ADRENERGIC CELL GROUP IN ROSTRAL VENTROLATERAL MEDULLA OF CAT - ITS CORRELATION WITH CENTRAL CHEMORECEPTORS

We have proposed a hypothesis that secondary neurons mediating central respiratory chemoreception are not restricted to the medullary superf icial layer. This idea was further examined in the present physiologic al and morphological studies. We identified the 'S' area, i.e. the med ullary surface area where cold blockade produced apnea, in anesthetize d, spontaneously breathing cat. We then evaluated how the apnea was mo dified by injection of CO2-saturated saline into the vertebral-basilar artery. The CO2 injection caused immediate reappearance of respirator y rhythm, although intensity of inspiratory activity was smaller than in the control. This incomplete recovery suggests that the responsive structure extends deeply below the surface. The extent of the cell gro up underlying the 'S' area was evaluated by morphological study. Medul lary transverse sections including the 'S' area were treated with thre e distinct antisera against phenylethanolamine N-methyltransferase (PN MT), dopamine-beta-hydroxylase (DBH), and 5-hydroxytryptamine (5-HT). The PNMT-labelled cell group was found to exactly underlie the 'S' are a, although the DBH-and the 5-HT-labelled cell groups did not show clo se topographic correlation with the 'S' area. PNMT cells were located in the region ventral to retrofacial nucleus within 0.5-1.5 mm depth b eneath the surface. These results suggest that adrenergic cells in the rostral ventrolateral medulla are important candidates for secondary neurons mediating central respiratory chemoreception.