The membrane potential (Um), the main factor of the excitation-contraction coupling, of human allantochorial placental vascular smooth muscle cells (VSMCs) has been previously shown to depend on voltage-sensitive K+ channels. These channels were blocked by high external K+. To characterize other channels which regulated Um, various constrictor or/and vasodilators and channel blockers were used. Serotonin depolarized VSMCs, in normal medium, but induced a more marked depolarization in VSMCs predepolarized by high external K+. This depolarization was inhibited by nifedipine, a blocker of voltage-gated Ca2+ channels. Acetylcholine, sodium nitroprusside (without effect on Um in normal medium), hyperpolarized the predepolarized-high K+ medium VSMCs. This hyperpolarization was inhibited after addition of charybotoxin (a blocker of Ca2+-activated K+ channels) or/and glibenclamide (a blocker of ATP-sensitive K+ channels). A similar effect was obtained with isoproterenol. These results indicated that membrane potential of human placental allantochorial VSMCs was regulated by voltage-gated, Ca2+- and ATP-sensitive K+ channels and by voltage-dependent Ca2+ channels.

The membrane potential (MP) of the smooth muscle cells of human allantochorial placental vessels is the major factor which explains the excitation-contraction coupling. Indeed, the smooth muscle cells of these vessels may be considered as tonic because they only respond to excitatory stimuli with graded depolarization. On the contrary, the phasic smooth muscles generate action potentials and some generate electrical slow waves as well. The depolarization of smooth muscle cell membranes may be a consequence of various factors, particularly the secretion of endothelium-derived depolarizing factors (EDDF). The modifications of the ionic composition of external medium interfere with the membrane potential values. The increase of [Mg2+]o (Cl- or SO4[2-]) depolarizes the membrane. This effect in vitro seems inconsistent with the known vasodilator action of external Mg2+. To explain this result, an hypothetical scheme is proposed on the probable targets of local and systemic Mg2+ effects: a direct action of external Mg2+ ions on the membrane potential by secretion of depolarizing endothelial factors which depolarize the membrane; an indirect action on the membrane potential by regulation of K+ and Ca2+ channels; an action on the concentration of internal Mg2+; an interaction with internal Ca2+ concentration and regulation of the Na+/Ca2+ exchanger. A data review of Mg2+ ions effects on smooth muscles is realized to corroborate this scheme.

Magnesium salts have been shown to depolarize the membrane of the smooth muscle cells of human placental arteries and veins with and without endothelial cells. In the present study, the influence of MgCl2 and MgSO4 was investigated on the membrane potential, Um, of the endothelial cells of the same vessels. Um was classically recorded with microelectrodes. The endothelial cell membrane of arteries was depolarized by MgCl2 (depolarization threshold, d th: 4 mM) and by MgSO4 (d th: 8 mM). A depolarization was also observed with the endothelial cell membrane of veins. The depolarization threshold with MgCl2 and 4MgSO4 was respectively 6 mM and 8 mM. The different thresholds indicate that the influence of MgCl2 on the endothelial cell membrane potential is higher and more direct than that of MgSO4, and confirm previous hypothesis on the effects of magnesium salts on the vascular smooth membrane cells.

Magnesium has been shown to produce various effects on vascular smooth muscle, in that its absence elicits an increase in muscle tone and increases sensitivity to a number of stimulatory agonists. In the present study, the influence of MgCl2 and MgSO4 was investigated in human placental chorionic muscle cells (from arteries and veins with or without endothelium), especially on the membrane potential, Um. Classically, Um was obtained from microelectrodes inserted into smooth muscle cells through the endothelium or directly. In arteries with endothelium, the smooth muscle cells were depolarized by MgSO4 (threshold: 6 mM) and MgCl2 (threshold: 8 mM). In endothelium-free arteries, the smooth muscle cells were also depolarized by MgSO4 (threshold: 8 mM) and MgCl2 (threshold: 6 mM). Identical results were obtained with veins, but thresholds were different. The different thresholds may indicate that MgCl2 influences the cell membrane potential directly, while MgSO4 interferes first with the endothelial cells, which may act as an intermediary between the Mg2+ ions and the membrane of the smooth muscle cells.

