Extracellular levels of the excitatory neurotransmitter glutamate in the nervous system are maintained by transporters that actively remove glutamate from the extracellular space. Homozygous mice deficient in GLT-1, a widely distributed astrocytic glutamate transporter, show lethal spontaneous seizures and increased susceptibility to acute cortical injury. These effects can be attributed to elevated levels of residual glutamate in the brains of these mice.

There are two major angiotensin II receptor isoforms, AT1 and AT2. AT1 mediates the well-known pressor and mitogenic effects of angiotensin II, but the signalling mechanism and physiological role of AT2 has not been established. Its abundant expression in fetal tissues and certain brain nuclei suggest possible roles in growth, development and neuronal functions. Here we report the unexpected finding that the targeted disruption of the mouse AT2 gene resulted in a significant increase in blood pressure and increased sensitivity to the pressor action of angiotensin II. Thus AT2 mediates a depressor effect and antagonizes the AT1-mediated pressor action of angiotensin II. In addition, disruption of the AT2 gene attenuated exploratory behaviour and lowered body temperature. Our results show that angiotensin II activates AT1 and AT2, which have mutually counteracting haemodynamic effects, and that AT2 regulates central nervous system functions, including behaviour.

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.

Prolonged or high-intensity exposure to visible light leads to photoreceptor cell death. In this study, we demonstrate a novel pathway of light-induced photoreceptor apoptosis involving the low-affinity neurotrophin receptor p75 (p75NTR). Retinal degeneration upregulated both p75NTR and the high-affinity neurotrophin receptor TrkC in different parts of Müller glial cells. Exogenous neurotrophin-3 (NT-3) increased, but nerve growth factor (NGF) decreased basic fibroblast growth factor (bFGF) production in Müller cells, which can directly rescue photoreceptor apoptosis. Blockade of p75NTR prevented bFGF reduction and resulted in both structural and functional photoreceptor survival in vivo. Furthermore, the absence of p75NTR significantly prevented light-induced photoreceptor apoptosis. These observations implicate glial cells in the determination of neural cell survival, and suggest functional glial-neuronal cell interactions as new therapeutic targets for neurodegeneration.

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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(+)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (4, LY354740), a highly selective and orally active group II metabotropic glutamate receptor (mGluR) agonist, has increased interest in the study of group II mGluRs. Our interest focused on a conformationally constrained form of compound 4, because it appeared that the rigid form resulted in not only selectivity for group II mGluR but was orally active. Therefore, we introduced a fluorine atom to compound 4, based on the molecular size (close resemblance to hydrogen atom) and electronegativity (effects on the electron distribution in the molecule) of this atom and carbon-fluorine bond energy. Compound (+)-7 (MGS0008), the best compound among 3-fluoro derivatives 7-10, retained the agonist activity of compound 4 for mGluR2 and mGluR3 ((+)-7: EC(50) = 29.4 +/- 3.3 nM and 45.4 +/- 8.4 nM for mGluR2 and mGluR3, respectively; 4: EC(50) = 18.3 +/- 1.6 nM and 62.8 +/- 12 nM for mGluR2 and mGluR3, respectively) and increased the oral activity of compound 4 ((+)-7: ED(50) = 5.1 mg/kg and 0.26 mg/kg for phencyclidine (PCP)-induced hyperactivity and PCP-induced head-weaving behavior, respectively; 4: ED(50) = >100 mg/kg and 3.0 mg/kg for PCP-induced hyperactivity and PCP-induced head-weaving behavior, respectively). In addition, a compound [(3)H]-(+)-7 binding study using mGluR2 or 3 expressed in CHO cells was successful ((+)-7: K(i) = 47.7 +/- 17 nM and 65.9 +/- 7.1 nM for mGluR2 and mGluR3, respectively; 4: K(i) = 23.4 +/- 7.1 nM and 53.5 +/- 13 nM for mGluR2 and mGluR3, respectively). On the basis of a successful result of compound 7, we focused on the introduction of a fluorine atom on the C6 position of compound 4. (1R,2S,5R, 6R)-2-amino-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid ((-)-11) exhibited a high degree of agonist activity for group II mGluRs equal to that of compound 4 or 7 ((-)-11: K(i) = 16.6 +/- 5.6 and 80.9 +/- 31 nM for mGluR2 and mGluR3, respectively). Our interest shifted to modification on CH(2) at C4 position of compound 11, since replacement of the CH(2) group with either an oxygen atom or sulfur atom yielded compound 5 or 6, resulting in increased agonist activity. We selected a carbonyl group instead of CH(2) at the C4 position of compound 11. The carbonyl group might slightly change the relative conformation of three functional groups, the amino group and two carboxylic acids, which have important roles in mediating the interaction between group II mGluRs and their ligand, compared with the CH(2) group of 4, oxygen atom of 5, and sulfur atom of 6. (1R,2S,5S,6S)-2-Amino-6-fluoro-4-oxobicyclo[3.1. 0]hexane-2,6-dicarboxylic acid monohydrate ((+)-14, MGS0028) exhibited a remarkably high degree of agonist activity for mGluR2 (K(i) = 0.570 +/- 0.10 nM) and mGluR3 (K(i) = 2.07 +/- 0.40 nM) expressed in CHO cells but not mGluR4, 6, 7, 1a, or 5 expressed in CHO cells (K(i) = >100 000 nM). Furthermore, compound (+)-14 strongly inhibited phencyclidine (PCP)-induced head-weaving behavior (ED(50) = 0.090 microg/kg) and hyperactivity (ED(50) = 0.30 ...

Melanin-concentrating hormone (MCH) is a cyclic peptide produced in the lateral hypothalamus. It has been implicated in a number of physiological processes including feeding behavior, energy balance, and the regulation of emotional states. (1-10 mg/kg) significantly reduced immobility time in the forced swimming test in rats, indicating antidepressantlike effects. Both ATC0065 and ATC0175 significantly reversed swim stress-induced anxiety in the elevated plus-maze test in rats and stress-induced hyperthermia in mice. ATC0175 significantly increased social interaction between unfamiliar rats and reduced separation-induced vocalizations in guinea pig pups, indicating anxiolytic potential. In contrast, ATC0065 and ATC0175 did not affect spontaneous locomotor activity or rotarod performance in rats. These findings indicate that ATC0065 and ATC0175 are potent and orally active MCHR1 antagonists with anxiolytic and antidepressant activity in rodents.Melanin-concentrating hormone (MCH) is a cyclic neuropeptide originally isolated from salmon pituitary (Kawaguchi et al., 1983). In mammals, MCH is produced predominantly by neurons in the lateral hypothalamus and zona incerta with extensive projections throughout the brain (Bittencourt et al., 1992). This expression pattern supports a role for MCH in numerous physiological processes including motivated behavior, stress responses, regulation of neuroendocrine function, and feeding.Several groups independently identified a G protein-coupled receptor, SLC-1/GPR24, as an MCH receptor (MCHR1) (Bachner et al., 1999;Chambers et al., 1999;Lembo et al., 1999;Saito et al., 1999;Shimomura et al., 1999), and MCHR2 was identified subsequently on the basis of the sequence homology to MCHR1 Hill et al., 2001;Mori et al., 2001;Sailer et al., 2001). Potential physiological functions of MCHR2 have not been elucidated due to the species-specific expression of the receptor (Tan et al., 2002); therefore, current research has focused on MCHR1.There are several lines of evidence implicating MCHR1 in feeding and energy homeostasis. MCHR1 mRNA is increased Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.