Related Experiment Videos
Circadian rhythm in muscarinic receptor subtypes in rat forebrain
E Marquez1, J Pavia, S Laukonnen
1Departamento de Farmacologia, Facultad de Medicina, Universidad de Malaga, Spain.
Abstract:
The binding of different ligands to muscarinic receptors in the central nervous system is regulated by several factors. Among these are the administration of drugs, disease, ontogeny or aging. Studies carried out in rat brains have demonstrated changes in the density of the muscarinic receptors at different times of the day. These changes might be related to variations in the circadian rhythms. In this work we have studied the binding of the [3H]-N-methyl-escopolamine, the agonist carbachol and the antagonist pirenzepine to muscarinic receptors in rat forebrains at 10.00, 14.00, 18.00, 22.00, 02.00 and 06.00 hr. We have observed changes in the density of muscarinic receptors but not changes in affinity to the radioligand. The Bmax values obtained by saturation studies were maximum at 14.00 hr and minimum at 02.00 hr (P less than 0.05 Mann-Whitney's test). Inhibition studies in the presence of the non-selective agonist carbachol and the selective antagonist pirenzepine, at the same time-points, did not show statistically significant changes in the Bmax values. These data indicate that changes in the Bmax values are only observed in the total population of muscarinic receptors and are not due to modifications in the subtypes of muscarinic receptors nor to the different affinity states of agonist binding.
Insights
Muscarinic receptor density in rat brains fluctuates daily, peaking at 2 PM and hitting a low at 2 AM. These diurnal changes in receptor number, not affinity, are linked to circadian rhythms.
Area of Science:
- Neuroscience
- Pharmacology
- Chronobiology
Background:
- Muscarinic receptors in the central nervous system are influenced by factors like drugs, disease, and aging.
- Previous studies in rats suggest daily variations in muscarinic receptor density, potentially linked to circadian rhythms.
Purpose of the Study:
- To investigate the diurnal binding patterns of muscarinic receptors in rat forebrains.
- To determine if changes in receptor density or affinity correlate with time of day.
Main Methods:
- Studied [3H]-N-methyl-escopolamine binding to muscarinic receptors in rat forebrains at six time points over 24 hours.
- Utilized saturation studies to determine Bmax (maximum binding capacity) and affinity.
- Conducted inhibition studies with carbachol and pirenzepine to assess receptor subtypes and affinity states.
Main Results:
- Observed significant diurnal variations in muscarinic receptor density (Bmax), with maximum binding at 14:00 hr and minimum at 02:00 hr (P < 0.05).
- No significant changes in receptor affinity to the radioligand were detected.
- Inhibition studies with carbachol and pirenzepine did not reveal statistically significant changes in Bmax, indicating no alterations in receptor subtypes or affinity states.
Conclusions:
- Diurnal variations in muscarinic receptor binding are primarily due to changes in the total receptor population (Bmax).
- These fluctuations are not attributed to modifications in specific muscarinic receptor subtypes or agonist binding affinity states.
- The findings support a link between muscarinic receptor density and circadian rhythms in the rat brain.