Viscerosensory input drives angiotensin II type 1A receptor-expressing neurons in the solitary tract nucleus.

Homeostatic regulation of visceral organ function requires integrated processing of neural and neurohormonal sensory signals. The nucleus of the solitary tract (NTS) is the primary sensory nucleus for cranial visceral sensory afferents. Angiotensin II (ANG II) is known to modulate peripheral visceral reflexes, in part, by activating ANG II type 1A receptors (AT1AR) in the NTS. AT1AR-expressing NTS neurons occur throughout the NTS with a defined subnuclear distribution, and most of these neurons are depolarized by ANG II. In this study we determined whether AT1AR-expressing NTS neurons receive direct visceral sensory input, and whether this input is modulated by ANG II. Using AT1AR-GFP mice to make targeted whole cell recordings from AT1AR-expressing NTS neurons, we demonstrate that two-thirds (37 of 56) of AT1AR-expressing neurons receive direct excitatory, visceral sensory input. In half of the neurons tested (4 of 8) the excitatory visceral sensory input was significantly reduced by application of the transient receptor potential vallinoid type 1 receptor agonist, capsaicin, indicating AT1AR-expressing neurons can receive either C- or A-fiber-mediated input. Application of ANG II to a subset of second-order AT1AR-expressing neurons did not affect spontaneous, evoked, or asynchronous glutamate release from visceral sensory afferents. Thus it is unlikely that AT1AR-expressing viscerosensory neurons terminate on AT1AR-expressing NTS neurons. Our data suggest that ANG II is likely to modulate multiple visceral sensory modalities by altering the excitability of second-order AT1AR-expressing NTS neurons.

Pleiotropy of the Drosophila melanogaster foraging gene on larval feeding-related traits.

Little is known about the molecular underpinning of behavioral pleiotropy. The Drosophila melanogaster foraging gene is highly pleiotropic, affecting many independent larval and adult phenotypes. Included in foraging's multiple phenotypes are larval foraging path length, triglyceride levels, and food intake. foraging has a complex structure with four promoters and 21 transcripts that encode nine protein isoforms of a cGMP dependent protein kinase (PKG). We examined if foraging's complex molecular structure underlies the behavioral pleiotropy associated with this gene. Using a promotor analysis strategy, we cloned DNA fragments upstream of each of foraging's transcription start sites and generated four separate forpr-Gal4s. Supporting our hypothesis of modular function, they had discrete, restricted expression patterns throughout the larva. In the CNS, forpr1-Gal4 and forpr4-Gal4 were expressed in neurons while forpr2-Gal4 and forpr3-Gal4 were expressed in glia cells. In the gastric system, forpr1-Gal4 and forpr3-Gal4 were expressed in enteroendocrine cells of the midgut while forpr2-Gal4 was expressed in the stem cells of the midgut. forpr3-Gal4 was expressed in the midgut enterocytes, and midgut and hindgut visceral muscle. forpr4-Gal4's gastric system expression was restricted to the hindgut. We also found promoter specific expression in the larval fat body, salivary glands, and body muscle. The modularity of foraging's molecular structure was also apparent in the phenotypic rescues. We rescued larval path length, triglyceride levels (bordered on significance), and food intake of for0 null larvae using different forpr-Gal4s to drive UAS-forcDNA. In a foraging null genetic background, forpr1-Gal4 was the only promoter driven Gal4 to rescue larval path length, forpr3-Gal4 altered triglyceride levels, and forpr4-Gal4 rescued food intake. Our results refine the spatial expression responsible for foraging's associated phenotypes, as well as the sub-regions of the locus responsible for their expression. foraging's pleiotropy arises at least in part from the individual contributions of its four promoters.

Functional and neurochemical characterization of angiotensin type 1A receptor-expressing neurons in the nucleus of the solitary tract of the mouse.

