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Biomedical subjects

M Hay

Publications and source records attributed to M Hay.

At least 37 records · Page 2Linked to original sources
PubMed1998

Measurement of synaptic vesicle exocytosis in aortic baroreceptor neurons.

The purpose of this study was to evaluate the use of the fluorescent membrane label FM1-43 as a measure of synaptic terminal exocytosis during stimulation of labeled aortic baroreceptor and unlabeled nodose ganglia neurons. Activation of the nerve terminals with electrical stimulation or depolarization with 90 mM KCl in the presence of 2.0 microM FM1-43 resulted in bright, punctate staining of synaptic boutons. Additional depolarization in the absence of dye resulted in destaining with a time course that was consistent and repeatable in multiple boutons within a given terminal. Destaining was dependent on calcium influx and was blocked by bath application of 100 microM CdCl2. Whole cell patch-clamp studies have reported that depolarization-induced calcium influx in aortic baroreceptor cell bodies is predominantly caused by the activation of omega-conotoxin GVIA (omega-CgTx)-sensitive N-type calcium channels. In addition, these N-type channels have been shown to be inhibited by activation of metabotropic glutamate receptors. In the present study, exocytosis in aortic baroreceptor terminals was not affected by bath application of 5 microM nifedipine and only partially inhibited by bath application of 2.0 microM omega-CgTx. However, depolarization-induced exocytosis was significantly inhibited by bath application of 200 microM L-AP4, a type III metabotropic glutamate receptor agonist. Results from this study suggest that 1) FM1-43 can be used to measure synaptic vesicle exocytosis in baroreceptor neurons; 2) the N-type calcium channel may not be involved in the initial phase of vesicle exocytosis; and 3) activation of L-AP4-sensitive metabotropic glutamate receptors inhibits 90 mM KCl-induced vesicle release.

Animals↗
PubMed1998

Glutamate in the nucleus of the solitary tract activates both ionotropic and metabotropic glutamate receptors.

Glutamate is the proposed neurotransmitter of baroreceptor afferents at the level of the nucleus of the solitary tract (NTS). Blockade of ionotropic glutamate receptors with kynurenic acid blocks the arterial baroreflex but, paradoxically, does not abolish the response to exogenous glutamate. This study tested the hypothesis that exogenous glutamate in the NTS activates both ionotropic and metabotropic glutamate receptors (mGluRs). In urethan-anesthetized rats, unilateral microinjections of glutamate into the NTS decreased mean arterial pressure, heart rate, and lumbar sympathetic nerve activity. The cardiovascular response to injection of glutamate was not altered by NTS blockade of mGluRs with alpha-methyl-4-carboxyphenylglycine (MCPG). Blockade of ionotropic glutamate receptors with kynurenic acid attenuated the response to glutamate injection. After combined NTS injection of MCPG and kynurenic acid, the response to glutamate was blocked. These data suggest that exogenous glutamate microinjected into the NTS acts at both ionotropic glutamate receptors and mGluRs. In addition, blockade of both classes of glutamate receptors is required to block the cardiovascular response to microinjection of glutamate in the NTS.

Animals↗
PubMed1997

Determination of catecholamines and methoxycatecholamines excretion patterns in pig and rat urine by ion-exchange liquid chromatography with electrochemical detection.

A simplified liquid chromatographic method for the simultaneous determination of free or total catecholamines and methoxycatecholamines in rat and pig urine is presented. The extraction procedure involves a two-stage batch extraction, with successive adsorption on cation- (catecholamine elution) and anion-exchange columns (methoxycatecholamine elution). The column eluates are successively monitored by reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. The proportion of conjugates for each compound was assessed in both species, through the comparison of concentrations with or without hydrolysis pretreatment. Conjugates were found to account for a small fraction of total catecholamines and methoxycatecholamines excretion (0 to 35%). The free fraction of each compound was highly correlated with the total amount. Furthermore, the hydrolysis procedure leads to partial degradation of metanephrine (25%) and to the production of compounds giving artefactual peaks. Thus, we do not recommend hydrolysis of rat and pig urines for catecholamine and methoxycatecholamine determination.

