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The fine structure of puromycin-induced changes in mouse entorhinal cortex
Abstract:
Bitemporal intracerebral injections of puromycin in mice suppress indefinitely expression of memory of avoidance-discrimination learning. Ultrastructural studies of the entorhinal cortex of puromycin-treated mice revealed the following: (a) Abnormalities were not observed in presynaptic terminals and synaptic clefts; many postsynaptic dendrites or somas contained swollen mitochondria. (b) Dispersion of polyribosomes into single units or condensation of ribosomes into irregular aggregates with loss of "distinctiveness" was noted in a few neurons 7-27 hr after puromycin treatment. (c) Cytoplasmic aggregates of granular or amorphous material were frequently noted within otherwise normal neuronal perikarya. (d) Mitochondria in many neuronal perikarya and dendrites were swollen. Mitochondria in axons, presynaptic terminals, and glial cells were unaltered. The relationships between these lesions and the effect of puromycin on protein synthesis and memory are examined. It is suggested that the disaggregation of polysomes is too limited to explain the effect of puromycin on memory. Special emphasis is given to the swelling of mitochondria. The possible mechanisms and the significance of this lesion are discussed.
Insights
Puromycin injections in mice impair memory formation by causing mitochondrial swelling in neurons. This cellular damage, particularly in the entorhinal cortex, affects memory expression and protein synthesis.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Puromycin is an antibiotic known to inhibit protein synthesis.
- Memory formation involves complex molecular and cellular processes within the brain.
- Understanding the cellular basis of memory impairment is crucial for neurological research.
Purpose of the Study:
- To investigate the ultrastructural changes in the mouse entorhinal cortex following puromycin administration.
- To correlate these cellular alterations with the observed suppression of avoidance-discrimination learning memory.
- To elucidate the role of protein synthesis inhibition and mitochondrial dysfunction in memory loss.
Main Methods:
- Bitemporal intracerebral injections of puromycin in mice.
- Ultrastructural analysis of the entorhinal cortex using electron microscopy.
- Assessment of memory expression for avoidance-discrimination learning.
Main Results:
- Puromycin treatment led to indefinite suppression of memory expression.
- Ultrastructural examination revealed swollen mitochondria in postsynaptic dendrites and somas, but not in presynaptic terminals or axons.
- Some neurons exhibited dispersed polyribosomes or irregular ribosome aggregates, while others showed cytoplasmic granular or amorphous material.
Conclusions:
- Mitochondrial swelling in neurons is a significant ultrastructural lesion associated with puromycin-induced memory suppression.
- The observed disaggregation of polysomes is likely insufficient to fully account for the memory deficits.
- Further investigation into the mechanisms and significance of mitochondrial swelling in neuronal function and memory is warranted.