Angiotensin II acts via two main receptors within the central nervous system, with the type 1A receptor (AT1AR) most widely expressed in adult neurons. Activation of the AT1R in the nucleus of the solitary tract (NTS), the principal nucleus receiving central synapses of viscerosensory afferents, modulates cardiovascular reflexes. Expression of the AT1R occurs in high density within the NTS of most mammals, including humans, but the fundamental electrophysiological and neurochemical characteristics of the AT1AR-expressing NTS neurons are not known. To address this, we have used a transgenic mouse, in which the AT1AR promoter drives expression of green fluorescent protein (GFP). Approximately one-third of AT1AR-expressing neurons express the catecholamine-synthetic enzyme tyrosine hydroxylase (TH), and a subpopulation of these stained for the transcription factor paired-like homeobox 2b (Phox2b). A third group, comprising approximately two-thirds of the AT1AR-expressing NTS neurons, showed Phox2b immunoreactivity alone. A fourth group in the ventral subnucleus expressed neither TH nor Phox2b. In whole cell recordings from slices in vitro, AT1AR-GFP neurons exhibited voltage-activated potassium currents, including the transient outward current and the M-type potassium current. In two different mouse strains, both AT1AR-GFP neurons and TH-GFP neurons showed similar AT1AR-mediated depolarizing responses to superfusion with angiotensin II. These data provide a comprehensive description of AT1AR-expressing neurons in the NTS and increase our understanding of the complex actions of this neuropeptide in the modulation of viscerosensory processing.

The Role of 18F-FDG PET/CT on Staging and Prognosis in Patients with Small Cell Lung Cancer.

BACKGROUND: We evaluated 18F-FDG PET/CT in small cell lung cancer (SCLC) staging and assessed metabolic (SUVmax, MTV and TLG) and morphologic (CTvol) variables as predictors for overall survival (OS) and progression-free survival (PFS). METHODS: Patients with newly diagnosed, histopathology-confirmed SCLC, who underwent 18F-FDG PET/CT were evaluated. A Cox proportional hazard model was used to determine the association between the primary tumour SUVmax, MTV, TLG and CTvol with OS and PFS. Similar evaluations were performed when hilar/mediastinal lymphadenopathy was included [total SUVmax (TSUVmax), total MTV (TMTV) and total TLG (TTLG)]. RESULTS: 55 patients were included. 18F-FDG PET/CT changed staging in 6/55 (10.9%) patients who were upstaged to extensive disease. TTLG (>443.8) was a significant variable for OS with HR=2.1 (CI 1.14-3.871, p=0.017). Patients with TTLG>443.8 had a median OS of 13.4 months compared to 25.7 months in patients with TTLG<443.8 (p=0.018). TMTV (>72.4) was significant for PFS with HR=2.3 (CI 1.11-4.8, p=0.025). A median PFS of 12.1 and 26.2 months was found with TMTV greater and less than 72.4, respectively (p=0.005). CONCLUSIONS: 18F-FDG PET/CT improved staging of patients with SCLC, and TTLG and TMTV can be used as prognostic variables for OS and PFS, respectively. KEY POINTS: • Identifying variables that predict the prognosis of patients with SCLC is important. • 18F-FDG PET/CT influences staging of patients with SCLC. • Metabolic parameters could be used as predictors for PFS and OS.

Survival of recipients of livers from donation after circulatory death who are relisted and undergo retransplant for graft failure.

Use of grafts from donation after circulatory death (DCD) as a strategy to increase the pool of transplantable livers has been limited due to poorer recipient outcomes compared with donation after brain death (DBD). We examined outcomes of recipients of failed DCD grafts who were selected for relisting with regard to waitlist mortality and patient and graft survival after retransplant. From the Scientific Registry of Transplant Recipients database, we identified 1820 adults who underwent first deceased donor liver transplant January 1, 2004 to June 30, 2011, and were relisted due to graft failure; 12.7% were DCD recipients. Compared with DBD recipients, DCD recipients had better waitlist survival (90-day mortality: 8%, DCD recipients; 14-21%, DBD recipients). Of 950 retransplant patients, 14.5% were prior DCD recipients. Graft survival after second liver transplant was similar for prior DCD (28% graft failure within 1 year) and DBD recipients (30%). Patient survival was slightly better for prior DCD (25% death within 1 year) than DBD recipients (28%). Despite higher overall graft failure and morbidity rates, survival of prior DCD recipients who were selected for relisting and retransplant was not worse than survival of DBD recipients.

