Reduced V1 vasopressin binding in the rat nucleus solitarii after nodose ganglionectomy

Infrared light elicits endothelium-dependent vasodilation in isolated occipital arteries of the rat via soluble guanylyl cyclase-dependent mechanisms

The left and right occipital arteries provide blood supply to afferent cell bodies in the ipsilateral nodose and petrosal ganglia. This supply is free of an effective blood-ganglion barrier, so changes in occipital artery blood flow directly affect the access of circulating factors to the afferent cell bodies. The application of infrared (IR) light to modulate neural and other cell processes has yielded information about basic biological processes within tissues and is gaining traction as a potential therapy for a variety of disease processes. To address whether IR can directly modulate vascular function, we performed wire myography studies to determine the actions of IR on occipital arteries isolated from male Sprague-Dawley rats. Based on our previous research that functionally-important differences exist between occipital artery segments close to their origin at the external carotid artery (ECA) and those closer to the nodose ganglion, the occipital arteries were dissected into two segments, one closer to the ECA and the other closer to the nodose ganglion. Segments were constricted with 5-hydroxytryptamine to a level equal to 50% of the maximal response generated by the application of a high (80 mM) concentration of K+ ions. The direct application of pulsed IR (1,460 nm) for 5 s produced a rapid vasodilation in occipital arteries that was significantly more pronounced in segments closest to the ECA, although the ECA itself was minimally responsive. The vasodilation remained for a substantial time (at least 120 s) after cessation of IR application. The vasodilation during and following cessation of the IR application was markedly diminished in occipital arteries denuded of the endothelium. In addition, the vasodilation elicited by IR in endothelium-intact occipital arteries was substantially reduced in the presence of a selective inhibitor of the nitric oxide-sensitive guanylate cyclase, 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ). It appears that IR causes endothelium-dependent, nitric-oxide-mediated vasodilation in the occipital arteries of the rat. The ability of IR to generate rapid and sustained vasodilation may provide new therapeutic approaches for restoring or improving blood flow to targeted tissues.

Vasopressin inhibits glutamate release via two distinct modes in the brainstem

The hypothalamus coordinates autonomic responses in part through arginine vasopressin (AVP) released in medial nucleus tractus solitarius (NTS). However, the mechanisms and sites of AVP action within NTS pathways are uncertain. In brainstem slices, we activated solitary tract (ST) primary afferents to release glutamate and tested whether AVP modulated synaptic transmission to second-order neurons. NTS neurons were classified as second order by ST synaptic characteristics or the presence of anterograde tracers from peripheral baroreceptor afferents. Stimulus recruitment curves indicated ST-EPSCs on individual neurons were evoked by stimulation of single ST axons. Variance-mean (V-M) analysis of ST-EPSCs in individual neurons revealed uniformly high release probability (p approximately 0.9) from an average of 19 release sites (N) and a quantal size (q) of 34.0 +/- 4.7 pA. In 26 of 49 neurons, AVP inhibited afferent synaptic transmission. In most neurons, AVP reduced ST-EPSC amplitudes (n = 20) by decreasing p to 0.65, whereas q, N, and conduction times were unaffected. The V1a antagonist SR49059 alone decreased ST-EPSC V and increased M, suggesting tonic AVP actions, and blocked exogenous AVP action (n = 4). In other neurons with identical ST release properties, AVP induced synaptic failures and increased conduction time without altering the V-M relationship of successful ST-EPSCs (n = 6). Interestingly, frequency-depressed ST-EPSCs were not affected by AVP. AVP failed to alter holding or voltage-dependent potassium currents. Thus, AVP regulates NTS neurons by two distinct novel and state-dependent mechanisms: one, an analog, graded presynaptic inhibition of terminal glutamate release and the other, a binary, extraterminal block of conducted excitation.

Non-angiotensin II [125I] CGP42112 binding is a sensitive marker of neuronal injury in brainstem following unilateral nodose ganglionectomy: Comparison with markers for activated microglia

Previously we reported that a non-angiotensin II [(125)I] CGP42112 binding site is up-regulated in rat brainstem nuclei as a result of unilateral nodose ganglionectomy. In the present study, we compared non-angiotensin II [(125)I] CGP42112 binding with microglia/macrophage activation following nodose ganglionectomy, using both in vitro autoradiography and immunohistochemistry. Specific [(125)I] CGP42112 binding was observed in the nucleus of the solitary tract (NTS) and revealed an AT(2) receptor component as well as a non-angiotensin II receptor component. Subsequent to unilateral nodose ganglionectomy, [(125)I] CGP42112 binding in the ipsilateral NTS was increased approximately two-fold and was also induced in the ipsilateral dorsal motor nucleus (DMX) and the nucleus ambiguus (n.amb). This non-angiotensin II [(125)I] CGP42112 binding site was displaced by CGP42112 but not other ligands. Increased [(3)H] PK11195 binding (a known marker of reactive gliosis) was also observed in the same brainstem nuclei as non-angiotensin II [(125)I] CGP42112 binding after nodose ganglionectomy. The similarity in binding patterns between [(125)I] CGP42112 and [(3)H] PK11195 was shown to be primarily due to retrograde degeneration in the ipsilateral NTS, DMX and n.amb, as both radioligands were localized to similar cellular targets within the interstial space and over cellular debris. Immunohistochemical data confirmed reactive gliosis within the ipsilateral NTS, DMX and n.amb, following nodose ganglionectomy, which was predominantly characterized by an increase in OX-42 immunoreactivity (a marker for activated microglia/macrophages), with only a small increase in glial fibrillary acidic protein immunoreactivity (a marker of astrogliosis) detected. These data demonstrate for the first time that non-angiotensin II [(125)I] CGP42112 binding is associated with activated microglia, as well as macrophages, following unilateral nodose ganglionectomy. Furthermore, these studies also demonstrate the potential use of non-angiotensin II [(125)I] CGP42112 binding as a marker for quantitating inflammatory events which occur as a result of damage to the CNS.

