Biomedical subjects

B Jarrott

Publications and source records attributed to B Jarrott.

At least 55 records · Page 3Linked to original sources

PubMed1996

Loss of [125I]-pindolol binding to beta-adrenoceptors on rat nodose ganglion after chronic isoprenaline treatment.

The nodose ganglion contains the cell bodies of afferent nerves which convey predominantly sensory information from the viscera to the central nervous system (CNS). Autoradiographic studies show binding sites for beta-adrenoceptor ligands are present on sections of the rat nodose ganglion and also on the corresponding inferior vagal ganglion in humans, indicating the presence of beta-adrenoceptors in these ganglia. Since prolonged stimulation of beta-adrenoceptors in rats with the nonselective beta-adrenoceptor agonist isoprenaline (400 micrograms kg-1 day-1 s.c.) for 14 days results in desensitisation and/or down-regulation of receptors in peripheral tissues, such as heart, kidney and blood vessels, the effects of this treatment on the beta-adrenoceptor population on the nodose ganglion have been examined. Using [125I]-pindolol as a radioligand, autoradiographic studies revealed that specific binding was reduced by 74% in ganglia from isoprenaline-pretreated rats compared to that in ganglia from vehicle-pretreated rats, demonstrating down-regulation of receptors by isoprenaline. [125I]-Pindolol binding was sensitive to inhibition by ICI 118.551 (selective beta 2-adrenoceptor antagonist) but not to atenolol (selective beta 1-adrenoceptor antagonist), indicating receptors are predominantly of the beta 2-adrenoceptor subtype. No change in binding was apparent over the vagus nerve. The nodose ganglion appears to be an additional site at which beta 2-adrenoceptors may be down-regulated in vivo, possibly interfering with normal baro-, chemo- and sensory reflexes.

Animals↗

PubMed1996

Radioligand binding and autoradiographic visualization of adenosine transport sites in human inferior vagal ganglia and their axonal transport along rat vagal afferent neurons.

The present study has employed membrane-binding studies and in vitro autoradiography to demonstrate the presence of adenosine transport sites in human inferior vagal ganglia using [3H]nitrobenzylthioinosine ([3H]NBMPR), a potent inhibitor of adenosine transport. In addition, [3H]NBMPR was used to determine whether adenosine transport sites are subject to axonal transport along the rat vagus nerve. Binding of [3H]NBMPR to human inferior vagal ganglia membranes was saturable and reversible. Saturation experiments revealed a single class of high affinity-binding sites with a Kd of 93.73 +/- 23.13 pM and Bmax of 413.50 +/- 50.40 fmol/mg protein. In displacement experiments, the adenosine transport inhibitor dipyridamole was the most potent displacer of [3H]NBMPR binding (Ki = 42.7 +/- 28.0 nM). Adenosine itself was able to fully displace [3H]NBMPR binding with a Ki of 115.0 +/- 34.0 microM. The A1/A2a adenosine receptor agonist 5'-(N-ethylcarboxamido)-adenosine (NECA) was able to fully displace [3H]NBMPR binding in only one experiment at a concentration of 100 microM, yielding an affinity 1000-fold higher than its affinity for adenosine receptors. All competition curves obtained from displacement experiments displayed monophasic profiles, indicating the presence of a single class of [3H]NBMPR binding sites. Incubation of human inferior vagal ganglia sections with [3H]NBMPR (0.7 nM) revealed dense binding which appeared to be consistent with the distribution of neuronal cell bodies in this tissue. Following unilateral ligation of the vagus nerve in the rat, accumulation of [3H]NBMPR binding sites occurred both proximal and distal to the vagal ligatures. These results suggest that [3H]NBMPR binds with high affinity to a single class of adenosine transport sites, and that these sites are present on vagal afferent neurons in the human and undergo bidirectional axonal transport along the rat vagus nerve.

Adenosine↗

PubMed1996

Neuropeptide Y gene expression and receptor autoradiography in hypertensive and normotensive rat brain.

