Reactions of cardiac postganglionic sympathetic neurons to movements of normal and inflamed knee joints.

The effects of passive movements of normal and inflamed knee joints on unitary activity in filaments of the inferior cardiac nerve (ICN) were studied in cats anesthetized with chloralose and urethane. The effects were compared with those obtained by electrical stimulation of afferent A- and C-fibers in the medial articular nerve, in muscle and in cutaneous hind limb nerves. The vagus nerves were cut and the right carotid artery was tied off. The left carotid sinus was intact. All ICN units used in this study displayed spontaneous activity which was usually related to the cardiac and respiratory rhythms. The ICN units were regularly excited by electrically evoked single or short repetitive A-volleys in articular, cutaneous and muscle nerves. The excitation was followed by a silent period. Inclusion of C-fibers in the afferent volleys gave a second, long-latency burst of impulses which was seen only with short repetitive stimulation. Passive movements in the normal working range of the joint did not influence the activity of ICN units. However, noxious joint movements, particularly of inflamed joints, led to pronounced excitation of ICN units accompanied by rises in blood pressure. Most of these effects could still be seen after all nerves to the hind limbs, except the medial articular nerve, were cut. It is proposed (a) that ICN units form a homogeneous population of sympathetic postganglionic units whose reaction pattern to somatovisceral input is distinctly different from that of other sympathetic subsystems, and (b) that articular receptors make a substantial contribution to the ICN input particularly when many fine afferent units are sensitized to mechanical stimulation by an acute joint inflammation.