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Biomedical subjects

D A Hopkins

Publications and source records attributed to D A Hopkins.

At least 73 records · Page 4Linked to original sources
PubMed1985

Ultrastructural studies of the nucleus ambiguus in cat and monkey following injection of HRP into the vagus nerve.

The fine structure of retrogradely labelled neurons in the nucleus ambiguus (NA) has been examined in cat and monkey (Macaca fascicularis) following injections of horseradish peroxidase (HRP) into the vagus nerve. Many retrogradely labelled neurons were observed in the NA although unlabelled neurons were also present within the boundaries of the NA as identified by the distribution of retrogradely labelled cells. In both species a wide range of sizes of labelled neurons (20-60 microns in long axis) was observed from rostral to caudal levels of the NA. Large labelled neurons were generally oval or spindle-shaped while smaller neurons were oval in cross-section. Unlabelled neurons observed among labelled NA neurons tended to be smaller on average than the labelled neurons and ranged in size from 15 to 30 microns in long axis. The unlabelled neurons typically had nuclei which were more invaginated than those of the labelled neurons. Quantitative analyses of the synaptic organization in the NA revealed high proportions of terminals containing round vesicles and making asymmetrical or symmetrical contact with the somata in both monkey and cat. Terminals containing pleomorphic vesicles and making symmetrical contact with somata were slightly less numerous. Retrogradely labelled neurons exhibited a positive correlation between the size of neuron and density of synapses on the surface. There tended to be a greater synaptic density on monkey NA neurons than on cat NA neurons of comparable size.

Accessory Nerve↗
PubMed1985

Axonal branching of canine sympathetic postganglionic cardiopulmonary neurons. A retrograde fluorescent labeling study.

In 11 dogs fluorescent retrograde tracers were injected into physiologically identified left-sided sympathetic cardiopulmonary nerves. When two different ipsilateral cardiopulmonary nerves were injected, labeled cells from each injected nerve had overlapping distributions in the middle cervical and stellate ganglia. Most retrogradely labeled neurons were located in the middle cervical ganglion and cranial pole of the stellate ganglion. Following the injection of two different tracers into two different nerves, some neurons in the middle cervical ganglion were retrogradely labeled with two tracers. Double-labeled neurons were rarely found in the stellate ganglion. There were areas within the ganglia in which labeled neurons projected predominantly to one cardiopulmonary nerve. In the thoracic autonomic nervous system Fast Blue was transported most effectively. Bisbenzimide was not transported as well as Fast Blue and Nuclear Yellow was very poorly transported in cardiopulmonary nerves. The results demonstrate that some efferent postganglionic sympathetic neurons project axons into at least two different cardiopulmonary nerves and that an anatomical substrate for axo-axonal reflexes exists in the thoracic sympathetic nervous system.

Animals↗
PubMed1985

Transnuclear transport and axon collateral projections of the mamillary nuclei in the rat.

Transnuclear transport of horseradish peroxidase (HRP) and wheat germ agglutinin-HRP conjugate (WGA-HRP) and the retrograde transport of fluorescent tracers were used to study axon collaterals of neurons in the mamillary nuclei. Tracers were injected into the thalamus or brain stem and after 18 hour-5 day survival periods, the brains were processed for fluorescence microscopy or for light and electron microscopic HRP histochemistry. Neurons in all divisions of the ipsilateral mamillary nuclei projected to both the thalamus and tegmentum. After HRP and WGA-HRP injections, anterogradely labeled axon terminals were observed in the known projection fields of the mamillary nuclei. Mamillary neurons were characterized by deeply invaginated, eccentrically located nuclei. Most labeled terminals of axon collaterals in the contralateral anterodorsal thalamic nucleus and dorsal and ventral tegmental nuclei contained round vesicles and formed asymmetrical synapses with somata and dendrites. The present results demonstrate that transnuclear transport of HRP and WGA-HRP can be used to study the connectivity and ultrastructure of axon collaterals and their cells of origin in the central nervous system in a manner comparable to that of transganglionic transport in the peripheral nervous system.

Animals↗
PubMed1984

Localization of sympathetic postganglionic and parasympathetic preganglionic neurons which innervate different regions of the dog heart.

