This project aims to validate in the ferret a qualitatively novel technology for imaging neural circuit function at a brain-wide scale and deploy it to study behavior-dependent information flow in the ferret auditory system. Hemodynamic neuroimaging methods like functional magnetic resonance imaging (fMRI) have revolutionized neuroscience by allowing researchers to characterize spatiotemporal features of brain-wide activity in humans and animals. A major disadvantage of such approaches, however, is their lack of specificity for well-defined cellular sources. A new type of genetically encodable molecular probe, called NOSTIC , addresses this problem by transducing intracellular calcium activity into artificial hemodynamic responses, permitting spatially comprehensive neuroimaging of genetically targeted cells and circuit elements. “Hemogenetic” signals arising from NOSTICs may be differentiated from endogenous blood flow changes by pharmacological means and can be detected with a combination of sensitivity, noninvasiveness, and mechanistic precision that will enable hemogenetic imaging to confront some of the most important problems in contemporary neuroscience. Here, NOSTIC will be combined with functional ultrasound (fUS) imaging [2,3], an emerging new imaging modality, to study information flow in the ferret auditory cortex, extending hemogenetics to a new species and detection modality. These efforts will aim at characterizing how task engagement gates feedforward flow of sensory information along the cortical hierarchy up to frontal areas .
Description of the work:
Preliminary experiments in our laboratory demonstrated the expression and the functional signature of NOSTIC. We will follow this validated protocol. Retrogradely transported HSV vectors encoding NOSTIC will be injected into ferret premotor cortex (PMC) approximately four weeks before experiments. Cranial windows will be exposed over auditory cortex in order to permit ultrafast power Doppler fUS data acquisition using an Iconeus One system equipped with a 256-channel linear transducer operating at 15 MHz. 4-plane imaging will be performed in head-fixed ferrets performing a Go/No-Go discrimination task, in a series of serially translated acquisition to cover a three dimensional volume; this procedure will be repeated both before and after administration of 1400W, a NOSTIC inhibitor, while ferrets will perform the task or passively listen to the sounds. Data will be analyzed to measure sound category-, behavior-, and 1400W-dependent response characteristics in auditory regions. Cortical responses will be examined to answer these questions: (1) From what auditory cortical regions do significant stimulus-driven inputs to PMC arise? (2) To what extent are ascending auditory inputs filtered or transformed with respect to mean response properties of their source brain regions? (3) Do sensory inputs from auditory cortex to PMC differ depending on behavioral state of the animal?
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