Laboratory of Sensory Physiology, IMB, UiO


Institute of Basic Medical Sciences
Laboratory of Sensory Physiology	Despite synaptic depression at the retinogeniculate relay, pronounced temporal summation of NMDA-R mediated EPSPs occurs during train-stimulation of afferents (Augustinaite & Heggelund, J Physiol 584: 297-315, 2007). Quantal size at retinogeniculate synapses on thalamacortical neurons (Paulsen & Heggelund, J Physiol 480: 505-511, 1994).
We study basic mechanisms of sensory processing in the brain with major emphasis on neurobiology of vision. Over many years we were engaged in neurophysiological studies of cortex. At present the activity is concentrated on thalamocortical interaction and signal processing in relay nuclei of the dorsal thalamus, using dLGN as model system. The focus is on basic mechanisms of synaptic transmission, and cellular integration of synaptic input. The primary objective is to unravel mechanisms through which thalamic nuclei preprocess, synchronize and regulate the input to cerebral cortex. Abnormal thalamic activity can give serious pathological conditions (e.g. epilepsy, chronic pain states, tremor in Parkinson patients, amnesia, attention deficits, sleep disorders). In this connection we study mechanisms related to epilepsy. Challenges Thalamic relay nuclei perform complex integrative functions in a two-way dialogue with cortex and control the major gateways to cortex in different ways depending on behavioral states (e.g. sleep/awake, attentive/drowsy). Important elements in this regulation are thalamic inhibitory (GABAergic) neurons. However, today relatively little is known about their functions. A major challenge for our current research is to unravel functional properties of these inhibitory neurons, and how their cellular properties and patterns of inhibition are modulated through input from state-related brainstem nuclei, and through input from cortex. Projects Cortical control of signal processing in thalamic circuits. Studies of synaptic transmission in thalamic neurons: involved transmitter receptors and short-term plasticity. Dendritic processing in thalamic neurons. Role of synapsins in inhibitory synaptic transmission in thalamic relay nuclei. Behavioral and electrophysiological characterization of epilepsy in synapsin I/II knockout mice. Single-unit studies of dynamic changes of receptive field organization during brief visual stimulation. Key achievements Showed that activity patterns govern synapse-specific AMPA receptor trafficking between deliverable and synaptic pools (Kielland et al. Neuron 62: 84-101, 2009). Discovered a mechanism that causes state-dependent changes between transient and sustained firing pattern in thalamocortical neurons (Augustinaite & Heggelund J Physiol 584: 297-315, 2007). Demonstrated fast and pronounced shrinkage of the receptive field center of thalamocortical neurons during brief visual stimulation (Ruksenas et al. J Neurophysiol 97:1445-1456, 2007). Showed differential involvement of synapsin in synapses on thalamocortical neurons (Kielland et al. J Neurosci 26: 5786-5793, 2006). Demonstrated that cholinergic input to thalamic interneurons can change the inhibition of thalamocortical neurons from long-lasting and wide-range to short-lasting and short-range inhibition (Zhu & Heggelund J Neurosci 21: 1148-1159, 2001). First determination of the quantal unit in a glutamatergic synapse in the mammalian brain from combined measurements of spontaneous and evoked postsynaptic currents (Paulsen & Heggelund J Physiol 480: 505-511, 1994). Showed that the two classes of thalamocortical neurons, lagged and nonlagged neurons, are generated through involvement of different types of glutamate receptors (Heggelund & Hartveit J Neurophysiol 63: 1347-1372, 1990). Made the first quantitative mapping of both excitatory and inhibitory subregions in receptive field of neurons in striate cortex and developed models for simple and complex neurons based on such data (Heggelund Exp Brain Res 42: 89-107, 1981; J Physiol 373: 277-310, 1986). Demonstrated neuronal plasticity of single neurons in striate cortex of adult animals (cat) (Creutzfeldt & Heggelund Science 188:1025-1027, 1975).



Group leader Professor Paul Heggelund Department of Physiology, Institute of Basic Medical Sciences University of Oslo PO Box 1103 Blindern NO-0317 Oslo Norway Tel: +47 22851289, Fax: +47 22851249, E-mail: paul.heggelund@medisin.uio.no