Biomedical subjects

S L Stuesse

Publications and source records attributed to S L Stuesse.

At least 37 records · Page 2Linked to original sources

PubMed1991

Localization of serotonin, tyrosine hydroxylase, and leu-enkephalin immunoreactive cells in the brainstem of the horn shark, Heterodontus francisci.

In previous studies on reptiles and elasmobranchs, we determined that some reticular groups are either absent or may be displaced compared to their locations in mammals. For example, nucleus raphe dorsalis, the largest serotoninergic cell group in mammals, is not present in rays, skates, or guitarfish. In the present study, we chose heterodontid sharks, a sister group to these batoids, for an out-group comparison of this and other characters. We identified cells in the brainstem of Heterodontus francisci by use of antibodies against tyrosine hydroxylase, serotonin, or leu-enkephalin and compared the distribution of these nuclei to descriptions in mammals and other elasmobranchs. The majority of tyrosine hydroxylase-positive cells were found in the midbrain tegmentum (A8-A10) and the hypothalamus. In addition, putative A1, A2, A5, A7 (noradrenergic) groups were found in the metencephalon and myelencephalon. Serotonin-positive cells were found in raphe nuclei and scattered lateral to the raphe. We identified probable homologues to raphe pallidus, raphe obscurus, raphe magnus, and raphe centralis superior (B8) cell groups, which have been described in mammals. A cluster of cells dorsomedial to the medial longitudinal fasciculus was identified as raphe dorsalis. The distributions of leu-enkephalin and serotonin immunoreactive cells were similar to each other, but the tyrosine-hydroxylase immunoreactive cells rarely intermingle with the former two immunoreactive cell types. Other reticular groups that contained both serotonin- and leu-enkephalin-positive cells included reticularis (r.) ventralis, r. magnocellularis, r. paragigantocellularis lateralis, r. pontis caudalis, and r. pontis oralis medialis and lateralis. Thus, this shark contains many of the major brainstem raphe and catecholaminergic cell groups described for rats, but the relative distribution of the immunopositive cell groups differs in mammals and cartilaginous fish.

Animals↗

PubMed1991

Serotoninergic and enkephalinergic cell groups in the reticular formation of the bat ray and two skates.

The distribution of cells which were immunohistochemically positive for leu-enkephalin (LENK+) or serotonin (5-HT+), two substances widely distributed in the reticular formation, was determined in two species of skates (Raja binoculata and Raja rhina) and a bat ray (Myliobatis californica). The Rajoids are closely related to the Rhinobatoids which contains Platyrhinoidis, an elasmobranch that does not have a nucleus raphe dorsalis. Myliobatis was chosen for an outgroup comparison. Most of the nuclei that were 5-HT+ were also LENK+. The greatest number of labeled cells was in the hypothalamus bordering the third ventricle and in the neurointermediate lobe of the pituitary. The mesencephalon was rich in cells in the ventral tegmental area bordering the red nucleus. In both genera, there were numerous 5-HT+ and LENK+ fusiform cells paralleling the ventral surface of the metencephalon and myelencephalon. These cells were located in several reticular nuclei but were especially prominent in nucleus reticularis (n.r.) pontis oralis, n.r. magnocellularis, and n.r. paragigantocellularis lateralis. The latter nucleus contained fewer LENK+ than 5-HT+ cells. In both genera, 5-HT+ and LENK+ cells were located in raphe pallidus, raphe obscurus, raphe magnus, raphe centralis superior, and raphe linearis. Minor differences in distribution of the remaining 5-HT+ and LENK+ cell groups were found, but these representative elasmobranchs lack a dorsal raphe nucleus which, in mammals, is the largest serotoninergic group.

Animals↗

PubMed1991

Low-pressure-sensitive baroreceptor fibers recorded from rabbit carotid sinus nerves.

