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Brain derived neurotrophic factor gene therapy prevents degeneration of spiral ganglion neurons in a mouse model of aminoglycoside ototoxicity
Otolaryngology Head and Neck Surgery V o l u m e 117
Number 2
ficity of viral infection and duration of expression of the transgene integrated into the cellular genome. The results of this work and future implications are discussed. (This work was made possible in part by a grant from the American Academy of Otolaryngology Foundation, Inc.)
Poster 35 Brain Derived Neurotrophic Factor Gene Therapy Prevents Degeneration of Spiral Ganglion Neurons in a Mouse Model of Aminoglycoside Ototoxicity HINRICH STAECKER, MD, PhD (presenter), RAMIN GABAIZEDEH, HOWARD FEDERO1-r,MD, and THOMAS R. VAN DE WATER, PhD, City Island, Bronx, and Rochester, N,Y,
(Second Place Resident Clinical Science Award) Destruction of auditory hair ceils results in the secondary degeneration of auditory neurons. This is due to the loss of neurotrophic factor support from the auditory hair cells, namely neurotrophin 3 (NT-3) that is normally produced by the inner hair cells. Both in vitro and in vivo studies have shown that delivery of either NT-3 or brain-derived neurotrophic factor (BDNF) to these neurons can replace the trophic support supplied by the hair cells and prevent their degeneration. To prevent the degeneration of auditory neurons that occurs following neomycin destruction of the auditory hair cells, we used a replication defective herpes simplex-1 vector (HSVbdnflac) to transfect the gene for BDNF into the damaged spiral ganglion. Four weeks after HSVbdnflac therapy, we were able to detect stable functional production of BDNF that supported the survival of auditory neurons and prevented the loss of these neurons from trophic factor deprivation-induced apoptosis.
Research Forum - - M o n d a y
P95
tory Neuroscience. In press). With noise bursts of different durations, two levels of suppression could be observed, as recently reported (Sridhar et al. J Neurosci 1995;15:366778). After the onset of a 1-second CLWN, the power value of the EBA decreased rapidly by 36.0% _+ 7.8% (n = 14), with a latency of less than 10 msec and a time decay of 13.1 _+ 1.0 msec (n = 3) (mean _+SD, fast effect). At the offset of the 1-second CLWN, EBA came back to prestimulation values with a similar latency and a time constant of 15.5 _+2.9 msec. During longer CLWN (>1 minute) EBA presented, after the fast decrease, an additional, slower decrease of 16.8% _+5.9% (n = 11), with a time decay of 18.4 -e 7.4 sec (n = 7) (slow effect) and then remained remarkably constant for as far as was observed, that is, over 2 hours (steady state). The average global suppression was thus up to 51.3% +__8.3% of the basal, pre-CL stimulation EBA value. Fast and slow changes in EBA power values were observed during continuous or intermittent CLWN stimulation, after a single injection of gentamicin (150 mg/kg). Gentamicin progressively and reversibly blocked the rapid effect, but the slow component of the efferent medial suppression remained remarkably unchanged. These observations indicate that the medial efferent olivocochlear system exerts sustained influences on outer hair cetls and that this effect develops in two different steps, which may have different basic cellular mechanisms. Poster 37
Inhibition of Nitric Oxide Synthase Causes Elevation of Hearing Thresholds CARLTON J. ZDANSKI, MD (presenter), VINCENT CARRASCO, MD, JIRl PRAZMA, MD, PhD, KENNETH JOHNSON, BA, and HAROLD C. PILLSBURYIII, MD, Chapel Hill, N.C.
