Biomedical subjects

T E Benson

Publications and source records attributed to T E Benson.

26 records · Page 2Linked to original sources

PubMed1991

Unmyelinated axons of the auditory nerve in cats.

This paper describes some central terminations of type II spiral ganglion neurons as labeled by extracellular injections of horseradish peroxidase (HRP) into the auditory nerve of cats. After histological processing with diaminobenzidine, both thick (2-4 microns) and thin (0.5 microns) fibers of the auditory nerve were stained. Whenever traced, thick fibers always originated from type I spiral ganglion neurons and thin fibers always from type II ganglion neurons. Because the labeling of type II axons faded as fibers projected into the cochlear nucleus, this report is limited to regions of the ventral cochlear nucleus near the auditory nerve root. The central axons of type II neurons are unmyelinated, have simple yet variable branching patterns in the cochlear nucleus, and form both en passant and terminal swellings. Under the light microscope, most swellings are located in the neuropil but they are also found in the vicinity of cell bodies, nodes of Ranvier of type I axons, and blood vessels. Eighteen en passant swellings in the neuropil were located by light microscopy and resectioned for electron microscopy; two of these swellings exhibited ultrastructural features characteristic of chemical synapses. The data indicate that inputs from outer hair cells might be able to influence auditory processing in the cochlear nucleus through type II primary neurons.

Animals↗

PubMed1990

Synapses formed by olivocochlear axon branches in the mouse cochlear nucleus.

Cochlear nucleus branches of thick olivocochlear axons were labeled by injections of horseradish peroxidase into the spiral ganglion of the cochlear basal turn in mice. Six labeled axons were traced by light microscopy, and selected portions of seven branches were sectioned serially for electron microscopic examination. Axonal branches most frequently terminated near certain granule cell regions of the ventral cochlear nucleus. This article describes terminals, synapses, and postsynaptic elements of these olivocochlear branches. The olivocochlear branches had both terminal and en passant boutons that contained round vesicles and made asymmetric synapses with other neuronal processes. About a quarter of the synapses also possessed additional specializations, postsynaptic, or subjunctional bodies. Mossy terminals, a multisynaptic type of terminal commonly found in granule cell regions, were not found arising from any of the labeled branches. No somatic synapses were found, although contacts with cell bodies were occasionally observed. The predominant synaptic target of olivocochlear branches were what appeared to be dendrites of large diameter. At least some of these large dendrites received multiple synapses from a single labeled olivocochlear branch. The morphological characteristics of reconstructed dendrites suggest that multipolar cells might be predominant targets for the medial olivocochlear system in the cochlear nucleus. This was demonstrated in one case in which a large dendrite was followed to its cell body of origin.

Animals↗

PubMed1988

Brainstem branches from olivocochlear axons in cats and rodents.

Horseradish peroxidase was used to label axons of olivocochlear (OC) neurons by intracellular injections in cats and extracellular injections in rodents. These axons arise from cell bodies in the superior olivary complex and project to the cochlea. En route to the cochlea, the thick axons (greater than 0.7 micron diam.) of medial olivocochlear (MOC) neurons formed collaterals that terminated in the ventral cochlear nucleus, the interstitial nucleus of the vestibular nerve (in cats), and the inferior vestibular nucleus (in rodents). The thin axons (less than 0.7 micron diam.), presumed to arise from lateral olivocochlear (LOC) neurons, did not branch near the CN. Within the CN, the MOC collaterals tended to ramify in and near regions with high densities of granule cells, regions also associated with the terminals of type II afferent axons (Brown et al.: J. Comp. Neurol. 278:581-590, '88). These results suggest that those fibers associated peripherally with outer hair cells (MOC efferents and type II afferents) are associated centrally with regions containing granule cells, whereas those fibers associated with inner hair cells peripherally (LOC efferents and type I afferents) are not.

Afferent Pathways↗

PubMed1986

Projection of septal organ receptor neurons to the main olfactory bulb in rats.

The septal organ of Masera is a distinct patch of olfactory epithelium on the septal wall of the nasal cavity. It lies ventral to the main olfactory receptor sheet. Central projections of the septal organ to the main and/or accessory olfactory bulb were studied with punctate HRP injections into the posterior dorsomedial olfactory bulb of rat pups. Injection sites encompassed 2-8% of the main olfactory bulb glomeruli and some injection sites were confined to the accessory olfactory bulb glomeruli. The distribution of receptor neurons in the septal organ that were labeled as a result of retrograde transport from the injection sites was determined. Olfactory receptor neurons were labeled in septal organs of those animals with injection sites confined to the main olfactory bulb. Subsequent to the posterior dorsomedial bulbar injections of this study, labeled receptor neurons were preferentially located in the posterior portion of the septal organ and were clustered about a plane dorsal to the plane bisecting the organ. Injections confined to the accessory olfactory bulb only labeled vomeronasal organ receptor neurons. Thus it is likely that the main olfactory bulb and not the accessory olfactory bulb is the bulbar terminus of septal organ receptor neurons. To date, experimental evidence suggests that the septal organ system may comprise an anatomically and functionally unique chemosensory pathway for odor detection.