Activity was recorded from physiologically identified baroreceptor or chemoreceptor fibers in carotid sinus nerves of urethane-anesthetized spontaneously breathing rabbits. A carotid sinus area was vascularly isolated so that carotid sinus pressure and perfusion medium (Locke's solution or rabbit blood) could be controlled. The cervical sympathetic, vagus, and aortic depressor nerves were bilaterally cut to eliminate vagal and cardiopulmonary reflexes. Baroreceptor fibers could be divided into two groups: fibers with a mean firing threshold of 47.6 +/- 1.9 mm Hg and no activity below this threshold (37 fibers) and fibers that were active at low intrasinus pressures (18.1 +/- 2.2 impulses/sec at an intrasinus pressure of 0 mm Hg). The baroreceptor fibers that were spontaneously active at low pressures were also chemically sensitive: discharge rate was increased by 5-hydroxytryptamine (10 fibers, p less than 0.01), nicotine (10 fibers, p less than 0.01), or hypercapnia (13 fibers, p less than 0.001). The activity of baroreceptor fibers with a clear pressure threshold was usually decreased by hypercapnia (26 of 27 fibers, from 18.8 +/- 3.1 to 13.2 +/- 3.9 impulses/sec). Chemoreceptor fibers failed to respond to intrasinus pressure changes from 0 to 100 mm Hg (n = 25 fibers, p greater than 0.5) but were sensitive to chemical changes, as expected. Thus, there is a subset of baroreceptor fibers that, under certain conditions, is spontaneously active at very low intrasinus pressures and responds to changes in the chemical milieu.

Action Potentials↗

PubMed1990

Projections from the medial agranular cortex to brain stem visuomotor centers in rats.

Projections from medial agranular cortex to brain stem in rat were determined by use of the anterograde tracers Phaseolus vulgaris leucoagglutinin, or wheat germ agglutinin conjugated horseradish peroxidase. Axonal trajectories were also followed by means of the Wiitanen modification of the Fink-Heimer degeneration technique. AGm was identified on the basis of its cytoarchitectonics. AGm projected to the anterior pretectal nucleus, the rostral interstitial nucleus of the medial longitudinal fasciculus, the medial accessory oculomotor nucleus of Bechterew, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the nucleus cuneiformis and subcuneiformis, intermediate and deep superior collicular layers, the paramedian pontine reticular formation (reticularis pontis oralis and caudalis, and reticularis gigantocellularis), and raphe centralis superior. Differences in connections between rostral and caudal injections were observed: pontine and medullary projections were lighter from the rostral portion of AGm than from the more caudal portions of AGm. The heaviest projections to the anterior pretectal nucleus were from the caudal portion of AGm. The subcortical projections were very similar to those described for the frontal eye field in monkeys, and the majority of them targeted areas thought to be involved in coordination of gaze with head and neck movements. Thus AGm in rats may contain the homologue of the primate frontal eye fields.

Animals↗

PubMed1990

Effects of calcium channel antagonists on the vagally mediated cardiac chronotropic response in dogs.

A brief electrical stimulation of the vagus nerve may elicit a triphasic response comprising (i) an initial prolongation of the same or the next cardiac cycle, (ii) a return of the subsequent cardiac cycle to about the level prior to vagal stimulation, and (iii) a secondary prolongation of cardiac cycle length that lasts several beats. We compared the effects of two calcium channel antagonists, verapamil and nifedipine, on this triphasic response to vagal stimulation in chloralose-anesthetized, open-chest dogs. In the absence of vagal stimulation, nifedipine (doses of 10, 40, and 50 micrograms/kg for a total dose of 100 micrograms/kg, i.v.) and verapamil (two doses of 100 micrograms/kg each, i.v.) increased the cardiac cycle length (A-A interval) by 16% (429 +/- 20 to 496 +/- 21 ms) and 29% (470 +/- 33 to 605 +/- 54 ms), respectively. Nifedipine (100 micrograms/kg total) attenuated the initial vagally mediated prolongation of the A-A interval, from 474 +/- 19 to 369 +/- 42 ms above the basal A-A interval. Following the initial prolongation of the vagal effect, other A-A intervals were not affected. In contrast, verapamil potentiated the vagally mediated initial prolongation in cardiac cycle length at the first dose administered (100 micrograms/kg) from 492 +/- 17 to 561 +/- 14 ms, but other increases in dosages had no further effect. Thus these two calcium channel antagonists have different effects on the sinoatrial chronotropic responses caused by brief vagal stimulation.