Neurones containing neuropeptide Y (NPY) may participate in central cardiovascular control by tonically influencing barosensitive neurones within the nucleus tractus solitarius. The present study has employed both in situ hybridisation histochemistry and receptor autoradiography, to visualise the expression of prepro-NPY mRNA in the forebrain and to determine the NPY receptor subtype(s) in the brainstem, respectively. Prepro-NPY gene expression was visualised in the hypothalamus, cortex, dentate gyrus and lateral reticular thalamus from age-matched spontaneously hypertensive rats (SHR) and normotensive Don Ryu rats (DRY) and Wistar Kyoto rats (WKY). Quantitative densitometry revealed an increase in the NPY transcript in the arcuate nucleus of SHR rats compared to their normotensive counterparts. Autoradiography using [125I]Bolton-Hunter-NPY (BH-NPY, 15 pM) demonstrated NPY binding sites in the area postrema, the commissural nucleus tractus solitarius (cNTS) and the inferior olivary complex. NPY (1 microM) and peptide YY (1 microM), but not [Leu31,Pro34]NPY (10-100 nM), fully inhibited the binding of [125I]BH-NPY. These results indicate that NPY receptors of the Y2 subtype predominate in the dorsal vagal complex. Unilateral nodose ganglionectomy resulted in a partial loss of NPY binding sites in the commissural NTS, but not the area postrema, suggesting that a proportion of binding sites (Y2 subtype) are present on central vagal terminals. While all three rat strains appear to have the same relative proportions of NPY receptor subtypes in the brainstem, the relevance of the differential NPY gene expression in the arcuate nucleus regarding central cardiovascular control mechanisms and/or the pathogenesis of hypertension remains to be elucidated.

Animals↗

PubMed1996

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius.

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Animals↗

PubMed1996

Markers of adenosine removal in normotensive and hypertensive rat nervous tissue.

Adenosine mechanisms are altered in brain stem nuclei associated with cardiovascular control in spontaneously hypertensive rats (SHR). Therefore, in the present study we used a number of techniques to compare the binding of the adenosine transport inhibitor [3H]nitrobenzylthioinosine ([3H]NBMPR) as well as adenosine deaminase immunoreactivity (ADA-IR) in brain stems and nodose ganglia of SHR and age-matched normotensive Donryu rats (DRY). Saturation binding revealed a single class of [3H]NBMPR binding sites in the dorsal brain stem of both strains, with Kd and Bmax values of 65 +/- 9 pmol/L and 282 +/- 31 fmol/mg protein, respectively, in SHR and 129 +/- 2 pmol/L and 217 +/- 23 fmol/mg protein in DRY. The Kd for [3H]NBMPR was significantly lower in SHR than in DRY. In competition assays, NBMPR, dilazep, dipyridamole, and adenosine displaced [3H]NBMPR binding, with Kd values of 0.21 +/- 0.04, 57.16 +/- 16.20, 1340 +/- 100, and 87000 +/- 12500 nmol/L, respectively, in DRY and 0.17 +/- 0.04, 28.24 +/- 3.60, 621 +/- 100, and 32000 +/- 6820 in SHR. Kd values for all displacers were lower in SHR; however, only values for dipyridamole and adenosine reached statistical significance. Autoradiography of adenosine transport sites with [3H]NBMPR revealed that unilateral nodose ganglionectomy reduced [3H]NBMPR binding on the denervated side of the nucleus tractus solitarius by 20.6 +/- 1.1% in DRY and 18.7 +/- 2.3% in SHR. The density of [3H]NBMPR binding in nodose ganglia was significantly lower in SHR (0.99 +/- 0.06 Bq/mm2) than in DRY (1.25 +/- 0.08). Immunohistochemical studies demonstrated ADA-IR in the dorsal vagal complex, associated with both nerve cells and fibers. Measurement of ADA-IR in the dorsal vagal complex with an 125I-labeled secondary antibody revealed a significantly higher level of ADA-IR in SHR (122%) than in DRY. In the nodose ganglia, ADA-IR was associated with a population of vagal perikarya. The present study helps provide a molecular explanation for the previously reported impaired cardiovascular responses to intra-nucleus tractus solitarius microinjection of adenosine in hypertensive rats.

Adenosine↗

PubMed1995

5-Hydroxytryptamine3 receptor modulation of excitatory amino acid release in the rat nucleus tractus solitarius.

In vivo microdialysis was employed to measure release of endogenous L-glutamate (GLU) and L-aspartate (ASP) in the medial nucleus tractus solitarius of urethane anaesthetised rats. Basal extracellular levels of these amino acids were stable following a 90 min equilibration period (6.3 +/- 0.24 and 3.4 +/- 0.6 pmol/20 microliters sample of GLU and ASP, respectively). Basal levels of endogenous extracellular GLU and ASP were increased over 2-fold and 3-fold, respectively, following local administration of the selective 5-hydroxytryptamine (5-HT3) receptor agonist phenylbiguanide (300 microM). Intracerebral administration of the selective 5-HT3 receptor antagonist ondansetron (30 microM) blocked the effect of phenylbiguanide on GLU release whilst the effect on ASP was variable and complex. These data suggest that 5-HT3 receptor activation in the rat nucleus tractus solitarius can affect excitatory amino acid neurotransmission in this region of the medulla oblongata.