The locations of sympathetic postganglionic and parasympathetic preganglionic neurons projecting to the heart have not yet been clearly established. Therefore, aliquots of horseradish peroxidase (HRP) were injected into specific regions of the heart, intraventricular cavity, pericardial sac, aortic arch, and the skin in 27 dogs. Following injections into the heart, aorta, or pericardial sac, retrogradely labeled neurons were present in the greatest numbers in the middle cervical ganglia bilaterally. Labeled neurons were located in the cranial poles of the stellate ganglia bilaterally and occasionally in the superior cervical ganglia. Labeled cells were also found in small ganglia located along cardiopulmonary nerves. Injections of HRP into specific areas of the heart did not result in labeling of cells in specific loci of the thoracic or cervical sympathetic ganglia. When the ansae were cut on one side, no labeled cells were found in the ipsilateral stellate ganglion or upper thoracic chain. Following injections into the skin of the left elbow or left cranial nipple, labeled cells were found in the stellate ganglia and the sympathetic chain and in one case in the middle cervical ganglion as well. These data suggest that postganglionic sympathetic neurons which project efferent axons to a specific cardiac region are not located in a specific region of a sympathetic ganglion or a specific sympathetic ganglion. Rather, neurons in one region of a sympathetic ganglion project axons to widespread areas of the myocardium. Sympathetic postganglionic neurons in the stellate ganglion or sympathetic chain project their axons to the heart via the subclavian ansae or interganglionic nerves, not via nerves arising directly from the sympathetic chain. Small numbers of labeled neurons were found in the medulla oblongata, thus indicating that in comparison to sympathetic postganglionic neurons relatively few preganglionic parasympathetic neurons project directly to the heart. When labeled cells were present in the medulla, the majority were located in the ventrolateral nucleus ambiguus.

Animals↗
PubMed1984

Brainstem cells of origin of the cervical vagus and cardiopulmonary nerves in the neonatal pig (Sus scrofa).

The distribution of the cells of origin of the cervical vagus and cardiopulmonary nerves has been studied in neonatal piglets (Sus scrofa) ranging in age from 1 to 60 days. Cardiopulmonary nerves were identified physiologically and anatomically prior to injection of horseradish peroxidase (HRP) into the nerves. Following injection of HRP into the cervical vagus nerve retrogradely labeled neurons were present in the dorsal motor nucleus of the vagus nerve (DMV), the nucleus of the solitary tract, the nucleus ambiguus (NA), ventrolateral to the NA and in an intermediate zone between the DMV and the NA. Two unique clusters of neurons were also retrogradely labeled after injections into the vagus nerve. One group was located lateral to the most caudal levels of the DMV and extended as far caudally as the C1 spinal segment. The second distinctive group was located ventrolateral to the nucleus ambiguus in a cell column identified as the ventrolateral nucleus ambiguus (VLNA). After injections of HRP into cardiopulmonary nerves, the majority of neurons were found in the VLNA and the distinct clusters of neurons in this cell column were particularly heavily labeled. Small numbers of cells were labeled in the DMV and NA and none were labeled in the solitary nucleus after cardiopulmonary nerve injections. There were no apparent age-related differences in the degree or distribution of retrograde labeling. The distribution of neurons in the medulla oblongata projecting into cardiopulmonary nerves in the piglet is similar to that described in other species, i.e., the nucleus ambiguus, particularly its ventrolateral cell column, is the primary site of cardiomotor neurons. In addition, in the piglet there is a morphologically distinct cluster of cells related to the heart, and possibly the lungs, which does not appear to be present in other species.

Animals↗
PubMed1984

Light and electron microscopic demonstration of hypothalamic projections to the parabrachial nuclei in the cat.

Hypothalamic connections with the parabrachial nuclei in the cat were studied at light and electron microscopic levels following wheat germ agglutinin-horseradish peroxidase injections into the parabrachial nuclei and electrolytic lesions in the hypothalamus. The greatest concentration of retrogradely labeled neurons occurred in the paraventricular nucleus. Labeled neurons were also seen within the preoptic, anterior, lateral, dorsomedial and ventromedial hypothalamic nuclei. Hypothalamic lesions resulted in the degeneration of terminals forming axosomatic and axodendritic synapses in the parabrachial nuclei, particularly its lateral division. These findings support the idea that hypothalamic connections to specific regions of the parabrachial nuclei may underlie the topographical functional organization demonstrated for these brainstem nuclei.

Amygdala↗
PubMed1984

Cardiac responses to stimulation of discrete loci within canine sympathetic ganglia following hexamethonium.

In dogs which had been administered hexamethonium, localized stimulation with bipolar electrodes in the middle cervical and stellate ganglia as well as ganglia in the caudal pole nerve and ventral ansa elicited alterations in cardiodynamics. The middle cervical and stellate ganglia were divided into 30 discrete regions in order to provide a standardized map of these ganglia. Of all the responses elicited. 5% consisted of increased heart rate while 38% consisted of augmented inotropism without accompanying chronotropic changes. Both rate and force were augmented in 57% of the responses. The sites in which stimulation consistently elicited chronotropic responses were located in right-sided ganglia. Loci which consistently generated force changes on stimulation were in the middle cervical and stellate ganglia bilaterally. Cardiac chronotropism and inotropism were augmented by stimulation of ganglia located in the ventral subclavian ansae or the left caudal pole nerve. No cardiac responses were elicited by stimulation within the superior cervical ganglia. It is concluded that localized stimulation of specific sites in the major thoracic ganglia or smaller mediastinal ganglia can alter cardiac chronotropism and/or inotropism.

