Abstract
The nucleus of the solitary tract (NTS) is the primary site of visceral afferents, such as baroreceptors and arterial chemoreceptors. Recent data from our laboratory have shown that the microinjection of acetylcholine (ACh) into the commissural moiety of the NTS (cNTS) of decorticated arterially-perfused in situ preparations of male juvenile rats did not change the sympathetic nerve activity (SNA), but increased the phrenic nerve activity (PNA). Furthermore, we demonstrated that the ACh-induced responses in cNTS involve the activation of both nicotinic and muscarinic receptors. However, nicotinic receptors seem to play a more relevant role in the control of breathing, especially considering that such receptor antagonism promotes a decrease in the KCN- activated peripheral chemoreflex tachypneic response. However, the effects of specific nicotinic and muscarinic agonists in the cNTS on respiratory and sympathetic responses have not been studied yet. Once established the involvement of nicotinic receptors in the cNTS on peripheral chemoreflex ventilatory responses activated by cytotoxic hypoxia (KCN), we intend to study the involvement of the cholinergic system in the cNTS on respiratory and sympathetic responses induced by hypoxic hypoxia, hypercapnia, or pH changes in the cNTS, as well as which cholinergic receptor subtypes are involved. Moreover, although the presence of a cholinergic system in the NTS has been described, the efferent projections of ACh-activated cNTS neurons, especially to medullary regions involved in the control of ventilation, has not been studied yet. Therefore, this project proposes to study, in detail, the effects of selective activation of distinct cholinergic receptors in the cNTS on respiratory and sympathetic activities, the role of the cholinergic system in cNTS on sympathetic and respiratory activities reflex changes in response to hypoxic hypoxia, hypercapnia and decrease in the cNTS pH and the efferent projections from neurons activated by ACh in the cNTS to medullary areas involved in the respiratory and sympathetic control. (AU)
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