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 latera l 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 ser ies of experiments, spike-triggered averaging of inferior cardiac SND was used in an attempt to identify LTF neurons with activity correlate d to the 10-Hz rhythm in SND. The discharges of only one of the 120 LT F neurons studied were correlated to this component of SND. In contras t, 17 of 79 neurons had activity correlated to the 2- to 6-Hz oscillat ion in experiments in which this component of SND was prominent. These data indicate that LTF neurons neither receive input from nor are com ponents of the 10-Hz rhythm generator. In a second series of experimen ts, muscimol was microinjected into the LTF bilaterally. Chemical inac tivation 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 v iew that LTF neurons have a permissive role in governing the 10-Hz rhy thm in SND, probably by acting on elements of the rhythm generator loc ated elsewhere. As expected, muscimol microinjections reduced the powe r in the 2- to 6-Hz band in SND in some experiments.