CRITERIA FOR INTRACELLULAR IDENTIFICATION OF PRE-SYMPATHETIC NEURONS IN THE ROSTRAL VENTROLATERAL MEDULLA IN THE RAT

Previous studies revealed that a relatively small group of reticulospi nal neurons located in the rostral ventrolateral medulla (RVLM) plays a key role in the generation of resting vasomotor tone and in reflex c ontrol of arterial blood pressure. These medullary pre-sympathetic neu rons have been extensively studied with extracellular microelectrodes, but so far few attempts have been made to examine their intracellular properties in vivo. This report, based on intracellular recordings fr om 8 RVLM pre-sympathetic neurons in anaesthetised rats, sets out crit eria for intracellular identification of such neurons. We propose that two features are sufficient to classify RVLM neurons as pre-sympathet ic during intracellular recording: inhibitory response to stimulation of the aortic depressor nerve with short bursts of pulses applied at l ow frequency; and antidromic stimulation from the upper thoracic segme nts. Cardiac oscillations in the membrane potential or responses durin g large changes in blood pressure can be due to movement artefact, and are therefore not reliable as a means of demonstrating baroreceptor i nput. Further intracellular studies of these neurons will undoubtedly result in further progress in understanding their function.