Research reportAcidic amino acid accumulation by rat choroid plexus during development
Introduction
In addition to acting as protein building blocks, the acidic amino acids, aspartate and glutamate, are major excitatory neurotransmitters in the central nervous system (CNS) 11, 31. Glutamate also plays an important role in the removal of ammonia and regulation of cerebral osmotic and anionic balance [32]. However, high levels of acidic amino acids in brain interstitial fluid (ISF) can cause neuronal damage 21, 30, and brain ISF levels of this group of amino acids are strictly controlled by glial cells through removal by high affinity uptake 14, 19. Furthermore, the blood–brain and blood–cerebrospinal fluid (CSF) barriers show a lower blood to tissue permeability for acidic amino acids compared to the neutral and basic amino acids 4, 5, 29, 37. The blood–brain barrier (BBB) is mainly involved in the efflux of the acidic amino acids out of the brain into blood 10, 22, 32. However, in our recent study, it was observed that the blood–CSF barrier also plays an important part in the exchange of the acidic amino acids between blood and brain, particularly during development [4]. The choroid plexuses which are a major site for the blood–CSF barrier undergo dramatic changes during postnatal development, which are both qualitative and quantitative 16, 17, 34, 35. Recently we have shown that there is greater acidic amino acid uptake into the CSF compared to the brain in neonatal rats, while in the adult uptake into the brain was more dominant [4]. The ISF surrounding the neurones and glia is in free exchange with the CSF, since the ependymal lining of the ventricles and subarachnoid space is permeable to all small molecules [9]. Therefore the level of amino acids in the CSF may have influence on levels in the brain ISF, and hence neuronal function. In this investigation the accumulation of acidic amino acids by the choroid plexus during development has been studied using two techniques: the recently developed bilateral in situ brain perfusion technique [28]for blood-to-choroid plexus transport, and the ventriculo-cisternal perfusion technique [7]for CSF to choroid plexus transport.
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Animals and anaesthesia
Adult Wistar rats of either sex, 7–10 weeks old, were obtained from Bantin and Kingman (UK). Pregnant rats arrived 1 week before delivering and pups then used at 1, 2, and 3 weeks of age. Rats were anaesthetised i.p. with fentanyl/fluanisone (0.3 ml/kg) and midazolam hydrochloride (2 mg/kg) and heparinised (100 000 U/kg, i.p.) in accordance with Animals (Scientific Procedures) Act 1986, UK.
Perfusion mediums
For in situ brain perfusion, a protein containing Ringer plasma substitute was used. This contained (in
Time-dependent uptake
The multiple time uptake profiles of 14C-labelled aspartate, glutamate, and NMDA into choroid plexuses of 1-, 2-, 3-week-old and adult rats are shown in Fig. 1.
[3H]Mannitol, the shaded area in each graph, was used as a vascular and extracellular space marker for the choroid plexus and measured simultaneously with the amino acids. Due to rapid accumulation, the amino acid Kin values were calculated using the line of best fit over the first 20 min of perfusion. For all the ages [14C]aspartate and
Discussion
These studies have shown variations with development in the uptake of acidic amino acids from both blood and CSF sides of the lateral ventricle choroid plexuses in the rat. [3H]Mannitol uptake from the blood side was also measured to monitor changes in the extracellular and vascular space of the choroid plexus during development. This extracellular space showed a reduction with age, in magnitude similar to the developmental changes in entry of [3H]mannitol into CSF from blood 4, 28. The values
References (37)
- et al.
Distribution of transferrin synthesis in brain and other tissues in the rat
J. Biol. Chem.
(1987) - et al.
Rat ceruloplasmin. Molecular cloning and gene expression in liver, choroid plexus, yolk sac, placenta and testis
J. Biol. Chem.
(1987) - et al.
The entry of acidic amino acids into brain and CSF during development using in situ brain perfusion in the rat
Dev. Brain Res.
(1995) - et al.
Transport of amino acids by the rabbit choroid plexus in vitro
Brain Res.
(1971) - et al.
Structure and expression of the rat transthyretin (prealbumin) gene
J. Biol. Chem.
(1988) - et al.
Interactions between neurons and astrocytes in the turnover of GABA and glutamate. GABA neurotransmission
Brain Res. Bull.
(1980) - et al.
Developmental studies of the compartmentalization of water and electrolytes in the choroid plexus of neonatal rat brain
Brain Res.
(1976) - et al.
A morphometric study on the development of the lateral ventricle choroid plexus, choroid plexus capillaries and ventricular ependyma in the rat
Dev. Brain Res.
(1990) - et al.
A morphometric analysis of the development of the fourth ventricle choroid plexus in the rat
Dev. Brain Res.
(1986) - et al.
Developmental changes in the pattern of amino acid transport at the blood–brain barrier in rat
Dev. Brain Res.
(1983)
The steady-state amino acid fluxes across the perfused choroid plexus of the sheep
Brain Res.
The uptake of anionic and cationic amino acids by the isolated perfused sheep choroid plexus
Brain Res.
Permeability of the developing blood–brain barrier to [14C]mannitol using the rat in situ brain perfusion technique
Dev. Brain Res.
Cerebral amino acid uptake in vivo in newborn mice
Brain Res.
Kinetic analysis of [36Cl]-, [22Na]- and [3H]mannitol uptake into the in vivo choroid plexus-cerebrospinal fluid brain system: ontogeny of the blood–brain and blood–CSF barriers
Dev. Brain Res.
Facilitated transport of amino acids through the blood–brain barrier of the dog studied in a single capillary circulation
Brain Res.
Protein synthesis and transport by the rat choroid plexus and ependyma
Cell Tissue Res.
The influx of amino acids into the brain of the rat in vivo: the essential compared with some non-essential amino acids
Proc. Roy. Soc. Lond. B
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2013, Molecular Aspects of MedicineCitation Excerpt :It was assumed in these studies that entry was via the blood–brain barrier interface and account was not taken of possible entry via the choroid plexuses. In addition, it was not clear from these reports if the CSF and choroid plexuses had been removed prior to analysis of brain samples; any choroid plexus tissue or CSF included in the brain samples would have led to an overestimate of the contribution of blood–brain barrier transport of the amino acids into the brain, because at least some amino acids accumulate in the choroid plexuses (al-Sarraf et al., 1997a) in addition to entering the CSF directly. Separate assessment of cerebrospinal fluid in the developing brain, which would mainly reflect entry across the choroid plexuses, has been examined by Segal and colleagues (al-Sarraf et al., 1997b).
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2009, NeuroscienceCitation Excerpt :Glu transport at the blood brain barrier (BBB) has been studied by both in vitro cell uptake assays and in vivo perfusion methods. The results demonstrate that the entrance of Glu from blood into brain is rather limited in comparison to that of neutral amino acids (al-Sarraf et al., 1995, 1997a,b; al-Sarraf and Philip, 2003) and is slow (Oldendorf, 1971; Sershen and Lajtha, 1976). Thus, the BBB helps to protect the brain from changes in circulating plasma Glu, though there are areas of increased vulnerability such as the circumventricular organs that do not contain a BBB (median eminence, area postrema, subfornical organ, subcommissural organ, pineal gland, neurohypophysis (Gross and Weindl, 1987).
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2018, Journal of Physiology
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Present address: Dept. of Gerontology, King's College London, Cornwall House, London SE1 8WA, UK.