The N-methyl-D-aspartate receptor pathway is involved in hypoxia-induced c-Fos protein expression in the rat nucleus of the solitary tract

In chloroplast photosystem II, the extrinsic polypeptide of 33 kDa is involved in the stabilization the Mn cluster in charge of water splitting and in the fulfilment of the Ca(2+)-cofactor requirement for oxygen evolution. The conformational analysis of the purified 33 kDa extrinsic polypeptide was carried out using FTIR spectroscopy with its self-deconvolution and second derivative resolution enhancement as well as curve-fitting procedures. The FTIR spectroscopic results showed that the isolated polypeptide is characterized by a major proportion beta-sheet conformation (36%) with 27% alpha-helix, 24% turn, and 13% beta-antiparallel structures.     

A cholecystokinin-B receptor antagonist potentiates GABAergic and glycinergic inhibition in the nucleus of the solitary tract of the rat

In both rodent and primate in vivo models, cholecystokininB (CCKB) antagonists such as PD134,308 have anxiolytic effects that may involve the potentiation of GABAergic transmission. We have investigated this interaction using exogenous application of GABA and whole cell patch recording techniques in neurons of the nucleus of the solitary tract (NTS) in brainstem slice preparations. In the presence of PD143,308 the magnitude of the GABA-evoked decrease in membrane input resistance was enhanced by 41.2 +/- 3.1% and the duration of the response was prolonged by 34.8 +/- 2.2%. Also, PD134, 308 potentiated glycine-evoked decreases in membrane input resistance, increasing the amplitude of the response by 62.8 +/- 4. 85 and prolonging the duration of the response by 23.5 +/- 3.6%. The effect of PD134,308 persisted in the presence of tetrodotoxin, after reversal of the transmembrane gradient of chloride ions and under conditions of exaggerated GABAA receptor desensitization. Our results demonstrate that at least part of the functional link between PD134,308 and the GABAA response occurs postsynaptically.     

Expression of a functional endothelin (ETA) receptor in human meningiomas

Endothelin (ET) receptor subtypes (ETA and ETB) in human meningiomas were characterized using quantitative receptor autoradiography. A single class of high-affinity 125I-ET-1 binding sites was localized in all meningioma tissue studied (dissociation constant: 2.4 +/- 0.3 nM, maximum binding capacity: 319 +/- 66 fmol/mg (mean +/- standard error of the mean for 13 tumors)). Unlabeled ET-1 showed a strong affinity for 125I-ET-1 binding to tissue sections of the tumors with a 50% inhibiting concentration (IC50) of 2.9 +/- 0.7 x 10(-9) M, whereas ET-3 showed a much lower affinity (IC50: 8.4 +/- 2.5 x 10(-6) M). Sarafotoxin S6c, a selective agonist for the ETB receptor, could not compete for 125I-ET-1 binding to meningiomas. Endothelin-1 significantly stimulated deoxyribonucleic acid (DNA) synthesis in a dose-dependent manner in cultured human meningioma cells. In contrast, no significant stimulation of DNA synthesis occurred with an S6c concentration up to 10(-7) M. Pretreatment of the meningioma cells with pertussis toxin, a bacterial toxin that adds adenosine 5'-diphosphate-ribose to the alpha subunit of guanine nucleotide binding (G) proteins such as Gi or G(o), induced a concentration-dependent reduction in ET-stimulated DNA synthesis in meningioma cells, but did not affect the epidermal growth factor-induced DNA synthesis. These observations suggest that the ETA receptor is predominantly expressed in human meningioma tissue and that ET may act as a growth factor on the meningioma cells by interacting with the ETA receptor and by pertussis toxin-sensitive mechanisms.     

Association between the amygdala and nucleus of the solitary tract in mu-opioid induced feeding in the rat

The central nucleus of the amygdala (CNA) and the nucleus of the solitary tract (NTS) are important in the regulation of ingestive behavior. We evaluated whether opioid-opioid signaling between the CNA and rostral NTS (rNTS) affect feeding behavior. To test this, rats were doubly cannulated with one cannula placed in the rNTS and one cannula in the CNA, allowing for co-administration of an opioid agonist into one site and an opioid antagonist into the other. Tyr-D-Ala-Gly-(me) Phe-Gly-ol (DAMGO) (2 nmol) injected into the CNA (CNA DAMGO) increased feeding more than two-fold compared to the vehicle-injected rats. This increase in food intake was blocked when doses of 26.5 and 79 nmol of naltrexone (NTX) were injected into the rNTs. In the reverse situation, rNTS DAMGO increased food intake above control levels, and CNA NTX blocked DAMGO-induced feeding when administrated in doses of 26.5 and 79 nmol. This suggests that a bi-directional opioid-opioid signaling pathway exists between the CNA and the rNTS which influences feeding via mu-opioid receptors.     

