Pre-treatment of BALB/c mice with a centrally acting serotonin antagonist (cyproheptadine) reduces mortality from Boophone disticha poisoning.

INTRODUCTION: Crude extracts of Boophone disticha are used in Southern African traditional medical practice for the management of various illnesses and conditions and have also been abused for their claimed euphoric and hallucinogenic effects. Unfortunately, ingestion of Boophone disticha has resulted in toxicity and death. The results of a recent acute toxicity study in a rat model insinuated that central nervous system (CNS) serotonin overdrive could be the cause of toxicity in B. disticha poisoning. The present work sought to test that hypothesis by investigating whether pre-treatment of B. disticha poisoned BALB/c mice with the CNS acting serotonin antagonist, cyproheptadine, has a dose-dependent protective effect on toxicity and mortality. METHODS: A hydroethanolic extract of B. disticha was used in all the experiments. Five groups each with 10 animals were constituted as follows; a negative control group (received 10 ml/kg Normal Saline), a positive control group (received 375 mg/kg of the B. disticha extract), and three test groups each receiving 10 mg/kg, 15 mg/kg and 20 mg/kg cyproheptadine intraperitoneally 15 minutes before oral gavage administration of 375 mg/kg B. disticha extract respectively. The Functional Observational Battery was used to evaluate neurobehavioral and physiological changes resulting from toxicity of the plant extract. The mice were then placed in an open field for another five minutes and the number of rearings and border crossings were counted and recorded. Gait abnormalities, involuntary motor movements, mobility, arousal and stereotypical behavior were also scored according to predefined criteria. All open field investigations were recorded electronically using a LABTEC Webcam(®) and results were later analysed and recorded by one of the group members. All results were entered on data collection forms. Time to death (survival time) was considered as the time period from dosage with Boophone disticha to time of death. The study follow up period was 7 days and those mice that were alive at the end of the 7 day follow-up period were considered as having survived the poisoning episode. The Kaplan Meier plot and Log-rank test were used to compare differences in mortality and median time to death for mice in the 5 treatment groups. RESULTS: We found that cyproheptadine pre-treatment led to a dose-dependent decrease in mortality from 80% in the group not pre-treated with cyproheptadine, to 30% in the 15 and 20 mg/kg cyproheptadine pre-treated groups (n = 10 per group, p < 0.05). There was also a dose-dependent increase in median survival times amongst the groups (p < 0.0001). Pre-treatment with cyproheptadine also resulted in a decrease of other toxic symptoms associated with Boophone disticha. CONCLUSIONS: We conclude that cyproheptadine has a dose-dependent protective effect on mortality and toxicity produced by exposure to Boophone disticha in our mouse model of toxicity.

Does olanzapine inhibit the psychomimetic effects of Δ9-tetrahydrocannabinol?

Δ9-Tetrahydrocannabinol (THC) produces transient psychomimetic effects in healthy volunteers, constituting a pharmacological model for psychosis. The dopaminergic antagonist haloperidol has previously been shown to reduce these effects. This placebo-controlled, cross-over study in 49 healthy, male, mild cannabis users aimed to further explore this model by examining the effect of a single oral dose of olanzapine (with dopaminergic, serotonergic, adrenergic, muscarinergic and histaminergic properties) or two oral doses of diphenhydramine (histamine antagonist) on the effects of intrapulmonarily administered THC. Transient psychomimetic symptoms were seen after THC administration, as measured on the positive and negative syndrome scale (20.6% increase on positive subscale, p<0.001) and the visual analogue scale for psychedelic effects (increase of 10.7 mm on feeling high). Following the combination of THC and olanzapine, the positive subscale increased by only 13.7% and feeling high by only 8.7 mm. This reduction of THC effects on the positive subscale failed to reach statistical significance (p=0.066). However, one-third of the subjects did not show an increase in psychomimetic symptoms after THC alone. Within responders, olanzapine reduced the effects of THC on the positive subscale (p=0.005). Other outcome measures included pharmacokinetics, eye movements, postural stability, pupil/iris ratio, and serum concentrations of cortisol and prolactin.

The neuronal selective nitric oxide synthase inhibitor, Nomega-propyl-L-arginine, blocks the effects of phencyclidine on prepulse inhibition and locomotor activity in mice.

Phencyclidine has frequently been used to model schizophrenia in animals. In the present study, the ability of the neuronal selective nitric oxide synthase (NOS) inhibitor, Nomega-propyl-L-arginine, to block the behavioural effects of phencyclidine in mice was investigated. N(omega)-propyl-L-arginine (20 mg/kg) was found to block both phencyclidine (4 mg/kg)-induced disruption of prepulse inhibition and phencyclidine-induced stimulation of locomotor activity in the mice tested. It is concluded that the NOS-sensitive behavioural effects of phencyclidine in rodents is dependent on neuronal NOS and that NO may play a role in the psychotomimetic effects of phencyclidine.

The nitric oxide synthase inhibitor, L-NAME, block phencyclidine-induced disruption of prepulse inhibition in mice.

RATIONALE: Schizophrenia is a major public health problem that affects approximately 1% of the population worldwide. Schizophrenia-like syndromes can be induced in humans by phencyclidine (PCP), a drug with marked psychomimetic properties. Recent studies show that the behavioural and biochemical effects of PCP in rats are blocked by nitric oxide synthase (NOS) inhibitors, suggesting that NO plays an important role in the pharmacological effects of PCP. OBJECTIVE: The aim of this study was to investigate if PCP-induced disruption of prepulse inhibition of acoustic startle could be blocked by the NOS inhibitor, L-NAME, in mice. RESULTS: The present study shows that PCP readily disrupts prepulse inhibition in mice normally without affecting pulse-alone trials. Furthermore, L-NAME blocked the PCP-induced disruption of prepulse inhibition in a dose-related manner. CONCLUSIONS: The PCP-induced disruption of prepulse inhibition and the ability of L-NAME to block this effect in both rats and mice suggest that this is a general and not a species-specific effect. The results of the present study further suggest that PCP exerts at least some of its actions in the central nervous system by a NO-dependent mechanism.

The adenosine A2A agonist CGS 21680 reverses the reduction in prepulse inhibition of the acoustic startle response induced by phencyclidine, but not by apomorphine and amphetamine.

Systemic administration of the selective adenosine A2A agonist CGS 21680, at the highest dose tested (0.5 mg/kg), selectively reversed the reduction in prepulse inhibition (PPI) of the acoustic startle response induced by the NMDA antagonist phencyclidine (PCP), but not by the dopaminergic agonists apomorphine and amphetamine. CGS 21680 by itself was without effect on PPI, but did reduce the amplitude of the startle response. PCP also reduced startle amplitude, but there was no additive or synergistic effect between PCP and CGS 21680 on the startle response. CGS 21680 (0.5 mg/kg) blocked the locomotor activating effect of amphetamine, but this may have been secondary to a reduction in spontaneous locomotion induced by this compound. Taken together, these results indicate that stimulation of adenosine A2A receptors produce no consequence on dopamine agonist-induced disruption in PPI, but regulate the inhibitory effect of NMDA receptor blockade on PPI. This finding raises the possibility that adenosine A2A agonists possess antipsychotic-like properties.