Posttrial corticosterone administration enhances the effects of incentive downshift: Exploring the boundaries of this effect.

Posttrial administration of corticosterone was previously shown to enhance consummatory successive negative contrast (cSNC) in rats. The present series of experiments provides additional information that helps determine the boundaries of this effect. Posttrial corticosterone administration (1) enhances cSNC when rats experience a large downshift (32% to 4% sucrose), but not after a small downshift (8% to 4% sucrose; Experiment 1); (2) has no effect in an anticipatory negative contrast situation in which 4% sucrose precedes 32% sucrose in daily trials (Experiment 2); (3) does not support the development of a conditioned taste aversion to 4% sucrose, in the absence of an incentive downshift (Experiment 3); and (4) facilitates the extinction of consummatory behavior (Experiment 4). These results suggest that corticosterone facilitates the encoding of an egocentric aversive memory of the incentive downshift experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Insular cortex and consummatory successive negative contrast in the rat.

Rats that are expecting a high value reward (e.g., 1.0 M sucrose) show an exaggerated underresponding when they are instead given a low value reward (e.g., 0.15% saccharin), an effect termed successive negative contrast (SNC). In the present experiment, insular cortex-lesioned (ICX) rats showed normal responsivity to sucrose and saccharin prior to the reward downshift. However, when switched from sucrose to saccharin during the postshift trials these rats displayed no evidence of SNC. Indeed, over the downshift trials these ICX rats consistently drank more saccharin than the ICX rats maintained on saccharin throughout the experiment. Potential interpretations are discussed including a lesion-induced impairment in the ability to accurately recognize the novelty of the postshift saccharin stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions eliminate successive negative contrast in rats: Evidence against a memory deficit.

Successive negative contrast is the exaggerated reduction of licking that occurs when rats expecting a high-value reward are given a low-value reward. This effect is typically investigated with a 24-hr retention interval between access periods. The present experiment tested the hypothesis that the absence of successive negative contrast in rats with bilateral lesions of the gustatory thalamus (GT) is due to a memory deficit. The results argue against this hypothesis by showing that, irrespective of retention-interval duration (7.5 min, 15 min, 45 min, 180 min, or 24 hr), lesioned rats failed to show successive negative contrast. As such, the data are consistent with the alternative view that GT lesions specifically disrupt the reward comparison mechanism that underlies successive negative contrast. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of corticosterone in trace and delay conditioned fear-potentiated startle in rats.

Emotional events often lead to particularly strong memory formation. Corticosterone, the final product of hypothalamic-pituitary-adrenal (HPA)-axis activation, has been suggested to play a critical role in this effect. Although a great deal of work has implicated the amygdala as a necessary structure for the effects of corticosterone, other studies have suggested a critical role for the hippocampus in determining the involvement of corticosterone. The current experiments examined this question by disrupting corticosterone synthesis with administration of metyrapone (25 or 100 mg/kg) prior to training in either dorsal hippocampus-independent delay fear conditioning or dorsal hippocampus-dependent trace fear conditioning. Metyrapone administration 2 hrs prior to training significantly attenuated corticosterone secretion during training, but these effects were transient as corticosterone levels were similar to control subjects following the test session. As hypothesized, only trace fear conditioning was impaired. This suggests that only fear conditioning tasks that are dependent on the dorsal hippocampus require HPA-axis activation in order to be learned. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigating the devaluation explanation for negative anticipatory contrast.

This study addressed whether negative anticipatory contrast results in a decrease in the value of the low-valued substance. Rats responded in training conditions designed to produce negative contrast. They then responded in test sessions in which the low-valued substance from the training sessions was the reinforcer for an operant response. Despite the finding of contrast in the training conditions, the low-valued substance was a more effective reinforcer early in testing after training conditions in which it had been followed by access to the high-valued substance than after training conditions in which it had not. The findings question the devaluation explanation for contrast but may be similar to other findings of reversals of "preference." (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effect of unconditioned stimulus magnitude on the emergence of conditioned responding.

