Effects of thermal acclimation on nervous conduction and muscle contraction in the frog Rana temporaria.

The effects of season and acclimation temperature on the latency of the leg withdrawal reflex and three of its components have been studied: conduction velocity in the sciatic nerve, spinal conduction time, and contraction time of gastrocnemius muscle. The latency of the leg withdrawal reflex was markedly shortened by cold acclimation: the reaction times were at 6 degrees C 1.54 s in 4 degrees C acclimated and 3.97 s in 24 degrees C acclimated winter frogs. Also, the temperature dependence of the reflex latency was reduced by cold acclimation. Thus, frogs acclimated to cold responded to external stimuli in cold more rapidly than warm-acclimated ones. This cold adaptation of the reflex could not be explained by changes in its studied components. These made up only one-tenth of the reflex response time, and either did not show significant cold acclimation (muscle contraction and spinal conduction times in summer) or showed inverse acclimation, especially when measured at high temperatures (i.e. conduction velocities were reduced by acclimation to cold). Thus, the cold acclimation of the reflex response probably resides in the sensory component of the response. The inverse temperature adaptation response of conduction velocities may reflect a reduced ion permeability across cellular membranes in cold which decreases metabolic energy expenditure during inactive periods.

Bacterial endotoxin and infection cause behavioural hypothermia in infant mice.

1. When placed in a temperature gradient, 3-10 day old mice injected with living Escherichia coli or with E. coli endotoxin, select 2-3 degrees C lower temperatures than their litter-mate controls injected with saline. 2. At the lower selected temperature (32 degrees C) young mouse pups resist bacterial infection for longer and tolerate higher doses of endotoxin than at the temperature selected by the controls (35 degrees C). 3. It is possible that a controlled hypothermic state, here called cryexia, is in small mammals an alternative strategy to fever for coping with infections.

Temperature effects on different organization levels in animals.

One of the central concepts in present biology is the recognition of different organization levels and their hierarchical array. Complex multicellular animals are constituted of organ systems, the organs of cells, the cells of organelles, membranes, and molecules. The primary effects of many environmental factors (e.g. light, concentrations of ions and molecules) can be delimited mainly to one level. Temperature, being the macroscopic physical measure of the random motion of smallest material particles, affects directly the animal life at all organization levels. The special physical nature of temperature means also, that during the history of life, organisms have always been subjected to temperature variations. Many different ways to evade the pervasive effects of temperature have been evolved during the course of evolution. The study of the temperature relations of organisms can therefore give models for other branches of environmental biology. The temperature limits and relations of an animal cannot be explained by the temperature relations and limits of its cells without taking into account such interactions between different types of cells, which are found only through the study of the organs. Also, the temperature limits and relations of animal cells cannot be explained just through the study of the constituent molecules. The possible interactions of the molecules (e.g. lipids and proteins in a cell membrane) are so manifold and complex that in order to ascertain the relative importance of them in the temperature relations of the cells we must rely in part on studies done on organelles (e.g. on the plasma membrane). The study of the thermal biology of animal cells thus exemplifies the situation often found in biology: the attainment of a reductive explanation is not always a one-way deduction, but it may involve modifications of the lower level concepts according to the knowledge derivable only from studies of the higher level systems.

Changes in cell membrane fluidity affect the sodium transport across frog skin and its sensitivity to amiloride.

1. 1-5 mM n-hexanol added to the outer (mucosal) medium of isolated skin of the frog Rana temporaria increases the short circuit current (Isc) across it. 2. This effect shows a saturable dependency on the outer sodium concentration, also when NaCl is replaced by Na2SO4. 3. n-Hexanol at a concentration of 1 mM, and cold acclimation of the frogs, which increases the fluidity of epidermal cell membranes, do not affect the sensitivity of Isc to the inhibiting effect of amiloride. 4. n-Hexanol at a concentration (5 mM) which causes a fluidization of cell membrane preparations from isolated frog epidermis also increases the sensitivity of Isc to amiloride. 5. The effects of low concentrations of n-hexanol and of cold acclimation probably depend on an increase of the permeability of apical membranes of epidermal cells to sodium caused by membrane fluidization. At higher concentrations of n-hexanol, a further disordering of the membrane structure occurs with a better access of amiloride to its action sites.

Comparative psychopharmacology.

Studies of the effects of psychoactive drugs and neurotransmitters on the behavior of invertebrates and poikilothermic vertebrates are reviewed. Dangers of reductive explanations are pointed out. Results and suggestions are given concerning the use of poikilothermic animals (1) in the development of screening tests, (2) in experiments on the action mechanisms of psychopharmaca, and (3) in the use of psychoactive drugs in the study of the mechanisms of animal behavior.

Temperature compensation of sodium transport and ATPase activity in frog skin.

Na+ transport across frog skin, measured as short-circuit current (SCC) shows perfect temperature compensation in frogs acclimated to 6 degrees, 12 degrees, and 23 degrees C as SCC values observed at the acclimation temperatures are equal (about 13 muA/cm2). Reacclimation experiments show that this is not a starvation effect. While very little temperature compensation is seen in the activity of Na+, K+-ATPase in epidermal homogenates from frog skins, the activity of Mg2+-ATPase shows inverse compensation at assay temperatures from 4 degrees to 48 degrees C. This ATPase is apparently activated either by Mg2+ or by Ca2+ and it probably controls the passive permeability of epidermal cells. It is suggested that the inverse temperature compensation in the activity of this enzyme is the main mechanism by which the observed perfect temperature compensation of Na+ transport across frog skin occurs.

ATPase stimulated by Na+ or K+ in gills of the freshwater mussel Anodonta.

1. Microsomal preparations from the gills of the freshwater mussel anodonta cygnea cellensis show Mg2+ -dependent Na+ - or K+ -stimulated ATPase activity, which is not inhibited by ouabain. 2. Na+ - or Ka+ -ATPase activity is decreased by Ca2+, acetylcholine, choline, and tetramethylammonium, but slightly increased by ethyl alcohol. 3. It is tentatively suggested that Na+ - or K+ -ATPase is involved in the mechanism of active monovalent cation uptake through the gills of freshwater mussels.