Auditory Functional MRI Findings in Patients with Unilateral Hearing Loss / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Auditory pathway is a unique sensory system in that its ascending pathway has both contralateral and ipsilateral projection to auditory cortex. It has been known that monaural auditory stimulation with auditory functional MRI (fMRI) in normal hearing subject produces bilateral auditory cortical activation, slightly lateralized to opposite side. Our goal was to assess the pattern of auditory cortical activation in patients with unilateral sensory neural hearing loss. SUBJECTS AND METHOD: Auditory fMRI studies using a single-shot gradient-recalled echo-planar imaging (EPI) sequence were performed in eight normal volunteers, thirteen patients with unilateral hearing loss of acute onset (AO, 3 months). A box-car design of 1, 000-Hz sine tone stimuli was given to right or left ear of normal volunteer and to healthy ears of patients. The data were analyzed by BOLD Analysis package. The lateralization index (LI) between contralateral and ipsilateral hemispheric activation were obtained by calculating and comparing the number of activated pixels in each auditory hemisphere. RESULTS: In normal volunteers, the LI was 2.9-5.2 for monaural stimuli suggesting contralateralization of auditory cortex to monaural stimuli. The LI was increased for the AO (8.1-19.2) and decreased for the LD (0.8-1.2). CONCLUSION: The auditory cortical activation in patients with unilateral sensory neural hearing loss showed different pattern according to the duration of hearing loss. The present results might suggest the time course of neuronal plasticity of auditory cortex after deterioration of input function of auditory ascending pathway.

The effect of sodium nitroprusside on muscle tension in guinea-pig ileum

Nitric oxide (NO) has been known as a mediator of nonadrenergic, noncholinergic inhibitory neurotransmitter in intestinal smooth muscles. It has been suggested that NO donor such as sodium nitroprusside (SNP) produces relaxation of smooth muscle via activation of guanylate cyclase and elevation of cGMP levels. We have therefore investigated the effects of NO, using SNP, on muscle tension in the longitudinal smooth muscle of guinea-pig ileum. The possible role of cGMP was also investigated as well as the involvement of K+ channel on SNP-induced inhibitory effect. The results are summarized as follows; high KCl-or CCh-activated contractions were inhibited by SNP in a concentration-dependent manner. 8-Br-cGMP also showed a similar effect in that of SNP. TEA (1 mM) significantly reduced the SNP-induced inhibitory effect. SNP-induced effect was further reduced by the presence of 10 mM TEA. On the other hand, 4-AP (0.1 mM), glibenclamide (10 muM) and apamin (0.1 muM) showed little effects on SNP-induced relaxation. Zaprinast significantly potentiated the SNP-induced inhibitory effect in all ranges. ODQ also significantly decreased the SNP-induced inhibitory effect. Pretreatment with CPA (10 muM) slightly reduced the SNP-induced inhibitory effect. From the above results, both effect mediated by NO and cGMP might be responsible for the activation of Ca2+/-activated K+ channel by SNP in guinea-pig ileum. And this K+ channel activation by SNP also contributes to the SNP-induced membrane hyperpolarization and relaxation.