Neurobiology Programme

Neurobiology is enjoying renaissance worldwide. Singapore is no different and the Department of Physiology at the National University of Singapore is focused on world-class research into cellular, system and behavioral functions of the central nervous system. In addition, the department is expanding to increase its representation in both research and postgraduate teaching in Neurobiology.

Research:

At present, Assoc Prof Sanjay Khanna, Ph.D. (University of British Columbia), Assoc Prof Soong Tuck Wah, Ph.D. (National University of Singapore) and Dr Alan Lee, Ph.D. (University of Hong Kong) directs the Neurophysiology Laboratory, Ion Channel & Transporter Laboratory and the Molecular Neurobiology Laboratory respectively in the department.

Neurophysiology Laboratory:

Sanjay Khanna is currently investigating the (a) role of medial septum and hippocampus in pain, and (b) the regulation of hippocampal function by the hypothalamic supramammillary nucleus. The hippocampus is the simplest part of the cortex known as the allocortex, and plays a role in learning and memory. In addition, more recent data from human and animal studies suggests a role for the region in pain. The hippocampus is strongly influenced by the medial septum and the supramammillary nucleus, which therefore, may modulate its role.

The technique currently used in research in the laboratory includes:

1. Extracellular electrophysiological recording of evoked potentials and single neurons from anaesthetized animals
2. Extracellular recording of neural signals from behaving animals
3. Immunocytochemistry
4. Intracerebral drug application
5. Behavioral analysis

A/P Khanna is collaborating with the following in his research endeavour:

• Philip Moore, Department of Pharmacology, NUS
• Shabbir Moochhala, Defense Medical Research Institute, Singapore
• Low Chian Ming, Department of Pharmacology, NUS
• Feng-Ru Tang, National Neuroscience Research Institute, Singapore

Molecular Neurobiology Laboratory:

In developing brain, growing axons are steered by an array of molecules to establish appropriate functional connections with postsynaptic targets. The resulting neural circuitry remains largely stable in adult stage, though a few privileged brain regions still retain certain extent of plasticity. This allows the nervous system to encode changes in external environment, thereby enabling the organism to learn from experience, and cope with new challenge. Alan Lee is currently focusing on two aspects of neurobiology:

1. The mechanisms of axon guidance; and
2. Neuronal plasticity that underlies learning and memory.

Axon Guidance

The establishment of a functional nervous system involves a concerted organization of cell migration, differentiation, and interconnection between neurons. It has long been proposed that the growth cone of a developing axon must be guided by certain cues before reaching its target. The last two decades have witnessed the discovery of molecules that are implicated in this process, like fasciclin, NCAM, L1-CAM, netrins, ephrins, slit, and semaphorins. Together with their receptors, they may serve as attractive and/or repulsive cues, acting locally or at a distance to attain proper patterning of the nervous system. Dr Lee's laboratory is interested in a novel class of guidance molecule Plexins, which interact with semaphorins and mediate axon guidance functions. The following questions are being addressed in the laboratory:

1. What are the interacting partners of plexins that contribute to axon guidance functions?
2. How is guidance signal being translated through plexins?
3. Any cross-talk between closely-related axon guidance molecules?
4. What are the physiological functions of plexins?

Axon guidance represents an important process to insure correct wiring of the nervous system, both in development and regeneration. Failure of the process may lead to neurological disorders. Understanding the mechanisms of axon pathfinding will not only help to delineate the pathoetiology of these diseases, but also shed light on potential clinical treatments of injured nervous systems.

Molecular genetics, cellular and biochemical approaches will be applied in the study.

Learning and Memory

The capacity of the brain to undergo plastic changes is conceived as a pre-requisite for learning and memory. Activity-dependent modifications of synaptic strength, coined synaptic plasticity represents one of the cellular mechanism that underlie this cognitive process. A growing body of evidence has pointed to the role of cell adhesion molecules (CAMs) in modulating synaptic structures in an activity-dependent manner. The following questions are currently being addressed in Dr Lee?s laboratory:

1. What are the molecular and cellular mechanisms upon which CAMs are involved in learning and memory?
2. What is the correlation between CAM functions and mental illness ?

Major approaches of this research include mouse molecular genetics, electrophysiology and behavioural analyses.

Understanding the cognitive functions of CAMs will not only help to answer the intriguing question on how memory is encoded and consolidated, but also shed light on the etiology of some neurological diseases.

Ion Channel & Transporter Laboratory:

A/P Soong Tuck Wah is currently investigating the structure-function relationship of voltage-gated calcium channels. Voltage-gated calcium channels are hetero-oligometric transmembrane protein complexes that play a role in neurotransmitter release, muscle contraction, hormone secretion and gene expression. Mutations in some of the voltage-gated calcium channel subunit genes have been shown to be associated with hypokalemic periodic paralysis, familial hemiplegic migraine,episodic ataxia, spinocerebellar ataxia and congenital stationary night blindness in human.

