Carotid nerve

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Electric and Dye Coupling Between Rat Carotid Body Cells and Between These Cells and Carotid Nerve Endings... 

Figure 1 Schematic diagram illustrating the basic features of chemotransduction from glomus cells to carotid nerve terminals (NT). The glomus cell is packed with dark-core vesicles and contains a plethora of chemical agents (list on the left). Natural stimulation (list at the bottom) releases these agents toward the endings of the carotid nerve (NT). The chemicals cross the synaptic cleft between glomus cells and nerve endings (horizontal open arrows).

More recently, we have tackled the problem of possible electrical connections between glomus cells and carotid nerve terminals and have started to study communications between glomus and sustentacular cells. Thus, results presented below are a synopsis of these studies in hopes of attaining a better understanding of the complexities of transduction in these receptors. 

Another aspect of the carotid body cellular syncytium is that there is a distinct possibility of direct connections between the carotid body cells (glomus and sustentacular) and the nerve endings of the carotid nerve. This study, still in its infancy, has been prompted by the discovery of Kondo and Iwasa (19) who found... 

Applications of cholecystokinin octapeptide (CCK-8), a secretagogue, increases the chemosensory discharge in the carotid nerve after a period of depression. In pancreatic acini CCK-8 induces electrical uncoupling (49). 

Kondo and Iwasa (19), with morphological techniques, described the presence of gap junctions between glomus cells and carotid nerve terminals. These junctions appeared within the more commonly observed chemical synapses between these... 

Figure 8 Left Diagram summarizing intercellular coupling between different structures in the carotid body. GC, glomus cells SC, sustentacular cells NT, carotid nerve terminal. Arrows show points (gap junctions) where there is transfer of information from one cell to another. Note that all structures are interconnected. Right A Lucifer Yellow microinjection into a cell with a complex shape stains this element and dye diffuses to many other structures in the organ. Clearly, some are glomus cells. The injected structure may be a sustentacular cell.

Zapata P. Chemosensory activity in the carotid nerve effects of pharmacological agents. In Gonzalez C, ed. The Carotid Body Chemoreceptors. New "Vork Springer Austin Landes, 1997 119-146. 

Later reports (4-9) have confirmed that carotid chemoreceptor function is permanently lost after resection of the carotid bodies in humans. Therefore, these reports provide a first indication that the carotid body parenchyma is required for oxygen sensing. In other words, carotid nerve chemosensory fibers by themselves are unable to detect changes in O2 level. 

Mitchell et al. (13) and Kienecker et al. (14) reported that the neuromata resultmg from carotid nerve section attained recovery of chemosensory responses. 

In a similar vein, Belmonte et al. (17) observed that carotid nerves regenerated into superior cervical ganglia, organs extremely well vascularized, also failed to regain chemoreceptor activity. Therefore, all evidence available suggests that regenerating chemosensory nerve fibers recover chemoreception only when reestablishing contact with carotid body tissue. 

Zapata P, Stensaas LJ, Ey2aguirre C. Axon regeneration following a lesion of the carotid nerve electrophysiological and ultrastmctural observations. Brain Res 1976 113 235-253. 

Belmonte C, Rigual R, Gallego R. Responses of carotid nerve fibres regenerating into the superior cervical ganglion. In Belmonte C, Pallot D, Acker H, Fidone S, eds. Arterial Chemoreceptors. Leicester Leicester Univ Press, 1981 125-132. 

Zapata P, Stensaas LJ, Eyzaguirre C. Recovery of chemosensoiy function of regenerating carotid nerve fibers. In Acker H, Fidone S, Pallot D, Eyzaguirre C, Lubbers DW, Torrance RW, eds. Chemoreception in the Carotid Body. Berlin Springer-Verlag, 1977 44-50. 

Alcayaga J, Iturriaga R, Varas R, Arroyo J, Zapata P. Selective activation of carotid nerve fibers by acetylcholine applied to the cat petrosal ganglion in vitro. Brain Res 1998 786 47-54. 

Fidone SJ, Sato A. A study of chemoreceptor and baroreceptor A and C-fibres in the cat carotid nerve. J Physiol 1969 205 527-548. 

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