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D Higgins

Publications and source records attributed to D Higgins.

At least 109 records · Page 6Linked to original sources
PubMed1985

Rapid changes in synaptic vesicle cytochemistry after depolarization of cultured cholinergic sympathetic neurons.

Sympathetic neurons taken from rat superior cervical ganglia and grown in culture acquire cholinergic function under certain conditions. These cholinergic sympathetic neurons, however, retain a number of adrenergic properties, including the enzymes involved in the synthesis of norepinephrine (NE) and the storage of measurable amounts of NE. These neurons also retain a high affinity uptake system for NE; despite this, the majority of the synaptic vesicles remain clear even after incubation in catecholamines. The present study shows, however, that if these neurons are depolarized before incubation in catecholamine, the synaptic vesicles acquire dense cores indicative of amine storage. These manipulations are successful when cholinergic function is induced with either a medium that contains human placental serum and embryo extract or with heart-conditioned medium, and when the catecholamine is either NE or 5-hydroxydopamine. In some experiments, neurons are grown at low densities and shown to have cholinergic function by electrophysiological criteria. After incubation in NE, only 6% of the synaptic vesicles have dense cores. In contrast, similar neurons depolarized (80 mM K+) before incubation in catecholamine contain 82% dense-cored vesicles. These results are confirmed in network cultures where the percentage of dense-cored vesicles is increased 2.5 to 6.5 times by depolarizing the neurons before incubation with catecholamine. In both single neurons and in network cultures, the vesicle reloading is inhibited by reducing vesicle release during depolarization with an increased Mg++/Ca++ ratio or by blocking NE uptake either at the plasma membrane (desipramine) or at the vesicle membrane (reserpine). In addition, choline appears to play a competitive role because its presence during incubation in NE or after reloading results in decreased numbers of dense-cored vesicles. We conclude that the depolarization step preceding catecholamine incubation acts to empty the vesicles of acetylcholine, thus allowing them to reload with catecholamine. These data also suggest that the same vesicles may contain both neurotransmitters simultaneously.

Acetylcholine↗
PubMed1984

Fetal rat sympathetic neurons maintained in a serum-free medium retain induced cholinergic characteristics.

When maintained in some serum-containing media, fetal rat sympathetic neurons acquire substantial choline acetyltransferase activity and form cholinergic synapses in vitro. However, when they are maintained in a serum-free, defined culture medium, choline acetyltransferase activity is not detected and cholinergic synapses are not observed. In this study, we have examined the effects of various times of exposure to a medium inducing cholinergic function on the properties of neurons subsequently maintained in defined medium. We report that 2-day, but not 2-h, exposure to this inducing medium causes a long-lasting (greater than 6 weeks) increase (7-10-fold) in the activity of choline acetyltransferase and that, under these conditions, sympathetic neurons in vitro form cholinergic, electrical and mixed function cholinergic and electrical synapses. We conclude that a relatively brief exposure to media inducing cholinergic function can cause long-lasting changes in the functional properties of sympathetic neurons in vitro.

Acetylcholine↗
PubMed1982

Electrotonic synapses are formed by fetal rat sympathetic neurons maintained in a chemically-defined culture medium.

Principal neurons from the superior cervical ganglia of rat fetuses were maintained for up to 101 days in dissociated cell cultures in a serum-free, chemically-defined medium; non-neuronal cells were killed by the periodic addition of fluorodeoxyuridine to the medium. Intracellular recordings, obtained at various times between 16th and 98th day in vitro, showed that these neurons could generate substantial (up to 90 mV) action potentials in response to depolarizing current injections; these responses were dependent on tetrodotoxin-sensitive Na+ channels, cobalt-sensitive Ca++ channels, and tetraethylammonium-sensitive K+ channels. Action potentials were often followed by prominent, long hyperpolarizing after-potentials (10-15 mV, greater than 150 ms); the duration of these after-potentials was reduced by the addition of Co++ (2-5 mM) to the perfusate. Acetylcholine depolarized these neurons by a hexamethonium-sensitive mechanism. To determine whether sympathetic neurons formed synapses in a defined medium, intracellular recordings were obtained from pairs of neighboring neurons. Synaptic interactions were frequently observed at all times in vitro (up to 60% of all pairs tested). At many synapses, both hyperpolarizing and depolarizing DC potential changes spread from one neuron to another. At other synapses, the spread of DC potential changes could not be directly demonstrated; however, interactions at such synapses were not inhibited by antagonists of several neurotransmitters, by elevation of the Mg++/Ca++ ratio, or by the addition of Co++. Thus most, if not all, of the synaptic interactions among sympathetic neuron were electronic; such electrical synapses were not observed among dorsal root ganglion neurons maintained in the same medium. These data indicate that, when maintained in a chemically-defined culture medium, sympathetic neurons of rat fetuses express many of the basic membrane properties observed in neurons of superior cervical ganglia recently removed from adult rats. However, fetal sympathetic neurons maintained in this defined medium also differ from their counterparts in vivo; they adopt a mode of synaptic transmission (electrical) that has not been observed in the sympathetic ganglia of the adult rat. Thus, as late as the 21st embryonic day, not only the choice of neurotransmitter, but also the mode of transmission has not been irrevocably determined in sympathetic neurons.

