Cholinergic modulation of single lateral geniculate neurons in the cat.

The effects of physosti~ine, nicotine and scopolamine were studied on the activity of single lateral geniculate neurons in the acute cat. Most of the lateral geniculate neurons selected were P-cells. These increased their responses to ipsilateral optic tract and midbrain reticular formation stimulation. Nicotine and physostigmine in doses of 25 pg/kg i.v. significantly increased the spontaneous firing rate of single geniculate neurons. Scopolamine in a dose of 0.5 mg/kg i.v. depressed their firing rates to control levels. Physostigmine enhanced their post-stimulus discharge rate to optic nerve stimulation. This enhancement was depressed by scopolamine. The effects of midbrain reticular formation stimulation were further enhanced by physosti~ine and reduced by scopolamine in about 86 % of lateral geniculate neurons studied. Generally, the effects of trains of pulses to the reticular formation (250 Hz/set, 50 msec train duration, 0.05-0.1 msec pulses) were more marked than single stimuli. It is concluded that a major cholinergic facilitatory system exists which influences lateral genicuiate neurons. It is postulated that this involves the reticular formation. Evidence is presented for a predominant muscarinic cholinergic mechanism.