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Comparative aspects of brain barrier systems for nonelectrolytes
The American Journal of Physiology
|January 1, 1978
Summary
The blood-brain and blood-cerebrospinal fluid barriers to inulin were compared across 11 vertebrate species. Findings reveal significant variations in barrier development, particularly in sharks and hagfish, suggesting evolutionary differences in central nervous system protection.
Area of Science:
- Comparative physiology
- Neuroscience
- Zoology
Background:
- The blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier are crucial for protecting the central nervous system (CNS) in vertebrates.
- Inulin is commonly used as a marker to assess the permeability of these barriers due to its low native concentration and limited transport across membranes.
Purpose of the Study:
- To compare the permeability of the blood-brain and blood-CSF barriers to inulin across a diverse range of 11 vertebrate species.
- To investigate potential age-related development of these barriers in certain shark species.
Main Methods:
- Systemic administration of radiolabeled [14C]inulin to 11 vertebrate species.
- Measurement of [14C]inulin concentrations in brain tissue and CSF after 20 hours.
- Calculation of barrier ratios (RB for brain and RCSF for CSF) to quantify inulin penetration.
- Analysis of radiolabeled urea and sucrose penetration in sharks to further assess barrier function.
- Comparison of inulin ratios in nurse sharks across a wide weight range to assess age-related changes.
Main Results:
- Mudpuppy, salamanders, red sculpin, and stingrays exhibited low inulin penetration (RB: 0.01-0.04, RCSF: 0.02-0.04), similar to mammals.
- Sharks (dogfish, nurse shark, lemon shark) showed higher inulin penetration (RB: 0.04-0.09, RCSF: 0.08-0.29), indicating less developed barriers.
- Hagfish displayed very high inulin penetration (RB=0.12), suggesting absent or poorly developed barriers.
- Barrier function in dogfish and little skate showed age-dependent development.
- Nurse sharks did not exhibit significant changes in inulin ratios with age/weight.
Conclusions:
- Vertebrate blood-brain and blood-CSF barriers exhibit significant diversity in their permeability to inulin, reflecting evolutionary adaptations.
- Sharks and hagfish possess less developed barriers to inulin compared to other studied vertebrates, including mammals.
- Barrier development can be influenced by age in some species, highlighting dynamic maturation processes within the CNS protective systems.