Neuronal activity with relation to cardiac rhythm in the lower brain stem of the dog.

Extracellular recordings of reticular neurons in the lower brain stem were performed in anesthetized dogs. Thirty out of 131 neurons showed rhythms of about 2-4 c/sec which were similar to heart or to EEG rhythms. By means of post-event-time histograms, correlations to the EEG delta-theta rhythm could be found in some neurons. These results were published elsewhere. Fixed relations of the neuronal activity to the cardiac rhythm could be verified in 7 neurons. Two neurons showed maxima 70 msec and 120 msec, respectively, after the beginning of the pulse wave. Two neurons showed minima after 110 msec and 130 msec, respectively. Three pulse-rhythmical neurons could not be classified in this way. This rhythmicity was changing or vanishing during the course of registration, but it could be strengthened experimentally by blood-pressure increase. It was shown that these neurons receive inputs from cardiovascular afferents and therefore are blood-pressure dependent neurons. From the finding that pulse-rhythmical modulation is different at different times under the same blood-pressure levels, it is assumed that there are varying strong influences from other systems to these neurons. The fact that these neurons are influenced by cardiovascular afferents does not mean, however, that they are cardiovascular neurons exclusively. It is suggested that blood-pressure reticular neurons may belong to the cardiovascular system as well as to other brain stem systems.