Animals↗
PubMed1997

Improved determination of urinary cortisol and cortisone, or corticosterone and 11-dehydrocorticosterone by high-performance liquid chromatography with ultraviolet absorbance detection.

A sensitive assay was developed for the determination of low levels of free (unconjugated) glucocorticoids in human, swine (cortisol and cortisone) and rat urine (corticosterone and 11-dehydrocorticosterone), using solid-phase extraction and HPLC with UV absorbance detection (254 nm). Precise quantitation is allowed by the use of internal standards (dexamethasone for swine urine and Reichstein's substance S for rat urine). This simple method allows the use of small urine samples (less than 2 ml), and is suitable for a wide range of applications in human and animal clinical and physiological studies.

Animals↗
PubMed1997

Interactions between vasopressin and baroreflex control of the sympathetic nervous system.

1. In addition to its effects at the renal tubules to influence water retention and at vascular smooth muscle to cause vasoconstriction, the hormone arginine vasopressin also appears to modulate cardiovascular reflex control of the sympathetic nervous system. Infusion or endogenous release of vasopressin results in enhanced baroreflex sympatho-inhibitory responses compared with other pressor agents. In addition, when changes in arterial pressure are imposed on an elevated background level of circulating vasopressin, due either to infusion or endogenous release, the arterial baroreflex response is shifted to lower pressures, and the maximum sympatho-excitation to a decrease in pressure is reduced. 2. Evidence suggests that vasopressin may influence cardiovascular reflex function at multiple sites. Nevertheless, the primary site involved in the effects of circulating vasopressin on baroreflex function appears to be in the central nervous system, specifically in the area postrema. Lesion of the area postrema abolishes the ability of circulating vasopressin to modulate arterial baroreflex and cardiopulmonary reflex function and electrical or chemical stimulation of this circumventricular organ mimics the effects of vasopressin. In addition, vasopressin has been shown to influence the activity of area postrema neurons in vivo and in vitro. Although not all studies agree, the effects of the area postrema and vasopressin on cardiovascular reflex function appear to be dependent on afferent input from peripheral baroreceptors. 3. Most evidence suggests that vasopressin exerts its effects on baroreflex function through a V1 vasopressin receptor mechanism. Systemic administration or microinjection into the area postrema of a specific V1 receptor antagonist abolishes the action of arginine vasopressin on arterial baroreflex and cardiopulmonary reflex control of the sympathetic nervous system. 4. The ability of vasopressin and the area postrema to influence baroreflex function appears to be dependent on an alpha 2-adrenoceptor mechanism at the level of the nucleus tractus solitarius (NTS). Blockade of alpha 2-adrenoceptors in the NTS abolishes the effects of vasopressin and the area postrema on the sympathetic nervous system. Facilitation of NTS processing of baroreceptor afferent inputs by the area postrema could contribute to the enhanced sympatho-inhibition and shift of the baroreflex curve to lower pressures during elevations in circulating vasopressin.

Afferent Pathways↗
PubMed1997

Administration of AVP to the area postrema alters response of NTS neurons to afferent inputs.

This study was designed to determine if arginine vasopressin (AVP) facilitates the response of nucleus of the solitary tract (NTS) neurons to baroreceptor input. In anesthetized sinoaortic-denervated vagotomized rabbits, AVP was intravenously infused (15 microg x kg(-1) x min(-1), 1 min) or microinjected into the area postrema (AP; 1 ng/nl, 10 nl). Extracellular recordings of evoked NTS neuronal responses to electrical stimulation of the aortic depressor nerve (ADN) or vagus nerve (1 Hz, 2-20 V, 0.05-0.6 ms) were evaluated before and after AVP administration. In neurons receiving input from the ADN (n = 19), 58% of them increased their responses after AVP (40.3 +/- 5.0 to 71.5 +/- 4,8%, P < 0.001). Similarly, in neurons activated by vagal stimulation (n = 22), 55% of them were facilitated during AVP administration (59.7 +/- 12.8 to 90.8 +/- 10.7%, P < 0.01). This action of AVP was independent of the mode of AVP administration, since either microinjection or venous infusion was effective in augmenting responses of NTS neurons to aortic/vagal stimulation. In an additional 37 spontaneous NTS neurons, AVP showed no effect on the mean baseline firing rate (8.9 +/- 1.3 vs. 9.6 +/- 1.3 spikes/s, P > 0.05), but increased neuronal activity in 54% of neurons (6.9 +/- 1.3 vs. 13.1 +/- 1.7 spikes/s, P < 0.01). In two rabbits pretreated with vasopressin antagonist (15 microg/kg iv), AVP failed to produce facilitatory effects (n = 8). The results of this study provide evidence in support of the hypothesis that circulating peptides modulate the arterial baroreflex via activation of neurons in the AP.

