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Biomedical subjects

A F Ryan

Publications and source records attributed to A F Ryan.

At least 127 records · Page 7Linked to original sources
PubMed1982

Tonotopic organization in the central auditory pathway of the Mongolian gerbil: a 2-deoxyglucose study.

The uptake of 2-deoxyglucose (2-DG) was employed to map functional activation of the central auditory pathway in the mongolian gerbil, during 85 dB SPL stimulation with pure tonal stimuli at frequencies of 0.75, 3.0, or 12.0 kHz. Pure tones produced foci of very high 2-DG uptake, when compared to adjacent tissue, in the cochlear nucleus, superior olivary complex, and inferior colliculus. Less distinct areas of elevated 2-DG uptake were seen in the dorsal and ventral nuclei of the lateral lemniscus, medial geniculate nucleus, and auditory cortex. Little or no change in the distribution of 2-DG uptake was noted in the nucleus of the trapezoid body. The location of discrete regions of relatively high 2-DG uptake varied systematically with stimulus frequency. The tonotopic organization demonstrated by 2-DG mapping agreed well with the results of previous electrophysiological studies for most structures. However, in the inferior colliculus, stimulus-evoked increases in 2-DG uptake were found to occur in a fixed pattern of three to four bands across the central nucleus, which did not correspond to any previously reported anatomical or physiological organization. Pure tonal stimuli activated discrete portions of this banding pattern. Also, a small area at the ventromedial edge of the colliculus was more broadly tuned than other regions of the nucleus. It is concluded that 2-DG uptake is well suited to the investigation of tonotopic organization. This technique reveals patterns of activation which have not been observed with other methodologies.

Animals↗
PubMed1982

Auditory stimulation alters the pattern of 2-deoxyglucose uptake in the inner ear.

The 2-deoxy-D-glucose (2-DG) autoradiographic technique was adapted for application to the inner ear. The uptake of [14C]-DG during silence was compared with that observed during exposure to wide band noise (WBN) or pure tones at an intensity level of 85 db SPL. In silence, the highest levels of 2-DG uptake were observed in the spiral ligament, spiral prominence and stria vascularis, with approximately equal levels of uptake in each structure. The high levels of 2-DG uptake observed in the ligament and prominence are surprising, and suggest a more active role for these structures in cochlear function than has previously been suspected. Levels of uptake in the organ of Corti, spiral ganglion and VIIIth nerve were much lower, although well above background. During exposure to WBN, 2-DG uptake increased markedly in the VIIIth nerve, and spiral ganglion throughout the cochlea, and in the organ of Corti in the lower basal turn. 2-DG uptake did not change significantly in the spiral ligament or stria vascularis. During pure tone exposure, increased 2-DG uptake was noted in localized regions of the VIIIth nerve and spiral ganglion.

Animals↗
PubMed1982

Functional ontogeny in the central auditory pathway of the Mongolian gerbil. A 2-deoxyglucose study.

The 2-deoxyglucose (2-DG) autoradiographic technique was used to map functional activity in the central auditory system of the mongolian gerbil, throughout the period of functional onset. Uptake of 2-DG during exposure to 105 dB SPL wide band noise (WBN) was compared to silence in adults and in neonates at 12, 14, 16 and 18 days after birth (DAB). At 12 DAB, WBN exposure increased 2-DG uptake relative to silence only in the ventral cochlear nucleus. At 14 DAB, 2-DG uptake increased during WBN in the entire cochlear nuclear complex, superior olivary complex, and ventral nucleus of the lateral lemniscus. These stimulus-evoked increases in 2-DG uptake were at adult levels. However, little or no stimulus-evoked increase was seen in higher auditory nuclei at 14 DAB. By 16 DAB, 2-DG uptake also increased during WBN exposure in the dorsal nucleus of the lateral lemniscus, inferior colliculus and medial geniculate nucleus. By 18 DAB, WBN exposure produced increases in 2-DG uptake of medullary and pontine auditory nuclei which exceeded those seen in adults. At higher levels of the pathway, increases were comparable to those seen in adults. WBN-induced increases in 2-DG uptake observed in the cochlear nuclear and superior olivary complexes of neonates were comparable in all regions at all ages, even at 12 DAB. However, the 2-DG uptake increases observed at 16 and 18 DAB were appreciably greater in those regions of the inferior colliculus and medial geniculate nucleus which respond to high frequencies.

