INTRODUCTION

From the evidence of a few longitudinal and many cross-sectional studies, human ageing can be characterised by a general decline in functional competence of the whole organism and a reduced capacity to respond as efficiently as younger individuals to internal and external stresses. This has become embodied in homeostatic theories of ageing, seen as a destabilisation of the internal environment of the organism and a limitation of the ability to bring about adaptive reactions. Because of their widespread influence on many integrated homeostatic mechanisms, the neural and endocrine centres of control in the hypothalamus are sometimes identified as possible centres of influence in the ageing process. Thus, theories attributing a key role to loss of sensitivity of hypothalamic neurones to neural or endocrine feedback signals have been proposed (Dilman, 1971; Dilman et al, 1979). Finch (1975, 1978, 1980) sees the loss of catecholamines in the hypothalamus and other parts of the brain as an important expression of the ageing process.

These theories seek to explain declining control of homeostasis in terms of metabolic and organisational deficiencies in hypothalamic nerve cells or their receptors. Though a number of observations testify to significant changes in centres of neural control which may be of value as biological markers of ageing (Reff & Schneider, 1982) it is probable that the decline in functional organisation of hypothalamic neurones controlling homeostasis is but an integral part of the overall ageing process, for structural and functional age changes can also be demonstrated in peripheral afferent and effector components of most physiological systems during ageing.