Acetylcholine↗
PubMed1982

Role of DNA repair in ethyl methanesulfonate-induced mutagenesis in Saccharomyces cerevisiae.

Ethyl methanesulfonate (EMS)-induced reversion of two sites which revert preferentially by GC to AT transitions, cycl-131 and cycl-115, has been examined in readiation sensitive, rad, mutants of yeast belonging to the rad52 epistasis group. The rad50, rad51, rad52, rad54 and rad56 mutants showed reducted reversion of both tester sites when stationary phase diploid cells were treated with EMS. No correlation was found between EMS-induced reversion and EMS-induced homologous mitotic intragenic recombination. Survival of rad6 rad52 double mutants following EMS treatment indicates that there is one epistasis group for the repair of EMS-induced lethal damage in yeast. A model involving misrepair mutagenesis of specific lesions is proposed to account for the experimental results.

DNA Repair↗
PubMed1981

Growth and development of sympathetic neurons in tissue culture.

Adrenergic neurons from the superior cervical ganglion of the neonatal rat, when studied under certain culture conditions, develop cholinergic properties including hexamethonium-sensitive synaptic interactions, choline acetyltransferase activity and synaptic endings containing clear vesicles. Evidence from correlative biochemical, physiological and morphological studies on populations of neurons indicates that cholinergic function is acquired by the majority of neurons and not by subpopulation. The factors that influence the development of cholinergic function in culture include the presence of non-neuronal cells, the addition of human placental serum and chick embryo extract to the culture medium as well as the stage of development at which the neurons are placed in culture. Neurons from mature rats, maintained as explants in culture, develop low choline acetyltransferase activity and the synaptic endings containing dense-cored vesicles. In contrast, if dissociated, these adult neurons develop several cholinergic characteristics. Studies to determine which adrenergic properties are retained in neurons expressing cholinergic characteristics have shown an increase in the activities of tyrosine hydroxylase and dopamine beta-hydroxylase in both explanted and dissociated perinatal neurons. In addition, tyrosine hydroxylase has been localized immunocytochemically in neurons identified as cholinergic by electrophysiological methods.

Animals↗
PubMed1981

Developmental changes in the sensitivity of the chick embryo ventricle to beta-adrenergic agonist during adrenergic innervation.

As early as the 4th embryonic day, the ventricle of the chick embryo responded to isoproterenol (Iso) with an increase in the force of contraction; at all ages studied, this positive inotropic effect was accompanied by an increased rate of tension development. There was a transient, 10-fold decrease in the sensitivity (increase in ED50) of the right ventricle to Iso between the 16th and 21st embryonic day. This change in the sensitivity to Iso was not due either to an increased inactivation of Iso by non-neuronal cells or to a change in the thickness of the ventricle. It was found that adrenergic nerves were first capable of altering ventricular contractility on the 16th embryonic day. Whereas they interfered with the function of adrenergic nerves, injections of reserpine or 6-hydroxydopamine had no effect on the subsensitivity to Iso. Furthermore, these agents did not affect the normal developmental changes in heart weight. We conclude that the local release of transmitter from adrenergic nerves does not cause the transient subsensitivity of the ventricle of the chick embryo to beta-adrenergic agonists.

Adrenergic beta-Agonists↗
PubMed1981

The immunocytochemical localization of tyrosine hydroxylase within rat sympathetic neurons that release acetylcholine in culture.

In vitro populations of neurons dissociated from the superior cervical ganglion of the rat embryo can acquire many of the properties of cholinergic neurons and yet retain some of the characteristics of adrenergic neurons. To determine whether one neuron can stably express properties of two transmitter systems, identified neurons were characterized by both immunocytochemical and electrophysiological methods. It was found that more than 90% of the neurons that formed functional cholinergic synapses had tyrosine hydroxylase within their cytoplasm. Furthermore, this mixed phenotypic expression persisted for more than 1 month. It is concluded that, under certain conditions in vitro, most neurons from the superior cervical ganglion have at least the potential for dual function.

Acetylcholine↗
PubMed1979

Dear Dr. Eger:.

Explore the source record for details and available documents.

Adult↗
PubMedDate not supplied

Hypothalamic Na+ and Ca++ ions and temperature set-point: new mechanisms of action of a central or peripheral thermal challenge and intrahypothalamic 5-HT, NE, PGEi and pyrogen.

