To study the function of GLAST, a glutamate transporter highly expressed in the cerebellar Bergmann astrocytes, the mouse GLAST gene was inactivated. GLAST-deficient mice developed normally and could manage simple coordinated tasks, such as staying on a stationary or a slowly rotating rod, but failed more challenging task such as staying on a quickly rotating rod. Electrophysiological examination revealed that Purkinje cells in the mutant mice remained to be multiply innervated by climbing fibres even at the adult stage. We also found that oedema volumes in the mutant mice increased significantly after cerebellar injury. These results indicate that GLAST plays active roles both in the cerebellar climbing fibre synapse formation and in preventing excitotoxic cerebellar damage after acute brain injury.

In the retina, the glutamate transporter GLAST is expressed in Müller cells, whereas the glutamate transporter GLT-1 is found only in cones and various types of bipolar cells. To investigate the functional role of this differential distribution of glutamate transporters, we have analyzed GLAST and GLT-1 mutant mice. In GLAST-deficient mice, the electroretinogram b-wave and oscillatory potentials are reduced and retinal damage after ischemia is exacerbated, whereas GLT-1-deficient mice show almost normal electroretinograms and mild increased retinal damage after ischemia. These results demonstrate that GLAST is required for normal signal transmission between photoreceptors and bipolar cells and that both GLAST and GLT-1 play a neuroprotective role during ischemia in the retina.L-Glutamate is the major excitatory neurotransmitter in the mammalian retina (1). High-affinity glutamate transporters are believed to be essential for terminating synaptic transmission as well as for keeping the extracellular glutamate concentration below neurotoxic levels (1, 2). Five subtypes of glutamate transporter (GLAST, GLT-1, EAAC1, EAAT4, and EAAT5) (3-8) have been cloned, but the contributions of individual transporter subtypes to retinal function are poorly understood. Studies have been hampered by the lack of subtype-selective glutamate transporter drugs. As an alternative approach, we have analyzed GLAST-and GLT-1-deficient mice (9, 10). Our results demonstrate that GLAST is required in retinal signal transmission at the level of the photoreceptor and bipolar cell and that GLAST and GLT-1 are crucial for the protection of retinal cells from glutamate neurotoxicity. MATERIALS AND METHODSImmunohistochemistry. Mice were anesthetized with diethyl ether and perfused transcardially with saline, followed by 4% paraformaldehyde in 0.1 M sodium phosphate buffer containing 0.5% picric acid at room temperature. Eyes were removed and postfixed overnight in the same fixative, and 7-m-thick paraffin or frozen sections were cut and mounted onto gelatin-and poly-L[D]-lysine-coated slides. The sections were incubated overnight with an affinity-purified rabbit polyclonal antibody against the carboxyl-terminal sequence of the mouse GLAST (1.0 g͞ml) (KKPYQLIAQDNEPEKPVAD-SETKM) (11, 12), an affinity-purified rabbit polyclonal antibody against the rat GLT-1 (0.2 g͞ml) [anti-B12; gift from N. C. Danbolt] (13), or a mouse monoclonal antibody against glutamate synthetase (GS) (2.0 g͞ml) (Chemicon) at room temperature. The sections were then incubated with biotinylated goat anti-rabbit IgG (Nichirei, Tokyo) for GLAST and GLT-1 or biotinylated rabbit anti-mouse IgG (Nichirei) for GS for 1 hr, followed by further incubation with streptavidin-Texas red (NEN) for 30 min at room temperature. Sections were examined by a confocal laser scanning microscope (Molecular Dynamics).Electroretinograms (ERGs). Mice (9-11 weeks old) were anesthetized by intraperitoneal injection of a mixture of xylazine (10 mg͞kg) and ketamine (25 mg͞kg). The pupils were dilat...

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There are two known major angiotensin II receptor subtypes, type 1 (AT1) and type 2 (AT2), both of which are present in the brain. AT1 and AT2 receptors occur in characteristic distributions that are highly correlated with the distribution of angiotensin II-like immunoreactivity in nerve terminals. Acting through the AT1 receptor in the central nervous system, angiotensin II has effects on fluid and electrolyte homeostasis, neuroendocrine systems, autonomic pathways regulating cardiovascular function and behavior. While the role of the AT2 receptor in the brain is less well understood, recent knockout studies point to their involvement in behavioral and cardiovascular functions. We discuss here evidence regarding the function of the AT2 receptor in the brain, determined using mice lacking the AT2 receptor.

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