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Age-dependent reduction in maximum electroshock convulsive threshold associated with decreased concentrations of
Abstract:
This study investigated modification of the tonic convulsive threshold to maximum electroshock in 15- and 30 day old rats treated with drugs which reduce steady-state concentrations of monoamines. On postnatal day 15, reduction of central catecholamine concentrations by 6-hydroxydopamine or of central serotonin concentrations by 5,7-dihydroxytryptamine or p-chloroamphetamine did not alter the tonic convulsive threshold. However, simultaneous depletion of catecholamines and serotonin by tetrabenazine was associated with a significant decrease in the tonic threshold. This effect could be reversed partially by simultaneous administration of the catecholamine and serotonin precursors, L-dihydroxyphenylalanine and 5-hydroxytryptophan, respectively. On postnatal day 30, reduction of brain serotonin concentration, but not catecholamine concentrations, was associated with a significant decrease of the tonic convulsive threshold. In a previous study, in which 7-8 day old rats were used, a tetrabenazine-induced decrease in the tonic convulsive threshold prevented by L-dihydroxyphenylalanine but not 5-hydroxytryptophan. Furthermore, intracisternal 6-hydroxydopamine, but not 5,7-dihydroxyhyptamine, decreased the threshold on postnatal day 8. Therefore, the results of the present day study involving 15- and 30 day old rats, together with the earlier findings in 7-8 day old rats, [28] suggest an apparent developmental transition from catecholaminergic to serotonergic dominance in regulation of the tonic convulsive threshold during the first postnatal month.
Insights
This study shows that in young rats, both catecholamines and serotonin are needed to maintain seizure threshold. By one month old, serotonin alone becomes crucial for regulating this threshold.
Area of Science:
- Neuroscience
- Developmental Biology
- Pharmacology
Background:
- Monoamines play a critical role in regulating neuronal excitability and seizure susceptibility.
- The relative contribution of different monoamine systems to seizure threshold may change during development.
Purpose of the Study:
- To investigate the developmental changes in the regulation of the tonic convulsive threshold by monoamines.
- To determine the specific roles of catecholamines and serotonin in modulating seizure threshold at different postnatal ages.
Main Methods:
- Treatment of rats at postnatal days 15 and 30 with drugs that deplete catecholamines (6-hydroxydopamine) or serotonin (5,7-dihydroxytryptamine, p-chloroamphetamine).
- Assessment of the tonic convulsive threshold to maximum electroshock following monoamine depletion.
- Administration of monoamine precursors (L-dihydroxyphenylalanine, 5-hydroxytryptophan) to assess reversibility of effects.
Main Results:
- On postnatal day 15, simultaneous depletion of catecholamines and serotonin significantly decreased the tonic convulsive threshold, an effect partially reversed by precursor administration.
- On postnatal day 30, depletion of serotonin alone, but not catecholamines, significantly decreased the tonic convulsive threshold.
- Comparison with previous findings in 7-8 day old rats indicates a developmental shift in monoaminergic regulation of seizure threshold.
Conclusions:
- The regulation of the tonic convulsive threshold in rats undergoes a developmental transition from reliance on both catecholamines and serotonin to a greater dependence on serotonin.
- This transition suggests a shift from catecholaminergic to serotonergic dominance in modulating seizure threshold during the first postnatal month.