Nitric oxide synthase in trigeminal ganglion cells projecting to the cochlea of rat and guinea pig

Association between convergence insufficiency and temporomandibular disorder cross-sectional study

OBJECTIVES

Evaluate whether there is an association between convergence insufficiency and temporomandibular disorder (TMD) and whether there is an association between pain and range of motion in different degrees of TMD.

METHODS

We evaluated 138 individuals with TMD and 46 without TMD using the Research Diagnostic Criteria for temporomandibular disorders, the Fonseca Anamnestic Index (FAI), Numeric Pain Rating Scale, and the measurement of mandibular range of motion (ROM). Convergence insufficiency was diagnosed using the convergence test and Convergence Insufficiency Symptom Survey. Analysis of variance was used to compare age and mandibular ROM. The Kruskal-Wallis was used to compare mandibular ROM and pain between groups. The chi-square test was used to evaluate associations between TMD subgroups and the FAI, sex, and ocular convergence.

RESULTS

The majority of individuals without TMD did not exhibit convergence insufficiency. The frequency convergence insufficiency was significantly higher among individuals with severe TMD (p < 0.003). Mean pain severity differed between individuals with and without TMD. Mandibular ROM diminished with the increase in TMD severity.

CONCLUSIONS

Convergence insufficiency, age, the increase in pain, and the reduction in mandibular range of motion were associated with the degrees of TMD severity. Despite the significant associations between convergence insufficiency and both pain and TMD severity, these variables cannot be indicated as predictive factors due to the low variability in the linear regression analysis.

CLINICAL RELEVANCE

The present findings can assist in decision making regarding the treatment of severe TMD and the evaluation of ocular convergence.

Dental Occlusion and Ophthalmology: A Literature Review

Stomatognathic system is strictly correlated to other anatomical regions; many studies investigated relationship between temporomandibular joint and posture, several articles describe cranio-facial pain from dental causes, such as trigger points. Until now less interest has been given to connections between dental occlusion and ophthalmology, even if they are important and involving. Clinical experience in dental practice claims that mandibular latero-deviation is connected both to eye dominance and to defects of ocular convergence. The trigeminal nerve is the largest and most complex of the twelve cranial nerves. The trigeminal system represents the connection between somitic structures and those derived from the branchial arches, collecting the proprioception from both somitic structures and oculomotor muscles. The intermedius nucleus of the medulla is a small perihypoglossal brainstem nucleus, which acts to integrate information from the head and neck and relays it on to the nucleus of the solitary tract where autonomic responses are generated. This intriguing neurophysiological web led our research group to investigate anatomical and functional associations between dental occlusion and vision. In conclusion, nervous system and functional pathways strictly connect vision and dental occlusion, and in the future both dentists and oculists should be more and more aware of this correlation for a better diagnosis and therapy.

Co-localization of the vanilloid capsaicin receptor and substance P in sensory nerve fibers innervating cochlear and vertebro-basilar arteries

Evidence suggests that capsaicin-sensitive substance P (SP)-containing trigeminal ganglion neurons innervate the spiral modiolar artery (SMA), radiating arterioles, and the stria vascularis of the cochlea. Antidromic electrical or chemical stimulation of trigeminal sensory nerves results in neurogenic plasma extravasation in inner ear tissues. The primary aim of this study was to reveal the possible morphological basis of cochlear vascular changes mediated by capsaicin-sensitive sensory nerves. Therefore, the distribution of SP and capsaicin receptor (transient receptor potential vanilloid type 1-TRPV1) was investigated by double immunolabeling to demonstrate the anatomical relationships between the cochlear and vertebro-basilar blood vessels and the trigeminal sensory fiber system. Extensive TRPV1 and SP expression and co-localization were observed in axons within the adventitial layer of the basilar artery, the anterior inferior cerebellar artery, the SMA, and the radiating arterioles of the cochlea. There appears to be a functional relationship between the trigeminal ganglion and the cochlear blood vessels since electrical stimulation of the trigeminal ganglion induced significant plasma extravasation from the SMA and the radiating arterioles. The findings suggest that stimulation of paravascular afferent nerves may result in permeability changes in the basilar and cochlear vascular bed and may contribute to the mechanisms of vertebro-basilar type of headache through the release of SP and stimulation of TPVR1, respectively. We propose that vertigo, tinnitus, and hearing deficits associated with migraine may arise from perturbations of capsaicin-sensitive trigeminal sensory ganglion neurons projecting to the cochlea.

Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephalic trigeminal nucleus

A characteristic peculiarity of the trigeminal sensory system is the presence of two distinct populations of primary afferent neurons. Most of their cell bodies are located in the trigeminal ganglion (TG) but part of them lie in the mesencephalic trigeminal nucleus (MTN). This review compares the neurochemical content of central versus peripheral trigeminal primary afferent neurons. In the TG, two subpopulations of primary sensory neurons, containing immunoreactive (IR) material, are identified: a number of glutamate (Glu)-, substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)-, cholecystokinin (CCK)-, somatostatin (SOM)-, vasoactive intestinal polypeptide (VIP)- and galanin (GAL)-IR ganglion cells with small and medium-sized somata, and relatively less numerous larger-sized neuropeptide Y (NPY)- and peptide 19 (PEP 19)-IR trigeminal neurons. In addition, many nitric oxide synthase (NOS)- and parvalbumin (PV)-IR cells of all sizes as well as fewer, mostly large, calbindin D-28k (CB)-containing neurons are seen. The majority of the large ganglion cells are surrounded by SP-, CGRP-, SOM-, CCK-, VIP-, NOS- and serotonin (SER)-IR perisomatic networks. In the MTN, the main subpopulation of large-sized neurons display Glu-immunoreactivity. Additionally, numerous large MTN neurons exhibit PV- and CB-immunostaining. On the other hand, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS-containing neurons can be detected in the caudal and the mesencephalic-pontine junction portions of the nucleus. Conversely, no immunoreactivity to any of the examined neuropeptides is observed in the cell bodies of MTN neurons but these are encircled by peptidergic, catecholaminergic, serotonergic and nitrergic perineuronal arborizations in a basket-like manner. Such a discrepancy in the neurochemical features suggests that the differently fated embryonic migration, synaptogenesis, and peripheral and central target field innervation can possibly affect the individual neurochemical phenotypes of trigeminal primary afferent neurons.

Co-existence of tyrosine hydroxylase and calcitonin gene-related peptide in cochlear spiral modiolar artery of guinea pigs

The distribution of tyrosine hydroxylase (TH) and calcitonin gene-related peptide (CGRP) on the cochlear spiral modiolar artery (SMA) was investigated in the guinea pig. The SMA was dissected from the modiolus so that the entire length of the vessel and many of its branches could be observed. Immunohistochemical labeling and double immunofluorescence were employed to localize each compound and to determine whether the TH and CGRP co-exist in neurons of the SMA. Microscopic examination of whole vessel preparations revealed numerous TH- and CGRP-positive neural networks innervating the SMA and its branches. The labeled neurons showed distinct arborization, varicosities and overlap, and were of different diameters. Confocal immunofluorescence microscopy of double-labeled TH and CGRP neurons showed that a number of the TH- and CGRP-positive neurons were co-labeled. Thus, TH and CGRP partially co-exist within the neuronal innervation of SMA. These findings support a hypothesis that specific neuropeptide and adrenergic neurons regulate cochlear blood flow.

Distribution and projections of nitric oxide synthase neurons in the rodent superior olivary complex

The superior olivary complex (SOC), a group of interrelated brainstem nuclei, sends efferents to a variety of neuronal structures including the cochlea and the inferior colliculus. The present review describes data obtained from rodents providing evidence that the gaseous, short-living neuroactive substance nitric oxide (NO) is produced in the SOC. The NO-synthesizing enzyme neuronal NO-synthase (nNOS) has been localized by means of several methods including histochemistry and immunohistochemistry. Perikarya containing nNOS were found in several nuclei of the SOC. Their largest numbers and percentages of total cells were observed in the medial nucleus of the trapezoid body. Stained terminals were observed mainly in the lateral superior olivary nucleus and in the superior paraolivary nucleus. While retrograde neuronal tracing identified a considerable number of nNOS-immunoreactive neurons as to be part of the olivo-cochlear pathway, the projection patterns of other nNOS-immunoreactive SOC cell groups remain to be investigated. We also review other putative sources of cochlear NO, and discuss the possible role of NO in the lower auditory brainstem and organ of Corti with regard to physiological and pathophysiological mechanisms.

Evidence for increased nitric oxide production in the auditory brain stem of the aged dwarf hamster (Phodopus sungorus): an NADPH-diaphorase histochemical study

Age-related changes of the auditory system such as presbyacusis are believed to be due, at least in part, to alterations of central structures. The superior olivary complex (SOC), a group of interrelated brain stem nuclei, projects to a variety of neuronal structures including the cochlea and the inferior colliculus (IC). The soluble gas nitric oxide (NO), believed to function as a neuroactive substance within the SOC and cochlea, is thought to be involved in ageing processes. Since it is unknown whether NO-production is altered in the ageing auditory system, the present study was conducted to investigate whether the number of NO-producing cells in the SOC is changed with increasing age. The histochemical detection of NADPH-diaphorase activity (NADPH-d), a marker for neurons containing NOS, was utilized to investigate the numbers of NO-producing cells in the SOC of adult and senile Djungarian dwarf hamsters (Phodopus sungorus). Our results demonstrate that the number of stained neurons was almost doubled in the SOC of senile hamsters. The most distinct changes were observed in the medial nucleus of the trapezoid body. In contrast, NO-producing preganglionic sympathetic neurons of the spinal intermediolateral nucleus, which was studied for comparison, did not exhibit significant differences between adult and senile animals. It is concluded that the increase of NO-production in the ageing auditory brain stem, as revealed by our data, may be related to hearing impairments with increasing age.