin treatment have been evaluated in rats performing an instrumental appetitive-to-aversive transfer task. We find that rats treated with phenytoin fail to acquire the avoidance response when transferred from an appetitive to an aversive context. This deficit is not due to any sensory or motor slowing resulting from the drug, nor is it a deficit that is specific to learning in an aversive context. Rather, we suggest that the deficits shown by phenytoin-treated rats in the appetitive-to-aversive transfer reflect a fundamental inability in altering the associations that were formed during the initial appetitive training.

Effects of diphenylhydantoin on behavior maintained by a multiple schedule of food reinforcement

Two white Carneaux pigeons were trained to peck for mixed grain according to a multiple fixed-ratio 50, variable-interval 30-sec schedule of reinforcement. After the rate of responding stabilized, the pigeons were given weekly doses of diphenylhydantoin or an equal volume vehicle Diphenylhydantoin produced a lengthening of the pre-ratio pause and general disintegration of responding during the FR component and a decreased rate of responding in the VI component.

Effects of marihuana cannabinoids on seizure activity in cobalt-epileptic rats

Rats rendered chronically epileptic by bilateral implantation of cobalt into frontal cortices were simultaneously prepared with permanent electrodes for longitudinal recording of the electroencephalogram (EEG) and electromyogram (EMG). Delta-8-tetrahydrocannabinol (delta-8-THC; 10 mg/kg), delta-9-tetrahydrocannabinol (delta-9-THC; 10 mg/kg), cannabidiol (CBD; 60 mg/kg), or polyvinylpyrrolidone (PVP) vehicle (2 ml/kg) was administered IP twice daily from day 7 through 10 after cobalt implantation, at which time generalized seizure activity in non-treated cobalt-epileptic rats was maximal. Relative to PVP-treated controls, CBD did not alter the frequency of appearance of seizures during the course of repeated administration. In contrast, both delta-8-THC and delta-9-THC markedly reduced the incidence of seizures on the first and second days of administration. Interictal spiking during this period, on the other hand, was actually enhanced. On the third and fourth days, tolerance to the effect on seizures was evident, with a return of seizure frequency of THC-treated rats to values not significantly different from those of controls. Unlike the effect on seizures, no tolerance developed to the marked suppression of rapid eye movement (REM) sleep induces by delta-8-THC and delta-9-THC. REM sleep remained reduced in the treated animals during the first 2 days after termination of THC administration. In contrast, REM sleep time was unaffected by repeated administration of CBD. These results suggest that delta-8-THC and delta-9-THC exert their initial anticonvulsant effect by limiting the spread of epileptogenic activity originating from the cobalt focus.

Levonantradol potentiates the anticonvulsant effects of diazepam and valproic acid in the kindling model of epilepsy

The anticonvulsant effects of the cannabinoid derivative levonantradol and its ability to potentiate the anticonvulsant effects of diazepam and valproic acid were studied in rats with previously established amygdala-kindled seizures. Levonantradol administered in doses of 100 to 400 micrograms/kg did not block any components of the motor seizure. However, levonantradol did increase the latency of appearance of fully kindled seizures at the 400 micrograms/kg dose. Administration of diazepam at doses of 1 or 2 mg/kg or valproic acid at doses of 100 or 200 mg/kg produced seizure control as measured by a reduction in motor components of the seizure or a reduction in afterdischarge length or both. The anticonvulsant effects of diazepam and valproic acid were potentiated by administration of 100 microgram/kg levonantradol without apparent increases in sedation. Although the mechanism underlying this potentiation of the antiepileptic effects of valproic acid and diazepam remains unknown, levonantradol may have potential as adjunctive therapy in the treatment of complex partial seizures.

