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Immunohistochemical localization of a GHB receptor-like protein isolated from rat brain

Institut de Chimie Biologique and INSERM U-575, Faculty of Medicine, 67085 Strasbourg, France.
The Journal of Comparative Neurology (Impact Factor: 3.51). 10/2006; 498(4):508-24. DOI: 10.1002/cne.21072
Source: PubMed

ABSTRACT Gamma-hydroxybutyrate (GHB) is a substance derived from the metabolism of GABA and is heterogeneously distributed in various regions of the brain. This compound possesses a neuromodulatory role on several types of synapses, particularly those using GABA as a neurotransmitter. At physiological concentrations, this effect of GHB is mediated via specific receptors that induce neuronal hyperpolarization and bind radioactive GHB with a specific distribution, ontogenesis, kinetics, and pharmacology. A membrane protein that possesses six to seven transmembrane domains and which binds and is activated by micromolar amounts of GHB was recently cloned from rat brain hippocampus. In order to study the regional and cellular distribution of this receptor in rat brain, we selected several specific peptides belonging to the extracellular domains of the receptor to be used as specific immunogens to raise polyclonal antibodies in the rabbit. Among the antisera obtained, one of them gave particularly good results in terms of specificity and reactivity at high dilution. Immunohistochemical analyses, both at the confocal and electron microscopic level, showed receptor protein distribution closely resembling the distribution of GHB high-affinity binding sites, except for cerebellum, where GHB receptor(s) of lower affinity exist(s). In all regions studied the GHB receptor-like protein labeling appears to be distributed specifically in neurons and not in glial cells. At the cellular level the antibody specifically labels dendrites, and no immunoreactivity was detected in presynaptic endings or in axons. Accordingly, electron microscopy reveals strong labeling of postsynaptic densities and of neuronal cytosol.

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    • "Subsequently, the number of neurons in CA1 hippocampal and prefrontal cortex (PFC) regions was estimated , using stereological methods. Both structures are clearly involved in spatial memory (Brasted et al. 2003 ; Yan et al. 2007) and have an elevated density of high-affinity GHB receptors (Andriamampandry et al. 2003 ; Kemmel et al. 2006 ; Maitre, 1997). "
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    • "ary nucleus, the arcuate nucleus, the polymorphic layer of the dentate gyrus, the laterodorsal tegmental nucleus, the precoeruleus region and the ventrolateral periaqueductal gray. Interestingly, the polymorphic layer of the dentate gyrus contains one of the highest densities of GHB receptors in the brain, suggesting that this might be the mechanism whereby GHB but not baclofen induced Fos expression in this region (Kemmel et al., 2006). Very low concentrations of GHB are capable of activating the G-protein-linked GHB receptor (Andriamampandry et al., 2003) and GHB promotes glutamate release in this hippocampus via a GHB receptordependent mechanism (Castelli et al., 2003). "
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