Electrophysiological characterisation of tachykinin receptors in the rat nucleus of the solitary tract and dorsal motor nucleus of the vagus in vitro

1. Recent studies have shown antagonists at the NK1 subtype of receptor for tachykinins are antiemetics and suggested that this may result from blockade of tachykinin-mediated synaptic transmission at a central site in the emetic reflex. 2. We have used intracellular recording in vitro to study the pharmacology of tachykinins in the nucleus of the solitary tract (NST) and dorsal motor nucleus of the vagus (DMNV). 3. Neurones in the NST were depolarized by substance P (SP), the presumed endogenous ligand for the NK1 receptor and these effects were mimicked by the NK1 agonists, SP-O-methylester (SPOMe), GR73632 and septide; however, SP was nearly an order of magnitude less potent than the latter two agonists. 4. In the DMNV, SP and NK1 receptor agonists evoked similar depolarising responses but SP appeared to be more potent than in the NST and was closer in potency to the other agonists. 5. NK1-receptor antagonists blocked responses to septide and GR73632 in the NST but had little effect on responses to SP and SPOMe. In contrast, in the DMNV the NK1-receptor antagonists blocked responses to septide and GR73632 but also reduced responses to SP and SPOMe. 6. Neurokinin A (NKA) was almost equipotent with septide and GR73632 in depolarizing both NST and DMNV neurones but these effects were not mimicked by a specific NK2-receptor agonist. Responses to NKA were unaffected by an NK2-receptor antagonist; however, the depolarizing effects of NKA were blocked by NK1-receptor antagonists. 7. Neurones in both DMNV and NST were unaffected by the endogenous NK3-receptor ligand, neurokinin B and by a specific agonist for this site, senktide. 8. The results with NK1 receptor agonists and antagonists suggest that the septide-sensitive NK1 site is involved in the excitation of both NST and DMNV neurones. The 'classical' NK1 receptor may play more of a role in the DMNV and a third unknown site may be responsible for the depolarizing response to SP in the NST. The effects of NKA are best interpreted as an action at the septide-sensitive NK1 site. This raises the possibility that anti-emetic action of the NK1 antagonists may be due to blockade of NKA transmission at the septide-sensitive site.     

Comparison of the acute effects of a selective endothelin ETA and a mixed ETA/ETB receptor antagonist in heart failure

OBJECTIVE: Both the selective endothelin (ET) ETA receptor and mixed ETA/ETB receptor antagonists improve haemodynamics in patients and experimental models with congestive heart failure (CHF) and reduce the mortality in CHF rats. However, it remains unclear which of these antagonists is superior in the treatment of CHF. In addition, there is little information as to whether these ET receptor antagonists contribute to the neuroendocrine regulation and body fluid balance. We therefore investigated the cardiorenal and neurohumoral benefits of selective ETA receptor and mixed ETA/ETB receptor antagonists in CHF. METHODS: We administered acutely either the selective ETA receptor antagonist FR139317 (FR, n = 6, 1 and 10 mg/kg) or the mixed ETA/ETB receptor antagonist TAK-044 (TAK, n = 6, 1 and 3 mg/kg) to conscious dogs with CHF induced by rapid right ventricular pacing for ten days. RESULTS: Both FR and TAK decreased the cardiac pressures and the plasma atrial natriuretic peptide level and increased the cardiac output and urinary sodium excretion. FR increased the urine flow rate in association with an increased glomerular filtration rate and renal plasma flow, while TAK reduced the plasma aldosterone level. Neither antagonist increased the plasma renin activity or norepinephrine levels. CONCLUSIONS: These ETA/ETB antagonist. However, the long-term administration of a mixed ETA/ETB receptor antagonist would improve not only the haemodynamics but also prevent fluid retention by suppressing secretion of aldosterone during the treatment of chronic CHF.     

