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D Felix

Publications and source records attributed to D Felix.

15 recordsLinked 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↗
PubMed1979

Spike activity and histofluorescence correlated in the giant dopamine neurone of Planorbis corneus.

The relationship between catecholamine fluorescence and electrical activity of the nerve cell has been investigated in the giant dopamine neuron (GDN) of the left pedal ganglion of the European water snail, Planorbis corneus. Electrical recordings were performed in vitro with intracellular microelectrodes on 35 GDN. The ganglion was frozen to -195 degrees C with the electrode in situ and processed for histochemical microfluorimetry. The intensity of catecholamine fluorescence was measured over different places (42/cell) throughout the cytoplasm of the GDN. In order to investigate the temporal relation between histochemical and electrophysiological parameters, the activity of 21 GDN was changed by administration of nicotine to the bathing solution (10(-5)--10(-7) M). This treatment was followed by depolarization in most of the GDN, with increased firing in two thirds and decreased activity in one third of the spontaneously active cells, whereas hyperpolarization was seen in 4 GDN, accompanied by a decrease in firing. Acetylcholine (10(-5) M) tested on one GDN caused depolarization and increased firing. A signigicant positive correlation was found between the fluorescence intensity of individual GDN and the firing rate of these cells as observed during the last 60 sec or the last 10 sec before freezing. The correlation coefficient dropped markedly when the first rates of the 2nd, 3rd, or 4th and 5th min before freezing were correlated with cellular fluorescence intensity. Intensity was not correlated with the resting membrane potential recorded at the time of freezing. The intensity response to activation was not uniform throughout the cytoplasm of GDN. Neurons with increased mean fluorescence intensity regularly showed small clusters and cristae of intensely fluorescent material surrounded by less fluorescent parts of the cytoplasm. This morphological observation of increased intensity differences between cytoplasmic structures was confirmed by the statistics of the intensity values determined in individual cells. The present observations demonstrate the existence of a relation between cell firing and neuronal dopamine fluorescence at the level of the individual nerve cell. The activity immediately preceding the time of freezing of the cell appears to be most important. Certain components of the cytoplasm appear to react preferentially; their subcellular nature remains to be elucidated. The link between electrical activity and cellular dopamine fluorescene was found to be basically the same in the giatn invertebrate neuron and in the dopamine nerve cells of rat substantia nigra.

Animals↗
PubMed1978

Angiotensin receptive neurones in the subfornical organ. Structure-activity relations.

A microiontophoretic study was performed of the actions of angiotensin II and angiotensin fragments on neurones of the subfornical organ (SFO). Adult cats were anaesthetized and the SFO exposed for penetration by a multibarrelled micropipette. We found that angiotensin II-[2--8]-heptapeptide shows a significantly higher stimulation of firing rate compared to angiotensin II. Angiotensin II-[5--8]-tetrapeptide still produced an excitatory action on a single units. Both the action of the heptapeptide and the tetrapeptide were blocked by [sar1, Ala8]-angiotensin II (P 113). In contrast, angiotensin II-[6--8]-tripeptide failed to enhance the firing rate of the same neurones. Our data indicate that angiotensin II and some shorter chain peptide fragments can directly affect neurones of the SFO. The study may give new insight in structure-activity relations for angiotensin II. The results support the hypothesis that the subfornical organ is a receptor site which is available to this peptide.

Acetylcholine↗
PubMed1977

Hypothalamic changes during the immune response.

The immune system is subject to an array of identified autoregulatory processes, but immunoregulation may also have a further basis in a network of immune-neuroendocrine interactions. Two antigens each produced an increase of more than 100% in electrical activity of individual neurones in the ventromedial but not in the anterior nucleus of the rat hypothalamus. Animals that failed to respond to antigen manifested no increase in the firing rate. These findings constitute the first evidence for a flow of information from the activated immune system to the hypothalamus, suggesting that the brain is involved in the immune response.

Action Potentials↗
PubMed1976

A quantitative correlation between single unit activity and fluorescence intensity of dopamine neurones in zona compacta of substantia nigra, as demonstrated under the influence of nicotine and physostigmine.