Regulation of angiotensinogen by angiotensin II in mouse primary astrocyte cultures.

Astrocytes are the major source of angiotensinogen in the brain and play an important role in the brain renin-angiotensin system. Regulating brain angiotensinogen production alters blood pressure and fluid and electrolyte homeostasis. In turn, several physiological and pathological manipulations alter expression of angiotensinogen in brain. Surprisingly, little is known about the factors that regulate astrocytic expression of angiotensinogen. There is evidence that angiotensinogen production in both hepatocytes and cardiac myocytes can be positively regulated via the angiotensin type 1 receptor, but this effect has not yet been studied in astrocytes. Therefore, the aim of this project was to establish whether angiotensin II modulates angiotensinogen production in brain astrocytes. Primary astrocyte cultures, prepared from neonatal C57Bl6 mice, expressed angiotensinogen measured by immunocytochemistry and real-time PCR. Using a variety of approaches we were unable to identify angiotensin receptors on cultured astrocytes. Exposure of cultured astrocytes to angiotensin II also did not affect angiotensinogen expression. When astrocyte cultures were transduced with the angiotensin type 1A receptor, using adenoviral vectors, angiotensin II induced a robust down-regulation (91.4% ± 1.8%, p < 0.01, n = 4) of angiotensinogen gene expression. We conclude that receptors for angiotensin II are present in extremely low levels in astrocytes, and that this concurs with available data in vivo. The signaling pathways activated by the angiotensin type 1A receptor are negatively coupled to angiotensinogen expression and represent a powerful pathway for decreasing expression of this protein, potentially via signaling pathways coupled to Gα(q/11) .

Phase I dose-finding study of paclitaxel with panitumumab, carboplatin and intensity-modulated radiotherapy in patients with locally advanced squamous cell cancer of the head and neck.

BACKGROUND: Panitumumab has the potential to improve the therapeutic ratio of concurrent chemoradiotherapy for squamous cell carcinoma of the head and neck (SCCHN). PATIENTS AND METHODS: This phase I dose-finding study investigated escalating doses of paclitaxel (Taxol) given concurrently with panitumumab, carboplatin and intensity-modulated radiotherapy (IMRT) for stage III-IVB SCCHN. Untreated patients with oral cavity, oropharynx, larynx, hypopharynx or unknown primaries were eligible. Additional eligibility criteria included measurable disease, good performance status and no contraindication to therapy. Patients received weekly fixed doses of panitumumab and carboplatin plus escalating doses of paclitaxel with IMRT. RESULTS: Nineteen patients were enrolled on to two dose levels (DLs): weekly paclitaxel 15 mg/m(2) (n = 3) and 30 mg/m(2) (n = 16). One dose-limiting toxicity occurred in DL 2, which was declared the maximum tolerated dose. All patients experienced mucositis, primarily grade 3 or more. Oral pain, xerostomia, dysphagia, weight loss, dermatitis, nausea and acneiform rash were frequent. All patients had partial response according to RECIST, whereas the overall complete clinical response rate was 95%. At median follow-up of 21 months, 18 of 19 patients (95%) remained disease free. CONCLUSIONS: Panitumumab, carboplatin, paclitaxel and IMRT are well tolerated and appear highly active in the treatment of SCCHN. Further study of this regimen in SCCHN is warranted.

Strange magnetism and the anapole structure of the proton.

The violation of mirror symmetry in the weak force provides a powerful tool to study the internal structure of the proton. Experimental results have been obtained that address the role of strange quarks in generating nuclear magnetism. The measurement reported here provides an unambiguous constraint on strange quark contributions to the proton's magnetic moment through the electron-proton weak interaction. We also report evidence for the existence of a parity-violating electromagnetic effect known as the anapole moment of the proton. The proton's anapole moment is not yet well understood theoretically, but it could have important implications for precision weak interaction studies in atomic systems such as cesium.

C1 neurons in the rat rostral ventrolateral medulla differentially express vesicular monoamine transporter 2 in soma and axonal compartments.

