Neurochemical Characterization Of Human Area V2

The distinctive border between areas V1 and V2 has facilitated greatly the determination of the laminar distributions of neurotransmitter receptors in area V2 of humans. [3H] Glutamate and NMDA receptors (labeled by [3H]TCP, [3H]glycine, or [3H]dizocilpine binding) are densely distributed in layer IVC of V1 but are not densely distributed in layer IV of V2. In contrast, kainate receptors (determined through binding of [3H]kainate) are not observed in layer IVC of V1 but are labeled in layer IV of V2. In addition, dense labeling of NMDA and AMPA receptors is observed in layer III of V2, whereas weaker labeling is observed in layers III-IVA of V1. Similarly, weak labeling of kainate receptors is observed in layer III of V2, whereas no labeling is observed in layer III of V1. Finally, whereas dense labeling of kainate receptors is observed in layers V and VI in both areas V1 and V2, weak AMPA receptor labeling is observed in layer V of V1 that is not observed in layer V of V2. These results are summarized in Table II.

In addition to the distribution of glutamate receptors, the distribution of GABAA receptors distinguishes area V2 from area V1. GABAa receptors are distributed in a bimodal pattern in V1 and a unimodal pattern in V2. This is due to a lack of GABAa receptor binding in layer IVB and weak binding in layer III of V1, whereas layers II-IV of V2 show dense GABAA binding.

Acetylcholine receptors have different laminar distributions in areas V1 and V2. Nicotinic receptors, determined through the binding of [3H]oxotremorine, have their highest densities in layers V and VI in both areas V1 and V2. In V1, binding sites are also apparent in layer IVC, whereas in V2, binding sites are observed in layers I and II. Muscarinic, M1 receptors, determined through the binding of [3H]N-methylscopola-mine, show their highest densities in layers II and III of

Table I

Modular Organization of V2a

Table I

Modular Organization of V2a

Structure

Size (mm)

Width of dense CO stripes

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