Although unconditioned stimulus (US) magnitude influences conditioning, no experiment has addressed whether it influences a decision point at which the organism first responds (Gallistel & Gibbon, 2000). Two appetitive conditioning experiments with rats confirmed that the rate of food cup entries and proportion of head jerking were related to the number of pellets (US) provided after the conditioned stimulus. In addition, the onset of responding measured by the number of reinforcers to a criterion or by a quantitatively identified change point also reflected US magnitude. Two aversive conditioning experiments also found that the amount and onset of freezing were related to footshock intensity. All experiments identified a trial at which responding increased abruptly in individual subjects. However, the point where the increase occurred was earlier with larger USs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gender differences in the negative affective priming of aggressive behavior.

The negative affective priming of aggression was examined across different aversive contexts (general stress exposure and frustration) with a laboratory aggression paradigm that measured the intensity of shocks participants delivered to a putative employee. Participants' emotional responses were gauged via startle eyeblink reactions and self-report mood ratings. Aside from gender differences in overall aggression, men but not women exposed to general stress showed significant increases in aggression across blocks. However, frustration produced increases in aggression in both genders. Although both genders showed robust startle increases during stress, startle activation was related to increases in aggression in men and decreases in aggression in women. These findings suggest that general stress and experiences of negative emotion trigger physical aggressive responses more strongly in men than in women. (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     

Analysis of the content of configural representations: The role of associatively evoked and trace memories.

Two experiments examined the content of configural learning in rats. In Experiment 1, after simple pre-exposure to two hybrid contexts (AB and CD), rats acquired a configural discrimination involving two of the contexts (A and C) and two auditory stimuli (X and Y; AX→food, AY→no food, CX→no food, and CY→food). When rats were then placed in context B, they were more likely to respond to X than Y, and when they were placed in context D the reverse was the case. Experiment 2 demonstrated that rats can acquire a configural discrimination involving the presence of context (A) and its memory trace (a; AX→food, AY→no food, aX→no food, and aY→food). These results show that associatively provoked memories (Experiment 1) and memory traces (Experiment 2) can participate in configural discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive task performance after lidocaine-induced inactivation of different sites within the basolateral amygdala and dorsal striatum.

To determine whether discrete components of amygdaloid and striatal memory systems could interact to guide behavior in a radial arm maze, conditioned cue preference (CCP) and win–stay accuracy were examined after lidocaine inactivation of either the rostral (rBLA) or caudal (cBLA) basolateral amygdala, the lateral (1DST) or medial (mDST) dorsal striatum, or a control site in rats. CCP expression was blocked only after rBLA or cBLA inactivation. IDST inactivation prevented attainment of criteria win–stay performance, whereas rBLA and mDST inactivation delayed it. Control site inactivation did not influence performance in either task. These findings suggest that the amygdala works independently of other memory systems to regulate learned responses in the CCP task, the rBLA may work cooperatively with the 1DST to guide behavior in the win–stay task, and the mDST is less critical than the 1DST for attaining criteria performance in the win-stay task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temperature and activity responses to sucrose concentration reductions occur on the 1st but not the 2nd day of concentration shifts, and are blocked by low, constant glucocorticoids.

