Conditioning of ictal and interictal behaviors in rats by amygdala kindling: Context as the conditional stimulus.

The authors showed that conditional effects of the stimulation environment modulate both the ictal and interictal behaviors of rats subjected to amygdala kindling. Rats received 53 stimulations to the left basolateral amygdala in 1 conditional stimulus (CS) context (CS+) and 53 sham stimulations (the stimulation lead was attached but no current was delivered) in another context (CS-), quasirandomly over 54 days. Three kinds of conditional effects were observed, First, after several stimulations, less ambulatory activity, more freezing, and less rearing reliably occurred in the CS + context than in the CS context. Second, after 45 stimulations, all of the rats chose the CS - context over the CS + context in a conditioned place preference test. Third, when the rats were finally stimulated in the CS- context, their motor seizures were less severe: Latencies were longer, motor seizures were shorter, convulsive patterns were of a lower class, and there were fewer falls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parabrachial nucleus lesions block taste and attenuate flavor preference and aversion conditioning in rats.

Rats with ibotenic acid lesions of the parabrachial nucleus (PBN) failed to learn a taste aversion induced by lithium chloride (LiCl) toxicosis. The same rats also did not learn to prefer a taste that was paired with intragastric (IG) carbohydrate infusions during 22 hr/day trials. The PBN-lesioned rats did learn to prefer a flavor (odor?+?taste) paired with the IG carbohydrate infusions over a different flavor paired with IG water. The PBN-lesioned rats also learned to avoid a flavor paired with IG LiCl infusions during 22 hr/day trials. The flavor preference and aversion, however, were less pronounced than those displayed by control rats. These data indicate that the PBN is essential for forming orosensory-viscerosensory associations when taste is the primary cue but is less critical when more complex flavor cues are available. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caffeine-reinforced conditioned flavor preferences in rats.

In 4 experiments, rats were trained to associate 1 of 2 differently flavored solutions with caffeine. During later 2-bottle extinction tests, they consistently preferred flavors that had been previously mixed with 2 lower (0.25 and 0.125 mg/ml), but not 2 higher (0.5 and 0.75 mg/ml), caffeine concentrations. Hunger during conditioning increased the size of these preferences, but neither preexposure to unflavored caffeine nor hunger during the choice test had any effect on them. Because caffeine is noncaloric, this last finding strengthens the hypothesis that hunger enhances the expression of only calorie-based conditioned flavor preferences. More fundamentally, the present results represent the first clear evidence that, through Pavlovian conditioning, rats can develop preferences for flavors associated with caffeine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning in flavor aversion: Evidence for learned changes in stimulus effectiveness.

Rats were exposed to the compound flavors AX and BX, presented in alternation, and to CX on a separate block of trials. Generalization to BX after aversion conditioning with AX was less than to CX. An equivalent effect was found when the nature of the common element was changed after preexposure but not when the common element was omitted during preexposure, during conditioning and test, or both. Rats conditioned with X alone again showed less aversion to BX than to CX; similarly, rats conditioned with a novel flavor (Y) showed less aversion to BY than to CY. These effects support the proposal that intermixed preexposure to AX and BX enhances the perceptual effectiveness of their unique features, A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative structure of fear memory after basolateral amygdala lesions in rats.

The authors have recently demonstrated that rats with basolateral amygdala (BLA) lesions acquire Pavlovian fear conditioning after overtraining. However, it is not known whether the associative basis of Pavlovian fear memory acquired by rats with BLA lesions is similar to that of intact rats. Associations are typically formed between the conditional (CS) and unconditional (US) stimuli (stimulus-stimulus; S-S), although it is possible for stimuli to enter into association with the responses they produce (stimulus-response; S-R). Indeed, the central nucleus of the amygdala, which is essential for fear conditioning in rats with BLA lesions, may mediate S-R associations in some Pavlovian tasks. The authors therefore used a postconditioning US inflation procedure (i.e., exposure to intense footshock USs) to assess the contribution of S-S associations to fear conditioning after overtraining in rats with BLA lesions. In Experiment 1, intact rats that were overtrained and later inflated displayed elevated freezing levels when tested, indicating that S-S associations contribute to overtrained fear memories. Interestingly, neither neurotoxic BLA lesions nor temporary inactivation of the BLA during overtraining prevented the inflation effect (Experiment 2 and 3, respectively). These results reveal that S-S associations support Pavlovian fear memories after overtraining in both intact rats and rats with BLA lesions, and imply that the central nucleus of the amygdala encodes CS-US associations during fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of central and basolateral amygdala lesions on conditioned taste aversion and latent inhibition.

