Journal Article

Extensive Lesions in Rat Insular Cortex Significantly Disrupt Taste Sensitivity to NaCl and KCl and Slow Salt Discrimination Learning

Blonde, Ginger D., Bales, Michelle B., Spector, Alan C.

2015

Overview

While studies of the gustatory cortex (GC) mostly focus on its role in taste aversion learning and memory, the necessity of GC for other fundamental taste-guided behaviors remains largely untested. Here, rats with either excitotoxic lesions targeting GC (n = 26) or sham lesions (n = 14) were assessed for postsurgical retention of a presurgically LiCl-induced conditioned taste aversion (CTA) to 0.1M sucrose using a brief-access taste generalization test in a gustometer. The same animals were then trained in a two-response operant taste detection task and psychophysically tested for their salt (NaCl or KCl) sensitivity. Next, the rats were trained and tested in a NaCl vs. KCl taste discrimination task with concentrations varied. Rats meeting our histological inclusion criterion had large lesions (resulting in a group averaging 80% damage to GC and involving surrounding regions) and showed impaired postsurgical expression of the presurgical CTA (LiCl-injected, n = 9), demonstrated rightward shifts in the NaCl (0.54 log10 shift) and KCl (0.35 log10 shift) psychometric functions, and displayed retarded salt discrimination acquisition (n = 18), but eventually learned and performed the discrimination comparable to sham-operated animals. Interestingly, the degree of deficit between tasks correlated only modestly, if at all, suggesting that idiosyncratic differences in insular cortex lesion topography were the root of the individual differences in the behavioral effects demonstrated here. This latter finding hints at some degree of interanimal variation in the functional topography of insular cortex. Overall, GC appears to be necessary to maintain normal taste sensitivity to NaCl and KCl and for salt discrimination learning. However, higher salt concentrations can be detected and discriminated by rats with extensive damage to GC suggesting that the other resources of the gustatory system are sufficient to maintain partial competence in these tasks, supporting the view that such basic sensory-discriminative taste functions involve distributed processes among central gustatory structures.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animals / Aversion learning / Avoidance Learning - drug effects / Avoidance Learning - physiology / Cerebral Cortex - drug effects / Cerebral Cortex - physiopathology / Conditioning / Cortex (gustatory) / Cortex (insular) / Cortex (somatosensory) / Damage detection / Discrimination / Discrimination Learning - drug effects / Discrimination Learning - physiology / Excitotoxicity / Gustatory system / Ibotenic Acid - toxicity / Laboratories / Learning / Lesions / Lithium chloride / Male / Memory / Neurons / Neurosciences / Operant conditioning / Potassium chloride / Potassium Chloride - administration & dosage / Rats / Rats, Sprague-Dawley / Rodents / Salts / Sensitivity / Sodium chloride / Sodium Chloride - administration & dosage / Somatosensory cortex / Sucrose / Sugar / Taste / Taste - drug effects / Taste - physiology / Taste aversion / Taste aversion learning / Taste discrimination / Taste discrimination learning / Taste Perception - drug effects / Taste Perception - physiology / Taste thresholds / Topography