Developmental regulation of the hypothalamic metabotropic glutamate receptor mGluR1

Abstract

The expression of the metabotropic glutamate receptor mGluR1 was studied with Northern and Western blot analysis, with immunocytochemistry, and with Ca2+ digital imaging in the developing rat hypothalamus. mGluR1 is coupled to a G protein and activation by glutamate and related agonists leads to intracellular phosphotidylinositol hydrolysis and Ca2+ mobilization. mGluR1 RNA could be detected in embryonic hypothalamus, and by the day of birth and prior to the primary period of synaptogenesis, both mGluR1 RNA and protein were strongly expressed. In parallel experiments with digital imaging of cultured hypothalamic cells, some embryonic day 18 hypothalamic neurons and many astrocytes after 3 d in vitro showed Ca2+ responses to quisqualate and t-ACPD, and to glutamate in the absence of extracellular Ca2+. A greater number of embryonic neurons responded to NMDA than to agonists of the metabotropic receptor. With increased development time in culture, the number of neurons that responded to metabotropic glutamate receptor agonists increased. In the adult hypothalamus, mGluR1-immunoreactive neurons were widespread, and particularly dense in the dorsomedial, lateral, and anterior hypothalamus/preoptic areas, and in the mammillary body. Strongly immunoreactive cells were interspersed among neurons with no immunoreactivity. In developing neurons a diffuse immunostaining appeared along dendrites and somata. With time, beginning in the first week after birth, strongly stained puncta appeared, possibly associated with synaptic specializations. These puncta were numerous on dendrites of some adult neurons, and were the most strongly stained regions of neurons. Neurons developing in vitro at low neuron densities showed a development of mGluR1 immunoreactivity similar to that of neurons in vivo, but with a delayed progression of immunostaining. We found no obvious staining of axons or of astrocytes. A strong expression of mGluR1 protein was found in the hypothalamus during the first 2 postnatal weeks; this expression was partially reduced in adults. In contrast, cerebellum showed no reduction in mGluR1 protein in adults. Together these data suggest a complex regulation of mGluR1 during development, with sufficient expression of functional receptors in the developing hypothalamus to modulate morphogenesis and synaptogenesis, and later to play a role in transduction of glutamate signals in the adult. Different regions of the brain showed dramatic differences in the way each expresses mGluR1 during development.

Dual neurotoxic and neuroprotective role of metabotropic glutamate receptor 1 in conditions of trophic deprivation – Possible role as a dependence receptor

“…In its capacity as a dependence receptor, mGlu1 may mediate neuronal apoptosis in response to a reduced concentration of glutamate and may play a crucial role in controlling the fate of neuronal cells in brain development. This is consistent with the toxic effect of mGlu1 antagonist CPCCOEt reported in differentiating Purkinje cells (Catania et al, 2001) and observations that mGlu1 expression is higher in neonatal and early postnatal than in the adult brain (Casabona et al, 1997;van den Pol et al, 1994). Moreover, mGlu1 is highly expressed in Cajal-Retzius cells of rat neocortex and hippocampus which are eliminated within ten days after birth (Lopez-Bendito et al, 2002).…”

Cytomegalovirus InducesInterferon-Stimulated Gene Expression and Is Attenuated by Interferon in the DevelopingBrain

“…A blot from this gel was hybridized sequentially overnight first with a 32 P-labeled OAS probe and subsequently with a radiolabeled mouse ␤-actin probe. Further details relating to the Northern blotting methods are found elsewhere (56).…”

Glutamate Inhibits GABA Excitatory Activity in Developing Neurons

“…The Northern results presented here are the results using PCR-amplified small DNA fragments, because these probes gave cleaner results with very little background versus restriction enzyme digested larger DNA fragments. Details are found in our previous papers (van den Pol et al, 1994;Ghosh et al, 1997).…”

“…Immunostaining for metabotropic glutamate receptors has shown widespread expression in different regions of the adult and developing hypothalamus (van den Pol, 1994;van den Pol et al, 1994van den Pol et al, , 1995. To test the hypothesis that the glutamate-mediated reduction in GABA-evoked C a 2ϩ rise was in part caused by activation of metabotropic glutamate receptors (mGluRs), we used two group I / II nonselective mGluR agonists, trans-(Ϯ)-1-amino-1,3-cyclopentanedicarboxylate (t-AC PD; Research Biochemicals), and (2S,1ЈS,2ЈS)-2-carboxycyclopropyl-glycine (L-CCG-I; Tocris Cookson).…”