Osteocalcin-immunoreactive neurons in the vagal and glossopharyngeal sensory ganglia of the rat

Pharmacological activation of transient receptor potential vanilloid 4 promotes triggering of the swallowing reflex in rats

The swallowing reflex is an essential physiological reflex that allows food or liquid to pass into the esophagus from the oral cavity. Delayed triggering of this reflex is a significant health problem in patients with oropharyngeal dysphagia for which no pharmacological treatments exist. Transient receptor potential channels have recently been discovered as potential targets to facilitate triggering of the swallowing reflex. However, the ability of transient receptor potential vanilloid 4 (TRPV4) to trigger the swallowing reflex has not been studied. Here, we demonstrate the involvement of TRPV4 in triggering the swallowing reflex in rats. TRPV4 immunoreactive nerve fibers were observed in the superior laryngeal nerve (SLN)-innervated swallowing-related regions. Retrograde tracing with fluorogold revealed localization of TRPV4 on approximately 25% of SLN-afferent neurons in the nodose-petrosal-jugular ganglionic complex. Among them, approximately 49% were large, 35% medium, and 15% small-sized SLN-afferent neurons. Topical application of a TRPV4 agonist (GSK1016790A) to the SLN-innervated regions dose-dependently facilitated triggering of the swallowing reflex, with the highest number of reflexes triggered at a concentration of 250 μM. The number of agonist-induced swallowing reflexes was significantly reduced by prior topical application of a TRPV4 antagonist. These findings indicate that TRPV4 is expressed on sensory nerves innervating the swallowing-related regions, and that its activation by an agonist can facilitate swallowing. TRPV4 is a potential pharmacological target for the management of oropharyngeal dysphagia.

Sensory neurons in the human jugular ganglion

The jugular ganglion (JG) contains sensory neurons of the vagus nerve which innervate somatic and visceral structures in cranial and cervical regions. In this study, the number of sensory neurons in the human JG was investigated. And, the morphology of sensory neurons in the human JG and nodose ganglion (NG) was compared. The estimated number of JG neurons was 2721.8-9301.1 (average number of sensory neurons ± S.D. = 7975.1 ± 3312.8). There was no significant difference in sizes of the neuronal cell body and nucleus within the JG (cell body, 1128.8 ± 99.7 μ m²; nucleus, 127.7 ± 20.8 μ m²) and NG (cell body, 963.8 ± 225.7 μ m²; nucleus, 123.2 ± 32.3 μ m²). These findings indicate that most of sensory neurons show the similar morphology in the JG and NG. Our immunohistochemical method also demonstrated the distribution of ion channels, neurotransmitter agents and calcium-binding proteins in the human JG. Numerous JG neurons were immunoreactive for transient receptor potential cation channel subfamily V member 1 (TRPV1, mean ± SD = 19.9 ± 11.5 %) and calcitonin gene-related peptide (CGRP, 28.4 ± 6.7 %). A moderate number of JG neurons contained TRPV2 (12.0 ± 4.7 %), substance P (SP, 15.7 ± 6.9 %) and secreted protein, acidic and rich in cysteine-like 1 (SPARCL1, 14.6 ± 7.4 %). A few JG neurons had vesicular glutamate transporter 2 (VGLUT2, 5.6 ± 2.9 %) and parvalbumin (PV, 2.3 ± 1.4 %). SP- and TRPV2-containing JG neurons had mainly small and medium-sized cell bodies, respectively. TRPV1- and VGLUT2- containing JG neurons were small to medium-sized. CGRP- and SPARCL1-containing JG neurons were of various cell body sizes. Sensory neurons in the human JG were mostly free of vasoactive intestinal polypeptide (VIP), tyrosine hydroxylase (TH) and neuropeptide Y (NPY). In the external auditory canal skin, subepithelial nerve fibers contained TRPV1, TRPV2, SP, CGRP and VGLUT2. Perivascular nerve fibers also had TRPV1, TRPV2, SP, CGRP, VIP, NPY and TH. However, PV- and SPARCL1-containing nerve endings could not be seen in the external auditory canal. It is likely that sensory neurons in the human JG can transduce nociceptive and mechanoreceptive information from the external auditory canal. Theses neurons may be also associated with neurogenic inflammation in the external auditory canal and ear-cough reflex through the vagus nerve.

