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M J Drescher

Publications and source records attributed to M J Drescher.

At least 37 records · Page 2Linked to original sources
PubMed1994

Glucocorticoid receptors in the mammalian inner ear: RU 28362 binding sites.

The effects of glucocorticoid hormones are thought to be initiated by binding of the steroid to stereospecific intracellular receptor proteins in target tissues. The synthetic glucocorticoid [3H]-RU 28362, which demonstrates negligible affinity for mineralocorticoid (Type I) receptors [Philibert et al., (1983) Endocrine Soc. Abstr. 65, 335], was employed to identify the high-affinity glucocorticoid (Type II) receptors in the inner ear. By Scatchard analysis, the Kd of the [3H]-RU 28362-cytoplasmic receptor complex was 11.4 x 10(-9) M for the lateral wall of the basal turn of the cochlea and 12.7 x 10(-9) M for the ampullae of the semicircular canals. The concentration of binding sites, Bmax, was 240 fmol/mg dry tissue for the cochlear specimen and 89 fmol/mg dry tissue for the ampullae. Time course studies indicated that the binding of [3H]-RU 28362 by inner ear tissues reached equilibrium within 30 min of incubation at 25 degrees C. Based on the total specific binding measured with [3H]-RU 28362, the glucocorticoid receptor concentration in the lateral wall of the basal turn of the cochlea appears to exceed that in the ampullae of the semicircular canal by a factor of 2.7. Substantial specific [3H]-RU 28362 binding to the cochlear lateral wall and ampullar tissue suggests the presence of glucocorticoid receptors and sites of glucocorticoid action in the inner ear.

Androstanols↗
PubMed1994

Immunohistochemical localization of S-100 protein in auditory and vestibular end organs of the mouse and hamster.

The distribution of S-100-like immunoreactivity in mouse and hamster auditory and vestibular end organs was determined by the use of immunohistochemistry. Within the organ of Corti, the cytoplasm of cells of Deiter and Hensen were strongly immunoreactive. Inner hair cells and the peripheral processes and cell bodies of the spiral ganglion were weakly immunoreactive for S-100, whereas the supranuclear regions of outer hair cells and cells underlying the basilar membrane were unstained. Immunoreactivity was observed near the base of outer hair cells. In the lateral wall of the cochlea, cellular components of the spiral ligament and a subpopulation of epithelial cells in the stria vascularis, identified as predominantly basal cells, were immunoreactive. For the saccule, utricle, and semicircular canals, S-100 immunoreactivity was observed in vestibular hair cells, types I and II, and the nerve calyces surrounding type I hair cells as well as in nerve fibers underlying the sensory epithelium. Weak S-100-like immunoreactivity was associated with vestibular nerve fibers and cell bodies in the vestibular ganglion. The localization of S-100-like immunoreactivity to the sensory cells and nerve fibers of the peripheral auditory and vestibular end organs is consistent with a functional role for S-100 proteins at these sites.

Animals↗
PubMed1993

Aldosterone mediates an increase in [3H]ouabain binding at Na+, K(+)-ATPase sites in the mammalian inner ear.

Na+,K(+)-ATPase has been implicated in the maintenance of high [K+], low [Na+] in endolymph of the inner ear, ionic properties considered to support transduction by the receptor cells. In exocrine ion-transporting epithelia, Na+,K(+)-ATPase activity is modulated by aldosterone, a mineralocorticoid hormone. In the present study, the effect of alteration of serum aldosterone levels on Na+,K(+)-ATPase in ion-transporting regions of the mammalian inner ear was investigated. A high Na+/low K+ diet offered ad libitum for 5 days was utilized to significantly decrease serum aldosterone in male Hartley guinea pigs compared to controls. An injection of aldosterone (10 micrograms/100 g b.wt.) 21 h prior to sacrifice resulted in significant elevation of serum aldosterone over that obtained with the high Na+/low K+ diet. Binding of [3H]ouabain, a specific inhibitor of Na+,K(+)-ATPase, was significantly elevated in microdissected lateral wall of the basal turn of the cochlea and in the ampulla of the semicircular canal, for aldosterone-injected vs. vehicle-injected animals. Serum [Na+] and [Cl-] were elevated in animals on the high Na+/low K+ diet and unaltered by administration of exogenous aldosterone. The enhancement of ouabain binding in inner ear tissues observed in aldosterone-injected animals, therefore, did not appear to reflect an alteration of serum electrolytes per se. The results of these experiments are consistent with the hypothesis that aldosterone increases the number of Na+,K(+)-ATPase sites in ion-transporting epithelia of the mammalian cochlea and semicircular canal.