Poster 36
Medial Efferent Induced Fast, Slow, and Steady-State Changes of Ensemble Background Activity of the Auditory Nerve Recorded From Extracochlear Electrode in Awake Guinea Pigs During Contralateral Acoustic Stimulation, Differential Action of Gentamicin DEFSEMARA LIMA DA COSTA, PhD (presenter), JEAN-PAUL ERRE, CHRISTOPHE BLANCHET, PhD, RENAUD CHARLET DE SAUVAGE, PhD, and JEAN-MARIE ARAN, PhD, Porto Alegre, Brazil, and Bordeaux, France
The function of the medial olivocochlear efferent system was observed in awake guinea pigs by recording, in the absence of ipsilateral external acoustic stimulation, the ensemble background activity (EBA) of the VIIIth nerve (Dolan et al. J Acoust Soc Am 1990;87:2621-7) from an electrode chronically implanted on the round window of one ear, without and with the presentation of a low-level white noise to the opposite ear. This EBA was measured by calculating the power value of the round window signal in the band 0.5 to 2.5 kHz, after digital or analog (active) filtering. The contralateral white noise (CLWN, 55 dB SPL) induced, via the medial efferent system, a decrease (suppression) of this EBA (Popelar et al. IEB 1994, abstract P33; Popelar et al. Audi-
(Third Place Resident Basic Science Award) Objective: Nitric oxide (NO) mediates the effects of excitatory amino acids (EAA) in the central nervous system (CNS). The EAA are thought to be the neurotransmitter(s) at the cochlear hair cell-afferent nerve synapse. Nitric oxide synthase (NOS) is present in spiral ganglion cells. This study investigates the role of NO in cochlear neurotransmission. Methods: In gerbils, cochlear compound action potentials (CAP) thresholds were recorded before and after cochlear perfusions with control solutions of artificial perilymph solution (APS) and tesl solutions of S-methyl-L-thiocitrulline (MTC), a competitive inhibitor of NOS. Cochleae were also preperfused with L-arginine (L-Arg) prior to perfusion with a mixture of MTC/L-Arg (to overcome competitive inhibition by MTC with L-Arg, the natural substrate of NOS). Results: Cochlear perfusion with MTC caused significant elevation of CAP threshold of 51 dB as opposed to insignificant elevations of only 10 dB in control animals. An insignificant threshold shift of 9 dB was observed when LArg was co-perfused with MTC. Conclusions: Nitric oxide is involved in neurotransmission/neuromodulation in the cochlea. Because NO is both a
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Number 2
ficity of viral infection and duration of expression of the transgene integrated into the cellular genome. The results of this work and future implications are discussed. (This work was made possible in part by a grant from the American Academy of Otolaryngology Foundation, Inc.)
Poster 35 Brain Derived Neurotrophic Factor Gene Therapy Prevents Degeneration of Spiral Ganglion Neurons in a Mouse Model of Aminoglycoside Ototoxicity HINRICH STAECKER, MD, PhD (presenter), RAMIN GABAIZEDEH, HOWARD FEDERO1-r,MD, and THOMAS R. VAN DE WATER, PhD, City Island, Bronx, and Rochester, N,Y,
(Second Place Resident Clinical Science Award) Destruction of auditory hair ceils results in the secondary degeneration of auditory neurons. This is due to the loss of neurotrophic factor support from the auditory hair cells, namely neurotrophin 3 (NT-3) that is normally produced by the inner hair cells. Both in vitro and in vivo studies have shown that delivery of either NT-3 or brain-derived neurotrophic factor (BDNF) to these neurons can replace the trophic support supplied by the hair cells and prevent their degeneration. To prevent the degeneration of auditory neurons that occurs following neomycin destruction of the auditory hair cells, we used a replication defective herpes simplex-1 vector (HSVbdnflac) to transfect the gene for BDNF into the damaged spiral ganglion. Four weeks after HSVbdnflac therapy, we were able to detect stable functional production of BDNF that supported the survival of auditory neurons and prevented the loss of these neurons from trophic factor deprivation-induced apoptosis.
