Research Synopsis:
I am characterizing the synaptic properties of sensory corticocortical connections (C-C) using physiological, anatomical and pharmacological methods in the mouse. Recent work in corticothalamic (C-T) systems has raised questions about the nature of sensory C-C connections. In previous studies, of both the somatosensory and visual systems, dual C-T pathways prompted a new classification scheme for glutamatergic synapses involved in sensory processing. Synaptic inputs in these pathways can be separated into the categories of: drivers and modulators. Drivers carry the information that mainly defines the receptive field of the postsynaptic cell. They produce large, all-or-none excitatory post-synaptic potentials (EPSPs) with paired pulse depression and activate only ionotropic glutamate receptors. Driving C-T cells originate in layer V of the cortex and terminate in dense arbors with large synaptic terminals. Modulators do not provide the main receptive field properties. They alter the probability that certain aspects of driving information will be transferred. Modulators also exhibit small, graded EPSPs with paired pulse facilitation and a metabotropic glutamate receptor component (in addition to the ionotropic component). Modulating C-T cells originate in layer VI of the cortex and terminate in sparse arbors with small synaptic terminals. Although a driver/modulator classification seems to apply between the thalamus and the cortex, it is unknown whether this applies between cortical areas. I have begun in the auditory cortex (ACx) and use the C-T pathway as a template to assess if feedforward and feedback C-C connections fit into the driver and modulator categories described. Furthermore, I am looking for unique characteristics in C-C pathways that deserve additional or even completely different patterns of classification. I plan to continue with other sensory cortical systems to assess if the C-C synaptic properties and routes of information transfer are similar.
