Charles H. Norris

Tulane University, New Orleans, Louisiana, United States

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Publications (55)190.89 Total impact

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    ABSTRACT: The mechanism by which human immunodeficiency virus type 1 induces depletion of CD4+ T-lymphocytes remains controversial, but may involve cytotoxic viral proteins. Synthetic peptides (lentivirus lytic peptide type 1) corresponding to the carboxyl terminus of the human immunodeficiency virus type 1 transmembrane glycoprotein induce cytopathology at concentrations of 100 nM and above. At these concentrations lentivirus lytic peptide type 1 disrupts mitochondrial integrity of CD4+ T-lymphoblastoid cells and induces other changes characteristic of necrosis. In contrast, at concentrations of 20 nM, lentivirus lytic peptide type 1 potently induces apoptosis. Thus, the mechanism by which human immunodeficiency virus type 1 mediates cell death, necrosis or apoptosis, may depend, in part, on the tissue concentration of transmembrane glycoprotein.
    Peptides 11/1999; 20(11):1275-83. DOI:10.1016/S0196-9781(99)00132-1 · 2.62 Impact Factor
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    Charles H Norris · Andrew J Miller · Paola Perin · Joseph C Holt · Paul S Guth ·
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    ABSTRACT: Previous studies have shown that galvanic stimulation of semicircular canal organs can modulate their afferent discharge. However, it has not been resolved whether this modulation derived from direct stimulation of hair cells, afferent nerve fibers, some combination of the two, or some as yet unknown path. This problem is addressed in the present study. Experiments were designed first to determine the gross current path necessary for the DC current to modulate afferent firing. These led to the conclusion that the current path had to flow between endolymph and perilymph across the neuroepithelium. Next, the various components in this established path were considered: the afferents, the hair cells, between the hair cells, or some combination of the three. These experiments led to the conclusion that the current pathway was across the hair cells causing transmitter release and thus affecting afferent activity.
    Hearing Research 10/1998; 123(1-2-123):31-40. DOI:10.1016/S0378-5955(98)00096-3 · 2.97 Impact Factor
  • P S Guth · P Perin · C H Norris · P Valli ·
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    ABSTRACT: Hair cells in mechanosensory systems transduce mechanical stimuli into biological signals to be presented to and analyzed by the brain. Vestibular hair cells transduce stimuli primarily associated with the organism's orientation and motion in space. When examined superficially it may appear that the hair cells act as passive transducers whereby mechanical stimulation of their hair bundle results in transmitter release at their afferent synapses. In fact, hair cell functions are more complicated, and the mechanical signals are heavily processed even before being encoded in afferent nerve activity. Hair cells are different from one another in morphology, biophysics, transmitter and transmitter receptor complements, not only across different organs (as one might expect), but even in the same organ. This review focuses on hair cell morpho-physiological properties, ionic conductances, neurotransmitters/modulators and their receptors, second messengers and effectors. Special features of hair cell neurotransmission, as the synaptic body and the presence of autoreceptors and local circuits, are also discussed, as is the possibility of a differential modulation of hair cell transmitter release in the resting and mechanically-stimulated states.
    Progress in Neurobiology 03/1998; 54(2):193-247. DOI:10.1016/S0301-0082(97)00068-3 · 9.99 Impact Factor
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    ABSTRACT: The carboxy-terminal 29 amino acids of the human immunodeficiency virus type 1 transmembrane glycoprotein (HIV-1 TM) are referred to as lentivirus lytic peptide 1 (LLP-1). Synthetic peptides corresponding to LLP-1 have been shown to induce cytolysis and to alter the permeability of cultured cells to various small molecules. To address the mechanisms by which LLP-1 induces cytolysis and membrane permeability changes, various concentrations of LLP-1 were incubated with Xenopus laevis oocytes, and two-electrode, voltage-clamp recording measurements were performed. LLP-1 at concentrations of 75 nM and above induced dramatic alterations in the resting membrane potential and ionic permeability of Xenopus oocytes. These concentrations of LLP-1 appeared to induce a major disruption of plasma membrane electrophysiological integrity. In contrast, concentrations of LLP-1 of 20-50 nM induced changes in membrane ionic permeability that mimic changes induced by compounds, such as the bee venom peptide melittin, that are known to form channel-like structures in biological membranes at sublytic concentrations. An analog of LLP-1 with greatly reduced cytolytic activity failed to alter the electrophysiological properties of Xenopus oocytes. Thus, by altering plasma membrane ionic permeability, the carboxy terminus of TM may contribute to cytolysis of HIV-1-infected CD4+ cells.
