The role of taurine in the survival and function of cerebellar cells in cultures of early postnatal cat

Influences of different developmental periods of taurine supplements on synaptic plasticity in hippocampal CA1 area of rats following prenatal and perinatal lead exposure

Background

Previous study has demonstrated that dietary taurine supplement protected rats from impairments of synaptic plasticity induced by postnatal lead exposure. However, little is known about the role of taurine in the presence of prenatal and perinatal lead exposure. We investigated the possible effect of taurine supplement on prenatal and perinatal lead-induced synaptic plasticity deficit and determined developmental periods critical for the effect of taurine.

Results

In the present study, taurine was administrated to prenatal and perinatal lead-exposed rats in different developmental periods: from prenatal to weaning (Lead+PW-Tau), from weaning to life (Lead+WL-Tau), and from prenatal to life (Lead+PL-Tau). We examined the input-output (I/O) function, paired-pulse facilitation (PPF) and the long-term potentiation (LTP) of field excitatory postsynaptic potential (fEPSP) in the hippocampal CA1 area of rats on postnatal days 18–25 (P18–25) or days 60–75 (P60–75). We found that (1) on P18–25, taurine had no evident effect on I/O functions and PPF ratios of lead-exposed rats but caused a 12.0% increase in the LTP amplitudes of these animals; (2) on P60–75, taurine significantly elevated lead depressed I/O functions and PPF ratios in Lead+PW-Tau and Lead+PL-Tau rats, but failed in Lead+WL-Tau rats. The amplitudes of LTP of lead-exposed rats were all significantly increased by additional taurine supplement in any developmental period compared with untreated rats. Thus, taurine appeared to have the most effect during the prenatal and lactation periods and its effects on younger rats would not be manifest until the adult life; and (3) the level of lead deposition in hippocampus was evidently reduced by additional treatment of taurine in lead-exposed rats, compared with untreated rats.

Conclusion

Taurine supplement can protect the adult rats from synaptic plasticity deficits following prenatal and perinatal lead exposure, and the protective effects are critical for the prenatal and lactation periods of lead-exposed rats.

Taurine as osmoregulator and neuromodulator in the brain

Taurine has been assumed to function as an osmoregulator and neuromodulator in the brain. The pertinent studies are now reviewed in an attempt to formulate a unifying hypothesis as to how taurine could simultaneously act in both roles. Neuromodulatory actions of taurine may also underlie its protective effects against neuronal overexcitation and glutamate agonist-induced neurotoxicity.

Effect of K+- and kainate-mediated depolarization on survival and functional maturation of GABAergic and glutamatergic neurons in cultures of dissociated mouse cerebellum

The effect of the depolarizing agents, an elevated potassium concentration (25 mM) or kainic acid (50 microM) on neuronal survival and differentiation was investigated in cultures of dissociated neurons from cerebella of 7-day-old mice. When maintained in the presence of an antimitotic agent such cultures consist primarily of glutamatergic and GABAergic neurons. Cell survival was monitored by measurement of DNA, and differentiation by determining uptake and depolarization coupled release of glutamate (D-aspartate as label) and GABA. The depolarizing agents were added separately or together either from the start of the culture period (7-8 days) or at day 5 in culture. The main findings are that K+ depolarization is important for differentiation of glutamatergic neurons but not for GABAergic neurons. This depolarizing signal is important during the early phase of development in culture. For glutamatergic neurons, kainate may replace K+ as a depolarizing signal whereas in case of the GABAergic neurons, kainate was toxic particularly during the late phase of development. It was further observed that the glutamatergic neurons when maintained in a medium with 5 mM K+ during the first 5 days in culture became sensitive to kainate toxicity when this amino acid was added at day 5. This was not the case when the medium contained 25 mM K+ from the start of the culture period.

Characterization of taurine transport in human glioma GL15 cell line: regulation by protein kinase C

Data describing characteristics of taurine transport system in human brain cells are not currently available. We have used GL15 cells, a cell line of human brain origin that keeps some properties of normal glial cells, to investigate these characteristics. The human glioma cell line GL15 was found to take up taurine. The uptake was strictly sodium-dependent. Replacement of NaCl with choline chloride almost totally abolished the uptake. There was also an anion requirement for the uptake system, and Cl- was the most potent among several monovalent anions tested. The uptake process was specific for beta-amino acids such as taurine, hypotaurine and beta-alanine. The kinetics of uptake were studied. Apparently, a single transport system with a K(m) of 8.95 +/- 0.26 microM was responsible for the uptake. A maximal velocity of 1.32 +/- 0.03 nmol/mg of protein/10 min was found. Stoichiometric analysis revealed that two Na+ and one Cl- ions were involved in the translocation of one taurine molecule. Phorbol 12-myristate 13-acetate (PMA), a potent stimulator of protein kinase C (PKC), inhibited taurine uptake. Maximal inhibition was obtained at 50 nM after 1 hr of treatment. This effect was prevented by pretreatment of the cells with chelerythrine, a potent and selective inhibitor of PKC. The transport of beta-alanine was inhibited to a comparative extent. The mechanism of this inhibition was not investigated, but it was found that this inhibitory effect was not prevented by cycloheximide, actinomycin D, colchicine or cytochalasin D, indicating that neither protein synthesis, nor microfilament function were involved. The effect of PMA was associated with an impairment of kinetic constants. It is concluded that human GL15 cells have a taurine transporter similar to that expressed in rodent glial cells, and that the activation of PKC can modulate the activity of this transporter.