[Correction Notice: An erratum for this article was reported in Vol 121(6) of Behavioral Neuroscience (see record 2007-18058-034). Figure 4 on p. 96 (Results and Discussion, Experiment 2: Behavioral section) was incorrect. The correct figure is provided in the erratum.] The present study examined the effects of neurotoxic lesions of the central nucleus (CNA) and basolateral complex (BLA) of the amygdala on conditioned taste aversion (CTA) in a latent inhibition design. In Experiment 1, lesions of the CNA were found to have no affect on CTA acquisition regardless of whether the taste conditioned stimulus (CS) was novel or familiar. Lesions of the BLA, although having no influence on performance when the CS was familiar, retarded CTA acquisition when the CS was novel in Experiment 2. The pattern of results suggests that the CTA deficit in rats with BLA lesions may be a secondary consequence of a disruption of perceived stimulus novelty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipating the Attack: Temporal Conditioning During Amygdala Kindling in Rats.

The present study showed that amygdala-kindled rats use short-interval timing superimposed on phase or ordinal timing to predict when a convulsion will occur. In 2 experiments, rats received 1 stimulation and 1 sham stimulation each day, always at the same times (conditioned stimulus [CS]+ and CS- times, respectively) and 150 s after rats had been placed in the testing chamber (the preadministration interval). As kindling progressed, the rats displayed more defensive behavior at the CS+ time than at the CS- time. Then, a stimulation-free peak-procedure test was conducted: At the CS+ time, but not at the CS- time, defensive behavior increased progressively as the 150-s preadministration interval elapsed, and then it gradually declined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Easy to Hard Effect and Perceptual Learning in Flavor Aversion Conditioning.

In experiments on the easy to hard effect, pretraining on an easy discrimination results in better performance on a harder version of the discrimination than pretraining on the hard discrimination itself. In addition, some theories posit that unreinforccd preexposure to the easy discrimination should be as effective as differentially reinforced easy pretraining in producing the easy to hard effect. Two experiments on flavor aversion conditioning in rats demonstrated the basic easy to hard effect. However, in neither experiment was easy preexposure more effective than hard preexposure in enhancing learning of the hard discrimination. Indeed, in Experiment 2, rats preexposed to an easy discrimination learned the hard discrimination significantly more slowly than those preexposed to the hard discrimination itself. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Conditioned effects of kindling three different sites in the hippocampal complex of the rat.

Rats received kindling stimulations to the perirhinal cortex (PRh), ventral hippocampus (VH), or dorsal hippocampus (DH) in 1 environment and an equivalent number of sham stimulations in a 2nd environment. The PRh-kindled rats displayed rapid kindling and a swift emergence of conditioned interictal defensiveness. In contrast, the VH- and DH-kindled rats displayed much slower kindling and slow or no conditioning, respectively. No effects of conditioning on the convulsions, comparable with those associated with amygdala kindling, were observed. These results establish the generality of some of the previously reported kindling-related conditioned effects, confirm the site specificity of some of these effects, and suggest that the convulsions, rather than the stimulations, function as the unconditioned stimuli for the conditioning of interictal behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Kindling-induced emotional behavior in male and female rats.

Modeling fear in animals is a critical approach for identifying the neural mechanisms involved in human disorders such as generalized anxiety and panic. Amygdala kindling has proven useful in this regard because it produces dramatic increases in fearful behavior. The purpose of this experiment was to compare the behavioral effects of kindling in male and female rats. Compared with the sham-stimulated rats, the kindled male and female rats showed similar increases in fearful behavior, with some sex differences in fear-related open-field activity. They also showed decreased immobility in the forced-swim test and increased sucrose consumption. These results suggest that kindling-induced fear is generally similar in male and female rats and that kindling does not appear to induce depression-like behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavor preferences produced by backward pairing with wheel running.