    AIDS Research and Human Retroviruses 12/1997; 13(17):1525-32. DOI:10.1089/aid.1997.13.1525 · 2.33 Impact Factor
  • U Ecke · K Begall · R G Amedee · C H Norris · W J Mann ·
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    ABSTRACT: In an attempt to destroy the peripheral vestibular labyrinth selectively in patients suffering from intractable vertigo as a result of end-stage Ménière's disease, 25 patients underwent selective chemical vestibulectomy between 1989 and 1994. As part of the procedure a certain quantity of streptomycin was placed between the bony and the membranous part of the lateral semicircular canal. The dosage of streptomycin used for successful ablation of vertigo varied between 250 and 100 micrograms. Within 12 months following the procedure all patients experienced a tremendous improvement in their overall condition. In spite of the fact that some patients noted an overall hearing improvement, increased cochlear thresholds were observed in a number of patients, which could not be ignored. The aim of this report is to detail the reliability of control of vertigo, conservation of hearing, and change in disability 12 months after surgery in the 23 patients (of 25) available for follow-up.
    ORL 07/1997; 59(4):209-14. · 0.88 Impact Factor
  • Anastas P. Nenov · Charles Norris · Richard P. Bobbin ·
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    ABSTRACT: Studies of K+ conductances in hair cells report that big-conductance Ca(2+)-dependent K+ (BK) channels carry parts of the outwardly rectifying currents. Lin et al. (1995) suggested that in guinea pig outer hair cells (OHCs) a portion of these currents is carried via a voltage-dependent and Ca(2+)-independent K+ channel. The present study tests the hypothesis that there are two separable current components of the outwardly rectifying currents by using patch clamp methods in OHCs to characterize the voltage dependence and sensitivity of the outwardly rectifying currents to channel blockers. Lowering of external Ca2+ caused no change in the currents while charybdotoxin (ChTx; 100 nM), a BK K+ channel blocker, and Cd2+ (200 microM), and L-type calcium channel blocker, abolished about 50% of the currents. Both ChTx and Cd2+ caused a depolarizing shift in the half-activation voltage paralleled by a decrease in the voltage sensitivity. 4-Aminopyridine (4-AP, 0.01 mM), an A-type and delayed rectifier type channel blocker, abolished about 50% of the currents and caused a hyperpolarizing shift in the half-activation voltage together with an increase in the voltage sensitivity. The outwardly rectifying currents were more sensitive to block by 4-AP at membrane voltages around 40 mV compared to voltages around -20 mV. The differences in the current characteristics may be due to two separate channel types, one of which is similar to the delayed rectifier type channels while the other may be similar to the BK Ca(2+)-dependent K+ channels. In addition, the largest outwardly rectifying currents were present in long OHCs with the smallest present in short OHCs.
