Subtypes of Layer 1 interneurons.
(a) Electrophysiological properties of the four different L1 subtypes: NDNF/NPY positive; NDNF/NPY negative, VIP, and alpha-7. Middle panel illustrates the response of the neurons to a threshold current injection. Notice that the NDNF/NPY positive population has a late spiking property, and the alpha-7 population has a depolarizing hump near threshold.
(b) The morphologies associated with the four subtypes. Notice the elaborate axonal and dendritic arborization of the neurogliaform and the canopy cells (NDNF population) mostly restricted to Layer 1; whereas the alpha-7 and VIP possess a descending axon projecting down to deeper layers.
(c) Relative proportions of the four interneuron subtypes in Layer 1.