Related Experiment Videos
Monoamine neurotransmitter metabolism in microencephalic rat brain after prenatal methylazoxymethanol treatment
Abstract:
Administration of methylazoxymethanol (MAM) in the fetal stage leads to forebrain microencephaly with a severe atrophy in cerebral cortex, striatum, and hippocampus. The concentration of endogenous monoamines was markedly increased in the atrophic regions while total amount was largely unchanged. Striatal dopamine and cortical noradrenaline nerve terminals from MAM treated animals showed unaltered sedimentation properties in a sucrose density gradient and were estimated to have normal transmitter levels. gamma-Butyrolactone induced increase in dopamine levels and its counteraction by apomorphine was essentially unaltered after MAM. These data give further support for the view that the monoamine nerve terminal fields develop to their normal size in the atrophic regions leading to a hyperinnervation. Analysis of monoamine metabolite levels, increase of monoamines after monoamine oxidase inhibition, and disappearance of catecholamines after tyrosine hydroxylase inhibition were conducted to obtain information on monoamine turnover. The results indicated an essentially unaltered, or a small reduction of, monoamine turnover in the atrophic regions when calculated per monoamine nerve terminal, while increased when calculated per unit weight of the tissue.
Insights
Methylazoxymethanol (MAM) exposure in fetal development causes brain atrophy and increased monoamine concentrations. Despite tissue damage, monoamine nerve terminals appear normally sized, suggesting hyperinnervation in affected brain regions.
Area of Science:
- Neuroscience
- Developmental Biology
- Toxicology
Background:
- Fetal exposure to methylazoxymethanol (MAM) induces microencephaly, characterized by severe atrophy in key brain regions like the cerebral cortex, striatum, and hippocampus.
- Monoamine neurotransmitter systems are crucial for brain function, and their development can be disrupted by developmental insults.
Purpose of the Study:
- To investigate the impact of fetal MAM exposure on monoamine levels, nerve terminal integrity, and turnover in atrophic brain regions.
- To determine if observed changes in monoamine concentration are due to altered nerve terminal development or function.
Main Methods:
- Administration of MAM during the fetal stage in animal models.
- Analysis of endogenous monoamine concentrations and metabolite levels in specific brain regions.
- Assessment of dopamine and noradrenaline nerve terminal properties using sucrose density gradient centrifugation.
- Evaluation of monoamine turnover through pharmacological challenges (e.g., gamma-butyrolactone, apomorphine, monoamine oxidase inhibition, tyrosine hydroxylase inhibition).
Main Results:
- MAM exposure led to significant atrophy in the forebrain, cerebral cortex, striatum, and hippocampus.
- Markedly increased concentrations of endogenous monoamines were observed in atrophic regions, while total amounts remained largely unchanged.
- Striatal dopamine and cortical noradrenaline nerve terminals exhibited normal sedimentation properties and transmitter levels.
- Pharmacological responses related to dopamine regulation were unaltered post-MAM exposure.
- Monoamine turnover per nerve terminal was unaltered or slightly reduced, but increased per unit weight of tissue in atrophic regions.
Conclusions:
- Fetal MAM exposure results in brain atrophy with hyperinnervation of monoamine nerve terminals in affected regions.
- Despite reduced tissue mass, monoamine nerve terminal fields develop to normal sizes, leading to increased density.
- Monoamine turnover is maintained on a per-nerve-terminal basis, suggesting functional compensation within the developing nervous system.