Animals↗

PubMed1995

Visualization of beta-adrenoceptor binding sites on human inferior vagal ganglia and their axonal transport along the rat vagus nerve.

DESIGN: Because of uncertainties regarding the complete antihypertensive mechanism of action of beta-adrenoceptor antagonists, the present study determined whether vagal afferent neurons of humans and rats possess beta-adrenoceptors. Such a location would provide an appropriate target for beta-blockers to modulate neurotransmission of barosensitive neurons, thereby affecting blood pressure. Therefore, in vitro receptor autoradiography of high-affinity beta-adrenoceptor binding sites was performed on slices of human and rat inferior vagal (nodose) ganglia with [125I]-pindolol. METHODS: Slide-mounted sections of human and rat inferior vagal ganglia were incubated with [125I]-pindolol in the absence or presence of propranolol (10 mumol/l) to define non-specific binding, atenolol (10 mumol/l) to inhibit binding to beta 1-adrenoceptors, or ICI 118551 (3 nmol/l) to inhibit binding to beta 2-adrenoceptors. Unilateral vagal ligation was also performed in the rat to study whether beta-adrenoceptors are subject to axonal transport along the vagus nerve. RESULTS: [125I]-pindolol bound with > 90% specific binding to sections both of human and of rat inferior vagal ganglia. Specific binding occurred over both neuronal perikarya and nerve fibres. In both species the beta 2-adrenoceptor subtype appeared to predominate, as defined by the differential ability of ICI 118551 (beta 2) and atenolol (beta 1) to inhibit the binding of [125I]-pindolol. Furthermore, unilateral vagal ligation in the rat caused an accumulation of specific binding adjacent to the ligature sites. CONCLUSIONS: We conclude that human and rat vagal afferent (and efferent) neurons possess beta-adrenoceptors that potentially could explain the mechanism of action of beta-adrenoceptor antagonists in the therapy of hypertension.

Animals↗

PubMed1995

Functional dopamine D2 receptors on rat vagal afferent neurones.

1. In the present study in vitro electrophysiology and receptor autoradiography were used to determine whether rat vagal afferent neurones possess dopamine D2 receptors. 2. Dopamine (10-300 microM) elicited a temperature- and concentration-dependent depolarization of the rat isolated nodose ganglion preparation. When applied to the tissue 15 min prior to agonist, raclopride (10 microM), clozapine (10 microM) or a mixture of raclopride and clozapine (10 microM each) all produced a threefold parallel shift to the right of the dopamine concentration-response curve. In contrast, SCH 23390 (100 nM), phentolamine and propranolol (1 microM each) failed to antagonize the dopamine-mediated depolarization. 3. [125I]-NCQ 298 (0.5 nM), a D2 selective radioligand, bound topographically to sections of rat brainstem. Densitometric quantification of autoradiograms revealed 93.8 +/- 0.5% specific binding of this salicylamide radioligand, as determined by raclopride (10 microM, n = 10 animals). Binding was highest in the nucleus tractus solitarius (NTS), particularly the medial and gelatinous subnuclei. In addition, specific binding was also observed in the interpolar spinal trigeminal nucleus and the inferior olive. 4. Unilateral nodose ganglionectomy caused a 36.6 +/- 3.0% reduction in specific binding in the denervated NTS compared to the contralateral NTS. Furthermore, the loss of binding was confined to the dorsal aspect of the medial subnucleus of the NTS. Sham surgery had no effect on the binding of [125I]-NCQ 298 in rat brainstem. 5. The present data provide evidence for the presence of functionally relevant dopamine D2 receptors on both the soma and central terminals of rat vagal afferent neurones. In addition, the majority of D2 receptors in the rat NTS appear to be located postsynaptically with respect to vagal terminals, and are presumably located either on ascending glossopharyngeal terminals, descending terminals from higher brain regions or on neuronal cell bodies within the NTS.

Afferent Pathways↗

PubMed1994

Heterocyclic amino alcohols related to ifenprodil as sigma receptor ligands: binding and conformational analyses.