Electrophysiologic properties of the cannabinoids

The effects of the psychoactive cannabinoid delta 9-tetrahydrocannabinol (THC) and the nonpsychoactive cannabinoid cannabidiol (CBD) were investigated comparatively on electrically caused transcallosal cortical evoked responses, electrically induced limbic after discharges, photically evoked cortical afterdischarges, spontaneous cortical focal epileptic potentials, and spinal monosynaptic reflexes. In each system, THC produced central excitation; for example, the drug's responses ranged from enhancement of synaptic transmission to precipitation of frank convulsions. In addition to central nervous system stimulation, THC usually elicited depression; the qualitative character of the effect of the drug was dependent upon the dosage and the test system. In contrast to THC, cannabidiol generated no CNS excitation: it was either depressant or inert in these test systems. The results clearly demonstrate the complexity of the CNS properties of THC and the selectivity of the depressant properties of cannabidiol; moreover, the data illustrate the wide range of neuropharmacologic responses that potentially any cannabinoid can effect.

Antiepileptic potential of cannabidiol analogs

In audiogenic seizure (AGS) susceptible rats, the acute (intraperitoneal and intravenous) dose-response effects of (--)-cannabidiol (CBD) for preventing AGS and for causing rototod neurotoxicity (ROT) were determined. Also, the anti-AGS and ROT effects of 10 CBD analogs, given in intravenous doses equivalent to the AGS-ED50 (15 mg/kg) and ROT-ID50 (31 mg/kg) of CBD, were ascertained. Compared to CBD, (--)-CBD diacetate and (--)-4-(2'-olivetyl)-alpha-pinene were equally effective whereas (--)-CBD monomethyl ether, (--)-CBD dimethyl ether, (--)-3'-acetyl-CBD monoacetate, (+)-4-(2'-olivetyl)-alpha-pinene, (--)-and (+)-4-(6'-olivetyl)-alpha-pinene, (+/-)-AF-11, and olivetol were less effective anticonvulsants. Except for (--)- and (+)-4-(2'-olivetyl)-alpha-pinene and olivetol, all analogs showed less ROT than CBD. Also, CBD and all analogs were not active in tetrahydrocannabinol seizure-susceptible rabbits, the latter a putative model of cannabinoid psychoactivity in humans. These data suggest anticonvulsant requirements of 2 free phenolic hydroxyl groups, exact positioning of the terpinoid moiety in the resorcinol system and correct stereochemistry. Moreover, findings of separation of anticonvulsant from neurotoxic and psychoactive activities, notably with CBD diacetate, suggest that additional structural modifications of CBD may yield novel antiepileptic drugs.

Effects of diphenylhydantoin on spontaneous motor activity

This study examined the effects off moderate, acute doses of diphenylhydantoin on the spontaneous motor activity of 30 rats. A dose of 30 mg/kg of the anticonvulsant drug produced an immediate, although short-lived (about 40 min), suppression of this behavior for albino rats.

Effects of cyclic analogs of GABA on protein synthesis and discrimination learning

Three cyclic analogs of gamma-aminobutyric acid (GABA)-5-ethyl, 5-phenyl, 2-pyrrolidinone (EPP), 5-diphenyl, 2-pyrrolidinone (DPP), and 5-methyl, 5-phenyl, 2-pyrrolidinone (MPP)- were studied in relation to protein synthesis and the latter in relation to discrimination learning. The present study shows that when different groups of rats were injected subcutaneously with 10 mg/kg of EPP or DPP, the protein synthesis in vitro was inhibited 75% in brain mitochondria. MPP at the same doses was the less potent inhibitor of mitochondria protein synthesis. Experiments on discrimination learning show that 10mg/kg of MPP enhance the response decision speed in presence of S(+) (white arm) and S(-) (black arm).

