The taste reactivity test. II. Mimetic responses to gustatory stimuli in chronic thalamic and chronic decerebrate rats.

The taste reactivity test described in the preceding paper was used to begin determining the capacity of brain stem structures to execute and regulate ingestive behavior. Both chronic thalamic and chronic decerebrate rat preparations were examined repeatedly, and their gustatory mimetic responses compared through frame-by-frame videotape analysis with the responses of neurologically normal controls. In response to orally injected taste stimuli, chronic decerebrate rats executed the same mimetic response components, and very similar response sequences observed in intact rats. In contrast, all taste stimuli elicited a quinine-like rejection sequence from chronic thalamic rats. In thalamic rats mimetic responses associated with ingestion were completely absent. Based on the similarities in the ingestion and rejection responses of decerebrate and intact rats, it appears that discriminative responses to taste result from integrative mechanisms complete within, or caudal to, the midbrain. Since decerebrate rats have the capacity to execute both ingestion and rejection response sequences, neural mechanisms rostral to the midbrain in some way suppress ingestion and/or releaser ejection responses in the thalamic preparation.