The sensitivity of paramedian reticular neurones to acetylcholine.

1. Of paramedian reticular neurones a significantly higher proportion of those antidromically activated from the cerebellum than of those orthodromically activated from this source were excited by acetylcholine. 2. Receptors for acetylcholine were of the muscarinic type. 3. No differences were found in the proportions of cholinoceptive and non-cholinoceptive cells responding to stimulation of cranial and limb nerves or to changes in blood pressure either spontaneous or induced. 4. Either a cholinergic pathway to paramedian reticular cells projecting to the cerebellum was not activated in these experiments or the receptors for acetylcholine are not located at synapses. An association between muscarinic receptors and acetylcholinesterase may be present with cells of this area.