Cellular and subcellular distribution of the amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit GluR2 in the rat dorsal vagal complex

Amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) type glutamate receptors are ligand gated ion channels made up of various combinations of four subunits termed GluR1-4. The GluR2 subunit controls several key features of the receptor including calcium permeability and inward rectification. In the present study, we analysed by immunocytochemistry the cellular and subcellular distribution of the GluR2 subunit in neurons of the dorsal vagal complex of the rat. GluR2 immunoreactivity was found both in the neuropile and in neuronal cell bodies. Perikaryal staining was strong in the dorsal motor nucleus of the vagus nerve and moderate in the medial part of the nucleus tractus solitarii as well as in the area postrema. The lateral part of the nucleus tractus solitarii was almost devoid of immunoreactivity except for the interstitial subnucleus which was filled with numerous strongly immunoreactive perikarya and large cell processes. Ultrastructural examination was carried out in the interstitial subnucleus. Peroxidase staining indicative of GluR2 immunoreactivity was observed in neuronal cell bodies and dendrites. No labeled axon terminal or glial cell body was found. Additional experiments performed using pre-embedding immunogold showed that most of the labeling in immunoreactive dendrites was intracytoplasmic.These results indicate that GluR2 immunoreactivity is differentially distributed among neurons in the dorsal vagal complex, thereby suggesting differences in the functional properties of AMPA receptors between neuronal populations. These results also suggest that AMPA receptors, at least those containing the GluR2 subunit, have no major role as presynaptic receptors within this region. Finally, they indicate the existence of large intracellular pools of GluR2 subunits within dendrites of immunoreactive neurons.     

Coexistence of NMDA and AMPA receptor subunits with nNOS in the nucleus tractus solitarii of rat

We previously showed that most neuronal nitric oxide synthase (nNOS)-containing neurons in the nucleus tractus solitarii (NTS) contain NMDAR1, the fundamental subunit for functional N-methyl-D-aspartate (NMDA) receptors. Likewise, we found that almost all nNOS-containing neurons in the NTS contain GluR1, the calcium permeable AMPA receptor subunit. These data suggest that AMPA and NMDA receptors may colocalize in NTS neurons that contain nNOS. However, other investigators have suggested that non-NMDA receptors are located primarily on second-order neurons and NMDA receptors are located predominantly on higher-order neurons in NTS. We now seek to test the hypothesis that NMDA receptors, AMPA receptors and nNOS are colocalized in NTS cells. We performed triple fluorescent immunohistochemical staining of nNOS, NMDAR1 and GluR1, and performed confocal laser scanning microscopic analysis of the NTS. The distributions of nNOS immunoreactivity (IR), NMDAR1-IR and GluR1-IR in the NTS were similar to those we reported earlier. Superimposed images revealed that almost all NMDAR1-IR cells contained GluR1-IR and almost all GluR1-IR cells contained NMDAR1-IR. Some double-labeled cells were additionally labeled for nNOS-IR. All nNOS-IR neurons contained both GluR1-IR and NMDAR1-IR. These studies support our hypothesis that NMDA and AMPA receptors are colocalized in NTS neurons and are consistent with a role of both types of ionotropic receptors in transmission of afferent signals in NTS. In addition, these data provide support for an anatomical link between ionotropic glutamate receptors and nitric oxide in the NTS.     

N-methyl-D-aspartate receptors on neurons that synthesize nitric oxide in rat nucleus tractus solitarii

