N-methyl-D-aspartate receptor subunit NR2B is widely expressed throughout the rat diencephalon: An immunohistochemical study

Abstract

Glutamate (Glu), a major excitatory neurotransmitter within the hypothalamus and thalamus, acts upon many receptors, including the N-methyl-D-aspartate (NMDA) subtype. Abundant evidence suggests that variations in the subunit composition of NMDA receptors (NMDA-Rs) contribute to differences in Glu's immediate electrophysiological effects as well as to the patterns of signal transduction cascades it triggers to mediate long-term changes in neuronal function. We have previously shown that hypothalamic NMDA-Rs containing the NR2B subunit may be involved in the control of eating as well as in the mediation of physiological responses to osmotic stimuli. To broaden our understanding of diencephalic NMDA-R participation in other functions, we localized the NR2B subunit in the diencephalon of the adult male rat using immunoperoxidase, immunogold, and immunofluorescence techniques and an affinity-purified polyclonal antibody specific for the NR2B subunit of the NMDA-R. In addition, we used a monoclonal NR2B antibody with immunoperoxidase detection to confirm the NR2B distribution seen with the polyclonal antibody. In the hypothalamus, the highest levels of NR2B immunoreactivity (-ir) were found in the magnocellular neurosecretory system, including the paraventricular and supraoptic nuclei. A new finding was that intense NR2B-ir was present within perivascular "accessory" magnocellular groups of this system, including the nucleus circularis, anterior fornical nucleus, and scattered clusters of lateral hypothalamic cells apposed to blood vessels. Robust NR2B-ir was also present within the arcuate nucleus, the median eminence, and the tuberal nucleus, and light immunostaining was found in all other hypothalamic nuclei examined. In the thalamus, the highest NR2B-ir was observed in the medial habenula and the anterodorsal, paraventricular, rhomboid, reticular, and dorsal lateral geniculate nuclei. As in the hypothalamus, all thalamic nuclei examined displayed at least light immunostaining for this subunit. Control sections, including those incubated with the polyclonal NR2B antibody preadsorbed with its fusion protein, were virtually devoid of immunostaining. This demonstration that the NR2B subunit of the NMDA-R is widely distributed in the diencephalon, implicates it in a wide variety of functions, and provides a useful anatomical framework for establishing a comprehensive map of Glu receptor populations within this major subdivision of the brain.

Lateral Hypothalamic Signaling Mechanisms Underlying Feeding Stimulation: Differential Contributions of Src Family Tyrosine Kinases to Feeding Triggered Either by NMDA Injection or by Food Deprivation

“…Thus, neither NMDA injection nor food deprivation appears to be associated with changes in the Tyr-P levels of the NR2A and NR2B NMDA-R subunits, although such changes may occur in only subpopulations of LHA neurons and, therefore, at levels that escaped detection by our methods. However, these results do confirm reports of NR2A and NR2B NMDA-R subunits in the LHA (Khan et al, 1999(Khan et al, , 2000b and also provide the first evidence that these subunits are tyrosine-phosphorylated in this region.…”

“…As described previously (Khan et al, 1999(Khan et al, , 2000b, adult male Sprague Dawley rats (325-475 gm; n ϭ 11) were anesthetized with sodium pentobarbital (60 mg/kg, i.p.) and perfused through the ascending aorta with at least 100 ml of cold, heparinized PBS (0.01 M sodium phosphate buffer in 0.9% saline, containing 200 U/l heparin), followed by at least 300 ml of ice-cold 4% p-formaldehyde in 0.1 M sodium phosphate buffer, pH 7.4.…”

“…strates sensitive to the feeding stimulation effects of neuropeptide Y, hypocretin/ orexin, or Glu (Stanley et al, 1992(Stanley et al, , 1993aKhan et al, 2000b;Marcus et al, 2001;Backberg et al, 2002;Lee and Stanley, 2002;Wolak et al, 2003), suggesting that Src can interact with signaling components of these neural substrates to influence feeding or other behaviors.…”

Enhanced NMDA receptor NR1 phosphorylation and neuronal activity in the arcuate nucleus of hypothalamus following peripheral inflammation

“…Furthermore, peripheral noxious stimulation modulates the spontaneous discharges of neurons in ARC, indicating that peripheral nociceptive information is sent to the hypothalamic nucleus and can result in neuronal activation in ARC [17] . In addition, glutamate and glutamate receptors, such as NMDA receptors, are highly expressed in the nuclei of the medial hypothalamus, including ARC [18][19][20][21][22][23][24] . Based on these observations, we hypothesized that hypothalamic ARC, a supraspinal center in pain modulation, might be a locus for central sensitization induced by injuries in peripheral tissues.…”

Glutamatergic Inputs in the Hypothalamic Paraventricular Nucleus Maintain Sympathetic Vasomotor Tone in Hypertension

“…14 -16 An abundance of glutamate-immunoreactive synapses [17][18][19] and the N-methyl-D-aspartate (NMDA) and ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor mRNA and proteins exist in the PVN. 20,21 The glutamatergic synaptic inputs to the PVN neurons are from glutamatergic interneurons within the PVN, subnuclei of the hypothalamus, and telencephalic regions. 14,22,23 Microinjection of glutamate or NMDA into the PVN increases arterial blood pressure, sympathetic nerve activity, and plasma norepinephrine concentration in anesthetized and conscious rats.…”