Biomedical subjects

D Felix

Publications and source records attributed to D Felix.

At least 55 records · Page 3Linked to original sources

PubMed1992

Effects of angiotensin II and its selective antagonists on inferior olivary neurones.

On the basis of biochemical and autoradiographic studies it has been shown that the inferior olivary nucleus (ION) contains predominantly angiotensin II (Ang II) receptors of the subtype 2 (AT2). In the present investigation we used microiontophoretic techniques to test the effect of Ang II on the spontaneous firing rate of rat neurones in the ION in vivo. Ang II excited the majority of histologically identified ION neurones. Furthermore, the antagonism of this angiotensin-induced excitation by selective angiotensin receptor blockers of subtype 1 and 2 (AT1 and AT2) was examined. The excitation could be blocked by low doses of the AT2-antagonists PD 123177 and CGP 42112A, whereas the AT1-antagonist DuP 753 was ineffective even at high doses. On a few occasions, however, ejection of the AT1-antagonist resulted in a potentiation of angiotensin-induced excitation. The results suggest that Ang II has an excitatory effect on a considerable number of ION neurones and that this effect is mediated by AT2-receptors.

Angiotensin II↗

PubMed1992

Effects of angiotensin analogues and angiotensin receptor antagonists on paraventricular neurones.

In a previous study we observed that most neurones in the paraventricular nucleus are excited by angiotensin-(1-7). In comparison with angiotensin III this excitatory action was significantly delayed. The aim of the present microiontophoretic study of angiotensin II-sensitive rat paraventricular neurones was to compare the effect of the angiotensin-analogues angiotensin-(1-7), angiotensin-(2-7), angiotensin II and angiotensin III on the spontaneous activity of these neurones and to test angiotensin receptor subtype 1 antagonists (CGP 46027 or DuP 753) and subtype 2 selective antagonists (CGP 42112A and PD 123177) in order to acquire more evidence of the receptor subtype present. As previously observed angiotensin II, angiotensin III and angiotensin-(1-7) excited most neurones. The effect of angiotensin-(1-7) was usually weaker than that of angiotensin II, and in contrast to angiotensin III the latencies were not significantly different. Angiotensin-(1-7) seemed to be active by itself, because its effect was antagonised by angiotensin receptor antagonists. Angiotensin-(2-7) was mostly inactive, although a few cells were excited. Whereas the excitatory effects of angiotensin-(1-7), angiotensin II and angiotensin III could always be inhibited with both angiotensin receptor subtype antagonists 1 and 2, that produced by angiotensin-(2-7) was only weakly antagonised, if at all. Subtype 1 selective antagonists were effective at lower concentrations than selective subtype 2 antagonists.

Angiotensin II↗

PubMed1992

Caroverine depresses the activity of cochlear glutamate receptors in guinea pigs: in vivo model for drug-induced neuroprotection?

With the aid of microiontophoretic techniques the action of caroverine, a quinoxaline-derivative, was tested on the receptor-linked depolarisation of the subsynaptic membrane of cochlear afferents. This membrane can be depolarised by the afferent transmitter agonist glutamate, mediated by NMDA and non-NMDA receptors and by acetylcholine, one of the different transmitter substances, released physiologically on axodendritic efferent synapses. Caroverine antagonized the membrane response to glutamate in an enduring but reversible manner. In contrast, the drug exhibited no effect on the depolarising action of acetylcholine. Therefore, the pharmacological profile of caroverine corresponded to the action of selective glutamate receptor antagonists. Since glutamate is likely to be the major mediator of neurotoxicity in the central nervous system, the selective glutamate-antagonism of caroverine is of particular interest, due to its putative neuroprotective competence. Caroverine is currently available clinically in some countries as a spasmolytic drug. Following these results it is proposed to test the drug for clinical efficacy in putatively glutamate-induced, excitotoxic disorders of the brain.

Animals↗

PubMed1992

The efferent modulation of mammalian inner hair cell afferents.

The results of immunocytochemical, enzymatic and electrophysiological studies have indicated that acetylcholine and GABA may act as neurotransmitters in lateral olivocochlear efferent endings on inner hair cell afferent dendrites. Since spike activity can be recorded in the dendritic region of inner hair cells, microiontophoretic techniques were used testing the possible neurotransmitter candidates, acetylcholine and GABA, on spontaneous and induced firing of the afferent dendrites. The experiments were carried out in anaesthetised guinea-pigs, the third and fourth turns of the cochlea being exposed for electrode penetration. Ejection of acetylcholine resulted in a pronounced dose-dependent increase in subsynaptic spiking activity. Furthermore, acetylcholine enhanced glutamate-induced activity. In contrast, even at high doses, GABA had very little effect on the spontaneous cochlear firing rate. When the firing rate had first been enhanced by glutamate or N-methyl-D-aspartate, however, this activation could be reduced by the ejection of GABA. A similar reduction was observed when the firing rate had been enhanced with acetylcholine. The results of our studies support the hypothesis that these substances are involved in efferent neurotransmission on inner hair cell afferent fibres. It should be pointed out, however, that besides acetylcholine and GABA, several opioids such as enkephalins and dynorphins seem to be involved in efferent cochlear innervation.