Animals↗

PubMed1985

High-resolution 2-deoxyglucose autoradiography in quick-frozen slabs of neonatal rat olfactory bulb.

We have used rapid freezing and freeze-substitution fixation to permit electron microscopic study of [3H]2-deoxyglucose autoradiographs. The techniques minimize diffusion of label into processing fluids and, by inference, migration of label within tissue. Slabs of olfactory bulbs from 12-day-old rats were quick-frozen after one hour of exposure to physiological olfactory stimuli. In light microscopic autoradiographs at low magnification, the neuropil of individual olfactory glomeruli appeared uniformly labeled with different levels of labeling in different glomeruli. At higher magnification, glomerular neuropil labeling consisted of small unlabeled regions surrounded by label clusters, suggesting greater deoxyglucose uptake by olfactory nerve terminals as compared with their postsynaptic dendrites. Periglomerular neurons were labeled differentially. Some microglia and glia precursor cells were heavily labeled in all bulbar laminae. The ultrastructure of cells and neuropil in all bulbar laminae was well-preserved. Cell processes and organelles could be identified in both stained sections and unstained electron microscopic autoradiographs. These experiments demonstrate the feasibility of combining quick-freezing with freeze substitution, in order to extend the resolution of studies using diffusable tracers such as 2-deoxyglucose. The results suggest that this is a promising method for assessing several controversies concerning deoxyglucose incorporation and neuronal and glial metabolism.

Animals↗

PubMed1984

Specific olfactory receptor populations projecting to identified glomeruli in the rat olfactory bulb.

A critical gap exists in our knowledge of the topographical relationship between the olfactory epithelium and olfactory bulb. The present report describes the application to this problem of a method involving horseradish peroxidase conjugated to wheat germ agglutinin. This material was iontophoretically delivered to circumscribed glomeruli in the olfactory bulb and the characteristics and distribution of retrogradely labeled receptor cells were assessed. After discrete injections into small glomerular groups in the caudomedial bulb, topographically defined populations of receptor cells were labeled. Labeled receptor cell somata appeared at several levels within the epithelium. The receptor cell apical dendrites followed a tight helical course towards the surface of the epithelium. The data thus far demonstrate that functional units within the olfactory system may include not only glomeruli as previously suggested but, in addition, a corresponding matrix of receptor cells possessing functional and topographical specificity.

Animals↗

PubMed1984

Effects of sensory deprivation on the developing mouse olfactory system: a light and electron microscopic, morphometric analysis.

Closure of the nostril by electrocauterization on postnatal day (PN) 1 or 2 was used to study effects of olfactory deprivation on developing olfactory epithelium (OE) and bulb (OB) in CD-1 mice. No damage was observed in OE sections 1 or 3 days after closure, and at PN 30 no difference was found in the number of OE receptors between closed and open sides. Odor deprivation and a decrease in functional activity in experimental bulbs was evident from deoxyglucose autoradiographs at PN 21 and PN 30. At PN 30 deprived bulbs appeared smaller than nondeprived bulbs. Nissl stains revealed normal cytoarchitecture, but a protargol stain demonstrated fewer intraglomerular dendrites in deprived bulbs. At PN 30, volumes of deprived bulbs were 26% smaller than nondeprived bulbs. The volume of each bulbar lamina was 13 to 35% smaller than the comparable nondeprived lamina except for the ventricular/subependymal zone which was not significantly different between bulbs. Volumes of bulbs contralateral to the closed naris and the volumes of their laminae were not significantly different from control bulbs, suggesting no hypertrophy of nondeprived laminae. Deprivation did not affect the number of mitral cells seen at PN 30, their nuclear size, or their number of nucleoli. Lateral olfactory tract cross-sectional area was also unaffected by deprivation. Mitral cell perikaryal size, however, was smaller in deprived bulbs. Soma surface areal density of deprived mitral-to-granule cell synapses in deprived bulbs was 65% of the nondeprived density, while the density of granule-to-mitral cell synapses was only 46% of the nondeprived density. It is concluded that neonatal naris closure brings about a functional deprivation of the OB without receptor degeneration. Neonatal olfactory deprivation affects the perikaryal surface area but not the number of mitral cells. Also, deprivation markedly affects the reciprocal synapses between mitral and granule cells. Olfactory sensation thus appears necessary for normal development of OB neurons and synapses.

Animals↗

PubMed1976

Cytotoxic testing for food allergy: evaluation of reproducibility and correlation.

Cytotoxic food tests still present conflicting opinions concerning their validity. Nine atopic patients with or without a history of food allergy were studied along with 5 nonatopic patients. All tests were conducted in a double-blind fashion with 6 determinations for each of 10 food antigens. Reproducibility of the test (5/6 positive or negative) was demonstrated with wheat, milk, yeast, chocolate, and orange. In the nonatopic group, reproducible results were obtained for wheat, egg, yeast, chocolate, and chicken. Clinical correlation with 11 foods in 7 patients was demonstrated. However, there were 46 positive tests without correlation and 2 negative tests with positive histories. Therefore, there appears to be reproducibility of the tests to only 3 foods but no apparent correlation with clinical symptoms. At the present time, cytotoxic tests offer no reliable help in establishing the diagnosis of food allergy.

Animals↗