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Biomedical subjects

B Dufy

Publications and source records attributed to B Dufy.

At least 91 records · Page 5Linked to original sources
PubMed1982

An electrophysiological study of cultured human pituitary cells.

The electrophysiological properties of tumoral pituitary cells were studied in 4 types of human adenomas including prolactinomas, growth-hormone-secreting tumors, adrenocorticotropin-hormone-secreting adenoma and 'non-functioning' tumors. Only 9% of the cells from prolactinomas and ACTH tumors were excitable but they never elicited spontaneous action potentials. These cells did not respond to substances known to act on the hormone-releasing process (thyreoliberin, dopamine). However, 37% of the cells cultured from growth-hormone-secreting adenomas and from 'non-functioning' tumors displayed action potentials. The action potential was calcium-dependent, i.e., it was blocked by cobalt, nickel and methoxyverapamil and could be recorded in a sodium-free medium. Thyreoliberin triggered action potentials, whereas dopamine and gamma-aminobutyric acid inhibited electrical activity. These results show that human tumoral pituitary cells in culture are able to generate Ca2+-dependent action potentials. The data from growth-hormone-secreting tumors are in good agreement with the stimulus-secretion coupling concept; however, differences in the response of cells cultured from other types of human pituitary tumors suggest that each type of adenoma has specialized membrane properties.

Action Potentials↗
PubMed1982

[45Ca flow from cultured pituitary cells: effect of TRH and potassium].

Potassium (KCl: 50 mM) increases the uptake of 45Ca by GH3/B6 pituitary cells whereas TRH (100 nM) does not modify the uptake. On the contrary, 45Ca efflux is quickly and transiently increased by TRH whereas KCl has no influence on the 45Ca outflow. Our results suggest that these two secretagogues act on the GH3 pituitary cells by different processes.

Animals↗
PubMed1981

Effects of estrogens on the responses of caudate neurons to microiontophoretically applied dopamine.

The electrical activity of caudate neurons and their response to iontophoretically applied dopamine (DA) were tested at different time intervals before and after i.m. injection of estradiol benzoate in rats ovariectomized one week previously. One hundred and three neurons were recorded before estradiol injection and, of these, 25% were spontaneously active and 75% were driven by glutamate. The firing activity of the majority (86%) of the neurons was inhibited on application of DA. At 2--6 after the estradiol injections, the proportion of spontaneously active neurons was elevated to 87% and their firing rate was dramatically increased. Concomitantly, the proportion of cells affected by DA decreased to 39%; moreover, the majority of cells responsive to DA was now excited following it. We conclude that estrogens are able to influence the global activity of caudate neurons and to reverse their sensitivity to DA. This action may be partly mediated by the pituitary since it was not observed in ovariectomized rats which were also hypophysectomized.

Action Potentials↗
PubMed1979

Membrane effects of thyrotropin-releasing hormone and estrogen shown by intracellular recording from pituitary cells.

The effects of thyrotropin-releasing hormone and 17 beta-estradiol on the electrical membrane properties of a prolactin-secretin pituitary cell line (GH3/B6) were studied with intracellular microelectrode recordings. Of the cells tested, 50 percent were excitable and displayed calcium-dependent action potentials when depolarized. When injected directly on the membrane of an excitable cell, thyrotropin-releasing hormone and 17 beta-estradiol induced action potentials within 1 minute. The spiking activity was preceded by a progressive increase of the input resistance without any detectable change in the resting membrane polarization. The results reveal a rapid effect of both substances on the membrane of GH3/B6 cells. In the case of thyrotropin-releasing hormone, which has both a short-term effect on release of prolactin and a long-term effect on its synthesis, the induced electrical activity may be associated with the stimulation of prolactin production. The physiological implication of 17 beta-estradiol-induced, calcium-dependent spiking activity remains to be elucidated.

Action Potentials↗
PubMed1979

[Electrophysiological study of hypothalamic neurons and gonadotropin regulation in rhesus monkey (author's transl)].

The electrical activity of various hypothalamic areas was recorded in anesthetized (sodium pentobartital) (n = 3) and unanesthetized (n = 3) ovariectomized rhesus monkeys. The plasma gonadotropin levels of the animals during the recording sessions were obtained by a chronic cardiac catheter. 1. Sodium pentobarbital greatly affected the electrical activity of most hypothalamic neurons (84%). The mean spontaneous electrical unit activity of neurons in the unanesthetized animals (n = 30) was 1.5 spike/sec. This value decreased to 0.1 spike/sec in the anesthetized group (n = 30). However, a small number of hypothalamic neurons were insensitive to the anaesthetic. 2. The multiunit electrical activity recorded in the median eminence showed marked periodic increases, about 200 sec before LH was observed to rise in the plasma (10/12). This increased firing lasted about 10 min (Fig. 1A). 3. In a few cases (2/12), however, increased firing was not associated with LH release. Since, in this area, multiunit activity represents the summation of a large number of axon terminals, the release of a hypothalamic hormone other than Gn-RH is put foreward as a possible hypothesis. 4. Of 51 neurons recorded in various hypothalamic areas, 3 showed periodic increases of electrical unit activity which corresponded to a rise in plasma LH levels (Fig. 1 B). These neurons are located in the arcuate area. 5. These results are consistent with the hypothesis of a relation between the electrical activity of some hypothalamic neurons and the periodical LH discharges observed in the ovariectomized rhesus monkey.