    Hearing Research 04/1997; 105(1-2):146-58. DOI:10.1016/S0378-5955(96)00207-9 · 2.97 Impact Factor
  • Anastas P. Nenov · Charles Norris · Richard P. Bobbin ·
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    ABSTRACT: The type of K+ channel involved in the acetylcholine (ACh) evoked response (Ksub; sub stands for suberyldicholine) in guinea pig outer hair cells (OHCs) is still uncertain. The present study tests the hypotheses that Ksub is one of the following: a big conductance Ca(2+)-dependent K+ channel (BK), a small conductance Ca(2+)-dependent K+ channel (SK), a KA type of K+ channel, or a Kn type of K+ channel. Patch-clamp technique in the whole-cell mode was used to record from single guinea pig OHCs. ACh (100 microM) was applied to voltage-clamped OHCs and the ACh-induced currents (IACh) were measured. Charybdotoxin (100 nM) had no effect on IACh, while apamin (1 microM) blocked more than 90% of IACh. Lowering the external Ca2+ concentration caused a hyperpolarizing shift of the IACh monitored as a function of the prepulse voltage. Increasing internal Mg2+ (Mgi2+) concentration caused a reduction in the outward IACh without affecting the inward IACh. The Ksub channel was found to be permeable to Cs+. In Cs+ solutions, IACh was 45% of the IACh in K+ solutions. The block of IACh by apamin, the dependence on extracellular Ca2+, the incomplete block of IACh by Cs+, and the ACh-induced Cs+ currents favor the hypothesis that Ksub belongs to the SK type of channels. An ionotropic/nicotinic nature of the ACh mechanism of action is favored. It is suggested that, in vivo, the amplitude of the ACh-induced hyperpolarization may depend on the Ca2+/Mg2+ ratio inside and outside the cell.
    Hearing Research 12/1996; 101(1-2):149-72. DOI:10.1016/S0378-5955(96)00143-8 · 2.97 Impact Factor
  • Anastas P. Nenov · Charles Norris · Richard P. Bobbin ·
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    ABSTRACT: The properties of the ACh (acetylcholine) response in guinea pig outer hair cells (OHCs) are not well understood. It has been shown that the response to ACh involves the activation of a Ca2+ dependent K+ selective conductance (referred to as Ksub where sub stands for suberyldicholine). In the present study, we examined the voltage dependence, the time dependence, and the desensitization of the ACh response. In addition, we examined the K+ selectivity of K(sub). These properties are important for aiding in the determination of the type of K+ channels activated by ACh. Patch-clamp technique in the whole-cell mode was used to record from single OHCs isolated from adult pigmented guinea pigs. ACh (100 microM) was applied to the voltage-clamped OHCs and the ACh induced currents (IACh) were measured. A voltage dependence of the ACh response was found with the ACh induced currents decaying monoexponentially at potentials positive to -30 mV. The decay of the ACh induced currents was faster soon after establishing the whole-cell mode of recording when compared to the decay of the currents some time later. This effect, referred to as the time dependence, was different from the desensitization of the response upon prolonged application of ACh. The desensitization of the ACh induced currents was about 50% after 2 min of continuous application of 100 microM ACh. The examined characteristics of the ACh response in guinea pig OHCs indicate a voltage and time dependence of the response and strong K+ selectivity of the Ksub.
    Hearing Research 12/1996; 101(1-2):132-48. DOI:10.1016/S0378-5955(96)00142-6 · 2.97 Impact Factor
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    A Makutonina · T G Voss · D R Plymale · C D Fermin · C H Norris · S Vigh · R F Garry ·
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    ABSTRACT: Alterations in plasma membrane function are induced by many cytopathic viruses, including human immunodeficiency virus type 1 (HIV-1). These alterations can result in changes in the intracellular content of ions and other small molecules and can contribute to cytolysis and death of the infected cell. The pH-sensitive fluorescent probe 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein-acetoxymethyl ester was used to quantitate intracellular pH (pHi) in HIV-1-infected T cells. Infection of cells from the CD4+ T-lymphoblastoid line HUT-78 (RH9 subclone) with HIV-1 strain LAI resulted in a significant decrease of pHi, from approximately 7.2 in mock-infected cells to below 6.7 by day 4 after infection, when cells were undergoing acute cytopathic effects. The pHi in persistently infected cells that survived the acute cytopathic effects of HIV-1 was approximately 6.8 to 7.0. Studies with amiloride, an inhibitor of the Na+/H+ exchange system, suggest that HIV-1-induced intracellular acidification in lymphocytes is due, in part, to dysfunction of this plasma membrane ion transport system. The alterations in pHi may mediate certain cytopathic effects of HIV-1, thereby contributing to depletion of CD4+ T lymphocytes in patients with AIDS.
