Differential expression of NMDA and AMPA/KA receptor subunits in the inferior olive of postnatal rats.

We have employed immunohistochemistry to determine the expression patterns of receptor subunits of N-methyl-d-aspartate (NMDA-NR1 and NR2A/B) and alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid/kainic acid (AMPA/KA-GluR1, GluR2, GluR2/3, GluR4, and GluR5/6/7) in the inferior olive of postnatal rats up to adulthood. Immunoreactivity for distinct receptor subunits was predominantly localized in the soma and dendrites of neurons. Semi-quantification showed that the overall immunoreactivity in the inferior olive of adults was intense for GluR1, moderate for NR1 and NR2A/B, and low for GluR2, GluR2/3, GluR4, and GluR5/6/7. At P7, GluR1 was restricted to the dorsomedial cell column, subnucleus beta, principal nucleus and ventrolateral protrusion while the other subunits were found in all subnuclei of the inferior olive. The immunoreactivities for all glutamate receptor subunits ranged from low to moderate. As the rats matured, the immunoreactivity of GluR4 decreased after the second postnatal week, while those of the other subunits showed a general trend of increase, reaching adult level during the third postnatal week. Double immunofluorescence revealed that all NR1-containing neurons exhibited NR2A/B immunoreactivity, indicating that native NMDA receptors comprise of hetero-oligomeric combinations of NR1 and NR2A/B. Furthermore, co-localization of NMDA and AMPA/KA receptor subunits was demonstrated in individual neurons of the inferior olive. All NR1-containing neurons exhibited GluR1 immunoreactivity, and all NR2A/B-containing neurons showed GluR5/6/7 immunoreactivity. Our data suggest that NMDA and AMPA/KA receptors are involved in glutamate-mediated neurotransmission, contributing to synaptic plasticity and reorganization of circuitry in the inferior olive during postnatal development.

Neurokinin B receptor (NK3)-containing neurons in the paraventricular and supraoptic nuclei of the rat hypothalamus synthesize vasopressin and express Fos following intravenous injection of hypertonic saline.

Subnuclear localization of neurokinin B receptor (NK3) in the paraventricular and supraoptic nuclei of the hypothalamus was immunohistochemically investigated in the rat. In the paraventricular hypothalamic nucleus, intense neurokinin B receptor-like immunoreactivity was found in the posterior magnocellular part, moderate to weak neurokinin B receptor-like immunoreactivity was seen in the other parts. In the supraoptic nucleus, intense neurokinin B receptor-like immunoreactivity was distributed in its principal part, and a few neurons with neurokinin B receptor-like immunoreactivity were found in the retrochiasmatic part. Co-localization of neurokinin B receptor-like immunoreactivity with vasopressin-like immunoreactivity was examined through serial adjacent sections. Neurons with both neurokinin B receptor-like immunoreactivity and vasopressin-like immunoreactivity were primarily found in the supraoptic nucleus and posterior magnocellular part of the pavaventricular nucleus. A small number of neurons with neurokinin B receptor-like immunoreactivity and vasopressin-like immunoreactivity were also seen in the circular nucleus and the region surrounding blood vessel in the anterior hypothalamus. Many neurokinin B receptor-containing neurons in the paraventricular and supraoptic nuclei, as well as in circular nucleus and the region surrounding the blood vessel, expressed Fos-like immunoreactivity after intravenous injection of hypertonic saline. The present study demonstrated that a large proportion of neurokinin B receptor-like immunoreactive neurons in the paraventricular hypothalamic and supraoptic nuclei contained vasopressin-like immunoreactivity, and expressed Fos-like immunoreactivity after intravenous administration of hypertonic saline. The results suggest that neurokinin B receptor in the two nuclei may be involved in modulation of the release of vasopressin when the internal environment is disturbed.

Substance P receptor-expressing neurons in the medullary and spinal dorsal horns projecting to the nucleus of the solitary tract in the rat.

By using substance P receptor (SPR) immunofluorescence histochemistry combined with fluorescent retrograde labeling, we examined the distribution of the trigeminal and spinal neurons with SPR-like immunoreactivity (-LI) projecting to the nucleus of the solitary tract in the rat. After injection of Fluoro-Gold (FG) into the nucleus of the solitary tract, FG-labeled neurons showing SPR-LI were mainly seen in lamina I of the medullary and spinal dorsal horns, lamina V and the lateral spinal nucleus of the spinal cord. The present results suggest that the trigeminal and spinal neurons with SPR-LI, especially those in lamina I may be involved in the transmission of somatic and/or visceral nociceptive information from the medullary and spinal dorsal horns to the nucleus of the solitary tract.

Direct projections from the periaqueductal gray to pontine micturition center neurons projecting to the lumbosacral cord segments: an electron microscopic study in the rat.

Direct projections from the periaqueductal gray (PAG) to the pontine micturition center neurons directly projecting to the lumbosacral cord segments were observed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the PAG and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. After injection of BDA into the ventrolateral part of the PAG, many BDA-labeled axons were seen light microscopically in Barrington's nucleus; a moderate number of them were found in the pontine tegmental region just ventral to Barrington's nucleus (D-region [Ding, Y-Q., Takada, M., Tokuno, H. and Mizuno, N., J. Comp. Neurol., 357 (1996) 318-330]). On the other hand, after injection of BDA into the dorsolateral part of the PAG, only a few BDA-labeled axons were seen in Barrington's nucleus or the D-region. BDA-labeled axon terminals were electron microscopically confirmed to be in synaptic contact with HRP-labeled dendrites and somata in Barrington's nucleus and the D-region. The results indicate that the ventrolateral part of the PAG is implicated in regulation of the micturition reflex.

Mesencephalic dopaminergic neurons expressing neuromedin K receptor (NK3): a double immunocytochemical study in the rat.

By using a double immunocytochemical method we examined the distribution of dopaminergic neurons expressing neuromedin K receptor (NKR; NK3) in the rat brain. The distribution of NKR-like immunoreactive (-LI) neurons completely overlapped that of tyrosine hydroxylase (TH)-LI neurons in the retrorubral field (A8), substantia nigra (A9), ventral tegmental area and nucleus raphe linealis (A10). Completely or partially overlapping distributions of NKR- and TH-LI neurons were found in certain regions of the hypothalamus (A11-A15) and olfactory bulb (A16). Neurons showing both NKR- and TH-like immunoreactivities, however, were only found in A8-A10: All of the NKR-LI neurons displayed TH-like immunoreactivity, and about 71-86% of the TH-LI neurons expressed NKR-like immunoreactivity. The present results provided morphological evidence for physiological modulation of dopaminergic neurons by tachykinins through NKR in A8-A10.

Neurokinin B receptor (NK3)-positive neurons expressing c-fos after chemical noxious stimulation on the peritoneum: a double staining study in the nucleus tractus solitarius of the rat.

Neurokinin B receptor (NKR; NK3)-like immunoreactivity (LI) was densely distributed in the nucleus tractus solitarius (NST) of the rat. Approximately 32% of the neurons with NKR-LI in the NST expressed c-fos protein after chemical irritation on the peritoneum with acetic acid. The present results suggest that neurons containing NKR in the NST may be involved in the integration of noxious afferent information from the peritoneum in the rat.