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Camp andCgmp play an important part in the central sections of vagal baroreceptor reflexes too, but apparently do not influence vagal pacemaker neurons.
Camp andCgmp always display opposite effects, thus supporting the Yin/Yang hypothesis.
The total baroreceptor reflex (experiments with angiotensin) is determined mainly by the carotid sinus reflex, which is known to have a lower threshold than the aortic reflex.
The lack of an effect ofIma in the total baroreceptor reflex in the cat might be due to a balanced compensation by opposite effects in the carotid sinus and aortic reflexes.
The organisation of the central substrate of the vagal carotid sinus reflex seems to be different from that of the aortic reflex and the Bezold-Jarisch reflex. The prominent behaviour of the carotid sinus reflex might be due to the significant changes which were induced by encephalization of the corresponding gill arch during the phylogenetic development of mammals.
Although the vagal system does not seem to contribute much to the central blood pressure effects of cyclic nucleotides in anaesthetized cats, this may be different in conscious animals where the blood pressure is well above the threshold of the baroreceptors (> 100 mm Hg).
KeywordsCyclic Nucleotide Carotid Sinus Veratridine Central Blood Pressure Pacemaker Neuron
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