Criteria for Intracellular Identification of Pre-Sympathetic Neurons in the Rostral Ventrolateral Medulla in the Rat

Abstract

Previous studies revealed that a relatively small group of reticulospinal neurons located in the rostral ventrolateral medulla (RVLM) plays a key role in the generation of resting vasomotor tone and in reflex control of arterial blood pressure. These medullary pre-sympathetic neurons 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 from 8 RVLM pre-sympathetic neurons in anaesthetised rats, sets out criteria for intracellular identification of such neurons. We propose that two features are sufficient to classify RVLM neurons as pre-sympathetic during intracellular recording: inhibitory response to stimulation of the aortic depressor nerve with short bursts of pulses applied at low frequency; and antidromic stimulation from the upper thoracic segments. Cardiac oscillations in the membrane potential or responses during large changes in blood pressure can be due to activity in normotensive rats. Interestingly, this pattern of regional sympathetic nerve responses to central neural administration of insulin is similar to that seen with systemic administration of insulin. Further, lesions of the anteroventral third ventricle hypothalamic (AV3V) region abolished increases in sympathetic activity to systemic administration of insulin with euglycemic clamp, suggesting that AV3V-related structures are critical for insulin-induced elevations in sympathetic outflow.

Key Words:

• Sympathoexcitatory neurons
• Intracellular recording
• Antidromic stimulation
• Central cardiovascular control