Age-related decline in cold tolerance can be retarded by brain stimulation

Cold-induced thermoregulation and biological aging

Aging is associated with diminished cold-induced thermoregulation (CIT). The mechanisms accounting for this phenomenon have yet to be clearly elucidated but most likely reflect a combination of increased heat loss and decreased metabolic heat production. The inability of the aged subject to reduce heat loss during cold exposure is associated with diminished reactive tone of the cutaneous vasculature and, to a lesser degree, alterations in the insulative properties of body fat. Cold-induced metabolic heat production via skeletal muscle shivering thermogenesis and brown adipose tissue nonshivering thermogenesis appears to decline with age. Few investigations have directly linked diminished skeletal muscle shivering thermogenesis with the age-related reduction in cold-induced thermoregulatory capacity. Rather, age-related declines in skeletal muscle mass and metabolic activity are cited as evidence for decreased heat production via shivering. Reduced mass, GDP binding to brown fat mitochondria, and uncoupling protein (UCP) levels are cited as evidence for attenuated brown adipose tissue cold-induced nonshivering thermogenic capacity during aging. The age-related reduction in brown fat nonshivering thermogenic capacity most likely reflects altered cellular signal transduction rather than changes in neural and hormonal signaling. The discussion in this review focuses on how alterations in CIT during the life span may offer insight into possible mechanisms of biological aging. Although the preponderance of evidence presented here demonstrates that CIT declines with chronological time, the mechanism reflecting this attenuated function remains to be elucidated. The inability to draw definitive conclusions regarding biological aging and CIT reflects the lack of a clear definition of aging. It is unlikely that the mechanisms accounting for the decline in cold-induced thermoregulation during aging will be determined until biological aging is more precisely defined.

Acute electrical stimulation of lateral hypothalamus increases natural killer cell activity in rats

Natural killer cell (NK) activity in WKA and SD rats was found to be significantly higher following electrical stimulation of the lateral hypothalamus (LH) compared to sham operated. There was no such difference between sham operated rats and those receiving electrical stimulation in the frontal cortex as a control. Operations were performed under sodium pentobarbital anesthetic, and NK activity against YAC-1 target cells was measured 20 h later using 51Cr release assay. The LH area stimulated is a potent reward center and that stimulation of this point increased NK activity opens the possibility that pleasure might play a role in cellular immunity.

Effect of electrical stimulation of "rewarding" areas of the hypothalamus on habituation and dishabituation to repeated mild cold exposures in C57BL/6J mice

Four groups of 12-month-old C57BL/6J male mice had chronic electrodes implanted in the median forebrain bundle. In three groups the "rewarding" property of electrical stimulation was determined during a single 30-min session of self-stimulation (ISS) before the beginning of the experiment. In the fourth group this test was postponed until the end of experiment. Every two weeks for 12 weeks all animals were subjected to repeated 3-hr cold stress tests consisting of partial physical restraint at an ambient temperature of 10 degrees C. The time interval between tests No. 3 and No. 4 was intentionally delayed up to four weeks. During the 4-week interval, animals of one of the groups tested for ISS remained in their home cages; mice of the second ISS-tested group received daily 30-min sessions of brain stimulation; and animals of the third ISS-tested group were placed daily for 30 min in the experimental chamber where they had been tested for ISS previously but received no brain stimulation. Animals of the fourth group, which were not tested for ISS prior to the experiment, also were placed daily in the experimental chamber without brain stimulation. Repeated cold testing resulted in improvement of cold tolerance (decrease of the rate of decline of colonic temperature during cold exposure) in the second and third tests relative to the first cold test in all groups (cold habituation).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 2-mercaptoethanol on some metabolic indices of ageing of CBA/Ca inbred mice

It has been shown in several studies that 2-mercaptoethanol (2-ME) improves the life span and aspects of life performance of laboratory animals. To obtain further details on the beneficial effects of 2-ME, a long-term study has been performed on male CBA/Ca inbred mice treated with this antioxidant. Four month-old mice were each given 4 micrograms of 2-ME in physiological saline via intraperitoneal (i.p.) injection 3 x per week. Measurements were made of the following: cold tolerance (heat performance), apparent total body protein turnover (T1/2), changes in the major lipid and fatty acid compositions of the liver, superoxide dismutase activity and formation of malondialdehyde and observations on a range of pathological changes. It was found that the basal rectal temperatures of the treated mice were higher and in the oldest group, heat performance capacity was better than those of the controls. After about 1 year of age the apparent biological half-life time of total body protein (T1/2) was observed to be shorter in the treated mice. Significant increases were observed to occur in the proportions of the polyunsaturated fatty acids in the lipids of the liver in the mice injected with 2-ME. Although no differences were observed in the superoxide dismutase activities, malondialdehyde concentrations in the livers of the experimental mice were significantly increased. Autopsy data showed that Dunn-sarcomas associated with amyloidoses occurred more frequently in the untreated mice.

