THE RECRUITMENT PATTERN OF SINGLE VASOCONSTRICTOR NEURONS IN HUMAN

The aim of this study is to determine the recruitment pattern among in dividual vasoconstrictor neurons under the baroreceptor-mediated influ ence in man. Spikes of single vasoconstrictor units were detected from microneurograms with a template-matching method. A total of 39 single vasoconstrictor units were detected. Single vasoconstrictor units wer e different from each other in their susceptibility to be activated in response to changes in the R-R interval or blood pressure, The units with higher firing probability had a shorter threshold R-R interval an d a higher threshold diastolic blood pressure than units with lower fi ring probability. In sympathetic responses consisting of only one spik e (single-spike responses), units with a lower threshold frequently ap peared and units with a higher threshold joined mull-spike responses. The units with a short threshold R-R interval tended to have a long in hibitory latency from R wave, suggesting low conduction velocity. The correlation between firing probability and firing threshold and that b etween appearance in single-spike response and multi-spike response su ggest a hierarchical manner of recruitment of vasoconstrictor units. F or beat-to-beat responses, however, some deviation from the hierarchic al recruitment was also observed. (C) 1997 Elsevier Science B.V.