The autonomic nervous system in old age

Anesthesia in the Elderly Patient Undergoing Otolaryngology Head and Neck Surgery

Geriatric patients undergoing surgery have a whole set of specific physiologic changes, perioperative needs, and postoperative complications. This review presents an overview of the basic concepts and the evolving challenges pertaining to the care of geriatric patients undergoing otolaryngologic procedures from the perspective of the anesthesiologist.

Age-associated synapse elimination in mouse parasympathetic ganglia

Little is known about the effects of aging on synapses in the mammalian nervous system. We examined the innervation of individual mouse submandibular ganglion (SMG) neurons for evidence of age-related changes in synapse efficacy and number. For approximately 85% of adult life expectancy (30 months) the efficacy of synaptic transmission, as determined by excitatory postsynaptic potential (EPSP) amplitudes, remains constant. Similarly, the number of synapses contacting individual SMG neurons is also unchanged. After 30 months of age, however, some neurons (23%) dramatically lose synaptic input exhibiting both smaller EPSP amplitude and fewer synaptic boutons. Attenuation of both the amplitude and frequency of miniature EPSPs was also observed in neurons from aged animals. Electron micrographs revealed that, although there were many vesicle-laden preganglionic axonal processes in the vicinity of the postsynaptic membrane, the number of synaptic contacts was significantly lower in old animals. These results demonstrate primary, age-associated synapse elimination with functional consequences that cannot be explained by pre- or postsynaptic cell death.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Effect of chronic autoimmune nerve growth factor deprivation on sympathetic neuroaxonal dystrophy in rats

Nerve growth factor (NGF) deficiency has been proposed as a possible pathogenetic mechanism underlying the sympathetic autonomic neuropathy which develops in clinical and experimental diabetes and aging. To determine if long-term NGF deficiency alone would reproduce the distinctive sympathetic neuropathology of streptozocin-induced diabetes or aging in rats, nondiabetic animals were deprived of NGF for 12 months using an autoimmune paradigm. Neuroaxonal dystrophy (NAD), the neuropathologic hallmark of experimental sympathetic diabetic neuropathy and aging, was not increased in frequency in prevertebral superior mesenteric or paravertebral superior cervical ganglia in comparison to age-matched controls. Residual neurons in chronically NGF deprived sympathetic ganglia did not show significant atrophy, chromatolysis, active neuronal degeneration or intraganglionic debris. Postganglionic noradrenergic axons in ileal mesenteric nerves also failed to develop NAD in chronic autoimmune NGF-deprived rats as they would have in animals diabetic for the same duration. These results suggest that simple, isolated NGF deficiency maintained for long periods of time in nondiabetic animals is not sufficient to produce NAD in the pattern of experimental rat diabetes and aging.

Differential regulation of tyrosine hydroxylase protein and activity in rabbit sympathetic neurones after long-term cold exposure: altered responses in ageing

The aim of this study was to investigate the response of sympathetic neurones to prolonged neural stimulation, using cold exposure as a non-invasive experimental paradigm. We examined the effects of prolonged (8 days and 4 wk) cold exposure on tyrosine hydroxylase (TH) protein and activity and neuropeptide Y (NPY) levels in sympathetic neurones of the superior cervical ganglion (SCG), together with NPY levels in the ear artery from young and aged rabbits. The main findings were as follows. In young rabbits, TH levels and TH activity were differentially regulated in response to prolonged cold exposure. TH levels rose whilst TH activity tended to decline. Decentralization of SCG from young animals before cold exposure abolished the rise in TH levels. TH activity in SCG from young rabbits was reduced by decentralization whilst cold exposure resulted in an increase in TH activity. Thus, TH activity was induced in the SCG in the absence of pre-ganglionic input, demonstrating a non-synaptic regulatory mechanism. In old rabbits, cold-induced changes were either delayed or failed to occur, indicating that the responses of sympathetic neurones to cold stress are impaired in old age.