The interaction of a novel series of heterocyclic amino alcohols with the sigma receptor site was assessed using radioligand binding and computerized molecular modelling. All heterocyclic amino alcohols, like the structurally related ifenprodil, fully inhibited the specific binding of [3H]R(+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([3H]3-PPP) to rat cerebral cortical membranes. All compounds recognised two populations of binding sites labelled by [3H]3-PPP and the proportion of sites in the high affinity state was 60-80% of the total sites. Some of the heterocyclic amino alcohols also displayed similar affinity for alpha 1-adrenoceptors labelled by [3H]prazosin, where the pattern of inhibition appears to be stereospecific, unlike that seen with the binding of [3H]3-PPP. The amino alcohols had negligible affinity for sites labelled by the N-methyl-D-aspartate channel ligand, [3H]-(N-1-[thienyl]cyclohexyl)piperidine. Quantitative conformational analyses indicated that the heterocyclic amino alcohols and ifenprodil fitted well to a sigma receptor site model; low energy conformers could be superimposed like other potent sigma receptor ligands with confidence to the sigma receptor model. Our results define a new class of sigma receptor ligands and extend the understanding of the molecular requirements for drugs active at the sigma receptor.

Adrenergic alpha-Antagonists↗

PubMed1994

Visualization of dopamine D2 binding sites on human inferior vagal ganglia.

The present study used in vitro autoradiography to assess whether high affinity D2 binding sites are present on sections of human inferior vagal ganglia, where arterial baroreceptor primary afferent cell bodies are located. Incubation of tissue sections with [125I]NCQ 298 (0.5 nM) revealed dense but non-uniform binding, with a well-defined topography, consistent with the localization of binding sites over cell bodies rather than nerve axons. Coincubation with the D2 antagonist raclopride (10 microM) completely abolished binding of [125I]NCQ 298. Densitometric quantification of autoradiograms estimated 82 +/- 4% specific binding for [125I]NCQ 298 (0.5 nM). These observations indicate the presence of D2 binding sites on sensory ganglia involved in cardiovascular control pathways in the human, and may help to explain some of the documented cardiovascular effects of dopamine.

Autoradiography↗

PubMed1994

Presynaptic adenosine A2a receptors on soma and central terminals of rat vagal afferent neurons.

The dorsal vagal complex of the medulla oblongata is a key centre involved in the regulation of numerous autonomic functions, including cardiovascular control. Adenosine has been implicated as a potential neuromodulator of the baroreceptor reflex, and therefore the current study has investigated the presence and characteristics of adenosine receptors on rat vagal afferent neurons. In the nodose-vagal grease gap preparation, the adenosine A2a agonist CGS-21680 evoked a depolarisation only in the presence of the selective adenosine A1 antagonist PACPX. Autoradiography using [3H]NECA (4 nM) with suppression of A1 binding enabled the first visualisation of high affinity adenosine A2 receptors in the nucleus tractus solitarius (NTS). Unilateral nodose ganglionectomy resulted in over 90% reduction in binding in the lesioned (ipsilateral) NTS compared to a sham control. Furthermore, local administration of CGS-21680 increased evoked glutamate release in the NTS, as measured by in vivo microdialysis. These data suggest the presence of presynaptic adenosine A2a receptors on both the soma and central terminals of rat vagal afferent neurons, and thereby support the hypothesis that adenosine may have a modulatory role in the baroreceptor reflex.

Adenosine↗

PubMed1994

[3H]adenosine transport in rat dorsal brain stem using a crude synaptosomal preparation.

The neuromodulator adenosine, has been shown to have the highest density of central uptake sites in the nucleus tractus solitarius in the dorsal brain stem. The nucleus tractus solitarius is involved in the central regulation of reflex cardiovascular activity suggesting that adenosine may also be involved in central cardiovascular control. Thus, the present study has characterized the transport of [3H]adenosine into rat dorsal brain stem synaptosomes. The process was found to be saturable and highly dependent on temperature. Furthermore, [3H]adenosine transport in rat dorsal brain stem synaptosomes was far more sensitive to the removal of sodium ions than has been previously reported for rat cortical synaptosomes. In addition transport was rapid, being linear for at least 30 s at 37 degrees C, reaching equilibrium within 1 min and had an apparent Km value of 2.7 +/- 0.2 microM (n = 4) and a Vmax value of 135.5 +/- 17.8 pmol/mg protein/min (n = 4). These kinetic parameters are within an order of magnitude of adenosine uptake processes found in rat cerebral cortical synaptosomes. Transport of [3H]adenosine was significantly inhibited by an excess of unlabelled adenosine (1 mM) and the adenosine uptake inhibitor S(4-nitrobenzyl)-6-thioinosine (100 microM) while morphine (150 microM) and flurazepam (150 microM) were largely ineffective as inhibitors of the process, in contrast with previous findings in rat cortical synaptosomes. The present findings demonstrate the presence of a high affinity transport system for adenosine in the rat dorsal brain stem which appears to differ in some properties to uptake processes found in rat cortex.

