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INTRODUCTION: The mammillary body is a part of so-called extended hippocampal system and its importance for memory is well known. Our previous study has revealed that pharmacological inactivation of the medial mammillary nucleus (MM) attenuates theta rhythm activity in the hippocampus (HP) in urethane-anesthetized rats. In this study, we examined the involvement of GABAergic transmission in the MM in the regulation of hippocampal theta rhythm. AIM(S): The aim of this study was to investigate whether local administration of GABAA receptor agonist (muscimol) into the MM affects theta rhythm in the HP in urethane-anesthetized rats. METHOD(S): Male Wistar rats were implanted with unilateral recording electrodes into the dorsal HP (CA1) and unilateral injection cannula into the lateral part of the MM. Animals received microinjection of either muscimol (n=5) or water (n=5). 1-min tail pinch stimulations were applied at 5- and 10-min intervals to evoke theta rhythm episodes in the HP. Changes in local field potential were assessed on the basis of percent change of total EEG signal power for 1-Hz bands. RESULTS: We found that intra-MM muscimol injection suppressed sensory-elicited theta rhythm in the HP. The infusion decreased the EEG signal power most significantly in 3–4 Hz band, down to 19.1%, and in 7–8 Hz band, down to 48.6%, in comparison to the pre‑injection conditions (100%). Simultaneously, the injection increased total power in delta frequency bands, up to 2415.6% in 0.5–1 Hz band. No significant changes in the hippocampal field activity were found after the water injections in the control water group. CONCLUSIONS: Our study revealed for the first time that GABAergic transmission of the MM is significantly involved in electrophysiological activity of the HP in urethane-anesthetized rats. The obtained results also confirmed the importance of the mammillary body in regulating a theta-rhythm signaling in the extended hippocampal system. FINANCIAL SUPPORT: This research was supported by the National Science Centre (DEC-2014/12/S/NZ3/00621).
BACKGROUND AND AIMS: The activity of serotonin (5-HT) in the brain is strictly connected with the raphe nuclei. They are connected mainly with and influence the prefrontal cortex and limbic structures. Clinical studies indicate that 30% of people with autism spectrum disorder (ASD) have elevated platelet 5-HT level. The aim of the study was to investigate whether chronic (16-days) electrical stimulation of the raphe magnus (RMg) in rats can evoke behaviours comparable with the behaviours present in people with ASD. METHODS: Male Wistar rats were implanted with electrodes into the RMg under isoflurane anaesthesia. After 10-days convalescence chronic electrical stimulation began. Rats were divided into stimulated (n=6) and non-stimulated (sham/n=7) groups. Every day 25 stimulation trials were carried out, consisting of 30 s stimulation followed by 20 s interval. In sham group no current was passed through the electrode. During stimulations the locomotor activity was measured. Furthermore, the rats’ anxiety level and social responses were analyzed respectively on the 3rd and 8th day after the first stimulation. RESULTS: Locomotor activity was significantly higher in the experimental groups. At the intensity of 60–90 μA we observed rapid breathing, sniffing, and cage exploration, and at 110–140 μA – cage exploration and circular body movements. The anxiety level, analyzed as the time spent in closed arms in the elevated plus maze test, was comparable; nevertheless, social activity, measured in the three chamber test as a preference to a social stimulus, was reduced in the stimulated rats. CONCLUSIONS: Electrical stimulation of the RMg induced hyperlocomotor and reduced social behaviours, which are the symptoms often present in the course of ASD. The obtained results suggest that hyperactivity of the serotonergic system may play a role in the development of ASD. The research was funded by Young Researcher grant, 538-L124- B598-14
Synchronous neuronal activity in the hippocampus (theta rhythm) can be elicited in urethanized rats with sensory stimulation as well as with electrical or pharmacological stimulation of different nuclei of the brainstem. It is known that two of these nuclei, the nucleus pontis oralis (RPO) and the pedunculopontine nucleus (PPN), play an important role in theta regulation, however, it is still unclear which of them is essential for expression of theta in the hippocampus. In the present study we investigated the effect of temporal inactivation of PPN on the hippocampal theta rhythm induced by electrical stimulation applied to RPO. The experiments were performed on 5 male Wistar rats in deep urethane anesthesia with its level monitored on the basis of breathing rate. Animals were implanted with bilateral recording electrodes into the dorsal hippocampus and stimulation electrode into the RPO. Hippocampal EEG was recorded during repeated electrical stimulation of RPO in control conditions and also following intra-PPN administration of procaine. In all animals electrical stimulation of the RPO (200 - 300 mA, 30 s) induced episodes of robust hippocampal theta rhythm in both hippocampi which lasted for the whole period of the electrical stimulation (30 s) with no latency. After temporal inactivation of the PPN by direct procaine microinjection (20% solution/0.5 μl), electrical stimulations of the RPO were not able to induce synchronous activity in the hippocampus. Neuronal activity within the RPO and PPN nuclei changes during sleep/wake cycle including paradoxical sleep, of which hippocampal theta rhythm is an important indicator. Regular theta rhythm in the hippocampus is also present during urethane anesthesia which was applied in our experiments. Our results indicate that undisturbed neuronal activity within the PPN is crucial for evoking hippocampal theta rhythm with electrical stimulation of RPO, which suggests superior role of the PPN.
Jurkowlaniec E., Trojniar W. and Tokarski J.: The EEG activity after lesions of the diencephalic part of the zona incerta in rats, Acta Physiol. Pol. Neocortical and hippocampal EEG activity was recorded in 23 rats subjected to the bilateral electrolytic lesions of the diencephalic zona incerta (ZI). The aim was to find whether damage to ZI can replicate insomnia and disturbances in cortical EEG desynchronization and hippocampal theta rhythm found after lesions of the lateral hypothalamic (LH) area. No effect of the ZI lesions on waking-sleep cycle was found. The amplitude and frequency of cortical waves and hippocampal theta rhythm during waking were changed only in some rats. These changes were small, short-lasting and bidirectional (toward and increase or decrease in different subjects). Both the amplitude and frequency of paradoxical sleep theta were depressed in part of animals. Thus the marked EEG changes after LH lesions can not be attributed to simultaneous damage of the adjacent subthalamic region. However, the ZI seems to constitute a part of a larger system regulating cortical arousal and hippocampal theta rhythm.
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