Masakazu Hamamoto

Structural basis for cholinergic regulation of neural circuits in the mouse olfactory bulb: Cholinergic circuits in the mouse olfactory bulb

Odor information is regulated by olfactory inputs, bulbar interneurons, and centrifugal inputs in the olfactory bulb (OB). Cholinergic neurons projecting from the nucleus of the horizontal limb of the diagonal band of Broca and the magnocellular preoptic nucleus are one of the primary centrifugal inputs to the OB. In this study, we focused on cholinergic regulation of the OB and analyzed neural morphology with a particular emphasis on the projection pathways of cholinergic neurons. Single‐cell imaging of a specific neuron within dense fibers is critical to evaluate the structure and function of the neural circuits. We labeled cholinergic neurons by infection with virus vector and then reconstructed them three‐dimensionally. We also examined the ultramicrostructure of synapses by electron microscopy tomography. To further clarify the function of cholinergic neurons, we performed confocal laser scanning microscopy to investigate whether other neurotransmitters are present within cholinergic axons in the OB. Our results showed the first visualization of complete cholinergic neurons, including axons projecting to the OB, and also revealed frequent axonal branching within the OB where it innervated multiple glomeruli in different areas. Furthermore, electron tomography demonstrated that cholinergic axons formed asymmetrical synapses with a morphological variety of thicknesses of the postsynaptic density. Although we have not yet detected the presence of other neurotransmitters, the range of synaptic morphology suggests multiple modes of transmission. The present study elucidates the ways that cholinergic neurons could contribute to the elaborate mechanisms involved in olfactory processing in the OB. J. Comp. Neurol. 525:574–591, 2017.

Prognostic Factors in Sudden Sensorineural Hearing Loss

Objective: 1) Assess the prognostic factors possibly affecting hearing recovery, such as age, severity of hearing loss, definitive episode of vertigo, tinnitus, and ear fullness. 2) Assess the effect of corticosteroids in sudden sensorineural hearing loss (SSHL). Method: We reviewed the medical records of 117 patients seen at the outpatient clinic of Kawasaki Medical School Hospital between 2004 and 2008. Hearing loss was graded from 1 to 4 according to the grading system by the Research Committee on acute profound deafness of the Japanese Ministry of Health and Welfare. Results: Eighty-five patients were Grade-1 (under 40 dB hearing thresholds at the average of 0.25, 0.5, 1, 2, and 4 KHz), 22 were Grade-2 (40 to 60 dB), 9 were Grade-3 (60 to 90 dB), and one was Grade-4 (90 dB and over). The recovery rates after the treatment of hydrocortisone (300 mg/d for 3 days, 100 mg/d for 3 days) were 88.2% in Grade-1, 50% in Grade-2, and 30% in Grade-3 and -4. The recovery rate was significantly higher in Grade-1 and in cases in which that treatment was started within 7 days from the onset. Conclusion: Our study indicates that the prognostic factors affecting hearing recovery are the severity of hearing loss and the duration of disease between the onset and the initial treatment of corticosteroid. The age, presence of vertigo, tinnitus, and ear fullness did not influence the recovery rate.

Sudden Sensorineural Hearing Loss: Effective Steroid Dose

has a correlation with the air-volume of temporal bone. In other words, for a bad-development temporal bone, the second genu of facial nerve presents also with underdevelopment, with a short tympanic segment and an anteriorly located mastoid segment. 2) There is no doubt that the CT of temporal bone is very important in diagnosis of facial nerve abnormalities in congenital aural malformation. The theory is confirmed by surgery that the more serious the congenital aural malformation, the worse the course of the facial nerve is.