Parvalbumin neurons in the forebrain as revealed by parvalbumin-Cre transgenic mice

Neurons expressing the calcium-binding protein parvalbumin (PV) constitute an abundant subpopulation of GABAergic neurons in the cerebral cortex. However, PV is not unique to the GABAergic neurons of the forebrain, but is also expressed in a small number of pyramidal neurons and in a large number of thalamic neurons. In order to summarize the PV neurons in the forebrain, we employed the PV-Cre transgenic mice in the present study. In the progeny of crossbreed between PV-Cre mice and GFP-Cre reporter mice, we found that the GFP-positive neurons include many excitatory neurons in the neocortex and the thalamus as well as GABAergic neurons in the cerebral cortex and basal ganglia. All the reported PV-positive GABAergic neurons in the cerebral cortex and the basal ganglia seemed to be included in the GFP-positive cells. We found GFP-positive layer V pyramidal neurons inhabit a broader neocortical area than was previously reported. They were located in the primary somatosensory, motor, and visual areas. The somatosensory area of the neocortex contained the greatest number of PV-positive pyramidal neurons. A large number of thalamic relay neurons and virtually all the reticular thalamic neurons appeared as GFP-positive. Thalamic relay nucleus and a neocortical area for the same modality corresponded and seemed to contain a characteristic amount of PV-positive excitatory neurons.