Synaptic connections of relay and local circuit neurons in the monkey's dorsal lateral geniculate nucleus.

The synaptic inputs to a single neuron's dendritic tree can be analyzed using electronmicroscopic reconstructions after intracellular injections of horseradish peroxidase. In the monkey's dorsal lateral geniculate nucleus, the proximal dendrites of magnocellular and parvocellular relay cells received retinal synapses and inhibitory synapses, while the intermediate and distal dendrites received cortical synapses. A local circuit neuron had both similar synaptic inputs and similar physiology to parvocellular relay neurons, but additionally had presynaptic dendrites and no axon. These results provide a wiring diagram for the neuronal types in this nucleus.