    Journal of Virology 11/1996; 70(10):7049-55. · 4.44 Impact Factor
  • Paul S. Guth · Charles H. Norris ·
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    ABSTRACT: In this article the evidence concerning the nature of the acetylcholine (ACh) receptors on hair cells is reviewed. A schematic organization of these receptors is offered, based on the evidence as follows. (1) There are two kinds of ACh receptors on hair cells: muscarinic-like and nicotinic-like. (2) The nicotinic-like receptor mediates a hyperpolarizing response to ACh and a consequent reduction in afferent firing. (3) The muscarinic-like receptors mediate both a depolarization and a hyperpolarization of hair cells. (4) The hyperpolarization results in a reduction in afferent firing and (5) the depolarization results in an increase in afferent firing.
    Hearing Research 10/1996; 98(1-2):1-8. DOI:10.1016/0378-5955(96)00031-7 · 2.97 Impact Factor
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    ABSTRACT: Biochemical and pharmacological evidence supports a role for nitric oxide (NO) in the cochlea. In the present experiments, we tested sodium nitroprusside (SNP), an NO donor, applied by intracochlear perfusions on sound-evoked responses of the cochlea (CM, cochlear microphonic; SP, summating potential; EP, endocochlear potential; CAP, compound action potential) and in vitro on outer hair cell (OHC) voltage-induced length changes and current responses. In vivo application of SNP in increasing concentrations (10, 33, 100, 330 and 1000 microM) reduced all sound-evoked responses starting at about 300 microM. The responses continued to decline after a postdrug wash. At 1 mM SNP decreased EP slowly (approximately 80 min) whereas at 10 mM it reduced EP more rapidly (approximately 20 min). Ferricyanide (1 mM) and S-nitroso-N-acetylpenicillamine (SNAP; 1 mM) had no effect on sound-evoked cochlear potentials. Ferricyanide (1 mM and 10 mM) and ferrocyanide (10 mM) had no effect on EP. In vitro, SNP (10 mM) significantly reduced both OHC voltage-induced length changes and whole-cell outward currents. Results suggest that SNP, possibly acting by released NO, influences cochlear function through effects at the stria vascularis and at the OHCs.
    Hearing Research 08/1995; 87(1-2):1-8. DOI:10.1016/0378-5955(95)00071-B · 2.97 Impact Factor
  • Chu Chen · Anastas Nenov · Charles H. Norris · Richard P. Bobbin ·
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    ABSTRACT: Ca2+ channel currents and their modulation by adenosine 5'-triphosphate (ATP) in acutely isolated guinea pig outer hair cells (OHCs) were investigated using the whole-cell patch-clamp technique. The current-voltage (I-V) relation of OHCs indicated that the Ca2+ channel opened near -30 mV, and the current reached a maximum at +10 and 0 mV in 20 mM Ca2+ and Ba2+ external solutions, respectively. BayK 8644 (BayK, 2 microM) caused a 3.5-fold increase in peak Ca2+ currents and shifted the I-V curves toward more negative potentials. These results suggest that the majority of Ca2+ channels in OHCs have L-type characteristics. The effects of ATP on Ca2+ channels of OHCs were heterogenous. ATP (100 microM) decreased Ca2+ channel currents by 31.7 +/- 5.6% at 0 mV and shifted Ca2+ tail activation curves toward more depolarized potentials in some cells (N = 6). By contrast, in others, ATP enhanced the currents by 43.5 +/- 12.5% at +10 mV (N = 6). In the presence of BayK, however, ATP-induced inhibition or enhancement of Ca2+ channel currents was attenuated. In addition, 100 microM ATP produced little effect on Ca2+ channel currents in another subpopulation of cells (N = 12). This heterogenous neuromodulation of Ca2+ channel currents by ATP may reflect a functional diversity among OHCs.
