Neural Plasticity and Cognitive Reserve

Zahra Bardai, BSc, MD, CCFP, MHSc, FCFP, Community Family Physician, Lecturer, University of Toronto, Assistant Clinical Professor (Adjunct), Department of Family Medicine, McMaster University, Hamilton, ON.

Abstract
Neural plasticity in the context of normal aging and dementia can be evaluated on a number of levels. Traditionally there has been much focus on cellular dysfunction, which is evidenced by the plaques and tangles that are the hallmarks of Alzheimer type dementia. Now, more than ever, there is an emerging spotlight on the preservation of functional levels despite failing cognition be it from normal aging, mild cognitive impairment (MCI) or diagnosed dementia. Neural plasticity can be viewed as the complex interaction between the neurons' electrical, biochemical and physical structure and the individual's behavioural, psychological and sociological activities.¹ This article will briefly review the neurobiology of cognition and the sequence of events that lead to its demise. The remainder of this review concentrates on tangible, evidence based strategies to uphold clinical cognition through the aging process.
Keywords: neural plasticity, aging, dementia, cognition, neurons.

…there were neurons in her head, not far from her ears, that were being strangled to death, too quietly for her to hear them. Some would argue that things were going so insidiously wrong that the neurons themselves initiated events that would lead to their own destruction. Whether it was molecular murder or cellular suicide, they were unable to warn her of what was happening before they died.

-Still Alice
Lisa Genova

Normal Aging of Teeth

Gregory An, DDS, MPH, Director, Geriatric Dentistry Fellowship Program, Harvard School of Dental Medicine, Harvard University, Cambridge, MA, USA.

The rate of edentulism (being toothless) is declining in older adults. Thanks to more effective community-based prevention programs , reliable treatment methods, and improved dental technology, people are retaining more of their natural teeth. Since it has been only recently that people have lived as long and retained so much of their teeth, research done in the area of normal and abnormal aging of the teeth is limited. This article reviews some of the current knowledge regarding normal aging of the different structures of teeth and clinical manifestations of advancing age. More specifically, age-related changes in tooth enamel, dentin, pulp, and cementum are reviewed.
Key words: aging, dental, teeth, older, adults.

Morphological and Cellular Aspects of the Aging Brain

John R. Wherrett, MD, PhD, FRCPC, Department of Medicine (Neurology), Toronto Western Hospital and University of Toronto, Toronto, ON.

Contemporary technologies, including digital imaging of the brain during life and quantative microscopy (unbiased stereology) for estimating histological features postmortem, have resulted in important new knowledge about changes in the brain that accompany healthy aging, including evidence that grey matter atrophies with an anterior-posterior gradient. Neurons shrink but numbers are preserved; however, there is moderate reduction in dendritic spines and in synapses that have altered function. This is to be interpreted in the light of evidence for neurogenesis continuing into late life. White matter volume increases into maturity, but in aging there is a marked reduction due mostly to a loss of small myelinated fibres. Cell inclusions characteristic of neurodegenerative disease are commonly found postmortem in the healthy aged.
Key words: brain, aging, morphometry, imaging.

Aging and the Male Gonads

Khaleeq ur Rehman, MBBS, MS(Urol), Department of Urology, McGill University, Montreal, QC.
Serge Carrier, MD, FRCS(C), Department of Urology, McGill University, Montreal, QC.

The increase in male life expectancy has raised concerns about the impact of aging on the male reproductive system. Male testicular function declines gradually with advancing age. In general, testicular perfusion is reduced, aging pigment is accumulated, and the tunica albuginea of the testes and basal membrane of the seminiferous tubules are thickened. The function of Sertoli cells and Leydig cells declines. Among the semen parameters, semen volume, sperm motility and sperm morphology are decreased. The hypothalamic-pituitary-gonadal axis is affected at all levels. In some aging men, the reduction of testosterone levels leads to sexual dysfunction and "andropause". Children born to older fathers carry a higher risk of genetic diseases. This review focuses on the effect of aging on the male gonads.
Key words: aging, gonads, fertility, testosterone.

Stem Cell Research May Offer Antidote to Aging of the Hematopoietic System

Kimby Barton, BSc, MSc
Assistant Editor, Geriatrics & Aging

The hematopoietic system is comprised of all the elements of the blood, together with the stem and progenitor cells that give rise to these elements, and these play a vital role in the functioning of a healthy person. The hematopoietic system is unusual in that most of its components have a short life span, a multiplicity of cell types are required for its normal function, and a wide dispersion of cells perform specific functions throughout the body. The short life span of many of its components renders necessary the continuous production of enormous numbers of cells. Consequently, stem and progenitor cells must be maintained in adequate numbers to meet this demand for cell production throughout a person's lifetime.

Age-related alterations have been found in almost all components of the hematopoietic system but historically it has been difficult to distinguish between changes that occur with advanced age and changes that occur as a result of an illness. This article will review some of the literature dealing with the effects of age on the hematopoietic system. Conflicting studies will leave some questions unanswered and a paucity of information in other areas suggests the need for further research.

Immunogerontology Sheds Light on Diseases of Old-Age

Rhonda L Witte, BSc

The immune system is an elegant example of nature's work. When functioning properly, it protects us against what is "foreign" and does not attack the "self". Throughout an individual's life, changes occur within the immune system which make defense mechanisms less effective. Immunogerontology--the study of the aging immune system--is an up and coming field of research that will help build our knowledge, not only about the aging immune system, but also about the immune system in general.

The Immune System

Our immune system can be broken down into two interacting components: innate (natural) immunity and acquired (specific) immunity.¹ Innate and acquired immunity differ regarding the effector cells and molecules that carry out their specific and essential functions. Natural immunity is composed of defense systems that are present before exposure to foreign macromolecules and infectious microbes. Physical barriers (i.e. the skin) phagocytic cells and eosinophils, a specific class of lymphocytes called natural killer cells, and a range of blood-borne molecules (i.e. soluble proteins of the complement cascade) make up the natural immune system.² Acquired immunity requires stimulation by exposure to foreign molecules and includes sub-types of lymphocytes (e.g. B- and T-cells), cutaneous and mucosal immune responses and antibodies which circulate to find their target.