Afferent Pathways↗
PubMed1997

Modification of feed intake response to a beta 2-agonist by bovine somatotropin in lactating or dry dairy cows.

The aim of this experiment was to show whether growth hormone could increase the effect of the beta 2-adrenergic agonist clenbuterol on feed intake. Two groups of Holstein cows [lactating (n = 4) and dry (n = 4)] were used to rule out the possible effects of increased energy requirements on feed intake. Treatments were administered according to a crossover experimental design with two 13-d periods and an 8-d readjustment interval. Treatments consisted of daily injections of 40 mg of bST or a placebo. Moreover, clenbuterol (3.16 micrograms/kg of BW) or saline challenges were infused intravenously for 4 h either on d 8 or on d 11 of each period. The cows were offered a dehydrated total mixed diet for ad libitum intake for 4 h twice daily. For both groups of cows, clenbuterol reduced DMI on the experimental day only, and bST intensified the effects of clenbuterol on DMI, causing a sharper decrease in DMI over 2 d. This enhancement of clenbuterol activity modified certain metabolic parameters including higher lipid mobilization during infusion and higher glycogenolysis. For dry cows, the initial rate of eating was reduced under bST treatment alone. During early lactation, bST, either by itself or through increased beta 2-adrenergic stimulation may restrict the development of intake by dairy cows over a few weeks.

Adrenergic beta-Agonists↗
PubMed1996

Synaptic connections and interactions between area postrema and nucleus tractus solitarius.

The purpose of this study was to examine whether there are separate excitatory and inhibitory pathways from the area postrema (AP) to the nucleus tractus solitarius (NTS) and to examine the synaptic interactions between inputs from the AP and solitary tract (ST) on the NTS neurons. The following observations were made: (1) the predominant projections from the AP to the NTS were excitatory. Among the cells that had AP input, 90% of the cells (43/48) were excited by AP stimulation while 10% (5/48) of the cells were inhibited; (2) inputs from the AP and ST mainly summated occlusively on the NTS neurons, but at near threshold of discharge, the input from one source could facilitate the generation of action potentials induced by the other; and (3) single conditioning stimulation of the AP did not significantly inhibit the NTS neuronal response to ST stimulation, but stimulation of the AP with a train of high frequency stimuli inhibited the response of NTS neurons to ST stimulation and inhibited the evoked response to AP stimulation. The results of this study may help in the understanding of the modulatory role of the AP in the baroreflex and the integration process in the NTS.

Action Potentials↗
PubMed1996

Construction and characterization of an azurin analog for the purple copper site in cytochrome c oxidase.

A protein analog of a purple copper center has been constructed from a recombinant blue copper protein (Pseudomonas aeruginosa azurin) by replacing the loop containing the three ligands to the blue copper center with the corresponding loop of the CuA center in cytochrome c oxidase (COX) from Paracoccus denitrificans. The electronic absorption in the UV and visible region (UV-vis) and electron paramagnetic resonance (EPR) spectra of this analog are remarkably similar to those of the native CuA center in COX from Paracoccus denitrificans. The above spectra can be obtained upon addition of a mixture of Cu2+ and Cu+. Addition of Cu2+ only results in a UV-vis spectrum consisting of absorptions from both a purple copper center and a blue copper center. This spectrum can be converted to the spectrum of a pure purple copper by a prolonged incubation in the air, or by addition of excess ascorbate. The azurin mutant reported here is an example of an engineered purple copper center with the A480/A530 ratio greater than 1 and with no detectable hyperfines, similar to those of the CuA sites in COX of bovine heart and of Paracoccus denitrificans.

