Cholinergic modulation of single lateral geniculate neurons in the cat

Abstract

The effects of physostigmine, 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 μg/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 physostigmine 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/sec, 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 geniculate neurons. It is postulated that this involves the reticular formation. Evidence is presented for a predominant muscarinic cholinergic mechanism.