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Updated: Jul 26, 2026
Functional Evaluation of Biological Neurotoxins in Networked Cultures of Stem Cell-derived Central Nervous System Neurons
Published on: February 5, 2015
Behavioural evaluation of long-term neurotoxic effects of NMDA receptor antagonists
W Zajaczkowski1, M Hetman, E Nikolaev
1Department of Molecular and Cellular Neurobiology, Nencki Institute of Experimental Biology, Pasteura 3, 02-093 Warsaw, Poland.
Abstract:
High doses of NMDA antagonists e.g. (+)MK-801 evoke neurodegeneration in retrosplenial cortex in rodents. To assess functional consequences of such treatment, three paradigms of two-way active avoidance learning (with visual or auditory conditioned stimuli) and additionally a spatial learning paradigm - radial maze - were used. Female rats were treated i.p. with 5 mg/kg of (+)MK-801. Recumbence, severe hypothermia and loss of body weight were observed for 3-7 days. Despite that, there were no statistically significant differences in performance of avoidance reaction between saline and (+)MK-801 treated animals trained 10-40 days after the drug administration. However, in the radial maze test (+)MK-801 impaired reference (but not working) memory in the experiment that started 8 days after the treatment. Similar effect was observed on reversal learning. The clinically used NMDA receptor antagonist memantine at the doses of 20 and 40 mg/kg had also no such long term negative effect on working memory during training (even positive effect was seen at 20 mg/kg) but at 40 mg/kg impaired learning on the first day of reversal. This indicates that (+)MK-801 neurotoxicity in the retrosplenial cortex is connected with subtle alterations in the learning performance that may be seen in some tests only. Moreover, memantine doses greatly exceeding therapeutically relevant range produce minimal functional alteration. An additional experiment revealed that the same dose of memantine results in two fold higher serum levels of the antagonist in female than male rats. Hence, considering that profiling studies are done in male rats, a safety factor of over 16 fold can be calculated for memantine.
Insights
High doses of NMDA antagonists like (+)MK-801 can cause neurodegeneration. While avoidance learning remained unaffected, spatial memory was impaired in rats, suggesting subtle learning deficits.
Area of Science:
- Neuroscience
- Pharmacology
- Cognitive Science
Background:
- NMDA receptor antagonists, such as (+)MK-801, can induce neurodegeneration in specific brain regions like the retrosplenial cortex in rodents.
- Understanding the functional consequences of such neurotoxicity is crucial for evaluating potential therapeutic applications and risks.
Purpose of the Study:
- To investigate the long-term functional effects of high-dose NMDA antagonist (+)MK-801 on learning and memory in female rats.
- To compare the effects of (+)MK-801 with the clinically used NMDA antagonist memantine on cognitive performance.
- To assess potential sex-based differences in memantine's pharmacokinetics and safety.
Main Methods:
- Female rats were treated with (+)MK-801 (5 mg/kg) or saline and tested on active avoidance learning (visual/auditory) and spatial learning (radial maze) at various time points post-treatment.
- The effects of memantine (20 and 40 mg/kg) on learning and reversal learning were also evaluated.
- Serum levels of memantine were measured in male and female rats to assess pharmacokinetic differences.
Main Results:
- (+)MK-801 treatment did not significantly affect active avoidance learning 10-40 days post-administration.
- (+)MK-801 impaired reference memory and reversal learning in the radial maze test when initiated 8 days after treatment.
- Memantine did not impair working memory and showed minimal effects on reversal learning, even at high doses, with higher serum levels observed in females.
Conclusions:
- Neurotoxicity induced by (+)MK-801 in the retrosplenial cortex is associated with subtle, test-dependent alterations in learning and memory.
- High doses of memantine, exceeding therapeutic levels, produce minimal functional deficits, suggesting a considerable safety margin.
- Sex differences in memantine pharmacokinetics necessitate careful consideration, especially when extrapolating safety data from male rodents to clinical applications.