Amino Acid Sequence↗
PubMed1996

Chronic neurosteroid treatment attenuates single cell GABAA response and its potentiation by modulators in cortical neurons.

In previous studies we have observed that chronic neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one (5 alpha 3 alpha) treatment produced downregulation of the GABAA receptors, heterologous uncoupling, and decreased heterologous efficacy at the GABAA receptor complex in cultured mammalian cortical neurons. In this study, using whole cell recording, we examined the consequence of chronic 5 alpha 3 alpha (1 microM; 5 days) treatment on GABA-induced currents in isolated cortical neurons. We observed that the GABA current was decreased by 78% after 5 days treatment of cortical cells with 1 microM 5 alpha 3 alpha. We also observed decreased pentobarbital, and 5 alpha 3 alpha potentiation of GABA currents after chronic 5 alpha 3 alpha treatment. These findings support the notion that GABA response, and its potentiation by pentobarbital, and neurosteroid, 5 alpha 3 alpha, are attenuated after chronic 5 alpha 3 alpha treatment.

Animals↗
PubMed1996

Changes in sexual function after radiotherapy treatment of prostate cancer.

OBJECTIVE: To assess sexual function before and after definitive irradiation for the treatment of cancer of the prostate. PATIENTS AND METHODS: The study comprised 67 patients (mean age 68 years) treated in five radiotherapy departments and assessed with repeated questionnaires about their libido, arousal, frequency and quality of intercourse, and sexual satisfaction. Interviews were obtained before radiotherapy and at the end of the first year after treatment. Sixty-three patients were married and 50 had a sexually effective partner. Forty-six patients presented with another pathology or medical treatment capable of inducing sexual dysfunction. Before radiotherapy, 40 patients were sexually active, with good to acceptable intercourse. RESULTS: Between 10 and 24 months after the end of radiotherapy, no disease progression was observed and prostate-specific antigen levels remained high in only two patients. Sexual function was preserved in 67% of patients but only 50% observed no change. The functional prognosis seemed to be related to the initial frequency and quality of intercourse; more than three times per month, the prognosis remained good, under three per month, it was poor. The patient's age was a predictive factor for the frequency of intercourse. CONCLUSION: Several causes of impairment of sexual function may be associated and can change over a long time. A longer survey should be conducted to analyse the organic response to radiation.

Aged↗
PubMed1996

Subcellular mechanisms of angiotensin II and arginine vasopressin activation of area postrema neurons.

Angiotensin II (ANG II) and arginine vasopressin (AVP) act on area postrema (AP) neurons to modulate the baroreflex. Because activation of AP neurons by either ANG II or AVP increases intracellular free Ca2+ concentrations ([Ca2+]i), the goal of this study was to analyze the factors affecting the [Ca2+]i responses to ANG II and AVP. Neurons were recovered from 14- to 16-day old rats and studied after 8-14 days in culture by use of the microscopic digital image analysis for fura 2-loaded cells. The effects of ANG II (100 nM) and AVP (100 nM) on [Ca2+]i were determined in normal (2 mM) and low (< 10 nM) extracellular Ca2+ concentrations. In 143 of 240 neurons, ANG II increased [Ca2+]i 4.65-fold after 20 s, and a similar response was observed in the absence of extracellular Ca2+ (3.65-fold after 20 s). After 60 s of observation, steady-state levels of increased [Ca2+]i were still present under both conditions. Pretreatment with AT1 antagonist or pertussis toxin abolished the response to ANG II. AVP also increased [Ca2+]i (3.6-fold at peak, 20 s) in normal and low extracellular Ca2+. Pretreatment with AVP V1 antagonist or pertussis toxin abolished the response to AVP. This study indicates that ANG II-induced increases in [Ca2+]i are independent of extracellular Ca2+ concentrations and involve the activation of AT1 receptors and a pertussis toxin-sensitive G protein. Although AVP affects a fewer number of AP neurons, the mechanisms of activation are also independent of extracellular Ca2+ concentration and are mediated by a pertussis toxin-sensitive G protein.

Angiotensin II↗
PubMed1996

Area postrema voltage-activated calcium currents.

