LATERAL TEGMENTAL FIELD NEURONS PLAY A PERMISSIVE ROLE IN GOVERNING THE 10-HZ RHYTHM IN SYMPATHETIC-NERVE DISCHARGE

Recordings from sympathetic nerves in decerebrate cats show a variable mixture of 10-Hz and 2- to 6-Hz discharges. Although medullary lateral tegmental field (LTF) neurons are considered to be a source of the 2- to 6-Hz oscillation in sympathetic nerve discharge (SND), their role in the control of the 10-Hz rhythm has not been critically evaluated. This issue served as the focus of the current study. In the first series of experiments, spike-triggered averaging of inferior cardiac SND was used in an attempt to identify LTF neurons with activity correlated to the 10-Hz rhythm in SND. The discharges of only one of the 120 LTF neurons studied were correlated to this component of SND. In contrast, 17 of 79 neurons had activity correlated to the 2- to 6-Hz oscillation in experiments in which this component of SND was prominent. These data indicate that LTF neurons neither receive input from nor are components of the 10-Hz rhythm generator. In a second series of experiments, muscimol was microinjected into the LTF bilaterally. Chemical inactivation of the LTF either eliminated the 10-Hz rhythm or reduced the power and peak frequency in this band of SND. These data support the view that LTF neurons have a permissive role in governing the 10-Hz rhythm in SND, probably by acting on elements of the rhythm generator located elsewhere. As expected, muscimol microinjections reduced the power in the 2- to 6-Hz band in SND in some experiments.