Differential age-, gender-, and side-dependency of vagus, spinal accessory, and phrenic nerve calibers detected with precise ultrasonography measures.

INTRODUCTION: The standard ultrasonographic measurement tools (trace, ellipse) of cross-sectional areas (CSAs) of very small nerves typically yield rough measures in full square millimeters. METHODS: In 70 volunteers, the elliptically shaped CSAs of mid-cervical vagus, accessory, and phrenic nerves were estimated with three methods: 2 on-board tools (area tracing, ellipse fitting) and an off-line calculation of the CSA after on-board measuring of its long-axis and short-axis diameters both displayed with 1-2 digits following the decimal point. RESULTS: CSA measures of all mid-cervical nerves obtained with the precise approach were smaller than the two standard measures (each P < 0.001). Larger CSA of right compared to left vagus nerve was detected with all methods. However, decrease of accessory and phrenic nerve CSAs with increasing age and larger size of vagus nerve CSA in women vs. men were evident only with precise measures. DISCUSSION: Small nerve CSA should preferably be estimated with precise measures. Muscle Nerve 59:486-491, 2019.

Functional redundancy and gustatory development in bdnf null mutant mice.

In the mouse nasopalate papilla and in the trenches of the foliate and vallate papillae, taste buds accumulated primarily during the first 2 weeks after birth. Null mutation for brain-derived neurotrophic factor caused extensive death of embryonic taste neurons, with the secondary outcome that most taste buds failed to form. However not all taste neurons died; functional redundancy rescued a variable number. The primary research objective was to identify the likely site of the taste neuron rescue factor that substituted for BDNF. In this quest taste bud abundance served as a useful gauge of taste neuron abundance. The proportion of taste buds that developed was variable and uncorrelated among the nasopalate, vallate, and foliate gustatory papillae within each bdnf null mutant mouse. Thus, in spite of shared IXth nerve innervation, the vallate and foliate papillae independently varied in residual gustatory innervation. This variation rules against the rescue of gustatory neurons by system-wide factors or by factors acting on the IXth ganglion or nerve trunk. Therefore it is likely that surviving BDNF-deprived taste neurons were stochastically rescued by a redundant neurotrophic factor at the level of the local gustatory epithelium. These findings broaden the classic expectation that target tissue supplies only a single neurotrophic factor that can sustain sensory (taste) neurons.