    Hearing Research 07/1995; 86(1-2):25-33. DOI:10.1016/0378-5955(95)00050-E · 2.97 Impact Factor
  • A Aubert · C H Norris · P S Guth ·
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    ABSTRACT: Previous studies have shown that low concentrations of exogenous ATP, added to the perilymphatic fluid, could modify the bioelectrical activity of the isolated semicircular canal of the frog (Rana pipiens). To test the hypothesis that ATP is endogenously present and active in the perilymphatic fluid, the influence of two ATP-purinoceptor antagonists, Reactive Blue 2 and suramin, and of the enzyme, nucleotide pyrophosphatase, were examined. When applied by perilymphatic bath substitution, the three compounds reduced, in a dose-dependent manner, the firing of the afferent fibers monitored in the absence of mechanically-applied stimulation. The response of the afferent fibers, recorded when the sensory cells were mechanically inhibited, was also reduced. No modification of the response of the excitatory phase of the mechanical stimulus was observed in the presence of the two antagonists. In contrast, the signal was significantly reduced by the enzyme. None of the three compounds exhibited an influence on the transepithelial potential, or its variation in response to mechanical stimulation. The ATP-induced modification of the firing rate of the afferent fibers, monitored in the absence of mechanical stimulation, was reduced in the presence of the three drugs. No influence of Reactive Blue 2 and suramin was observed on the increase of the spontaneous firing induced by carbachol. In contrast, the effect of carbachol was decreased by nucleotide pyrophosphatase. The excitatory influence of glutamate on the spontaneous firing was not modified by Reactive Blue 2, while it was slightly increased by suramin and nucleotide pyrophosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)
    Neuroscience 03/1995; 64(4):1153-60. DOI:10.1016/0306-4522(94)00434-7 · 3.36 Impact Factor
  • Carlos Erostegui · Anastas P. Nenov · Charles H. Norris · Richard P. Bobbin ·
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    ABSTRACT: Acetylcholine (ACh), the major neurotransmitter released by efferent nerve fibers in the cochlea, has been shown to activate a Ca(2+)-dependent K+ conductance in outer hair cells (OHCs). Previously we reported that this ACh operated conductance is permeable to Cs+. The purpose of the present study was to characterize further this Cs(+)-permeable channel and its dependency on Ca2+ using isolated OHCs and the patch clamp technique in the whole cell configuration. The changes in the ACh response were examined when Cs+, Ba2+, Cd2+, N-methyl-D-glucamine (NMG+) and tetraethylammonium (TEA+) were placed in the external or internal solutions. Cs+ substituted for K+ in carrying the ACh-evoked Ca(2+)-dependent K+ current. When NMG+/TEA+ was substituted for internal K+ ACh-evoked an inward and an outward current, and Cs+ substituted for external K+ blocked the outward but not the inward current evoked by ACh suggesting it was carried by K+. In the NMG+/TEA+ condition, when the cell was held at different Vh values for an extended period of time, the ACh-induced K+ current rectified. In Ba2+ (3 mM) with zero Ca2+ ACh failed to induce any detectable current and the ACh response slowly recovered from the Ba2+ block, suggesting a block at an intracellular site. Cd2+ (1 mM) readily and reversibly blocked ACh-induced currents even when carried by Cs+. This data suggests that ACh opens a channel selective for K+, conductive to Cs+ and dependent on Ca2+.
    Hearing Research 01/1995; 81(1-2):119-29. DOI:10.1016/0378-5955(94)90159-7 · 2.97 Impact Factor
  • A Aubert · C.H. Norris · P.S. Guth ·
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    ABSTRACT: In the present study, the influence of extracellular ATP and ATP agonists in the physiology of the vestibular organs was examined, using the in vitro model of the isolated semicircular canal of the frog (Rana pipiens). The firing activity of the afferent nerve, the d.c. nerve potential and the transepithelial potential were measured in the absence and presence of mechanical stimulation of the sensory epithelium. Administration of ATP into the perilymphatic compartment, from 10(-12) to 10(-3) M, increased the firing rate of the afferent fibers recorded in the absence of mechanical stimulation. Recordings of the d.c. nerve potential indicated that the afferent fibers were hyperpolarized. The presence of the purine also modified the transepithelial potential. During mechanical stimulation of the sensory epithelium, both the evoked afferent firing and the evoked variation of the d.c. nerve potential were reduced in the presence of ATP. However, ATP did not effect the evoked modulation of the transepithelial potential, evoked by the mechanical stimulation. Administration of the P2x purinoceptor agonists, alpha, beta-methylene-ATP and beta, gamma-methylene-ATP, at concentrations between 10(-12) and 10(-3) M, did not significantly modify the different bioelectrical activities investigated. In contrast, 2-methylthio-ATP, a P2y purinoceptor agonist, more potent and efficacious than ATP in its effect on the spontaneous firing. Concurrently, no modification of the d.c. nerve potential, the transepithelial potential and their variation during mechanical stimulation was observed. In opposition to the ATP effect, the total amplitude of the evoked firing was increased in the presence of 2-methylthio-ATP. These data suggest that extracellular ATP, present in the perilymphatic compartment, may act as a neuromodulator in the vestibular physiology. The effects of the purine appear to be mediated by the activation of a P2y subtype of purinoceptor. The absence of an effect of ATP and 2-methylthio-ATP on the evoked variation of the transepithelial potential suggest that the purine did not affect the processes responsible for the generation of the receptor potential but more likely modified the mechanisms involved in the release of the neurotransmitter from the hair cells and/or acted on the afferent endings.