Development of intrinsic electrophysiological properties in neurons from the gustatory region of rat nucleus of solitary tract

There is no current understanding of the nature or time course of maturation of intrinsic electrophysiological properties for neurons in the gustatory region of the nucleus of the solitary tract (NST). Therefore, we used whole cell recordings in an in vitro slice preparation of the rat brainstem to characterize development of resting membrane, action potential and repetitive discharge properties of cells in gustatory NST at postnatal days 5, 10, 15, 20, and 30, and adult ages. Neurons were filled with Biocytin to verify location and characterize morphology. Membranes from younger neurons demonstrated a steeper current-voltage relation or higher input resistance, and a longer time constant than mature cells. Action potentials in younger cells had a slower rate of rise and were longer in duration. The afterhyperpolarization that typically follows the spike discharge usually had one phase in younger neurons, but was characterized by two or more phases in an increasing proportion of older cells. The repetitive discharge frequency in response to a range of depolarizing current pulses increased during development, and frequency/current plots were steeper in older compared with younger neurons. However, in all age groups there was clear accommodation of the discharge frequency. The greatest changes in resting membrane, action potential, and discharge properties were observed between P5 and P15, and mature values were generally reached by P20. At each postnatal age, neurons could be categorized in four neuron groups, based on the discharge pattern in response to a hyperpolarizing/depolarizing current protocol. Anatomical reconstructions indicated that although cells increased in overall dendritic expanse during development, neurons became less complex as illustrated by decreases in number of dendritic branch points, and in number and density of spines. The timing of major developmental differences in intrinsic electrical characteristics observed here is associated with a period of previously reported maturational changes in extracellular taste responses to number and concentration of chemical stimuli. However, further alterations in extracellular taste responses proceed after apparent maturation of intrinsic neural properties.     

Subtype-specific desensitization of human endothelin ETA and ETB receptors reflects differential receptor phosphorylation

Endothelins regulate blood pressure in mammals through G protein-coupled receptors. Two receptor subtypes, ETA and ETB, exist which differ by their agonist profiles. Here we show subtype-specific differences in the inactivation of these endothelin receptors. Using a modified inositol phosphate accumulation assay, we found that stimulation of ETA by endothelin-1 results in sustained activation of the subtype, retaining >30% of its initial activity even 20 min after agonist administration, whereas the ETB rapidly deactivated after agonist stimulation, losing >80% of its initial activity within 5 min after endothelin application. The discrepancy in receptor inactivation is reflected by subtype-specific differences in receptor phosphorylation. Whereas ETA failed to undergo ligand-induced phosphorylation, the ETB was rapidly phosphorylated in response to agonist stimulation. By contrast, the kinetics of ligand-induced internalization were essentially identical for the receptor subtypes, suggesting endothelin receptor internalization being independent of ligand-induced receptor phosphorylation. Interestingly, a strong correlation was observed between the time course of ETA inactivation and ETA internalization. Therefore, our data suggest a subtype-specific inactivation of human endothelin receptors: fast receptor phosphorylation in the case of ETB and slow receptor internalization in the case of ETA. Subtype-specific modulation of endothelin receptors may account for the short-term hypotensive effects of endothelins via rapidly down-regulating ETB receptors and the long-lasting hypertensive effects due to sustained ETA activation.     

Calcitonin gene-related peptide innervation of A2-catecholamine cells in the nucleus of the solitary tract of the rat

By using double immunolabeling light and electron microscopic techniques, dense neuronal network of calcitonin-related peptide (CGRP) has been visualized in the nucleus of the solitary tract with complete overlapping of the tyrosine hydroxylase (TH)-containing cells. TH-immunoreactive perikarya and dendrites were seen in synaptic contact with CGRP-immunopositive fibers, indicating that CGRP, by carrying sensory signals may influence autonomic regulatory mechanisms in the NTS through local catecholaminergic neurons.     