Acetylcholine↗

PubMed1991

An immunocytochemical comparison of the angiotensin and vasopressin hypothalamo-neurohypophysial systems in normotensive rats.

In the present study we investigated the possibility that angiotensin II/III and vasopressin coexist in the hypothalamo-neurohypophysial pathway. For our experiments 8-week-old male rats not treated with colchicine were used. The anatomical orientation of the entire pathway for angiotensin and vasopressin was facilitated by examining a series of subsequent coronal, horizontal and sagittal sections. Arching fibre tracts are formed mainly by projections emanating from cell bodies in the paraventricular nucleus, the accessory magnocellular nuclei, the supraoptic nucleus and the retrochiasmatic part of the supraoptic nucleus. The majority extend as far as the median eminence and the neurohypophysis, where major terminal fields exist. However, there is a difference between the staining pattern within the suprachiasmatic nucleus and the hypophysis. The results clearly show the colocalization of angiotensin and vasopressin in neurones as well as in fibres of the hypothalamo-neurohypophysial system.

Angiotensin II↗

PubMed1991

Vasopressin and angiotensin II are absent but spontaneously reappear in solitary hypothalamic neurons of the homozygous Brattleboro rat.

The homozygous Brattleboro rat (di/di) synthesizes a vasopressin (VP) precursor with a different C-terminus, which is not packaged in granules. In addition, the expression of a coexisting peptide, angiotensin II (Ang II), is disturbed. During postnatal life a small but increasing number of solitary post-mitotic hypothalamic neurons of the di/di rat undergoes a switch to a genuine heterozygous phenotype. Here we report the reappearance of Ang II in these heterozygous cells, which suggests that for the expression of Ang II a normal VP precursor is required. Based upon the present study and literature data it is proposed that at the level of the endoplasmic reticulum a compartmentalization of the synthesis of various peptide precursor occurs.

Angiotensin II↗

PubMed1991

N-methyl-D-aspartate-induced oscillations in excitatory afferent neurotransmission in the guinea pig cochlea.

With the aid of microiontophoretic techniques we tested the action of N-methyl-D-aspartate (NMDA) and an NMDA antagonist in the dendritic region of inner hair cell afferent fibers. In the majority of units tested NMDA enhanced the spontaneous firing rate. Furthermore, the activation of NMDA receptors triggered unusual depolarization patterns: (1) slow-frequency oscillation with a periodicity of about 3/min; (2) a fast oscillatory pattern of burst firing with a rhythmic interburst frequency of about 2/s. These findings provide evidence for NMDA receptor properties in the cochlea similar to those of analog channels in the central nervous system.

Action Potentials↗

PubMed1991

Glutamate receptors in afferent cochlear neurotransmission in guinea pigs.

With the aid of microinotophoretic techniques we tested the action of the transmitter candidate glutamate (Glu) at the afferent synapses of inner hair cells (IHC) in guinea pigs. In order to determine the various types of glutamate receptors, further agonistic excitatory amino acids (EAA) as well as competitive EAA-antagonists were used. Applied perisynaptically, Glu, aspartate, N-methyl-D-aspartate (NMDA), quisqualate (Q) and kainate (K) activate the subsynaptic, phasic firing activity of the afferent dendrites. The NMDA-induced activation is augmented by simultaneous application of glycine. The firing rate induced by Glu and NMDA is blocked by the specific NMDA-antagonist D-2-amino-7-phosphonoheptanoate (AP-7). Furthermore, activity induced by Glu and Q decreases under the influence of the selective Q-antagonist glutamic acid diethylester (GDEE). These results are consistent with the hypothesis that Glu acts as a possible afferent neurotransmitter of the IHC. This neurotransmission is mediated by postsynaptic EAA-receptor subpopulations which are sensitive to NMDA, Q and K. The activity of the NMDA-receptors depends, however, on the amount of glycine available. Our data suggest that the afferent synapses of the IHC possess functional properties which are equivalent to the properties of glutamatergic NMDA-sensitive and NMDA-non-sensitive synapses in the central nervous system.

Afferent Pathways↗

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↗

PubMed1990

A microiontophoretic study of the role of excitatory amino acids at the afferent synapses of mammalian inner hair cells.

