[Autonomic reflexes: focusing on the arterial baroreceptor-vasoconstrictor reflex]

The arterial baroreceptor-sympathetic vasoconstrictor reflex (baroreceptor reflex), among autonomic reflexes, is summarized. Arterial baroreceptor afferents terminate in the caudal part of the nucleus tractus solitarius. Excitation of the baroreceptor afferents activates neurons in the caudal ventrolateral medulla that send axonal projections to the rostral ventrolateral medulla. These neurons (CVLM neurons) then inhibit tonic activity of sympathoexcitatory reticulospinal neurons in the rostral ventrolateral medulla (RVLM neurons). Tonic activity of RVLM neurons are responsible for tonic activity of the peripheral vasoconstrictors. These two kinds of neurons are essential neuronal components for the baroreceptor reflex. Both the neurons may also participate in various vasoconstrictor reflexes, such as the somato-and viscero-sympathetic vasoconstrictor reflexes.