Inferior Olive Lesions Impair Concurrent Taste Aversion Learning in Rats

Abstract

Taste aversion learning can be established according to two different procedures, concurrent and sequential. For the concurrent task, two different taste stimuli are offered at the same time, one associated with simultaneous intragastric administration of an aversive stimulus and the other associated with physiological saline. This discrimination is learned by sham-lesioned control animals and by animals with lesions in the cerebellar cortex but not by rats lesioned in the inferior olive. At the same time, animals with lesions in the inferior olive and sham-lesioned animals achieve sequential learning when the gustatory stimuli are offered individually during each daily session. The results obtained show that electrolytic lesions in the inferior olive impair acquisition of concurrent learning and are analyzed in terms of an anatomical system consisting of the vagus nerve, inferior olive, and cerebellum, which differentiates between the two modalities of taste aversion learning, concurrent and sequential.

Effects of a Flavor-Placement Reversal Test after Different Modalities of Taste Aversion Learning

“…The concurrent TAL has already been observed in both intact animals (Arnedo et al, 1990) and lesioned animals (Agüero et al, 1997;Mediavilla et al, 1999). Similarly, this paper shows that long-term, or sequential, TAL can be established in intact animals when hypertonic NaCl is used as the aversive stimulus and there is a 15-min delay between presentation of the flavor stimulus and administration of the associated intragastric substance.…”

“…In this regard, the objective of this study was to analyze the flexibility of the concurrent and sequential TAL paradigms, and the results obtained seem to support the concept of two different modalities of TAL. Sequential TAL is maintained after changes are introduced in the context compared to the learning situation, specifically reversal of the positions in which the flavor stimuli are presented (Test 2 for the sequential group in Experiment 1; Mediavilla et al, 1998Mediavilla et al, , 1999. However, this same modification was critical in the concurrent TAL paradigm because the animals were unable to recognize the gustatory stimulus and harmless substance (physiological saline) in a different context from that in which the association was originally acquired.…”

“…In this and other related studies (Mediavilla et al, 1998(Mediavilla et al, , 1999, the experimental procedure was repeated over the course of five trials. A reversal test was conducted in a new session 6 h after the last session and after it had been verified statistically that the animals had, in fact, learned the task.…”

“…The first, called short-term or concurrent TAL, takes place by presenting two gustatory stimuli at the same time on a daily basis, one of which is paired with simultaneous intragastric administration of hypertonic NaCl. Several trials are normally needed for the task to be learned, but the association required can be achieved by intact animals Mediavilla, Molina, & Puerto, 1998, 1999 as well as animals lesioned in the area postrema (AP) (Arnedo et al, 1990), lateral parabrachial nucleus (lPBN) (Agüero, Gallo, Arnedo, Molina, & Puerto, 1997), and cerebellar cortex (Mediavilla et al, 1999). In contrast, it is blocked after vagotomy (Arnedo et al, 1990;Arnedo, Gallo, Agüero, & Puerto, 1991;Arnedo, Gallo, Agüero, Molina, & Puerto, 1993) and electrolytic lesioning of the medial parabrachial nucleus and several regions of the cerebellar circuit (Agüero et al, 1997;Mediavilla et al, 1998Mediavilla et al, , 1999.…”

Electrolytic Lesions of the Pedunculopontine Nucleus Disrupt Concurrent Learned Aversion Induced by NaCl

“…Concurrent (short-term) TAL tasks are achieved correctly by the control group in experment 1 and by animals lesioned in other areas involved in TAL, such as the AP , lPBN (Agüero et al, 1997) and cerebellar cortex (Mediavilla, Molina, & Puerto, 1999). For this reason, our results also appear to be independent of any unspecific effects of the lesions.…”