The following questions are being addressed in Assoc Prof Soong's laboratory:

1. What are some possible associations of neurological disorders to ion channel genes?
2. What are the mutations in Asiatic populations of known genes associated with calcium channelopathies?
3. How is the regulation of transcription of voltage-gated calcium channel genes associated with ion channel disorders?
4. What is the phenotypic diversity of voltage-gated calcium channels that can potentially be generated by alternative splicing of the various genes encoding the alpha1-subunits?
5. What are the ligands that interact with voltage-gated calcium channels?

It is anticipated that such focused research will shed light on the physiology and pathophysiology of wild type and mutant voltage-gated calcium channel genes in excitable cells.

The methods used include patch clamp electrophysiology, molecular genetics, cellular biology and transgenic mice technology.

Assoc Prof Soong is collaborating with the following in his research endeavour:

• Prof David Yue, Department of Biomedical Engineering, The Johns Hopkins School of Medicine, USA
• Prof Ted Dawson, Department of Neurology, The Johns Hopkins University School of Medicine, USA
• Prof Cheah Jin Seng, Department of Medicine, National University of Singapore
• Dr Daphne Khoo and Dr Ho Su Chin, Singapore General Hospital
• Dr Lai Poh San, National University of Singapore
• Dr Low Chian Ming, Department of Pharmacology, National University of Singapore
• Dr Lim Kah Leong, National Neuroscience Institute

Representative Publications:

Khanna, S . Nociceptive processing in the hippocampus and entorhinal cortex, neurophysiology and pharmacology. In RF Schmidt and WD Willis (eds.) 'Encyclopedia of Pain', Springer, Berlin, 2007

Tai, S.K., Huang, F.-D., Moochhala, S. and Khanna, S. (2006) Hippocampal theta state in relation to formalin nociception. Pain 121: 29-42.

Jiang, F. and Khanna, S. (2006) Microinjection of carbachol in the supramammillary region suppresses CA1 pyramidal cell synaptic excitability. Hippocampus 16: 891-905.

Jiang, F. and Khanna, S. (2004) Reticular stimulation evokes suppression of CA1 synaptic responses and generation of theta through separate mechanisms. European Journal of Neuroscience 19: 295-308

Khanna, S ., Chang, L.S., Jiang, F. and Koh, H.C. (2004) Nociception-driven decreased induction of Fos protein in ventral hippocampus field CA1 of the rat. Brain Research 1004: 167-176.

Khanna S (1997) Dorsal hippocampus field CA1 pyramidal cell responses to a persistent versus and acute nociceptive stimulus and their septal modulation. Neuroscience, 77: 713-721.

Law JW, AY Lee, M Sun, SK Chung, A Dityatev, M Schachner and F Morellini (2003) Decreased anxiety, impaired place learning and increased CA1 basal excitatory synaptic transmission in mice with conditional ablation of the neural cell adhesion molecule L. Neuroscience, 23:10419-10432.

Bukalo O*, N Fentrop*, AY Lee*, B Salmen*, JW Law, CT Wotjak, M Schweizer, A Dityatev and M Schachner. Conditional ablation of the neural cell adhesion molecule NCAM reduces precision of spatial learning, long-term potentiation and depression in the CA1 subfield of mouse hippocampus (accepted for publication) *Authors of equal contribution listed in alphabetical order

Soong TW, CD DeMaria, RS Alvania, LS Zweifel, MC Liang, S Mittman, WS Agnew and DT Yue (2002) Systematic identification of splice variants in human P/Q-type (Cav2.1) channels: Implications for current density and Ca2+ -dependent inactivation. Journal of Neuroscience, 22: 10142-10152.

DeMaria CD, TW Soong, BA Alseikhan, RS Alvania and DT Yue (2001) Calmodulin bifurcates the local Ca2+ signal that modulates P/Q-type Ca2+ channels. Nature, 411: 484-489.

Zhang L, T Lee, Y Wang and TW Soong (2000) Heterologous expression, functional characterization and localization of two isoforms of monkey iron transporter. Biochemical Journal, 349: 289-297.

Bourinet E*, TW Soong*, K Sutton, S Slaymaker, E Mathews, A Monteil, GW Zamponi, J Nargoet and TP Snutch (1999) Splicing of a1A subunit gene generates phenotypic variants of P- and Q-type calcium channels. Nature Neuroscience, 2: 407-415. * joint first authors

Stea A, TW Soong and TP Snutch (1995) Determination of PKC-dependent modulation of a family of neuronal calcium channels. Neuron, 15: 929-940.

De Leon M, Y Wang, L Jones, E Perez-Reyes, X Wei, TW Soong, TP Snutch and DT Yue (1995) An essential structural domain for Ca-sensitive inactivation of L-type Ca channels. Science, 270: 1502-1506.

Soong TW, A Stea, CD Hodson, SJ Dubel, SR Vincent and TP Snutch (1993) Structure and functional expression of a member of the low voltage-activated calcium channel family. Science, 260: 1133-1136.

Teaching:

The Department contributes to teaching of neuroscience to 2nd year Medical students and system neurophysiology to Dental, Pharmacy and Nursing students. Science students are taught a level 3 neurobiology module in the pass course. The major focus of this module is cellular and molecular neurobiology. A system neurobiology module is taught at honours level. The Department also offers a postgraduate neurobiology module.

The teaching method incorporates didactic lectures, tutorials and self-directed learning modules.