Aldosterone↗
PubMed1993

Acetylcholinesterase activity is associated with efferent endings in the sensory epithelia of the utricle and semicircular canals of the rainbow trout inner ear.

The mechanosensory hair cells of the utricle and semicircular canals of the trout inner ear are morphologically similar to type II hair cells of the avian and mammalian vestibular end organs. These cells are innervated by two types of nerve terminals. The nonvesiculated terminals are considered to be afferent, and the vesiculated endings are presumed to be efferent. The presumptive efferent endings contain numerous clear, round vesicles and a few that are dense-cored. Histocytochemical, electron microscopic analysis has localized acetylcholinesterase activity to plasma membranes of vesiculated, presumptive efferent nerve terminals in sensory epithelia of the utricle and semicircular canals. No reaction product was observed at the receptoneural synapse or found in nonvesiculated, presumptive afferent endings. Control specimens incubated in the presence of eserine sulfate, an inhibitor of acetylcholinesterase, were devoid of reaction product. These results support the tenet that vesiculated nerve endings in the sensory epithelia of the utricle and semicircular canals of the trout are cholinergic.

Acetylcholinesterase↗
PubMed1993

High affinity aldosterone binding sites (type I receptors) in the mammalian inner ear.

The presence of aldosterone (Type 1) binding sites in the mammalian inner ear has been previously suggested by an increase in inner ear Na, K-ATPase ouabain binding sites in response to the administration of aldosterone in vivo (Pitovski et al., 1993). Type I binding sites have now been identified and characterized in the lateral wall of the basal turn of the cochlea and in the ampullae of the semicircular canals of the guinea pig. In the presence of RU 28362, which blocks low-affinity binding of the labeled hormone to Type II sites, [3H]-aldosterone binds to a single class of high-affinity (Type I) sites with Kd values of 34.7 nM in lateral wall of the basal turn of the cochlea and 31.3 nM in the ampullae of the semicircular canals. Bmax is 17.1 fmol/mg dry tissue for the cochlear sample and 17.4 fmol/mg dry tissue for the ampullae, comparable to reported values in renal tissue (17-31 fmol/mg protein). Thus, the results of receptor-binding experimental protocols with [3H]-aldosterone clearly suggest that these inner ear tissues are a target site of mineralocorticoid action.

Aldosterone↗
PubMed1993

Immunohistochemical localization of S-100 protein in the saccule of the rainbow trout (Salmo gairdnerii R.).

The distribution of S-100-like immunoreactivity in the trout saccule (a presumed organ of hearing in fish) has been determined by means of immunohistochemistry. Within the sensory epithelium of the saccular macula, hair cells and myelinated saccular nerve fibers were found to be immunoreactive. Hair-cell immunoreactivity was relatively uniform throughout the macula except at the extreme periphery (rostral, caudal, ventral and dorsal), where staining was either decreased or absent. The immunoreactivity associated with myelinated nerve fibers was greatest at the peripheral edges of the nerve processes, a position corresponding to the location of Schwann cells. However, the nerve processes themselves (within and subjacent to the sensory epithelium), as well as cell bodies within the saccular nerve, were also immunoreactive. Thus, the immunoreactivity of the saccular nerve observed above the basal lamina can be attributed to the saccular nerve processes as well as to nerve-associated Schwann cells. Overall, the immunoreactivity displayed by hair cells was less intense than that associated with myelinated saccular nerve, as evidenced by a disappearance of signal in hair cells first, upon serial dilution of antibody. No S-100-like immunoreactivity was observed in supporting cells within the sensory epithelium or in epithelial cells in non-sensory regions. A concentration of S-100-like immunoreactivity in hair cells and saccular nerve is suggestive of the presence of S-100 calcium-binding protein-mediated activities in these cell types.

Animals↗
PubMed1992

Glutamate, of the endogenous primary alpha-amino acids, is specifically released from hair cells by elevated extracellular potassium.

A hair cell (octavolateralis mechanoreceptor cell) sheet preparation from the trout saccular macula was superfused with bicarbonate-based physiological saline. Among the primary amine-containing compounds resolved by cation-exchange HPLC, glutamate alone was released in a statistically significant manner with elevation of extracellular [K+] from 3.5 to 14 mM in the presence of 1.8 mM calcium. Release of glutamate averaged 10.9 +/- 2.5 pmol (mean +/- SEM) over a 10-min period for a hair cell sheet preparation representing 20 micrograms of cell protein. No potassium-evoked release of glutamate was observed in 0 mM calcium/10 mM magnesium saline, suggesting calcium dependency. Because the sheet preparation, by the method of its isolation, contained only the hair cell as the intact cell type, release of glutamate, induced by relatively small increases in extracellular potassium, can be attributed directly to the receptor cell. The specific release of glutamate and its block by magnesium are consistent with the hypothesis that glutamate is one neurotransmitter/neuromodulator mediating receptoneural transmission in the octavolateralis periphery.

