Inhibitory influence of morphinans on ictal and interictal EEG changes induced by cortical application of penicillin in rabbits: a comparative study with NMDA antagonists and pentobarbitone

Effects of second generation tetracyclines on penicillin-epilepsy-induced hippocampal neuronal loss and motor incoordination in rats

Epileptic seizures cause pathological changes such as sclerosis and pyramidal neuronal loss in the hippocampus. Experimentally, epilepsy can be induced by application of various chemicals directly to the cerebral cortex. In this study, epilepsy was induced in rats by intracortical application of 500 IU penicillin G, and the effect of minocycline and doxycycline on the resulting motor incoordination (rotarod) and hippocampal neuronal loss in CA1, CA2 and CA3 fields (optical fractionator method) were investigated. The rotarod performance was reduced in the epilepsy group to 285.1+/-6.9 s (P<0.05 vs. sham-300 s). Minocycline and doxycycline increased this performance to 297.4+/-1.0 s and 296.9+/-1.2 s respectively. No significant difference was detected between minocycline and doxycycline. The present results also showed that the number of neurons (x10(3)) in the sham group was 150+/-9. In the penicillin-epileptic rats, the number was decreased to 105+/-7 (P<0.01). Minocycline, but not doxycycline (125+/-8), significantly increased the number to 131+/-3 (P<0.05). In conclusion, the second generation tetracycline minocycline decreased the loss of hippocampal neurons and motor incoordination in penicillin-epileptic rats. Minocycline could protect against a variety of neurological insults including epilepsy.

The beta-lactam antibiotics, penicillin-G and cefoselis have different mechanisms and sites of action at GABA(A) receptors

The action of the beta-lactam antibiotics, penicillin-G (PCG) and cefoselis (CFSL) on GABA(A) receptors (GABA(A)-R) was investigated using the two-electrode voltage clamp technique and Xenopus oocyte expressed murine GABA(A)-R. Murine GABA(A)-Rs were expressed in Xenopus oocytes by injecting cRNA that encoded for each subunit (alpha1, beta2, and gamma2) and the effects of PCG and CFSL on the alpha1beta2gamma2s subunit receptors were examined using two-electrode voltage clamp. Using the alpha1beta2gamma2s GABA(A)-R, PCG and CFSL inhibited GABA-induced currents in a concentration-dependent manner, with IC(50)s of 557.1+/-125.4 and 185.0+/-26.6 microM, respectively. The inhibitory action of PCG on GABA-induced currents was non-competitive whereas that of CFSL was competitive. Mutation of tyrosine to phenylalanine at position 256 in the beta2 subunit (beta2(Y256F)), which is reported to abolish the inhibitory effect of picrotoxin, drastically reduced the potency of PCG (IC(50)=28.4+/-1.42 mM) for the alpha1beta2(Y256F)gamma2s receptor without changing the IC(50) of CFSL (189+/-26.6 microM). These electrophysiological data indicate that PCG and CFSL inhibit GABA(A)-R in a different manner, with PCG acting non-competitively and CFSL competitively. The mutational study indicates that PCG might act on an identical or nearby site to that of picrotoxin in the channel pore of the GABA(A)-R.

Efficacy of vancomycin/tri-iododecyclemethyl ammonium chloride-coated ventriculostomy catheters in reducing infection

OBJECTIVE

The biotoxicity of tri-iododecyclemethyl ammonium chloride (TDMAC)-coated catheters in the brain was tested, as was the efficacy of the vancomycin-bonded, TDMAC-coated catheters to inhibit staphylococcal growth in vitro and to delay the onset of clinical manifestations of catheter-related staphylococcal ventriculitis in rabbit experimental model.

METHODS

The brain toxicity of the TDMAC-coated catheters was tested in New Zealand White rabbits. The efficacy of the vancomycin-bonded, TDMAC-coated catheters in the inhibition of staphylococcal growth was tested in agar seeded with Staphylococcus aureus and Staphylococcus epidermidis strains. Sections of vancomycin-bonded, TDMAC-coated catheters were placed in saline solution for testing of drug release over time. Stereotactic placement of ventriculostomy catheters was performed in two groups of New Zealand White rabbits. In the experimental group, vancomycin-bonded, TDMAC-coated catheters were used. In the control group, TDMAC-coated catheters were used. Staphylococcal colonies were inoculated at the exit site of the catheters. Culture of the catheter tips was performed at the time of death of the animals.

RESULTS

No toxic reactions were seen at the implantation sites or in surrounding brain. Significant inhibition of growth of both S. aureus and S. epidermidis was noted with the vancomycin-bonded catheters (P = 0.01). Vancomycin continued to be released from catheters for the full 6 days of the study. The median interval to development of clinical manifestations of ventriculitis among the experimental group of rabbits was 53 days; among the control group, the interval was 27 days (P < 0.001).

CONCLUSION

Vancomycin-bonded, TDMAC-coated ventriculostomy catheters bind and release the drug at levels exceeding the minimum inhibitory concentration for S. aureus and S. epidermidis for at least 6 days and can significantly delay the onset of infectious ventriculitis in a rabbit model.

NMDA antagonists: antiepileptic-neuroprotective drugs with diversified neuropharmacological profiles

In conclusion, NMDA antagonists as anticonvulsants are especially active in preventing the generalization of the behavioural and electrical seizures and display a typical spectrum of in vitro antiepileptiform activities. In addition, based on in vitro and in vivo limbic kindled studies, the drugs should be regarded more as an antiepileptiform than as an anticonvulsant drugs. As neuroprotective drugs, NMDA antagonists are effective against many types of neuronal injury and show a window of activity which does not exceed 1-2 h, thus suggesting an influence of NMDA receptors in the 'early' or 'acute' mechanisms of brain damage. Among NMDA antagonists, glycine antagonists or the morphinans dextromethorphan and dextrorphan showed a spectrum of antiepileptiform and neuroprotective activities broader than other NMDA antagonists. The primary pharmacological activities of NMDA antagonists are accompanied by some effects including perturbation of many sensory, psychological or motor processes. Typical behavioural and EEG changes were also induced by the drugs. In spite of the side-effects elicited by the drugs, differential effects detected among the various classes of NMDA antagonists (i.e. lack of induction of typical EEG-behavioural effects and of typical cortical neurotoxicity) might render some of these suitable for full clinical application as anticonvulsant-neuroprotective drugs.

Diphenylhydantoin potentiates the EEG and behavioural effects induced by N-methyl-D-aspartate antagonists in rats

The N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors are involved in the electrical and behavioural generalization of epileptiform activity within the brain. In rats, both competitive and non-competitive NMDA antagonists induce three dose-dependent stages of EEG patterns: 1) increase in cortical desynchronization periods; 2) increase in amplitude of cortical high frequency (20-30 Hz), low voltage (30-50 microV) background activity; 3) appearance of cortical slow (2-3 Hz) wave-sharp wave complexes. These EEG changes are accompanied by stimulatory-depressive behavioural effects such as stereotypy (circling, head weaving) and ataxia. In the present study, the influence of the prototypic anticonvulsant diphenylhydantoin (DPH) has been tested on the EEG and behavioural effects induced by the non-competitive NMDA antagonists phencyclidine (PCP) and dizocilpine (MK-801) and by the competitive NMDA antagonist cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755). Even though DPH (up to 100 mg/kg IP) did not markedly affect basal cortical EEG activity, at doses of 10-100 mg/kg IP it potentiated all the EEG effects induced by the NMDA antagonists. These data support involvement of NMDA neurotransmission in the pharmacological effects of DPH.