Laminar distribution of receptors in monkey (Macaca fascicularis) geniculostriate system

We have examined the laminar distributions of eight types of receptor in the primary visual cortex (area 17) and the lateral geniculate nucleus (LGN) of the macaque monkey. The receptor populations and subpopulations examined included those selective for gamma-aminobutyric acid (GABA) (using [3H]-muscimol as ligand), L-glutamate-related receptors (using [3H]-L-glutamate and [3H]-AMPA), muscarinic acetylcholine (using [3H]-quinuclidinyl benzilate--QNB and [3H]-N-methyl scopolamine--NMS), cholecystokinin (CCK) (using [3H] pentagastrin), benzodiazepine (using [3H]-flunitrazepam), and adenosine (using [3H]-cyclohexyladenosine--CHA). Each of the receptors examined exhibited characteristic and differing laminar patterns of binding in the striate cortex. Perhaps reflecting the high density of cell bodies and synapses in layer 4C, most receptors, except those labelled by [3H]-L-glutamate or [3H]-AMPA, showed dense concentrations in this layer. Layers 4B and 5, which contain relatively few cell bodies and heavy myelin concentrations, were in general lightly labelled. Layer 6 showed relatively heavy labelling when [3H]-AMPA (quisqualate) or [3H]-pentagastrin (CCK) were used as ligands. The superficial layers of the cortex were zones of relative concentration of GABA, benzodiazepine, acetylcholine, glutamate-related, and adenosine receptors. In general, the binding patterns resembled those previously described for cat visual cortex, but there were also some clear differences. The distributions of all of these receptors likely reflect the differential input substances to different laminae of the visual cortex. Of the receptors examined, only those for GABA, benzodiazepine, and acetylcholine were found in substantial concentration in the LGN. Of these, GABA and benzodiazepine receptors showed especially dense binding in the magnocellular layers of the LGN compared to the parvicellular layers.