Inhibitory Roles of Layer I Neurons in Rat Barrel Cortex

Trustees Of Boston University, Boston

Investigators

Abstract

The mammalian cerebral cortex is the vastly complex and enigmatic neural structure responsible for cognitive abilities such as reasoning, imagining and perceiving. A very useful model system for investigation of the poorly understood cellular mechanisms underlying cortical function is the rat somatosensory cortex, which contains discrete columns or "barrels" of vertically-aligned, input-specific cells that process sensory information from a single whisker. Barrel cortex has six layers (I-VI), each comprised of cells with characteristic electrophysiological, morphological and/or connectional properties. The functional integrity of input-specific barrels is dependent upon a balance of inhibitory and excitatory interactions of local inhibitory cells (interneurons) and excitatory output cells (pyramidal cells) between and within layers. In recent years, progress has been made in detailing the characteristics and interactions of cells in layers II-VI of cerebral cortex, but little is known of the properties of Layer I (LI) neurons and virtually nothing is known of the role(s) they play in the microcircuitry of cortical columns. This is a very significant gap, because LI is ubiquitous throughout the cerebral cortex, and, unlike other cortical layers, contains a cellular population comprised almost exclusively of inhibitory interneurons. LI cells are strategically positioned to exert profound inhibitory influences on pyramidal output cells, which receive many intra- and extracortical inputs on their complex processes in LI. The goal of the proposed studies is to gain an understanding of the role of LI neurons in functional columns of cerebral cortex using the rat barrel cortex as a model system. The overall hypothesis is that LI interneurons can be grouped into distinct classes that play important roles in maintaining input-specific sensory integration within and between barrels, through distinct inhibitory actions on LII/III pyramidal cells and on other LI neurons. Physiological recordings with intracellular biocytin filling of LI interneurons and LII/III pyramidal cells in in vitro slices of rat barrel cortex will be employed in experiments designed to test this hypothesis. Data from these studies will yield vital information on the role of distinct classes of interneurons in the cortical circuits responsible for integration of sensory information.