Reward devaluation disrupts latent inhibition in fear conditioning.

Three experiments explored the link between reward shifts and latent inhibition (LI). Using consummatory procedures, rewards were either downshifted from 32% to 4% sucrose (Experiments 1-2), or upshifted from 4% to 32% sucrose (Experiment 3). In both cases, appropriate unshifted controls were also included. LI was implemented in terms of fear conditioning involving a single tone-shock pairing after extensive tone-only preexposure. Nonpreexposed controls were also included. Experiment 1 demonstrated a typical LI effect (i.e., disruption of fear conditioning after preexposure to the tone) in animals previously exposed only to 4% sucrose. However, the LI effect was eliminated by preexposure to a 32%-to-4% sucrose devaluation. Experiment 2 replicated this effect when the LI protocol was administered immediately after the reward devaluation event. However, LI was restored when preexposure was administered after a 60-min retention interval. Finally, Experiment 3 showed that a reward upshift did not affect LI. These results point to a significant role of negative emotion related to reward devaluation in the enhancement of stimulus processing despite extensive nonreinforced preexposure experience.

c-Fos positive nucleus reveals that contextual specificity of latent inhibition is dependent of insular cortex.

The present study analyzed the functional activity of granular and agranular insular cortices in contextual specificity of latent inhibition using a conditioned taste aversion paradigm. c-Fos immunolabeling was examined in insular cortex in preexposed and no preexposed groups under similar and different context conditions. Result showed that the exposition to a novel taste increased c-fos activity in insular cortex. However, a context shift caused an increase in immunolabeling in animals preexposed to saccharine. These results suggest insular cortex is part of a complex system to evaluate taste-response, and it may read the meaning of taste stimuli depending on the context.

Differential implication of dorsolateral and dorsomedial srtiatum in encoding and recovery processes of latent inhibition.

The dorsal striatum has been ascribed to different behavioral roles. While the lateral area (dls) is implicated in habitual actions, its medial part (dms) is linked to goal expectancy. According to this model, dls function includes representation of stimulus-response associations, but not of goals. Dls function has been typically analyzed with regard to movement, and there is no data indicating whether this region could processes specific stimulus-outcome associations. To test this possibility, we analyzed the effects of dls and dms inactivation on the retrieval phase, and dms lesion on the acquisition phase of a latent inhibition procedure using two conditions, long and short presentations of the future conditioned stimulus. Contrary to current theories of basal ganglia function, we report evidence in favor of the dls involvement in cognitive processes of learning and retrieval. Moreover, we provide data about the sequential relationship between dms and dls, in which the dms could be involved, but it would not be critical, in new learning and the dls could be subsequently involved in consolidating cognitive routines.

Neural basis of the spatial navigation based on geometric cues.

Recent studies have found that hippocampus of mammals and birds and the lateral pallium of the fish telencephalon are critical for learning the geometric properties of space. Nevertheless, other studies suggest that navigation based on geometric information is primarily supported by proximal cues near the target location. According to this hypothesis, animals could use a taxon strategy to navigate an environment where only geometric cues are available and the results from lesion studies could be masking other effects related to the use of featural information. In the present study, we examined the effects of lesions to the lateral pallium of goldfish in the encoding of geometric spatial information. Goldfish with telencephalic lesions were trained to search for a goal in a rectangular-shaped arena with either one or two possible goals. Lateral pallium lesions do not interfere with goal location when the geometric information defined the goal unambiguously. Present results suggest that the geometric information is sensitive to be encoded in taxon strategies and therefore it could not depend directly on the correct functioning of the hippocampal system.

Ventral subiculum involvement in latent inhibition context specificity.

The subiculum is the main structure linking the hippocampus with several cortical and subcortical areas. In particular, ventral subiculum might act as an interface between the hippocampus, a contextual information processor, and cortical and subcortical processing systems related to motivation, such as the ventral striatum. Electrophysiological studies have shown a relationship between ventral subiculum and ventral striatum, namely a strong influence on mesolimbic system and the activity of dopaminergic neurons in the ventral tegmental area. Dopamine activity in this system has received special attention for its role in the latent inhibition phenomenon. However, the functional relationship between mesolimbic system and this behavioral process remains unclear. Two experiments were performed to analyze the role of ventral subiculum on latent inhibition. The results showed that ventral subiculum is involved in contextual processing that modulates the expression of latent inhibition. These findings are consistent with electrophysiological studies revealing the ventral subiculum as a structure modulating the mesolimbic DA system and DA release in the nucleus accumbens.

Influence of distal and proximal cues in encoding geometric information.

Vertebrates use geometric and featural information for spatial navigation. When both geometric and featural cues are available, animals can use a variety of spatial strategies based on this information. To examine the nature of these strategies, we manipulated the spatial relationship between a conspicuous cue and the position of the goal when goldfish (Carassius auratus) were searching for the exit of a rectangular environment with one distinctive wall. Two groups of fish were used, one with the distinctive wall close to the goal and the other with the distinctive wall on the other end of the enclosure. Results showed that fish encoded featural and geometric information in both conditions but the spatial relationship between the goal and the distinctive wall influences the characteristics of the encoding of the spatial cues and the strategy used to locate the goal. These results suggest that fish in both procedures use the local featural cues associated with the goal instead of the whole set of spatial cues as previous studies propose.

Taste memory trace disruption by AP5 administration in basolateral amygdala.

N-methyl-D-aspartate receptor has been related to learning and memory processes. Its characteristics make it a key candidate in the modulation of associative processes at physiological level. Traditionally, the main efforts have been directed to show its role in excitatory conditioning. Nevertheless, the studies that have analyzed its implication in inhibitory learning are scarce. We present an experiment where a preexposure effect on the conditioning (latent inhibition) is disrupted by 2-amino-5-phosphonopentanoic acid administered in basolateral amygdala. This data shows interference on taste memory trace, and attenuation of the inhibition effect.

Evaluación de la eficacia y tolerancia del Saccharomyces Boulardii (Florestor) en pacientes con diarrea aguda: Un estudio multicéntrico / Evaluation of the tolerance and efficacy of saccharomyces boulardii in patients with acute diarradea: Multicentric study

Se evaluó la eficacia y la tolerancia del Florestor (Saccharomyces boulardii, dosis diaria oral 400 mg) en el síndrome de diarrea aguda, mediante un estudio clínico abierto y multicéntrico, donde se incluyeron 230 niños con edades comprendidas entre 3 meses y 5 años. La evaluación del total diario de puntos antes y después de tratamiento con Florestor mostró una diferencia estadísticamente significante (p<0,001). Esta cuantificación de la eficacia reflejó indirectamente porcentajes de curación de 91,7 por ciento a los tres días de tratamiento. Al tercer día de tratamiento, la eficacia clínica fue considerada como muy eficaz o eficaz en un 99,1 por ciento del total de pacientes. En un 96 por ciento del universo de los 230 pacientes, la tolerancia fue expresada como excelente o buena. Se concluye que florestor es un producto seguro y eficaz para el tratamiento de la diarrea aguda, no complicada, asociado a la rehidratación oral en niños ambulatorios con edades entre 3 meses y 5 años