Vesicular monoamine transporter 2 (VMAT2) packages biogenic amines into large dense core and synaptic vesicles for either somatodendritic or synaptic release from neurons of the CNS. Whilst the distribution of VMAT2 has been well characterized in many catecholaminergic cell groups, its localization amongst C1 adrenergic neurons in the medulla has not been examined in detail. Within the rostral ventrolateral medulla (RVLM), C1 neurons are a group of barosensitive, adrenergic neurons. Rostral C1 cells project to the thoracic spinal cord and are considered sympathetic premotor neurons. The majority of caudal C1 cells project rostrally to regions such as the hypothalamus. The present study sought to quantitate the somatodendritic expression of VMAT2 in C1 neurons, and to assess the subcellular distribution of the transporter. Immunoreactivity for VMAT2 occurred in 31% of C1 soma, with a high proportion of these in the caudal part of the RVLM. Retrograde tracing studies revealed that only two of 43 bulbospinal C1 neurons contained faint VMAT2-immunoreactivity, whilst 88 +/- 5% of rostrally projecting neurons were VMAT2-positive. A lentivirus, designed to express green fluorescent protein exclusively in noradrenergic and adrenergic neurons, was injected into the RVLM to label C1 neurons. Eighty-three percent of C1 efferents that occurred in close proximity to sympathetic preganglionic neurons within the T(3) intermediolateral cell column contained VMAT2-immunoreactivity. These data demonstrate differential distribution of VMAT2 within different subpopulations of C1 neurons and suggest that this might reflect differences in somatodendritic vs. synaptic release of catecholamines.

Options for combining altered fractionation with IMRT.

We set out to investigate IMRT-based concomitant boost. Eight patients with stage III/IV squamous cell carcinoma of the head and neck treated with once daily with chemoradiotherapy at the Dana-Farber/Brigham and Women's Hospital had their treatment plans reviewed with IRB approval. Each case was replanned for treatment with a a concomitant boost regimen. Plans delivered 1.9 Gy in 30 fractions to 57 Gy with a boost of 1.5 Gy in 10 fractions for a total dose of 72 Gy. The boost was planned with both IMRT and 3-D conformal, to compare the two techniques. For each patient, both plans (IMRT-IMRT and IMRT-3DCRT) were evaluated for target and avoidance coverage, monitor units and integral dose. Finally, we evaluated the plans for time to completion. The IMRT-IMRT and IMRT-3-DCRT techniques were equivalent for target coverage. 100% coverage of the GTV and PTV was achieved with 97% of the prescription dose. Hot spots were seen 104% to 108% with IMRT-IMRT plan and from 102-111% with the IMRT-3DCRT plans. The IMRT-IMRT boost had double the monitor units as the 3-DCRT boosts. When the total monitor units from both the initial and boost portions of the plans were e combined there was not a significant difference. There was a slight increase in integral dose with the IMRT-IMRT plans of mean 3.8%. Planning time was increased for the 3-DCRT boost as opposed to the IMRT boost (mean 3.5 hours vs. 1.5 hours). More time was needed for quality assurance of the IMRT-IMRT plans (3.0 hours vs. 1.5 hours for IMRT-3-DCRT). We found that both IMRT-based concomitant-boost strategies are achievable and produce good dosimetric results.

Respiratory modulation of sympathetic nerve activity is enhanced in male rat offspring following uteroplacental insufficiency.

Sympathetic nerve activity to the cardiovascular system displays prominent respiratory-related modulation which leads to the generation of rhythmic oscillations in blood pressure called Traube-Hering waves. An amplification of this respiratory modulation of sympathetic activity is observed in hypertension of both genetic, the spontaneously hypertensive rat, and induced, chronic intermittent hypoxia or maternal protein restriction during gestation, origin. Male offspring of mothers with uteroplacental insufficiency, induced by bilateral uterine vessel ligation at 18 days of gestation, are also hypertensive in adulthood. In this study we examined whether these male offspring display altered respiratory modulation of sympathetic activity at pre-hypertensive ages compared to controls. Respiratory, cardiovascular and sympathetic parameters were examined using the working heart-brainstem preparation in 35 day old male rats that had reduced birth weight due to uteroplacental insufficiency. Whilst all respiratory parameters were not different between groups, we observed an enhanced respiratory-related burst of thoracic sympathetic nerve activity and amplified Traube-Hering waves in the growth-restricted group. This group also showed an increased sympathetic and bradycardic response to activation of peripheral chemoreceptors. The observations add support to the view that altered respiratory modulation of sympathetic activity represents a common mechanism involved in the development of several forms of hypertension.

