Effect of iontophoretically applied biogenic amines and of cholinomimetic substances upon the activity of neurons in the superior colliculus and mesencephalic reticular formation of the cat

1. The effects of iontophoretically applied cholinomimetic substances and of biogenic amines were tested in movement sensitive neurons of the colliculus superior and in neurons of the subtectal mesencephalic reticular formation. 2. Most collicular neurons were strongly excited by Glutamate which prevented neuronal adaptation and restored excitability in totally habituated neurons. GABA proved to be a strong depressant of collicular neurons. 3. Serotonine, Noradrenaline and Dopamine effectively depressed spontaneous, Gl-induced and stimulus driven activity of collicular units. Some units were selectively responsive to Serotonine, or to Catecholamines; others responded equally well to either group of substances. This suggests the existence of separate Serotonine respectively Catecholamine receptors. 4. Only a small proportion of collicular units (7%) was excited or depressed by cholinomimetic substrances. 5. The pharmacological properties of reticular units corresponded essentially to those of collicular neurons: GABA, Serotonine, Noradrenaline and Dopamine proved to be strong depressants of spontaneous, Gl-induced and stimulus driven activity. Selective responsiveness to Serotonine or to Catecholamines was found in some neurons. Cholinomimetic substances failed to influence a significant proportion of reticular units. Glutamate application produced strong excitation and led to an increase of somato-sensory receptive fields.