The aim of this study was to determine whether neuronal nitric oxide synthase and N-methyl-D-aspartate receptors are co-localized in the rat nucleus tractus solitarii. Such co-localization would support the hypothesis that nitric oxide participates in nucleus tractus solitarii-mediated functions, such as cardiovascular regulation, by a link to N-methyl-D-aspartate receptors. We used double fluorescent immunohistochemistry using antibodies against neuronal nitric oxide synthase and N-methyl-D-aspartate receptor subunit 1, the fundamental subunit for functional N-methyl-D-aspartate receptors. Labeled brainstem sections were examined with confocal laser scanning microscopy. Most of the N-methyl-D-aspartate receptor subunit 1 immunoreactivity was in cell bodies and proximal dendrites of the numerous labeled cells in the brainstem. High levels of N-methyl-D-aspartate receptor subunit 1 immunoreactivity were present in the dorsal motor nucleus of vagus, hypoglossal nucleus and nucleus ambiguus. All subnuclei of the nucleus tractus solitarii contained moderate levels of N-methyl-D-aspartate receptor subunit 1 immunoreactivity. The distribution of neuronal nitric oxide synthase immunoreactivity in the nucleus tractus solitarii was similar to that described in earlier reports. Superimposition of images revealed that almost all neuronal nitric oxide synthase immunoreactive neurons in the nucleus tractus solitarii contained N-methyl-D-aspartate receptor subunit 1 immunoreactivity, but a lesser portion of N-methyl-D-aspartate receptor subunit 1-immunoreactive cells contained neuronal nitric oxide synthase immunoreactivity. Although all nucleus tractus solitarii subnuclei contained double-labeled neurons, the central subnucleus exhibited the highest density of double-labeled neurons.Co-localization of neuronal nitric oxide synthase and N-methyl-D-aspartate receptor subunit 1 in the nucleus tractus solitarii provides anatomical support for the hypothesis that N-methyl-D-aspartate receptor activation can affect nucleus tractus solitarii-controlled functions via actions on neurons that synthesize nitric oxide.     

Apposition of neuronal elements containing nitric oxide synthase and glutamate in the nucleus tractus solitarii of rat: a confocal microscopic analysis

The distribution of glutamate and neuronal nitric oxide synthase in the rat nucleus tractus solitarii was investigated by double fluorescent immunohistochemistry combined with confocal laser scanning microscopy. Cells and fibers that exhibited neuronal nitric oxide synthase immunoreactivity alone, glutamate immunoreactivity alone or both immunolabels were present in all subnuclei of the nucleus tractus solitarii, but staining intensities differed between the subnuclei. The percentages of double-labeled glutamate-immunoreactive cells also differed between the subnuclei. The central subnucleus contained the highest percentage of double-labeled glutamate-immunoreactive cells and the medial subnucleus contained the lowest. The percentages of double-labeled neuronal nitric oxide synthase-immunoreactive neurons likewise differed between the subnuclei. The central subnucleus contained the highest percentage of double-labeled neuronal nitric oxide synthase-immunoreactive neurons and the commissural subnucleus contained the lowest. Because of our interest in cardiovascular regulation, the anatomical relationship between glutamate-immunoreactive and neuronal nitric oxide synthase-immunoreactive fibers in the dorsolateral and commissural subnuclei was further examined at higher magnification. Close appositions were observed between neuronal nitric oxide synthase-immunoreactive and glutamate-immunoreactive fibers, between double-labeled and glutamate-immunoreactive fibers, and between neuronal nitric oxide synthase-immunoreactive and double-labeled fibers. We recognized that a single visual perspective might cause labeled fibers that pass in close proximity to appear to make contact. Therefore, we constructed three-dimensional images from serial optical sections obtained from the dorsolateral and commissural subnuclei by means of a confocal scanning microscope. Rotation of the three-dimensional images caused some fibers that had seemed to be in close apposition to other structures to separate from those structures. In contrast, some glutamate-immunoreactive and some neuronal nitric oxide synthase-immunoreactive fibers remained in close apposition regardless of the angle at which they were viewed.This study supports there being an anatomical link between glutamatergic and nitroxidergic systems in the nucleus tractus solitarii. Recognized physiological interactions between the two systems could occur through such a link.     

