Lm. Bianchi-da-silva et al., Baroreceptor control of heart rate in the awake toad: peripheral autonomiceffectors and arterial baroreceptor areas, J AUTON NER, 80(1-2), 2000, pp. 31-39
Systemic injection of sodium nitroprusside (30 mu g/kg, i.v.) in the awake
Bufo paracnemis toad induced a fall in arterial blood pressure and tachycar
dia. This tachycardia, but not the hypotension, was significantly reduced i
n toads with bilateral electrolytic lesion of the caudal and commissural re
gions of the solitary tract nucleus and in animals with transection of the
spinal cord, 2 mm below the obex. This indicates that the tachycardia is re
flex, depends on the integrity of the solitary tract nucleus and is due to
descending spinal autonomic activation. Pretreatment with propranolol (4 mg
/kg, i.v.) significantly reduced the tachycardia but did not block it compl
etely, showing the importance of beta-adrenoceptors in its genesis. The ref
lex increase in heart rate induced by nitroprusside was not statistically s
ignificant in animals with bilateral section of the laryngeal nerve, whose
baroreceptor fibers originate from the pulmocutaneous artery or in animals
in which the bilateral section of the laryngeal nerve was performed togethe
r with section of the glossopharyngeal nerves, which incorporate fibers ori
ginating from the carotid labyrinth. The reduction of the reflex tachycardi
a was significant in toads with aortic arch denervation alone or combined w
ith section of the laryngeal nerves or in animals with complete denervation
of the three baroreceptors areas. These results suggest that the region of
the aortic arch, when submitted to unloading, is the most important barore
ceptor zone for cardiac compensation in toads. (C) 2000 Elsevier Science B.
V. All rights reserved.