Dibenzocycloalkenimine (MK-801) stimulates phosphoinositide hydrolysis in rat cerebral cortical slices)

The behavioural effects of MK-801 in rats: involvement of dopaminergic, serotonergic and noradrenergic systems

The non-competitive NMDA receptor antagonist, MK-801 (dizocilpine), induces in rats a characteristic behavioural syndrome with ataxia, stereotypies and hyperlocomotion. At least part of this behavioural syndrome is thought to be related to interactions between glutamatergic and dopaminergic neurotransmission. Based on recent biochemical evidence that serotonin (5-HT) might also be involved in the effects of MK-801 several 5-HT receptor ligands were tested for effects on MK-801-induced behaviours. The 5-HT1A receptor ligands, ipsapirone and NAN-190, which are known to display antagonist-like properties in functional models of postsynaptic 5-HT1A receptor activity attenuated or blocked the hyperlocomotion and head weaving observed after administration of MK-801, whereas the 5-HT2 receptor antagonist, ritanserin, was ineffective in this respect. The dopamine receptor antagonist, haloperidol, and the alpha 1-adrenoceptor antagonist, prazosin, also attenuated behaviours induced by MK-801. In contrast to its effects on stereotypies induced by MK-801, ipsapirone potentiated rather than attenuated the stereotyped behaviour induced by the dopamine receptor agonist, apomorphine, indicating that antagonism of MK-801-induced stereotypies by ipsapirone may not be related to the dopaminergic system. The data indicate that, in addition to catecholaminergic systems, serotonergic neurotransmission is significantly involved in the mechanisms by which MK-801 alters behaviour in rats.

Neuroprotective effects of SKF 10,047 in cultured rat cerebellar neurons and in gerbil global brain ischemia

BACKGROUND AND PURPOSE

Excitatory amino acids and their receptors are involved in mediating ischemic neuronal damage. The sigma-agonists are believed to interact with the N-methyl-D-aspartate receptor. Therefore, we studied the neuroprotective, hypothermic, and motor deficit effects of the sigma-agonist SKF 10,047 and the N-methyl-D-aspartate antagonist MK-801.

METHODS

Neuroprotective effects were compared using an in vitro ischemia model of cultured rat cerebellar granule cells and the gerbil model of global brain ischemia induced by 5 minutes of bilateral carotid artery occlusion followed by 7 days of reperfusion.

RESULTS

In vitro, (+)MK-801 protected against 100 microM glutamate with a 50% protective concentration of 30 nM, followed by (-)MK-801 (150 nM), cyclazocine (0.5 microM), (+)SKF 10,047 (3.3 microM), pentazocine (5 microM), and (-)SKF 10,047 (10 microM). In vivo, (+)SKF 10,047 pretreatment (60 mg/kg) or multiple postischemic treatments provided neuroprotection comparable with MK-801 pretreatment (10 mg/kg). When ischemic animals were administered the multiple dosing regimen of (+)SKF 10,047, no hypothermic effect was noted in the temporalis muscle over 4 hours' postischemia. Motor deficits monitored by a swing grid test showed that 50% recovery from (+)SKF 10,047 was 5.5 times faster than recovery from MK-801.

CONCLUSIONS

These results are the first to report a hypothermia-free, in vivo neuroprotective effect of (+)SKF 10,047, a prototypical drug of the sigma-agonist class.

Pertussis toxin potentiates seizures induced by pilocarpine, kainic acid and N-methyl-D-aspartate

Previous studies with lithium have shown that it potentiated the in vivo response to cholinomimetics in rats, resulting in seizures at otherwise non-convulsant doses, but did not affect seizure activity induced by a number of chemical convulsants including kainic acid and N-methyl-D-aspartate (NMDA). In vitro experiments have suggested that lithium interferes with receptor-mediated second messenger production, possibly due to an action at G-proteins. The present study tested the hypothesis that selective inhibition of G-proteins by in vivo administration of pertussis toxin would induce effects similar to those of lithium. The results reported here demonstrate that pertussis toxin mimics lithium in potentiating the convulsant response to pilocarpine in rats. The effect of pertussis toxin was dose-dependent and the extent of potentiation was over 13-fold, which was remarkably similar to lithium. The seizures were prevented by pretreatment with atropine, phenobarbital or diazepam. L-Phenylisopropyladenosine (L-PIA) and MK-801 also demonstrated anticonvulsant activity, with MK-801 also protecting the rats against the rapid death associated with pertussis toxin/pilocarpine-induced seizures. Thus, seizures were cholinergically initiated and were controlled by the same drugs as were lithium/pilocarpine-induced seizures. The results illustrate that in several respects the response to cholinomimetics is modified in a similar manner by lithium and pertussis toxin. However, pertussis toxin lacks the specificity of lithium as it also potentiated the convulsant effects of kainic acid and NMDA.

Comparison of pharmacodynamic effects of the non-competitive NMDA receptor antagonists MK-801 and ketamine in pigs

The non-competitive NMDA receptor antagonists MK-801 and ketamine were injected into pigs via chronically implanted intravenous catheters, and the animals were observed closely for alterations in general behaviour, heart rate, respiration and body temperature. MK-801 produced head shakes, sterotypies, 'psychotic' behaviour (e.g., hyperexcitation and screaming), and ketamine-like anesthetic effects in pigs at doses of 0.1-1.6 mg/kg. Almost the same behavioural pattern of effects was observed after i.v. injection of ketamine, 15mg/kg. Furthermore, both drugs reduced heart rate and increased respiration rate and body temperature. The most marked differences between MK-801 and ketamine were that MK-801 had a much longer duration of action and the catalepsy produced by MK-801 was much more pronounced. When animals were first anesthetized with pentobarbital, MK-801 did not alter the cardiovascular functions. In pigs genetically susceptible to induction of malignant hyperthermia by volatile anesthetics, MK-801 did not produce signs characteristic of fulminant malignant hyperthermia. The data show that MK-801 produces psychomotor and anesthetic effects that are almost indistinguishable from those observed after traditional dissociative anesthetics, such as phencyclidine and ketamine. With respect to the behavioural similarities between MK-801 and phencyclidine or ketamine, it seems unlikely that MK-801 will be useful clinically as an anticonvulsant or anxiolytic drug, but the data indicate that the drug may be suited as a long-acting dissociative anesthetic.