Colocalization of neurokinin-1, N-methyl-D-aspartate, and AMPA receptors on neurons of the rat nucleus tractus solitarii

Substance P (SP) and glutamate are implicated in cardiovascular regulation by the nucleus tractus solitarii (NTS). Our earlier studies suggest that SP, which acts at neurokinin 1 (NK1) receptors, is not a baroreflex transmitter while glutamate is. On the other hand, our recent studies showed that loss of NTS neurons expressing NK1 receptors leads to loss of baroreflex responses and increased blood pressure lability. Furthermore, studies have suggested that SP may interact with glutamate in the NTS. In this study, we sought to test the hypothesis that NK1 receptors colocalize with glutamate receptors, either N-methyl-d-aspartate (NMDA) receptors or AMPA receptors or both in the NTS. We performed double-label immunofluorescent staining for NK1 receptors and either N-methyl-d-aspartate receptor subunit 1 (NMDAR1) or AMPA specific glutamate receptor subunit 2 (GluR2) in the rat NTS. Because vesicular glutamate transporter 2 (VGLUT2) containing fibers are prominent in portions of the NTS where cardiovascular afferent fibers terminate, we also performed double-label immunofluorescent staining for NK1 receptors and VGLUT2. Confocal microscopic images showed that NK1 receptors-immunoreactivity (IR) and NMDAR1-IR colocalized in the same neurons in many NTS subnuclei. Almost all NTS neurons positive for NK1 receptor-IR also contained NMDAR1-IR, but only 53.4% to 74.8% of NMDAR1-IR positive neurons contained NK1 receptors-IR. NK1 receptor-IR and GluR2-IR also colocalized in many neurons in NTS subnuclei. A majority of NK1 receptor-IR positive NTS neurons also contained GluR2-IR, but only 45.8% to 73.9% of GluR2-IR positive NTS neurons contained NK1 receptors-IR. Our results also showed that fibers labeled for VGLUT2-IR were in close apposition to fibers and neurons labeled for NK1 receptor-IR. The data support our hypothesis, provide an anatomical framework for glutamate and SP interactions, and may explain the loss of baroreflexes when NTS neurons, which could respond to glutamate as well as SP, are killed.     

Nitroxidergic neurons in rat nucleus tractus solitarii express vesicular glutamate transporter 3

Earlier we reported that glutamate transporter (VGLUT) 2 and neuronal nitric oxide synthase (nNOS) are colocalized in some fibers and are present in apposing fibers in the nucleus tractus solitarii (NTS). Those findings provided anatomical support for a hypothesized physiological link between glutamate and nitric oxide (NO.) in the NTS. Recently a third class of VGLUT, VGLUT3, was identified, but its distribution in NTS and its anatomical relationship with nNOS have not been shown. In this study we tested the hypothesis that neurons and fibers containing VGLUT3 lie in close proximity to those containing nNOS and that both proteins colocalize in some neurons and fibers in the NTS. We perfused rats and obtained brain stem sections and nodose ganglion sections for immunofluorescent staining analyzed by confocal microscopy. The NTS contained moderate VGLUT3-immunoreactivity (IR), with the intermediate, medial and interstitial subnuclei containing higher VGLUT3-IR than other subnuclei. Although all three forms of VGLUT were present in the NTS, VGLUT3-IR was not colocalized with either VGLUT1-IR or VGLUT2-IR in either processes or cells in the brain stem. Cells and processes containing both VGLUT3-IR and nNOS-IR were noted in all NTS subnuclei and in the nodose ganglion. Triple immunofluorescent staining revealed that cells double-labeled for nNOS-IR and VGLUT3-IR were all additionally labeled for neuronal nuclear antigen (NeuN), a neuronal marker. These findings support our hypothesis that neurons and fibers containing VGLUT3 lie in close proximity to those containing nNOS and that both proteins colocalize in some neurons and fibers in the NTS.     

Localization of vesicular glutamate transporters and neuronal nitric oxide synthase in rat nucleus tractus solitarii

