Via descendente rostroventromedial bulbar que medeia as respostas cardiovasculares evocadas pela coluna dorsolateral da substância cinzenta periaquedutal

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Universidade Federal de Goiás


Periaqueductal gray is a midbrain region surrounding the cerebral aqueduct that projects to areas controlling behavioral and autonomic outputs. The activity of the lateral and dorsolateral columns of PAG is required for expressing the behavioral and physiological components of defense reactions. Cardiovascular responses evoked from PAG include increases in blood pressure, positive chronotropism and regional tissue perfusion changes. However, literature is scarce on the descending pathways controlling cardiovascular responses evoked from PAG. Since Raphe Pallidus (RPa) is a medullary region comprising sympathetic premotor neurons projecting to preganglionic spinal segments connected to sympathetic supplies innervating the heart, it is worth considering the PAG-RPa path. i) to assess whether PAG projects to RPa; ii) to evaluate the amplitude of the inotropic and chronotropic responses evoked from PAG; iii) to assess whether cardiovascular responses evoked from PAG rely on RPa. Experiments were conducted in Wistar rats (300g) and were approved by CEUA - UFG (092/18). In a first set of experiments (n=3), monosynaptic retrograde tracer Retrobeads were injected into RPa, and PAG slices were analyzed. Other two groups of (n = 6 each) were anesthetized with urethane (1.2 g / kg) and chloralose (120 mg / kg) ip and underwent tracheostomy, cannulation of the femoral artery and vein, catheterization of cardiac left ventricular and craniotomy. After a cardiovascular parameters’ stabilization, one group was injected vehicle into RPa 20min before injection of the GABAA receptor antagonist, bicuculline Methiodide (BIC 40 pmol / 100nL) into the lateral / dorsolateral PAG. The other group was injected with the GABAA receptor agonist muscimol (20mM – 100nL) into the RPa, 20 minutes before injecting the BIC (40 pmol / 100nL) into lateral / dorsolateral PAG. Responses to these injections were accompanied during 40min and compared between groups. Our results were: i) retrogradely labeled neurons were found in all PAG columns; ii) PAG activation by BIC caused positive chronotropism and inotropism, which are accompanied by afterload increases (as evidenced by arterial pressure increases); iii) Inhibition of RPa neurons with Muscimol reduced heart rate, arterial and ventricular pressures. The subsequent injection of BIC into PAG still increased arterial pressure, heart rate and cardiac inotropy outcomes, but the magnitude of these responses was significantly smaller than those evoked by BIC into PAG without inhibiting RPa. PAG neurons project directly to RPa. PAG activation increases cardiac chronotropy and inotropy, and these responses seem to partially rely on medullary ventromedial RPa neurons.



MORAES, G. C. A. Via descendente rostroventromedial bulbar que medeia as respostas cardiovasculares evocadas pela coluna dorsolateral da substância cinzenta periaquedutal. 2020. 62 f. Dissertação (Mestrado em Ciências Biológicas) - Universidade Federal de Goiás, Goiânia, 2020.