In order to investigate the possible relationship between neuronal activity and cellular fluorescence intensity, extracellular recordings of single unit activity and determinations of fluorescence intensity of dopamine (DA) neurones by histochemical microfluorimetry were performed in the same (rostral) part of zona compacta of substantia nigra in male rats. In urethane anaesthesia, zona compacta neurones characteristically showed a slow and fairly regular type of firing. Nicotine (1 mg/kg s.c.) induced a transient decrease in unit activity for 1 min followed by a sustained increase in firing rate. During that stage, 4-5 neurones/rat were recorded at different anteroposterior levels, each during 200 sec. Microfluorimetric examination of the fluorescence intensity developed at the end of the 30-min observation period by the DA neurones of the same area revealed a marked rise in cellular fluorescence intensity. Similar results were obtained with a lower dose of nicotine and/or a shorter observation period. Additional microiontophoretic experiments supported the view that extracellular recordings of the correlative electrophysiological-microfluorimetric investigation belonged to DA neurones. Release of DA from terminals was indicated by an increase in HVA concentration of caudate-putamen in rats subjected to the same nicotine treatment. When tested on one cell during a prolonged period of time, physostigmine (0.25 mg/kg i.p.) caused an initial increase in firing rate of zona compacta neurones (5-10 min) followed by a decrease of unit activity (15-23 min). In agreement with previous observations in mice, fluorescence intensity of nigral DA neurones likewise showed a biphasic change with an initial rise and subsequent decrease (examined at 9.5 and 22-23.5 min, respectively). When mean unit activity and mean fluorescence intensity of individual rats out of various experimental groups were related to each other, a highly significant positive correlation between neuronal fluorescence intensity and firing rate was found. The results obtained with physostigmine demonstrate that mean intensity closely paralleled mean unit activity in time, so that this correlation was maintained. These findings indicate that cellular fluorescence intensity of DA neurone groups can be used as an index of the level of neuronal activity, except for cases where a drug treatment interferes directly with catecholamine synthesis or storage mechanisms.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1976

Specific angiotensin II receptive neurons in the cat subfornical organ.

To test if neurons in the subfornical organ (SFO) are specifically sensitive to angiotensin II (AII) we have applied the AII analog sar1-ala8-AII (P113) directly on to cells in the SFO by microiontophoresis. Adult cats were anesthetized and the SFO exposed for penetration by a 5-barreled micropipette electrode. Of 22 units which responded positively to AII, 7 were also positive to acetylcholine. P113 alone produced either no effect or a decrease in unit firing. P113 plus AII produced antagonism in 17 of 18 units. P113 plus acetylcholine produced antagonistic effects in 5 of 14 cases. Only two units were completely antagonized and 5 units showed agonistic interaction. The most sensitive antagonism with respect to dose of P113 was on neurons responsive only to AII and not to both AII and acetylcholine. We conclude that there are specific AII neurons in the SFO.

Acetylcholine↗
PubMed1976

Peptide and acetylcholine action on neurones of the cat subfornical organ.

Angiotensin II, related oligopeptides and acetylcholine were tested on neurones of the cat subfornical organ (SFO). Angiotensin II activates SFO-neurones by local administration onto the surface, by i.v. injection or with the aid of microiontophoretic techniques. Application of related oligopeptides, bradykinin, physalaemin and eledoisin showed no comparable results. Activation of neurones similar to those observed after angiotensin II was obtained with acetylcholine. About 30% of the cells tested were excited by both substances, 56% of tested SFO-cells responded only to angiotensin II, but not to acetylcholine. Atropine sulphate prevents specifically the acetylcholine excitation. Since angiotensin II is involved in regulatory mechanism of thirst, these results suggest the possibility that the SFO is one of the sites, where dipsogenic receptors for this circulating peptide are located.

Acetylcholine↗
PubMed1976

Effect of p-nitrophenyl diazonium fluoroborate on cholinergic mechanisms.

Electrophysiological experiments were done to investigate the effect o p-nitrophenyl diazonium fluoroborate (p-NPD) on motor endplates of the frog's m. cutaneus pectoris. The compound has no direct depolarizing effect on the postsynaptic membrane and stabilizes it irreversibly when added to the bath. Longtime iontophoretical applications of p-NPD produce a biphasic effect: initially a potentiation of the depolarizations due to acetylcholine (ACh) (both iontophoretically applied and presynaptically liberated), and subsequently an inhibition of the response to ACh. When the acetylcholinesterase (AChE) is inactivated previously, only the inhibiting effect of the compound is demonstrable. The association constant of p-NPD to purified AChE and to membrane fragments of electroplax was determined by biochemical methods. The compound's affinity to the AChE was found to be about 20 times greater than to the acetylcholine receptor (AChR). Iontophoretical application of p-NPD to cholinergic neurons in the hippocampal cortex of the cat also produced the characteristic biphasic effect on ACh-induced activity of these investigated neurons. The results suggest that the biphasic effect depends on the capacity of p-NPD to combine with both the AChE and the AChR. The AChE is first inhibited with low concentrations thereby potentiating the ACh response. At higher concentrations the AChR's are progressively inhibited too, thereby diminishing the excitability of the postsynaptic membrane up to a complete block.

Acetylcholine↗
PubMedDate not supplied

Efferent controlled integrating fuctions of primary vestibular afferents.

The vestibular type II receptor cells of mammalians are multiply innervated. Their afferents are integrating neurons consisting of many inputs but only one output. They transform the irregular spontaneous input activity into a regular output. Under the influence of efferent activity following the stimulation of the contralateral labyrinth, this regular output activity becomes irregular. This efferent influence upon afferent spontaneous activity is analysed by means of an existing computer model of an integrating cell. The analysis confirms a high functional interdependence of both labyrinths.

Animals↗