Role of nitric oxide in the nucleus of the solitary tract of rats

We have determined the role of nitric oxide (NO) in the nucleus of the solitary tract (NTS) of normotensive Wistar rats. The unilateral microinjection of Nomega-nitro-l-arginine methyl ester (10 nmol) to block the synthesis of NO into the NTS significantly decreased the arterial pressure, heart rate (HR) and renal sympathetic nerve activity (RSNA) (-19+/-2 mmHg, -23+/-5 beats/min, -30+/-2%, respectively). The microinjection of carboxy-2-phenyl-4,4,5, 5-tetramethylimidazoline-1-oxyl 3-oxide (Carboxy PTIO) (trapper of NO; 0.1 nmol) into the NTS also decreased arterial pressure and RSNA. Conversely, the microinjection of Et2N[N(O)NO]Na (NOC 18) (NO donor; 10 nmol) caused increases in arterial pressure, HR and RSNA (+14+/-2 mmHg, +11+/-2 beats/min, +38+/-7%, respectively), which was inhibited by the pre-microinjection of Carboxy PTIO (0.1 nmol). On the other hand, not only l-arginine (10 nmol) but also d-arginine (10 nmol), which is inactive to produce NO, significantly decreased the arterial pressure and RSNA. These results suggest that (1) NO acts at the NTS to increase the arterial pressure and RSNA, and (2) the microinjection of l-arginine as well as d-arginine led to decreases in arterial pressure and RSNA that were not mediated by the formation of NO in the NTS.     

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.     

Vestibular nucleus neurons, projecting to the "gastric" area of the solitary tract nucleus

OBJECTIVES: To describe the natural recovery of visuospatial neglect in stroke patients and the distribution of errors made on cancellation tests using a standardised neuropsychological test battery. METHOD: A prospective study of acute (< seven days) patients with right hemispheric stroke. Patients identified with visuospatial neglect were followed up for three months with monthly clinical and neuropsychological testing RESULTS: There were 66 patients with acute right hemispheric stroke assessed of whom 27 (40.9%) had evidence of visuospatial neglect. Patients with neglect, on admission, had a mean behavioural inattention test (BIT) score of 56.3, range 10-126 (normal>129). Three of the subtests identified errors being made in both the right and left hemispaces. During follow up, recovery occurred across both hemispaces, maximal in the right hemispace. Recovery from visuospatial neglect was associated with improvement in function as assessed by the Barthel score. At the end of the study period only six (31.5%) patients had persisting evidence of neglect. On admission the best predictor of recovery of visuospatial neglect was the line cancellation test (Spearman's rank correlation r=-0.4217, p=0.028). CONCLUSION: The demonstration of errors in both hemispaces has implications for the theory that neglect is a lateralised attentional problem and is important to recognise in planning the rehabilitation of stroke patients.     

The interaction of endothelin receptor responses in the isolated perfused rat lung

To gain more insight into the complex pulmonary interactions of endothelins (ET), we studied airway and vascular responses to endothelins in isolated perfused rat lungs in the presence of the novel ET(B)-receptor antagonist BQ788. In particular we focused on airway responses and on prostacyclin release. The effectiveness of BQ788 in our system was shown by its ability to concentration-dependently prevent vasoconstriction (IC50 0.1 microM), bronchoconstriction (IC50 0.1 microM) and prostacyclin production (IC50 < 0.1 microM) induced by the ET(B)-receptor agonist IRL1620 (1 nmol). Airway responses to ET-1: ET-1-induced bronchoconstriction was aggravated by BQ123 (1 or 8 microM), while BQ788 pretreatment (1 or 8 microM) showed no significant effect. Simultaneous treatment with 8 microM BQ123 and BQ788 attenuated the ET-1-induced bronchoconstriction. Vascular responses to ET-1: ET-1 (1 nmol)-induced vasoconstriction was potentiated by BQ788 (1 or 8 microM), but attenuated by the ET(A)-receptor antagonist BQ123 (1 microM). In the presence of BQ788 diminished amounts of the stable prostacyclin metabolite 6-keto-PGF1alpha were detected in the perfusate. Simultaneous treatment with 8 microM BQ123 and BQ788 completely prevented the ET-1-induced vasoconstriction. Conclusions: Both ET(A)- and ET(B)-receptors contribute to ET-1-induced vasoconstriction and bronchoconstriction. The ET-1-induced vasoconstriction is attenuated by stimulation of ET(B)-receptors, a response that is partly mediated by prostacyclin. Due to the mutual interactions between ET(A)- and ET(B)-receptors, simultaneous inhibition of both receptors is required to prevent the deleterious effects of ET-1 on lung functions.     

