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Biomedical subjects

F M Smith

Publications and source records attributed to F M Smith.

13 recordsLinked to original sources
PubMed1992

Electrophysiological properties of in vitro intrinsic cardiac neurons in the pig (Sus scrofa).

Physiological properties and synaptically mediated responses of 34 ganglionated plexus neurons from the right atrium of the pig heart were studied with in vitro intracellular recording techniques. Whole-cell input resistance of these neurons was lower, time constant was shorter, and threshold for directly evoked action potentials was higher than the same properties in extracardiac autonomic neurons. Long intracellular depolarizing current pulses (400-500 ms) failed to generate more than one or two action potentials. Nicotinic and non-nicotinic synapses were present on neurons in cardiac ganglia and neuronal properties could be modified by norepinephrine. Based on their physiological properties, cardiac ganglionated plexus neurons in the pig appear to represent a distinct population of autonomic neurons that may be capable of intracardiac integration of efferent information to the heart.

Animals↗
PubMed1992

Baroreflex control of arterial blood pressure during involuntary diving in ducks (Anas platyrhynchos var.).

The dynamic role of arterial baroreceptors in control of mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), hindlimb vascular (HLVR) and total peripheral (TPR) resistance responses to forced dives was investigated in acutely and chronically barodenervated ducks. To activate the baroreflex, the proximal end of one aortic nerve was stimulated electrically with bipolar electrodes that had been implanted under pentobarbital sodium anesthesia. Predive nerve stimulation caused CO to fall (by reducing HR; stroke volume remained constant), producing a decrease in MAP to half the prestimulation level. During diving (for 2.5-min periods) nerve stimulation did not affect HR and MAP after the first minute of submersion. Neither HLVR nor TPR contributed to the fall in MAP during aortic nerve stimulation before or during diving. The effects of nerve stimulation on HR and MAP were maintained to the end of dives in animals given 100% O2 to breathe before diving. In separate experiments, increasing arterial chemoreceptor input by perfusing one vascularly isolated carotid body with venous blood caused a reduction in the effects of aortic nerve stimulation on MAP. Arterial baroreceptors may thus act on HR to alter MAP early in the dive, but as the dive progresses the baroreflex is attenuated by an increase in peripheral chemoreceptor drive.

Animals↗
PubMed1991

Activity of in vivo atrial and ventricular neurons in chronically decentralized canine hearts.

The spontaneous activity of 175 neurons located in the ventral right atrial and ventral interventricular ganglionated plexi was recorded in eight anesthetized dogs, the hearts of which were chronically decentralized at least 2 wk before recordings were made. Ganglia were subsequently identified anatomically in the immediate vicinity of the recording sites. Spontaneous activity was correlated with the cardiac cycle in 57% of the atrial and 62% of the ventricular neurons and with the respiratory cycle in 29% of the atrial and 28% of the ventricular neurons. Spontaneous cardiovascular-related activity was recorded when systemic arterial pressure was between 80 and 175 mmHg. The activity of 23 atrial and 15 ventricular neurons was altered when discrete regions of the heart were mechanically distorted by gentle touch. These data imply that cardiac ganglionated plexi contain afferent neurons that receive inputs from limited regions of the heart. The spontaneous activity generated by intracardiac neurons was not altered when extracardiac tissues were distorted. These results demonstrate that neurons in ganglia on chronically decentralized hearts can generate spontaneous activity, a large fraction of which is correlated with cardiovascular or respiratory events.

Adipose Tissue↗
PubMed1991

Murine immune responses to recombinant Toxoplasma gondii antigens.

Recombinant proteins of the RH strain of Toxoplasma gondii were produced by expression in Escherichia coli as glutathione S-transferase (GST) fusion proteins. Enzyme-linked immunosorbent assays were established using 2 of these fusion proteins termed H4/GST and H11/GST. The assays were able to detect antibodies in the sera of mice orally infected with either the cyst or oocyst stage of a pork isolate of T. gondii. In addition, the sera from mice infected with 1 of 4 different T. gondii isolates were investigated for their binding to these fusion proteins. Antibodies in the sera of all mice bound to H11/GST, but not all sera recognized H4/GST. Delayed-type hypersensitivity (DTH) responses to the fusion proteins were found when the mice were sensitized intradermally with H4/GST and H11/GST and challenged with the homologous fusion protein. However, no DTH response was recorded when mice were challenged with homologous fusion proteins after infection with T. gondii, or after immunization with a sonicate of the RH strain of the parasite. In addition, cellular responses were not stimulated against either of the fusion proteins in in vitro assays. These 2 fusion proteins were recognized by anti-T. gondii antibodies in experimental murine infections, and they are therefore potential candidates as antigens in assays for the diagnosis of human toxoplasmosis.

Animals↗
PubMed1990

Cardiac effects induced by chemically activated neurons in canine intrathoracic ganglia.