Previously we reported that glutamate and neuronal nitric oxide synthase (nNOS) colocalize in neurons of the nucleus tractus solitarii (NTS). That finding provided anatomical support for the suggestion that nitric oxide and glutamate interact in cardiovascular regulation by the NTS. Here we test the hypothesis that nNOS colocalizes with vesicular glutamate transporters (VGluT1 and VGluT2) in the NTS. Immunoreactivity (IR) for VGluT better identifies glutamatergic terminals than does glutamate-IR, which may label metabolic as well as transmitter stores of the amino acid. We used fluorescent immunohistochemistry combined with confocal laser scanning microscopy to study IR for VGluT1, VGluT2 and nNOS in rat NTS. A high density of VGluT1-IR positive fibers was present in the gracilis and cuneatus nuclei while in the NTS we found a moderate density in the lateral and interstitial subnuclei and a low density in the dorsolateral, ventral and intermediate subnuclei. The medial, central, commissural and gelatinosus subnuclei contained few VGluT1-IR containing fibers. Thus, VGluT1 containing fibers are not prominent in portions of the NTS where cardiovascular afferent fibers terminate. In contrast, we found a high density of VGluT2-IR containing fibers in the gelatinosus subnucleus and subpostremal area and a moderate density in cardiovascular regions such as the dorsolateral and medial subnuclei as well as in the central and lateral subnuclei. We found a low density in the ventral, intermediate, interstitial and commissural subnuclei. VGluT1-IR and VGluT2-IR rarely colocalized in fibers within the NTS. VGluT1-IR did not colocalize with nNOS, but VGluT2-IR and nNOS-IR colocalized in fibers in all NTS subnuclei. When compared with the other NTS subnuclei, the dorsolateral, gelatinosus and subpostremal subnuclei had higher frequencies of colocalization of VGluT2-IR and nNOS-IR. VGluT2-IR positive fibers were also apposed to nNOS-IR positive fibers throughout the NTS. These data support our hypothesis and confirm that glutamatergic fibers in the NTS contain nNOS.     

Soluble guanylate cyclase and neuronal nitric oxide synthase colocalize in rat nucleus tractus solitarii

Nitric oxide has been implicated in transmission of cardiovascular signals in the nucleus tractus solitarii (NTS). Pharmacological studies suggest that activation of neurons by nitric oxide in the NTS may involve soluble guanylate cyclase (sGC). However, anatomical data supporting this suggestion have not been available. In this study, we tested the hypothesis that neurons and fibers containing neuronal nitric oxide synthase (nNOS) lie in close proximity to those containing sGC and the two enzymes colocalize in some neurons and fibers in the NTS. We perfused six rats and obtained brain stem sections for double immunofluorescent staining utilizing antibodies selective for sGC and for nNOS combined with confocal microscopy. The distribution and staining intensity of nNOS-immunoreactivity (IR) was similar to our earlier reports. IR of sGC was present in cell bodies, proximal dendrites and fibers of many brain stem regions. Strong sGC-IR was noted in the hypoglossal, dorsal motor nucleus of vagus and gracilis nuclei. The NTS exhibited moderate sGC-IR. Superimposed images showed that many NTS neurons contained both nNOS-IR and sGC-IR. The percentage of sGC-IR positive cells that were also nNOS-IR positive differed among NTS subnuclei. Similarly, the percentage of nNOS-IR positive cells that were also sGC positive differed among NTS subnuclei. Fibers stained for both nNOS-IR and sGC-IR were also present in NTS subnuclei. In addition, we identified fibers that were stained for nNOS-IR or sGC-IR alone and often found such singly labeled fibers apposed to each other. These data support our hypothesis and provide anatomical support for the suggestion that nitroxidergic activation of the NTS involves sGC.     

Glycine receptor (gephyrin) immunoreactivity is present on cholinergic neurons in the dorsal vagal complex

We previously demonstrated that microinjection of exogenous glycine into the nucleus tractus solitarii of anesthetized rats elicits responses that are qualitatively like those elicited by microinjection of acetylcholine at the same site. The responses to glycine, like those to acetylcholine, are blocked by administration of a muscarinic receptor antagonist and prolonged by administration of an acetylcholinesterase inhibitor. Furthermore, glycine leads to release of acetylcholine from the nucleus tractus solitarii and surrounding dorsal vagal complex. An anatomical framework for interactions between glycinergic and cholinergic neurons was established by studies that identified glycine terminals and receptors in the dorsal vagal complex. The current study investigated the relationship between glycine receptors and neuronal elements that were immunoreactive for choline acetyltransferase in the dorsal vagal complex. Neurons that were immunoreactive for choline acetyltransferase were located in the dorsal motor nucleus of the vagus, hypoglossal nucleus and nucleus ambiguus, and stained cells were also present in medial, intermediate, and ventrolateral subnuclei of the nucleus tractus solitarii. We found that glycine receptors, immunolabeled with an antibody to gephyrin, were present on cholinergic dendrites in the nucleus tractus solitarii. Gephyrin immunoreactivity was also present on dendrites that did not stain for choline acetyltransferase. These data further support the contribution of cholinergic neurons in mediating cardiovascular responses to glycine in the nucleus tractus solitarii.     