    Neuroscience 11/1994; 62(3):963-74. DOI:10.1016/0306-4522(94)90487-1 · 3.36 Impact Factor
  • P S Guth · A Dunn · K Kronomer · C H Norris ·
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    ABSTRACT: Stimulation of the efferent nerves to the vestibular organs of the frog's inner ear produces either facilitation or inhibition of afferent firing. Similarly, application of acetylcholine (ACH), the major transmitter of the efferents, can produce both facilitation and/or inhibition as previously reported [Guth et al. (1986) Acta Otolaryngol. 102, 194-204; Norris et al. (1988) Hear. Res. 32, 197-206]. The firing rates of afferent neurons of the semicircular canal (SCC) using multiunit recordings are generally facilitated by ACH. Conversely, the firing rates of afferent units innervating the saccule are generally inhibited by ACH. This latter inhibition is antagonized by strychnine more potently than by curare, which is more potent than atropine. When inhibition is antagonized by strychnine or curare an underlying facilitation is revealed. The inhibition of saccular afferents by ACH shows desensitization requiring about 20 min to recover. The ACH-induced inhibition is mimicked by nicotine at very high concentrations but not by dimethyl phenylpiperazinium or cytisine. The fact that multiunit afferent firing from the SCC is generally facilitated while that from the saccule is generally inhibited by ACH suggests a different distribution of ACH receptors and receptor types (i.e. muscarinic or nicotinic and their subtypes) in the two organs and demonstrates the usefulness of recording from multiple units simultaneously. The difference in distribution of ACH receptors may be important for understanding the physiology of vestibular efferents.
    Hearing Research 06/1994; 75(1-2):225-32. DOI:10.1016/0378-5955(94)90073-6 · 2.97 Impact Factor
  • Carlos Erostegui · Charles H. Norris · Richard P. Bobbin ·
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    ABSTRACT: Acetylcholine (ACh) is the major neurotransmitter released from the efferent fibers in the cochlea onto the outer hair cells (OHCs). The type of ACh receptor on OHCs and the events subsequent to receptor activation are unclear. Therefore we studied the effect of agonists and antagonists of the ACh receptor on isolated OHCs from the guinea pig. OHCs were recorded from in whole cell voltage and current clamp configuration. ACh induced an increase in outward K+ current (IACh) which hyperpolarized the OHCs. No desensitization to ACh application was observed. Cs+ replaced K+ in carrying the IACh. The IACh is Ca(2+)-dependent, time and voltage sensitive, and different from the IKCa induced by depolarization of the membrane potential. When tested at 100 microM, several agonists also induced outward current responses (acetylcholine > suberyldicholine > or = carbachol > DMPP) whereas nicotine, cytisine and muscarine did not. The IACh response to 10 microM ACh was blocked by low concentrations of traditional and non-traditional-nicotinic antagonists (strychnine > curare > bicuculline > alpha-bungarotoxin > thimethaphan) and by higher concentrations of muscarinic antagonists (atropine > 4-DAMP > AF-DX 116 > pirenzepine). Pharmacologically, the ACh receptor on OHCs is nicotinic.
