Role of gustatory thalamus in anticipation and comparison of rewards over time in rats

Abstract

Rats reduce intake of a palatable saccharin solution when it is followed by access to a preferred sucrose solution. This phenomenon, referred to as an anticipatory contrast effect (ACE), is thought to occur because the value of the saccharin conditioned stimulus pales in comparison to the highly rewarding sucrose unconditioned stimulus expected in the near future. Although relatively little is known about the underlying neural substrates, lesions of the gustatory thalamus fully disrupt the phenomenon (Reilly S, Bornovalova M, and Trifunovic R. Behav Neurosci 118: 365-376, 2004; Reilly S and Pritchard TC. Behav Neurosci 110: 746-759, 1996). The present set of experiments revisited this issue to determine the nature of this deficit. Rats with bilateral ibotenic acid lesions of the gustatory thalamus were given 3-min access to 0.15% saccharin and, after a 0-s or 5-min interval, were given 3-min access to either the same saccharin solution or a highly preferred 1.0 M sucrose solution. In experiment 1, ACE testing began with the 5-min interstimulus interval (ISI) and then switched to the 0-s ISI. For experiment 2, the order of ISI testing was reversed. The results show that axon-sparing, neurotoxic lesions of the gustatory thalamus prevent ACEs with a 0-s ISI and lead to a reversal (i.e., a reinforcement effect) with a 5-min ISI. Together, the results suggest that the lesion leads to a specific reward comparison deficit, whereby the rats fail to compare the value of an available reward with the memory of a preferred reward that is anticipated in the near future.

Amphetamine-induced taste aversion learning in young and old F-344 rats following exposure to 56Fe particles

“…Grigson and collaborators (Grigson et al 1998(Grigson et al , 2002Schroy et al 2005) have proposed that the treatment with drugs of abuse, such as cocaine, morphine and amphetamine, do not cause a taste aversion per se. Rather, treatment with these drugs suppresses intake of the normally preferred sucrose solution by interfering with the reinforcing aspects of the solution.…”

“…In this interpretation, the sucrose becomes a conditioned stimulus predicting the forthcoming presentation of the more rewarding amphetamine. This effect, called the anticipatory contrast effect, is observed when saccharin is paired with drugs of abuse or when a weaker saccharin solution is paired with a subsequent stronger solution (Grigson and Freet 2000;Schroy et al 2005). Additional support comes from the observation that ibotenic acid lesions of the gustatory thalamus disrupt the avoidance of the saccharin produced by injection of drugs of abuse, but not by injection of lithium chloride (Grigson and Freet 2000;Schroy et al 2005;Reilly et al 2004).…”

Reward comparison: the Achilles’ heel and hope for addiction

“…The suppressive effects of cocaine and sucrose, but not LiCl, are augmented in rats with a history of chronic morphine treatment [57]. Finally, bilateral lesions of the gustatory thalamus or gustatory cortex disrupt the suppressive effects of morphine, cocaine, and sucrose, but have no impact on the development of a LiCl-induced CTA [58][59][60][61][62][63][64][65]. Taken together, the data confirm that drug-induced suppression of CS intake is not mediated by a conditioned taste aversion like that induced by the aversive agent.…”

Intermittent access to preferred food reduces the reinforcing efficacy of chow in rats

“…The hypophagia of once acceptable food has often been interpreted to result from a corrective energy homeostasis mechanism to oppose weight gain (4, 18, 58) or caloric conditioning (13,83,90). Alternatively, some investigators have proposed nonnutritional contributions, including "negative contrast" (21, 24, 32, 77), due to recent experience of or the prospect of access to a more rewarding alternative (30,31,38,79); "food withdrawal," analogous to an aversive state of drug withdrawal (87); or opponent-process decrements in brain reward function (84).The first aim of the present study was to test the hypothesis that the "energy compensation" explanation is sufficient to account for undereating of an otherwise acceptable diet following extended access to a more preferred diet. For this purpose, rats were provided cycles of 5-day access to an otherwise palatable diet followed by 2-day access to an even more preferred diet.…”