Abstract
The aim of this study is to elucidate that cardiovascular sympathetic premotor neurons in the medulla oblongata are composed by different kinds of neurons.
We recorded responses of reticulospinal neurons (antidromically activated by electrical stimulation of the dorsolateral funiculus of the spinal cord) and the cutaneous, the cardiac and the renal sympathetic nerves to stimulation of the baroreceptor afferents, warm stimulation of the POAH (49°C), and hypoxia (3%O2, 97%N2) in anesthetized and immobilized rabbits.
The activities of non-barosensitive reticulospinal neurons in the rostral ventromedial medulla (Type I) and cutaneous sympathetic nerves were inhibited by warm stimulation of the POAH. However, barosensitive reticulospinal neurons in the rostral ventrolateral medulla (RVLM) and renal sympathetic nerve did not respond to this stimulation. This result suggested that Type I neurons were premotor neurons for cutaneous vasoconstrictors.
Barosensitive reticulospinal neurons in the RVLM were divided into two groups; neurons inhibited by hypoxia (Type II) and ones excited by it (Type III). Because activity of the cardiac sympathetic nerve was inhibited by hypoxia but activity of the renal nerve was excited, it was concluded that neurons of the Type II neurons were premotor neurons for cardiac sympathetic preganglionic fibers. The Type III neurons group might be premotor neurons for vasoconstrictors of visceral organs and/or muscles. [Jpn J Physiol 54 Suppl:S100 (2004)]