Glycine receptor (gephyrin) immunoreactivity is present on cholinergic neurons in the dorsal vagal complex

We previously demonstrated that microinjection of exogenous glycine into the nucleus tractus solitarii of anesthetized rats elicits responses that are qualitatively like those elicited by microinjection of acetylcholine at the same site. The responses to glycine, like those to acetylcholine, are blocked by administration of a muscarinic receptor antagonist and prolonged by administration of an acetylcholinesterase inhibitor. Furthermore, glycine leads to release of acetylcholine from the nucleus tractus solitarii and surrounding dorsal vagal complex. An anatomical framework for interactions between glycinergic and cholinergic neurons was established by studies that identified glycine terminals and receptors in the dorsal vagal complex. The current study investigated the relationship between glycine receptors and neuronal elements that were immunoreactive for choline acetyltransferase in the dorsal vagal complex. Neurons that were immunoreactive for choline acetyltransferase were located in the dorsal motor nucleus of the vagus, hypoglossal nucleus and nucleus ambiguus, and stained cells were also present in medial, intermediate, and ventrolateral subnuclei of the nucleus tractus solitarii. We found that glycine receptors, immunolabeled with an antibody to gephyrin, were present on cholinergic dendrites in the nucleus tractus solitarii. Gephyrin immunoreactivity was also present on dendrites that did not stain for choline acetyltransferase.These data further support the contribution of cholinergic neurons in mediating cardiovascular responses to glycine in the nucleus tractus solitarii.     

Endomorphin 1‐ and Endomorphin 2‐Containing Neurons in Nucleus Tractus Solitarii Send Axons to the Parabrachial Nuclei in the Rat

Endomorphin‐1 (EM1) and endomorphin‐2 (EM2) are the selective endogenous ligands for the μ‐opioid receptor (MOR). Since EMs‐expressing neuronal cell bodies or axonal components have been observed, respectively, in the nucleus tractus solitarii or the parabrachial nuclei, we examined if EMs‐expressing neurons in the NTS of the rat might send their axons to the PBN. Immunofluorescent stainings for EM1 or EM2 were combined with retrograde or anterograde tract‐tracing method. After injecting tetramethyl rhodamine dextran‐amine (TMR) into the parabrachial nuclei of rats, some EM1‐ or EM2‐immunoreactive neurons in the nucleus tractus solitarii were labeled retrogradely with TMR. The majority of the EM1/TMR and EM2/TMR double‐labeled neurons were observed in the medial, commissural, and dorsolateral subnuclei of the nucleus tractus solitarii. Following injection of biotinylated dextran amine (BDA) into the medial, commissural, or dorsolateral subnuclei of the nucleus tractus solitarii, EM1‐ or EM2‐immunopositive axons and axon terminals were anterogradely labeled with BDA mainly in the lateral parabrachial nucleus. The present results have indicated that endomorphinergic neurons in the nucleus tractus solitarii project to the parabrachial nuclei. This suggests that EMs released from NTS‐PBN projection fibers may bind to MOR on the PBN neurons to be implicated in processing of visceral information within the parabrachial nuclei. Anat Rec, 292:488–497, 2009. © 2009 Wiley‐Liss, Inc.     

