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1

Cellular correlates of kainate-induced posterior hypothalamic theta rhythm in vitro

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Caban B., Staszelis A., Kazmierska P., Siwiec M., Sowa J., Kowalczyk T.
Acta Neurobiologiae Experimentalis
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2018
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tom 78
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nr Suppl.1
Hippocampal formation (HPC) theta rhythm is known to be one of the most synchronized EEG pat‑ terns in mammals. Theta field potentials in the HPC of rats are high‑amplitude, almost sinusoidal, waves in a 3‑12 Hz frequency range. It is well‑known that the posterior hypothalamic area (PHa including the supra‑ mammillary nucleus and posterior hypothalamic nuclei) is an important node in the pathway of HPC theta gen‑ eration, i.e. the ascending brainstem‑hippocampal syn‑ chronizing pathway. Furthermore, HPC theta frequency is at least partially modulated by the PHa through the activity of neurons firing in the frequency of HPC the‑ ta, at least during animals’ immobility‑related behav‑ iors. The PHa is thought to complement the activity of the medial septal area, widely known as the pacemaker of HPC theta rhythm. However, in our previous studies we discovered for the first time that cholinergic theta rhythm can also be recorded locally in deafferented pos‑ terior hypothalamic slices. Hence, in the present study we investigated PHa‑recorded theta‑related single cell activity in relation to local theta rhythm following ka‑ inic acid administration. 36 in vitro experiments were performed using brain slices (=72) taken from 36 adult Wistar rats. Each slice was perfused with 0.1 μM kain‑ ic acid to induce rhythmic activity and neuronal firing. Both field activity and corresponding cellular activity were recorded extracellularly. The relation of neuronal firing patterns to local field theta rhythm was investi‑ gated according to an existing universal classification of HPC theta‑related neurons. This study resulted in re‑ cording 17 theta‑related neurons and 77 neurons classi‑ fied as non‑related to local theta rhythm. A new neuron type (=21 cells) has been identified amongst the non‑re‑ lated group, which we termed timing cell, with a very rhythmic firing pattern in a nearly fixed frequency in the theta band. Kainate‑induced neuronal activity, re‑ corded in the posterior hypothalamic area in vitro, re‑ sembles cholinergically‑induced PHa neuronal activity, as well as well‑documented patterns of theta‑related cell discharges in the hippocampal formation in vitro and in vivo. Newly discovered PHa timing cells are discussed in light of an HPC theta rhythm frequency control mecha‑ nism. Supported by National Science Centre, Poland, No. UMO‑2017/25/B/NZ4/01476.
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NMDA-induced posterior hypothalamic theta rhythm recorded in vitro

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Staszelis A., Caban B., Kazmierska-Grebowska P., Sowa J. E., Siwiec M., Kowalczyk T.
Acta Neurobiologiae Experimentalis
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2019
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tom 79
|
nr Suppl.1
INTRODUCTION: Theta rhythm is one of the brain rhythms’ patterns, which are evidence for neuronal synchrony. This pattern of rhythmic activity is related to sensorimotor integration, mnemonic functions, or spatial orientation and navigation. However, it is also linked to pathological conditions, for instance: Alzheimer’s disease, post‑traumatic stress disorder, and depression. In the last decade, we discovered that the posterior hypothalamic area (PHa) is not only a modulator of brainstem information going to the hippocampus, but also is capable of generating theta rhythm independently. AIM(S): The aim of the present study was to determine if NMDA (N-Methyl-D-aspartic acid) is capable of eliciting well-synchronized theta activity in PHa preparations. METHOD(S): The study was performed on 40 PHa slices prepared from 20 male Wistar rats. Each animal was anesthetized with isoflurane and decapitated. The PHa slices were dissected and transferred into the recording chamber, perfused with artificial cerebrospinal fluid, and treated with NMDA (300 µM) and D-AP5 (D‑(–)‑2‑amino‑5‑phosphonopentanoic acid) (200 µM). The field recordings were performed with glass electrodes filled with 2.0 M sodium acetate. RESULTS: Perfusions of PHa slices with 300 µM NMDA resulted in well-synchronized theta episodes which were blocked after the path application of 200 µM D‑AP5. CONCLUSIONS: The present data shows that excitation of NMDA-type glutamatergic receptors in PHa neural networks leads to the generation of local theta rhythms. FINANCIAL SUPPORT: Supported by NCN grant no. 2017/25/B/NZ4/01476.
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Posterior hypothalamic "timing cell" activity and kainite-induced local theta rhythm in both in vitro and in vivo preparations

