Annals of Neurosciences, Vol 14, No 3 (2007)
Annals of Neurosciences, Volume 14, Issue 3 (July), 2007
THE EXPANDING FRONTIERS OF NEUROSCIENCES
Corresponding address
PN Tandon
President, National Brain Research Centre
1, Jagriti Enclave, Vikas Marg, New Delhi-110 092 India
It has been claimed that the brain remains the single most defiant piece of ignorance. For several millennia the brain was a matter of interest to only philosophers. No doubt physicians of the vintage of Charak and Susruta in India, and Hippocrates in Greece, among others, made interesting observations on diseases affecting it. During Renaissance Descarte localized the point of interaction between the soul and the body to the pineal gland. Notwithstanding the remarkable contributions by the neurologists, psychiatrists and psychologists of the 18th and 19th century, it will be no exaggeration to say that the real scientific studies on the brain awaited the postulation of the Neuron Hypothesis by the Spanish neuroanatomist Santiago Ramon Y Cajal in 1906 - exactly a century ago1. This was soon followed by the elaboration of the Synaptic Hypothesis by Cajal and his contemporary neurophysiologist in England, Charles Sherrington2. This in turn led to the identification of electro-chemical basis of generation and transmission of nerve impulse, successively elaborated by Neurotransmitter and Ionic Hypothesis over the next half a century. It is not my purpose to recount the history of neuroscience research. (Those interested are referred to a seminal paper on the subject by Albright et al 2000). However, it is worth mentioning that the last two decades have witnessed an explosion of interest in the field primarily due to the advances in diverse disciplines like molecular biology, immunology, genetics, biotechnology on one hand and microelectronics, computers, newer imaging techniques on the other. Not surprising, it is claimed that 90 per cent of all we know about neurosciences has accumulated during of this period.
Neuroscience research is a continuum of study from the molecular to the behavioural level. It encompasses the body of research directed towards understanding the molecular, cellular, intercellular processes-mediated through electrochemical signals, in the nervous system, integrated to subserve behaviour (Figure 1).
Fig. 1: Molecules to Behaviour
Ultimate Goals of Neurosciences are
- To know the Human Brain,
- To Protect the Human Brain,
- Treat the Diseased Brain,
- To Recreate the Human Brain, and
“Ultimately to unravel the Mystery of MIND”
Global Burden of “Brain” Disease (WHO 1996)4 Brain disorders are currently estimated to affect as many as 1.5 billion people world-wide -a number that is expected to grow as life expectancy increases. Although brain disorders account for only 12% of all deaths, in developing countries they are responsible for at least 27% of all years of life lived with disability.
Major Research Advances During the Decade of the Brain: The decade of 1990s was declared as the “Decade of the Brain”, which prompted accelerated efforts to stimulate neuroscience research globally. The major gains of researchers some have been summarized by Jones and Mendell 1999 and Tandon 2000) (5–6).
- Cloning of genes for familial Alzheimer's, Huntington's and Parkinson's disease.
- Cloning of genes for families of receptors and ion channels leading to new insights into causes and potential treatments of many disease.
- Discovery of molecular basis of neural plasticity and of substances mediating new brain growth and survival leading to new approaches to promote recovery after brain and spinal injury.
- Elucidation of the molecular mechanisms underlying neuronal death in patients with stroke, degeneration and injury. This has led to new therapeutic strategies.
- Advances in molecular neuropharmacology have led to new treatments for depression and obsessive-compulsive disorder.
- Revolutionary imaging techniques have revealed brain systems underlying attention, memory, emotions, schizophrenia and addiction, and thus elucidating dynamic changes in normal brain functions.
- The discovery that neurons can be induced to divide, and the detection of stem cells in the brain and spinal cord, providing new approaches to recovery of function after brain and spinal injury.
- Techniques of genetics and molecular biology have led to the discovery of molecules for guidance of nerve fibers during development, leading to understanding of disorders of brain development and the potential for repair of the injured nervous system.