Previous findings (N. Pecoraro, J. Chou-Green, & M. F. Dallman, 2003; N. Pecoraro & M. F. Dallman, 2005) indicated that unexpected reductions in sucrose concentration in once daily meals result in a febrile response on the 1st, but not the 2nd day of a concentration shift. This study shows that this day-specific fever is blocked by adrenalectomy accompanied by constant low corticosterone replacement. Rats implanted with telemetry probes were adrenalectomized and given low-corticosterone pellets or were sham operated. Food-restricted rats were given 2 rounds of sucrose concentration downshifts, as follows: 32% sucrose (14 days), 4% sucrose (6 days), 32% sucrose (4 days), and 4% sucrose (4 days). Intact rats showed more pronounced anticipation of the sucrose than did rats having low, clamped corticosterone. Only intact rats showed a 4-hr, postshift temperature burst on the 1st, but not the 2nd day of the shift to 4% sucrose, during both rounds of shifting. Increased activity accompanied the fever. These data confirm previous findings, show them to be dependent on high corticosterone, and appear to be related to a host of day-specific alterations in other motor outflows following unexpected downward shifts in palatable sucrose concentrations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The bed nucleus of the stria terminalis is critically involved in enhancing associative learning after stressful experience.

Exposure to an acute stressful event enhances trace eyeblink conditioning in male rats, even when rats begin training days after the stressor (Shors, 2001). The authors examined whether the bed nucleus of the stria terminalis (BNST), an area involved in stress and anxiety, is critically involved in this effect and, if so, when. The authors found that excitotoxic lesions to the BNST prevented the enhanced conditioning after stressor exposure. In addition, temporary inactivation of the BNST during the stressor did not alter enhanced responding, whereas inactivation during training prevented the enhancement. These data indicate that stressful experience induces persistent changes in the BNST that are necessary for enhancing learning well after the stressful event has ceased. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption of Pavlovian contextual conditioning by excitotoxic lesions of the nucleus accumbens core.

Nucleus accumbens (NAcc) core lesions were performed either before or after Pavlovian aversive conditioning. NAcc core lesions had no effect on discrete-cue or contextual conditioned freezing during acquisition. During retention testing, neither pre- nor posttraining lesions had any effect on conditioned freezing to the discrete cue. However, pretraining lesions resulted in a profound impairment of contextual conditioned freezing in a retention test, and posttraining lesions resulted in a smaller impairment. NAcc core lesions had no effect on sensory or motor processes, as measured by shock reactivity and spontaneous locomotor activity. These results suggest that during acquisition, processes independent of the NAcc core mediate contextual conditioned freezing, but that the NAcc is implicated in the retention of this aversive memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perinatal inhibition of aromatization enhances the reward value of sex.

Paced mating reduces the aversive properties and increases the positive characteristics of mating, inducing a reward state. Pacing is able to induce conditioned place preference (CPP), whereas nonpaced mating does not. The authors hypothesized that the aversive properties of mating are caused by androgens from adjacent males or from the mother during fetal life. To test whether aromatization of androgens induces the aversive properties of mating, female rats were treated perinatally with 1,4,6-androstatriene-3, 17-dione (ATD) to inhibit aromatization. When adults, these females were ovariectomized and hormonally primed to evaluate CPP after paced and nonpaced mating. During paced mating, control females showed higher return latencies after ejaculation, whereas ATD-treated females did not show a similar increase. In CPP tests, both paced and nonpaced mating induced a reward state in ATD-treated females, whereas only paced mating induced a reward state in control females. These results show that the perinatal inhibition of aromatization enhances the rewarding properties of mating, suggesting that estradiol induced the aversive properties of mating and/or modified the perinatal organization of the neuronal pathways in females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term retention of the classically conditioned eyeblink response in rats.

Retention of the classically conditioned eyeblink response in rats was tested with a conditioned stimulus (CS)-alone extinction test and 2 sessions of reacquisition training. Retention of the eyeblink conditioned response (CR) during both tests was highest 24 hrs and 1 mo after initial acquisition. Three months after initial acquisition, responding during the CS-alone test was at baseline, but there was significant savings during reacquisition. By 6 mo after initial acquisition, the memory for the eyeblink CR was not expressed in either test. The group differences in retention, despite initial acquisition of the eyeblink CR to equal levels, suggest that rat eyeblink conditioning may provide a useful behavioral model for studying the neural processes underlying memory retention and loss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of the retrosplenial and posterior parietal cortices to cue-specific and contextual fear conditioning.

