Excitation of certain posterolateral hypothalamic units by cyclopropane and ether

1. Extracellular activity was recorded from single units in the posterolateral hypothalamus in nineteen cats before, during, and after the administration of the inhalation anaesthetics cyclopropane, diethyl ether and halothane.2. Unit discharge was significantly increased by 25-50% cyclopropane in eighteen of the forty-four cells tested with this anaesthetic, and in seven of fourteen cells tested with diethyl ether. This excitatory effect was associated with cortical EEG suppression.3. The remaining cells tested were depressed by cyclopropane or ether, and this also occurred during halothane administration.4. Excitation of certain cells in the posterolateral hypothalamus is discussed in relation to the increased preganglionic sympathetic activity evoked by cyclopropane and ether.