1. Calcium currents in rabbit area postrema neurons were studied with the perforated patch-clamp technique. Experimental conditions eliminated Na+ and K+ currents and identified both low- and high-threshold voltage-activated calcium currents. 2. Low-threshold, T-type calcium currents were observed in 64% of the area postrema neurons recorded. This current activated near -60 mV and had an average peak amplitude of -36.2 +/- 5 pA (mean +/- SE) at -40 mV. This current began rapid inactivation near -95 mV, reached half-maximal inactivation at -71 mV and was totally inactivated by -40 mV. 3. A high-threshold transient current was recorded in all area postrema neurons, which consisted of both a transient and sustained component. This current was present at voltages greater than -40 mV and the transient component of this current was responsible for the majority of the total Ca2+ current. 4. Nickel ions (10 microM) effectively reduced both the T-type current and the high-threshold current. Cadmium ions (100 microM) effectively reduced the high-threshold current while having insignificant effects on the low-threshold current. 5. Application of the dihydropyridine antagonist nimodipine (1-10 microM) had no effect on either the low- or high-threshold voltage-activated calcium Ca2+ in area postrema neurons. In addition, application of omega-conotoxin-GVIA (2-10 microM) was also without effect on either the low- or high-threshold voltage-activated Ca2+ current, suggesting that area postrema neurons possess neither L- or N-type voltage-activated Ca2+ currents. 6. Application of omega-conotoxin MVIIC (10 microM) significantly inhibited the peak high-threshold Ca2+ current by 65.4% suggesting that area postrema neurons do possess a omega-conotoxin MVIIC-sensitive high-threshold Ca2+ channel. 7. Arg-vasopressin (150 nM) significantly increased the transient component of the high-threshold Ca2+ current but had little effect on either the low-threshold or the high-threshold sustained component.

Angiotensin II↗
PubMed1995

Membrane properties of area postrema neurons.

Intrinsic membrane properties, voltage-dependent sodium and voltage-dependent potassium currents of area postrema neurons in culture have been characterized with respect to their voltage dependence, time dependence and sensitivity to specific blocking agents. The area postrema is a hindbrain circumventricular organ which is known to have an important role in the central regulation of cardiovascular function. This study is the first to describe the biophysical properties of ion channels present in rat area postrema neurons. Recordings in current-clamp mode revealed a mean resting membrane potential of -55.0 +/- 1.6 (n = 24) mV and an input resistance of 213.6 +/- 23 M omega. For the 24 neurons tested, the evoked action potential had a mean threshold of 38.8 +/- 2 mV and a mean amplitude of 107.3 +/- 15 mV. Our results show that the area postrema possesses only one principle sodium current which is completely abolished by 5 microM tetrodotoxin (TTX) (n = 28). This current activated near -50 mV and reached peak amplitude at -30 mV. The area postrema does not possess a TTX insensitive sodium current. The area postrema has at least two types of potassium currents. All area postrema neurons studied with tetraethylamonium (TEA) (n = 40) showed the presence of a slowly activating outward current which was present at voltages greater than -40 mV and was blocked by 10 mM TEA. In addition, 75% of the neurons studied (n = 30/40) also showed a rapidly inactivating, 4-AP sensitive IA type current which activated near -30 mV. Angiotensin II attenuated both the peak and the steady-state potassium currents, suggesting that angiotensin II may modulate area postrema activity by inhibiting voltage-gated potassium channels.

4-Aminopyridine↗
PubMed1995

Metabotropic glutamate receptor inhibition of visceral afferent potassium currents.

