TEMPERATURE ACCLIMATION AND THE NERVOUS SYSTEM

1. The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog. The heat and cold tolerances of peripheral conduction are probably both increased by cold acclimation in the frog. 2. The properties of compound action potentials are not suitable for temperature acclimation studies, since different neuronal populations in the same nerve have been found to exhibit different temperature characteristics. 3. Single but septate giant nerve fibres of earthworms show compensatory temperature acclimation of the conduction properties, the form of the action potential and of the axonal cable properties, especially below 13–19 °C. 4. The fatty acids and the plasmalogen aldehydes of the phospholipids of the goldfish brain are more unsaturated at lower acclimation temperatures. 5. The Na⁺-K⁺ ATPase activity of the earthworm nerve cord shows compensatory acclimation at low temperatures. 6. The spontaneous activity of the central nervous system of insects is altered in a compensatory manner by temperature acclimation. In fish, the cold tolerance of simple and complex reflexes and of conditioning is adaptively altered by temperature acclimation. The role of the central nervous system, especially of the thermoregulatory centre, in the temperature acclimation of homeotherms is established. 7. There are adaptive isoenzymes of acetylcholinesterase in the brain of the rainbow trout. These isoenzymes differ from each other in respect of the temperature dependence of their enzyme-substrate affinity. The synthesis of acetylcholine receptor molecules may also be affected by temperature acclimation. 8. The metabolism of putative synaptic neurotransmitters (5-hydroxytryptamine, adrenaline, noradrenaline) is altered in the frog and mouse brains during the early phases of temperature acclimation. These changes may initiate the physiological processes connected with temperature acclimation. 9. The neuromuscular transmission in the frog shows after acclimation to cold, increased resistance to it and some indications of temperature compensation. 10. Changes in neurosecretion seem to be involved in temperature acclimation both in poikilotherms and homeotherms. The fast axonal transport of proteins shows compensatory acclimation to cold in the frog.