A COMPARATIVE-STUDY OF PRE-SYMPATHETIC AND BOTZINGER NEURONS IN THE ROSTRAL VENTROLATERAL MEDULLA (RVLM) OF THE RAT

The aim of this study was to investigate the degree of functional and anatomical overlap between two major neuronal subpopulations in the ro stral ventrolateral medulla: pre-sympathetic (sympathoexcitatory) neur ons, and expiratory neurons of the Botzinger complex. Extracellular re cordings were made with dye-filled microelectrodes in pentobarbital an esthetized, paralyzed and artificially ventilated adult Wistar rats. T ests applied included stimulation of baroreceptor afferents, activatio n of peripheral chemoreceptors and lung stretch receptors, changes in central respiratory drive with hyper- or hypoventilation, nociceptive stimulation, and antidromic stimulation from the T-2 segment of the sp inal cord or medulla oblongata at obex level. The two groups of neuron s showed different patterns of spontaneous activity and generally diff erent responses to these stimuli. The recording positions showed some overlap, but the majority of Botzinger neurons were dorsolateral to pr e-sympathetic neurons. There was a large overlap between the location of pre-sympathetic neurons and the lateral part of the C1 adrenergic g roup, but only a small overlap between these adrenergic neurons and Bo tzinger neurons. These results indicate that the anatomically adjacent pre-sympathetic and Botzinger expiratory neurons form two functionall y distinct neuronal subpopulations.