Parvalbumin in the monkey striate cortex: a quantitative immunoelectron-microscopy study

Parvalbumin (PV) is present in a subpopulation of interneurons in the visual cortex, and also in thalamic afferents to the neocortex of primates. The object of this study is to confirm by immunoelectron-microscopy the presence of intrinsic and extrinsic connections containing parvalbumin in the monkey visual cortex, by the demonstration of parvalbumin-immunoreactivity in symmetric and asymmetric synapses. We analyzed the distribution of parvalbumin-immunoreactive profiles at the ultrastructural level in the primary visual cortex of old world monkeys (Macaca fascicularis). It has been shown by others that parvalbumin-immunoreactive cells resemble non-spiny stellate cells, double-bouquet cells, chandelier and basket cells. These neurons are known to be inhibitory and to form symmetric synapses. In fact, we observed that the vast majority of parvalbumin-immunoreactive synaptic contacts in the primary visual cortex of Macaca fascicularis are of the symmetric type (81.7%). Since parvalbumin-positive asymmetric contacts are also present (18.3%) and occur mostly in the thalamic recipient layers, 4C and 4A (9.9%), these afferents probably derive from parvalbumin-immunoreactive neurons located in the dorsal lateral geniculate nucleus of the thalamus.