The retrosplenial cortex (RSP) and the posterior parietal cortex (PPC) are the primary sources of cortical sensory input to the postrhinal cortex (POR) in rodents. Together, these areas compose a major corticohippocampal circuit that is involved in processing visuospatial information. The POR has been implicated in contextual learning and memory, consistent with the type of information presumably being processed by this region. By comparison, little is known about the role of the RSP or the PPC in contextual learning. In the present study, rats were trained either before or after surgery in a standard signaled fear conditioning task in which an auditory cue was paired with foot shock. Contextual fear and tone-specific fear were assessed in subsequent test sessions. In Experiment 1, electrolytic damage to the RSP either before or immediately after training impaired the expression of contextual fear but not tone-specific fear. In contrast, electrolytic damage to the PPC had no effect on conditional fear to the context or the tone in Experiment 2. These findings indicate that the RSP, but not the PPC, contributes to the processing of contextual information by the POR corticohippocampal processing stream. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Boosting cholinergic activity in gustatory cortex enhances the salience of a familiar conditioned stimulus in taste aversion learning.

The cholinergic system is important for learning, memory, and responses to novel stimuli. Exposure to novel, but not familiar, tastes increases extracellular acetylcholine (ACh) levels in insular cortex (IC). To further examine whether cholinergic activation is a critical signal of taste novelty, in these studies carbachol, a direct cholinergic agonist, was infused into IC before conditioned taste aversion (CTA) training with a familiar taste. By mimicking the cholinergic activation generated by novel taste exposure, it was hypothesized that a familiar taste would be treated as novel and therefore a salient target for aversion learning. As predicted, rats infused with the agonist were able to acquire CTAs to familiar saccharin. Effects of carbachol infusion on patterns of neuronal activation during conditioned stimulus–unconditioned stimulus pairing were assessed using Fos-like immunoreactivity (FLI). Familiar taste–illness pairing following carbachol, but not vehicle, induced significant elevations of FLI in amygdala, a region with reciprocal connections to IC that is also important for CTA learning. These results support the view that IC ACh activity provides a critical signal of taste novelty that facilitates CTA acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pretraining NMDA receptor blockade in the basolateral complex, but not the central nucleus, of the amygdala prevents savings of the conditional fear.

The acquisition of conditional freezing is abolished by N-methyl-D-aspartate (NMDA) receptor antagonism in the basolateral complex of the amygdala (BLA) during fear conditioning, suggesting that memory formation is prevented. The present study examined whether there is residual memory, or "savings," for fear conditioning in rats trained under amygdaloid NMDA receptor blockade. Rats infused with D,L-2-amino-5-phosphonovalerate (APV) into the BLA or central nucleus of the amygdala (CEA) during fear conditioning did not acquire either auditory or contextual fear conditioning. However, savings of conditional fear was exhibited by rats infused with APV into the CEA but not the BLA. These results suggest that both the BLA and CEA play a critical role in the acquisition of conditional fear but that the BLA is able to process and retain some aspects of aversive memories in the absence of the CEA. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Administration of a Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor prevents the learning deficit observed in spinal rats after noncontingent shock administration.

Research has shown that spinal rats given shock to the hind leg when it is in an extended position (contingent shock) will learn to maintain a flexion response. However, subjects that experience shock irrespective of leg position (noncontingent shock) do not exhibit this learning. The current studies examined the role of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in this learning deficit. Subjects were given intrathecal injections of CaMKII inhibitor solution or artificial cerebrospinal fluid (aCSF) 15 min prior to and immediately or 4 hr following noncontingent shock training. Results demonstrate that the CaMKII inhibitor successfully reversed the learning deficit when injected prior to and immediately following training. These results indicate the importance of CaMKII in the learning deficit present in spinal animals trained with noncontingent shock. (PsycINFO Database Record (c) 2010 APA, all rights reserved)