PRESENCE OF VASOMOTOR AND RESPIRATORY RHYTHMS IN THE DISCHARGE OF SINGLE MEDULLARY NEURONS INVOLVED IN THE REGULATION OF CARDIOVASCULAR-SYSTEM

We analyzed the discharges of 77 single neurons located in the rostral ventrolateral medulla (RVLM, n = 25), caudal ventrolateral medulla (C VLM, n = 18), lateral tegmental field (LTF, n = 19) and caudal raphe n uclei (n = 15). These recordings were made from 36 vagotomized and sin oaortic denervated cats that were either decerebrate (n = 27) or anest hetized with urethane (n = 9) and from 3 decerebrate cats with intact sinoartic and vagal nerves. These neurons were classified as sympathet ic-related (n = 61) if spike triggered averaging showed that their nat urally occurring discharges were correlated to either the cardiac rela ted (2-6 Hz) or a faster (10 Hz) oscillation in inferior cardiac sympa thetic nerve discharge, Neurons were classified as sympathetic-unrelat ed (n = 16) if they lacked these characteristics. We used autoregressi ve spectral techniques to detect additional slower oscillations hidden in the variability of neuronal discharge and possibly correlated to t he oscillations of systolic arterial pressure (SAP). This analysis rev ealed the existence of a low frequency (LF) oscillation (0.12 +/- 0.02 Hz) in the discharges of 36 sympathetic-related and 9 sympathetic-unr elated neurons. In relation to 35 neurons in 21 animals there was also an LF component in SAP variability. In 29 instances the LF neuronal d ischarges and SAP variabilities were significantly correlated. In addi tion, there was a high frequency (HF) oscillation (0.34 +/- 0.06 Hz) i n the discharges of 59 medullary neurons. In 56 cases the HF in neuron al discharge variability cohered to that in SAP variability, These dat a are the first to demonstrate the existence of an LF component in the discharges of individual medullary neurons, at least some of which we re likely to be involved in the regulation of the cardiovascular syste m. Since these oscillations were evident in cats with section of sinoa ortic and vagal nerves, they likely reflect central rhythmogenic prope rties.