Adenosine↗

PubMed1994

L-glutamate as a neurotransmitter at baroreceptor afferents: evidence from in vivo microdialysis.

In vivo microdialysis was employed to measure release of endogenous L-glutamate and L-aspartate in the region of the dorsomedial medulla oblongata including the medial nucleus tractus solitarius of the anaesthetized rat. Basal extracellular levels of these amino acids were stable and increased over two-fold when the perfusate was changed to a high KCl (80 mM) artificial cerebrospinal fluid. This high K(+)-evoked release was calcium-dependent, while basal levels were insensitive to removal of calcium ions from the perfusate. An intravenous infusion of phenylephrine, which elevated blood pressure, caused a marked increase of both spontaneous and evoked release of glutamate. In contrast aspartate efflux was not significantly altered. The present data provide evidence that the excitatory amino acids, glutamate and aspartate, serve a neurotransmitter function in the nucleus tractus solitarius of the rat. Furthermore, the increase in glutamate release following baroreceptor activation with phenylephrine suggests that glutamate may be a neurotransmitter at baroreceptor afferent nerve terminals within the nucleus tractus solitarius. On the other hand, aspartate appears to be possibly an inter-neuronal transmitter in this brain region.

Animals↗

PubMed1994

Regional haemodynamic effects of the novel AT1 receptor antagonist, CV-11974, in conscious rats.

CV-11974, a newly developed angiotensin II (AII) subtype 1 (AT1) receptor antagonist, lowers mean arterial pressure (MAP) in various hypertensive animal models. The aim of this study was to examine the regional haemodynamic effects of CV-11974, which contribute to its hypotensive action, in conscious, chronically instrumented spontaneously hypertensive rats (SHR) and renal hypertensive 2-kidney, 1-clip (2K1C) rats, as well as in appropriate normotensive Wistar Kyoto and sham-operated rats. In SHR, CV-11974 (0.1 mg/kg, i.v.) lowered MAP and increased renal blood flow and conductance, indicating renal vasodilatation. However, there were minimal changes in blood flow in the mesenteric or hindquarters vascular beds. By contrast, in 2K1C rats, CV-11974 caused marked hypotension which was associated with substantial vasodilatation in all three vascular beds. The cardiovascular effects of exogenous AII were also blocked by CV-11974. These results suggest that there are subtle differences in the haemodynamic profile of CV-11974 in the two hypertensive rat models, despite similar resting MAP, since this compound caused a relatively selective renal vasodilatation in SHR, but more widespread vasodilatation in 2K1C rats.

Angiotensin Receptor Antagonists↗

PubMed1993

Nitric oxide increases interstitial excitatory amino acid release in the rat dorsomedial medulla oblongata.

In vivo microdialysis was employed to measure release of the neuroactive amino acids L-glutamate (Glu) and L-aspartate (Asp) in the dorsomedial medulla oblongata of the anaesthetised rat. Basal levels of endogenous extracellular Glu and Asp were increased over 5-fold and 3-fold, respectively, following perfusion with a depolarising stimulus of KCl. Intracerebral administration of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP, 30 microM) caused a 5-fold increase in extracellular Asp and a 2-fold increase in extracellular Glu, which was blocked by Methylene blue. These data suggest that NO, acting through guanylate cyclase, can affect excitatory amino acid neurotransmission in the dorsomedial medulla oblongata.

Amino Acids↗

PubMed1993

125I-ifenprodil: synthesis and characterization of binding to a polyamine-sensitive site in cerebral cortical membranes.