Aging↗
PubMed1982

Intracochlear microprobe analysis.

Energy dispersive x-ray analysis (EDXA) or "microprobe analysis" provides cochlear physiologists with a means of accurately assessing relative ionic concentrations in selected portions of the auditory mechanism. Rapid freezing followed by lyophilization allows the recovery of fluid samples in crystalline form not only from perilymphatic and endolymphatic spaces, but also from much smaller subregions of the cochlea. Because samples are examined in a solid state, there is no risk of diffusion into surrounding or juxtaposed fluids. Samples of cochlear tissues may also be evaluated without the danger of intercellular ionic diffusion. During direct visualization by scanning electron microscopy, determination of the biochemical makeup of the material being examined can be simultaneously, assuring the source of the data collected. Other potential advantages and disadvantages of EDXA are reviewed. Initial findings as they relate to endolymph, perilymph, stria vascularis, and the undersurface of the tectorial membrane are presented.

Cochlea↗
PubMed1981

Increasing intensities of wide band noise increase [14C]2-deoxyglucose uptake in gerbil central auditory structures.

The [14C]2-deoxyglucose (2DG) technique has been used to map the effects of increasing intensities of wide band noise on 2DG uptake in mongolian gerbil brain auditory structures. Animals were injected with [14C]2DG and exposed to silence or continuous wide band noise at 25 dB, 45 dB, 65 dB, 85 dB or 105 dB SPL. Brains were removed, frozen-sectioned and autoradiographed on X-ray film. The ratio of the optical density of gray matter structures to the optical density of cerebellar peduncles in each animal was used to semiquantitate the results. The dorsal and ventral cochlear nuclei, superior olive/trapezoid body, inferior colliculus, and the dorsal and ventral nuclei of the lateral lemniscus all showed increases in 2DG uptake during exposure to wide band noise (WBN). As noise intensity increased from 0 to 105 dB SPL, 2DG uptake increased regularly to a maximum at 85 or 105 dB SPL. As WBN intensity increased, deeper layers of inferior colliculus were activated. The medial geniculate nucleus and auditory cortex showed a lesser increase in 2DG uptake during noise exposure. Non-auditory structures, including the cerebellar cortex and the medullary reticular nuclei, showed no increase in 2DG uptake during noise exposure at any intensity tested.

Animals↗
PubMed1981

Neural phase-locking properties in the absence of cochlear outer hair cells.

A combined regimen of kanamycin sulfate treatment (175 mg/kg/day) and behavioral evaluation of resulting audiometric threshold shifts was used to produce selective outer hair cells (OHC) loss in chinchillas. This protocol resulted in a 3-7 mm region in the cochlear base in which OHCs were completely absent and inner hair cells (IHCs) were largely resent and normal at both light and electron microscopic levels. Partial OHC loss was associated with audiometric threshold shifts in excess of 15 dB, while complete OHC loss was associated with audiometric threshold shifts in excess of 40 dB. After recovery periods of at least three weeks, phase-locking was examined across frequency for auditory nerve (VIIIth nerve) and ventral cochlear nucleus (VCN) neurons. The frequency range for neural phase-locking in normal subjects extended up to approximately 4 kHz for VIIIth nerve fibers and 3 kHz for VCN neurons. Following kanamycin intoxication, however, the frequency range for neural phase-locking in both of these auditory regions varied with characteristic frequency (CF): neurons whose CF corresponded to normal cochlear regions exhibited phase-locking throughout the normal frequency range; neurons whole CF corresponded to cochlear regions with selective OHC loss exhibited a marked reduction in the frequency range over which they could phase-lock.

Animals↗
PubMed1981

Rapid and efficient immobilization of soluble and small particulate antigens for solid phase radioimmunoassays.

