Hippocampal interneurons and network oscillations

The hippocampal formation is important for acquisition of short-term memory, the recall of episodic memory and spatial navigation. Oscillatory brain activity at various frequencies are believed to form the temporal and cellular time frame for encoding this information. In the hippocampus two classes of neurons can be distinguished: pyramidal cells and interneurons. The pyramidal cells are output cells, which are believed to encode the information in the hippocampus. Interneurons are inhibitory local-circuit neurons that control and regulate input, computation, and output of pyramidal cells, and also contribute to various network oscillations. The interneurons can be further divided into subclasses based on their axonal projection. There are interneurons that innervate only the soma and proximal dendrites of pyramidal cells, other contact the distal dendrites, and some interneurons only target the axon initial segment of pyramidal cells. In the present project the activity of interneurons will be recorded in anesthetized rats during behavioural relevant oscillations and the identity of the interneurons will be determined afterwards with anatomical methods. With this unique method we might be able to bring together the temporal information on the spike timing of the interneurons with the spatial information on where they contact pyramidal cells with inhibitory synapses. Additionally we will investigate this spatio-temporal relationship in various brain states connected to different network oscillations. Knowledge of this dynamic properties of interneurons might help to understand how the flow of information is shaped in the hippocampus and how cell assemblies, that underlie the encoding of memory, can be formed, consolidated, and retrieved. In other experiments we plan to investigate the cellular and molecular mechanisms underlying network oscillations. For this we will perform paired recordings of pyramidal cells and interneurons, or two interneurons simultaneously. The correlation between the spike timing between cell pairs will be investigated together with possible anatomical connections between them. Additionally we will also perform pharmacological experiments, in which the effect of receptor-specific drugs will be investigated on network oscillations and on the firing properties of single cells. These experiments might help to understand how synapic connections and receptors contribute to network oscillations in the brain.

The hippocampal formation is important for acquisition of short-term memory, the recall of episodic memory and spatial navigation. Oscillatory brain activity at various frequencies are believed to form the temporal and cellular time frame for encoding this information. In the hippocampus two classes of neurons can be distinguished: pyramidal cells and interneurons. The pyramidal cells are output cells, which are believed to encode the information in the hippocampus. Interneurons are inhibitory local-circuit neurons that control and regulate input, computation, and output of pyramidal cells, and also contribute to various network oscillations. The interneurons can be further divided into subclasses based on their axonal projection. There are interneurons that innervate only the soma and proximal dendrites of pyramidal cells, other contact the distal dendrites, and some interneurons only target the axon initial segment of pyramidal cells. In the present project the activity of interneurons will be recorded in anesthetized rats during behavioural relevant oscillations and the identity of the interneurons will be determined afterwards with anatomical methods. With this unique method we might be able to bring together the temporal information on the spike timing of the interneurons with the spatial information on where they contact pyramidal cells with inhibitory synapses. Additionally we will investigate this spatio-temporal relationship in various brain states connected to different network oscillations. Knowledge of this dynamic properties of interneurons might help to understand how the flow of information is shaped in the hippocampus and how cell assemblies, that underlie the encoding of memory, can be formed, consolidated, and retrieved. In other experiments we plan to investigate the cellular and molecular mechanisms underlying network oscillations. For this we will perform paired recordings of pyramidal cells and interneurons, or two interneurons simultaneously. The correlation between the spike timing between cell pairs will be investigated together with possible anatomical connections between them. Additionally we will also perform pharmacological experiments, in which the effect of receptor-specific drugs will be investigated on network oscillations and on the firing properties of single cells. These experiments might help to understand how synapic connections and receptors contribute to network oscillations in the brain.