Showing papers by "Ole Paulsen published in 2000"

Distinct frequency preferences of different types of rat hippocampal neurones in response to oscillatory input currents

Abstract: Coherent network oscillations at several distinct frequencies occur during various behavioural states in animals (Buzsaki et al. 1983; Singer, 1993; Steriade et al. 1993), including humans (Berger, 1929; Kahana et al. 1999). This has led to the suggestion that these oscillations play a role in these behaviours. However, the function of this oscillatory activity in terms of neuronal signal processing remains unknown. In the hippocampus, the CA3 subfield can intrinsically generate population oscillations at theta (4-7 Hz) (MacVicar & Tse, 1989; Cobb et al. 1999; Fellous & Sejnowski, 2000) and gamma frequencies (30-100 Hz) (Bragin et al. 1995; Fisahn et al. 1998) and such activity can propagate to the CA1 (Fisahn et al. 1998). Although pyramidal cells and some subpopulations of interneurones show intrinsic oscillations at theta frequencies (Leung & Yim, 1991; Cobb et al. 1995; Chapman & Lacaille, 1999) and other types of interneurones are known to play an important role in gamma oscillations (Whittington et al. 1995; Traub et al. 1996; Fisahn et al. 1998), the way in which network oscillations affect the activity of individual neurones in the network is unknown. Extracellular recording of such network activity reveals oscillations which appear sinusoidal (Leung & Yim, 1986) and occur at several distinct frequencies superposed on each other (Buzsaki et al. 1983; Bragin et al. 1995). The coherent network activity, controlled by, among others, the medial septal input, contributes to the synaptic inputs on individual hippocampal neurones, which is seen collectively during intracellular recordings in vivo as sinusoidal oscillations at several distinct frequencies (Soltesz & Deschenes, 1993; Fig. 1A). An understanding of how different types of neurones within a network respond to oscillatory input patterns may provide important clues as to the roles that different cell types play in the information transfer through the network. Neurones transfer information by transforming input signals into trains of discrete action potentials. We therefore investigated the effect of sinusoidal inputs at various distinct frequencies on action potential generation in different neuronal types, and specifically asked whether different neurones exhibit any frequency preference in their response to sinusoidal input current. Figure 1 Frequency preference of signal transfer in distinct types of hippocampal neurones Frequency preference of action potential generation could be due to active membrane properties. An enhanced voltage response in a neuronal membrane to a narrow bandwidth of input frequencies is termed resonance (Hutcheon & Yarom, 2000). Neocortical neurones show resonant behaviour (Gutfreund et al. 1995; Hutcheon et al. 1996), and frequency preference has also been shown to exist at subthreshold membrane potentials in hippocampal pyramidal neurones (Leung & Yu, 1998). However, the frequency preferences of different types of hippocampal neurones at threshold have not been reported. The aim of this study was to investigate how different types of neurones within the hippocampal CA1 network respond to oscillatory input patterns, by analysing their action potential discharge in response to intracellular sinusoidal current. The possible mechanisms underlying action potential transfer properties were studied by investigating the resonance properties of the neurones at membrane potentials close to the firing threshold.