In 3 experiments rats given 8 sessions of preexposure to wheel running acquired a preference for a flavor that was given immediately after each of 4 subsequent sessions of wheel running. Such flavor preference was less likely when rats were given the same conditioning procedure but without preexposure to wheels (Experiment 1) or when access to flavor was delayed by 30 min following a wheel session (Experiment 2). When rats were given a flavor before each wheel session, the resulting conditioned aversion was greater in rats that had no prior exposure to wheel running (Experiment 3). These results show that whether an aversion or preference for a flavor is produced by wheel running depends on an interaction between prior wheel experience and the sequence of events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Valence dependent asymmetric release of norepinephrine in the basolateral amygdala.

Emerging evidence from literature on humans suggests the valence of emotionally laden environmental stimuli may dictate whether amygdala activation is greater in one hemisphere relative to the contralateral side. However, only a paucity of animal studies attempt to unravel the mechanisms underlying the selective, valence-dependent initiation of activity in the amygdala of opposing hemispheres. The present studies assessed whether exposure to positive or negative appetitive conditions in an operant learning task differentially impacts norepinephrine activation of the left versus right amygdala, respectively. Dialysate samples of norepinephrine were collected from the basolateral nucleus of male Sprague–Dawley rats. Fluctuations in norepinephrine activity were sampled during training conditions involving an abrupt shift (i.e., increase or decrease) in the magnitude of food rewards normally provided for bar press responses. In a subsequent study, dialysate samples of norepinephrine were collected before, during, and after presentation of a negatively valenced stimulus involving footshock delivery during Pavlovian fear conditioning. Norepinephrine concentrations in the left but not right basolateral amygdala were elevated in groups presented with a positive experience of an unexpected increase in food reward after bar pressing (p     

Extinction of conditioned flavor preferences.

In a series of 4 experiments, the effects of extinction on flavor preferences conditioned by mixing flavor cues with a nutrient were examined. In each experiment it was observed that rats preferred a flavor cue that had not undergone extinction to one that had. In addition, this preference was reversed in subjects trained thirsty (Experiments 1 and 2) if the associated nutrient had been devalued prior to the test or the preference for the nonextinguished cue was attenuated by nutrient devaluation in subjects trained hungry (Experiments 3 and 4). The results suggest that extinction may weaken associations between the flavor and the specific sensory properties of the nutrient and, for subjects trained hungry, between the flavor and the motivational components of the nutrient as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context conditional flavor preferences in the rat based on fructose and maltodextrin reinforcers.

In three experiments, rats were exposed to a flavor preference procedure in which flavor A was paired with the reinforcer and flavor B presented alone in Context 1, while in Context 2 flavor A was presented alone and flavor B with the reinforcer. With fructose as the reinforcer both two- and one-bottle training procedures produced a context-dependent preference (Experiments 1 and 2). With maltodextrin as the reinforcer two-bottle training produced a context-dependent preference (Experiment 1). Following one-bottle training with maltodextrin reinforcement rats demonstrated a context-dependent preference when the conditioned stimulus (CS)- was presented with a dilute solution of the reinforcer during training (Experiment 3B) but not when the CS- was presented alone (Experiments 2 and 3A). The pattern of results with maltodextrin reinforcement suggests that there was competition between the cue flavors and the taste of the maltodextrin as predictors of the postingestive consequences of the maltodextrin reinforcer. The fact that rats were able to display context-dependent flavor preferences is consistent with the idea that learned flavor preferences rely on the sort of cue-consequence associations that underpin other forms of conditioning which produce accurate performance on biconditional tasks. The differences between fructose- and maltodextrin-based preferences are discussed in terms of configural and elemental learning processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Protein kinase Mzeta maintains fear memory in the amygdala but not in the hippocampus.

Recent work on the long-term stability of memory and synaptic plasticity has identified a potentially critical role for protein kinase Mzeta (PKMζ). PKMζ is a constitutively active, atypical isoform of protein kinase C that is believed to maintain long term potentiation at hippocampal synapses in vitro. In behaving animals, local inhibition of PKMζ disrupts spatial memory in the hippocampus and conditioned taste aversion memory in the insular cortex. The role of PKMζ in context fear memory is less clear. This study examined the role of PKMζ in amygdala and hippocampal neurons following a standard fear conditioning protocol. The results indicate that PKMζ inhibition in the amygdala, but not in the hippocampus, can disrupt fear memory. This suggests that PKMζ may only maintain select forms of memory in specific brain structures and does not participate in a universal memory storage mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of brain lesions on taste-potentiated odor aversion in rats.