Effects of nitric oxide synthase inhibition and endothelin ETA receptor blockade on haemodynamics in hypertensive rats

1. The objectives of the present study were to study regional differences in haemodynamics between spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats induced by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) and the endothelin ETA receptor antagonist BQ 123 in vivo in tissues known to be important for blood pressure (BP) regulation (heart, kidney and skeletal muscle). Furthermore, the effect of acetylcholine (ACh) infusion (2 micrograms/kg per min) was examined after L-NMMA or BQ 123. The microsphere method was used for determinations of cardiac index (CI) and regional haemodynamics. 2. NG-Monomethyl-L-arginine (20 mg/kg) increased BP (26-48%; P < 0.01) and reduced CI in both rat strains. BQ 123 (1 mg/kg) reduced BP slightly (-4 to 11%; P < 0.05). 3. NG-Monomethyl-L-arginine significantly increased myocardial and skeletal muscle vascular resistance in SHR only; however, in the kidney, L-NMMA reduced blood flow and increased vascular resistance in both rat strains. 4. BQ 123 induced minor changes in regional haemodynamics that were not significantly different between the two strains. 5. Acetylcholine following BQ 123 induced an increase in myocardial blood flow in WKY rats, but decreased blood flow in SHR. Acetylcholine following L-NMMA reduced myocardial blood flow in both strains. 6. Acetylcholine following BQ 123 induced renal vasodilation in WKY rats but, following L-NMMA, ACh did not induce renal vasodilation in either rat strain. In contrast, L-NMMA did not abolish the vasodilation of acetylcholine in skeletal muscle in WKY rats. 7. In conclusion, the contribution of nitric oxide to basal vessel tone was not impaired in the heart, skeletal muscle and kidney in SHR. Antagonism of ETA receptors caused similar haemodynamic responses in both rat strains in these organs. Furthermore, NOS inhibition, but not ETA blockade, blunted the expected ACh-induced vasodilation in the heart and kidney in WKY rats, but not in skeletal muscle in both strains.     

Oxytocinergic inputs to the nucleus of the solitary tract and dorsal motor nucleus of the vagus in neonatal rats

BACKGROUND: Cetirizine is a H1 histamine antagonist which possesses anti-inflammatory properties through inhibition of leucocyte recruitment and activation, and reduction of ICAM-1 expression on mucosal epithelial cells. No studies have addressed the potential anti-inflammatory activities of cetirizine on skin keratinocytes. OBJECTIVES: Cetirizine and hydrocortisone were compared in their capacity to counteract human keratinocytes activation by IFNgamma. In particular, expression of immuno-modulatory membrane molecules and chemokine release have been examined. METHODS: Keratinocyte cultures established from normal skin of healthy donors were activated by IFNgamma (100-500 U/mL) in the absence or presence of cetirizine (10(-3)-10(3) microM) or hydrocortisone (10(-3)-10(2) microM), and tested for expression of ICAM-1, HLA-DR, MHC class I and CD40 as well as for release of RANTES, IL-8, macrophage chemotactic protein-1 (MCP-1) and granulocyte macrophage-colony stimulating factor (GM-CSF). RESULTS: Cetirizine at high concentrations (10(2)-10(3) microM) markedly inhibited IFNgamma-induced expression of membrane ICAM-1, HLA-DR and up-regulation of MHC class I, but had no effect on CD40 expression. In contrast, hydrocortisone (10(2) microM) enhanced IFNgamma-induced membrane ICAM-1, reduced expression of HLA-DR and did not alter expression of MHC class I and CD40. Consistently, high doses of cetirizine decreased, whereas hydrocortisone increased, soluble ICAM-1 levels in the supernatants of IFNgamma-treated keratinocytes. The inhibiting and stimulating effects of cetirizine and hydrocortisone, respectively, on ICAM-1 expression were confirmed at the mRNA level by Northern blot analysis. Finally, cetirizine, but not hydrocortisone, inhibited the release of MCP-1 and RANTES from IFNgamma-stimulated keratinocytes. In contrast, hydrocortisone, but not cetirizine, reduced GM-CSF and IL-8 release. CONCLUSIONS: The results indicate that cetirizine has the capacity to block the IFNgamma-induced activation of keratinocytes, and thus can exert important regulatory effects on TH1 cell-mediated immune responses in the skin. The high doses required for evidencing these activities suggest the potential benefits of a topical use of cetirizine.     