Animals↗
PubMed1983

Direct amygdaloid projections to the dorsal motor nucleus of the vagus nerve: a light and electron microscopic study in the rat.

The projections from the central nucleus of the amygdala to the dorsal vagal complex were examined in the rat by means of anterograde and retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase and anterograde degeneration. Light microscopic findings confirmed that the amygdala projects to the dorsal motor nucleus (DMV) and the nucleus of the solitary tract. Electron microscopic experiments demonstrated degenerating axosomatic and axodendritic terminals in the DMV following electrolytic lesions in the central nucleus of the amygdala.

Afferent Pathways↗
PubMed1982

Reciprocal connections between the amygdala and parabrachial nuclei: ultrastructural demonstration by degeneration and axonal transport of horseradish peroxidase in the cat.

An ultrastructural analysis of the connections of the amygdala with the parabrachial nuclei (PBN) was carried out after electrolytic lesions or injections of horseradish peroxidase in the amygdala. Degenerating and labeled terminals originating from the amygdala formed axosomatic and axodendritic synapses in the PBN. In some instances, anterogradely labeled terminals synapsed with retrogradely labeled neurons. These results demonstrate that the amygdala and PBN have close reciprocal synaptic connections.

Amygdala↗
PubMed1982

Ultrastructural identification of labeled neurons in the dorsal motor nucleus of the vagus nerve following injections of horseradish peroxidase into the vagus nerve and brainstem.

The efferent connections of two types neurons in the dorsal motor nucleus of the vagus nerve (DMV) were studied in the cat by light and electron microscopy following horseradish peroxidase (HRP) injections into the cervical vagus nerve or brainstem. After injections of HRP into the vagus nerve, up to 80% of medium-sized neurons averaging 26 x 20 micrometers in 1-micrometer-thick sections were retrogradely labeled while no small neurons were labeled in the DMV. Incubation with either diaminobenzidene (DAB) or p-phenylenediamine-pyrocatechol (PPD-PC) chromogens yielded electron-dense reaction products localized mainly in lysosomes. Identification of label at the ultrastructural level was facilitated by omitting lead citrate staining and by counting numbers of lysosomes, which were higher in labeled neurons. Quantitative comparisons of the dimensions of labeled and unlabeled somata demonstrated that retrograde transport and incorporation of HRP had no effect on cell size within the 2-3-day survival times used in this study. In order to determine whether neurons in the DMV project to higher levels of the brain stem, large injections of HRP (1-3 microliters) were made into the pons, mesencephalon, hypothalamus, and amygdala. After injections of HRP into the brainstem, only small neurons, measuring 17 x 10 micrometers, were retrogradely labeled. Approximately 90% of the small neurons remained unlabeled following the HRP injections. The ultrastructural features of the labeled small neurons included an invaginated nucleus, low cytoplasmic/nuclear ratio, and relatively fewer organelles than the medium-sized neurons. A quantitative analysis of labeled and unlabeled small neurons demonstrated that the labeled neurons were significantly larger than the unlabeled small neurons. Thus, two populations of small neurons may exist in the DMV. One population appears to have ascending projections to higher levels of the brainstem while the other more numerous population may be interneurons or project for only short distances.

Amygdala↗
PubMed1982

The ultrastructure of the subnucleus gelatinosus of the nucleus of the tractus solitarius in the cat.