A rapid method of antigen immobilization (10 min.) was developed using soluble antigens (bovine serum albumin, epidermal growth factor, and goat IgG) and small particulate antigens (Keyhole limpet hemocynanine and E. coli) by drying them on filter paper discs. This technique results in a high % of the soluble antigen remaining firmly bound, goat IgG (89%), bovine serum albumin (73%). All the antigens we tested retained their antigenicity after drying as detected by [125I] labeled staphylococcal protein A radioimmunoassay. This method of antigen immobilization was compared to adsorption to plastic wells and was found to be much faster (10 min vs 18 hrs) and was 5 times more efficient than adsorption to plastic wells. Using this technique, we were able to detect as little as 40 ng of bovine serum albumin. These characteristics suggest that this technique of soluble antigen immobilization may be useful in rapid detection of antibodies to many different antigens, as well as detecting ng amounts of the antigens directly.

Animals↗
PubMed1980

Ultrastructural correlates of selective outer hair cell destruction following kanamycin intoxication in the chinchilla.

Kanamycin ototoxicity, combined with behavioral audiometry to evaluate threshold shifts, was used to destroy outer hair cells (OHCs) in the basal cochlea of the chincilla while leaving the inner hair cell (IHC) population largely intact. After survival times of four weeks to one year, transmission electron microscopy was employed to determine the condition of surviving hair cells and neural elements. Throughout the region of OHC loss, IHCs and their innervation were normal in appearance if their adjacent supporting cells were undamaged. When IHC supporting cells, specifically the inner pillar cells, were damaged or absent, damage to IHCs was commonly observed. Such supporting cell-related damage included extrusion of the cuticular plate from the surface of the reticular lamina, encapsulation and/or fusion of stereocilia, and gross distortion of hair cell shape. When the outer supporting cells of the organ of Corti were undamaged following OHC loss, outer spiral fibers were found to have survived in near-normal numbers in the region from 0.5-1.0 mm basal to the basal most surviving OHC, but suffered progressive attrition toward the basal end of the cochlea. It is concluded that kanamycin-induced OHC loss can occur without concommitant IHC damage or outer spiral fiber loss.

Animals↗
PubMedDate not supplied

Immunobiology of the inner ear.

Immunologic mechanisms may play an etiologic role in ear disease, and many disorders long considered idiopathic are now being examined for such an immunologic basis. While it is possible that many of these idiopathic diseases will ultimately prove not to be immunologically mediated, the outcome of these research endeavors will certainly clarify some of the basic mechanisms of host immunity involved in ear disease. The immunobiology of diseases that affect the inner ear is discussed from both experimental and clinical viewpoints.

Animals↗
PubMedDate not supplied

Elaboration of systemic immunity following inner ear immunization.

The development of systemic humoral and cellular immunity following antigen presentation in the inner ear was compared with that seen following middle ear and peritoneal inoculation routes. Antibody developing against keyhole limpet hemocyanin was measured by a sensitive enzyme-linked immunofiltration assay, and cell-mediated immunity was measured by in vitro lymphocyte blastogenesis. The inner ear and peritoneal routes of antigen presentation resulted in a parallel rise in antibody over a 3-week period. In contrast, the middle ear route resulted in a weak, transient antibody response by 2 weeks. The acquisition of cell-mediated immunity occurred earliest (day 14) in the group receiving antigen intraperitoneally. A significant but smaller proliferative response was also seen in the group receiving antigen via the inner ear route on days 14 and 21. In contrast, the middle ear route failed to result in cell-mediated immunity. These studies indicate that the inner ear is an effective route of antigen processing which results in the acquisition of systemic humoral and cellular immunity. The development of systemic immunity, in turn, has been found to be protective of the inner ear.

Animals↗
PubMedDate not supplied

The disintegrin kistrin inhibits neurite extension from spiral ganglion explants cultured on laminin.

