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Published on: November 20, 2015
Glycogen phosphorylase activity in the cerebral cortex of rats during development: effect of homocysteine-induced
1Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
Insights
Developing rat brains rapidly activate glycogen phosphorylase during seizures, converting phosphorylase b to a. This rapid activation, particularly in younger rats, suggests a cAMP-independent mechanism involving Ca2+ for energy mobilization.
Area of Science:
- Neuroscience
- Biochemistry
- Developmental Biology
Background:
- Glycogen phosphorylase is crucial for energy metabolism in the brain.
- Its activity and regulation change during postnatal development.
- Understanding its role during seizures is vital for brain energy homeostasis.
Purpose of the Study:
- To investigate total and active glycogen phosphorylase in developing rat cerebral cortex.
- To assess the enzyme's response to induced seizures across different postnatal ages.
- To elucidate the regulatory mechanisms of glycogen phosphorylase activation during seizures.
Main Methods:
- Induced seizures in Wistar rats aged 7, 12, and 18 days using DL-homocysteine thiolactone HCl.
- Measured total and active glycogen phosphorylase (phosphorylase a) activity.
- Assessed cyclic AMP (cAMP) levels.
Main Results:
- Total and active glycogen phosphorylase significantly increased from postnatal day 7 to 18.
- Seizures induced a rapid increase (34-90%) in active phosphorylase across all age groups.
- In 7-day-old rats, phosphorylase a remained low despite activation, correlating with slow glycogenolysis.
- cAMP levels were unchanged in younger rats during seizures, suggesting cAMP-independent activation.
Conclusions:
- Developing rat brains exhibit rapid conversion of phosphorylase b to a in response to seizures.
- A cAMP-independent mechanism, likely involving Ca2+, mediates phosphorylase a activation in immature brains.
- This activation pathway is critical for meeting increased cellular energy demands during seizures in developing animals.
Abstract:
The aim of the present study was to examine the total, as well as the active form of glycogen phosphorylase in the rat cerebral cortex during development, and to assess the response of the enzyme to induced seizures. Seizures were induced in 7-, 12- and 18-day-old male Wistar rats by i.p. administration of DL-homocysteine thiolactone HCl. Total glycogen phosphorylase activity increased from 54.76 + 2.33 to 181.14 +/- 5.79 micromol/g/h and phosphorylase a from 3.45 +/- 0.45 to 63.73 +/- 1.41 micromol/g/h, from postnatal day 7 to 18, respectively. In 7-day-old pups phosphorylase a corresponded to only 6% of total activity. At the onset of seizures a marked rise (34-90%) in active phosphorylase occurred in all age groups. Thus, in the brains of immature animals a rapid conversion of phosphorylase b to a can occur in response to increased cellular activity. However, in 7-day-old rats, in spite of marked activation, phosphorylase a remained very low (6.0 +/- 0.42 micromol/g/h) and can thus explain the slow onset of glycogenolysis in this age group. Cyclic AMP levels remained unchanged at the onset of seizures in 7- and 12-day-old pups, and only a mild (+ 25%) rise was observed in 18-day-old rats. The marked increase of phosphorylase a in 7- and 12-day-old rats thus occurred in the presence of unchanged levels of cAMP, suggesting the involvement of cAMP-independent mechanism of activation, in which Ca2+ most probably plays a role.
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