The brain angiotensin system: insights from mapping its components.

Mapping of components of the angiotensin (Ang) system in the brain suggests that it serves multiple central roles, including regulation of fluid and electrolyte balance, central autonomic control, and pituitary hormone release.

Identification of CNS neurons with polysynaptic connections to both the sympathetic and parasympathetic innervation of the submandibular gland.

Coordinated modulation of sympathetic and parasympathetic nervous activity is required for physiological regulation of tissue function. Anatomically, whilst the peripheral sympathetic and parasympathetic pathways are separate, the distribution of premotor neurons in higher brain regions often overlaps. This co-distribution would enable coordinated regulation and might suggest individual premotor neurons could project to both sympathetic and parasympathetic outflows. To investigate this one submandibular gland was sympathectomized. One of two isogenic strains of the pseudorabies virus, expressing different fluorophores, was injected into the cut sympathetic nerve and the other into the submandibular gland. Independent labeling of the peripheral sympathetic and parasympathetic pathways was observed. Dual-labeled neurons were observed in many CNS regions known to be involved in regulating salivary function. We propose these observations highlight a common pattern of organization of the CNS, providing the anatomical framework for the fine control of organ function required for homeostatic regulation and the coordination of organ responses to enable complex behaviors.

Effect of occlusion on Trichophyton mentagrophytes infections in guinea pigs.

The effect of occlusion and griseofulvin on the duration and severity of acute dermatophytosis was assessed in guinea pigs. Sixty guinea pigs given standard Trichophyton mentagrophytes infections were divided into 5 groups: (A) control, (B) intermittent wet occlusion, (C) continuous-wet occlusion, (D) griseofulvin, (E) griseofulvin-continuous-wet occlusion. Lesions were largest in the control group, smallest in the griseofulvin-continuous-occlusion group, and of intermediate area in the other groups. The degree of inflammation and alopecia was not affected by occlusion, but was markedly reduced or eliminated with griseofulvin. Healing of the lesions occurred more rapidly in the griseofulvin-continuous-occlusion group than in any other group. This study suggests that either occlusion of the inoculated site or oral griseofulvin markedly reduces the expected area of the fungal lesion, and occlusion together with griseofulvin shortens the duration of the lesion.

Effects of prolonged continuous exposure of human skin to water: a reassessment.

Continuous exposure of human skin to water in small plastic cups for periods of 72 and 144 hr produced a mild, transient dermatitis in half the sites tested. The degree of dermatitis was only slightly greater at 144 than at 72 hr, and was unrelated to the pH of the water samples. Comparison of soap-pretreated to non-pretreated skin areas showed a significant tendency for the more severe dermatitis to be present on the non-pretreated skin areas at higher pH's. There was virtually no coating of hairs with waxy yellowish material (clumps of bacteria), and no lesion was produced that resembled warm-water-immersion injuries.

The brain renin-angiotensin system: location and physiological roles.