Localization of AT(2) receptors in the nucleus of the solitary tract of spontaneously hypertensive and Wistar Kyoto rats using [125I] CGP42112: upregulation of a non-angiotensin II binding site following unilateral nodose ganglionectomy

We have examined the binding distribution of a selective AT(2) receptor ligand [125I] CGP42112 in the brain of adult Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). AT(2) receptor localization was also examined in the rat brainstem following unilateral nodose ganglionectomy. Specific [125I] CGP42112 binding was observed in discrete brain regions from both rat strains, including the nucleus of the solitary tract (NTS), and did not differ between WKY and SHR. [125I] CGP42112 binding in the NTS revealed an AT(2) receptor component that was displaceable by PD 123319 and Ang II (50-58%), as well as a non-angiotensin II receptor component (42-49%). Following unilateral nodose ganglionectomy, [125I] CGP42112 binding density on the denervated side of the NTS was increased approximately two-fold in both WKY and SHR. This increased [125I] CGP42112 binding density in the ipsilateral NTS was comprised of a greater non-angiotensin II component than that observed in the sham groups, since only approximately 30% was displaced by PD123319 and angiotensin II. Furthermore, [125I] CGP42112 also revealed high binding density on the denervated side in the dorsal motor nucleus and the nucleus ambiguus in both WKY and SHR. AT(2) receptor immunoreactivity was also visualised in the NTS of sham operated rats, but was not observed in the dorsal motor nucleus or the nucleus ambiguus, nor was it up-regulated following nodose ganglionectomy. These results demonstrate, for the first time, an AT(2) receptor binding site in the NTS, as well as a non-angiotensin II [125I] CGP42112 binding site. These studies also demonstrate that nodose ganglionectomy represents a useful model in which to study a non-angiotensin II [125I] CGP42112 binding site that is up-regulated following degeneration of afferent vagal nerves.

Characterisation of vasopressin V(1A), angiotensin AT(1) and AT(2) receptor distribution and density in normotensive and hypertensive rat brain stem and kidney: effects of restraint stress

In the present study, we have examined neurochemical correlates that may be involved in the differential cardiovascular responses observed in normotensive and hypertensive rats during stress. Using a restraint stress paradigm, both normotensive Wistar Kyoto (WKY) and Spontaneously Hypertensive rats (SHR) underwent acute (1 h restraint in a perspex tube), chronic (1 h restraint for ten consecutive days) or no restraint (control) stress. Following cessation of restraint, rats were processed by incubating sections of brain stem and kidney with [125I]-HO-LVA (0.03 nM) or [125I]Sar(1)Ile(8)-AngiotensinII (0.5 nM), in the presence of PD123319 (10 microM) or losartan (10 microM), to determine the distribution and density of vasopressin V(1A), angiotensin AT(1) and AT(2) receptors, respectively. Analysis of autoradiograms indicated changes in the density of radioligand binding in acutely and chronically-stressed rats, as compared to controls. For example, V(1A) binding in the medial nucleus tractus solitarius (SolM) decreased in the WKY but increased in the SHR. AT(1) binding in SolM did not significantly change in the WKY but decreased in the SHR with repeated restraint. In kidney slices, AT(1) binding decreased with stress in the WKY (-17%) but increased in SHR (+10-15%). AT(2) binding in the kidney showed a pattern similar to that of AT(1) binding in SHR, but not WKY. Graded increases in V(1A) binding were measured in kidney medulla and cortex of both strains (+50-60% with chronic restraint). These results suggest that physiological adaptation to restraint is associated with specific changes in V(1A), AT(1) and AT(2) receptor density within brain nuclei and kidney.

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.

Morphological and electrophysiological evidence for postsynaptic localization of functional oxytocin receptors in the rat dorsal motor nucleus of the vagus nerve

The vagal complex is innervated by oxytocin immunoreactive axons of hypothalamic origin. The presence of oxytocin binding sites in the dorsal motor nucleus of the vagus nerve of the rat was evidenced by autoradiography with a radioiodinated oxytocin antagonist as ligand. Two weeks following a unilateral vagotomy, distal to the nodose ganglion, binding sites were reduced below the level of detection in the ipsilateral dorsal motor nucleus of the vagus nerve. Choline acetyltransferase immunoreactivity was also markedly reduced in the vagal motoneurons whose axons had been transected. Electrophysiological studies were performed in vitro in brainstem slices from control rats. In antidromically identified vagal motoneurones, oxytocin applied at 0.1-1.0 microM either caused a reversible depolarization or generated, under voltage-clamp conditions, a transient inward current. These responses persisted under the condition of synaptic uncoupling. Taken together these observations favour the notion that oxytocin of hypothalamic origin acts directly on rat vagal motoneurones.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)