Circuit analysis in the olfactory cortex.

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DESCRIPTION (provided by applicant): The broad goal of the proposed project is to understand the fundamental mechanisms of cortical processing in the olfactory system and their role in seizure initiation. The work will specifically address three synaptic pathways in olfactory cortex which may contribute to epileptogenesis. Whole-cell patch-clamp of cortical pyramidal cells in anterior olfactory nucleus (AON) and piriform cortex will be used to study the response to stimulation of input from the olfactory bulb. Paired recordings will be used to study the interactions of cells within and between the cortical regions being studied (including important inhibitory inputs) and immunochemistry and confocal imaging to compliment electrophysiological results. Two types of principal neurons in the olfactory bulb project to the olfactory cortex: tufted and mitral cells. Tufted cells project to AON and ventrorostral anterior piriform cortex (aPCvr), while mitral cells project to the entirety of olfactory cortex. While tufted and mitral cells carry different information about the olfactory world, the physiological response and functional significance of this is not known. We will separate the response, in cortex, to these two types of inputs. The aPCvr is reciprocally connected to an underlying cortex which is highly susceptible to the initiation of tonic-clonic seizures, leading to the hypothesis that tufted cell input plays a special role in the initiation of seizures in piriform cortex. The aPCvr receives feedforward input from the AON. Critically, AON feedforward excitation terminates directly adjacent to the cell bodies of pyramidal cells in anterior piriform, while olfactory bulb terminals are on the distal apical dendrites. Therefore it appears that AON input, but not olfactory bulb input, may be the driving input to this epileptogenic brain region. Recordings of piriform cortical pyramidal cells during stimulation of their AON inputs will allow detailed study of this previously unexplored synaptic connection. Axo-axonic cartridge endings of chandelier cells, and cholecystokinin positive basket cell bodies and endings are absent from aPCvr. I will study the synaptic influence of these inhibitory neurons in piriform cortex. Relevance of Research to Public Health The cortex of the olfactory system is known to be an important site for the initiation of some types of epileptic seizures. Study of the sensory input to and synaptic connections between cells in this region will help understand the mechanisms that underlie seizure initiation. A long-term commitment to the development of better treatments for epilepsy depends critically on an understanding of underlying circuitry.