Angiotensinogen, the precursor molecule for angiotensins I, II and III, and the enzymes renin, angiotensin-converting enzyme (ACE), and aminopeptidases A and N may all be synthesised within the brain. Angiotensin (Ang) AT(1), AT(2) and AT(4) receptors are also plentiful in the brain. AT(1) receptors are found in several brain regions, such as the hypothalamic paraventricular and supraoptic nuclei, the lamina terminalis, lateral parabrachial nucleus, ventrolateral medulla and nucleus of the solitary tract (NTS), which are known to have roles in the regulation of the cardiovascular system and/or body fluid and electrolyte balance. Immunohistochemical and neuropharmacological studies suggest that angiotensinergic neural pathways utilise Ang II and/or Ang III as a neurotransmitter or neuromodulator in the aforementioned brain regions. Angiotensinogen is synthesised predominantly in astrocytes, but the processes by which Ang II is generated or incorporated in neurons for utilisation as a neurotransmitter is unknown. Centrally administered AT(1) receptor antagonists or angiotensinogen antisense oligonucleotides inhibit sympathetic activity and reduce arterial blood pressure in certain physiological or pathophysiological conditions, as well as disrupting water drinking and sodium appetite, vasopressin secretion, sodium excretion, renin release and thermoregulation. The AT(4) receptor is identical to insulin-regulated aminopeptidase (IRAP) and plays a role in memory mechanisms. In conclusion, angiotensinergic neural pathways and angiotensin peptides are important in neural function and may have important homeostatic roles, particularly related to cardiovascular function, osmoregulation and thermoregulation.

Localization and characterization of insulin receptors in rat brain and pituitary gland using in vitro autoradiography and computerized densitometry.

In order to identify likely sites of action in insulin in rat brain we have used the technique of in vitro autoradiography and computerized densitometry to map, characterize, and quantify its receptors in coronal and sagittal sections. A discrete and characteristic distribution of insulin receptor binding was demonstrated, with specific binding representing 92% of total binding. Displacement and specificity competition curves in olfactory bulb are typical for authentic insulin receptors, and computer analysis indicates a single class of binding site with a dissociation constant (Kd) 0.48 nM for choroid plexus and 0.44 nM for olfactory bulb external plexiform layer. Insulin receptor density is maximum in the choroid plexus, and high in the external plexiform layer of olfactory bulb. Structures of the limbic system and hypothalamus reveal moderate to high insulin receptor density, particularly the lateral septum, amygdala, subiculum, hippocampal CA1 region, mammillary body, and arcuate nucleus. Moderate insulin receptor density occurs in regions of cerebral cortex and cerebellum, and moderate to low binding occurs in discrete brainstem and midbrain structures. Insulin binding in the pituitary gland is greatest in the anterior lobe, with clear distinction from intermediate and posterior lobes. The circumventricular organs and the thalamus show low insulin binding. We conclude that insulin receptors are widespread throughout rat brain, with concentration in regions concerned with olfaction, appetite, and autonomic functions. The distribution is distinct from other neuropeptides and not related to either vascularity or cell density. A common feature of regions rich in insulin receptors is that they contain dendritic fields receiving rich synaptic input. Whether insulin plays a specific neurotransmitter or metabolic role in these sites remains unclear, but these studies have provided detailed information on potential sites of action of insulin in the brain, and will allow further studies to examine insulin receptor function in specific brain regions.

Angiotensin II receptors and angiotensin converting enzyme in the medulla oblongata.

Quantitative in vitro autoradiography was used to map angiotensin II (ANG II) receptors and angiotensin converting enzyme (ACE) in sections from rat, rabbit, sheep, and human medulla oblongata and to follow changes in receptor and ACE density after disruption of vagal projections by nodose ganglionectomy in the rat. ANG II receptors and ACE are both concentrated in the nucleus of the solitary tract and dorsal motor nucleus of vagus of the rat, rabbit, sheep, and human. An ANG II receptor-containing band connecting the nucleus of the solitary tract with the dorsolateral medulla was seen in rabbit and human tissue, providing evidence for association of ANG II receptors with vagal afferent fibers. ANG II receptors were found to be concentrated in the rostral and caudal ventrolateral medulla, which corresponded to the region of C1 and A1 catecholamine-containing cell groups in the rabbit. This localization was also evident in rat and human tissue. In all four species, a prominent, ANG II receptor-rich band in the intermediate reticular nucleus was found to connect the ventrolateral medulla and the dorsal vagal complex. In humans and sheep, this band contains puncta that overlie cell bodies. One week after nodose ganglionectomy in the rat, the density of ANG II receptors in the ipsilateral dorsal vagal complex fell markedly. This fall was most prominent in the rostral dorsal motor nucleus of vagus (to 46% of control density) and in the nucleus of the solitary tract (to 56% of control). ACE levels and calcitonin gene-related peptide receptor density were unchanged in both nuclei after ganglionectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping of angiotensin II receptor subtype heterogeneity in rat brain.

