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B3 - Mechanisms underlying fast switches between oscillatory network states in HC

Principal investigator(s):

Institut für Physiologie & Pathophysiologie
Universität Heidelberg
Im Neuenheimer Feld 326
69120 Heidelberg


Projects within the BCCN:

The project deals with network oscillations which entrain neurons into coherent rhythmic activity patterns. The resulting patterns are believed to form elementary representations in sensory, motor, mnemonic and higher-order cognitive systems (Egorov and Draguhn, 2013). One remarkable feature of network oscillations is their state dependence, i.e., different patterns and different frequency domains prevail in different behavioral states like slow-wave sleep, REM sleep, awake immobility or locomotor activity (Brankack et al., 2012). The project should elucidate mechanisms of such state-dependent transitions between different oscillation modes. Special emphasis was on the role of neuromodulatory substances like acetylcholine (Fischer et al., 2014; Zylla et al., 2013) or GABAergic modulators (Scheffzük et al., 2013).
We performed electrophysiological recordings in living mice and in mouse brain slices. In a first major subproject, we induced state transitions by applying acetylcholine to brain slices which switched activity from sharp wave-ripple complexes (very fast oscillations) to gamma oscillations (30 – 100 Hz). We showed that an intermittent phase of gamma activity induced plasticity in the neuronal ensembles activated by sharp wave ripples (Zylla et al., 2013).
In a second phase of the project, we recorded gamma and theta rhythms in living anaesthetized or freely moving mice. Here, we discovered that respiration induced an independent rhythm which entrained neurons in the entire forebrain, including hippocampus and parietal cortex (Yanovski et al., 2014). Since respiration frequency overlaps with the theta band in mice, both rhythms may be confounded when activity is recorded without monitoring respiration.
The project did not require major readjustments. Following the discovery of respiration-related network oscillations in the hippocampus, this area became a major field of interest and is presently studied with high intensity within the lab (Nguyen Chi et al., 2016; Tort et al., 2013; Zhong et al., 2016). This shift in the type of activity studied stays well within the general aim of the project, since we focus on the state-dependent transition and overlap between theta and respiration-induced oscillations.
Both major results provide a basis for further scientific studies and may become relevant as test systems for drugs or new approaches for clinical monitoring. Indeed, the respiration-induced electroencephalographic rhythm has recently been found in humans. It is well feasible to use this signal for monitoring sleep, states of anesthesia or drug effects.

Participating groups:

Key publications:

(2016) Hippocampal Respiration-Driven Rhythm Distinct from Theta Oscillations in Awake Mice J Neurosci 36:162-177 .
Thome C, Kelly T, Yanez A, Schultz C, Engelhardt M, Cambridge SB, Both M, Draguhn A, Beck H, Egorov AV (2014) Axon-Carrying Dendrites Convey Privileged Synaptic Input in Hippocampal Neurons Neuron 83:1418–1430 .
Yanovsky Y, Ciatipis M, Draguhn A, Tort ABL, Brankack J (2014) Slow Oscillations in the Mouse Hippocampus Entrained by Nasal Respiration J. Neuroscience 34:5949 –5964 .
Reichinnek S, von Kameke A, Hagenston AM, Freitag E, Roth FC, Bading H, Hasan MT, Draguhn A, Both M (2012) Reliable optical detection of coherent neuronal activity in fast oscillating networks in vitro Neuroimage 60:139-152 .
(2011) Cellular correlate of assembly formation in oscillating hippocampal networks in vitro Proc Natl Acad Sci U S A 108:E607-616 .