Frogs were submitted in acute experiments to electrical stimulation of both ipsi- and contralateral homologous olfactory nerve bundles subserving the dorsal olfactory mucosae. Mitral layer responses on one side were recorded. When both stimulations were given at different onset times and equal intensity, the ipsilateral mitral layer response fell to a sharp minimum of 42% when the contralateral stimulation was given 25 ms before the ipsilateral one. When both stimuli were adjusted for maximal temporal inhibition and the intensity of the contralateral stimulation was varied, the amplitude of the ipsilateral response decreased as the intensity of the contralateral stimulation increased until intensity equalization was obtained. This interbulbar inhibition was suppressed either by sagittal transection through the interbulbar adhesion or local infusion of bicuculline in the ipsilateral olfactory bulb. It was unaffected by transection of habenular commissure. These findings suggest first, that the neuroreceptors located in the dorsal olfactory mucosae project to both olfactory bulbs, and second, that it exists at mitral layer level of the frog, a reciprocal inhibition which can subserve frog orientation towards proximal odour source.

Whether or not the frog olfactory neuroreceptor cells project bilaterally to the olfactory bulb is still a debated question. We therefore decided to ascertain whether bilateral projections of the primary olfactory input exist and if so to investigate their extent. Reproducible extracellular bilateral bulbar potentials were recorded in the frog following electrical stimulation of dorsal or ventral olfactory nerve bundles. The general features of the contralateral evoked responses were very similar to those of the ipsilateral response. The contralateral response disappeared after transection of the rostral part of the olfactory interbulbar adhesion but not following transection of the habenular or anterior commissures. Horseradish peroxidase labelling showed that the fiber terminations of the olfactory nerve bundle was not restricted to the ipsilateral olfactory bulb but included the medial aspects of the contralateral bulb. The intertelencephalic sections increased the magnitude of the ipsilateral evoked responses. Olfactory bulb isopotential maps revealed a rough topographical correspondence between the olfactory neuroepithelium and bulb along the medio-lateral axis as well as along the dorso-ventral axis. In addition, a projection of the medial and central part of the olfactory sac to the medial part of the contralateral olfactory bulb through the interbulbar adhesion was confirmed. These findings suggest first, that the fibers from the neuro-receptors located in either the ventral or the dorsal olfactory mucosae project to both olfactory bulbs, and second, that the left and right bulbs exert a constant inhibition on each other via the habenular commissure.

Bulbar potentials wer bilaterally recorded in the frog following electrical stimulation of one olfactory nerve bundle. The general features of the contralateral evoked response were very similar to those of ipsilateral ones. The contralateral response was shown to be produced in situ, not being electronically transmitted from the bulb on the stimulated side. Its response disappeared after section of the olfactory interbulbar adhesion but was not affected by sectioning through either the anterior or the habenular commissure. It was concluded that messages from the neuroreceptors belonging to either the ventral or the dorsal olfactory mucosa on one side, reach both olfactory bulbs.

Etude electrophysiologique du role des cations divalents et monovalents (calcium, sodium, potassium) dans la formation de l'electroolfactogramme au niveau de l'epithelium olfactif de grenouille draine par differentes solutions et stimule par des odeurs d'acetate d'amyle

La stimulation electrique d'un rameau du nerf olfactif suscite, chez la grenouille, des reponses electriques sur les deux bulbes olfactifs, ipsi et contralateral. La reponse contralaterale est de forme et d'amplitude comparables a celles de la reponse ipsilaterale. Nous montrons qu'elle est engendree in situ et n'est pas transmise electroniquement par le bulbe situe du cote stimule; elle disparait apres section de la partie rostrale de la zone de contact entre les deux bulbes mais demeure apres section des commissures anterieure ou habenulaire. On en conclut que les neurorecepteurs localises au sein de la muqueuse olfactive se projettent bilateralement sur les bulbes olfactifs