Rats failed to acquire aversions to odor stimulus, which was followed 30 min later by an unconditioned stimulus (US). However, when the odor stimulus was accompanied by a taste stimulus, they acquired odor aversions as well as taste aversions. In this phenomenon, referred to as a taste-potentiated odor aversion, lesions of the amygdala disrupted both taste and odor aversions, whereas lesions of the parvicellular part of ventroposteromedial thalamic nucleus (VPMpc) or insular cortex (IC) disrupted taste aversion but attenuated only odor aversion. These results suggest that both taste and odor stimuli are associated with US in the amygdala and that taste inputs delivered to the amygdala through the IC and/or VPMpc play an important role in potentiation of odor aversion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forebrain structures specifically activated by conditioned taste aversion.

This study investigates which forebrain structures show Fos protein expression during conditioned taste aversion (CTA) acquisition and whether Fos expression depends on the aversion strength. A novel taste paired with an intraperitoneal injection of a low dose of the malaise-inducing agent lithium chloride (LiCl) induced a weak CTA, whereas associating this novel taste with a high dose of LiCl induced a strong CTA. Increasing the strength of the gastric malaise alone enhanced Fos expression in central, basal, and lateral amygdala nuclei and decreased Fos expression in the nucleus accumbens core. Taste-malaise association induced specific Fos activation in the insular cortex (with both the low and the high doses of LiCl) and the nucleus accumbens shell (with the high LiCl dose only). No significant variation of Fos expression was measured in the perirhinal cortex. Several forebrain areas may be sites of taste-malaise convergence during CTA acquisition depending on the strength of the aversion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Importance of retronasal and orthonasal olfaction for odor aversion memory in rats.

The role of odors in food memory formation, especially for aversions, has long been considered secondary to taste. However, the importance of odor ingestion in conditioned odor aversion (COA) has recently challenged this assumption (B. M. Slotnick, F. Westbrook, & F. M. C. Darling, 1997). The aim of the present study was to evaluate the respective role of orthonasal and retronasal olfactory experience in COA acquisition, long-term retention, extinction, and spontaneous recovery. To this end, the odor was presented either close to the drinking spout (orthonasal stimulation) or close to and mixed with the drinking water (eliciting both orthonasal and retronasal stimulation). The authors brought evidence that odor ingestion was crucial for COA acquisition, especially when odor presentation and gastric malaise were separated by long delays. On the contrary, once formed, a distal (orthonasal) odor recognition was sufficient for COA to be retrieved. COA was odor specific and long lasting (more than 50 days). Moreover, results brought evidence for a spontaneous recovery of odor aversion tested 57 days after its extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced discrimination between flavor stimuli: Roles of salience modulation and inhibition.

Rats were given intermixed preexposure to the compound flavors AX and BX and to the compound CX in a separate block of trials (4 presentations of each compound). In Experiment 1, rats showed less generalization of conditioned aversion from AX to BX than from CX to BX, a perceptual learning effect. Experiment 2 showed that the formation of an excitatory association proceeded more readily between A and B than between C and B, suggesting that intermixed preexposure maintains the effective salience of A and B and does not establish inhibition between them, a process that would require prolonged preexposure. According to this analysis, salience modulation and associative inhibition may contribute to perceptual learning at different stages of preexposure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of flavor preference depends on type of test and on recent drinking history.

The persistence of a conditioned flavor preference was examined in 3 experiments. All contained an initial acquisition phase in which half the rats were given almond odor mixed with sucrose (AS) in some sessions and water (W) only in other sessions, whereas the other half (controls) were given explicitly unpaired exposures to almond (A) and sucrose (S) in separate sessions. Subsequent 2-bottle choice tests revealed a persistent preference for A, despite extinction exposure to A or S, but this depended on the choice offered on test: Exposure to A did not extinguish the preference for A over W but did reduce the preference for AS over S; conversely, exposure to S did not extinguish the preference for AS over S but did reduce the preference for A over W. These results indicate that flavor preferences can be resistant to extinction procedures but suggest that the expression of such preferences in choice tests depends on an adaptation-level process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)