Participation of the noradrenergic neurons of Locus Coeruleus in the central generation of inspiratory and expiratory activities in response to the activation of the central chemoreceptors of rats

Author(s)

Karolyne Silva Magalhães

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-02-25

Examining board members

Davi José de Almeida Moraes; Mateus Ramos Amorim; Luiz Guilherme de Siqueira Branco; Glauber dos Santos Ferreira da Silva

• Advisor: Davi José de Almeida Moraes

Abstract

In basal conditions, inspiration is an active phenomenon while expiration is a passive phenomenon. Under conditions of high metabolic demands, such as increased in partial pressure of CO2 and [H+] in arterial blood (hypercapnia/acidosis), there is an increase in inspiratory activity, expiration becomes active, producing increases in abdominal muscle activity, and the resistance of the upper airways reduces. The Locus Coeruleus (LC) contains noradrenergic (NE) neurons that increase their firing frequency when exposed to elevated CO2/[H+] levels and communicate with respiratory brainstem neurons to make compensatory adjustments in lung ventilation during hypercapnia/acidosis. Using in situ preparations of rats, we evaluated the contribution of LC NE neurons in the central generation of inspiratory and expiratory activities, as well as in the control of upper airway resistance in basal conditions and in response to hypercapnia/acidosis. LC NE neurons were selectively acutely and reversibly silenced by application of the insect allatostatin peptide (Alst) after cellular transfection using a lentiviral vector for expression of Alst Drosophila receptors coupled to inhibitory G protein (AlstR). Ten to twelve days after, we performed the dorsal approach of the in situ preparation of rats. The phrenic (PN), abdominal (AbN), hypoglossal (HN) and cervical vagus (cVN) nerves were recorded and analyzed in different phases of the respiratory cycle. Single unit extracellular records of LC neurons were also performed. Respiratory frequency (fR), duration of inspiration (DI) and expiration (DE), active expiration, the magnitude of respiratory modulation and the firing frequency of LC neurons were also evaluated. Selective inhibition of LC NE neurons using Alst did not produce significant changes in the activity of respiratory motor nerves, fR, DI and DE in normocapnia. Inhibition of these neurons before and/or during hypercapnia/acidosis significantly reduced AbN amplitude and its incidence, as well as the inspiratory responses of PN and HN (amplitude) and post-inspiratory activity (glottal adduction) of the cVN. In the absence of active expiration after the inhibition of LC NE neurons, the DI, DE and the pre-inspiratory activity of cVN (glottal abduction) and HN (tongue protrusion) were normalized. The perfusion of Alst in in situ preparations of rats withoutthe expression of the AsltR during hypercapnia/acidosis did not change the pattern of the recorded respiratory motor nerves, the incidence of active expiration, fR, DI and DE. Among the registered LC neurons, we found three populations with different patterns of respiratory modulation and one with tonic activity. Hypercapnia/acidosis increased the magnitude of the respiratory modulation and their firing frequency. These data demonstrate that LC NE neurons exert an important excitatory modulatory role in the central generation of inspiration, active expiration and in the control of upper airway resistance evoked by hypercapnia/acidosis in in situ preparations of rats (AU)

• FAPESP's process: 17/09071-9 - Participation of the noradrenergic neurons of locus coeruleus in the central generation of inspiratory and expiratory activities in response to the activation of the central chemoreceptors of rats
• Grantee: Karolyne Silva Magalhães
• Support Opportunities: Scholarships in Brazil - Master