Phase-dependent activity of neurons in the rostral part of the thalamic reticular nucleus with saccharin intake in a cue-guided lever-manipulation task.

Neurons in the rostral part of the thalamic reticular nucleus (rTRN) receive somatosensory and motor information and regulate neural activities of the thalamic nuclei. Previous studies showed that when activity in visual TRN neurons is suppressed prior to the visual stimuli in a visual detection task, the performance of the task improves. However, little is known about such changes in the rTRN preceding certain events. In the present study, we performed unit recordings in the rTRN in alert rats during a cue-guided lever-manipulation task in which saccharin was provided as a reward. Changes in neural activity during saccharin intake were observed in 56% (51 of 91) of the recorded neurons; the firing rates increased in 21 neurons and decreased in 23 neurons. Seven neurons both increased and decreased their firing rates during saccharin intake. Changes in firing rates during the reward-waiting stage between task termination and saccharin intake were also observed in 73% (37 of 51) of the neurons that responded to saccharin intake. Increased activity during saccharin intake did not correlate with increased activity during lever-manipulation or activity during the reward-waiting stage. However, decreased activity during saccharin intake was correlated with activity during the reward-waiting stage. These results suggest that rTRN neurons have phase-dependent changes in their activity and regulate the thalamic activities. Furthermore, the decreased activity of rTRN neurons before reward may contribute to refine somatosensory and motor information processing in the thalamic nuclei depending on the status of mind such as expectation and attention.

Cytoarchitecture-Dependent Decrease in Propagation Velocity of Cortical Spreading Depression in the Rat Insular Cortex Revealed by Optical Imaging.

Cortical spreading depression (SD) is a self-propagating wave of depolarization accompanied by a substantial disturbance of the ionic distribution between the intra- and extracellular compartments. Glial cells, including astrocytes, play critical roles in maintenance of the extracellular environment, including ionic distribution. Therefore, SD propagation in the cerebral cortex may depend on the density of astrocytes. The present study aimed to examine the profile of SD propagation in the insular cortex (IC), which is located between the neocortex and paleocortex and is where the density of astrocytes gradually changes. The velocity of SD propagation in the neocortex, including the somatosensory, motor, and granular insular cortices (5.7 mm/min), was higher than that (2.8 mm/min) in the paleocortex (agranular insular and piriform cortices). Around thick vessels, including the middle cerebral artery, SD propagation was frequently delayed and sometimes disappeared. Immunohistological analysis of glial fibrillary acidic protein (GFAP) demonstrated the sparse distribution of astrocytes in the somatosensory cortex and the IC dorsal to the rhinal fissure, whereas the ventral IC showed a higher density of astrocytes. These results suggest that cortical cytoarchitectonic features, which possibly involve the distribution of astrocytes, are crucial for regulating the velocity of SD propagation in the cerebral cortex.