Three main factors in rat shuttle behavior: their pharmacology and sequential entry in operation during a two-way avoidance session

The effects of eserine (0.1 mg/kg), nicotine (0.2 mg/kg), atropine (2 mg/kg), methylatropine (5 mg/kg), clonidine (0.2 mg/kg), phenoxybenzamine (10 mg/kg), apomorphine (0.5 mg/kg), and haloperidol (0.5 mg/kg), i.p., on shuttle responses to a buzzer (SBs) were studied on four different behavioral paradigms in rats: (a) D test: 50 buzzers and 25 shocks at random intervals and in random order; (b) DP test: 50 buzzers paired on all trials with shocks irrespective of the performance of SBs (Pavlovian conditioning); (c) DC test: 50 buzzers followed at a randomly variable interval by shocks unless there was an SB; (d) DPC test: 50 buzzer-shock trials omitting shocks every time there was an SB (two-way avoidance). Shock-induced drive was assumed to equally pervade all four situations; stimulus contiguity ('pairing') was present only in the DP and DPC tests; and the avoidance 'contingency' was present only in the DC and DPC paradigms. An analysis of the distribution of SB performance in control animals over the 10 successive blocks of 5 buzzers of each session revealed that the response level was similar for all tests during the first 2 blocks; that of the DC and DPC groups increased above the level of the other two from the third block on; and from the fifth block on, SB performance was higher in the DPC than in the DC group and in the DP over the D group. At all blocks the sum of SBs obtained in the D test, plus DP-D, plus DC-D, gave a value quite close to that experimentally determined in the DPC group. This was interpreted as showing that during the first 10 buzzers drive was the main (or the only) factor influencing SB performance in all groups; after the third block of 5 buzzers 'contingency' became a factor on its own; and 'pairing' assumed some control over SB behavior only from the fifth block on. Eserine depressed SBs in the D test, starting from the first block of buzzers; its effect was antagonized by atropine and by methylatropine. Clonidine depressed responding in the DP and DPC paradigms, and its effect was blocked by phenoxybenzamine. Nicotine, eserine, and apomorphine increased, and atropine, methylatropine, and haloperidol decreased SB performance in both the DC and the DPC test; the effect of the two former substances could be antagonized by any of the two anticholinergic agents, and haloperidol antagonized that of apomorphine. The possibilities are discussed of: (a) a peripheral cholinergic mechanism which inhibits drive; (b) a similar mechanism which favors operation of the 'contingency' factor; (c) a dopaminergic mechanism in 'contingency'; (d) a central adrenergic inhibitory mechanism in 'pairing'.

Delta 9-tetrahydrocannabinol produced discrimination in pigeons

In an operant situation pigeons learned to peck one response key 90 min after an injection of 0.25mg/kg delta9-tetrahydrocannabinol (delta9-THC) and another key when trained nondrugged. When tested with doses of delta9-THC lwer than the training dose the birds disciminated 0.20 mg/kg of the drug from the nondrugged state but not 0.15 mg/kg or lower doses. The animals were able to discriminate the drug state from the nondrugged 180 min but not 360 min after the injection At a shorter interval (45 min) both drug and nondrug responding appeared. Cannabinol and cannabidiol (4.0 - 8.0 mg/kg) did not elicit any drug responses, nor did pentobarbital, ditran or amphetamine. Tests with LSD resulted in both drug and nondrug responding. When administering noncannabinoid drugs in combination with delta9-THC 0.15 mg/kg the birds responded at the key associated with the drug state, suggesting interactional effects.

Absence of interaction between delta9-tetrahydrocannabinol (delta-THC) and cannabidiol (CBD) in aggression, muscle control and body temperature experiments in mice

In this report we give the results of some experiments on the effects of the hashish constituents delta9-tetrahydrocannabinol (THC) and cannabidiol (CBD) on mice. THC produced a dose dependent depression of aggression in isolated mice and a dose dependent depression of body temperature in group caged mice. The drug did not alter motor co-ordination. CBD showed a small, not significant influence on aggressiveness, and no in fluence on body temoerature and muscle control. The dame experiments were carried out with combinations of THC and CBD in several dosages. In these experiments no interaction between both compounds was seen. This means that there can only be an additive action and not potentiation in the pharmacological sense. It also means that the in vitro inhibition by CBD of the drug metabolizing enzymes, responsible for biotransformation of THC. is not strong enough to result in changed effects of THC in the living animal.