Behavioural and neurochemical comparison of chronic intermittent cathinone, mephedrone and MDMA administration to the rat.

The synthetic cathinone derivative, mephedrone, is a controlled substance across Europe. Its effects have been compared by users to 3,4-methylenedioxymethamphetamine (MDMA), but little data exist on its pharmacological properties. This study compared the behavioural and neurochemical effects of mephedrone with cathinone and MDMA in rats. Young-adult male Lister hooded rats received i.p. cathinone (1 or 4 mg/kg), mephedrone (1, 4 or 10mg/kg) or MDMA (10mg/kg) on two consecutive days weekly for 3 weeks or as a single acute injection (for neurochemical analysis). Locomotor activity (LMA), novel object discrimination (NOD), conditioned emotional response (CER) and prepulse inhibition of the acoustic startle response (PPI) were measured following intermittent drug administration. Dopamine, 5-hydroxytryptamine (5-HT) and their major metabolites were measured in striatum, frontal cortex and hippocampus by high performance liquid chromatography 7 days after intermittent dosing and 2h after acute injection. Cathinone (1, 4 mg/kg), mephedrone (10mg/kg) and MDMA (10mg/kg) induced hyperactivity following the first and sixth injections and sensitization to cathinone and mephedrone occurred with chronic dosing. All drugs impaired NOD and mephedrone (10mg/kg) reduced freezing in response to contextual re-exposure during the CER retention trial. Acute MDMA reduced hippocampal 5-HT and 5-HIAA but the only significant effect on dopamine, 5-HT and their metabolites following chronic dosing was altered hippocampal 3,4-dihydroxyphenylacetic acid (DOPAC), following mephedrone (4, 10mg/kg) and MDMA. At the doses examined, mephedrone, cathinone, and MDMA induced similar effects on behaviour and failed to induce neurotoxic damage when administered intermittently over 3 weeks.

Animal models of stroke: do they have value for discovering neuroprotective agents?

There has been a series of high-profile failures of drugs in clinical trials of acute ischaemic stroke that were designed to meet criteria necessary for drug regulatory approval. This has, again, called into question the value of animal models for identifying effective neuroprotective agents. Here, we review evidence that physiological changes (reperfusion, hyperglycaemia, hypothermia and blood pressure) produce comparable changes in outcome in both animal models and human stroke patients, which indicates that the models should identify clinically effective neuroprotective agents. We suggest that most clinical failures have occurred because compounds were administered differently in animal and clinical studies. We review earlier guidelines on the information that is necessary from preclinical studies before a compound enters clinical trials, and propose modifications to these guidelines.

Pharmacology of ischemia-induced glutamate efflux from rat cerebral cortex in vitro.

Simulated ischemic conditions (hypoxia-hypoglycaemia) in vitro enhanced glutamate efflux from rat cerebrocortical prisms. Here we characterised efflux mechanisms using pharmacological tools. The Na(+) channel blocker TTX (1 microM) did not affect ischemia-induced efflux, while sipatrigine (100 microM), a Na(+)/Ca(2+) channel blocker and omega-conotoxin MVIIC (2 microM), an N/P/Q type Ca(2+) channel blocker, inhibited efflux by fractions of 0.53 and 0.46, respectively (1.00 corresponding to total inhibition). Omission of extracellular Ca(2+) and addition of EGTA (2 mM) inhibited ischemia-induced efflux only during the first 25 min of incubation. A similar result was observed on omission of extracellular Ca(2+) together with addition of La(3+) (10 microM) and Mg(2+) (6 mM). TTX, sipatrigine and La(3+)/Mg(2+) all inhibited control efflux. Ischemia-induced efflux was sensitive to the volume activated anion channel inhibitor NPPB (100 microM) only after the first 25 min of incubation, with the maximal fraction inhibited being 0.54. The glutamate transporter inhibitor D,L-TBOA reduced ischemia-induced efflux throughout a 45-min incubation period, and enhanced efflux from control tissue. D,L-TBOA inhibited efflux at 30 min by a maximum fraction of 0.49, at 50 microM. These data indicate that the early phase of ischemia-induced glutamate efflux is in part Ca(2+) dependent, while the later phase involves volume activated anion currents and both phases involve excitatory amino acid transporters.

In vitro blood-brain barrier permeability and cerebral endothelial cell uptake of the neuroprotective nitrone compound NXY-059 in normoxic, hypoxic and ischemic conditions.

The free radical trapping nitrone compounds alpha-phenyl-N-tert-butylnitrone (PBN), 2-sulfophenyl-N-tert-butylnitrone (S-PBN) and disodium 2,4-disulfophenyl-N-tert-butyl nitrone (NXY-059) are effective neuroprotective agents in experimental models of both transient and permanent focal ischemia. A recent in vivo study suggested that NXY-059 had poor brain uptake in a transient ischemia model. We have now examined its blood-brain barrier permeability and cerebral endothelial uptake during hypoxic and ischemic conditions using an in vitro model of the blood-brain barrier. The in vitro blood-brain barrier permeability and cerebral endothelial uptake of NXY-059 and S-PBN were low during normoxic conditions. In contrast, PBN had very high blood-brain barrier penetration in vitro which confirmed earlier in vivo results. The permeability of [14C]NXY-059 increased 3.5 times after 9 h of hypoxia or 3 h of ischemia. There was, respectively, a 5-fold and more than 10-fold increase, after 6 and 9 h of ischemia. The control molecule [3H]inulin (M(r) approximately 5000) showed a similar increase in permeability under the same experimental conditions indicating a major change in the transport properties of the endothelium. There was a 60% reduction in the ATP levels of astrocytes after 3 h of ischemia and a 90% reduction after 9 h. The reduction in ATP levels in endothelial cells was somewhat lower. The uptake of NXY-059 in cerebral endothelial cells under normoxic, hypoxic or 9 h of ischemic conditions was negligible. NXY-059, S-PBN and PBN showed no effects on vesicular transport or the integrity of the blood-brain barrier in normoxic or ischemic conditions, nor did the compounds induce any change in the ATP levels of the cells. In conclusion, it is possible that the increase in blood-brain barrier permeability of [14C]NXY-059 which occurs during prolonged ischemia in vitro reflects a change which may be of importance to the neuroprotective effects of this nitrone free radical trapping agent.