The results presented indicate that L-glutamate is involved in mediating excitatory afferent neuro-transmission in the mammalian cochlea. Glutamate applied directly into the subsynaptic inner hair cell region of the adult guinea pig with the aid of microiontophoretic techniques evoked neuronal firing. By using competitive antagonists for glutamate receptors, a further study was carried out in order to identify possible receptor types. Such included N-methyl-D-aspartate (NMDA), kainate and quisqualate receptors, which are defined by selective agonist action. The glutamate-induced cochlear firing rate was antagonized by D-2-amino-7-phosphonoheptanoate (AP-7), suggesting that the receptor involved is of the NMDA type. Further studies with glutamic acid diethylester (GDEE) showed that glutamate-induced activity could also be blocked by this substance. Since GDEE depresses responses to quisqualate, non-NMDA receptors also have to be taken into consideration.

2-Amino-5-phosphonovalerate↗

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↗

PubMed1989

Effects of hypothalamic releasing hormones and biogenic amines on identified neurones in the circumoesophageal ganglia of the water snail (Planorbis corneus).

1. The effect of locally applied releasing hormones, thyrotropin-releasing hormone (TRH) and luteinizing-hormone-releasing hormone (LHRH) and the putative neurotransmitters, acetylcholine (ACh) and dopamine (DA), on the neuronal excitability of identified invertebrate giant dopaminergic neurone (GDN) and serotoninergic neurone (5-HT) (Planorbis corneus) were investigated by intracellular recording in vitro. 2. The membrane potential of GDN was of the order of -60 to -70 mV. The microiontophoretically applied substances produced membrane depolarization as well as spike activation. Their order of efficacy was as follows: TRH greater than ACh greater than DA greater than LHRH. 3. The effects of the tested TRH, ACh, LHRH and DA on serotoninergic neurones were less pronounced. 4. During ACh depolarization the membrane resistance of GDN was found to be strongly reduced, whereas TRH produced only a small reduction in membrane resistance. 5. Dihydro-beta-erythroidin (DHE) added to the bath solution reversibly blocked ACh depolarization without influencing TRH depolarization. Concentrations of atropine sulfate required to block the ACh depolarization were higher by at least 100 order of magnitude. 6. These effects are discussed in relation to the immunoreactive TRH detected earlier in the central nervous system of invertebrates and vertebrates. The results are consistent with the postulate that TRH acts as a neuromodulator and/or neurotransmitter on invertebrate and vertebrate neurones.

Acetylcholine↗

PubMed1988

A comparison of two bactericidal handwashing agents containing chlorhexidine.

The skin disinfectant properties of two handwashing agents containing chlorhexidine, 'Uniscrub' and 'Hibiscrub', have been compared. The two products were assessed according to their ability to remove both transient organisms and natural or resident bacteria from the skin. They were found to be equally effective as antibacterial hand disinfection agents.

Bacteria↗

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

The effects of the aminopeptidase inhibitors amastatin and bestatin on angiotensin-evoked neuronal activity in rat brain.

During a recent comparison of iontophoretically applied angiotensin II (AII) and angiotensin III (AIII) in the paraventricular nucleus of the rat, we observed that the response latency for AIII was much shorter than that for AII. This suggested that AII may have to be converted to AIII before it becomes active. To test this hypothesis we performed 3 experiments. (1) We examined the effects of bestatin, an aminopeptidase B inhibitor, on the activity of applied AII and AIII. (2) Next, we monitored the effects of amastatin, a specific aminopeptidase A inhibitor, on the action of co-applied AII or AIII. (3) And, finally, we examined the response to the aminopeptidase-resistant analog Sar1-AII, both applied alone and in combination with AII or AIII. Bestatin, while having no activity of its own, dramatically enhanced the actions of both AII and AIII. Amastatin, on the other hand, had little effect on AII's action and diminished or totally blocked AII-dependent activity. Like bestatin, amastatin had no effect alone. Sar1-AII reduced spontaneous activity of angiotensin-sensitive neurons and inhibited the actions of AII and AIII in a reversible manner. The same cells were also blocked by the recognized angiotensin antagonist Sar1, Ile8-AII. In total these results strongly support the notion that AII must be converted to AIII in the brain before it is activated.

Aminopeptidases↗

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

Angiotensin-sensitive neurons in the rat paraventricular nucleus: relative potencies of angiotensin II and angiotensin III.

Angiotensin-activated neurons were examined using microiontophoretic methods in the paraventricular nucleus (PNV) of the rat. In all cases angiotensin III (AIII) was more potent than angiotensin II (AII). This greater sensitivity to AIII was manifested by lower thresholds, shorter latencies, and higher spike frequencies/amplitudes of applied current. The superior potency of AIII was further exaggerated in the spontaneously hypertensive rat (SHR) compared with normotensive Wistar Kyoto (WKY) rats. Postactivity for both AII and AIII was greatly prolonged in SHR. This appeared specific since no prolongation in acetylcholine postactivity was seen in SHR. These data support the notion that AIII may be the centrally active form of angiotensin and are consistent with an obligatory conversion of AII to AIII prior to activation. The selective enhancement of postactivity observed in SHR following angiotensin application suggests a possible defect in signal termination.

Angiotensin II↗