Gustatory insular cortex lesions disrupt drug-induced, but not lithium chloride-induced, suppression of conditioned stimulus intake.

Abstract

Rats suppress intake of a normally preferred 0.15% saccharin conditioned stimulus (CS) when it is paired with an aversive agent like lithium chloride (LiCl) or a preferred substances such as sucrose or a drug of abuse. The reward comparison hypothesis suggests that rats avoid intake of a saccharin cue following pairings with a drug of abuse because the rats are anticipating the availability of the rewarding properties of the drug. The present study used bilateral ibotenic acid lesions to examine the role of the gustatory cortex in the suppression of CS intake induced by cocaine, morphine, and LiCl. The results show that bilateral lesions of the insular gustatory cortex (1) fully prevent the suppressive effects of both a 15- and a 30-mg/kg dose of morphine, (2) attenuate the suppressive effect of a 10 mg/kg dose of cocaine, but (3) are overridden by a 20 mg/kg dose of the drug. Finally, these same cortical lesions had no impact on LiCl-induced conditioned taste aversion. The current data show that the insular taste cortex plays an integral role in drug-induced avoidance of a gustatory CS.

Pontine and thalamic influences on fluid rewards: III. Anticipatory contrast for sucrose and corn oil

“…Other data demonstrate that these subregions project directly to the ventral edge of primary somatosensory cortex in the same modality specific order [38, 44]. This proves the area we damaged not only contains neurons that respond to gustatory and lingual somatosensory stimuli, but also that these cells form one limb of a classic thalamocortical circuit [45]. …”

Pontine and thalamic influences on fluid rewards: II. Sucrose and corn oil conditioned aversions

“…This demonstrates that the thalamic lesions did affect at least one taste-guided behavior. In prior experiments using similar procedures, somewhat more medial thalamic damage as well as lesions of gustatory cortex disrupted suppression of a taste CS when it was paired with either a highly preferred drug or sucrose [38–40]. The third paper in this series, then, uses sham feeding of sucrose and corn oil to test whether the PBN or TOA lesion will disrupt comparison of the relative value of different stimulus concentrations in an anticipatory contrast paradigm.…”

Morphine-induced suppression of conditioned stimulus intake: Effects of stimulus type and insular cortex lesions

“…This analysis anticipates that IC lesions should delay but not prevent the acquisition of drug-induced CS suppression. Interestingly, Geddes, Han, Baldwin, Norgren and Grigson (2008; Experiment 1) recently reported that ICX rats required twice as many CS-US pairings as SHAM subjects (6 versus 3 trials, respectively) for a cocaine US (10 mg/kg) to suppress intake of a Polycose CS3. Furthermore, Roman and Reilly (2009), in a study showing that IC lesions disrupt morphine-induced saccharin suppression, provided some evidence, albeit between-phase rather than across-groups, that latent inhibition influences drug-induced CS suppression in neurologically intact rats.…”