The release of catecholamines in hypothalamus and locus coeruleus is modulated by peripheral chemoreceptors

To investigate whether impulses from chemoreceptors influence the release o f catecholamines in the hypothalamus and the locus coeruleus, the two brain areas were superfused simultaneously and bilaterally with artificial cereb rospinal fluid through push-pull cannulae. The release of catecholamines wa s determined in the superfusate before and during chemoreceptor stimulation by bicarbonate solution saturated with carbon dioxide (CO2-NaHCO3) or KCN. Experiments were carried out on intact cats after carotid body denervation (CD). Intracarotid infusion of CO2-NaHCO3 increased arterial blood pressure and e nhanced the release of noradrenaline but not dopamine in the posterior hypo thalamus and the locus coeruleus. Following CD, the enhancing effect of CO2 -NaHCO3 on the noradrenaline release in the posterior hypothalamus was abol ished, while the effect on blood pressure was slightly enhanced. CD reverse d the NaHCO3-induced release of noradrenaline in the locus coeruleus to a d ecreased noradrenaline outflow. Intracarotid infusion of KCN led to a fall in blood pressure. KCN increased the release rates of noradrenaline and, to a lesser extent, that of dopamine in the posterior hypothalamus, as well a s the release of noradrenaline in the locus coeruleus. CD abolished the KCN -induced fall of blood pressure and the increased release of noradrenaline and dopamine in the posterior hypothalamus. Similar to CO2N-aHCO(3). the en hancing effect of KCN on the noradrenaline release in the locus coeruleus w as reversed following CD to a reduced noradrenaline outflow. Superfusion of the posterior hypothalamus and the locus coeruleus with KCN did not influe nce either blood pressure or the release rates of noradrenaline and dopamin e in these brain areas. The findings show that impulses originating from chemoreceptors of the caro tid body increase the release rates of the catecholamines in the posterior hypothalamus and the locus coeruleus, thus underlining the importance of ca techolaminergic neurons of these brain areas in cardiovascular control.