Taurine deficiency in dissociated mouse cerebellar cultures affects neuronal migration

The role of taurine in the process of neuronal migration was studied in a microwell cell culture system. Immunocytochemical analysis of the cellular composition of this culture system revealed the presence of the astrocytic marker GFAP in some structures such as the aggregates of neuronal bodies and in those cables used for migration, resembling what is described in vivo. The neuronal marker gamma-enolase stained practically all structures, including the aggregates and all cables. The intracellular taurine concentration was reduced by 60% in mouse cerebellar granule cells treated with a blocker of taurine transport, guanidinoethane sulfonate (GES). Under these conditions cell migration was markedly reduced to approximately 50% of that in untreated cultures. Both, taurine depletion and impairment of cell migration induced by GES were prevented by adding taurine to the culture medium. Taurine deficiency similarly affected different morphological parameters such as the number of cables suitable for neuronal migration as well as the number of migrating neurons. The number of aggregates of neuronal bodies was significantly increased, by about 30%, as a consequence of the reduced migration. Taurine alone did not exert any effect on the parameters evaluated. GES treatment of granule cells did not affect mitochondrial metabolism or K(+)-stimulated Ca(2+)-dependent [3H]-D-aspartate release. This suggests that the described effects of taurine deficiency were not due to an alteration of neuronal viability and that the action of GES was not simply due to unspecific and deleterious effects. These results are in agreement with those obtained in in vivo studies. This approach represents a useful model to investigate the role played by taurine in the process of neuronal migration.

Taurine in the developing cat: uptake and release in different brain areas

Taurine is an important modulator of neuronal activity in the immature brain. In kittens, taurine deficiency causes serious dysfunction in the cerebellar and cerebral visual cortex. The processes of taurine transport in vitro were now studied for the first time in different brain areas in developing and adult cats. The uptake of taurine consisted initially of two saturable components, high- and low-affinity, in synaptosomal preparations from the developing cerebral cortex and cerebellum, but the high-affinity uptake component completely disappeared during maturation. The release of both endogenous and preloaded labeled taurine from brain slices measured in a superfusion system was severalfold stimulated with a slow onset by depolarizing K+ (50 mM) concentrations. K+ stimulation released markedly more taurine from the cerebral cortex, cerebellum and brain stem in kittens than in adult cats. The responses were largest in the cerebellum. Both uptake and release of taurine are thus highly efficient in the brain of kittens and may be of significance in view of the vulnerability of cats to taurine deficiency.

The effect of a taurine modified diet on normal and hydropic ears of the guinea pig

Taurine is recognised as the major osmoregulating amino acid in the brain as well as other organs. Its possible influence on normal cochlear function and on hydropic cochleas of the guinea pig was investigated here. Normally hearing adult guinea pigs were placed on either a taurine-depleting diet (B-alanine) or a taurine-supplemented diet. At the end of 6 weeks the compound action potential audiograms (CAP) in the two groups were similar and appeared not to be different from a third control group receiving a non modified diet which suggested that a taurine-modified diet had not affected normal cochlear function. In hydropic ears the taurine-depleting diet was observed, in some cases, to moderately slow down the early phase of the characteristic progression of the CAP sensitivity loss. These data are in favor of a homeostatic role for taurine in the inner ear of the guinea pig under particular conditions such as osmoregulatory stress.

Visualization of taurine, GABA and glutamate in developing feline cerebellum by immunohistochemistry

The localization of taurine, GABA and glutamate in developing feline cerebellum was performed using antibodies raised against the amino acids conjugated to bovine serum albumin with glutaraldehyde. Distinct patterns of immunostaining were observed for each of the amino acids. Taurine-like immunoreactivity reached a peak at 4 weeks after birth, as did GABA-like immunoreactivity, whereas glutamate-like immunoreactivity was greatest in the mature cerebellum. Purkinje cells are all taurine-positive in cerebellum from neonatal animals, whereas in the mature cerebellum they appear to contain only GABA and glutamate, with virtually no taurine, in contrast to observations reported with rodent cerebellum. Ultrastructural studies and immunogold labelling visualized by electron microscopy show that the band of taurine-like immunoreactivity observed in newborn feline cerebellum is localized within dendrites, axons and glial processes. Granule cells migrating through this region also show prominent taurine-like immunoreactivity.