The characteristics of binding sites in rat cerebral cortical synaptic membranes labeled by 125I-ifenprodil, a noncompetitive NMDA receptor antagonist, are described. 125I-ifenprodil was synthesized using Na125I in the presence of chloramine-T and purified by paper chromatography. Binding of the 125I-ligand was optimal at pH 7.7 in 5 mM Tris.HCl buffer. Equilibrium binding of 125I-ifenprodil was displaced by spermine (1 mM) but not by ifenprodil or its analogue, SL 82.0715 (both 16.7 microM). Zn2+, Ca2+, and Mg2+ inhibited specific binding of 125I-ifenprodil in a concentration-dependent manner, with IC50 values of 0.11, 1.1, and 1.7 mM, respectively. The dissociation constant (KD) for unlabeled ifenprodil determined by saturation binding was 205 nM. Scatchard plots of saturation data appeared curvilinear but were best described by a single-binding-site model (Hill coefficient = 0.95), with a density of binding sites (Bmax) of 141 pmol/mg of protein. Binding of 125I-ifenprodil was inhibited by polyamines, with a rank potency order of spermine > spermidine > putrescine = 1,3-diaminopropane. The pattern of inhibition produced by spermidine was apparently competitive. Ifenprodil congeners also fully inhibited polyamine-sensitive binding of 125I-ifenprodil, with a rank potency order of ifenprodil > SL 82.0715 = tibalosine > nylidrin = isoxsuprine. It was found that sigma/antitussive agents partially inhibited specific binding, but inclusion of the sigma drug GBR 12909 had little effect on the binding of 125I-ifenprodil, suggesting this site was not involved. The binding site labeled by 125I-ifenprodil is polyamine sensitive, has a discrete pharmacological profile, and apparently is unrelated to the sigma site.

Animals↗

PubMed1992

Presence of functional vasopressin V1 receptors in rat vagal afferent neurones.

The nucleus of the solitary tract (NTS) is one of the brain regions by which arginine vasopressin (AVP) influences blood pressure. This series of experiments in adult male rats was designed to determine whether the AVP binding sites which have been demonstrated in the NTS by in vitro autoradiography might be presynaptic on vagal afferents from the nodose ganglion; whether the AVP binding sites on vagal afferent neurones are functional receptors; and whether vagal transport of AVP receptors to other organs also occurs. High affinity binding sites (using the selective V1 antagonist radioligand [125I][d(CH2)5,Sar7]AVP and in vitro autoradiography) with characteristics of V1 receptors in the medial subnucleus of the NTS were reduced by 40% ipsilateral to nodose ganglionectomy. The nodose ganglion itself also contained high affinity V1 AVP binding sites that localised over cell bodies of vagal sensory neurones. That these binding sites were functional receptors was apparent when low concentrations of AVP but not oxytocin were found to depolarize the isolated nodose ganglion utilizing the 'silicone grease gap' technique. Furthermore, the actions of AVP were antagonised by low concentrations of a selective V1 receptor antagonist. However, there was no accumulation of AVP binding sites adjacent to either the proximal or distal vagal ligations suggesting that peripheral vagal transport of AVP receptors may not occur. Therefore these results are consistent with functional AVP V1 receptors occurring in the nodose ganglion. These receptors may occur on central terminals of vagal sensory neurones in the medial subnucleus of the NTS, but there was no evidence for peripheral transport of AVP V1 receptors.

Animals↗

PubMed1992

Alpha 2-adrenoceptor and catecholamine-insensitive binding sites for [3H]rilmenidine in membranes from rat cerebral cortex.

The kinetic and pharmacological characteristics of the binding of the oxazoline antihypertensive drug, [3H]rilmenidine, to membranes of rat cerebral cortex have been determined. Computerised resolution of curvi-linear, equilibrium binding isotherms was consistent with the existence of two distinct binding sites for [3H]rilmenidine: Kd 17.3 +/- 7.41 nM, Bmax 0.197 +/- 0.06 pmol/mg protein and Kd 254 +/- 48 nM, Bmax 1.59 +/- 0.08 pmol/mg protein. Moreover, the resolution of two association and dissociation rates also suggested the existence of two binding site populations. Drug inhibition studies revealed that specific binding of [3H]rilmenidine (2 nM) was only inhibited by a maximum of 50% by the catecholamines, adrenaline and noradrenaline, but was completely inhibited by some oxazolines, by guanabenz (a guanidino drug) and by several imidazoline compounds including naphazoline, oxymetazoline and clonidine. Binding isotherms for these drugs were also best fit by a two-site model. The relative Ki values at the high affinity site for [3H]rilmenidine and the number of these high affinity sites are consistent with this site being an alpha 2-adrenoceptor. The high affinity of oxymetazoline and low affinity of prazosin for high affinity [3H]rilmenidine binding sites together with the rank order of potency of oxymetazoline greater than phentolamine greater than SKF 104078 greater than ARC-239 greater than prazosin suggest that [3H]rilmenidine binds to the alpha 2A sub-type of adrenoceptor. Computer-resolved Ki values for drugs at the larger number of lower affinity binding sites were very similar to Ki values determined in the presence of 10 microM adrenaline (used to block alpha 2-adrenoceptor binding).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