Research Forum - - M o n d a y
P95
tory Neuroscience. In press). With noise bursts of different durations, two levels of suppression could be observed, as recently reported (Sridhar et al. J Neurosci 1995;15:366778). After the onset of a 1-second CLWN, the power value of the EBA decreased rapidly by 36.0% _+ 7.8% (n = 14), with a latency of less than 10 msec and a time decay of 13.1 _+ 1.0 msec (n = 3) (mean _+SD, fast effect). At the offset of the 1-second CLWN, EBA came back to prestimulation values with a similar latency and a time constant of 15.5 _+2.9 msec. During longer CLWN (>1 minute) EBA presented, after the fast decrease, an additional, slower decrease of 16.8% _+5.9% (n = 11), with a time decay of 18.4 -e 7.4 sec (n = 7) (slow effect) and then remained remarkably constant for as far as was observed, that is, over 2 hours (steady state). The average global suppression was thus up to 51.3% +__8.3% of the basal, pre-CL stimulation EBA value. Fast and slow changes in EBA power values were observed during continuous or intermittent CLWN stimulation, after a single injection of gentamicin (150 mg/kg). Gentamicin progressively and reversibly blocked the rapid effect, but the slow component of the efferent medial suppression remained remarkably unchanged. These observations indicate that the medial efferent olivocochlear system exerts sustained influences on outer hair cetls and that this effect develops in two different steps, which may have different basic cellular mechanisms. Poster 37
Inhibition of Nitric Oxide Synthase Causes Elevation of Hearing Thresholds CARLTON J. ZDANSKI, MD (presenter), VINCENT CARRASCO, MD, JIRl PRAZMA, MD, PhD, KENNETH JOHNSON, BA, and HAROLD C. PILLSBURYIII, MD, Chapel Hill, N.C.
Poster 36
Medial Efferent Induced Fast, Slow, and Steady-State Changes of Ensemble Background Activity of the Auditory Nerve Recorded From Extracochlear Electrode in Awake Guinea Pigs During Contralateral Acoustic Stimulation, Differential Action of Gentamicin DEFSEMARA LIMA DA COSTA, PhD (presenter), JEAN-PAUL ERRE, CHRISTOPHE BLANCHET, PhD, RENAUD CHARLET DE SAUVAGE, PhD, and JEAN-MARIE ARAN, PhD, Porto Alegre, Brazil, and Bordeaux, France
The function of the medial olivocochlear efferent system was observed in awake guinea pigs by recording, in the absence of ipsilateral external acoustic stimulation, the ensemble background activity (EBA) of the VIIIth nerve (Dolan et al. J Acoust Soc Am 1990;87:2621-7) from an electrode chronically implanted on the round window of one ear, without and with the presentation of a low-level white noise to the opposite ear. This EBA was measured by calculating the power value of the round window signal in the band 0.5 to 2.5 kHz, after digital or analog (active) filtering. The contralateral white noise (CLWN, 55 dB SPL) induced, via the medial efferent system, a decrease (suppression) of this EBA (Popelar et al. IEB 1994, abstract P33; Popelar et al. Audi-
(Third Place Resident Basic Science Award) Objective: Nitric oxide (NO) mediates the effects of excitatory amino acids (EAA) in the central nervous system (CNS). The EAA are thought to be the neurotransmitter(s) at the cochlear hair cell-afferent nerve synapse. Nitric oxide synthase (NOS) is present in spiral ganglion cells. This study investigates the role of NO in cochlear neurotransmission. Methods: In gerbils, cochlear compound action potentials (CAP) thresholds were recorded before and after cochlear perfusions with control solutions of artificial perilymph solution (APS) and tesl solutions of S-methyl-L-thiocitrulline (MTC), a competitive inhibitor of NOS. Cochleae were also preperfused with L-arginine (L-Arg) prior to perfusion with a mixture of MTC/L-Arg (to overcome competitive inhibition by MTC with L-Arg, the natural substrate of NOS). Results: Cochlear perfusion with MTC caused significant elevation of CAP threshold of 51 dB as opposed to insignificant elevations of only 10 dB in control animals. An insignificant threshold shift of 9 dB was observed when LArg was co-perfused with MTC. Conclusions: Nitric oxide is involved in neurotransmission/neuromodulation in the cochlea. Because NO is both a
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