Influence of ganglioglomerular nerve on carotid chemoreceptor activity in the cat

The dependence of the carotid chemoreceptor responses to blood-borne stimuli on the ganglioglomerular nerve (GGN) activity was investigated in cats which were anesthetized, paralyzed and artificially ventilated. The activity of a few carotid chemoreceptor afferents from a slip or from the cut left carotid sinus nerve (CSN) and the activity of a few GGN fibers were recorded. The responses of the same chemoreceptor afferents to steady-state hypoxia at a constant paCO2 and to steady-state hypercapnia during hyperoxia were compared before and after the transection of the ipsilateral ganglioglomerular nerve (IGGN). Similarly the effects of IGGN transection on the responses of the same chemoreceptor afferents to graded doses of intravenous injections of sodium cyanide (20-60 micrograms) and nicotine (20-60 micrograms) at constant blood gas levels were studied. On the average, IGGN transection during normoxia only slightly changed the carotid chemoreceptor activity. Also, it did not significantly change the hypoxic and hypercapnic responses, and those to sodium cyanide and nicotine injections. Thus, the mean carotid chemoreceptor responses to physiological and pharmacological stimuli were largely independent of the GGN. However, certain GGN fibers were strongly stimulated by hypoxia and hypercapnia. Clearly, the total GGN traffic to the carotid body was not sufficiently strong to exert a significant control over the mean carotid chemoreceptor activity.