Animals↗
PubMed1991

The histochemical localization of acetylcholinesterase in the rainbow trout saccular macula by electron microscopy.

The hair cells of the teleost saccular macula are morphologically similar to type II vestibular hair cells of higher vertebrates. The two types of nerve endings at the base of the saccular hair cells are the non-vesiculated endings, thought to be afferent, and the vesiculated terminals, presumed to be efferent. The vesicles in the presumptive efferent endings are predominantly round and clear, and a few are dense cored. The morphological characteristics of the vesiculated endings resemble those of presumptive efferent cholinergic endings present in the inner ear of higher vertebrates. In the present study, vesiculated nerve endings were examined histochemically for acetylcholinesterase. The reaction product was observed along the plasma membranes of the vesiculated nerve endings synapsing both with the hair cells and afferent endings, but was not seen at non-vesiculated endings on hair cells. No staining was observed in control specimens incubated in the presence of eserine sulfate, an inhibitor of acetylcholinesterase. These results suggest that the vesiculated nerve endings in the trout saccular macula contain cholinergic elements.

Acetylcholinesterase↗
PubMed1991

N-acetylhistidine, glutamate, and beta-alanine are concentrated in a receptor cell layer of the trout inner ear.

An epithelial sheet isolated from the trout saccular macula, highly enriched in acousticolateralis receptor cells (hair cells), has been analyzed for primary amine-containing compounds. The hair cell preparation, compared to the saccular nerve, was found to contain elevated levels of the presumptive receptoneural transmitter, glutamate, as well as beta-alanine, and components eluting in the positions of the standards phosphoserine and phosphoethanolamine on cation-exchange HPLC. Saccular nerve contained a different spectrum of primary amines and was elevated specifically in carnosine/homocarnosine. Acid hydrolysis of perchlorate extracts of both hair cell and nerve fractions yielded large amounts of histidine. For the saccular nerve fraction, production of histidine by acid hydrolysis was matched by production of beta-alanine and gamma-aminobutyric acid (GABA) and disappearance of carnosine/homocarnosine. The dipeptides carnosine and homocarnosine have been chromatographically resolved by expanded HPLC and found to be present in saccular nerve in a ratio of approximately 10:1, respectively. Production of histidine in the hair cell extract was not coupled with production of beta-alanine and GABA. The hair cell histidine-containing unknown, present in millimolar concentration, has been identified as N-acetylhistidine by the hydrolysis and rechromatography of fractions from cation-exchange HPLC. The large and specific presence of N-acetylhistidine in the hair cell preparation, together with electrophysiological evidence for its facilitatory action on afferent fibers in the frog semicircular canal, is suggestive of a role for this molecule as well as glutamate in acousticolateralis receptoneural transmission.

Animals↗
PubMed1990

Argiotoxin-636 blocks effects of N-methyl-D-aspartate on lateral line of Xenopus laevis at concentrations which do not alter spontaneous or evoked neural activity.

Activity of primary afferent neurons in acousticolateralis organs can be modulated by excitatory amino acids (EAA) and their antagonists, and EAA are among the better candidates for the transmitter(s) between hair cells and afferent neurons. Argiotoxin-636 (ATX) is a spider venom toxin that is a selective antagonist of the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors in vertebrates. In the present study, the effects of NMDA alone and in combination with ATX on resting firing rate (spontaneous activity) and mechanically stimulated activity of lateral line afferent neurons of post-metamorphic Xenopus laevis were compared. Perfusion of NMDA (100 or 200 microM) typically produced a biphasic effect on spontaneous activity consisting of a transient increase followed by a decrease in firing rate. Mechanical stimulation applied after the initial response to NMDA produced an increase in firing activity that was not significantly different from the increase in firing activity evoked in the absence of NMDA. ATX at 1-2 microM did not alter either spontaneous or evoked activity, but blocked in a reversible manner both the excitatory and inhibitory actions of NMDA on spontaneous activity. These results suggest the presence of an NMDA receptor in the lateral line but do not support the hypothesis that the generation of action potentials by the afferent transmitter is solely dependent on activation of postsynaptic NMDA receptor-ion channels.