Animals↗

PubMed1988

Verapamil potentiates vagally mediated atrioventricular chronotropic responses in dogs.

When the cervical vagus nerve is briefly stimulated, a triphasic cardiac chronotropic response ensues: the cardiac cycle length initially increases, then briefly decreases, and subsequently increases again. Verapamil, a calcium channel blocker, alters these responses to acetylcholine when the heart is in sinoatrial nodal rhythm. We investigated whether verapamil has a similar effect on parasympathetic modulation of the cardiac cycle when the heart is in atrioventricular rhythm. Atrioventricular rhythm was induced in anesthetized, open-chest dogs by infusion of sodium pentobarbital into the sinoatrial nodal artery. Verapamil was administered by bolus injection through a femoral vein. Verapamil accentuated the initial lengthening of the cardiac cycle by approximately 55% (from 301 to 466 ms). The acceleratory phase of this triphasic response and the secondary cardioinhibition were not significantly affected by verapamil. Thus, the initial action of acetylcholine at the atrioventricular node is potentiated by verapamil when the vagus is activated with brief stimuli.

Acetylcholine↗

PubMed1988

Autonomic modulation of atrioventricular conduction in ouabain-treated dogs.

There is a pronounced interaction between the two autonomic divisions in the control of some cardiac variables, e.g., heart rate and contractility; usually parasympathetic activation suppresses the sympathetic effects. There is controversy about whether a similar interaction occurs for atrioventricular (AV) conduction. We have previously been unable to describe such an interaction in adult dogs, although others found a sympathetic-parasympathetic interaction when the dog heart was paced at very short intervals (200-240 ms). We reasoned that a cardiac glycoside (ouabain 20 micrograms/kg iv), which accentuates the parasympathetic effect, might expose any autonomic interaction. The atrial and ventricular electrograms, heart period, and atrioventricular conduction time (A-A and A-V intervals) were measured in 18 anesthetized, open-chest adult dogs. The sinoatrial (SA) node was suppressed by injection of Nembutal (pentobarbital sodium) through the SA nodal artery, and the hearts were paced at 500- to 700-ms intervals. The sympathetic and vagus nerves were stimulated bilaterally at three levels before and after ouabain or a diluent was given. Data were analyzed by analysis of variance. We found that there was no significant sympathetic-parasympathetic interaction (P greater than 0.05) even after ouabain had potentiated the vagal effect by up to 100%. Thus, in dogs, control of AV conduction time by either autonomic division is independent of activity of the other divisions when the cycle length is not abbreviated.

Animals↗

PubMed1988

Evolution of the reticular formation.

The reticular formation of mammals contains numerous nuclei which can be recognized by their projection patterns, cytoarchitectonics, and neuropeptide/neurotransmitter content. We have identified reticular nuclei in representatives from numerous reptilian groups and ascertained presence or absence of these reticular nuclei in an attempt to use neuronal occurrence as a tool to determine phylogenetic relationships. Recently these studies have been extended to two elasmobranchs, a galeomorph shark and a ray. In this report, we concentrate on three medullary spinal projecting reticular nuclei, reticularis gigantocellularis, reticularis magnocellularis, and reticularis paragigantocellularis. We found that all three nuclei were present in rats, lizards, and elasmobranchs, but one nucleus was absent in crocodilians, and two nuclei were absent in turtles. Thus brain organization may give us clues to phylogenetic relationships. Moreover, these three reticular nuclei exhibited remarkably similar cellular morphology in mammals, reptiles, and elasmobranchs.

Animals↗

PubMed1986

Afferent and efferent components of the facial nerve in a frog, Rana pipiens.

