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3 Acta Neurobiologiae Experimentalis

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Noradrenergic, serotoninergic and dopaminergic activity in the rat hippocampal slices during orexin-induced theta rhythm

100%

Ubraniak L. , Kazmierska P. , Wieczorek M. , Konopacki J.

nr Suppl.1

Orexins are two neuropeptides appearing to be particularly interesting in terms of hippocampal (HPC) EEG development. Recent studies conducted in our laboratory demonstrated that orexin A induce theta oscillations in HPC slices in certain concentrations. The lack of data concerning the influence of orexins on the changes in the activity of other neurotransmission systems encouraged our research. Thus the aim of the study was to investigate the changes in the activity of monoaminergic neurotransmitter systems in isolated HPC slices, which were used in EEG recordings. Experiments were performed on 50 slices obtained from 6 Wistar rats in accordance to Local Ethical Commission. Slices were subjected to neurochemical analysis immediately after the section, after the 45 min incubation in artificial cerebrospinal fluid (ACSF), and after incubation in ACSF with Orexin A for additional 45 min. Analysis of the concentration of monoamines and their metabolites was determined using high-performance liquid chromatography with electrochemical detection. To determine the changes in the activity of NE, 5-HT and DA systems, we calculated their utilization indexes, i.e. ratio of metabolite to its parent amine. Preliminary results suggest an increase in the particular neurotransmitter systems activity in hippocampal slices in that experimental conditions.

Theta oscillations in a novel in vitro preparation of posterior hypothalamus

75%

Kowalczyk T. , Golebiewski H. , Caban B. , Bocian R. , Kazmierska P. , Konopacki J.

nr S

Theta rhythm is the best synchronized EEG activity recorded from the mammalian brain. In rodents, this EEG pattern consists of high-voltage, regular, almost sinusoidal oscillations in the frequency range of 3-12 Hz. Hippocampal formation (HPC) is considered to be the main structure involved in the generation of this activity. Extensive anatomical and electrophysiological studies performed in rodents have revealed that the ascending brainstemhippocampal synchronizing pathway originates in the nucleus reticularis pontis oralis (RPO), next RPO fibres ascend to posterior hypothalamic (PH) region and then PH neurons projects to medial septal area which is well known as a hippocampal theta rhythm “pacemaker”. Earlier results suggest that the posterior hypothalamic region is only a modulator of hippocampal formation type II theta. Our preliminary studies suggest that this area is also capable of generation of local type II theta, which can be produced independently of the HPC theta rhythm. The purpose of the present study was to evoke the theta activity by tonic cholinergic (carbachol) or cholinergic/GABAergic (carbachol/bicuculine) bath perfusion in completely deaferentated posterior hypothalamus i.e. in novel PH slice preparations maintained in vitro. Experiments were performed on 25 posterior hypothalamic slices delivered from 25 Wistar rats. Slices were perfused with artificial cerebrospinal fluid containing carbachol (50 μM; 10 slices) or carbachol and bicuculine (50 μM and 10 μM respectively; 15 slices). Well synchronized hypothalamic theta activity was recorded in 7 carbachol-treated PH slices and in 13 PH slices perfused with carbachol/bicuculine.

Theta oscillations in the posterior hypothalamic area-in vivo approach

75%

Bocian R. , Klos-Wojtczak P. , Kowalczyk T. , Caban B. , Kazmierska P. , Konopacki J.

nr 3

Numerous studies showed that occurrence of hippocampal theta rhythm is critically dependent on the integrity of a number structures localized at the level of brainstem and diencephalon. In detailed electrophysiological studies, conducted on anesthetized rats, we demonstrated that the posterior hypothalamic area (PHa), is not only a modulator of hippocampal formation theta but also could generate theta activity independently. The most effective areas in generation of examined EEG pattern were the supramammillary and posterior hypothalamic nuclei. Pharmacological manipulation reviled that PHa theta activity had a cholinergic (muscarinic) profile. Local injection of orexin A and B never induced theta activity in PHa. Finally, we showed that mineralocorticoid receptor but not gap junction play crucial role in generation of the posterior hypothalamic theta rhythm. Studies supported by NCN grant no. 2011/01/B/NZ4/00373.