The effects of changes in ambient and central temperature, amines, PGEu and pyrogen were investigated with respect to the mechanism of Na+-Ca++ ratio in the posterior hypothalamus of the unrestrained cat. Guide tubes were implanted bilaterally above the posterior hypothalamic area of 23 cats so as to accommodate push-pull cannulae. After a Na+ or Ca++ sensitive site was identified by perfusion at 50 mul/min of an artificial CSF containing 10.4 mM excess Ca++ ions or 13.6 mM excess Na+ ions, several types of experiments were undertaken with the results summarized as follows: if the cat was exposed to a cold or warm environmental temperature as the posterior hypothalamus was perfused with excess cation, the typical hypothermia was produced by Ca++ and hyperthermia by Na+ ions. However, if the cat was exposed to peripheral cooling or warming 30 min prior to the perfusion, the fall or rise produced by Ca++ or Na+ was attenuated or prevented. In other experiments, 1.0 muCi 45Ca++ was injected in the ion sensitive site in the posterior hypothalamus to label stores of the cation. Raising of ambient temperature caused a retention of 45Ca++ in this hypothalmic area, whereas a cold environmental temperature enhanced the efflux of 45Ca++ at the same perfusion site. The magnitude of change in 45Ca++ efflux depended upon the intensity of the thermal challenge. Similarly, warming of the anterior hypothalmic, preoptic area by means of implanted thermodes caused an immediate diminution in 45Ca++ efflux in the posterior hypothalamus, whereas cooling of this anterior region augmented the extrusion of 45Ca++ ions from the posterior area. When substances which produce a temperature change were applied to the same thermosensitive zone, the direction of shift in 45Ca++ flux in the posterior area corresponded to the signal for heat production or heat loss. That is, the microinjection of 5-HT, PGE1 or Salmonella typhosa into the anterior hypothalamus enhanced the efflux of 45Ca++ in the posterior hypothalamus as hyperthermia developed, whereas a similar microinjection of norepinephrine reduced the 45Ca++ output from the same sites. Finally, locally anesthetizing the cells of the anterior hypothalamus by the nerve blocker, procaine, prevented the cold and heat-induced 45Ca++ eflux and retention, respectively. These results suggest that if the Na+-Ca++ ratio in the posterior hypothalamus establishes and maintains the set-point for body temperature of 37 degrees -38 degrees C, the mechanism of lability of Ca++ through changes in binding characteristics, transport, or metabolism of the cation serves two purposes: (1) the active defense of the set-point temperature through gradations in ion shifts; and (2) the upward or downward change in set-point value, pathological or normal, triggered by virtue of impulses relayed from the anterior hypothalamus.

Animals↗
PubMedDate not supplied

Anxiety and endocrine responses to surgery: paradoxical effects of preoperative relaxation training.

It has been argued that surgery is a form of psychological stress, and that the response to it should therefore be modifiable by psychological means. To test this hypothesis, we assessed the effect of preoperative relaxation instructions on endocrine, cardiovascular, and subjective responses in 21 patients undergoing minor abdominal surgery. Controls (N = 19) received general procedural information. In the relaxation group only, there was a significant increase in cortisol and adrenaline concentration from immediately before induction of anesthesia to immediately after surgery. Noradrenaline values were unaffected by relaxation. In contrast, relaxation reduced state-anxiety on the preoperative day and the two postoperative days; maximal peroperative systolic and diastolic blood pressures were also reduced. The results are consistent with previous evidence that adrenaline and cortisol responses to surgery are greater in less anxious patients.

Adaptation, Psychological↗
PubMedDate not supplied

Lung volume reduction for emphysema and the Canadian Lung Volume Reduction Surgery (CLVR) Project.

OBJECTIVE: To review the literature on the surgical treatment of emphysema and to present preliminary results from a pilot study of lung volume reduction (LVR) surgery. DESIGN: Case series of consecutive patients referred for LVR surgery. Outcomes were quality of life, pulmonary function and exercise capacity. SETTING: Two university-affiliated hospitals in Ontario. POPULATION STUDIED: Patients between the ages of 40 and 75 years with emphysema who had severe airflow limitation, hyperinflation of the lungs and impaired quality of life. INTERVENTION: Bilateral reductions with multiple wedge resections of the lung using a linear stapling device with bovine pericardial buttressing were completed via a median sternotomy. MAIN RESULTS: Of 50 patients referred, 24 underwent LVR surgery. Mean age of the cohort was 63 years. Operative 30-day or in hospital mortality was 8%. Two other patients (8%) died from respiratory failure after LVR within the first year. Postoperative complications included prolonged air leaks (six of 24), tracheobronchitis (five of 24), mechanical ventilation (four of 24) and pneumonia (three of 24). Mean length of stay was 18 days (median 12 days). At one year, there was a sustained decrease in total lung capacity from 133% to 123% predicted. There were improvements in forced expiratory volume in 1 s, from 22% of predicted preoperatively to 32% postoperatively, and in 6 min walk performance, from 345 to 381 m. Improvements were also noted in the quality of life assessments. CONCLUSIONS: Preliminary results suggest that LVR surgery is feasible and may improve the patient's quality of life, pulmonary function and exercise capacity. A randomized clinical trial comparing LVR plus the best medical management with the best medical management alone is currently underway to determine the effectiveness of LVR.

Adult↗