The dorsomedial region of the nucleus of the tractus solitarius termed the subnucleus gelatinosus (SNG) was studied at the light and electron microscopic level in the cat. In cresyl violet and luxol fast blue stained sections the SNG contained small neuronal somata that were scattered throughout a pale-staining neuropil containing few myelinated fibers. These neurons were difficult to impregnate with Golgi staining techniques, but in successful impregnations the somata were observed to be 10--19 micrometers in diameter and bore few sparsely branching primary dendrites. Spines were present on the dendrites of some neurons and were more numerous on distal portions of the dendritic tree. Ultrastructural examination of the SNG revealed that the neuronal complement consisted of round, oval, or spindle shaped neurons with little or no organized Nissl substance. Rare myelin-like ensheathments of neuronal perikarya were also observed. Bundles of fine unmyelinated axons that coursed mainly longitudinally were a prominent feature of the area. The most common type of axon terminal observed contained mainly round clear vesicles, approximately 31 nm in diameter, and made asymmetrical synaptic contact with a dendritic profile. Pleomorphic vesicle-containing terminals involved in symmetrical synaptic contact were also commonly seen. Axodendritic and axosomatic synapses were associated with terminals containing either round clear vesicles or pleomorphic vesicles. Less commonly, dendrodendritic and dendrosomatic synapses were seen, the presynaptic elements of which contained pleomorphic vesicles. Following removal of a nodose ganglion, degenerating terminals of vagal afferent fibers were observed throughout the neuropil. Such terminals contained round, clear vesicles with an occasional large, dense-cored vesicle, and made axodendritic and axosomatic synaptic contacts.

Animals↗
PubMed1982

Physiological studies of canine sympathetic ganglia and cardiac nerves.

Anatomical studies have indicated that the middle cervical ganglion is the primary locus of sympathetic postganglionic neurons which have axons projecting in canine cardiac nerves. Small regions of thoracic sympathetic ganglia were stimulated electrically with bipolar electrodes and the generated compound action potentials were recorded from ipsilateral cardiac nerves. Several procedures were used to distinguish the effects of stimulating preganglionic axons, ganglionic sites and postganglionic axons. Following hexamethonium it was found that only low frequency stimulation (e.g. 1 Hz) of ganglionic sites resulted in the generation of compound action potentials in cardiac nerves. These ganglionic sites were located throughout the middle cervical ganglion, but only in the cranial medial pole of the stellate ganglion. Stimulation of a single locus in a stellate or middle cervical ganglion generated compound action potentials in all major ipsilateral sympathetic cardiac nerves. A ganglion was also identified at the junction of the thoracic vagus and the cranial vagal nerve which may be as important as the right stellate ganglion in cardiac regulation. These results demonstrate that there are discrete loci in thoracic ganglia which contain neurons projecting in several ipsilateral cardiac nerves. Low frequency stimulation of these loci was found to be optimal for generation of compound action potentials.

Animals↗
PubMed1982

Medullary cells of origin of physiologically identified cardiac nerves in the dog.

Individual cardiac nerves from which stimulation elicited cardioinhibition (bradycardia and negative inotropism) were identified in 24 of 38 dogs. Subsequently, 3-25 microliters of 30% horseradish peroxidase (HRP) were injected into an identified cardiac nerve. After a 3-day survival period, the medulla oblongata was processed for HRP histochemistry. Retrograde labeling was observed to be concentrated primarily in the ipsilateral nucleus ambiguus (NA) and in medium-sized neurons located ventral and lateral to the larger neurons of the principal NA cell column. This latter location was so characteristic that it has been designated the ventrolateral nucleus ambiguus (VLNA). Labeled neurons were found at all levels of the NA and VLNA and their distribution was similar irrespective of the cardiac nerve injected. Relatively few labeled neurons were observed in the dorsal motor nucleus of the vagus nerve (DMV) except after injections into the left and right recurrent cardiac nerves and the left cranial vagal nerve. In some dogs labeled cells were present only in and ventrolateral to the NA and not in the DMV, even though stimulation of the injected nerve elicited both bradycardia and negative inotropism. These results demonstrate that ventrolateral regions of the NA represent the major site of cardioinhibitory motor neurons in the dog that they can regulate both rate and force.

Afferent Pathways↗
PubMed1981

Localization of sympathetic postganglionic neurons of physiologically identified cardiac nerves in the dog.

Cardiac nerves were identified physiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labelphysiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labelphysiologically and injected with horseradish peroxidase in 38 dogs. Retrogradely labeled neurons were present in the greatest number in the middle cervical ganglion, whereas fewer labeled neurons were present in the stellate ganglion. Only occasional neurons in the superior cervical ganglion were labeled, and no labeled cells were found in the T3 to T6 paravertebral ganglia or in the ganglia contralateral to the nerve injected. following injections into specific cardiac nerves, retrograde labeling was widespread within the middle cervical ganglion, and the distributions of labeled neurons from different nerves overlapped considerably. In the middle cervical ganglion there was little or no regional grouping of cells projecting to specific cardiac nerves. within the stellate ganglion, however, te cardiac-sympathetic cells were clustered primarily at the cranial pole near toe origin of the ventral and dorsal ansae. Mediastinal ganglia and ganglia located in cardiac nerves were frequently as heavily labeled as the ipsilateral stellate ganglion. The occurrence of heavy labeling in mediastinal and cardiac nerve ganglia indicates that these hitherto unreported ganglia play a significant role in cardiac neural regulation. These data imply that the organization of sympathetic neurons controlling the heart is much more complex than has previously been considered.

