Direct measurement of neuronal ensemble activity using photoacoustic imaging in the stimulated Fos-LacZ transgenic rat brain: A proof-of-principle study

Abstract

Measuring neuroactivity underlying complex behaviors facilitates understanding the microcircuitry that supports these behaviors. We have developed a functional and molecular photoacoustic tomography (F/M-PAT) system which allows direct imaging of Fos-expressing neuronal ensembles in Fos-LacZ transgenic rats with a large field-of-view and high spatial resolution. F/M-PAT measures the beta-galactosidase catalyzed enzymatic product of exogenous chromophore X-gal within ensemble neurons. We used an ex vivo imaging method in the Wistar Fos-LacZ transgenic rat, to detect neuronal ensembles in medial prefrontal cortex (mPFC) following cocaine administration or a shock-tone paired stimulus. Robust and selective F/M-PAT signal was detected in mPFC neurons after both conditions (compare to naive controls) demonstrating successful and direct detection of Fos-expressing neuronal ensembles using this approach. The results of this study indicate that F/M-PAT can be used in conjunction with Fos-LacZ rats to monitor neuronal ensembles that underlie a range of behavioral processes, such as fear learning or addiction.

Keywords: ANSI, American national standards institute; AP, anterior-posterior; Brain; CNR, contrast-to-noise ratio; Cocaine; DMSO, dimethyl sulfoxide; DV, dorsal-ventral; F/M-PAT, functional molecular photoacoustic tomography; FOV, field-of-view; Fear conditioning; Fos; GRIN, gradient-index; IL, infralimbic cortex; ML, medial-lateral; Neuronal ensemble; OCT, optical coherence tomography; OPO, optical parametric oscillator; PA, photoacoustic; PBS, phosphate buffer saline; PL, prelimbic cortex; Photoacoustic imaging; SNR, signal-to-noise ratio; US, ultrasound; X-gal; X-gal, beta-D-galactosidase; fMRI, functional magnetic resonance imaging; mPFC, medial prefrontal cortex.