Plasticity of Astroglial Glutamate and γ‐Aminobutyric Acid Uptake in Cell Cultures Derived from Postnatal Mouse Cerebellum

Abstract

The plasticity of astroglial glutamate and gamma-aminobutyric acid (GABA) uptakes was investigated using mouse cerebellar cell cultures. The influence of external factors, such as different sera and/or the presence of neurons, was examined. Control autoradiography experiments showed that after short-term exposure to radioactive amino acids, granule cells took up neither glutamate nor GABA, and beta-alanine predominantly inhibited astroglial GABA uptake. Astroglial uptake was quantified by measuring the radioactivity taken up by the cells in the culture and relating this measurement to the number of glial fibrillary acidic protein-positive cells present. Glutamate uptake was investigated in astroglial cultures and subcultures and in neuronal-astroglial cultures derived from postnatal day 4 mouse cerebella. In the absence of neurons, glutamate uptake increased during the first 9 days after plating and then leveled off. At 14 days in vitro in horse serum, which favors the differentiation of fibrous-like astrocytes, glutamate uptake related to astrocyte number was twice as high as in fetal calf serum. In the presence of cerebellar neurons, this rate was even higher. The specificity of the responsiveness of astrocytes to neurons with respect to glutamate uptake was investigated by comparing GABA uptake in the different culture conditions. Neurons also increased the rate of GABA uptake by astrocytes. Another component of the astroglial plasma membrane, the density of beta-adrenergic receptors, was, however, not markedly affected by the presence of neurons. Hence, these results showed that in astrocytes plated from postnatal day 4 mouse cerebella, the level of neurotransmitter uptake can be regulated in vitro by factors present in sera and by cerebellar neurons in the culture. However, this plasticity declined during development because astrocytes plated from postnatal day 8 cerebella and cultured under identical conditions were less active in glutamate uptake and were insensitive to the presence of horse serum. The latter observation suggested that the metabolic plasticity of astrocytes is restricted to a period defined early in cerebellar development and is no longer evident by postnatal day 8.

High Affinity Glutamate Transporters: Regulation of Expression and Activity

“…Several types of metabotropic and ionotropic glutamate receptors are expressed in neurons and astrocytes (54,55), and their possible involvement in the regulation of glutamate uptake is an obvious issue. More than a decade ago, Schousboe and co-workers (56) reported the up-regulation of the glutamate uptake in astroglial cultures supplemented with conditioned media from neuronal cultures, an observation subsequently confirmed by others (57). The magnitude and specificity of the effect seemed to be dependent on the regional origin of the cultures used.…”

“…However, several growth factors, cytokines, and hormones so far tested had no apparent effect on the expression of glutamate transporters in vitro (91), and only tumor necrosis factor-␣ and glucocorticoids were capable of inhibiting the glutamate uptake in cultured astrocytes without affecting the transporter protein levels (94,95). However, horse serum, which compared with fetal calf serum contains higher concentrations of some unidentified differentiation-promoting factors, markedly up-regulates glutamate uptake in cerebellar astrocytes (57). In an early study, yet unknown macromolecular factors released from neurons were strongly suspected to up-regulate glutamate transport in astroglial cultures, although the precise molecular nature of this phenomenon could not be established because of the unavailability of molecular probes for individual glutamate transporters (91).…”

Spontaneous intracellular calcium oscillations in cortical astrocytes from a patient with intractable childhood epilepsy (Rasmussen's Encephalitis)

“…Astrocytes can express GluR3 (Condorelli et al, 1993); however, a combination of multiple media changes and receptor turnover over the period of 3 weeks when oscillations were observed probably would have eliminated this possibility. Astrocytes displaying different characteristics over time in culture is not a novel observation (Andersson et al, 1994;Nilsson et al, 1992;Shao and McCarthy, 1993;Thio et al, 1993;Voisin et al, 1993). It is possible that the change in behavior over time is simply due to culture conditions.…”

[1‐13C]Glucose metabolism in rat cerebellar granule cells and astrocytes in primary culture

“…For instance, it has been shown that glutamine synthesis (Hayashi et al, 1988;Mearow et al, 1990) and glutamate uptake by astrocytes (Voisin et al, 1993), on the one hand, and glutamate synthesis and release from granule cells (Westergaard et al, 1991), on the other hand, are modulated by the presence of granule cells and astrocytes, respectively. Moreover, cooperativity between neurons and astroglia for CO, fixation has been proposed by Kaufman and Driscoll (1992).…”