Resting state functional connectivity MRI in isoflurane-anesthetized rat brain

• Resting state functional connectivity MRI (rs-fcMRI) provides a unique opportunity to investigate the architecture of intrinsic functional connectivity of the rat brain based on the spontaneous low-frequency fluctuations of the BOLD signal. It is of particular importance in translational medicine, since it allows to measure drug effects on functional brain connectivity in preclinical animal models and to compare with the effect of the same drugs on the functional connectivity in the human brain.

• Here we investigated intrinsic functional connectivity in isoflurane-anesthetized rat brain and its modulation as a result of administration of two different drugs: 1. scopolamine (SA) and 2. a memory enhancing compound (MEC).

• Animals• -11 adult male Long-Evans (LE) rats (230-270 g) rats• - Isoflurane gas (1.0-1.5 %) • Experimental procedure• 20min long resting state fMRI acquisitions was started 10min before the

initiation of the SA and MEC infusion.

• ‘SEED’ selection:• Seed regions of interest (ROI) ( ~3×3×3 voxels) were selected in dorsal and

ventral hippocampus, prefrontal cortex (PFC), temporal and parietal cortex, periaqueductal gray matter (PAG), dorsal striatum (caudate and putamen) and amygdala based on anatomical T1-weigted GEMS scans and with reference to the Paxinos and Watson rat brain atlas as well.

• Resting-state specific preprocessing was performed on the data sets: • -spatial filtering with a Gaussian kernel of 2 voxels FWHM• -voxel-wise regression analysis to remove artefacts due to changes in

grey matter, and skull signals;• -band-pass filtering (0,009-0,08 Hz);

• Data were segmented according to the administration time of the drug compounds: 8.5 min intrinsic and 8.5min drug modulated resting state activity were analysed for each animal.

• Reference time course from a seed ROI was then correlated with the• entire data set. Group-wise (random effects) statistical parametric maps

was obtained based on individual correlation coefficient maps and their contrasts.

Resting state activity based intrinsicconnectivity maps

Group level correlation matrix (t-statistic based on the individual correlation coefficients). As expected, there are strong positive correlations between the same anatomically localized brain regions of the two hemispheres. Furthermore negative correlations between the striatum and PAG (and hippocampus and PFC) are in agreement with the relevant literature.

Resting state activity based intrinsicconnectivity maps

SEED

DorsalHippocampus

VentralHippocampus

PFC

Temporal cortex

Resting state activity based intrinsicconnectivity maps

SEED

PAG

Caudate/Putamen

Amygdala

Amygdala,ventral hyppocampus versus (negative correlation) ACC, PFC (Liang et al Neuroimage, 2011)

Pharmacological modulation of the resting state activity

Random effects group analysis of the differences between the scopolamine and memory enhancing compound induced changes in the resting state activity. Increased functional connectivity of the dorsal hippocampus(A) and ventral hippocampus (B) as a result of MEC administration compared to scopolamine injection can be seen.

Pharmacological modulation of the resting state activity

Random effects group analysis of the differences between the scopolamine and memory enhancing compound induced changes in the resting state activity.

Conclusion• Using the seed-based rs-fcMRI approach we showed that the

functional connectivity of different anatomically localized brain regions was preserved under isoflurane-anesthesia.

• In specific brain regions SA and MEC had an opposite effect on functional connectivity: intrinsic BOLD signal co-fluctuations were reduced and enhanced by SA and MEC, respectively.

• These results provide support for the application of rs-fcMRI in isoflurane-anesthetized rat brain to investigate normal and pathological brain functions as well as drug effects in preclinical animal models.

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ROI analízis

Hipp cortex PFC DMPAG LPAG SCN stri tempo pariet0

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Preklinikai Képalkotó Laboratórium 2012. február

Resting state fMRI patkányban

Független komponens analízissel hálózatok azonosíthatók éber patkányban:

1. Cerebellar Network

2. (Visuo-) Spatial System

3. Basal Ganglia-Hypothalamus Network

4. Basal Ganglia-Thalamus-Hippocampal Network

5. Autonomic Network

6. Sensory (Exteroceptive) Network

7. Interoceptive Network