Animals↗
PubMed1981

A light and electron microscopic study of the dorsal motor nucleus of the vagus nerve in the cat.

The morphology of the dorsal motor nucleus of the vagus nerve (DMV) in the cat was studied with the aid of light and electron microscopy. In frozen sections stained by the Kluver-Barrera method or stained to show retrograde labeling in the DMV following injections of horseradish peroxidase (HRP) in the cervical vagus nerve and the stomach wall a range of sizes of DMV neurons was observed but it was observed but it was not possible to distinguish separate types. In contrast, two distinct types of neurons, one medium-sized and the other small, were identified with the light microscope in Golgi-Cox and 1-micrometer Epon sections and with the electron microscope in ultrathin sections. The medium-sized neurons had a range of sizes but generally measured 18 X 25 micrometers and possessed three to four proximal dendrites which branched two or three times. Spines were observed occasionally on the soma and on dendrites. These neurons contained a well-developed cytoplasm and a noninvaginated round to oval nucleus. The small neurons generally measured 9 X 14 micrometers and were round or slightly elongated in shape. Their dendritic processes were fewer and thinner than those of the medium-sized neurons and extended for shorter lengths. Their soma contained scanty cytoplasm and an invaginated nucleus. The medium-sized neurons outnumbered the small neurons by more than three to one but both neuronal types were distributed evenly throughout the nucleus. The medium-sized neurons seemed to correspond in size to the parasympathetic efferent neurons of the viscera as indicated by the HRP studies. Axosomatic synapses on both types of neurons and axodendritic synapses were observed in the DMV. Terminals containing mainly small clear round vesicles and making asymmetrical contract with the postsynaptic membrane were involved in the majority of synapses on both the soma and dendrites. Terminals containing predominantly pleomorphic vesicles and making symmetrical contact with the postsynaptic membrane were also common, comprising up to one-third of all synapses observed. Serial sections revealed that most synaptic terminals contained varying numbers of large (75--110 nm) dense-cored vesicles. Smaller dense-cored vesicles (45--55 nm) were sometimes observed, often close to the area of synaptic contact. Terminals 1--2 micrometers in diameter which contacted dendrites 1--3 micrometers in diameter formed the most common synaptic combination throughout the rostral to caudal extent of the DMV. No distinct regional differences were observed with respect to distribution of synaptic types.

Afferent Pathways↗
PubMed1979

Gastric afferents to the nucleus of the solitary tract in the cat.

Afferent projections of the vagus nerve (X) were investigated following nodose ganglion injections of [3H]leucine or horseradish peroxidase (HRP) and stomach wall injections of HRP. Ganglionic injections demonstrated a projection to the solitary nucleus (SN) including the part designated as the area subpostrema (ASP). A projection to the area postrema was also seen following [3H]leucine injections. Stomach wall injections of HRP labelled fibres and terminals bilaterally in the ASP and more ventral parts of the SN. These results provide the first morphological evidence of gastric afferents of X projecting to an area of the SN previously implicated in gastric functions.

Animals↗
PubMed1978

Amygdaloid projections to the mesencephalon, pons and medulla oblongata in the cat.

Amygdalotegmental projections were studied in 26 cats after injections of horseradish peroxidase (HRP) in the diencephalon, midbrain and lower brain stem and in 6 cats after injection of 3H-leucine in the amygdala. Following HRP injections in the posterior hypothalamus, periaqueductal gray (PAG) and tegmentum many retrogradely labeled neurons were present in the central nucleus (CE) of the amygdala, primarily ipsilaterally. Injections of HRP in the posterior hypothalamus and mesencephalon also resulted in the labeling of neurons in the basal nucleus, pars magnocellularis. Following 3H-leucine injections in CE and adjacent structures autoradiographically labeled fibers were present in the stria terminalis and ventral amygdalofugal pathways. In the mesencephalon heavily labeled fiber bundles were located lateral to the red nucleus. Labeled fibers and terminals were distributed to the mesencephalic reticular formation, substantia nigra, ventral tegmental area and PAG. In the pontine and medullary tegmentum the bulk of passing fibers was located laterally in the reticular formation. Many labeled fibers and terminals were distributed to the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus and lateral tegmental fields. Many terminals were also present in the solitary nucleus and dorsal motor nucleus of the vagus nerve. The location of the cells of origin and the distribution of the terminals of the amygdalotegmental projection suggest that this pathway plays an important role in the integration of somatic and autonomic responses associated with affective defense.

Amygdala↗