Abstract
1. The distribution of cholinoceptive and non-cholinoceptive cells in various nuclei of the caudal medulla of the rat is described. 2. The nature of the responses of cells of the paramedian reticular nucleus and of the perihypoglossal nuclei to electrophoretically applied acetylcholine (ACh) was investigated. 3. In unanaesthetized decerebrate preparations ACh responses were usually of a "fast onset-fast offset" nature. Dihydro-beta-erythroidine was a more effective antagonist than atropine. 4. In rats anaesthetized with barbiturate nearly all the tach responses showed a slower onset and prolonged action. Atropine was the more effective antagonist. 5. The synaptic responses of cells of the paramedian reticular and perihypoglossal nuclei to stimulation of glossopharyngeal, superior laryngeal, lingual and hypoglossal nerves were investigated. It is concluded that ACh does not mediate the responses at the level of these nuclei.