Biomedical subjects

R L Gulley

Publications and source records attributed to R L Gulley.

28 records · Page 2Linked to original sources

PubMed1977

Aspartic acid and glutamic acid levels in the cochlear nucleus after auditory nerve lesion.

Aspartic acid, glutamic acid and alanine were measured in the cochlear nucleus after lesioning the auditory nerve by cochlear ablation. Ultrastructural analysis of the cochlear nucleus showed that most primary auditory terminals were degenerating one day after cochlear ablation; the terminals were enlarged and the number of synaptic vesicles was reduced. Primary auditory terminals were virtually gone three days after cochlear ablation. Aspartic acid decreased after cochlear ablation in parallel with the morphological degeneration of the primary auditory terminals. The level of total aspartic acid in the cochlear nucleus had decreased more than 8% one day after cochlear ablation and more than 30% after two days, and remained at this level up to 28 days. Glutamic acid also decreased in the cochlear nucleus after cochlear ablation but not in parallel with the morphological degeneration of the primary auditory terminals. Following a slight increase one day after cochlear ablation, total glutamic acid decreased about 10% after two days and continued to decrease slowly through to day 28. Alanine dropped slowly after cochlear ablation and not in parallel with the degeneration of the primary terminals. Levels of other amino acids measured were unchanged or had increased two days after cochlear ablation. Aspartic acid and glutamic acid did not decrease in the superficial layers of the dorsal cochlear nucleus, an area receiving little or no primary innervation.

Alanine↗

PubMed1977

Freeze-fracture studies on the synapses in the organ of Corti.

Receptoneural junctions and synapses in the organ of Corti of the chinchilla have been examined with the freeze-fracture technique. The presynaptic membranes at the receptoneural junctions of inner and outer hair cells have many structural features in common with membranes found at chemical synapses outside the organ of Corti. However, the membranes of the postsynaptic afferent terminals are quite different depending on whether they are part of an inner or outer hair cell synapse. These differences in the distribution of intramembrane particles suggest that the transmitters, or transmitter actions, may be different at these two synapses. The distribution of particles in the postsynaptic membrane at efferent synapses with outer hair cell differs from that in the postsynaptic membrane at efferent synapses with afferent terminals or fibers, suggesting that transmitter actions at these locations could also differ.

Animals↗

PubMed1977

Regional specialization of the hair cell plasmalemma in the organ of corti.

Nonjunctional and nonsynaptic membranes of hair cells in the chinchilla organ of Corti were examined using the freeze-fracture technique. Cytoplasmic leaflets of the apical membranes of hair cells have particles, 6-12 nm in diameter, but many more particles are found on apical membranes of outer hair cells than on inner hair cells. Cytoplasmic leaflets of the lateral membranes of outer hair cells are covered with large particles, but the corresponding regions of the inner hair cell membrane have fewer particles and these are small or medium-sized. Two types of particle aggregate also distinguish this region of the inner hair cell. The first consists of patches of particles closely spaced in rectilinear arrays. The second consists of parallel strands of widely spaced large particles similar in size, but not in distribution, to the large particles on the lateral membranes of the outer hair cells. The basal membrane of outer hair cells is distinguished from that of inner hair cells by plaques consisting of cross-hatched incisures in the external membrane leaflet. While the significance of these anatomical features is not yet apparent, they give the hair cell plasmalemma a richness or regional specialization found in few other cells and suggest that there are important functional differences between inner and outer hair cells.

Animals↗

PubMed1977

Remodeling of neuronal membranes as an early response to deafferentation. A freeze-fracture study.

The early effects of deafferentation on the postsynaptic membrane beneath the end bulb of Held in the anteroventral cochlear nucleus (AVCN) were studied with the freeze-fracture technique. Three distinct responses were seen on the external membrane leaflet after cochlear ablation. Within 12 h the number of nonaggregate particles increased 147% by the addition of new particles to the membrane. The increase in number of nonaggregate particles continued until 4 days after cochlear ablation. The other responses occurred later, after degenerative changes were present in the end bulb. Between 1 and 2 days after cochlear ablation, the number of perisynaptic aggregates surrounding the postsynaptic active zone decreased to 10% of normal numbers. By 4 days, all perisynaptic aggregates had disappeared from the membrane. Coated vesicles may be involved in removing these aggregates. Between 1 and 3 days, the number of junctional aggregates decreased, but the size of the aggregates increased, apparently as a result of coalescence of nearby junctional aggregates. The total number of particles in junctional aggregates in the membrane was not altered during the first 6 days after cochlear ablation. The three separate responses suggest the existence of at least three different types of intramembranous particles on the external leaflet of the principal cell membrane, with each type dependent upon different cues for its maintenance in the membrane.

Afferent Pathways↗

PubMed1976

Intercellular junctions in the reticular lamina of the organ of Corti.

Junctions between the cells in the reticular lamina of the organ of Corti were examined in thin sections and after freeze-fracturing to find a structural basis for the large ionic differences between the endolymph and perilymph. The apices of the cells in the reticular lamina are joined by a band of tight junctions spaced at 140 A intervals. Beneath this apical band the organization of the tight junctions depends on whether they join a supporting cell and a hair cell, or two supporting cells. At hair cell junctions with supporting cells, there is an extensive labyrinth of tight junctions enclosing lengthy, tortuous passages whose walls are composed of either multiple parallel or single junctions. At appositions between two supportinc cells, maculae or fasciae occludentes lie immediately beneath the apical bands of closely spaced tight junctions, near the top of the zonulae adherentia which are characteristic of appositions between supporting cells. The complexes of tight junctions, or zonulae occludentes, between extralaminar supporting cells differ from those in the reticular lamina. The extralaminar cells are joined by a band of four to seven branching, anastomotic tight junctions. Thus, these junctions are like zonulae occludentes in other tissues. The novel organizations of the tight junctions in the reticular lamina, different from those between the extralaminar supporting cells, suggests a special role for these junctions in the reticular lamina. Two sizes of gap junctions link, and presumably couple, supporting cells in the reticular lamina.

Animals↗

PubMed1975

The visual connections of the adult flatfish, Achirus lineatus.

Metamorphosis in the flatfish is characterized by the migration of one eye around the dorsal surface of the head to a position adjacent to the other eye on the new top side of the animal. The visual connections of the adult flatfish, Achirus lineatus, were examined. Either the migrating or non-migrating eye was removed and the animal allowed to survive for one to three weeks. Alternate sections of the brain were stained by a modification of the Fink-Heimer technique, or with cresyl violet. The diencephalic visual connections of the flatfish were similar to those of other teleosts with contralateral projections to the nuclei corticalis, dorsomedialis thalami, pretectalis, and the corpus geniculatum laterale. The distribution of the retinal efferents to the optic tectum is unique in the flatfish. In the medial one-third of the tectum, terminal degeneration was found in three bands in the stratum opticum (SO) and the stratum griseum et fibrosum superficiale (sgfs). In the middle part of the tectum, two bands of degeneration remained over the sgfs. The lateral part of the tectum has only a very small amount of degeneration distributed radomly in scattered clusters over the deep SO and superficial sgfs. The Nissl preparations also reflected the differences between the medial and lateral parts of the tectum. Distinct layer was lacking in the medial tectum with a conspicuously absent large cell layer in the stratum griseum centrale (sgc). In contrast, the lateral tectum had a typical tectal stratification. Most notable were the large neurons of the sgc.

Animals↗

PubMed1974