Afferent Pathways↗
PubMed1989

Protein associated with the sensory cell layer of the rainbow trout saccular macula.

A protein has been detected that is associated with the saccular hair cell layer of the rainbow trout, Salmo gairdnerii R. By one- and two-dimensional SDS polyacrylamide gel electrophoresis, the molecular weight and isoelectric point of this protein are estimated to be 13.6 and 8.8 kDa, respectively. The 13.6 kDa protein cannot be detected electrophoretically in brain, gill, liver, and fractions containing the basal lamina, non-sensory epithelium, and saccular nerve. This protein does not bind antibodies to bovine myelin basic protein, while trout myelin basic proteins in the same molecular weight range do. In addition, the protein does not bind concanavalin A or react with the periodic acid-Schiff reagent. The 13.6 kDa band represents about 1% of the total protein in saccular sensory epithelium, and may be a marker protein for the hair cell layer.

Animals↗
PubMed1987

Potassium-evoked release of endogenous primary amine-containing compounds from the trout saccular macula and saccular nerve in vitro.

An in vitro preparation of the trout saccular macula, containing a large number of hair cells, served as a potential source of neurotransmitter(s) released at the acousticolateralis hair cell-afferent nerve synapse. An in vitro preparation of the saccular nerve, maintained in parallel, served to indicate the potential neural contribution to overall release from the macula. Efflux of 27 primary amine-containing compounds from the macula and nerve fractions was monitored by cation-exchange HPLC with fluorescence detection, and release by 53.5 mM potassium was determined at 1.45 mM calcium, 0.35 mM magnesium or 0 mM calcium, 10.1 mM magnesium. Taurine was released from the saccular macula in the greatest amount, accounting for 72% of the total evoked release of primary amine-containing compounds. Its release was calcium dependent and its time course prolonged. The contribution by myelinated nerve and associated Schwann cells within the macula to overall release of taurine from the macula in the presence of calcium, as determined from the saccular nerve preparation, was only 2%. Other components specifically released from the macula included ethanolamine, phosphoserine, beta-alanine, and glycine. Glutamate and aspartate were released from both the macula and saccular nerve fractions by potassium in the presence of calcium and in a ratio of 6:1 (glutamate:aspartate) for the macula and 7.5:1 for the nerve. The release of aspartate, but not that of glutamate, was lowered in saline containing 0 mM calcium, 10.1 mM magnesium. The calculated contribution from neural elements to overall release from the macula was 10% for aspartate and 18% for glutamate. These studies demonstrate that both the macula and saccular nerve fractions release the 'excitatory neurotransmitter' candidates aspartate and glutamate. Calcium-dependent, potassium-evoked release of taurine appears to be specific to the hair cell-supporting cell population of the saccular macula, and taurine may, therefore, be involved directly or indirectly in hair cell neurotransmission in labyrinthine organs. This study represents the first detailed biochemical characterization of efflux and release for an in vitro hair cell system of relatively high purity with respect to hair cells.

Amino Acids↗
PubMed1987

Spontaneous neural activity of a mechanoreceptive system is undiminished by replacement of external calcium with equimolar magnesium in the presence of EGTA.

Primary afferent neurons of the lateral-line mechanosensory organs, which are believed to be closely related to the auditory and vestibular organs, exhibit "spontaneous" action potentials in the absence of mechanical stimulation of the receptor cells (hair cells). Sinusoidal mechanical stimulation of the hair cells enhances the impulse rate of the afferent neurons. The spontaneous activity is found to be a decreasing function of increasing concentration of either external magnesium or calcium, when each cation is varied in the absence of the other and bath-applied to the synaptic side of the lateral-line mechanoreceptors. One mM to 6 mM magnesium with 5 mM EGTA (the latter for chelation of remaining traces of calcium) permits undiminished spontaneous afferent activity of lateral-line neurons for as long as 3 to 4 hours. With bath-applied calcium, mechanical stimulation results in evoked incremental activity--defined as total activity with stimulation minus spontaneous activity--which significantly increases with increasing calcium concentration. However, with magnesium and EGTA in the bath, mechanical stimulation produces no increase in the neural firing rate above spontaneous rate for any magnesium concentration tested. Taken together, these results suggest that spontaneous activity, in contrast to evoked incremental activity, does not require external calcium in the bath, and production of spontaneous neural action potentials may proceed via mechanisms that are modifications of those of classical stimulus-secretion coupling.

