Intrapericardiac injections of algogenic chemicals excite primate C1-C2 spinothalamic tract neurons

Extracellular potentials of 38 C1-C2 spinothalamic tract (STT) neurons in a nesthetized monkeys (Macaca fascicularis) were examined for responses to in trapericardiac injections of an algogenic chemical mixture (adenosine, 10(- 3) M; bradykinin, prostaglandin E-2, serotonin, histamine, each 10(-5) M). Chemical stimulation of cardiac/pericardiac receptors increased activity of 21 cells, decreased activity of 5 cells, and did not change activity of 12 cells. Cells excited by chemical stimuli received input from noxious mecha nical stimulation of somatic fields; most receptive fields included the nec k, inferior jaw, or head areas. Nerve ablations in 11 cells excited by intr apericardiac chemicals showed that cardiac input activated by algogenic che micals traveled primarily in vagal afferent fibers to C1-C2 segments; phren ic or cardiopulmonary sympathetic inputs were predominant in 2 of 11 cells. These results supported the concept that activation of cardiac vagal affer ents might lead to the production of referred pain sensation in somatic fie lds innervated from high cervical segments.