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Kowalczyk T., Staszelis A., Kazmierska-Grebowska P., Sowa J. E., Siwiec M., Caban B.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
|
nr Suppl.1
INTRODUCTION: Theta rhythm typically occurs during memory processes, REM sleep, and spatial navigation but also in epilepsy, migraines, or even mild Alzheimer’s disease (AD). Recent evidence shows that well-synchronized theta rhythm can successfully be recorded locally from the posterior hypothalamic area (PHa), specifically from the supramammillary nucleus (SuM) and the posterior hypothalamic nuclei (PH). The population of theta-related cells in the PHa were found to be similar types to those found in the hippocampal formation. In addition, a new type of cells has been found in the posterior hypothalamic region and based on its regular firing pattern and possible pacemaker role these cells were termed “timing”. AIM(S): The aim of the present study was to investigate the timing of cell populations in both in vivo and in vitro PHa after theta rhythm induction by kainic acid (KA) application. METHOD(S): Twenty in vivo experiments were performed on 20 urethanized rats and 22 in vitro experiments were performed on 40 PHa slices obtained from 22 rats. Theta rhythm and single unit activity were evoked by intra-PHa microinjection of KA (in vivo) or by bath perfusion of PHa slices with KA-containing artificial cerebrospinal fluid (in vitro). RESULTS: A total number of 123 posterior hypothalamic neurons were recorded during both in vivo and in vitro experiments. Among them, 28 neurons were classified as “timing cells” according to their very regular pattern of discharges in a steady frequency in the theta band (3‑12 Hz). Eight timing cells were recorded in in vivo PHa and 20 timing cells were recorded in PHa slices. CONCLUSIONS: The present data show that glutamatergic stimulation of PHa neuronal network with kainic acid results in the activation of specific subpopulation of neutrons, characterized by regular firing pattern in theta frequency range. The role of PHa “timing cell” activity is discussed regarding hippocampal theta rhythm frequency programing. FINANCIAL SUPPORT: Supported by NCN grant No. 2017/25/B/NZ4/01476.
4

Postnatal development of theta-related cell activity in posterior hypothalamic slices

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Konopacki J., Caban B., Kazmierska P., Bocian R., Klos-Wojtczak P., Staszelis A., Kowalczyk T.
Acta Neurobiologiae Experimentalis
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2017
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tom 77
|
nr Suppl.1
INTRODUCTION: Hippocampal formation (HPC) theta rhythm is one of the best examples of neural synchrony in the mammalian brain. It is well-known that the pathway of theta generation originates in the pons, from where it projects to the posterior hypothalamic nuclei, and finally through the medial septal area reaches the HPC. Recent evidence shows that well-synchronized theta rhythm can also successfully be recorded locally from the posterior hypothalamic area (PHa) maintained in vivo and in vitro, specifically from the supramammillary nucleus (SuM) and the primary posterior hypothalamic nuclei (PH). Furthermore, the neuronal activity of the PH and SuM nuclei can be characterized according to the universal classification of theta-related cells which was earlier created for the hippocampus. AIM(S): The purpose of the present study is to investigate theta-related cell activity in posterior hypothalamic slices taken from adolescent rats in order to examine the age at which theta rhythm and accompanying theta-related neuronal activity appears in rats’ PHa. METHOD(S): Forty‑five experiments have been carried out using brain slices taken from 55 Wistar rats aged: 8–10 (A); 13–15 (B); 18–19 (C) and 22–24 (D) days. Each brain slice was perfused with 75 µM carbachol (cholinergic agonist) to induce theta rhythm and accompanying theta-related cell activity in the SuM and PH nuclei. RESULTS: This study resulted in recording 16 theta-related neurons, 56 timing neurons, and 103 neurons classified as non‑related to PHa theta among three experimental groups (B–D). There was no significant theta oscillations and accompanying cell discharges in slices taken from 8–10 days old rats. CONCLUSIONS: Theta oscillations as well as theta-related neuronal activity can be observed in PHa slices delivered from rats not younger than 13–15 days. FINANCIAL SUPPORT: Supported by NCN grant 2013/11/B/NZ4/04872.
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