Animals↗
PubMed1978

Identification of inhibitory and stimulatory control of prolactin secretion in the rhesus monkey.

In the unanesthetized, ovariectomized rhesus monkey, gonadotropin secretion is episodic while prolactin (Prl) release is relatively constant. Under pentobarbital anesthesia, however, Prl secretion also becomes pulsatile in synchrony with the discharges of LH. This finding suggests that the anesthesia has unmasked normally inhibited Prl releasing stimuli which are driven by the circhoral 'clock' that also times the discharges of GnRH.

Animals↗
PubMed1978

Effects of protein synthesis inhibitors on the negative feed-back effect of estrogen on LH release.

Ovariectomized female rabbits were pretreated with actinomycin D (80 microgram/100 g body weight) cycloheximide (300 microgram/100 g body weight) or chloramphenicol (300 microgram/100 g body weight) 4 h before an intravenous injection of 25 microgram of estradiol benzoate. Actinomycin D, cycloheximide and chloramphenicol decreased basal gonadotropin levels, but actinomycin D was less active than chloramphenicol and cycloheximide. Despite this effect on basal levels, such treatment did not prevent the effect of estradiol benzoate on LH release. Moreover, no significant impairment of the LH response to LH-RH was found. The interpretation of experiments using drugs such actinomycin D, cycloheximide or chloramphenicol requires caution; however, one cannot disregard the possibility that the negative feed-back effect of estrogen, in contrast to the positive effect, may not be mediated by RNA-dependent DNA and the protein-synthesizing systems.

Animals↗
PubMed1976

Effects of estrogen on the electrical activity of identified and unidentified hypothalamic units.

Experiments performed on unanesthetized ovariectomized female rabbits demonstrated the effects of estradiol benzoate (EB; 20 microng i.v.) on the electrical activity of hypothalamic units which send their axons to the median eminence. Of a total of 1,840 cells recorded in hypothalamic and preoptic areas, 46 (2.5%) were antidromically activated by stimulating the median eminence. Under the present experimental conditions, EB induced a progressive diminution in the mean firing rate of these cells observed throughout the recording period (30-120 min). In addition to cells projecting to the median eminence, neurons which could not be antidromically invaded using our techniques were observed to be sensitive to estrogen. Estrogen administration produced a long-lasting inhibition of antidromically activated cells and a depression of much shorter duration (15-20 min) of unidentified nonstimulated units. These data suggest the existence of two types of hypothalamic neurons sensitive to estrogen.

Animals↗
PubMed1975

Hypothalamic supraoptic neurones: rates and patterns of action potential firing during water deprivation in the unanaesthetized monkey.

Extracellularly recorded action potentials were obtained from hypothalamic supraoptic neurones in unanaesthetized rhesus monkeys. Rates and patterns of firing were studied during an initial control period, during 5 successive days of water deprivation and during 4 further days when drinking water was again available. During water deprivation, plasma osmolarity increased progressively from about 300 mOsmoles/kg to about 340 mOsmoles/kg; control values were again reached after 3 days of rehydration. Systematic changes in action potential firing accompanied the changes in plasma osmolarity. Under control conditions, the majority of cells fire slowly and irregularly (type i), whilst a few cells exhibited phases of alternating activity and silence (type p). As dehydration progresses, the frequency of neuronal firing increase and the pattern of firing changes. By the third day the majority of cells are type p with few type i cells being found. By the fourth day, the population consists of type p cells with some others showing a high continuous rate of firing (type c). By the fifth day, these two cell types are found in approximately equal proportions. Rehydration of the animal reverses the situation. We propose that type i cells contribute little, if at all, to hormone secretion, while type p and type c cells would be in a more actively secreting state. According to this view, the three firing patterns would represent different activity states of the same functional population stimulated by the unspecific stimulus of water deprivation rather than functionally different neurones. However, the use of stimuli which selectively release either oxytocin or vasopressin may be needed to answer this problem.

Action Potentials↗
PubMed1975

Effect of ovariectomy and estradiol benzoate treatment on LH-RH induced LH and FSH release in the female rabbit.

Synthetic LH-RH (0.75 and 2.5 mug/animal) was administered to mature intact and castrated female rabbits. The animals were injected for 3 consecutive days with either 40 mug estradiol benzoate (EB) dissolved in 0.5 ml propylene glycol 60%, water 40% or with the solvent alone. LH-RH was injected i.v. on the 4th day. In intact rabbits EB priming increased the pituitary LH response while LH basal levels were lowered. In the unprimed castrated rabbits, basal FSH and LH levels and the cumulative responses to LH-RH were higher than in intact control animals; EB priming lowered basal LH levels and cumulative responses to the values of intact control rabbits while both basal FSH levels and the cumulative responses were less influenced by the treatment. It is concluded that estrogen acts at both hypothalamic and pituitary levels to modify the LH responses to endogenous LH-RH, and that the complete inhibition of FSH hypersecretion in the ovariectomized rabbit probably needs another ovarian factor.

Animals↗