去窦弓神经后大鼠臂旁核亚核内Fos和NADPH-d的分布

目的探讨大鼠臂旁核神经型一氧化氮合酶是否参与减压反射的调节。方法用Fos蛋白免疫组织化学结合还原型尼克酰胺腺嘌呤二核苷酸脱氢酶(NADPH-d)组织化学双重染色的方法,观察去窦弓神经后Fos和NADPH-d在臂旁核各亚核内的分布情况。结果与假手术组和正常对照组相比,臂旁外侧核外亚核、内侧核外亚核和K-F核内Fos免疫阳性反应明显增强。在这些Fos阳性神经元的表面通常可见NADPH-d阳性纤维终末分布,但偶见Fos和NADPH-d双标神经元。结论臂旁外侧核外亚核、内侧核外亚核和K-F核内部分神经元可被去窦弓神经术特异性激活;一氧化氮可能主要通过突触前机制参与此刺激的传递过程。     

Distribution of six neuropeptides in the nucleus tractus solitarii of the rat: an immunohistochemical analysis

Distribution of substance P-, [Leu]enkephalin-, cholecystokinin-8-, neurotensin-, avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive structures were investigated in the nucleus tractus solitarii of the rat by means of the indirect immunofluorescence method. The density of the immunoreactive structures varied markedly according to neuropeptides or subnuclei, with the medial and commissural nuclei containing the highest density. This suggests that the peptides examined play a role in cardiovascular function. However, as seen in the substance P- and [Leu]enkephalin-like immunoreactive structures, these peptides were widely distributed in the nucleus tractus solitarii in addition to the commissural and medial nuclei; a high density of immunoreactive fibers in the ventral, dorsolateral and intermediate subnuclei. In addition to the immunoreactive fiber plexus, a group of immunoreactive cells was also identified in the subnuclei mentioned above. These findings strongly suggest that substance P- and [Leu]enkephalin-like immunoreactive structures are involved not only in cardiovascular function but also in other functions such as respiration, at least in the rat. Finally, the present study demonstrated that the area postrema, particularly its lateral portion, contains various neuropeptide-like structures, both neurons and fibers, substance P-, [Leu]enkephalin-, cholecystokinin-8- and neurotensin-like immunoreactive neurons and fibers, and avian pancreatic polypeptide- and gamma-melanocyte stimulating hormone-like immunoreactive fibers.     

大鼠孤束核内降钙素基因相关肽能神经的分布及其与儿茶酚胺能神经元的关系

用双重免疫染色包埋前免疫电镜法，在光镜和电镜水平观察了大鼠孤束核内降钙素基因相关肽神经元的分布及其神经末梢与儿茶酚胺能神经元之间的关系。降钙素基因相关肽阳性神经元呈棕色，主要分布于孤束核的连合亚核、内侧亚核以及背侧周边区。在孤束核的尾侧部、连合亚核的腹外侧部及背侧周边区观察到蓝绿色的酪氨酸羟化酶阳性神经元和棕色的降钙素基因相关肽阳性神经元和神经纤维，其中一些神经元内两者共存。电镜观察结果：酪氨酸羟化酶阳性神经元细胞质内有棒状或卵圆形的电子密度较高的吲哚-β-半乳糖苷酶反应产物，降钙素基因相关肽阳性神经末梢内见到电子密度较高的DAB反应产物以及清亮小泡和颗粒小泡。降钙素基因相关肽阳性神经末梢和酪氨酸羟化酶阳性神经元之间形成对称性轴一体突触。     

Glycine-containing terminals in the rat dorsal vagal complex

The present study examined the distribution of glycine and glycine-receptors in the dorsal vagal complex using pre-embedding immunocytochemistry. Glycine-immunoreactive terminals were present in moderate densities in the medial, intermediate, interstitial, commissural and ventrolateral subnuclei of the nucleus tractus solitarii. The dorsolateral nucleus tractus solitarii and the dorsal vagal motor nucleus contained only very few, scattered glycine-containing terminals. Glycine terminals appeared to be concentrated in regions of the dorsal vagal complex receiving primary vagal afferents, though previous studies have suggested that glycine is not present in these afferents. A conspicuously high concentration of glycine terminals was observed in the medial nucleus tractus solitarii where a population of cholinergic neurons has been identified previously. Ultrastructurally glycine immunoreactivity was principally associated with terminals containing flattened, pleomorphic vesicles and forming symmetrical synaptic contacts, mostly with dendrites. Glycine receptor immunoreactivity was present throughout the dorsal vagal complex with little evidence of subnuclear localization. With electron-microscopic examination, glycine receptor immunoreactivity was associated with dendritic membranes and was associated presynaptically with terminals containing flattened pleomorphic vesicles.

