Preclinical study investigating the potential of low-dose-rate brachytherapy with 32P stents for the prevention of restenosis of paranasal neo-ostia.

PURPOSE: Ostial restenosis is a common cause of failures in paranasal sinus surgery. The aim of the current study was to investigate the use of low-dose-rate brachytherapy to prevent neo-ostial restenosis in an animal model. METHODS AND MATERIALS: In 14 rabbits, maxillary neo-ostia were created and measured. One side each was stented with a regular silicone stent, the other side was either not stented (n = 7) or stented with a phosphorous-32 implanted stent depositing a low-dose radiation of 15 Gy (n = 7) within 1 week, after which all stents were removed. After a period of additional 12 weeks of recovery, the animals were sacrificed, the neo-ostia were again measured, and the areas and histopathologic changes compared in between the groups. RESULTS: After 15-Gy stenting, the mean ostial areas were even slightly enlarged by 5.1% compared to the area at stent removal, whereas a significant reduction in area, indicating a process of restenosis, by 56.1% or 54.0% was seen in the control groups with no stent and normal stent, respectively. Furthermore, no indication for adverse histopathologic radiation effects was seen in the 15-Gy group. CONCLUSIONS: Low-dose-rate brachytherapy with phosphorous-32 doped silicone stents showed promising results in the prevention of neo-ostium restenosis in this proof-of-concept study, indicating that further preclinical and clinical testing may be warranted.

Midazolam reverses salicylate-induced changes in brain-derived neurotrophic factor and arg3.1 expression: implications for tinnitus perception and auditory plasticity.

Tinnitus is a phantom auditory perception, which can be induced via application of concentrated sodium salicylate, and is known to be associated with hearing loss and altered neuronal excitability in peripheral and central auditory neurons. The molecular features of this excitability, however, has been poorly characterized to date. Brain-derived neurotrophic factor (BDNF), the activity-dependent cytoskeletal protein (Arg3.1, also known as Arc), and c-Fos are known to be affected by changes in excitability and plasticity. Using reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry, the expression of these genes was monitored in the rat auditory system after local (cochlear) and systemic application of salicylate. Induction of tinnitus and hearing loss was verified in a behavioral model. Regardless of the mode of salicylate application, a common pattern became evident: 1) BDNF mRNA expression was increased in the spiral ganglion neurons of the cochlea; and 2) Arg3.1 expression was significantly reduced in the auditory cortex. Local application of the GABA(A) receptor modulator midazolam resulted in the reversal not only of salicylate-induced changes in cochlear BDNF expression, but also in cortical Arg3.1 expression, indicating that the tinnitus-associated changes in cochlear BDNF expression trigger the decline of cortical Arg3.1 expression. Furthermore, local midazolam application reduced tinnitus perception in the animal model. These findings support Arg3.1 and BDNF as markers for activity changes in the auditory system and suggest a role of GABAergic inhibition of cochlear neurons in the modulation of Arg3.1 plasticity changes in the auditory cortex and tinnitus perception.

Sphingosine-1-phosphate modulates spiral modiolar artery tone: A potential role in vascular-based inner ear pathologies?

OBJECTIVE: The mechanisms regulating spiral modiolar artery (SMA) tone are not known, yet their characterization is pivotal for understanding inner ear blood flow regulation. Sphingosine-1-phosphate (S1P), known to stimulate vasoconstriction in several vascular beds, is a candidate regulator of SMA tone with potential pathophysiological relevance. METHODS: Gerbil SMAs were isolated, cannulated and pressurized (30 mm Hg transmural) for experimentation under near-in vivo conditions. For functional experiments, vascular diameter and intracellular Ca2+ were simultaneously measured. Standard RT-PCR and immunohistochemical techniques were also employed. RESULTS: mRNA transcripts encoding sphingosine kinase, S1P phosphohydrolase and three S1P receptors (S1P(1-3)) were detected in the SMA. S1P induced dose-dependent vasoconstriction of the SMA (EC50 = 115 nmol/L), and enhanced the apparent Ca2+-sensitivity of the contractile apparatus. Noradrenaline did not elicit vasoconstriction. The Rho kinase inhibitor Y27632 (1 micromol/L) reversed S1P-induced vasoconstriction and the S1P-mediated enhancement of Ca2+-sensitivity. RhoA was observed to translocate to the plasma membrane in response to stimulation with 30 micromol/L S1P. CONCLUSION: We conclude that all key signalling pathway constituents are present at the mRNA level for S1P to act as an endogenous regulator of SMA tone. S1P stimulates potent, RhoA/Rho kinase-dependent SMA vasoconstriction and Ca2+ sensitization. The high sensitivity to S1P suggests that SMA vasoconstriction is likely to occur under pathological conditions that increase intramural S1P concentrations (i.e., inflammation). From a clinical perspective, the present study identifies new potential therapeutic targets for the treatment of vascular-based, "stroke-like" inner ear pathologies: the enzymes responsible for S1P bioavailability and the S1P receptors.

