Parkinson disease (PD) is a progressive neurodegenerative disease whose progression may be slowed, but at present there is no pharmacological intervention that would stop or reverse the disease. Liver X receptor β (LXRβ) is a member of the nuclear receptor super gene family expressed in the central nervous system, where it is important for cortical layering during development and survival of dopaminergic neurons throughout life. In the present study we have used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to investigate the possible use of LXRβ as a target for prevention or treatment of PD. The dopaminergic neurons of the substantia nigra of LXRβ −/− mice were much more severely affected by MPTP than were those of their WT littermates. In addition, the number of activated microglia and GFAPpositive astrocytes was higher in the substantia nigra of LXRβ −/− mice than in WT littermates. Administration of the LXR agonist GW3965 to MPTP-treated WT mice protected against loss of dopaminergic neurons and of dopaminergic fibers projecting to the striatum, and resulted in fewer activated microglia and astroglia. Surprisingly, LXRβ was not expressed in the neurons of the substantia nigra but in the microglia and astroglia. We conclude that LXR agonists may have beneficial effects in treatment of PD by modulating the cytotoxic functions of microglia.midbrain | neurodegeneration | neuroinflammation P arkinson disease (PD) is a common neurodegenerative disorder whose clinical features include tremor, slowness of movement, stiffness, and postural instability (1). PD is characterized by microgliosis, astrogliosis, progressive degeneration of dopaminergic neurons, presence of Lewy bodies in dopaminergic neurons, and α-synuclein accumulation in substantia nigra pars compacta (2). Although there are drugs that alleviate symptoms of PD, chronic use of these drugs results in debilitating side effects (3), and none seems to halt the progression of the disease. The etiology of PD remains unknown, but environmental toxins, genetic factors, and mitochondrial dysfunction are thought to be involved. Neuroinflammation (microglial activation, astrogliosis, and lymphocyte infiltration) results in production of cytotoxic molecules (4-9) that are directly involved in neuronal degeneration. It is now recognized that targeting neuroinflammation is one intervention that can slow down the progression of PD (10).1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that targets rather specifically dopaminergic neurons that are involved in PD; its administration leads to severe and irreversible PD-like syndrome in humans and nonhuman primates, with most of the biochemical and pathological hallmarks of PD (11), i.e., marked loss of dopaminergic neurons, astrogliosis, and activated microglia in the substantia nigra pars compacta (12). In 2002, Wu et al. (13) showed that dopaminergic neurons in the substantia nigra could be protected from MPTP-induced damage by the tetracycline derivative minocycline. This capaci...

An estrogen receptor (ER) β ligand (LY3201) with a preference for ERβ over ERα was administered in s.c. pellets releasing 0.04 mg/d. The brains of these mice were examined 3 d after treatment had begun. Although estradiol-17β is known to increase spine density and glutaminergic signaling, as measured by Golgi staining, a clear reduction in spines was evident on the dendritic branches in LY3201-treated mice but no morphological alteration and no difference in the number of dendritic spines on dendritic stems were observed. In the LY3201-treatment group, there was higher expression of glutamic acid decarboxylase (GAD) in layer V of cortex and in the CA1 of hippocampus, more GAD + terminals surrounding the pyramidal neurons and less glutamate receptor (NMDAR) on the neurons in layer V. There were no alterations in expression of Iba1 or in Olig2 or CNPase. However, GFAP + astrocytes were increased in the LY3201-treatment group. There were also more projections characteristic of activated astrocytes and increased expression of glutamine synthetase (GS). No expression of ERβ was detectable in the nuclei of astrocytes. Clearly, LY3201 caused a shift in the balance between excitatory and inhibitory neurotransmission in favor of inhibition. This shift was due in part to increased synthesis of GABA and increased removal of glutamate from the synaptic cleft by astrocytes. The data reveal that treatment with a selective ERβ agonist results in changes opposite to those reported in estradiol-17β-treated mice and suggests that ERα and ERβ play opposing roles in the brain.neurotransmitter | glutamate toxicity | cerebral cortex | hippocampus O f the two estrogen receptors (ERs), ERα appears to be the major player in regulating the reproductive system, whereas both receptors ERα and ERβ are involved in regulation of mood and affective disorders (1, 2). Several studies show that ERα activation is anxiogenic (3-5), whereas ERβ activation is anxiolytic and controls expression of fear and anxiety-like behaviors (6-9). Not surprisingly, estradiol (E2), which binds equally well to ERα and ERβ, has unpredictable effects on abnormal psychiatric behaviors, depending on dose, treatment regimens, or animal models (10-13). In hippocampal cultures both exogenous (E2) treatment and locally synthesized E2 up-regulate ERα and down-regulate ERβ expression (14). Thus, E2 has unpredictable effects on the balance between anxiogenic and anxiolytic effects, in part because E2 has opposite effects on ERα and ERβ (15). Using subtype-selective ligands, we can begin to study the outcome of selective activation or inhibition of a particular receptor subtype involved in different behaviors.Spines and the synapses located on neurons are the sites at which neuronal communication occurs and are essential for complex behavioral phenomena and cognition. In the mature CNS, alterations in synapse structure and function continue to be a dynamic process that is of fundamental importance to learning and memory as well as other adaptive abilities of the brain. Studies...