The seventh cranial nerve in Rana pipiens is a slender nerve with limited peripheral distribution. We investigated the afferent and efferent components of this nerve by labeling its major branch, the hyomandibular, with horseradish peroxidase. The efferent portion of the seventh nerve originates from a small cell group in the upper medulla which contains two subdivisions. Afferent fibers carried in nerve VII travel in the solitary tract and the dorsolateral funiculus. The solitary component consists of a small number of ascending fibers that reach the level of the trigeminal nucleus and a large descending component that terminates slightly caudal to the obex in the commissural nuclei of the solitary complex. Afferent fibers also descend in the dorsolateral funiculus; many of these fibers cross dorsal to the central canal in the lower medulla. Most of the fibers in the dorsolateral funiculus terminate in the ipsilateral and contralateral dorsal horns and in nuclei of the dorsal column. A few ipsilateral fibers reach lower thoracic levels of the spinal cord.

Afferent Pathways↗

PubMed1986

Verapamil potentiates vagally mediated sinoatrial chronotropic responses in dogs.

A brief burst of electrical stimuli delivered to the vagus nerve during the cardiac cycle elicits a triphasic cardiac chronotropic response. The cardiac cycle length initially increases, then briefly decreases, and subsequently increases again. We studied the effects of a calcium channel blocking agent, verapamil, on these responses to vagal stimulation during sinoatrial nodal rhythm in anesthetized, open-chest dogs. Verapamil increased the basal cardiac cycle length only slightly; however, the primary cardioinhibition was accentuated approximately 40% (from 396 to 555 ms) by verapamil. Neither the acceleratory phase of this triphasic response nor the secondary cardioinhibition was significantly affected by verapamil. These results indicate that verapamil potentiates the initial action of acetylcholine at the sinoatrial node when the vagus is activated with brief stimuli.

Acetylcholine↗

PubMed1986

Sympathetic and periodic vagal influences on antegrade and retrograde conduction through the canine atrioventricular node.

Concurrent stimulation of the parasympathetic and sympathetic branches of the autonomic nervous system causes a diminished sympathetic response at high levels of vagal activity. This "accentuated antagonism" has been demonstrated for cardiac chronotropic, inotropic, and dromotropic responses. The effect on conduction was demonstrated with tonic stimulation of the vagus nerve. However, normally the vagus nerve fires periodically at certain times in the cardiac cycle. Thus, we have studied whether a similar interaction exists in the modulation of atrioventricular condition when short bursts of vagal stimulation were placed in various portions of the cardiac cycle. Anesthetized open-chest mongrel dogs were instrumented for stimulation of the cervical vagi and stellate ganglia when the heart was paced. We determined the relationship between cardiac cycle length, direction of action potential propagation, and levels of sympathetic and vagal activation and their effects on atrioventricular conduction times. All of the factors investigated, namely levels of vagal and stellate stimulation, pacing intervals, and direction of propagation of action potentials, affected atrioventricular conduction times. Furthermore, the vagal effect was greater at short cardiac cycle lengths. When bursts of vagal stimulation were timed to result in maximal or minimal prolongation of atrioventricular conduction, no significant effects of sympathetic-parasympathetic interaction on atrioventricular conduction times were apparent. However, an analysis of the differences in prolongation of atrioventricular conduction with periodic vagal stimulation revealed that a significant sympathetic-vagal interaction existed for these differences. Thus, autonomic neurotransmitters differentially affect cardiac conduction times depending on time of application of the stimulus.

Action Potentials↗

PubMed1984

Projections to the cardioinhibitory region of the nucleus ambiguus of rat.

