Cardiocardiac Reflexes — The Role of the Spinoreticular Tract
The heart contains receptors that continually sense information during normal and pathological conditions. After the mechanical or chemical receptors transduce information into electrical impulses, the spikes are carried in both sympathetic and vagal afferent pathways (1,2). The sympathetic afferent information can be transmitted to several destinations. Sympathetic afferent activity can synapse on postganglionic sympathetic efferent neurons located in the inferior and middle cardiac ganglia to affect the function of the heart (3). Information can enter the gray matter of the spinal cord and, either directly or indirectly, modulate the activity of sympathetic preganglionic efferent fibers of the heart (4) or other visceral structures such as the kidney (5). Once information reaches the spinal cord it can also be transmitted to supraspinal structures for complex integration. The work described in this chapter will focus on the transmission of noxious and innocuous information from the heart by the spinoreticular tract (SRT). Much of the SRT terminates in regions of medullary reticular formation involved in reflex cardiovascular adjustments and the motivational-affective behavioral aspects of pain (6). This chapter will describe the effects of coronary artery occlusion, intracardiac injections of bradykinin and generation of premature ventricular contractions on the activity of cells of origin in the SRT. The results indicate that these noxious and innocuous stimuli are capable of increasing the discharge rate of thoracic SRT cells. This study also demonstrates that vagal afferent stimulation suppresses sympathetic afferent information originating from the heart.
KeywordsVagal Stimulation Coronary Artery Occlusion Premature Ventricular Contraction Stellate Ganglion Intracardiac Injection
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