Lesions of the basolateral, but not central, amygdala impair flavour-taste learning based on fructose or quinine reinforcers

Examining affective structure in chickens: valence, intensity, persistence and generalization measured using a Conditioned Place Preference Test

When measuring animals' valenced behavioural responses to stimuli, the Conditioned Place Preference (CPP) test goes a step further than many approach-based and avoidance-based tests by establishing whether a learned preference for, or aversion to, the location in which the stimulus was encountered can be generated. We designed a novel, four-chambered CPP test to extend the capability of the usual CPP paradigm to provide information on four key features of animals' affective responses: valence, scale, persistence and generalization. Using this test, we investigated the affective responses of domestic chickens (Gallus gallus domesticus) to four potentially aversive stimuli: 1. Puffs of air; 2. Sight of (robotic) snake; 3. Sprays of water; 4. Sound of conspecific alarm calls. We found conditioned avoidance of locations associated with the air puffs and water sprays (Friedman's χ2 (3) = 13.323 p > .005; χ2 (3) = 14.235 p > .005), but not with the snake and alarm calls. The scale of the learned avoidance was similar for the air puff and water spray stimuli, but persistence and generalization differed. We conclude that the four chambered CPP test can have a valuable role to play in making multi-feature measurements of stimulus-generated affective responses, and we highlight the value of such measurements for improving our understanding of the structure of affect in chickens and other animals.

Conditioned flavor preferences in animals: Merging pharmacology, brain sites and genetic variance

The elucidation of the behavioral, neurochemical, neuroanatomical and genetic substrates mediating the development of conditioned flavor preferences (CFP) is one of the multi-faceted scientific contributions that Dr. Anthony Sclafani has made to the study of food intake. This review summarizes the results of thirty-five publications over nearly twenty years of collaborations between the Sclafani and Bodnar laboratories. This includes the different approaches employed to study the orosensory (flavor-flavor) and post-ingestive (flavor-nutrient) processes underlying CFP including its acquisition (learning) and expression. It describes how CFP is elicited by different sugars (sucrose, glucose, fructose) and fats (corn oil) in rats, and how strain-specific CFP effects can be observed through the use of inbred mouse strains to evaluate genetic variance. The roles of pharmacological substrates (dopamine, glutamate, opioids, acetylcholine, GABA, cannabinoids) mediating sugar- and fat-CFP acquisition and expression are elucidated. Finally, neuroanatomical sites of action (nucleus accumbens, amygdala, medial prefrontal and orbital frontal cortices, lateral hypothalamus) are evaluated at which dopamine signaling mediates acquisition and expression of different forms of CFP.

Modulation of the magnitude of conditioned taste aversion in rats with excitotoxic lesions of the basolateral amygdala

The amygdala is one of the structures involved in the acquisition of conditioned taste aversion (CTA). Nevertheless, the specific roles that the nuclei of this structure play in CTA learning are controversial. Electrolytic lesions applied to the basolateral nucleus of the amygdala can eliminate or reduce the acquisition of this learning. This effect has been attributed to the involvement of fibers that pass through this nucleus and connect with other structures that are critical for CTA. Excitotoxic lesions may allow a clearer insight as to the potential involvement of this nucleus in the acquisition of CTA. The few studies to date that have used this paradigm have shown effects on taste aversion learning after applying extensive lesions to the amygdala. Thus, the aim of the present study was to determine the effect of selective excitotoxic lesions of the basolateral amygdala on the acquisition of CTA. The effects of these lesions on learning were compared with the effects observed in animals with sham lesions and animals with lesions of the hippocampus, which is a structure apparently not involved in CTA. The results revealed a decreased aversion in animals with basolateral lesions compared with both the sham and hippocampus-lesioned groups. Based on these findings, the role of this specific nucleus of the amygdala in the acquisition of taste aversion is briefly discussed.

The basolateral nucleus of the amygdala mediates caloric sugar preference over a non-caloric sweetener in mice

Neurobiological and genetic mechanisms underlying increased intake of and preference for nutritive sugars over non-nutritive sweeteners are not fully understood. We examined the roles of subnuclei of the amygdala in the shift in preference for a nutritive sugar. Food-deprived mice alternately received caloric sucrose (1.0 M) on odd-numbered training days and a non-caloric artificial sweetener (2.5 mM saccharin) on even-numbered training days. During training, mice with sham lesions of the basolateral (BLA) or central (CeA) nucleus of the amygdala increased their intake of 1.0 M sucrose, but not saccharin. Trained mice with sham lesions showed a significant shift in preference toward less concentrated sucrose (0.075 M) over the saccharin in a two-bottle choice test, although the mice showed an equivalent preference for these sweeteners before training. No increased intake of or preference for sucrose before and after the alternating training was observed in non-food-deprived mice. Excitotoxic lesions centered in the BLA impaired the increase in 1.0M sucrose intake and shift in preference toward 0.075 M sucrose over saccharin. Microlesions with iontophoretic excitotoxin injections into the CeA did not block the training-dependent changes. These results suggest that food-deprived animals selectively shift their preference for a caloric sugar over a non-caloric sweetener through the alternate consumption of caloric and non-caloric sweet substances. The present data also suggest that the BLA, but not CeA, plays a role in the selective shift in sweetener preference.

