Biomedical subjects

N Geary

Publications and source records attributed to N Geary.

76 records · Page 5Linked to original sources

PubMedDate not supplied

Muramyl peptides and the functions of sleep.

Muramyl peptides (MPs) are bacterially derived sleep factors which stimulate slow wave sleep. In the neonate, MPs are capable of inducing quiet sleep and suppressing active sleep. Given that active sleep is thought to be important for brain development during this period, the possibility that changes in the availability of MPs in the neonate may affect brain development was examined. Rat pups were given muramyl dipeptide (MDP) twice daily for the first 14 days post partum. It was hypothesised that MDP would stimulate quiet sleep at the expense of active sleep as has been shown in the young rabbit. There was no effect on neonatal levels of quiet sleep or active sleep. There was, however, a variety of effects, apparently unrelated to the sleep functions of MDP. These effects were changes in adult learning, serotonin metabolism and brain anatomy. The function of sleep in the mediation of the sleep-independent effects of MPs was examined, in particular the opposite effects of MDP on host immunity depending on the sleepiness of the host. In this light sleep does indeed serve to mediate the effects of MPs and it is speculated that many of the effects observed here may change in response to sleep levels in individuals. The notion that autonomic signalling between brain and spleen is more efficient during sleep is presented as an example of a function of sleep that may modulate the immunological effects of MPs.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMedDate not supplied

Pancreatic glucagon fails to inhibit sham feeding in the rat.

Rats were equipped with chronic gastric cannulas, and the effects of intraperitoneal injections of pancreatic glucagon on sham feeding, with cannulas open, and real feeding, with cannulas closed, were compared. Glucagon (100-2,500 micrograms/kg) suppressed cumulative food intake during real feeding tests 9-33%, but had no effect during sham feeding. Despite their increased food intakes, sham feeding rats took discrete meals terminated by the behavioral satiety sequence. In addition to not affecting total intake, glucagon failed to affect meal size, latency to rest, or intermeal interval during sham feeding. To investigate the possibility that glucagon did not inhibit sham feeding because it did not elicit hyperglycemia, we measured hepatic vein blood glucose after glucagon injections in sham feeding rats: glucagon elicited marked hyperglycemia during sham feeding. Therefore, the absence of glucagon's satiety effect in sham feeding is not due to the lack of hepatic glycogenolysis and hyperglycemia. These results suggest that some mechanism other than hyperglycemia which normally accompanies food ingestion is necessary for glucagon to have a satiety effect.

Animals↗

PubMedDate not supplied

Glucagon-(1-21) fails to inhibit meal size in rats.

Rats were intraperitoneally injected with 115 or 230 nmol/kg pancreatic glucagon or equimolar doses of glucagon-(1-21) just before refeeding at the beginning of the dark phase after a 12 hr period of food deprivation. Glucagon-(1-21) and pancreatic glucagon have been reported to have similar visceral effects, but glucagon-(1-21) does not have pancreatic glucagon's metabolic effects. In this experiment, both doses of pancreatic glucagon, but neither dose of glucagon-(1-21), significantly decreased meal size. This indicates that the C-terminal octapeptide of pancreatic glucagon is necessary for its satiety effect, just as it is for its metabolic effects.

Animals↗

PubMedDate not supplied

Spontaneous meal patterns in female rats with and without access to running wheels.

Rats display strong behavioral rhythms during the ovarian cycle. During estrus, food intake is minimal due to a decrease in meal size, and locomotor activity is maximal. To investigate how activity influences feeding patterns across the ovarian cycle, we used a computerized system to monitor spontaneous meal patterns in intact, cycling female rats with and without access to running wheels. We found that running wheel access decreased dark meal frequency, increased dark meal size, and increased 24-h water intake during each phase of the ovarian cycle. In contrast, body weight, 24-h food intake, and the ovarian rhythms of reduced food intake, meal size, and body weight during estrus were not affected by running wheel access. In particular, the reduction in food intake during estrus was due to a selective reduction in dark meal size, not dark meal frequency, and this occurred independent of wheel access. These data indicate that estrus-related changes in spontaneous meal patterns and locomotor activity are independently controlled and that the reduction in food intake during estrus involves a selective change in the neurobiological controls of meal size.

Animals↗