The effects of metabotropic glutamate receptor activation (mGluR) on voltage-gated potassium currents have been characterized in visceral sensory afferent neurons. L-Glutamate is known to be a primary neurotransmitter in visceral afferents which terminate at the level of the nucleus of the solitary tract (NTS). Synaptic communication between these afferents and the NTS has been shown to involve both postsynaptic ionotropic and presynaptic metabotropic glutamate receptor activation. The purpose of the present study was to determine the effects of mGluR activation on voltage-gated potassium currents in visceral sensory neurons. Application of mGluR agonist t-ACPD inhibited both the peak and the steady state voltage-gated potassium current in 39 out of 56 visceral afferent neurons tested (70%) by 22.0 +/- 3 and 22.8 +/- 2%, respectively. Voltage and pharmacological protocols were utilized to isolate the potassium current affected by mGluR activation. Increasing the holding potential from -100 mV to -30 mV only partially attenuated the inhibitory effects of t-ACPD (decreased effect by 11%), suggesting that t-ACPD modulates both a voltage insensitive and a voltage-sensitive potassium current. In addition, 4-aminopyridine (5 microM) was applied to eliminate the 4-AP sensitive transient current. Also, this protocol only partially attenuated the inhibitory effects of t-ACPD (decreased effect by 6.3%), suggesting that mGluR activation inhibits both a 4-AP-sensitive and 4-AP-insensitive potassium current in visceral afferent neurons. Results from this study suggest that mGluRs may regulate visceral sensory afferent neuronal activity through inhibition of voltage-gated potassium channels.

4-Aminopyridine↗
PubMed1995

Intra-operative radiotherapy in soft tissue sarcomas.

We treated 31 soft tissue sarcoma bearing patients with intraoperative radiation therapy (IORT) with ages ranging from 26 to 71: first curative intent treatment, 16 patients; and recurrent tumors, 15 patients. The tumor site was the pelvis and the retroperitoneal spaces in 13 patients and the limbs or the trunk in 18 patients. The histological type was: malignant histiocytofibroma, 14 patients; liposarcomas, 10 patients; malignant schwanoma, 1 patient; leiomyosarcoma, 2 patients; hemangiopericytoma, 1 patient; embryonic rhabdomyosarcoma, 2 patients; and synovialosarcoma, 1 patient. All the patients were diagnosed without any distant metastatic evolution at the moment of the treatment. All the patients except one underwent a complete surgical excision without any gross residual disease and received an intraoperative radiation single dose of 10 Gy in one case, 12.5 Gy in one case, 13 Gy in one case, 15 Gy in 17 cases, 18 Gy in three cases, 20 Gy in seven cases and 25 Gy in one case. Thereafter the treatment was completed by a postoperative X-ray dose of 45-50 Gy in 4.5-5 weeks for 16 patients. Local control (LC) was obtained in 27 out of 31 patients (87%), with a minimal follow-up duration of 2 years. Eleven out of 31 patients died: seven with local control (one from an intercurrent disease, six from distant metastasis) and four with local failure inside the IORT fields. Twenty patients are alive with no evolutive disease in 19 cases and with a distant metastasis in one case.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Neoplasms↗
PubMed1994

Stimulation of area postrema by vasopressin and angiotensin II modulates neuronal activity in the nucleus tractus solitarius.

There is an abundance of evidence suggesting that the area postrema (AP) is involved in the central actions of arginine-vasopressin (AVP) and angiotensin II (Ang II) on cardiovascular regulation. Furthermore, recent studies have shown that activation of the AP facilitates the response of nucleus tractus solitarius (NTS) neurons to tractus stimulation. In the present study, using the perfused rabbit brain slice preparation, we examined the response of NTS neurons when AVP and Ang II were microinjected onto the AP. Spontaneous or solitary tract stimulation-induced neuronal activity was recorded extracellularly from the medial NTS before, during and after AVP or Ang II application. An increase or decrease in activity by more than 30% of the baseline value was considered excitatory or inhibitory. The effects of AVP were studied in 57 NTS cells, 14 of which were spontaneously active and 43 were driven by tract stimulation. Of the cells with evoked activity, 49% were excited, 19% were inhibited, and 32% did not respond. The percentage of cells responding to AVP was similar in spontaneously active cells. The effects of Ang II were tested in 85 cells including 54 with evoked activity and 31 with spontaneous activity. In NTS cells with evoked activity, AP application of Ang II caused inhibition in 37%, excitation in 7%, while 56% did not respond. The proportion of cells responding to Ang II was similar in spontaneously active cells. These results suggest that AVP may act on the AP to increase the excitatory response of NTS neurons while the actions of Ang II result in an inhibitory influence.

Angiotensin II↗