Distribution of Fos-Like Immunoreactivity, Catecholaminergic and Serotoninergic Neurons Activated by the Laryngeal Chemoreflex in the Medulla Oblongata of Rats

Review: Neuropathology findings in autonomic brain regions in SUDEP and future research directions

Autonomic dysfunction is implicated from clinical, neuroimaging and experimental studies in sudden and unexpected death in epilepsy (SUDEP). Neuropathological analysis in SUDEP series enable exploration of acquired, seizure-related cellular adaptations in autonomic and brainstem autonomic centres of relevance to dysfunction in the peri-ictal period. Alterations in SUDEP compared to control groups have been identified in the ventrolateral medulla, amygdala, hippocampus and central autonomic regions. These involve neuropeptidergic, serotonergic and adenosine systems, as well as specific regional astroglial and microglial populations, as potential neuronal modulators, orchestrating autonomic dysfunction. Future research studies need to extend to clinically and genetically characterized epilepsies, to explore if common or distinct pathways of autonomic dysfunction mediate SUDEP. The ultimate objective of SUDEP research is the identification of disease biomarkers for at risk patients, to improve post-mortem recognition and disease categorisation, but ultimately, for exposing potential treatment targets of pharmacologically modifiable and reversible cellular alterations.

Role of central kisspeptin and RFRP-3 in energy metabolism in the male Wistar rat

Kisspeptin (Kp) and (Arg)(Phe) related peptide 3 (RFRP-3) are two RF-amides acting in the hypothalamus to control reproduction. In the past 10 years, it has become clear that, apart from their role in reproductive physiology, both neuropeptides are also involved in the control of food intake, as well as glucose and energy metabolism. To investigate further the neural mechanisms responsible for these metabolic actions, we assessed the effect of acute i.c.v. administration of Kp or RFRP-3 in ad lib. fed male Wistar rats on feeding behaviour, glucose and energy metabolism, circulating hormones (luteinising hormone, testosterone, insulin and corticosterone) and hypothalamic neuronal activity. Kp increased plasma testosterone levels, had an anorexigenic effect and increased lipid catabolism, as attested by a decreased respiratory exchange ratio (RER). RFRP-3 also increased plasma testosterone levels but did not modify food intake or energy metabolism. Both RF-amides increased endogenous glucose production, yet with no change in plasma glucose levels, suggesting that these peptides provoke not only a release of hepatic glucose, but also a change in glucose utilisation. Finally, plasma insulin and corticosterone levels did not change after the RF-amide treatment. The Kp effects were associated with an increased c-Fos expression in the median preoptic area and a reduction in pro-opiomelanocortin immunostaining in the arcuate nucleus. No effects on neuronal activation were found for RFRP-3. Our results provide further evidence that Kp is not only a very potent hypothalamic activator of reproduction, but also part of the hypothalamic circuit controlling energy metabolism.

Medullary tyrosine hydroxylase catecholaminergic neuronal populations in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) is mechanistically complex and one probable cause is seizure‐related respiratory dysfunction. Medullary respiratory regulatory nuclei include the pre‐Bötzinger complex (pre‐BötC) in the ventrolateral medulla (VLM), the medullary raphé nuclei (MR) and nucleus of solitary tract in the dorsomedial medulla (DMM). The region of the VLM also contains intermingled tyrosine hydroxylase (TH) catecholaminergic neurones which directly project to the pre‐BötC and regulate breathing under hypoxic conditions and our aim was to evaluate these neurones in SUDEP cases. In post‐mortem cases from three groups [SUDEP (18), epilepsy controls (8) and non‐epilepsy controls (16)] serial sections of medulla (obex + 2 to + 13 mm) were immunolabeled for TH. Three regions of interest (ROI) were outlined (VLM, DMM and MR) and TH‐immunoreactive (TH‐IR) neurones were evaluated using automated detection for overall labeling index (neurones and processes) and neuronal densities and compared between groups and relative to obex level. C‐fos immunoreactivity was also semi‐quantitatively evaluated in these regions. We found no significant difference in the density of TH‐IR neurones or labeling index between the groups in all regions. Significantly more TH‐IR neurones were present in the DMM region than VLM in non‐epilepsy cases only (P < 0.01). Regional variations in TH‐IR neurones with obex level were seen in all groups except SUDEP. We also identified occasional TH neurones in the MR region in all groups. There was significantly less c‐fos labeling in the VLM and MR in SUDEP than non‐epilepsy controls but no difference with epilepsy controls. In conclusion, in this series we found no evidence for alteration of total medullary TH‐IR neuronal numbers in SUDEP but noted some differences in their relative distribution in the medulla and c‐fos neurones compared to control groups which may be relevant to the mechanism of death.