The nucleus ambiguus is a brainstem structure which sends projections through the vagus nerve to the viscera, primarily heart, lung, and gut. The anatomical relationship between the nucleus ambiguus and other brain structures has not been elucidated nor has the cardiac region been identified physiologically in rats. We have attempted to clarify which areas of the nucleus ambiguus are cardioinhibitory and to determine other regions of the brain which send direct projections to this physiologically identified cardiac region. Stimulating electrodes were positioned stereotaxically in the medulla of anesthetized rats. Small currents were passed through the electrodes to locate regions in the ventrolateral medulla which slowed heart rate. In each rat, the area found was small (less than 200 micron in diameter), very specific, and located in the rostral portion of the nucleus ambiguus. Micro-quantities of horseradish peroxidase were then iontophoretically ejected into this brainstem area; 24-72 hours following the HRP injection, the rats were processed for HRP reaction product using the tetramethybenzidine method. The major brain area which sent projections to the rostral nucleus ambiguus was the ipsilateral medial subnucleus of the solitary tract. A few labeled cells were found in the ipsilateral ventrolateral subnucleus of the solitary tract, parabrachial complex, the paraventricular nucleus of the hypothalamus, and the contralateral nucleus ambiguus. Control injections in reticular areas surrounding the rostral nucleus ambiguus showed no label in the medial solitary nucleus.

Animals↗

PubMed1984

A horseradish peroxidase investigation of carotid sinus nerve components in the rat.

The brainstem location of afferent and efferent components in rat carotid sinus nerve (CSN) was determined by transecting the CSN and applying horseradish peroxidase. Afferent label was heaviest in the ipsilateral medial solitary nucleus ( mNTS ). Afferents were also found in the ipsilateral ventrolateral solitary nucleus, area postrema, and bilaterally in the commissural nucleus of the solitary complex. Efferent labeled cells were found in the ipsilateral rostral nucleus ambiguus and the inferior salivatory nucleus. The CSN afferents in the mNTS terminated rostral to neurons which project to the nucleus ambiguus thus implicating the existence of interneurons in the baroreceptor reflex pathway.

Animals↗

PubMed1984

Organization within the cranial IX-X complex in ranid frogs: a horseradish peroxidase transport study.

Cranial nerves IX and X in frogs have been described as originating from a nuclear group referred to as the IX-X complex. We studied the central nervous system components of this complex in Rana pipiens and R. catesbiana by labeling peripheral branches of cranial nerves IX and X and identifying the central nervous system contributions of these branches. Various peripheral nerves (IX and the cardiac, gastric, pulmonary, and laryngeal branches of X) were identified and soaked in horseradish peroxidase (HRP). One to 2 weeks later, the frogs were killed and processed for HRP by the tetramethylbenzidine method. Glossopharyngeal efferents originated from a small ventrolateral cell group found at the level of IX root exit. Vagal efferents formed a single column of cells in a ventrolateral position from the level of the brainstem exist of the vagus nerve (approximately 2,000 micrometers above the obex) to 200 micrometers below the obex (values given are for an 80-g frog). This cell group was separate from and just caudal to efferent cells of the glossopharyngeal nerve. Within the vagal portion of the column, cells projecting through the gastric branch were found throughout the rostral-caudal extent of the nucleus. "Cardiac" cells tended to be more rostral than "pulmonary" cells, and both groups of cells were located in the middle of the nucleus. "Laryngeal" cells were located more caudally in the nucleus. This peripheral representation within the vagal nucleus corresponds more closely to the organization found in the mammalian nucleus ambiguus, rather than to the apparent lack of organization found in the mammalian dorsal motor nucleus. Afferents of IX and X entered slightly rostral to the ventral roots of their respective nerves and descended in two tracts. The majority entered the tractus solitarius and descended in a medial position to cervical spinal cord. A portion of the afferents from the vagus nerve crossed the midline in the lower myelencephalon just dorsal to the central canal and ascended a short distance on the contralateral side. Within the solitary tract, vagal afferents were located in a ventrolateral position as they descended to below the obex. Glossopharyngeal afferents filled the remainder of the tract. A smaller portion of afferents from both IX and X did not enter the solitary tract but descended in the spinal tract of V and the dorsolateral funiculus of the spinal cord (Lissauer's tract) to thoracic levels. Afferents of IX also formed a rostral bundle which extended in the solitary tract to the caudal metencephalon.

Animals↗

PubMed1983

Afferent and efferent components of the hypoglossal nerve in the grass frog, Rana pipiens.

