Neurological tests and behavioral deficits in chronic thalamic and chronic decerebrate rats

Abstract

The taste reactivity of chronic decerebrate rats is very similar to intact rats although chronic thalamic rats display only the quinine-like rejection sequence. The performance of intact (n = 12), decerebrate (n = 10) and thalamic (n = 10) preparations was further compared across a set of simple behavior tests to more broadly assess the behavioral capacities of the rodent brain stem. Decerebrate rats were immobile. They exhibited no spontaneous activity other than grooming, but often overreacted with well-coordinated movements (i.e., running, jumping and climbing) to seemingly inappropriate activating stimuli such as tail pinch, handling or water squirted on the fur. Decerebrates had lower thresholds for elicited attack and grooming behaviors than thalamic or intact rats. The thalamic preparation exhibited a wider range of intact neurological responses than the decerebrate. Cage climbing, resistance to gravity, suspension and muscle tone reactions, rhythmic vibrissae movements and examination of object with snout and mandible were difficult to distinguish from controls. Decerebrates either did not perform these responses or did so in a clearly different manner. In contrast, grooming behavior in thalamics was much less effective than in decerebrates. Thalamic rats spontaneously executed grooming sequences, but the responses were misdirected and ineffective. Despite their relative immobility, decerebrates coordinated grooming sequences and maintained their fur. No single mechanism appears to account for the constellation of deficits and capacities observed in either chronic thalamic or chronic decerebrate rats.