Use of motor performance tests to differentiate aging effects from disease effects

Influence of age and treadmill running on motor performance in rats

The influence of treadmill running on age-dependent changes of motor performance was investigated in differently old female Sprague-Dawley rats. Following 12 months of exercise training a test battery including gait analysis, spontaneous motor activity, and three more motor tasks of different complexity was performed. The influence of age on motor performance depended on the complexity of the motor requirement. Simple tests were less affected by age than more complex ones. Treadmill running induced positive effects on the age-dependent impairment of various motor functions in middle-aged (14-18 months old) and aged (23-27 months old) rats. The positive influence of exercise training is explained by benefits of endurance training to the cardiovascular, neuromuscular, and central nervous systems.

Increased expression of serotonin transporter messenger RNA in raphe neurons of the aged rat

The action of serotonin (5-hydroxytryptamine; 5HT) in the nervous system is terminated by reuptake of the neurotransmitter into the presynaptic nerve terminal via a plasma membrane-bound transporter protein. Recently, cDNAs encoding serotonin transporter protein were cloned. Using in situ hybridization we have studied the expression of serotonin transporter mRNA in the bulbospinal 5HT system of adult (2-3 months) and aged (30 months) rats. In adult rats, serotonin transporter mRNA labelled neurons were detected in the nucleus raphe obscurus, pallidus and magnus. In all aged rats, the optical density of the serotonin transporter mRNA labelling of individual cell profiles was increased by 20-30% (P < 0.001) when compared with adult rats. Five of the six aged rats studied had various degrees of hindlimb motor dysfunctions. In rats with the most pronounced signs of hindlimb motor dysfunction the number of labelled neurons was increased by 25-75% (P < 0.01) when compared with young adult rats. It is concluded that an increased serotonin transporter gene expression is present in the bulbospinal 5HT system of aged animals.

The serotoninergic bulbospinal system and brainstem-spinal cord content of serotonin-, TRH-, and substance P-like immunoreactivity in the aged rat with special reference to the spinal cord motor nucleus

The 5-hydroxytryptamine (5HT) containing bulbospinal pathway was studied with immunohistochemical (IF) and chemical techniques in 2-3 and 30 months old male Sprague-Dawley rats. The coexisting neuropeptides substance P (SP), thyrotropin-releasing hormone (TRH) and galanin were also analysed. Furthermore, the expression of mRNA encoding aromatic L-amino acid decarboxylase (AADC), prepro-TRH, and preprotachykinin (prepro-SP) was analysed with in situ hybridization (ISH) in the midline raphé nuclei inthe lower brainstem. The results showed a decreased number of axonal 5HT fibers with a normal morphology in the ventral horn of the aged rat lumbosacral spinal cord, and several 5HT immunoreactive (IR) fibers with an aberrant morphology, suggestive of axonal degeneration, were intermingled. This was evident in both the dorsal and ventral horn of the spinal cord. The 5HT-IR fibers with an aberrant morphology usually also contained TRH-and/or SP- and/or galanin-like immunoreactivity (LI) in the ventral horn. These signs of degeneration were clearly less evident in the thoracic and cervical spinal cord segments. Moreover, these changes varied between aged litter-mates. This was in agreement with behavioural signs of motor disturbances, present in about 40% of the aged rats and which in all cases were confined to the hindlimbs. Chemical analyses disclosed significantly lower levels of TRH-LI and, in particular, SP-LI in both the ventral and dorsal quandrants of the spinal cord in the aged rat compared to young adults. The differences were largest in the lumbar regions of the spinal cord. Corresponding analysis of 5HT and 5-hydroxyindoleacetic acid (5HIAA) in the same tissue specimens revealed largely unaltered levels of 5HT and a slight increase in 5HIAA, indicating the possibility of an increased 5HT turnover in the aged rat spinal cord. Neurons in nucleus raphé obscurus and nucleus raphé pallidus were immunoreactive to 5HT, and after pretreatment with colchicine to TRH-, SP-, and galanin-LI as well. There was no obvious difference in number of labeled cells, or labeling intensity, between colchicine-treated young adult and aged rats, although, in the corresponding region of medulla oblongata, chemical analysis disclosed significantly lower levels of 5HT, TRH, and, in particular, SP in untreated aged rats. In contrast, in situ hybridization analysis revealed increased mRNA levels encoding prepro-TRH and prepro-SP in old rats, while mRNA content encoding AADC mRNA was similar in young adult and aged rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular aging in Syrian hamsters: similarities between normal aging and disease

The functional status of the cardiovascular system in health and cardiomyopathic (CM) hamsters was assessed throughout their lives by measuring heart weight and fluid in the pleural and peritoneal cavities. An index of cardiovascular age was developed from a multiple regression model of changes in these variables with chronological age. This index showed parallel changes in healthy and CM hamsters with increasing age, but CM hamsters with shorter lifespans underwent the changes at earlier ages. It was also a better predictor of viability than chronological age. The cardiovascular age index correctly predicted the early death of those hamsters which died before the average death age, whereas they should have been alive according to their chronological age. Conversely, hamsters which lived beyond the average death age had cardiovascular ages younger than the average death age, whereas their chronological ages erroneously indicated they should have been dead. This index may have been able to assess viability because it was correlated with histopathological signs of congestive heart failure in both strains of hamsters, as well as with the total amount of pathology found in them. Hamsters which die naturally at a particular age should have older cardiovascular indices than those sacrificed at the same age, and CM hamsters which died at 11-13 months of age did have older cardiovascular ages than hamsters that were sacrificed at these ages. Three experiment examined the effects of various treatments on the index of cardiovascular age. Life in constant light decreased the cardiovascular age of CM hamsters by 30% and extended life by 25%. Chronic digitalis treatment will improve cardiovascular performance, and it prevented increases in cardiovascular age during the end stages of heart failure. Finally, life-threatening chronic stress increased cardiovascular age in CM hamsters, which suggested that severe stress brought CM hamsters nearer to death. However, it was not possible to determine whether the effects of these treatments were on aging or health. Thus, the data suggested that aging, at least in hamsters, may be closely related to the natural development of heart failure which represents a common end stage of life in both cardiomyopathic hamsters and very old, supposedly healthy hamsters.