Effects of sulfur dioxide on resistance to bacterial infection in mice

Continuous exposure to approximately a 10-ppm concentration of sulfur dioxide for periods of up to 3 weeks reduced the resistance of female mice to infection by aerosol inoculation with Klebsiella pneumoniae. The mortality rate rose and survival time shortened in SO₂-exposed animals compared to controls. Insofar as these results can be extrapolated to humans, the SO₂ concentration used in this work is only found on certain industrial premises.     

Endorphinergic mechanisms in the control of food and water intake

The recent discovery of opiate receptors and endogenous opiates (endorphins) within the brain has led to a variety of speculations concerning the physiological significance of these mechanisms. One suggestion has been that endorphinergic mechanisms may be involved in the control of food and water intake. Administration of drugs believed to block opiate receptors has been shown to reduce food and water intake in experimental animals while opiate agonist drugs can, under certain conditions, increase eating and drinking. It has also been shown that endorphin levels in the brain and pituitary may change with food deprivation and in obese animals. The evidence is therefore consistent with a role for endorphins in the control of appetite. However, it will be for future research to define more precisely the nature of the mechanisms involved.     

Effect of adrenergic blockers and depleters on food intake in rats

In rats kept at a constant temperature (24 +/- 1.5 degrees C) and on a reversed day/night cycle (light from 11 p.m. to 11 a.m.), the amount of food eaten during the first 2 h of darkness and during 24 h was measured every day. When reserpine or guanethidine were injected 5 min before the beginning of the dark period on four consecutive days, there was no significant change in the 0.5-, 1-, or 24-h food intake on the injection days, but there was a significant increase in the 0.5-, 1- and 2-h food intake during the next five to eight days, without any change in the 24-h intake. A single injection of dichloroisoproterenol produced no change on the day of injection but it induced a significant increase in the 0.5-, 1- and 2-h intake on the following 15 days, without any change in the 24-h intake. The increase in the early night-time feeding without any change in the 24-h intake was interpreted as an increase in meal size (diminished preabsorptive satiation) compensated by a decrease in meal frequency. Both reserpine and guanethidine are catecholamine depleters but the latter does not penetrate into the brain. Dichloroisoproterenol is a beta-blocker acting on the glycogenolytic effects of catecholamines. The results thus agree with the hypothesis that glycogenolysis elicited by the liberation of intrahepatic catecholamines from the sympathetic nerve endings and chromaffin cells plays a role in preabsorptive satiation.     

The regulation of feeding: locusts and blowflies are not so different from mammals

The regulation of feeding in two insect groups, the locusts and the blowflies, is reviewed. The patterning of feeding is discussed first, and then the underlying mechanisms are considered in detail. The concept of "central excitability" is the key to understanding the controls of feeding. It represents a central nervous mechanism for tuning the sensitivity of the insect to food-related stimuli. The level of central excitation is influenced positively by food and also non-food stimuli, both from within and outside the animal, and negatively by deterrent stimuli and by feedbacks from peripheral systems such as stretch receptors on the gut wall, hormones and blood composition. Sustained gustatory input is required if feeding is to continue, once initiated. The level of central excitation present as a meal begins influences ingestion rate and the amounts of negative feedback tolerated before feeding stops. The duration of intervals between meals is then a function of a number of excitatory stimuli and of feeding-induced changes which reduce the likelihood of further feeding, e.g., hormone release, changes in nutrient composition or osmotic pressure of the blood, and gut distension. Other areas reviewed include changes in the regulation of feeding during the life history and the control of drinking.