Afferent pathways for cardiac-somatic motor reflexes in rats

The present study used a rat model in which algogenic chemicals were infuse d into the pericardial sac to evoke spasmlike contractions in paraspinal mu scles. The following techniques were used to study the roles of sympathetic (SCA) and vagal cardiac afferents (VCA) in electromyographic (EMG) respons es to pericardial algogenic chemicals: chemical stimulation, electrical sti mulation, and nerve transection. Activation with bradykinin (n = 46) produc ed a significantly higher peak response than infusion of an algogenic mixtu re (n = 53) containing chemicals that also activate VCA. Electrical stimula tion of SCA produced bilateral EMG activities (7 of 7). Electrical stimulat ion of VCA did not evoke EMG activity but inhibited the chemically evoked E MG response (12 of 12). The chemically evoked response was decreased after transection of the left sympathetic chain (n = 22) and was increased after bilateral vagotomy (n = 19). These results suggest an excitatory and inhibi tory role for SCA and VCA, respectively. Therefore, in addition to spinotha lamic convergence of somatic and visceral afferents, activation of SCA to g enerate spasmlike muscle contractions could account in part for anginal pai n, and VCA activation could attenuate this effect.