Tandon and Gouri Devi 2000 have reviewed the contributions of the Indian neuroscientists during this decade7.
Advances in Technologies for the Neuroscience
The impending and recent advances in technologies promise to change our conceptual understanding of brain function at every level, from molecular to the synapse, to the neural circuit, to the intact behaving organisms. These are expected to permit us to come to grips with the enormous complexity of the brain, both in health and diseased states.
Techniques for detailed molecular structure of ion-channels, neurotransmitter receptors, transporter systems and other membrane bound proteins ultimately at the atomic-scale level High resolution electron microscopy X-ray Crystallography.
Techniques for structural & functional genomics Identifying, cloning, sequencing of genes, Use of microarray Gene knockout and knock-in models. Microsensor arrays capable of measuring neurotransmitter levels from as many as 16 sites simultaneously. Capillary electrophoresis able to sample ultra-small volumes- a billionth to a trillionth of a litre. Newly developed optical imaging techniques using Laser scanning microscope and other Fluorescent imaging technologies-using spectroscopy based methods. Nanoscale optical probes have been used with Mass spectroscopy capillary-electrophoresis at electrochemistry sensitivity level as low as 1 million molecules.
- Single cell biosensors
- Laser microscopy-high-resolution optical imaging of the dynamics of ion-concentrations, membrane potentials, cortical signal mechanisms and neuronal circuitry are already proving remarkably fruitful. New non-linear laser microscopy is being experimented with.
- Two Photon Microscopy for in-vivo studies of intact brain
- New imaging techniques-SPECT, PET, fMRI, MRS (Figure 2)
Fig. 2: CHIP associates with the ataxin-3 aggregates. The neuro2a cells were sequentially transfected with CHIP and truncated ataxin-3-EGFP fusion constructs containing 20Q and 80Q. 48 h later, cells were processed for immunofluorescence staining using v5 antibody. Cy3-conjugated secondary antibody was used to stain the CHIP.
Arrow indicates the recruitment of CHIP to the ataxin-3 aggregates.
New Disciplines in Neurosciences
As a result of these advances a number of new disciplines in neurosciences have emerged :
- Developmental Neurobiology
- Neurogenetics
- Computational Neuroscience & Modeling
- Neuroinformatics
- Cognitive Neuroscience
- Artificial Intelligence, Neural Net Work, Robotics
- Augumentative & Restorative Neuroscience
Restorative Neurology
While advances in all these fields, individually or in combination, promise to enhance our understanding of the nervous system, from the stand point of a clinician maximum excitement, no doubt, is in the field of restorative neurology. Just to mention a few of these developments with great potentials for therapeutic applications are :
Neural Transplantation
Developments in molecular biology, developmental biology, biotechnology, neural transplantation have opened up new possibilities to help in regeneration or replacement of the damaged nervous system. Foetal neural tissue and stem cells obtained from a variety of sources hold great promise. A great excitement was created among both the basic scientists and clinicians in 1980s when it was demonstrated that foetal neural tissue could replace damaged brain tissue and restore lost neural function ((8–11). However, owing to a variety of reasons this enthusiasm could not provide the desired results. In the meanwhile two other discoveries i.e., evidence of neurogenesis at least in some parts of the brain even in adults and the isolation of stem cells capable of differentiating into neural cells provided new direction to search for replacement therapy. (12–16).
