Temperature acclimation in the central nervous system of rainbow trout ( Salmo gairdnerii)

Abstract

1. 1. The midbrain response to direct electrical stimulation of the retina was measured in rainbow trout acclimated to 10°C and following transfer and acclimation to 4 and 16°C. The evoked midbrain potential consisted first of a positive deflection upon which was superimposed two negative spikes of supposed pre-synaptic origin, and secondly of a slow negative potential, interpreted as post-synaptic in origin. 2. 2. Transfer of 10° acclimated trout to 4° caused an average 39 per cent protraction of the entire midbrain response pattern. After 21 days' acclimation to 4°, the negative spike latencies had decreased to 18 and 19 per cent above the 10° controls and the duration of the slow potential had decreased to 16 per cent above the 10° controls. 3. 3. Transfer of 10° acclimated trout to 16° caused an initial shortening of the negative spike latencies and slow potential duration. These values lengthened somewhat during acclimation to 16° but, since a similar lengthening occurred int he 10° controls, the change was judged noncompensatory. 4. 4. Thus, significant compensation occurred in response to low temperature acclimation (4°) but not to high temperature acclimation (16°). These results contrast with brain tissue respiration measurements that show that metabolic compensation is much more complete between 10 and 16° than between 4 and 10°.