    Hearing Research 05/1994; 74(1-2):135-47. DOI:10.1016/0378-5955(94)90182-1 · 2.97 Impact Factor
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    P.S. Guth · C.D. Fermin · M Pantoja · R Edwards · C Norris ·
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    ABSTRACT: The list of distinguishing morphological features of hair cells includes: Type I and Type II afferent innervation, and length, shapes and arrangements of stereo- and kinocilia. We now add to this list the shapes of the hair cells themselves and their placement within the mechanosensory organ, in this case the semicircular canal. Although hair cells of the crista ampullaris of the frog are only of Type II they may now be further classified into three sub-groups according to shape: club-, cigar- and pear-shaped. The cigar- and club-shaped hair cells are each about 40% while the pear-shaped cells are about 20% of the total numbers of hair cells in the crista. The differently-shaped hair cells also distribute differently along the crista. The cigar- and club-shaped are more-or-less uniformly distributed with somewhat higher concentrations at the ends of the crista than in the center. The pear-shaped hair cells, on the other hand, are mostly concentrated toward the center of the crista. This distribution of the pear-shaped hair cells, and their shape is reminiscent of the distribution of calyceal endings (Type I hair cell) in the cristae of amniotes [Goldberg et al., Hear. Res. 49, 89-102 (1990) in Chinchilla; Fernandez et al., Soc. Neurosci. Abstr. 17, 312 (1991) in Monkey]. There are some quantitative differences between hair cells of the same shape but from different portions of the crista. For instance, pear-shaped hair cells of the center are generally of greater cross-sectional area than those of the ends.(ABSTRACT TRUNCATED AT 250 WORDS)
    Hearing Research 03/1994; 73(1):109-15. DOI:10.1016/0378-5955(94)90288-7 · 2.97 Impact Factor
  • Anthony J. Ricci · Carlos Erostegui · Richard P. Bobbin · Charles H. Norris ·
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    ABSTRACT: The morphological characteristics of isolated guinea-pig outer hair cells (OHCs) and frog semicircular canal hair cells (SCCHCs) were reviewed. Active and passive electrophysiological properties of OHCs and SCCHCs were compared utilizing the whole cell variant of the patch clamp technique. Results lead to the conclusion that both hair cell types are similarly viable. SCCHCs were dominated by inactivating outward conductances and were strongly inwardly rectified. In contrast, OHCs demonstrated little inactivation or rectification. The differences in electrophysiological properties between the two cell types may reflect the separate functions these cells have in the ear.
    Comparative Biochemistry and Physiology Part A Physiology 01/1994; 107(1-107):13-21. DOI:10.1016/0300-9629(94)90266-6 · 2.17 Impact Factor
  • C H Norris · A Aubert · R G Amedee ·
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    ABSTRACT: In developing the technique of selective chemical vestibulectomy, the destructive effect of streptomycin on the hair cells of the inner ear was well established. However, in both animal and human studies, a rapid onset of the drug's vestibular inhibition was observed in addition to a more slowly developing long-term destructive effect. In previous laboratory studies, streptomycin had been given only by a systemic route, and only the chronic long-term effects had been observed. In this study, an isolated semicircular canal was prepared and streptomycin was placed into the perilymph bathing the canal. The spontaneous and evoked afferent nerve activity were recorded prior to streptomycin application, during application, and after a washout period. During streptomycin application, the activity of the semicircular canal was reversibly inhibited in a dose dependent manner. After a sufficient washout period (5-10 min), the preparation had completely recovered from the drug's effect. Thus, there are two phases in the vestibular inhibition by streptomycin: an early reversible phase that subsequently can transform into a later irreversible phase.
    The American journal of otology 08/1993; 14(4):373-9.

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1k Citations
190.89 Total Impact Points


  • 1977-1999
    • Tulane University
      • • Department of Otolaryngology
      • • Department of Pharmacology
      • • Department of Medicine
      New Orleans, Louisiana, United States
  • 1988-1997
    • Louisiana State University Health Sciences Center New Orleans
      • Department of Physiology
      New Orleans, Louisiana, United States
  • 1990-1994
    • University of New Orleans
      New Orleans, Louisiana, United States