In amphibians, the spinomedullary region of the central nervous system is compressed rostrocaudally because of the absence of a neck. In Ranid frogs, the hypoglossal nerve emerges as the ventral ramus of the second spinal nerve. The first spinal nerve, though present in tadpoles, is absent as a separate nerve in adults. To investigate the central nervous system components of the hypoglossal nerve in Rana pipiens, we soaked identified, transected branches of this nerve in horseradish peroxidase, a retrograde and anterograde tracer. We found that the hypoglossal nerve in these frogs originates from two efferent nuclei located in the caudal medulla, a medial and a lateral one. Afferent fibers, primarily from the tongue, are also found in the hypoglossal nerve and travel in the dorsolateral funiculus of the spinal cord, descending to thoracic levels of the cord. Efferents to intrinsic tongue muscles and the genioglossus muscle originate in the medial medullary nucleus. Efferents to the sternohyoid muscle, which travel through the hypoglossal nerve, originate in the lateral medullary nucleus. Since in mammals the sternohyoid muscle is innervated by the first spinal nerve, we have obtained experimental evidence that the hypoglossal nerve in Rana pipiens contains components of this spinal nerve.

Afferent Pathways↗

PubMed1983

Effects of digoxin on the control of heart rate and atrioventricular conduction in the dog.

The effects of digoxin on the chronotropic and dromotropic responses of the heart to autonomic neural stimulation were determined in anaesthetised, open chest dogs. Digoxin did not alter the negative chronotropic response of the heart to vagal stimulation. In contrast, digoxin reduced the positive chronotropic response to sympathetic stimulation by 40%. There was a pronounced vagal-sympathetic interaction such that the positive chronotropic response to strong sympathetic stimulation was attenuated by 72% when a near maximal vagal stimulation was delivered concurrently. However, digoxin did not alter this autonomic interaction. In addition, digoxin did not alter the positive dromotropic response evoked by the sympathetic stimulation. In contrast, digoxin potentiated the increase in A-V conduction time evoked by vagal stimulation (10 Hz) by 147%. No significant vagal-sympathetic interaction in the autonomic control of the dromotropic response was observed; ie, the responses of A-V conduction to combined sympathetic and vagal stimulation were essentially the algebraic sum of the responses to the individual stimulations. This lack of autonomic interaction in modulating A-V conduction time was not altered by digoxin, despite its potentiation of the dromotropic response to vagal stimulation.

Animals↗

PubMed1982

Cardiac vagal preganglionic fibers in neonatal rats: a comparison with cervical vagal components.

Origins of cardiac innervation were determined by injection of horseradish peroxidase (HRP) into the myocardium of rats. Bilaterally labeled efferent cells in the brainstem were found in the rostral nucleus ambiguus (NA) with fewer cells in the dorsal motor nucleus (DMN). No afferent labeling was seen. In young rats, but not in adults, there was labeling in the ventral horn of the cervical spinal cord. A unilateral vagotomy prior to the HRP injection resulted in labeled cells in the brainstem contralateral to the vagotomy while cells in the spinal cord remained bilateral. Thus the label in these spinal cord cells may represent HRP uptake by fibers of passage. These results were compared to the afferent and efferent vagal components of the entire cervical vagus nerve.

Animals↗

PubMed1982

Vagal control of heart period in alloxan diabetic rats.

Autonomic neuropathies are a frequent complication to diabetes in humans. Similar neuropathies have not been well-documented in animal models. To determine if diabetic rats would develop parasympathetic neuropathies, rats were made diabetic by the injection of alloxan into the tail vein and then maintained on daily injections of insulin. At various times subsequent to the induction of diabetes (3-5 weeks, 7-9 weeks, and 14 weeks), the effect of constant frequencies of vagal stimulation on the efferent cardiac chronotropic response was evaluated using analysis of variance techniques. It was found that the vagal parasympathetic effect was accentuated in diabetic rats. That is, at a given frequency of supramaximal vagal stimulation, the heart rate slowed more in diabetic rats than in nondiabetic rats. Whether a similar phenomenon exists in humans is not known.

Analysis of Variance↗