Laryngeal Mask Ventilation during Tracheostomy Improves Intraoperative Hemodynamic Stability in Patients Undergoing Total Laryngectomy

Background and objectives: Laryngectomy with extensive extirpational neck dissection is still the treatment of choice for patients with advanced laryngeal cancer. During the initial part of laryngectomy – tracheostomy, there is a significant upper airway obstruction, caused by the cancer process itself and worsened by surgical pressure and manipulation during creation of tracheostomy. This study aims to make comparative assessment of the patient’s hemodynamic parameters, operated using three of the most popular approaches during tracheostomy: local anesthesia with preserved spontaneous ventilation; general anesthesia with ventilation by endotracheal intubation and general anesthesia with ventilation by laryngeal mask airway.

Methods: A prospective cohort study was conducted in a tertiary referral center. Sixty patients with advanced laryngeal cancer appointed for total laryngectomy, were enrolled in the study. They were randomly assigned into three groups, according to the ventilation method used during the tracheostomy.

Results: Patients who underwent tracheostomy under local anesthesia displayed statistically the highest levels of SAP, DAP, MAP and heart rate intraoperatively. The group of patients who underwent tracheostomy with endotracheal intubation, also displayed significantly higher levels of hemodynamic parameters during the procedure compared with the group with laryngeal mask airway ventilation, despite the fact that both groups were under general anesthesia.

Conclusions: To our knowledge, this is the first study to demonstrate that laryngeal mask ventilation during tracheostomy improves intraoperative hemodynamic stability in patients undergoing total laryngectomy compared to endotracheal intubation.

Vagal Afferent Processing by the Paratrigeminal Nucleus

The paratrigeminal nucleus is an obscure region in the dorsal lateral medulla, which has been best characterized as a collection of interstitial cells located in the dorsal tip of the spinal trigeminal tract. The paratrigeminal nucleus receives afferent input from the vagus, trigeminal, spinal, and glossopharyngeal nerves, which contribute to its long-known roles in the baroreceptor reflex and nociceptive processing. More recently, studies have shown that this region is also involved in the processing of airway-derived sensory information. Notably, these studies highlight an underappreciated complexity in the neuronal content and circuit connectivity of the paratrigeminal nucleus. However, much remains to be understood about how paratrigeminal processing of vagal afferents is altered in disease. The aim of the present review is to provide an update of the current understanding of vagal afferent processing in the paratrigeminal nucleus and to explore how dysregulation at this site may contribute to vagal sensory neural dysfunction during disease.

Medullary mediation of the laryngeal adductor reflex: A possible role in sudden infant death syndrome

The laryngeal adductor reflex (LAR) is a laryngeal protective reflex. Vagal afferent polymodal sensory fibres that have cell bodies in the nodose ganglion, originate in the sub-glottal area of the larynx and upper trachea. These polymodal sensory fibres respond to mechanical or chemical stimuli. The central axons of these sensory vagal neurons terminate in the dorsolateral subnuclei of the tractus solitarius in the medulla oblongata. The LAR is a critical, reflex in the pathways that play a protective role in the process of ventilation, and the sychronisation of ventilation with other activities that are undertaken by the oropharyngeal systems including: eating, speaking and singing. Failure of the LAR to operate properly at any time after birth can lead to SIDS, pneumonia or death. Despite the critical nature of this reflex, very little is known about the central pathways and neurotransmitters involved in the management of the LAR and any disorders associated with its failure to act properly. Here, we review current knowledge concerning the medullary nuclei and neurochemicals involved in the LAR and propose a potential neural pathway that may facilitate future SIDS research.