Parasympathetic preganglionic cardiac motoneurons labeled after voluntary diving

Abstract

A dramatic bradycardia is induced by underwater submersion in vertebrates. The location of parasympathetic preganglionic cardiac motor neurons driving this aspect of the diving response was investigated using cFos immunohistochemistry combined with retrograde transport of cholera toxin subunit B (CTB) to double-label neurons. After pericardial injections of CTB, trained rats voluntarily dove underwater, and their heart rates (HR) dropped immediately to 95 ± 2 bpm, an 80% reduction. After immunohistochemical processing, the vast majority of CTB labeled neurons were located in the reticular formation from the rostral cervical spinal cord to the facial motor nucleus, confirming previous studies. Labeled neurons caudal to the rostral ventrolateral medulla were usually spindle-shaped aligned along an oblique line running from the dorsal vagal nucleus to the ventrolateral reticular formation, while those more rostrally were multipolar with extended dendrites. Nine percent of retrogradely-labeled neurons were positive for both cFos and CTB after diving and 74% of these were found rostral to the obex. CTB also was transported transganglionically in primary afferent fibers, resulting in large granular deposits in dorsolateral, ventrolateral, and commissural subnuclei of the nucleus tractus solitarii (NTS) and finer deposits in lamina I and IV-V of the trigeminocervical complex. The overlap of parasympathetic preganglionic cardiac motor neurons activated by diving with those activated by baro- and chemoreceptors in the rostral ventrolateral medulla is discussed. Thus, the profound bradycardia seen with underwater submersion reinforces the notion that the mammalian diving response is the most powerful autonomic reflex known.

Repetitive Diving in Trained Rats Still Increases Fos Production in Brainstem Neurons after Bilateral Sectioning of the Anterior Ethmoidal Nerve

“…The activation of these secondary neurons then, in turn, activates other brainstem neurons responsible for the efferent aspects of the diving response. More specifically, neurons in the caudal pressor area (CPA), nucleus of the solitary tract (NTS), raphe nuclei (Ra), rostrolventrolateral medulla (RVLM), catecholaminergic regions (A1, A2, A5, C1, and C2), locus coeruleus (LC), Kölliker-Fuse area (KF), and Parabrachial nucleus (PB) all show an increase in Fos expression during repetitive diving in rats trained to voluntarily swim underwater (McCulloch and Panneton, 2003 ; Panneton et al, 2010a , 2012a , 2014 ).…”

Current status and potential challenges of mesenchymal stem cell-based therapy for malignant gliomas

“…Several signalling pathways, such as the TGF-β superfamily [ 36 , 37 ], Hedgehog [ 38 ], and Wnt signalling [ 39 ], regulate and control the biological characteristics of MSCs. Recently, some new mechanisms, including miRNAs [ 40 , 41 ] and lncRNAs [ 42 ], were reported to regulate the biological features. With a better understanding of MSCs, studies have aimed to modulate the biological characteristics of MSCs to treat several diseases, such as myocardial infarction, nerve injury, and arthritis.…”

Diving Response in Rats: Role of the Subthalamic Vasodilator Area

“…Projections of the medullary dorsal horn neurons receiving ethmoidal nerve afferents are observed in pre-Botzinger and trapezoid nuclei ( 31 ), which are known to participate in respiratory regulation ( 32 – 34 ) and may be involved in the apneic component of DR ( 1 ). DR-associated bradycardia most probably involves activation of parasympathetic preganglionic neurons of nucleus ambiguus, which receive projections from medullary dorsal horn neurons targeted by ethmoidal afferents ( 35 ).…”