Late evolutionary appearance of 'peripheral-type' binding sites for benzodiazepines

Area of Science:

• Neuroscience
• Evolutionary Biology
• Pharmacology

Background:

• Benzodiazepines are widely used drugs targeting specific receptors in the brain.
• Two main types of benzodiazepine binding sites exist: 'brain-specific' and 'peripheral-type'.
• The evolutionary history and distribution of these binding sites across different species are not fully understood.

Purpose of the Study:

• To investigate the presence and distribution of 'brain-specific' and 'peripheral-type' benzodiazepine binding sites in non-mammalian vertebrates.
• To compare these findings with those in mammals to infer evolutionary patterns.
• To understand the potential functional significance of peripheral-type benzodiazepine binding sites.

Main Methods:

• Radioligand binding assays were employed to quantify benzodiazepine binding sites.
• Central nervous system and cardiac tissues from four classes of non-mammalian vertebrates were analyzed.
• Binding site densities were compared between non-mammalian and mammalian tissues.

Main Results:

• 'Brain-specific' benzodiazepine binding sites were detected in the central nervous system of all non-mammalian vertebrates studied.
• Conversely, 'peripheral-type' benzodiazepine binding sites were found at very low or undetectable levels in the central nervous system of these species.
• The density of 'peripheral-type' binding sites in non-mammalian vertebrate heart tissue was significantly lower (≤2%) than in mammalian cardiac tissue.

Conclusions:

• The findings indicate a recent evolutionary emergence of 'peripheral-type' benzodiazepine binding sites.
• These sites likely possess specialized functions in both peripheral tissues and the central nervous system.
• This evolutionary perspective provides insights into the diversification of benzodiazepine receptor systems.