ETA receptor-mediated role of endothelin in the kidney of DOCA-salt hypertensive rats

Renal effects of FR139317, an endothelin ETA receptor antagonist, were examined using anesthetized normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The intravenous bolus injection of FR139317 (10 mg/kg) produced a slight decrease in mean blood pressure (MAP; -13%) in the control rats and this hypotension was accompanied by a moderate renal vasodilation (renal vascular resistance: RVR; -12%). In the DOCA-salt hypertensive rat, FR139317 had a more pronounced hypotensive effect (MAP; -26%) accompanied by a potent renal vasodilation (RVR; -33%). FR139317 significantly increased renal blood flow only in the DOCA-salt rats. In contrast, FR139317 produced a significant decrease in urine flow and urinary sodium excretion only in control rats. Northern blot analysis revealed that the renal prepro endothelin-1 (ET-1) mRNA level was significantly increased in DOCA-salt hypertensive rats. Thus, it seems likely that endogenous ET-1 is responsible for the maintenance of DOCA-salt-induced hypertension. We also suggest that at least in part, ET-1 and ETA receptors are involved in renal hemodynamic abnormalities in DOCA-salt-induced hypertension. The augmentation of renal ET-1 production may possibly have a function in the development and maintenance of DOCA-salt-induced hypertension.     

Electrophysiological and morphological properties of neurons acutely isolated from the rostral gustatory zone of the rat nucleus of the solitary tract

The biophysical and morphological characteristics of acutely isolated neurons from the rostral nucleus of the solitary tract (rNST) were investigated under current clamp conditions and compared with the results obtained from neurons recorded in brain slices. The passive membrane properties of the isolated neurons were similar to rNST neurons in brain slices and the neurons maintained their morphological characteristics although their dendritic tree was truncated. The isolated neurons also retained their characteristic repetitive firing properties. In addition we also noted developmental changes in the intrinsic membrane properties of the isolated neurons, such as a shortening in action potential duration, decrease in membrane time constant and input resistance, that occurred when these parameters were compared in neurons isolated from young (5-10 days) and older animals. These enzymatically dispersed neurons therefore retained both the membrane properties and morphology observed in the intact brainstem and in vitro brain slice preparation. The use of this isolated neuron preparation provides a basis for further study of rNST neurobiology.     

Immunolabeling of Mu opioid receptors in the rat nucleus of the solitary tract: extrasynaptic plasmalemmal localization and association with Leu5-enkephalin

Activation of the mu opioid receptor (MOR) by morphine within the caudal nucleus of the solitary tract (NTS) is known to mediate both cardiorespiratory and gastrointestinal responses. Leu5-enkephalin (LE), a potential endogenous ligand for MOR, is also present within neurons in this region. To determine the cellular sites for the visceral effects of MOR ligands, including LE, we used immunogold-silver and immunoperoxidase methods for light and electron microscopic localization of antisera against MOR (carboxyl terminal domain) and LE in the caudal NTS of rat brain. Light microscopy of coronal sections through the NTS at the level of the area postrema showed MOR-like immunoreactivity (MOR-LI) and LE labeling in punctate processes located within the subpostremal, dorsomedial and medial subnuclei. Electron microscopy of sections through the medial NTS at this level showed gold-silver particles identifying MOR-LI prominently distributed to the cytoplasmic side of the plasma membranes of axons and terminals. MOR labeled terminals formed mostly symmetric (inhibitory-type) synapses but sometimes showed multiple asymmetric junctions, characteristic of excitatory visceral afferents. MOR-LI was also present along extrasynaptic plasma membranes of dendrites receiving afferent input from unlabeled and LE-labeled terminals. We conclude that MOR ligands, possibly including LE, can act at extrasynaptic MORs on the plasma membranes of axons and dendrites in the caudal NTS to modulate the presynaptic release and postsynaptic responses of neurons. These are likely to include local inhibitory neurons and both gastric and cardiorespiratory afferents known to terminate in the subnuclei with the most intense MOR-LI.