Angiotensin II (Ang II) exerts a number of central actions on fluid and electrolyte homeostasis, autonomic activity, and neuroendocrine regulation. In order to evaluate likely sites where these actions are mediated, Ang II receptor binding was localized in rat brain by in vitro autoradiography with the aid of the antagonist analogue 125I-[Sar1, Ile8]Ang II. Two subtypes of Ang II receptor have been identified using recently developed peptide and nonpeptide antagonists. In the periphery, the receptor subtypes differ in distribution, second messenger coupling, and function. Brain Ang II receptor subtypes were therefore differentiated into AT-1 (type I) and AT-2 (type II) subtypes by using unlabelled nonpeptide antagonists specific for the two Ang II subtypes. AT-1 binding was determined to be that inhibited by Dup 753 (10 microM) and AT-2 binding to be that inhibited by PD 123177 (10 microM). The reducing agent dithiothreitol (DTT) decreased binding to AT-1 receptors and enhanced binding to AT-2 receptors. Many brain structures, such as the vascular organ of the lamina terminalis, subfornical organ, median preoptic nucleus, area postrema, nucleus of the solitary tract, and dorsal motor nucleus of the vagus, which are known to be related to the central actions of Ang II, contain exclusively AT-1 Ang II receptors. By contrast, the locus coeruleus, ventral and dorsal parts of lateral septum, superior colliculus and subthalamic nucleus, many nuclei of the thalamus, and nuclei of the inferior olive contain predominantly AT-2 Ang II receptors. The detailed binding characteristics of each subtype were determined by competition studies with a series of analogues of angiotensin and antagonists. The pharmacological specificity obtained in rat superior colliculus and the nucleus of the solitary tract agreed well with published data on AT-1 and AT-2 receptors, respectively. There was a high degree of correlation between the distribution of Ang II binding sites with published data on Ang II-immunoreactive fields and on the sites of Ang II-responsive neurons. The present study also reveals pharmacological heterogeneity of brain Ang II receptors. The subtype-specific receptor mapping described here is relevant to understanding the role of angiotensin peptides in the central nervous system and newly discovered central actions of nonpeptide Ang II receptor antagonists.

Localization of angiotensin II receptor binding in rabbit brain by in vitro autoradiography.

Binding of 125I-[Sar1,Ile8] angiotensin II (AII) to sections of brains from both wild and laboratory rabbits was determined by in vitro autoradiography. In the forebrain, specific high density binding was observed in the olfactory bulb, organum vasculosum of the lamina terminalis (OVLT), subfornical organ, median eminence, lateral septum, median preoptic nucleus and hypothalamic paraventricular, supraoptic and arcuate nuclei. In the midbrain, binding of the radioligand was observed in the interpeduncular and parabrachial nuclei, in the locus coeruleus, and ventrolateral pons. In the hind brain, there was dense binding of 125I-[Sar1,Ile8] AII to the nucleus of the solitary tract (NTS) and to both rostral and caudal parts of the reticular formation of the ventrolateral medulla oblongata. Weaker specific binding of the radioligand to the molecular layer of the cerebellum, to the nucleus of the spinal trigeminal tract, dorsal motor nucleus of the vagus, area postema, and to a band of tissue connecting the NTS to the ventrolateral medulla was also observed. Binding of the ligand to circumventricular organs such as the OVLT, subfornical organ, and median eminence suggests that these are sites in the brain of the rabbit at which blood-borne AII may exert influences on the central regulation of fluid balance and pituitary hormone secretion, although AII of neuronal origin could also act at these sites. Binding of the radioligand in several other brain regions suggests that angiotensin II of cerebral origin may be involved in a number of different aspects of brain function in the rabbit. The finding of dense binding in the NTS and ventrolateral medulla, which are involved in autonomic activity and are also sites of catecholamine-containing neurons, raises the possibility of angiotensin interaction with these neurons and involvement in autonomic function.