Desynchronization of Theta Oscillations in Prefrontal Cortex during Self-stimulation of the Medial Forebrain Bundles in Mice

Stimulation of the medial forebrain bundle (MFB) can reinforce intracranial self-stimulation (ICSS) in rodents (i.e., reward-seeking behavior). The MFB stimulation produces a highly reliable behavioral output that enabled a clear distinction of the animal behavioral states between the non-ICSS and ICSS periods. However, the cortical states during these reward-seeking behaviors are not fully characterized in comparison to those during volitional behavior. This study was designed to characterize the cortical rhythms of and coherence between prefrontal cortex and hippocampus during the wheel-turning behavior reinforced by the ICSS in comparison to the wheel-turning without ICSS. We used a wheel for freely moving mice, which was programmed to deliver cathode currents through an electrode in the MFB at each one-quarter turn of the wheel to induce ICSS. The wheel-turning epochs were extracted from the pre-ICSS, ICSS and post-ICSS sessions and the prefrontal EEGs and the hippocampal LFPs in the epochs were analyzed with power and synchronization analyses. During the ICSS, the EEG power decreased at 6~10 Hz in the prefrontal cortex, while was not significantly altered in the hippocampus. Furthermore, we found that the phase synchrony between the prefrontal cortex and the hippocampus corresponding to information transmission between the two regions during reward-seeking motion decreased preceding MFB stimulation reinforced by ICSS. Our findings suggest that theta-activity can be reliably dissociated from active behavior if the animal is involved in self-stimulation.

Relationship between Hippocampal Theta Rhythm and Pressor Effect during Noxious Stimulus in Rabbits / 第三军医大学学报

It is known that hippocampal EEG and blood pressure can be influenced bynoxious stimuli, but the relationship between the hippocampal theta rhythm andthe pressor effect has not been made clear. In this article, the relationship betweennoxious stimulus and the central cholinergic activity after the hippocampal thetarhythm was inhibited or blocked was studied.There was an obvious correlation between the duration of the hippocampal theta rhythm and that of the pressor effect when an noxious stimulus was given. But the duration and reaction of pressor effect were inhibited if 100 ?g of atropine was injected into one of the lateral ventricles and it was strengthened if 100 ?g of mascarine was injected intraventricularly. After the clectrocoagulation of the medial septum, the hippocampal theta rhythm could not be evoked by noxious stimulus and the pressor effect was also obviously inhibited.These results seem to indicate that the hippocampus plays a role in the regulation of blood pressure, the mechanism of which may be mediated through the central cholinergic system.