Regional or global cardiac responses were elicited when various chemicals were injected into discrete loci within acutely decentralized stellate and middle cervical ganglia. Nicotine (100 micrograms), acetylcholine (100 micrograms), or isoproterenol (1, 2, or 5 micrograms) in 1 microliters of normal saline was administered individually into 30 discrete loci within each stellate ganglion and 25 within each middle cervical ganglion. Cardiac augmentation was elicited when approximately 1 site per ganglion was injected with nicotine or acetylcholine. Similar injections into sites approximately 1-2 mm away from an active site usually failed to elicit cardiac responses. Isoproterenol elicited cardiac augmentations when injected into, on average, 3 different loci per ganglion. The responses elicited by isoproterenol injections were eliminated when the efferent sympathetic nerves arising from an injected ganglion were divided or when timolol maleate (0.1 mg/microliters normal saline) was previously injected into the same locus. These data indicate that the effects elicited by injecting isoproterenol into an intrathoracic ganglion locus were not due to leakage of this agent into the blood in sufficient quantities to directly activate cardiac myocytes. When L-glutamic acid (100 microliters of 1 M solution in normal saline) or L-aspartic acid (100 microliters of 1 M solution in normal saline) was injected into a stellate ganglion or middle cervical ganglion, positive chronotropic and/or inotropic responses were elicited. When DL-homocysteic acid (100 microliters of 1 M solution in normal saline) was administered no augmentation occurred. It is concluded that intrathoracic ganglion cardiac neurons can be activated by nicotinic or beta-adrenergic agonists, as well as by specific amino acids. These neurons are located throughout the stellate and middle cervical ganglia, cardiac neurons in one ganglionic locus being capable of activation by more than one of these chemicals.

Acetylcholine↗
PubMed1990

Cardiac responses to electrical stimulation of discrete loci in canine atrial and ventricular ganglionated plexi.

The purpose of the present study was to examine cardiac effects induced by electrical stimulation (1-4 V, 1 ms, 200 Hz) of discrete loci within the ganglionated plexi located on canine atria and ventricles. When 20 loci in the right atrial ventral ganglionated plexi of 11 anesthetized open-chest dogs were stimulated, bradycardia and/or right and left atrial force suppression occurred when, on average, 15% of these loci were stimulated. Bradycardia and atrial force suppression were elicited when, on average, 8% of 15 loci in the left atrial ventral ganglionated plexi of eight dogs was stimulated. When these loci were restimulated after acute decentralization, cardiac responses were attenuated or occasionally eliminated. After atropine (1 mg/kg iv) administration, repeat stimulation of loci in the right but not left atrial ganglionated plexus induced tachycardia. Stimulation of loci in the right ventricular ganglionated plexus after the subsequent administration of desipramine (1 mg/kg iv) in six dogs resulted in an increase in right ventricular conus intramyocardial pressure. After hexamethonium administration (10 mg/kg iv, followed by a continuous infusion of 1 mg.kg-1.min-1), sympathetic responses were no longer elicited from one of the five dogs in which loci in the right atrial ganglionated plexi and from two of the six dogs in which loci of the right ventricular ganglionated plexus had elicited responses. We conclude that atrial and ventricular ganglionated plexi contain efferent parasympathetic, efferent sympathetic, and afferent neurons.

Animals↗
PubMed1990

Effects of acute and chronic baroreceptor denervation on diving responses in ducks.

To investigate the effects of barodenervation on the cardiovascular responses to forced submersion, we implanted snares around the aortic nerves innervating the baroreceptors in anesthetized (pentobarbital sodium, 35-45 mg/kg) ducks (Anas platyrhynchos). Snares were withdrawn 1 wk after surgery to effect barodenervation in the absence of complications from surgical trauma or anesthesia. After barodenervation, resting heart rate (HR), hind limb vascular resistance (HLVR), and mean arterial pressure (MAP) all increased, with different time courses, over the 16-day observation period. Bradycardia developed during forced submersion in ducks before and after barodenervation, although this response was reduced for 1-3 days after nerve section. The HR response to diving intensified 4-5 days after denervation, and the level of dive bradycardia at 16 days was similar to that before denervation. End-dive MAP fell further, as a proportion of predive MAP, with time after baroreceptor loss. The absolute level of HLVR reached during diving was unaffected by barodenervation. These results show that diving responses develop in the absence of baroreceptors, but MAP in the dive is not maintained as well in barodenervates as in baroreceptor-intact animals.

Animals↗
PubMed1975

Viscosities of acacia and sodium alginate after sterilization by cobalt-60.

Acacia and sodium alginate powders were sterilized by cobalt-60 irradiation to a total dose of 2.5 Mrad with no increase in residual radioactivity of the gums as a result of the treatment. Viscosity measurements showed an 11% reduction in the viscosity of acacia in water and a 16% decrease in the intrinsic viscosity in barium chloride solution due to the irradiation. Viscosities of sodium alginate solutions in 0.1 N sodium chloride showed a 70% decrease in intrinsic viscosity, indicating changes in the molecular structure corresponding to degradation to 30% of the original degree of polymerization. This dose of gamma-radiation from cobalt-60 is not an appropriate method of sterilization for these gums.

Acacia↗