Altered Ethanol Consumption in Osteocalcin Null Mutant Mice

Osteocalcin (OC) is an abundant extracellular calcium-binding protein synthesized by osteoblasts. Although most OC is bound to hydroxyapatite mineral during bone formation, a consistent amount is released directly to circulation. Plasma OC (pOC) levels are highly sensitive to stressful stimuli that alter stress-responsive hormones, such as glucocorticoids (cortisol or corticosterone) and the catecholamines norepinephrine and epinephrine. To gain a better understanding of the apparent relationship of OC to the effects of ethanol (EtOH) and the stress responses, we compared mice that have OC (WT [OC+/+] and HET [OC+/-]) with OC null mutants (KO [OC-/-]), which have no OC in either plasma or in bone. One experiment included chronic unpredictable stress, a second was conducted in the absence of any known stressors other than EtOH, while a third imposed a more severe acute immobilization stress in addition to EtOH consumption. The data obtained confirmed significant differences in EtOH consumption in mice that previously experienced various stressful stimuli. We also determined that adrenal tyrosine-hydroxylase expression was inversely proportional to EtOH consumption and tended to be lower in KO than in WT. Data suggest that OC possesses the ability to modulate the adrenal gene expression of the catecholamine synthetic pathway. This modulation may be responsible for differences in EtOH consumption under stress.

Decreased sensory responses in osteocalcin null mutant mice imply neuropeptide function

Osteocalcin, the most abundant member of the family of extracellular mineral binding gamma-carboxyglutamic acid proteins is synthesized primarily by osteoblasts. Its affinity for calcium ions is believed to limit bone mineralization. Several of the numerous hormones that regulate synthesis of osteocalcin, including glucocorticoids and parathyroid hormone, are also affected by stressful stimuli that require energy for an appropriate response. Based on our observations of OC responding to stressful sensory stimuli, the expression of OC in mouse and rat sensory ganglia was confirmed. It was thus hypothesized that the behavioral responses of the OC knockout mouse to stressful sensory stimuli would be abnormal. To test this hypothesis, behaviors related to sensory aspects of the stress response were quantified in nine groups of mice, aged 4-14 months, comparing knockout with their wild-type counterparts in six distinctly different behavioral tests. Resulting data indicated the following statistically significant differences: open field grooming frequency following saline injection, wild-type > knockout; paw stimulation with Von Frey fibers, knockout < wild-type; balance beam, knockout mobility < WT; thermal sensitivity to heat (tail flick), knockout < wild-type; and cold, knockout < wild-type. Insignificant differences in hanging wire test indicate that these responses are unrelated to reduced muscle strength. Each of these disparate environmental stimuli provided data indicating alterations of responses in knockout mice that suggest participation of osteocalcin in transmission of information about those sensory stimuli.

The survival of vagal and glossopharyngeal sensory neurons is dependent upon dystonin

The vagal and glossopharyngeal sensory ganglia and their peripheral tissues were examined in wild type and dystonia musculorum mice to assess the effect of dystonin loss of function on chemoreceptive neurons. In the mutant mouse, the number of vagal and glossopharyngeal sensory neurons was severely decreased (70% reduction) when compared with wild type littermates. The mutation also reduced the size of the circumvallate papilla (45% reduction) and the number of taste buds (89% reduction). In addition, immunohistochemical analysis demonstrated that the dystonin mutation reduced the number of PGP 9.5-, calcitonin gene-related peptide-, P2X3 receptor- and tyrosine hydroxylase-containing neurons. Their peripheral endings also decreased in the taste bud and epithelium of circumvallate papillae. These data together suggest that the survival of vagal and glossopharyngeal sensory neurons is dependent upon dystonin.

Peptide 19 in the rat vagal and glossopharyngeal sensory ganglia

Peptide 19 (PEP 19) is a 7.6-kDa polypeptide which binds to calmodulin and inhibits calcium-calmodulin signaling. In this study, PEP 19-immunoreactivity (PEP 19-IR) was examined in the rat vagal and glossopharyngeal sensory ganglia. Twenty-nine percent, 59%, and 41% of sensory neurons contained PEP 19-IR in the jugular, petrosal, and nodose ganglia, respectively. These neurons were of various sizes (jugular, mean +/- SD = 635.8 +/- 392.6 microm2, range = 105.9-1695.9 microm2; petrosal, mean +/- SD = 370.9 +/- 228.5 microm2, range = 57.7-1662.7 microm2; nodose, mean +/- SD = 380.5 +/- 157 microm2, range = 87.5-950.4 microm2) and scattered throughout these ganglia. Double immunofluorescence method revealed that PEP 19-IR neurons which had parvalbumin-IR were rare in the ganglia (jugular, 4%; petrosal, 10%; nodose, 8%). PEP 19-IR neurons which contained calbindin D-28k were abundant in the petrosal (20%) and nodose (22%) ganglia but not in the jugular ganglion (8%). Retrograde tracing method indicated that many PEP 19-IR neurons projected to the circumvallate papilla and soft palate. In the soft palate, taste buds were innervated by PEP 19-IR nerve fibers. The present study suggests that PEP 19-IR neurons include chemoreceptors in the vagal and glossopharyngeal sensory ganglia.