Neurogenesis: The demonstration of stem cells in adult human brain and at the same time isolation and culture of embryonic stem cells capable of producing both neuronal and glial cells were two revolutionary advances in late 1990s with unparalleld potentials for therapy. Generation of new neurons till recently believed to occur only during embryonic development has now been unequivocally demonstrated to occur throughout life at least in some areas of the adult human brain. Several recent studies have demonstrated the role of glia in this process. As well as providing structural support for nerve cells, astrocytes are now known to modulate the environment around neurons, release a range of neuronal growth factors and help to maintain the cellular barrier between blood and the brain. They may also control neuronal life more directly by regulating the production of synapses. Astrocytes can also instruct unspecialised cells to become neurons - a process called neurogenesis (17). The authors discovered that adult astrocytes from hippocampus are capable of regulating neurogenesis by instructing the stem cells to adopt a neuronalfate. “Our findings together with recent reports that astrocytes regulates synapse formulation and synaptic transmission, reinforce the emerging views that astrocytes have an active regulatory role rather that merely supportive role traditionally assigned to them in the mature control nervous system. Those interested in the subject of regeneration in the central nervous system may like to see a recent volume of the Philosophical Transactions of the Royal Society, Volume 361, 29th September, 2006 devoted to “The regenerating brain”.
Potential Uses of STEM Cells
- For replacement of lost or degenerating nervous tissue.
- Genetically engineered to express exogenous genes for neurotransmitters, neurotrophic factors and metabolic enzymes.
- For ex-vivo gene therapy - e.g. engineered to transfer genes to suppress tumour growth.
- For purpose of exploring the normal process of neuronal development. (Figure 3)
Fig. 3: Differentiation of embryonic stem cells to tyrosine hydroxylase positive neuron in-vitro. (Courtesy Dr. Shyamala Mani : NBRC, Manesar)
Neural Prosthesis
Advances in solid state electronics, polymer chemistry, new materials (including nano-materials) and computer sciences promise to provide newer and better prosthetic devices to substitute for lost function (Cochlear implants already in use, retinal implants in advanced stage of development) (18). Visual prothesis, mind-machine interaction technologies are being extensively investigated. Researchers may be a long-way from making a-cyborg but they are coaxing neurons to grow in patterns that could form a link between biology and silicon circuits. Building neuronal networks from the ground up, one neuron at a time and communicating with them via micro-electronics offers a way of developing neural circuits on actual micro-electronics (19).
Genetic Engineering and Gene Therapy
Recent advances in genetics and human genome have not only paved the way for exploring the genetic basis of a host of neurological disorders but also the possibility of gene therapy for their treatment (20). Progressive improvements in genetic engineering are expected to remedy genetic defects in not too distant a future. In addition gene therapy could be utilized to replace deficient neurotransmitters, neurohormones and growth factors. Therapeutic trials are already underway to utilize gene therapy for treatment of gliomas.
Simultaneously techniques have been developed for isolating and multiplying large populations of neural progenitors making it possible to generate particular type of neurons in a test tube. This raises new hopes for therapeutic use of such cells to replace neurons lost due to pathological conditions-trauma, degeneration, stroke etc. Some exciting work in this field is ongoing at NBRC (21,22) (Figure 4).
Fig. 4: Cells derived from human fetal brain. A) Grown in vitro to differentiate as neurons & glia. B) Confocal images of human neurosphere differentiating into Human neurons. Courtesy : Dr. Pankaj Seth, NBRC, Manesar
Neurodegenerative Diseases
Recent advances in molecular biology has led to better understanding of the pathogenesis of hitherto poorly understood degenerative disorders of the nervous system. Notwithstanding differences in detailed pathogenetic mechanisms for individual disorders, a common cascade of events seems to be operative resulting in neuronal death (Figure 5). This knowledge has helpedin identifying drug targets to minimise or possibly arrest the progressive of the disease. An unexpected observation in a variety of neurodegenerative disorders is the role played by inflammation in the pathogenesis of these diseases. This has brought to light the role of astrocytes and microglia in the progression of disease. There are also hints that glia may be promising therapeutic targets - a possibility that researchers have scarcely begun to explore. Glia may have key roles in central nervous system disorders from neuropathic pain and epilepsy to neurodegenerative diseases such as Alzheimer's and may even contribute to schizophernia depression and other psychiatric disorders (23,24). Many of the drugs we already have now might conceivably work on glia and people just haven't realised it yet.