Action Potentials↗
PubMed1987

Calcium and magnesium dependence of spontaneous and evoked afferent neural activity in the lateral-line organ of Xenopus laevis.

1. Rates of spontaneous and mechanically evoked neural impulses from the Xenopus laevis lateral line were compared in the presence of calcium and/or magnesium or in the absence of either divalent cation, bath-applied to the synaptic side of the mechanoreceptors. 2. Spontaneous activity and total activity during mechanical stimulation decreased with increasing calcium or magnesium concentration. 3. Activity during stimulation minus spontaneous activity increased with increasing calcium concentration and decreased with increasing magnesium concentration. 4. At constant divalent cation concentration, increasing calcium/magnesium increased total stimulated activity minus spontaneous activity, while spontaneous activity remained essentially constant. 5. Membrane charge screening and mass action of divalent cations at voltage-dependent cation channels are hypothesized to account for the effects observed.

Action Potentials↗
PubMed1987

Amino acids, including neurotransmitter candidates, in a hair cell-enriched fraction from the lateral line of Xenopus laevis.

A hair cell-enriched neuromast fraction from the lateral line of Xenopus laevis was compared with adjacent tactile organ and epidermis for content of primary amine-containing components. Of 32 components quantitated by cation-exchange HPLC with fluorescence detection of orthophthalaldehyde adducts, L-alpha-amino adipic acid, O-phosphoethanolamine, L-alpha-glycerophosphorylethanolamine, O-phospho-L-serine, and L-lysine were elevated in concentration in the neuromast relative to the tactile organ an/or epidermis. L-Aspartic acid, L-asparagine, L-glutamic acid, and taurine were present at higher levels in the tactile organ or epidermis than in the neuromast. Taurine was found in only trace amounts in the neuromast. The tactile organ and epidermis contained at least 3 unidentified primary amine components that were absent or reduced in amount in the neuromast. This study demonstrates that the epidermally-derived, hair cell-containing neuromast of the lateral line of Xenopus laevis is different in molecular composition from surrounding epidermally-derived tissue. Such differences may reflect specialized mechanoreceptive function.

2-Aminoadipic Acid↗
PubMed1986

Potassium-stimulated efflux of radiolabeled products formed from L-[14C(U)]-glutamine in vitro by the saccule of the rainbow trout (Salmo gairdnerii R.).

Samples of saccular macula from the rainbow trout were incubated in vitro with uniformly-labeled L-[14C]-glutamine, and radiolabeled products, released by potassium-induced depolarization in the presence of calcium, were examined. Most of the effluxed radioactivity was distributed in six (of 17) thin-layer chromatographic fractions. Fractions corresponding to aspartate and glutamate showed highly significant increases in radioactivity (as percent of total recovered radioactivity) during high-potassium treatment. Radioactivity in a fraction with an RF close to that of ornithine also significantly increased during potassium, and dropped sharply after potassium. The origins of the thin-layer fractions, with respect to sensory and neural elements in the saccular macula samples, are discussed.

Animals↗
PubMed1983

Effect of sound stimulation at several levels on concentrations of primary amines, including neurotransmitter candidates, in perilymph of the guinea pig inner ear.

Perilymph, which bathes the sensory cells of the cochlea, was collected from guinea pigs exposed to noise and analyzed via two cation-exchange HPLC procedures with fluorescence detection, resolving 51 and 81 primary-amine compounds, respectively, at a sensitivity limit of 0.1 pmol relative to leucine. During a first period, each animal was either exposed to noise at 80, 90, or 115 decibels sound-pressure level or maintained in silence (controls), and during a second period, the same animal was maintained in silence. Perilymph was collected during both periods, and perilymphatic components were compared, within animals and across animals, for several levels of sound stimulation. A gamma-aminobutyric acid-like component was elevated in the first period in proportion to stimulus intensity by the various methods of comparison, suggesting an auditory-neurotransmitter role for this component. Aspartic acid was elevated in the second period, 2-3.5 h after onset of sound stimulation, compatible with the release of aspartic acid from central auditory synapses. In addition, a methionine-enkephalin-like component, distinct from leucine-enkephalin, was detected in perilymph from control animals and was elevated in response to noise at 115 decibels. Regression coefficients, determined for the relation between sound intensity and first-period concentrations or the difference between first and second-period concentrations, indicated zero linear regression at p = 0.05 for glutamic acid, aspartic acid, glycine, taurine, and 39 other perilymphatic components, consistent with the hypothesis that these compounds are unlikely to be peripheral auditory neurotransmitters.

Acoustic Stimulation↗