Mini Review: Central Organization of Airway Afferent Nerve Circuits.

Airway afferents monitor the local chemical and physical micro-environments in the airway wall and lungs and send this information centrally to regulate neural circuits involved in setting autonomic tone, evoking reflex and volitional respiratory motor outflows, encoding perceivable sensations and contributing to higher order cognitive processing. In this mini-review we present a current overview of the central wiring of airway afferent circuits in the brainstem and brain, highlighting recent discoveries that augment our understanding of airway sensory processing. We additionally explore how advances in describing the molecular diversity of airway afferents may influence future research efforts aimed at defining central mesoscale connectivity of airway afferent pathways. A refined understanding of how functionally distinct airway afferent pathways are organized in the brain will provide deeper insight into the physiology of airway afferent-evoked responses and may foster opportunities for targeted modulation of specific pathways involved in disease.

In vivo imaging of the nucleus of the solitary tract with Magnetization Transfer at 7 Tesla.

The nucleus of the solitary tract (NTS) is a nuclei complex with, among others, a high concentration of noradrenergic neurons (including the noradrenergic subnuclei named A1 and A2) in the medulla. The NTS regulates several cognitive, neuroendocrine and autonomic functions. No method currently exists to anatomically visualize the NTS in vivo. Several noradrenergic and dopaminergic nuclei have been successfully imaged using Magnetization Transfer (MT) contrast manipulation. We therefore hypothesized that an efficient, high-resolution MT-weighted sequence at 7 T might successfully image the NTS. In this study, we found a hyperintensity, similar to hyperintensities found in other noradrenergic and dopaminergic nuclei, consistent with the expected NTS location, and specific to the MT-weighted images. The localization of the hyperintensity was found to be consistent between individuals and slices and in good correspondence to a histological atlas and a meta-analytic map of fMRI-based NTS activation. We conclude that the method may, for the first time, achieve NTS imaging in vivo and within a clinically-feasible acquisition time. To facilitate NTS research at lower field strengths, an NTS template was created and made publicly available.

Ramsay Hunt syndrome associated with solitary nucleus, spinal trigeminal nucleus and tract, and vestibular nucleus involvement on sequential magnetic resonance imaging.

Ramsay Hunt syndrome (RHS) is an acute peripheral facial nerve paralysis typically accompanied by erythematous vesicular lesions of the auricular skin. The etiology is considered to be geniculate ganglionitis due to reactivation of varicella-zoster virus (VZV). Encephalitis is a rare but serious complication of VZV reactivation. Clarifying the regional and temporal evolution of the lesions on magnetic resonance imaging (MRI) would help with understanding the pathology of the lesion, but this information is lacking in encephalitis with RHS. Therefore, here, we reviewed sequential MR images in three RHS cases complicated by brainstem lesions. All the regions of the lesions represent specific neuronal structures-the ipsilateral solitary nucleus (SN) and spinal trigeminal nucleus and tract (STNT) in case 1; bilateral SN, ipsilateral STNT, and vestibular nucleus in case 2; ipsilateral SN and vestibular nucleus in case 3-and this seems to account for the persistent robust symptoms. Case 1 initially showed no abnormalities on MRI and cases 2 and 3 showed weak signals on the first MRI which subsequently plateaued. These observations suggest the timeframe within which it becomes possible to detect regional and temporal evolution, namely, that the distribution of the affected regions expands between weeks 2 and 5 after onset of facial paralysis. These observations and the findings of a literature review indicate that the SN, STNT, and vestibular nucleus are relatively prone to developing encephalitis after RHS.

Quantitative autoradiography of adrenergic, neuropeptide Y and angiotensin II receptors in the nucleus tractus solitarii and hypothalamus of rats with experimental hypertension.

Catecholamines, neuropeptide Y (NPY) and angiotensin II (Ang II) are known to participate in the central control of blood pressure. However, the modulation of these neurotransmitter receptors in response to a hypertensive stimulus is not appropriately established. The purpose of the present study was to examine binding parameters of alpha(2)-adrenergic, NPY and Ang II receptors in the nucleus tractus solitarii (NTS) and paraventricular hypothalamic nucleus (PVN) following a hypertensive stimulus in the aortic-coarcted rat by means of quantitative receptor autoradiography. No changes were seen in binding parameters of alpha(2)-adrenergic and NPY receptors in the NTS of the hypertensive rat compared to control. However, an increased affinity (54%) of noradrenaline competing for 3H-PAC was seen in the PVN. Moreover, an increased binding (49%) of 125I-PYY was also observed in the PVN. The affinity of Ang II for 125I-Sar(1)Ile(8)-Ang II binding sites was also increased (57%) in the NTS of the hypertensive rat. No changes in the binding parameters of radioactive Ang II were observed in the PVN. The results suggest that systems involved with hypertension like Ang II in the NTS and catecholamines in the PVN might collaborate in the development/maintenance of high blood pressure in the aortic-coarcted rat.