Impact of axon initial segment variability and plasticity onto neuronal excitability in CA1 pyramidal cell

Dolenc, Jan (author), Kreft, Marko (mentor), Draguhn, Andreas (comentor)

The hippocampus is considered to be one of the most thoroughly researched parts of the brain. The primary type of hippocampal nerve cells are pyramidal cells, which make up most of the cells in hippocampal pyramidal layer. In our study we focused on CA1 pyramidal cells, more specifically on the specialized proximal part of their axons, the axonal initiation segment (AIS). The aim of the study was to learn more about the variability of AIS within the CA1 pyramidal layer of the hippocampus, to determine its impact on neuronal excitability and to monitor changes in AIS morphology due to external factors in order to understand its plasticity. Acute mouse brain slices from two genetic lines were used for the experiments: the wild-type Black 6 and the transgenic mouse line, which expressed the fluorescent fusion protein ankyrin G-GFP under the ankG promoter. Our results confirmed that the length of the AIS varies greatly between neurons within the CA1 pyramidal layer of the hippocampus. It has been shown that neurons in the more dorsal parts of the hippocampus have on average longer AIS than neurons located ventrally. It was also determined that the maximum number of action potentials triggered by a single stimulation with a high electric current depends on the length of the AIS. Longer AISs contribute to a greater number of consecutive action potentials. We have shown that even after the death of an organism, spontaneous changes in the length of the AIS occur. In our study we demonstrated how elevated extracellular potassium concentration affects the activity of CA1 pyramidal cells and their AIS. The increased potassium concentration has caused shortening of the AIS and a decrease in their fluorescence intensity.

• Language: English
• Keywords: biology, neurobiology, hippocampus, pyramidal cell, axon initial segment, plasticity
• Work type: Master's thesis/paper
• Organization: BF - Biotechnical Faculty
• Year: 2020
• PID: 20.500.12556/RUL-121564
• COBISS.SI-ID: 44387331
• Publication date in RUL: 16.10.2020

Secondary language

• Language: Slovenian
• Title: Vpliv variabilnosti in plastičnosti aksonskega iniciacijskega segmenta na nevronsko vzdražnost CA1 piramidalnih celic

Abstract

Hipokampus velja za najbolj temeljito raziskani del možganov. Primarni tip živčnih celic hipokampusa so piramidalne celice, ki predstavljajo večino celic v njegovi piramidalni plasti. V naši raziskavi smo pozornost posvetili piramidalnim celicam CA1, natančneje specializiranemu proksimalnemu delu njihovih aksonov, aksonskemu iniciacijskemu segmentu (AIS). Cilj raziskave je bil izvedeti več o variabilnosti AIS znotraj CA1 piramidalne plasti hipokampusa, ugotoviti njen vpliv na nevronsko vzdražnost in spremljati spremembe v morfologiji AIS zaradi zunanjih dejavnikov, da bi razumeli njegovo plastičnost. Za eksperimente smo uporabljali akutne rezine mišjih možganov iz dveh genetskih linij: divji tip Black 6 in transgeno mišjo linijo, ki je pod ankG promotorjem izražala fluorescenčni fuzijski protein ankirin G-GFP. Naši rezultati so potrdili, da dolžina AIS zelo variira med nevroni znotraj CA1 piramidalne plasti hipokampusa. Izkazalo se je, da imajo nevroni v bolj dorzalnih delih hipokampusa v povprečju daljše AIS kot nevroni, ki so locirani ventralno. Ugotovili smo tudi, da je maksimalno število akcijskih potencialov, sproženih z eno stimulacijo z visokim električnim tokom, odvisno od dolžine AIS. Daljši AIS omogočajo večje število zaporednih akcijskih potencialov. Dokazali smo, da se tudi po smrti organizma dogajajo spontane spremembe v dolžini AIS. V naši raziskavi smo prikazali, kako povišana zunajcelična koncentracija kalija vpliva na aktivnost CA1 piramidalnih celic in njihove AIS. Povišana koncentracija kalija je povzročila krajšanje AIS in zmanjšanje intenzivnosti njihove fluorescence.

• Keywords: biologija, nevrobiologija, hipokampus, piramidalna celica, AIS, plastičnost