Diverse role of neurogliaform cells in cortical microcircuits

Cortical circuits consist of two major types of neurons: the excitatory pyramidal cells and the inhibitory interneurons. While pyramidal cells mostly do not differ from each other in their morphological and physiological features, interneurons show diversity of great extent. The different interneuron populations can be described with distinct morphology and in accordance with this with distinct firing patterns. These inhibitory cells innervate their postsynaptic targets with GABAergic synapses in contrast with pyramidal cells which operate via glutamatergic synapses. During my Ph.D. studies I focused on scrutinizing the peculiar role of one of the numerous interneurons, the neurogliaform cells in information processing of neocortical circuits. Morphological and electrophysiological diversity of neocortical neurons The principal cells of the neocortex are the pyramidal cells (Zigmond et al., 1999). They are also the numerically dominant cell type of the cortex. In the association cortex pyramidal cells form about 80% of the neurons (Sloper et al., 1979; Winfield et al., 1980). They can be found in all cortical layers except layer I. Their common characteristic features are the spiny dendrites. A typical pyramidal cell has a triangular cell body, a thick, radially oriented apical dendrite, forming a terminal tuft in the most superficial cortical layer and a set of basal dendrites. Despite all of these, the term " pyramidal cells " is referred to a diverse cell group, where these principal cells differ from each other not only by their appearance but by their connectivity as well. Their variability in cell size, dendritic arborization and the presence of their axonal collaterals depends on the laminar localization of the neuron. Using glutamate as neurotransmitter, they are responsible for the majority of excitatory postsynaptic potentials (EPSP) evoked in their postsynaptic cell-pairs. Pyramidal cells mainly innervate dendritic spines of other pyramidal cells and dendritic shafts of aspiny interneurons through asymmetric synapses. No excitatory synapses are made on the somata of pyramidal cells. 4 GABAergic interneurons constitute only a minor fraction of the total number of GABAergic cells have influenced both the origin and the backpropagation of the action potentials, and play an important role in the synchronization of the activity of different cell-populations. Despite their small numbers, these interneurons are extremely diverse in their morphological, electrophysiological and molecular properties (Fairen et al. Gupta et al., 2000), therefore it is possible to classify between them on the basis of these characteristics. Functional characterization is based on action potential firing …