In frogs, underwater electro-olfactograms (EOGs) in response to 10(-5) M isoamyl acetate were recorded under restricted cationic environments. The olfactory mucosa was superfused by sodium-free sucrose solutions, and the effect of the addition of millimolar concentrations of calcium, cobalt, barium, or cadmium was studied. Only calcium and barium restored the response; sodium and cobalt were less efficient. Cobalt did not alter the restoring effect of calcium. Cadmium resulted in irreversible blocking irrespective of the presence of calcium. These results are discussed in terms of possible ionic mechanisms mediating olfactory responses.

Neural spike activity was recorded from 50 single mitral cells in the Rabbit olfactory bulb, with variable intensity of the odour stimulation. Six different concentrations were used for two olfactory stimuli, isoamyl acetate and propanol. The discharge frequency of 40 p. 100 of the cells remained constant regardless of the stimulus concentration; most of these cells (80%) showed inhibitory responses. On the other hand, most of the excitatory responses varied depending on stimulus concentration; the frequency vs stimulus concentration function either increased (25% of cells) or decreased (17%), or displayed a maximum (12%).

The analysis of amplitude variations of local E.O.G. collected from 121 points of the olfactory epithelium of the frog, in response to 20 olfactory stimuli, shows: 1. There is a strong correlation between the amplitude of the local E.O.G., and the density of the olfactory receptors in the corresponding recording area. 2. A population of about 400 to 700 receptors contains all kinds of olfactory sensibility, but with variable proportions according to the recording point. 3. At the level of the sampled receptors, spreading over about one sixth of the olfactory surface, an anterio-posterior differentiation appears. 4. The topographical distribution of the local E.O.G. elicited by the 20 stimuli was significantly different from one animal to the other.

Journal Article Neural mechanisms in the anterior olfactory nucleus of the rabbit and their possible relevance to localization of an olfactory source Get access G. Daval, G. Daval Laboratoire de Neurophysiologie comparée, Université Pierre et Marie Curie9, quai St. Bernard 75005 Paris, France Search for other works by this author on: Oxford Academic PubMed Google Scholar J. Leveteau J. Leveteau Laboratoire de Neurophysiologie comparée, Université Pierre et Marie Curie9, quai St. Bernard 75005 Paris, France Search for other works by this author on: Oxford Academic PubMed Google Scholar Chemical Senses, Volume 4, Issue 2, July 1979, Pages 135–140, https://doi.org/10.1093/chemse/4.2.135 Published: 01 July 1979 Article history Received: 03 October 1978 Accepted: 22 May 1979 Published: 01 July 1979

The autoradiographic method has been used in the Rat to map active regions in the olfactory bulb after a pulse of 14C-2-deoxyglucose with electrical stimulation of the lateral olfactory tract. The highest optical densities were found at the external plexiform, mitral, internal plexiform and granular layers; the lowest was found in the glomerular layer.

The responses to odour stimulation of 61 single mitral cells and of 64 single anterior olfactory nucleus (AON) units were simultaneously recorded from rabbits. The test battery consisted of 6 chemical stimuli delivered at two intensity levels corresponding to a hundred-fold difference in concentration. The odour discrimination reaches its best for the mitral cells stimulated weakly; it decreased somewhere when the same cells are stimulated strongly. At AON level the odour discrimination already limited in the case of weak stimuli, almost disappears for strong stimuli. Multidimensional analysis of the odour similarities, respectively in the olfactory bulb and the AON, reveals an unexpectedly high loading of the first axis with an intensity factor. Our results indicate that the discriminatory ability in the mitral cells and in the AON cells are respectively better and poorer than in the chemoreceptors.