The influence of laminin-1 (LN) and tenascin-C (TN), extracellular matrix molecules expressed spatially and temporally along the neural growth route from spiral ganglion (SG) neurons to the cochlear sensory cells, was evaluated in cultured SG explants from postnatal day 4 rats. Increasing concentrations of LN resulted in a strong, dose-dependent increase in the length of neurites and in a higher number of neural processes, while varying TN concentrations had relatively minor effects on both parameters. The results suggest differential receptor activation by LN and TN. When explants grown on LN were treated with Kistrin, an inhibitor of the alphavbeta3 integrin, the LN-induced increase in neurite length was reduced in a dose-dependent manner. However, the number of extending neurites was not affected, indicating that different receptors mediate this response, perhaps by increasing neuronal survival.

Animals↗
PubMedDate not supplied

Cholinergic and purinergic neurohumoral signalling in the inner ear: a molecular physiological analysis.

The ability to identify the expression of the protein subunits which assemble to form ionotropic receptors for acetylcholine and extracellular adenosine 5'-triphosphate (ATP) in individual cells of the inner ear provides examples of the high resolution and exquisite sensitivity which molecular biology brings to the study of hearing and balance. The data from these studies provide both fine detail with respect to the classification of the elements involved and an overview of the sites of potential interaction of both extracellular and intracellular signalling pathways. The high sensitivity necessitates a molecular physiological approach when using these techniques so that these data on the site and extent of expression can be balanced against functional significance. With the demonstration of expression of the alpha 9 subunit of the nicotinic acetylcholine receptor in cochlear outer hair cells, molecular biology has provided an explanation for the unusual cholinergic receptor pharmacology of the olivocochlear efferent innervation which has confounded investigators for decades. In addition, a role for extracellular ATP as a signalling molecule regulating electrochemical gradients and neurotransmission within the inner ear is supported by the extent of P2 receptor expression in this tissue, data which beg for intense functional study.

Adenosine Triphosphate↗
PubMedDate not supplied

Humoral and cell-mediated immunity in peripheral blood following introduction of antigen into the middle ear.

Serum levels of specific IgG and the sensitization of peripheral blood T-lymphocytes were measured in guinea pigs after single-dose antigenic sensitization by two routes: intratympanic and intradermal injection. Keyhole limpet hemocyanin (KLH) served as the antigen. Intratympanic injection of antigen resulted in much lower levels of circulating anti-KLH IgG than intradermal injection. When KLH was conjugated with alum to produce nonspecific inflammation and serve as adjuvant, the intratympanic route was considerably enhanced, but remained much less effective than the intradermal route. Development of an IgG response was also somewhat less rapid following intratympanic than following intradermal administration. Marked sensitization of circulating T-lymphocytes was seen after intradermal injection of alum-precipitated KLH. A much weaker, though still positive, response was seen after intradermal injection of KLH alone and with the intratympanic injection of alum-precipitated KLH. No T-lymphocyte sensitization could be detected after intratympanic injection of KLH alone. It was concluded that the afferent limb of both humoral (IgG) and cell-mediated immunity was operative in the middle ear. Therefore, the middle ear does not represent an immunologically "privileged" site. On the other hand, the afferent limb from the middle ear appears to operate less effectively and rapidly than that from the dermis. This observation is consistent with observations in other mucosal systems.

Animals↗
PubMedDate not supplied

Effect of a middle ear immune response on inner ear antibody levels.

The effect of a middle ear immune response upon antibody levels in the perilymphatic compartment of the inner ear was investigated in the guinea pig. Animals were systemically sensitized with keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) until high circulating levels were achieved. The middle ear cavity was then challenged with KLH, resulting in a vigorous immune response with effusion and mucosal inflammation. Antibody levels against KLH and BSA were then compared in serum, middle ear effusions, and perilymph. Anti-KLH levels in perilymph were found to increase substantially during middle ear response to challenge, while the anti-BSA levels did not, indicating a local origin for the anti-KLH antibody. The most likely explanations for these findings are inner ear antibody originated in the middle ear and diffused across the round window membrane, or antigen diffused across the round window membrane and evoked local production of antibody within the inner ear.

Animals↗