Overall, the present data provide evidence consistent with a neurotransmitter role for glycine in the dorsal vagal complex. The presence of glycine in regions of the dorsal vagal complex receiving vagal afferents suggests a prominent role for this neurotransmitter in autonomic regulation.     

Substance P-like immunoreactive neurons in the nucleus tractus solitarii of the rat send their axons to the nucleus accumbens

By a double-labeling method combining the retrograde tracing of horseradish peroxidase with an immunocytochemical technique, substance P-like immunoreactive neurons in the medial and commissural subnuclei of the nucleus tractus solitarii (NTS) of the rat were found to send axons to the nucleus accumbens.     

孤束核中含生长抑素的神经细胞和神经纤维——免疫电镜研究

本文报道用免疫电镜方法研究大白鼠延髓孤束核联合亚核内含生长抑素(SRIF)的神经细胞及神经末梢。实验结果表明,孤束核内的SRIF样免疫反应阳性胞体为中小型细胞,呈梭形或椭圆形。含SRIF样免疫反应的轴突主要构成轴轴突触,后者为通道突触或终末突触。含SRIF的孤束核神经细胞本身不接受含SRIF的神经纤维支配,但其树突可与未标记的轴突形成轴树突触。     

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons projecting from the midbrain periaqueductal gray to the nucleus tractus solitarii in the rat.

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons in the midbrain periaqueductal gray (PAG) were observed to send their axons to the nucleus tractus solitarii in the rat by the retrograde horseradish peroxidase tracing method combined with the immunocytochemical technique. These neurons were most frequently observed in the ventrolateral subnucleus and ventral portion of the medial subnucleus of the PAG at the entire rostrocaudal levels.     

Glutamatergic neurons say NO in the nucleus tractus solitarii

Both glutamate and nitric oxide (NO) may play an important role in cardiovascular reflex and respiratory signal transmission in the nucleus tractus solitarii (NTS). Pharmacological and physiological data have shown that glutamate and NO may be linked in mediating cardiovascular regulation by the NTS. Through tract tracing, multiple-label immunofluorescent staining, confocal microscopic, and electronic microscopic methods, we and other investigators have provided anatomical evidence that supports a role for glutamate and NO as well as an interaction between glutamate and NO in cardiovascular regulation in the NTS. This review article focuses on summarizing and discussing these anatomical findings. We utilized antibodies to markers of glutamatergic neurons and to neuronal NO synthase (nNOS), the enzyme that synthesizes NO in NTS neurons, to study the anatomical relationship between glutamate and NO in rats. Not only were glutamatergic markers and nNOS both found in similar subregions of the NTS and in vagal afferents, they were also frequently colocalized in the same neurons and fibers in the NTS. In addition, glutamatergic markers and nNOS were often present in fibers that were in close apposition to each other. Furthermore, N-methyl-d-aspartate (NMDA) type glutamate receptors and nNOS were often found on the same NTS neurons. Similarly, alpha-amino-3-hydroxy-5-methylisoxozole-proprionic acid (AMPA) type glutamate receptors also frequently colocalized with nNOS in NTS neurons. These findings support the suggestion that the interaction between glutamate and NO may be mediated both through NMDA and AMPA receptors. Finally, by applying tracer to the cut aortic depressor nerve (ADN) to identify nodose ganglion (NG) neurons that transmit cardiovascular signals to the NTS, we observed colocalization of vesicular glutamate transporters (VGluT) and nNOS in the ADN neurons. Thus, taken together, these neuroanatomical data support the hypothesis that glutamate and NO may interact with each other to regulate cardiovascular and likely other visceral functions through the NTS.