Auditory nerve fibre responses to salicylate revisited.

Ototoxicity of salicylate is accompanied by a temporary hearing loss and tinnitus and has therefore been used to study tinnitus in animal models. Salicylate induced elevated central auditory activity has been interpreted as a correlate of tinnitus. Whether this elevated activity in the central auditory system is due to an increased activity in the auditory nerve is still under discussion. To explore this issue, we recorded the activity of single auditory nerve fibres in anaesthetised gerbils following systemic injection of salicylic acid. Firstly, compound action potential (CAP) thresholds were determined at 5-0 min intervals. Fifteen to 30 min after 200 mg/kg salicylic acid, threshold loss developed in the high frequency range. At 2 h CAP threshold loss reached a plateau amounting to 15-20 dB above 16 kHz, 0-5 dB below 2 kHz. An almost immediate start of threshold loss was observed after 400 mg/kg salicylic acid. A plateau of threshold loss was reached after 1.5 h with values of 25 dB in the high, 5-10 dB in the low frequency range. Secondly, responses of single auditory nerve fibres were studied after administration of 200 mg/kg salicylic acid. Frequency tuning curves and rate intensity (RI) functions at characteristic frequency (CF) were measured. Two hours and more after application, single fibre thresholds were elevated by about 20 dB at all CFs. Sharpness of tuning was reduced. Mean spontaneous rate was significantly reduced at CFs below 5 kHz (mean: 44 vs 28 AP/s). At CFs above 5 kHz mean spontaneous rate remained unchanged. In RI functions no change in maximum discharge rate was observed. The altered response properties can be interpreted by the known effects of salicylate on the prestin mediated active process of the outer hair cells. The elevated activity in the central auditory system after salicylate intoxication thus cannot be caused by cochlear nerve hyperactivity.

Neurotransmission of the cochlear inner hair cell synapse--implications for inner ear therapy.

The cochlear inner hair cells (IHCs) are connected to afferent type I auditory neurons and use probably L-glutamate as a neurotransmitter. This IHC synapse receives efferent input from the lateral part of the efferent olivocochlear system with neurons originating in the brainstem and terminating below IHCs synapsing with the afferent type I dendrites. A number of substances have been proposed to function as neurotransmitter or neuromodulator in the lateral efferent system: acetylcholine, gamma-aminobutyric acid (GABA), dopamine, enkephalin and dynorphin. With the aid of microiontophoretic techniques, we studied several transmitter candidates and characterized their receptor subtypes as well as their function on spontaneous or evoked activity of afferent dendrites. The results showed that the glutamatergic transmission of IHCs is facilitated by all types of glutamate receptors: ionotropic glutamate receptors of the N-methyl-D-aspartic acid (NMDA) and a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type as well as group I and II metabotropic glutamate receptors. This excitatory glutamatergic transmission is under inhibitory control of GABA (mediated by GABA(A) receptors) and dopamine (mediated by D1 and D2 receptors). In contrast, acetylcholine was able to excite afferent dendrites via muscarinic receptors. These results demonstrate that the lateral efferent system has modulatory function on the glutamatergic neurotransmission of IHCs. Excitation of afferent dendrites by glutamate released from IHCs can thus be tuned in different physiological or pathophysiological conditions. This could have therapeutic implications as it is known that noise exposure is followed by an excitotoxic injury of the IHC synapse. During overexcitation of IHCs, a possible therapy based on the neurochemical data would be (a) glutamate antagonists, (b) dopamine agonists, (c) GABA agonists or a combination from a, b and a, c.

Different action of memantine and caroverine on glutamatergic transmission in the mammalian cochlea.

Glutamate is the major transmitter candidate between inner hair cells and the afferent neurons of the mammalian cochlea. We investigated the action of memantine (1-amino-3,5-dimethyl-adamantane) and the quinoxaline derivative caroverine [1-diethylaminoethyl-3,8-(p-methoxybenzyl)-1,2-dihydro-quinoxaline-dione] on the glutamatergic transmission in the guinea pig cochlea utilizing extracellular recording techniques and microiontophoretic ejection of substances. While memantine was able to inhibit the NMDA (N-methyl-D-aspartate)-induced firing, the AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-stimulated activity was unaffected. In contrast, caroverine could block both NMDA- as well as AMPA-induced firing. As memantine and caroverine are currently in clinical use, these substances could be introduced to the treatment of several cochlear disorders.