Habituation and dishabituation to repeated mild cold exposures in C57BL/6J mice

Every two weeks for 12 weeks four groups of C57BL/6J male mice, initially 12 months old, were subjected to three-hour cold stress tests, which consisted of a partial physical restraint at an ambient temperature of 10 degrees C. The control group experienced six consecutive tests; one experimental group skipped the cold exposure during test No. 4 but was physically restrained at room temperature; the other two experimental groups omitted test No. 4. One of these groups spent the four weeks between test No. 3 and test No. 5 in their home cages, while the other was subjected to daily, 30-minute sessions of electrical stimulation of the hypothalamus through electrodes implanted in the "rewarding" area of the medial forebrain bundle. All animals in this group showed self-stimulating behavior in the test session which preceded cold stress test No. 1. During test No. 3, all four groups showed an improvement of cold tolerance relative to their first tests; body mass and colonic temperature prior to cold exposure remained unchanged. The two experimental groups that were not exposed to cold during test No. 4 and did not receive brain stimulation, demonstrated a significant worsening of cold tolerance during the subsequent test. Their body mass and baseline colonic temperatures did not change. The control group and the group which was subjected to brain stimulation during the interval between tests No. 3 and No. 5 did not demonstrate any changes in cold tolerance. These data demonstrated habituation to repeated mild cold exposures and dishabituation after interruption of cold exposures.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of voluntary and forced exercise on thermoregulation and survival in aged C57BL/6J mice

To evaluate the effect of exercise on thermoregulation in senescent animals, three groups of male C57BL/6J mice aged 28-30 months were tested for cold tolerance, defined as the rate of decline in colonic temperature during 3 h exposure to 10 degrees C ambient temperature. Following this test, the mice were exposed to one of the following exercise conditions: forced exercise on a treadmill for 60 min daily at a rate of 5 m/min; continuous access to voluntary exercise in wheel-activity cages, which resulted in a mean rate of 1.1 m/min; or no expressed exercise with 60 min daily placement on the non-activated treadmill. After 3 weeks, assessment of cold tolerance was repeated. A combined mortality rate of 36% was observed in the exercise groups for this period, while there were no deaths in the non-exercised group. The high mortality rate among exercised animals indicated that these regimens were hazardous for aged mice. Moreover, between tests the non-exercised group exhibited a 0.6 degree C increase in body temperature and 38% improvement in cold tolerance which could be interpreted as a normal adaptation for repeated cold exposure. In contrast, no significant change in either of these variables was observed among survivors in the exercise groups. Thus, introduction of these exercise regimens in senescent mice decreased survival and did not improve the age-related impairment in thermoregulation.

Electrical stimulation of the medial forebrain bundle-posterior lateral hypothalamus attenuates gastric lesions

The major purpose of Experiment 1 was to see if electrical stimulation of the brain in an area that supports self-stimulation can act during stress to attenuate the severity of gastric lesions produced by six hours of tailshock and restraint. It was found that rats receiving electrical stimulation of the medial forebrain bundle-posterior lateral hypothalamus had significantly less gastric pathology than control subjects not receiving stimulation. Further experiments sought to examine characteristics of the stimulation that would account for this finding. Experiments 2 and 3 studied signal and analgesic properties, respectively, of the brain stimulation, but did not find evidence for their involvement in the effect.

Effect of intermittent feeding on thermoregulatory abilities of young and aged C57BL/6J mice

At 6 mth of age, male C57BL/6J mice were subjected to an intermittent schedule of feeding (every-other-day) or continued to be maintained on an ad libitum diet (24% protein). This regimen of dietary restriction resulted in increased mean and maximum lifespan (11%) compared to the survival of ad libitum-fed mice. At 8 and 26 mth of age, different groups of mice were tested for cold tolerance during 3 h exposure to 10 degrees C. Aged mice (26 mth) fed ad libitum compared to young mice (8 mth) on the same diet had significantly lower baseline colonic temperatures prior to cold exposure, and impaired cold tolerance, as measured by the rate of decline in colonic temperature during cold exposure. Dietary restriction by intermittent feeding had no significant effect on cold tolerance in young mice or baseline colonic temperature in young or aged mice. However, the cold tolerance of aged mice subjected to 20 mth of intermittent feeding was markedly improved over that of aged cohorts maintained on an ad libitum diet and in fact was indistinguishable from that of young counterparts. Thus, it appeared that this regimen of dietary restriction when implemented in young adults prevented the age-related decline in cold tolerance observed among ad libitum fed mice of this strain.