The manganese enhanced magnetic resonance imaging (MEMRI) in based on the advantage of manganese ions accumulation in active neurons to cause decreased T1 relaxation time and so enhanced signal intensity in MRI. The MEMRI technique was applied only in few cases to map brain activity involved in higher brain functions of rodents, however. MEMRI technique in mapping of brain areas involved in operant condition was never examined yet.

Therefore, in the present experiments we examined whether the MEMRI is able to discriminate among activities of brain areas after application of water rewarded operant signal discrimination (OSD) task. T1 relaxation time was determined and T1 maps were calculated in rats before and after systemic injection of MnCl₂. The changes in T1 maps in learned animals tested in OSD task were compared to group of rats with drinking after water deprivation and group of animals similarly motivated

and participated in the same OSD signal context without operant responding. To determine T1 a turbo spin echo inversion recovery sequence was used. T1 maps were calculated from the images with different inversion times applying a three-parameter fit.

Results showed that in rats with OSD compared to group with third motivation and drinking the following areas were more active: secondary motor cortex, primary somatosensory cortex, auditory, visual, agranular insular, retrosplenial, piriform, ectorhinal, perirhinal and entorhinal cortices, cortical amygdaloid nuclei, ventrolateral preoptic nucleus, supraoptic nucleus, lateral hypothalamus, ventral tegmental area.

Compared the signal intensity between groups executed the OSD task and controls without operant responding, the same brain areas had higher signal intensity, but differences in activity pattern of the following areas were observed: visual cortex, temporal assotiation cortices, amygdalo-hippocampal area, subiculum, olfactory tubercle, tractus olfactorius, central and medial amygdaloid nuclei. The following brain structures showed higher activity in controls with thirst motivated drinking compared to OSD learned animals: striatum, nucleus accumbens shell, ventral pallidum, zona incerta, hippocampus, thalamus, subthalamus, hypothalamus, substantia nigra, pontin nuclei.

IN CONCLUSION, the activity-induced MEMRI is a reliable method in rodents to detect local brain activity changes related to thirst motivated behaviour, operant responding in itself and responses elicited by OSD task.

Supported by NKTH-OTKA K68431, SROP-4.2.2/B-10/1-2010-0029, SROP-4.2.1.B-10/2/KONV-2010-0002 and by the HAS.