Anxiety disorders are the most prevalent mental disorders in adolescents in the United States. Female adolescents are more likely than males to be affected with anxiety disorders, but less likely to have behavioral and substance abuse disorders. The prefrontal cortex (PFC), amygdala, and dorsal raphe are known to be involved in anxiety disorders. Inhibitory input from the PFC to the amygdala controls fear and anxiety typically originating in the amygdala, and disruption of the inhibitory input from the PFC leads to anxiety, fear, and personality changes. Recent studies have implicated liver X receptor β (LXRβ) in key neurodevelopmental processes and neurodegenerative diseases. In the present study, we used elevated plus-maze, startle and prepulse inhibition, open field, and novel object recognition tests to evaluate behavior in female LXRβ KO (LXRβ −/− ) mice. We found that the female LXRβ −/− mice were anxious with impaired behavioral responses but normal locomotion and memory. Immunohistochemistry analysis revealed decreased expression of the enzyme responsible for GABA synthesis, glutamic acid decarboxylase (65+67), in the ventromedial PFC. Expression of tryptophan hydroxylase 2 in the dorsal raphe was normal. We conclude that the anxiogenic phenotype in female LXRβ −/− mice is caused by reduced GABAergic input from the ventromedial PFC to the amygdala.

In the past year, two members of the nuclear receptor family, liver X receptor β (LXRβ) and thyroid hormone receptor α (TRα), have been found to be essential for correct migration of neurons in the developing cortex in mouse embryos. TRα and LXRβ bind to identical response elements on DNA and sometimes regulate the same genes. The reason for the migration defect in the LXRβ −/− mouse and the possibility that TRα may be involved are the subjects of the present study. At E15.5, expression of reelin and VLDLR was similar but expression of apolipoprotein E receptor 2 (ApoER2) (the reelin receptor) was much lower in LXRβ −/− than in WT mice. Knockout of ApoER2 is known to lead to abnormal cortical lamination. Surprisingly, by postnatal day 14 (P14), no morphological abnormalities were detectable in the cortex of LXRβ −/− mice and ApoER2 expression was much stronger than in WT controls. Thus, a postnatal mechanism leads to increase in ApoER2 expression by P14. TRα also regulates ApoER2. In both WT and LXRβ −/− mice, expression of TRα was high at postnatal day 2. By P14 it was reduced to low levels in WT mice but was still abundantly expressed in the cortex of LXRβ −/− mice. Based on the present data we hypothesize that reduction in the level of ApoER2 is the reason for the retarded migration of later-born neurons in LXRβ −/− mice but that as thyroid hormone (TH) increases after birth the neurons do find their correct place in the cortex.