Catecholamines
- A number of catecholamines (such as noradrenaline and dopamine) act as neurotransmitters in the central nervous system
- Unregulated entry across the blood brain barrier can result in permanent neuroexcitatory damage
Amino acids
- Similarly to catecholamines a number of amino-acids (such as glycine and glutamic acid) act as neurotransmitters in the central nervous system
- Unregulated entry across the blood brain barrier can result in permanent neuroexcitatory damage
Ammonia (NH3)
- Ammonia is potentially neurotoxic in significant concentrations
- It is a small lipophilic molecule which may be expected to cross the BBB
- It is rapidly metabolised by the enzymatic barrier to glutamine, preventing passage across the BBB in relevant quantities
Macromolecules
- Plasma proteins such as albumin and plasminogen are damaging to nervous tissue and can lead to apoptosis
- The BBB prevents passage of such molecules leading to low CSF levels
- Results in a lower ability to buffer changes in pH
Charged Ions
- The BBB is impermeable to H+ and HCO3- ions due to their charge
- However it is permeable to CO2 which can pass freely through into the CSF
- In this way CO2 from arterial blood can become converted in to H+ and HCO3- ions which become trapped lowering the pH of CSF