Participation of the area postrema in learned aversions induced by body rotation

Place preferences induced by electrical stimulation of the external lateral parabrachial subnucleus in a sequential learning task: Place preferences induced by NLPBe stimulation

It is known that electrical stimulation of the external lateral parabrachial nucleus (NLPBe) can sustain concurrent taste and place learning. Place preferences can be learned through different procedures. Previous studies demonstrated that electrical stimulation of the PBNLe can generate aversive and preference place learning using concurrent procedures. In the concurrent procedure, the animals can move freely in the maze, and intracranial electrical stimulation is associated with their voluntary stay in one of the two maze compartments. However, the rewarding properties of most stimuli, whether natural or drugs of abuse, have usually been investigated using the sequential procedure, in which animals are confined while receiving the unconditioned stimulus and then undergo a choice test without stimulation in a later phase. This study examined whether this stimulation can sustain place preference learning in sequential tasks. Results demonstrated that place preferences can also be induced by the electrical stimulation of the NLBe using sequential procedures. These findings suggest that the NLPBe may form part of a brain reward axis that shares certain characteristics with those observed in the processing of natural rewarding agents and especially of drugs of abuse.

Effects of a flavor-placement reversal test after different modalities of taste aversion learning

Taste aversion learning is induced through two different behavioral procedures: a short-term or concurrent (two-daily flavors) and a long-term or sequential (one-daily flavor) procedure. For the concurrent group of animals, two gustatory/olfactory stimuli are presented separately but at the same time on a daily basis. One is paired with simultaneous intragastric administration of hypertonic NaCl and the other with physiological saline. For the sequential group, the two stimuli are presented on alternate days, one of them followed by intragastric injection of the aversive stimulus and the other by saline, both after a delay of 15 min. The two groups learned the task, but when they were subjected to a flavor-placement reversal test only the sequential group was successful in achieving it. In a second experiment, three groups of animals had to learn concurrent or sequential discrimination tasks (with either simultaneous or delayed administration of the visceral stimulus) using only spatial/proprioceptive cues. The data show that none of the groups learned them under these conditions. The results are discussed in terms of the different modalities of learning. Short-term and long-term taste aversion learning are different in the anatomical structures involved, the number of trials required for acquisition and, as shown in this paper, flexibility.

Retention of concurrent taste aversion learning after electrolytic lesioning of the interpositus-dentate region of the cerebellum

Lesions in the interpositus-dentate region of the cerebellum impair short-term, or concurrent, TAL. In this type of learning, animals must discriminate between two flavor stimuli presented at the same time, one of which is associated with an aversive product. The task is learned by the control animals, and within this group the animals that acquire it adequately enough (15/22, 70% criterion) retain the learned taste discrimination when they are subjected to it again after being lesioned in the interpositus-dentate region. These results suggest that the deep nuclei are essential in the concurrent TAL acquisition process, but not in its retention.

Bilateral tetrodotoxin blockade of the rat vestibular nuclei substitutes the natural unconditioned stimulus in taste aversion learning

The aversive effects of bilateral transient blockade of the lateral vestibular nucleus caused by tetrodotoxin microinjections were tested using conditioned taste aversion in the first experiment. Male Wistar rats received tetrodotoxin injections (10 ng) after drinking a coffee solution (0.5%), either in the lateral vestibular nucleus (LVN), the parabrachial nucleus or the dopaminergic area A8. Two days later they drank a cider vinegar solution (3%) not followed by injections. In a later choice test, only the group receiving the injection in the lateral vestibular nucleus displayed a coffee aversion. In a second experiment the role of the peripheral vestibular symptoms induced by LVN inactivation on substituting the aversive stimulus was explored in the same behavioral task. Rats anesthetized (Pentobarbital, 25 mg/kg) before tetrodoxin LVN blockade, that did not show peripheral symptoms, did not develop learned aversions. The coffee preference ratios did not differ to those animals receiving only anesthesia or those that remained undisturbed. These results showed that the bilateral blockade of the vestibular nuclei may induce peripheral vestibular symptoms that that may substitute the aversive stimulus in taste aversion learning.

Inferior olive lesions impair concurrent taste aversion learning in rats

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.

Functional blockade of the parabrachial area by tetrodotoxin disrupts the acquisition of conditioned taste aversion induced by motion-sickness in rats

The role of the parabrachial area in conditioned taste aversion (CTA) induced by motion-sickness was studied in male Wistar rats. In the first experiment, one-trial conditioned taste aversion, to a 0.5% decaffeinated coffee solution, was induced by 30 min of vertical rotatory motion (80 rev./min) in intact rats. In the second experiment, reversible blockade of the neural activity in various brainstem sites was induced by bilateral intracerebral injections of tetrodotoxin (TTX) (10 ng/microl) after conditioning. Blockade of the parabrachial area, but neither A8 nor lateral vestibular nucleus, disrupted the acquisition of (CTA). The results are discussed in terms of an associative role of the parabrachial area in body rotation-induced taste aversion learning, as the area was intact during sensory processing and testing.

Bilateral lesions in the cerebellar interpositus-dentate region impair taste aversion learning in rats

Taste Aversion Learning (TAL) has been induced through two different behavioral procedures: a short-term o concurrent (two-daily flavors) and a long-term (one-daily flavor) procedure. For the first, two gustatory/olfactory stimuli are presented separately but at the same time on a daily basis. One of the flavors is paired with simultaneous intragastric administration of hypertonic NaCl and the other is paired with physiological saline. In the long-term procedure, the two stimuli are presented on alternate days, one of them followed by intragastric injection of the aversive stimulus, and the other by saline. The subjects for both types of tests were animals that had been lesioned in the interpositus-dentate region of the cerebellum. The experiments show that the lesions disrupt short-term TAL, but have no effect on long-term TAL. The results are discussed in terms of the role of the cerebellum in relation to TAL and the different anatomical substrates of both learning modalities.

Distribution of lithium in the rat brain after a single administration known to elicit aversive effects

In order to get insight into the brain areas involved in the initial unpleasant effects resulting from the administration of lithium (Li+), its distribution was mapped in the rat brain using the 6Li(n,alpha)3H nuclear reaction after a single injection of 6Li2SO4 at doses and latencies corresponding to the elicitation of such unpleasant effects. An improved method for visualization and measurement of local Li+ concentrations was used consisting in diffracting light along the tracks left by alpha particles in a dielectric detector. The distribution of Li+ was found less homogeneous than when Li+ was administered chronically. Periaqueductal and periventricular structures were the brain areas containing the highest concentrations of Li+.

The functional relevance of the lateral parabrachial nucleus in lithium chloride-induced aversion learning

Lesions to the lateral parabrachial nucleus (PBN), one of the subnuclei that make up the pontine parabrachial complex, impairs the acquisition of taste aversion learning (TAL) with LiCl as the toxic stimulus. In this experiment, PBNl-lesioned and control rats were trained to learn a delayed task with a 15-min interval between presentation of the gustatory and the aversive stimulus. The impairment in learning observed after lesions of the PBNl is discussed in terms of disruption of the transmission of toxic stimuli (LiCl) processed by the humoral pathway and the area postrema (AP).