Fig. 5: Molecular Cascade Following Neuronal Insult
Research currently in progress in the laboratory of Professor Vijayalakshmi Ravindranath at the National Brain Research Centre, Manesar, have demonstrated the reversal of brain pathology, in a rodent model of Alzheimer's disease following treatment with a herbal medicine (25). Others have shown promising results using a vaccine. In a mouse model of Alzheimer's disease, immunization with Aâ inhibits the formation of amyloid plaques or even reversed plaque formation and neural damage. A single dose of an adeno-associated virus (AAV) vaccine generated autoantibodies against the NR1 sub-unit of NDMA receptor was associated with strong anti-epileptic and neuroprotective activity in rats for both a kainate- induced seizure model and also MCA occlusion model of stroke.
New Insights in Brain Functions Resulting From New Imaging Technology:
While advances in molecular biology, genetics, DNA technology and developmental neurobiology have advanced our understanding of the nervous system in health and disease, there are unparalleled developments for exploring higher mental functions in intact human volunteers as a result of new imaging techniques - CAT, fMRI, PET, SPEGT etc. The burgeoning field of Cognitive Neuroscience promises to unravel the mystery of brain-mind relationship as never before. It is now possible to image brain areas during sensory perception, memory, intention, emotions, thought and even spiritual experiences. Time does not permit to discuss this during this talk, but let me quote. VS. Ramachandran, “By combining behavioural studies on patients with brain lesions, with functional imaging and viewing the results from an evolutionary perspective we can begin to elucidate these different components of self and finally tackle the mystery of how the components interact to generate awareness and self consciousness” (25).
Before I close let me not forget to point out that while advances in basic neuroscience have immense value for clinicians, lessons learnt at the bedside likewise have enhanced our understanding of the functioning of the human brain (26). Paul Broca in the middle of 19th Century laid the foundation of holistic approach of studying the localisation of functions in the brain. Since that time study of a variety of clinical syndromes-Anton syndrome, Cotard's syndrome, Split brain syndrome or symptoms like various types of aphasia, agnosia, apraxia, acalculia, pain asymbolia, blind sight, synesthesia, neglect etc - a remarkable knowledge of “New Phrenology” has accumulated.
Conclusions:
“The recent advances in neurobiology have no doubt resulted from the modern developments in molecular biology, genetic engineering, recombinant DNA technology, use of transgenic animals with “knock out” or “knock in” genes. At the other end o the spectrum is the emerging discipline of cognitive science. So far the neuroscientists in the country have not paid due attention to these development's. Not surprisingly we have no meeting ground with the scientists working in the field of neural networks, artificial intelligence, computers and communication sciences, etc. A close interaction between these disciplines and biology is being increasingly exploited to advances the frontiers of brain research. (27). Basic neuroscience activity in the country remains compartmentalised, discipline bound (neuroanatomy, neurophysiology, neurochemistry etc) with hardly any interaction amongst themselves or with clinical neuroscientists. Except for a few individuals and groups, in general basic neuroscience research has not received due attention. The efforts of the Indian Academy of Neurosciences to promote this activity are commendable, however, these still remains subcritical. There are only a few centres in the country providing a comprehensive course in neurosciences. These include Jiwaji University, Gwalior, NIMHANS Bangalore, TIFR, Mumbai and NBRC Manesar. Such courses need to be initiated at many more academic institutions. The Academy should actively promote such initiatives.
In the end, I take this opportunity to invite each one of you, on behalf of the Director and faculty to visit NBRC, utilize its outstanding facilities and plan collaborative research (Figure 6).
The National Brain Research Centre Manesar, India
References:
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21. Mani Shyamala, NBRC: Personal communication.
22. Seth Pankaj, NBRC: Personal communication.
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24. Tandon PN. Brain cells: Recently Unveiled Secrets: Their clinical significance (In Press).
25. Ravindranath V. Personal communication.
26. Ramachandra VS A Brief Tour of Human Consciousness. PI Press New York 2004.
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28. Tandon PN. The new millennium: Unfinished agenda and tasks ahead Neurology India 1997; 45: 4–8.
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