PubMed Health⌕ Search

Biomedical subjects

H Imboden

Publications and source records attributed to H Imboden.

27 records · Page 2Linked to original sources
PubMed1991

Neurophysiological responses to angiotensin-(1-7).

The aim of this study was to investigate the action of the heptapeptide angiotensin-(1-7) on the spontaneous activity of paraventricular neurons using microiontophoresis. Recent immunocytochemical investigations have shown that this product of angiotensin I is predominantly located in cells and fibers of the forebrain and brain stem. Our results show that most neurons in the paraventricular nucleus are excited by angiotensin-(1-7) at a dose of 50-80 nA. In comparison with angiotensin II or angiotensin III, the onset of response and the occurrence of the maximal effect were significantly delayed. With higher doses of angiotensin-(1-7), there was a decrease in latency and a dose-dependent increase in firing frequency. Of all the angiotensin compounds tested, angiotensin III was the most potent. Preliminary results obtained with an angiotensin antagonist show that the action of angiotensin II, angiotensin III, and angiotensin-(1-7) is blocked by the angiotensin receptor subtype 2 antagonist CGP 42112A. Because the angiotensin-(1-7) system in the brain is associated with central vasopressinergic pathways, vasopressin was tested in a similar way. Neurons in the paraventricular nucleus that were excited by iontophoretically applied angiotensins showed a weak response to vasopressin. Occasionally, a small excitatory action was observed. Our results support the hypothesis that the heptapeptide angiotensin-(1-7) is a biologically active neuropeptide. The data also suggest that amino terminal fragments of angiotensin II are not inactive degradation products.

Angiotensin I↗
PubMed1989

Hypothalamic angiotensinergic fibre systems terminate in the neurohypophysis.

A new affinity-purified anti-angiotensin II/III antibody ('BODE') was used to determine the location of angiotensin-like immunoreactivity in the paraventriculo-hypophysial pathway, especially in the pituitary. Angiotensin-like immunoreactivity was shown to be concentrated in the neurohypophysis and was characterised by a dense plexus of fibres and terminals.

Angiotensin II↗
PubMed1988

The hypothalamic-angiotensin system: location and functional considerations.

Improved immunohistochemical and quantitative microiontophoretic methods were used to characterise angiotensinergic and angiotensin-sensitive neurones in the paraventricular nucleus (PVN) of the rat. The results can be summarised as follows: 1) Angiotensinogen was found in PVN neurones, astrocytes in the diencephalon which make putative contacts with microvessels, and in cells of the choroid plexus. 2) Affinity-purified angiotensin II/III antibodies were used to locate immunoreactive AII/III in large PVN neurones and their fibre tracts which project either caudally or ventrally to the neurohypophysis. 3) Quantitative microiontophoretic studies showed that PVN neurones are more sensitive to angiotensin II than to angiotensin II. 4) Iontophoretic co-application of the selective aminopeptidase inhibitors bestatin and amastatin, together with angiotensin II and angiotensin III produced results consistent with a central role for angiotensin III.

Aminopeptidases↗
PubMed1987

Improved immunohistochemical staining of angiotensin II in rat brain using affinity purified antibodies.

Recent immunohistochemical studies that have sought to detect angiotensin II/III (AII/AIII) immunoreactive material in the brain have been forced to rely on a small number of antisera because most AII/AIII antibodies have unexplainably proved unsuitable for immunohistochemistry. Although extremely useful tools, these antisera have suffered from high background staining. The purpose of this study was to re-examine and characterize the staining using the most popular AII/AIII antiserum (Denise) before and after purification on an AII CH-sepharose affinity column. The use of crude AII/AIII antiserum resulted in the staining of large varicosities and cell bodies. Fibres were all but invisible owing to extensive background staining. In contrast, the purified antibodies yielded little background staining and produced a discrete staining of AII/AIII fibres with small varicosities in the paraventricular-hypophysial pathway and of cell bodies of large hypothalamic neurones. In addition punctate staining demarcated the perikarya of some neurones and resembled boutons containing immunoreactive AII/AIII. Biochemical and histochemical analysis of the crude antiserum, the affinity purified antibodies and other fractions off the sepharose column demonstrated that a large portion of the total staining (various types of background) seen with crude antiserum and column fractions was not to AII/AIII or several angiotensin-derived fragments. Furthermore, successful preabsorption blanks for the purified antibodies could only be achieved with AII coupled through its N-terminal, suggesting that these purified antibodies reacted best with conjugated angiotensin in the fixed tissue. In total the results of this study indicate that the background staining seen with crude antiserum is not to AII/AIII. The use of affinity purified antibodies greatly enhances resolution, enabling one to visualise even small fibres in rats not treated with colchicine, and should improve our ability to develop accurate maps of central angiotensinergic pathways.

Angiotensin II↗
PubMed1987

Localization of angiotensinogen in multiple cell types of rat brain.

Angiotensinogen was localized in 3 cell types in brain using immunohistochemical methods. These locations included subpopulations of neurons in nuclei that co-stain for angiotensin II, subpopulations of astrocytes that make putative contacts with brain microvessels, and cells of the choroid plexus. These findings are consistent with multiple functions for brain angiotensinogen as a precursor for neuronal angiotensin II and as a potential source for angiotensin II that is locally produced in the brain.

Angiotensin II↗
PubMed1987

Comparison of angiotensin II staining in rat brain using affinity purified and crude antisera.

The use of affinity purified ANG II antiserum as opposed to crude antiserum greatly enhanced the staining resolution in rat brain. This improved resolution was due to a complete loss of background staining and an apparent increase in specific staining that was totally blockable by preabsorption. With the purified antibody it was easily possible to visualise the finest fibres in rats not treated with colchicine. Furthermore, the improved technique permitted a clearer visualisation of an ANG II-like immunoreactive product in cell bodies. This use of affinity purified antibody should greatly facilitate the mapping of central angiotensinergic pathways.

Angiotensin II↗
PubMedDate not supplied

Substance P in the auditory hair cells in the guinea pig.

Previous immunohistochemical and electrophysiological studies on various neurotransmitters revealed the tachykinin substance P (SP) as a neuromodulator in the auditory system of mammals. This study was performed in order to determine the immunohistochemical expression and distribution pattern of SP in the organ of Corti, especially in the inner (IHC) and outer hair cell (OHC) region of the guinea pig. We examined the immunoreactivity of SP of surface preparations by means of a fluorescence and a laser scanning microscope. The electrophysiological action of SP, N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were recorded at the subsynaptic afferent region of the IHCs using micro-iontophoretic techniques. The SP-like immunostaining could be detected at the basal and apical pole of the IHCs with a gradient distribution pattern from the basal to the apical turn. Furthermore, we could demonstrate SP-like immunoreactivity in OHCs with different occurrence in turns as well as in rows. Electrical activity was induced by applying SP, NMDA and AMPA perisynaptically to the IHCs. The selective SP antagonist spantide (D-Arg1, D-Trp7,9, Leu11-substance P) specifically blocked the SP-induced activity but without altering the activity of NMDA and AMPA. In contrast, specific NMDA or AMPA antagonists reversibly blocked either the NMDA- or AMPA-induced responses without affecting the SP-induced activity. These immunohistochemical and electrophysiological results confirm that SP may represent a neuromodulator function at the synapses of the IHCs in the guinea pig.

Animals↗