Orexin-1 receptor antagonist in central nucleus of the amygdala attenuates the acquisition of flavor-taste preference in rats

Previous studies demonstrated that the intracerebroventricular administration of SB-334867-A, a selective antagonist of orexin OX1R receptors, blocks the acquisition of saccharin-induced conditioned flavor preference (CFP) but not LiCl-induced taste aversion learning (TAL). Orexinergic fibers from the lateral hypothalamus end in the central nucleus of the amygdala (CeA), which expresses orexin OX1R receptors. Taste and sensory inputs also are present in CeA, which may contribute to the development of taste learning. This study analyzed the effect of two doses (1.5 and 6μg/0.5μl) of SB-334867-A administered into the CeA on flavor-taste preference induced by saccharin and on TAL induced by a single administration of LiCl (0.15M, 20ml/kg, i.p.). Outcomes indicate that inactivation of orexinergic receptors in the CeA attenuates flavor-taste preference in a two-bottle test (saccharin vs. water). Intra-amygdalar SB-334867-A does not affect gustatory processing or the preference for the sweet taste of saccharin given that SB-334867-A- and DMSO-treated groups (control animals) increased the intake of the saccharin-associated flavor across training acquisition sessions. Furthermore, SB-334867-A in the CeA does not block TAL acquisition ruling out the possibility that functional inactivation of OX1R receptors interferes with taste processing. Orexin receptors in the CeA appear to intervene in the association of a flavor with orosensory stimuli, e.g., a sweet and pleasant taste, but could be unnecessary when the association is established with visceral stimuli, e.g., lithium chloride. These data suggest that orexinergic projections to the CeA may contribute to the reinforcing signals facilitating the acquisition of taste learning and the change in hedonic evaluation of the taste, which would have important implications for the OX1R-targeted pharmacological treatment of eating disorders.

Differential changes in amygdala and frontal cortex Pde10a expression during acute and protracted withdrawal

Alcohol use disorders are persistent problems with high recidivism rates despite repeated efforts to quit drinking. Neuroadaptations that result from alcohol exposure and that persist during periods of abstinence represent putative molecular determinants of the propensity to relapse. Previously we demonstrated a positive association between phosphodiesterase 10A (PDE10A) gene expression and elevations in relapse-like alcohol self-administration in rats with a history of stress exposure. Because alcohol withdrawal is characterized by heightened anxiety-like behavior, activation of stress-responsive brain regions and an elevated propensity to self-administer alcohol, we hypothesized that Pde10a expression also would be upregulated in reward- and stress-responsive brain regions during periods of acute (8-10 h) and protracted (6 weeks) alcohol withdrawal. During acute withdrawal, elevated Pde10a mRNA expression was found in the medial and basolateral amygdala (BLA), as well as the infralimbic and anterior cingulate subdivisions of the medial prefrontal cortex, relative to alcohol-naïve controls. The BLA was the only region with elevated Pde10a mRNA expression during both acute and protracted withdrawal. In contrast to the elevations, Pde10a mRNA levels tended to be reduced during protracted withdrawal in the dorsal striatum, prelimbic prefrontal cortex, and medial amygdala. Together these results implicate heightened PDE10A expression in the BLA as a lasting neuroadaptation associated with alcohol dependence.

The neurobiology of depression and antidepressant action

We present a comprehensive overview of the neurobiology of unipolar major depression and antidepressant drug action, integrating data from affective neuroscience, neuro- and psychopharmacology, neuroendocrinology, neuroanatomy, and molecular biology. We suggest that the problem of depression comprises three sub-problems: first episodes in people with low vulnerability ('simple' depressions), which are strongly stress-dependent; an increase in vulnerability and autonomy from stress that develops over episodes of depression (kindling); and factors that confer vulnerability to a first episode (a depressive diathesis). We describe key processes in the onset of a 'simple' depression and show that kindling and depressive diatheses reproduce many of the neurobiological features of depression. We also review the neurobiological mechanisms of antidepressant drug action, and show that resistance to antidepressant treatment is associated with genetic and other factors that are largely similar to those implicated in vulnerability to depression. We discuss the implications of these conclusions for the understanding and treatment of depression, and make some strategic recommendations for future research.

Differential involvement of the basolateral amygdala and orbitofrontal cortex in the formation of sensory-specific associations in conditioned flavor preference and magazine approach paradigms

Four experiments examined the roles of the basolateral amygdala and orbitofrontal cortex in the formation of sensory-specific associations in conditioned flavor preference and conditioned magazine approach paradigms using unconditioned stimulus (US) devaluation and selective Pavlovian-instrumental transfer procedures in Long Evans rats. Experiment 1 found that pre-training amygdala and orbitofrontal cortex lesions had no detectable effect on the formation or flexible use of sensory-specific flavor-nutrient associations in a US devaluation task, where flavor cues were paired either simultaneously or sequentially with nutrient rewards in water-deprived subjects. In Experiment 2, pre-training amygdala and orbitofrontal cortex lesions both attenuated outcome-specific Pavlovian-instrumental transfer. Experiment 3 indicated that amygdala lesions have no effect on the formation of sensory-specific flavor-nutrient associations in a US devaluation task in food-deprived subjects. Finally, Experiment 4 demonstrated that the outcomes used in Experiment 3 were sufficiently motivationally significant to support conditioned flavor preference. These findings suggest that, although both orbitofrontal cortex and amygdala lesions attenuate the acquisition of sensory-specific associations in magazine approach conditioning, neither lesion reduces the ability to appropriately respond to a flavor cue that was paired with a devalued outcome.