Sensory Neurons in the Human Geniculate Ganglion

Abstract

The geniculate ganglion (GG) contains visceral and somatic sensory neurons of the facial nerve. In this study, the number and cell size of sensory neurons in the human GG were investigated. The estimated number of GG neurons ranged from 1,580 to 2,561 (mean ± SD = 1,960 ± 364.6). The cell size of GG neurons ranged from 393.0 to 2,485.4 μm² (mean ± SD = 1,067.4 ± 99.5 μm²). Sensory neurons in the GG were significantly smaller in size than those in the dorsal root (range = 326.6-5343.4 μm², mean ± SD = 1,683.2 ± 203.8 μm²) or trigeminal ganglia (range = 349.6-4,889.28 μm², mean ± SD = 1,529.0 ± 198.48 μm²). Sensory neurons had similar cell body sizes in the GG and nodose ganglion (range = 357.2-3,488.33 μm², mean ± SD = 1,160.4 ± 156.61 μm²). These findings suggest that viscerosensory neurons have smaller cell bodies than somatosensory neurons. In addition, immunohistochemistry for several neurochemical substances was performed on the human GG. In the ganglion, sensory neurons were mostly immunoreactive for secreted protein, acidic and rich in cysteine-like 1 (94.3%). One third of GG neurons showed vesicular glutamate transporter 2 immunoreactivity (31.3%). Only 7.3% of GG neurons were immunoreactive for transient receptor potential cation channel subfamily V member 1. Sensory neurons in the human GG may respond to gustatory, nociceptive, and/or mechanoreceptive stimuli from tongues, soft palates, and external auditory canals.

Distribution of neuronal cells which contain dopamine β‐hydroxylase, tyrosine hydroxylase, neuropeptide Y and vasoactive intestinal polypeptide in the human internal carotid nerve

“…The diameter of nucleoli in ICN neurons was also measured in some sections of each sample. The total number of ICN neurons was estimated by the average diameter of nucleoli (Table 2) and the thickness of sections (8 μm) (Hedreen, 1998; Sato et al, 2017).…”