Effect of age and cold shock on the SDH activity of brain mitochondria and carbohydrate contents of brain of male garden lizard

Effect of two inhibitors on succinic dehydrogenase activity in cerebral hemispheres of male garden lizards of three different age groups

Age changes in the specific activity of cerebral succinic dehydrogenase (SDH) and the effect of two inhibitors (malonate and p-chlorophenoxy acetic acid) on enzyme activity were traced in a short-lived species of reptile, Calotes versicolor, the garden lizard. The enzyme activity reached a peak level in middle-aged lizards followed by a decline in old counterparts. The enzyme inhibitions by both the inhibitors were significantly higher in old than in middle-aged and young lizards suggesting a change in specificity of SDH molecules during ageing.

Age-dependent changes in rat brain mitochondria of synaptic and non-synaptic origins

Synaptic and non-synaptic mitochondria were isolated from the brains of 3- 12-and 28-30-month-old female Fisher 344 rats. Total oxygen consumption and oxygen consumption due to mitochondrial respiration decreases 83% with increasing age in synaptic mitochondria using malate plus glutamate as substrate, but only 33% in non-synaptic mitochondria; succinate-driven activity is not affected. Succinate-driven superoxide generation decreases over 90% in both fractions; malate plus glutamate-driven superoxide generation decreases 50% in synaptic mitochondria only. The amount of c- and a-type cytochromes decreases approximately 50% in synaptic mitochondria. The absorbance wavelength maximum of cytochrome b decreases 2.6 nm in synaptic mitochondria from senescent brains but only 1.6 nm in non-synaptic mitochondria.

Age-related changes in thermoregulation in male albino rats

Male Sprague Dawley rats were followed longitudinally from 3 to 24 months of age. Resting oxygen consumption (VO2), measured in the thermal neutral zone (29 +/- 1.0 degrees C) decreased 47% between 3 and 24 months of age with a stable period from 6 to 9 months. Changes in rectal temperature in general followed changes in VO2. On the average the decline in rectal temperature from 3 to 24 months was 0.8 degrees C. Thermal conductance dropped initially from 3 to 6 months and remained stable during further age periods. Thermal circulation index rose slightly from 3 to 13 months, and dropped thereafter from 13 to 24 months. When animals were exposed to a mild cold challenge (18-19 degrees C for 90 min.), the increase in VO2 was the same from 3 to 13 months of age. At 24 months this increase was significantly higher. The capacity for non-shivering thermogenesis (NST) measured after norepinephrine stimulation declined from 3 to 6 months, remained stable from 6 to 9 months and declined to 13 months. The capacity for NST after a mild cold challenge was significantly decreased at 24 months of age. These results suggest that shivering thermogenesis (ST) may be the main source of heat production in the old organism when faced with a mild cold challenge. Since ST is more energy consuming than NST it may explain the accidental hypothermia which occurs often in the elderly.