The rostral ventrolateral medulla mediates suppression of the circulatory system by the ventromedial nucleus of the hypothalamus.
We recently reported that a train of episodic neural discharges within the ventromedial nucleus of the hypothalamus (VMH) associated with suppression of the circulatory system had been determined by monitoring multiple unit activity (MUA). Abrupt increases in neural activity (MUA volleys; 1 to 4 min in duration) accompanied transient decreases in heart rate (HR) and blood pressure (BP), and showed circadian rhythm, occurring every 15 to 30 min in the light phase but seldom in the dark phase. The present study was aimed to determine if neurons in the vasomotor area of the rostral ventrolateral medulla (RVL) are involved in this VMH-induced cardiovascular suppression. MUAs of the VMH and RVL were monitored simultaneously with HR and BP in urethane-anesthetized rats. In synchrony with each MUA volley in the VMH, spontaneous activity of RVL neurons significantly decreased, as well as HR and BP. These RVL neurons are most likely vasomotor neurons because MUA of the RVL was attenuated by baroreceptor reflex activation, and electrical stimulation of these cells through the MUA recording electrodes produced pressor responses. These data suggest that VMH neurons that show a train of episodic discharges suppress the circulatory system at least in part by inhibiting the excitability of vasomotor neurons in the RVL.
Hirasawa
M
M
Department of Veterinary Physiology, Veterinary Medical Science, University of Tokyo, Japan.
Nishihara
M
M
Takahashi
M
M
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D004558:Electric Stimulation; D004594:Electrophysiology; D006339:Heart Rate / Q000502:physiology; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D008839:Microelectrodes; D051381:Rats; D017208:Rats, Wistar; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology*