Learning-induced plasticity in the medial geniculate nucleus is expressed during paradoxical sleep.

Fear conditioning to an acoustic stimulus produces increases in tone-evoked discharges of neurons in the medial division of the medial geniculate nucleus (MG). This study examined the responses of MG neurons to a conditioned tone presented in paradoxical sleep (PS). After 1 session of habituation to a tone, awake rats underwent conditioning in 3 sessions during which the tone was used as the CS preceding a footshock. Control rats received unpaired presentations of tone and shock. The same tone, which never awakened the animal, was presented during PS following each daily session. Responses of MG neurons to the tone in PS were increased after conditioning. This enhancement was as large as that in waking and was manifested earlier after tone onset than in waking. No change appeared after pseudoconditioning. These results demonstrate that associatively induced plasticity in the MG can be expressed during PS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Appetitive conditioning-induced plasticity is expressed during paradoxical sleep in the medial geniculate, but not in the lateral amygdala.

This study examined whether neurons in the medial division of the medial geniculate (MGm) and the dorsal part of the lateral amygdala (LAd) express learning-induced plasticity in paradoxical sleep (PS) after appetitive conditioning, as they do in PS after fear conditioning. Rats received tone-food pairings in 3 sessions. After each session, the tone was presented at a nonawakening intensity during PS. Multiunit activity was simultaneously recorded in MGm and LAd. During waking, increases in tone-evoked discharges developed in MGm and LAd; however, as training continued, they lessened in LAd, but not in MGm. During PS, conditioned tone responses were expressed in MGm, but not in LAd. Thus, these results demonstrate dissociation of MGm and LAd plasticity. Moreover, compared with fear conditioning results, they suggest that expression of amygdalar plasticity in PS depends on the emotional salience of the stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuronal plasticity induced by fear conditioning is expressed during paradoxical sleep: Evidence from simultaneous recordings in the lateral amygdala and the medial geniculate in rats.

The lateral amygdala (LA) and its afferent connections from the medial geniculate (MG) play a pivotal role in auditory fear conditioning. The authors evaluated whether those neurons could express in paradoxical sleep (PS) physiological plasticity acquired in waking. After a habituation session, rats received tone–footshock pairings in 3 sessions. After each session, the tone alone was presented during PS episodes. Multiunit activity was simultaneously recorded in the LA and the medial part of the MG. Both in LA and MG, conditioned responses emerged rapidly (within 5 trials), were expressed with short latency (     

Avoidance learning in rats: Genetic evidence for two distinct behavioral processes in the shuttle box.

Used an 8 * 8 diallel cross of rats (Roman high, low, and control avoidance; Maudsley reactive and nonreactive; Tryon maze bright and dull; and Wistar albino) to analyze sequentially a conditioned avoidance response (CAR) within a session of 30 trials. On early conditioning trials, the F1 hybrids scored fewer avoidances than the parental strains, whereas on later trials the hybrids were superior to parents. This finding was confirmed within a session of 100 trials in a 3 * 3 diallel and interpreted to mean that 2 distinct adaptive behavior patterns underlie shuttle-box CAR acquisition in rats. There appears to be a tendency to develop an adaptive inactivity or "freezing" behavior pattern and later, as conditioning proceeds, to develop an equally adaptive but more active behavior pattern of "fleeing." Implications for 2-process theories of avoidance conditioning are considered briefly. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining intracranial self-stimulation ameliorates the detrimental effects of parafascicular thalamic lesions on active avoidance in young and aged rats.

To evaluate whether intracranial self-stimulation (SS) ameliorates conditioning deficits induced by parafascicular nucleus (PF) damage in young and aged rats, the authors gave rats a daily session of 2-way active avoidance until a fixed criterion was achieved. Four experimental groups were established in both young and aged rats: SS treatment after every conditioning session (SS groups), pretraining PF lesions (lesion groups), PF lesions and SS treatment (L + SS groups), and controls. SS treatment not only canceled the detrimental effects of PF lesions, but also improved conditioning in lesioned rats (L + SS groups). This effect was more powerful in aged rats. SS treatment compensated for memory deficits generated by hypofunctionality of arousal systems such as that involving the PF. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining paradoxical sleep in rats is increased after spatial learning in the Morris water maze.

The role of posttraining paradoxical sleep (PS) in spatial or nonspatial learning in the Morris water maze was evaluated. Sprague-Dawley rats were given a 12-trial training session in either the hidden or the visible platform versions of the task. Subgroups then underwent paradoxical sleep deprivation (PSD) beginning at different times after training. Rats with PSD imposed from 14 hr after spatial training had poorer retest scores than any other group. Other rats, implanted with electrodes to permit continuous recording of sleep electroencephalography, were found to undergo a prolonged period of elevated PS after spatial training. By contrast, rats trained in the nonspatial version of the water maze task did not show retention deficits after PSD or elevated PS after training. These results support a role for PS in spatial, but not nonspatial, learning in the Morris water maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term memory facilitation in rats by posttraining epinephrine.

Effects of posttraining epinephrine (EPI) on retention of a massed (1 session, 30 trials) 2-way active avoidance task in rats were studied. The rats received an injection of 0.05 mg/kg EPI, 0.01 mg/kg EPI, or distilled water immediately after the training session. EPI did not improve retention 24 hrs after the training session (Exp 1) but enhanced retention 20 days after the training session (Exp 2). The group receiving the smaller dose of EPI had better retention than the group receiving the larger dose, indicating dose dependency. The authors suggest that the process of consolidation of massed 2-way active avoidance conditioning is long and elaborative. Posttraining EPI would facilitate this active process of consolidation, improving performance as consolidation goes on. This facilitation needs, at least under certain conditions, more than 24 hrs to be expressed as a higher level of performance on the retention test. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned irrelevance: No more than the sum of CS and US preexposure effects?

In the 1st experiment, 1 group of rats (Group Learned Irrelevance [LIRR]) experienced uncorrelated presentations of a noise and shock; a 2nd group (Group Control [CON]) experienced noise and shock in separate phases of training. Six conditioning sessions followed, each consisting of a single noise-shock pairing. Group LIRR conditioned to the noise more quickly than Group CON. The 2nd experiment was identical to the 1st, except that rats were given 6 noise-shock pairings in each conditioning session. In this experiment, Group LIRR learned more slowly than Group CON. These results suggest that learned irrelevance is in part the product of context specificity of latent inhibition, in which the context is the aftereffect of shock presentation. The implications of this for theories of learned irrelevance are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of hippocampal NMDA receptors in retention of shuttle avoidance conditioning in rats

The purpose of this research was to evaluate the role of hippocampal N-methyl-D-aspartate (NMDA) receptors in acquisition and consolidation of memory during shuttle avoidance conditioning in rats. Adult male Wistar rats were surgically implanted with cannulae aimed at the CA1 area of the dorsal hippocampus. After recovery from surgery, animals were trained and tested in a shuttle avoidance apparatus (30 trials, 0.5-mA footshock, 24-h training-test interval). Immediately before or immediately after training, animals received a bilateral intrahippocampal 0.5-microliter infusion containing 5.0 microgram of the NMDA competitive receptor antagonist aminophosphonopentanoic acid (AP5) or vehicle (phosphate-buffered saline, pH 7.4). Infusion duration was 2 min per side. Pre-training infusion of AP5 impaired retention test performance (mean +/- SEM number of conditioned responses (CRs) during retention test session was 16.47 +/- 1.78 in the vehicle group and 9.93 +/- 1.59 in the AP5 group; P < 0.05). Post-training infusion of AP5 did not affect retention (mean +/- SEM number of conditioned responses during retention test session was 18.46 +/- 1.94 in the vehicle group and 20.42 +/- 2.38 in the AP5 group; P > 0.10). This impairment could not be attributed to an effect on acquisition, motor activity or footshock sensitivity since AP5 affected neither training session performance measured by the number of CRs nor the number of intertrial crossings during the training session. These data suggest that NMDA receptors in the hippocampus are critical for retention of shuttle avoidance conditioning, in agreement with previous evidence showing a role of NMDA receptors in fear memory.     

Fear-potentiated startle conditioning to explicit and contextual cues in Gulf War veterans with posttraumatic stress disorder.

Aversive conditioning to explicit and contextual cues was examined in Gulf War veterans with and without posttraumatic stress disorder (PTSD) by use of the startle reflex methodology. Veterans participated in a differential aversive conditioning experiment consisting of 2 sessions separated by 4 or 5 days. Each session comprised two startle habituation periods, a preconditioning phase, a conditioning phase, and a postconditioning extinction test. In contrast to the non-PTSD group, the PTSD group showed a lack of differential startle response in the presence of a conditioned stimulus with or without an unconditioned stimulus in Session 1 and an increase in the baseline startle response during Session 2. The PTSD group also exhibited normal differential conditioning following reconditioning in Session 2. These data suggest that individuals with PTSD tend to generalize fear across stimuli and are sensitized by stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dihydropyridine Ca2+ channel antagonists inhibit the salvage pathway for DNA synthesis in human vascular smooth muscle cells

Using electroencephalographic methods, rats learning or not learning a two-way active avoidance task were found to differ significantly in the structure of sleep determined the day before training. The main differences concerned (i) synchronized sleep episodes followed by wakefulness, which were longer and fewer in learning rats; (ii) paradoxical sleep episodes, which were longer in learning rats. Significant correlations were present between the number and/or the average duration of synchronized sleep episodes followed by wakefulness or by paradoxical sleep and the number of avoidances or escapes scored in the training session. Power spectral analysis indicated that the relative output in the 6-7-Hz region was higher in learning rats, notably during short episodes of synchronized sleep followed by paradoxical sleep. As two-way active avoidance training induces comparable modifications in postacquisition sleep (Ambrosini et al., Physiol. Behav., 51, 217-226, 1992), the features of preacquisition sleep which prevail in learning rats might directly determine their capacity to learn. Alternatively, they might reflect the existence of a genetic determinant independently conditioning the ability to learn.     

Effects of lesions to the hippocampus on contextual fear: Evidence for a disruption of freezing and avoidance behavior but not context conditioning.

The effects of ibotenic lesions of the hippocampus on conditioning to contextual cues during classical fear conditioning in rats were evaluated by (a) the amount of freezing elicited by contextual cues and (b) the relative avoidance of a shock compartment. In Experiment 1, lesions to the hippocampus had no effect on contextual freezing and marginally affected avoidance after repeated sessions. Experiment 2 showed that lesions to the hippocampus disrupted avoidance when tested after a single conditioning session, while leaving unaffected the acquisition of contextual freezing. Experiment 3 indicated that these lesions decreased the acquisition of contextual freezing when higher footshock intensity was used but had no effect on avoidance after repeated conditioning sessions. These results show that freezing and avoidance do not quantify context conditioning similarly. They further indicate that lesions to the hippocampus may disrupt the expression of these behaviors used as measures of context conditioning but not the acquisition of context conditioning per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shuttle-box memory facilitation by posttraining intracranial self-stimulation: Differential effects in rats with high and low basic conditioning levels.

The effects of intracranial self-stimulation (ICSS) on retention (after 24 hr, 7, 15, or 60 days) of a massed 2-way active avoidance task were studied in independent groups of rats. All groups showed a higher performance on the retention session than on the acquisition one. In the control subjects. the higher retention performances were observed in the 7- and 15-day groups. However, the ICSS treatment facilitated the 24-hr retention compared with its control group, allowing the treated subjects to achieve the same level of performance on the 24-hr retention session than that achieved by the control rats at the 7-day retention test. In the 24-hr groups, the facilitatory ICSS effect was stronger in the subjects with a low level of conditioning and weaker in those with a high level. Results suggest that posttraining ICSS accelerates memory consolidation and equalizes the performance of poor and good learners. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relations between behavioral arousal and plasma cortisol levels in monkeys performing repeated free-operant avoidance sessions.

The hypothesis that increases in adrenocorticoid levels sensitively reflect behavioral arousal was tested by subjecting 8 adult male rhesus monkeys to repeated sessions of free-operant avoidance; these sessions produced varying degrees of behavioral arousal over time, which were quantified by a behavioral scoring technique. Cortisol was reliably elevated only in the most aroused Ss early in the 1st avoidance session. Although Ss were still aroused later in the session, cortisol had returned to basal levels. During subsequent avoidance sessions, cortisol returned to basal levels and did not increase significantly even when arousal was further manipulated by the superimposition of unavoidable shock during the final avoidance session. The addition of unavoidable shock was associated with a significant correlation between arousal, as reflected by increases in response rate, and magnitude of change, usually decreases, in mean cortisol levels. The frequent occurrences of dissociations between cortisol levels and behavioral arousal, as reflected by behavioral score, operant rate, and shock frequency, indicated that cortisol levels are of little use as a neuroendocrine index of arousal. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fear conditioning-induced plasticity in auditory thalamus and cortex: To what extent is it expressed during slow-wave sleep?

After fear conditioning to a tone, rats received nonawakening presentations of the tone alone during slow-wave sleep (SWS) episodes. Multiunit activity was recorded in the medial part of the medial geniculate (MGm) and in the primary auditory cortex (ACx). Although tone-evoked responses were increased in MGm and ACx during the 3 conditioning sessions, group data failed to show any significant changes during SWS. Nonetheless, the few recordings (5/29) that exhibited the strongest conditioned responses during wakefulness expressed enhanced responding during SWS. Compared with previous data obtained in MGm during paradoxical sleep, associative plastic changes were less easily expressed during SWS. These results are discussed with regard to functional changes that occur in the thalamocortical system across vigilance states. (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)     

Functional dissociation within the caudate nucleus of rats.

Reports results of 3 experiments with a total of 134 male albino rats. Ss with posteroventral caudate nucleus lesions were impaired, relative to controls, on 1-way, 2-way, and passive avoidance conditioning; anterodorsal caudate lesions interfered only with 2-way and passive avoidance learning. The anterodorsal group was significantly more impaired than the posteroventral group on the 2-way task, and there were also important differences in passive avoidance learning. Enhancement of positive and negative cues in a 2-way avoidance task selectively benefited the anterodorsal group. It is concluded that the caudate nucleus was functionally dissociated with respect to avoidance conditioning. The importance of the caudate nucleus in motor control and spatial orientation is discussed. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The generation and maintenance of schedule-induced polydipsia in normal male rats without weight reduction

Experiment One demonstrated that two normal male Sprague-Dawley rats (approximately 60 days old) with free access to food and two control rats whose weights were held constant by dietary restriction acquired schedule-induced polydipsia (SIP) in daily 33-35 min sessions of fixed-time 60-s food delivery. Three of the rats showed rapid acquisition of SIP; the fourth acquired SIP more slowly and consumed less per session the other three rats. After a 36-40 day period without sessions, the constant-weight rats showed a 37% decrease in overall consumption due to reduced drinking bout length. The SIP of the free-feeding rats was not affected by the interruption. After 90-100 periodic food delivery sessions, all subjects consumed an average of 11.2-12.2 mL per session compared with 1.8-4.8 mL per session in baseline sessions with massed food presentations. Experiment Two replicated the acquisition phase of Experiment One using two non-weight-reduced rats of the age and size of those typically used in SIP studies (approximately 30 weeks old). Both acquired SIP, although one showed only a small average increase in consumption per session over baseline (2.8 mL/session under periodic food vs. 0.8 mL following massed-food presentations). Before weight reduction, the stronger drinker consumed approximately 8.8 mL per session compared with an average of 0.6 mL per session in baseline. After weight reduction, both exhibited strong SIP (18-19 mL per session in the final five sessions). This study demonstrates that weight reduction is not a necessary condition for the generation and maintenance of SIP in rats.     

Characterization of transition sleep episodes in baseline EEG recordings of adult rats

By scoring 5-s EEG epochs and calculating spectral power of consecutive EEG segments as short as 1-s, transition sleep (TS) episodes were identified in baseline recordings of adult rats. TS episodes were characterized by the abrupt appearance of theta and alpha waves within an ongoing period of slow-wave sleep (SS). They were followed by paradoxical sleep (PS) or, somewhat more frequently, by a period of wakefulness (W) that often led to an additional SS. Statistical values of the main variables of TS-->(W) and TS-->(PS) episodes are presented, together with comparable data concerning previous SS and following W or PS episodes. On the whole, TS episodes were more numerous than PS episodes, and less numerous than SS episodes. Their average duration was considerably shorter. As a consequence of the identification of TS and of brief W or PS epochs intervening within SS, the number of SS episodes was estimated to be considerably higher than previously assessed, and their average duration considerably shorter.     

Effects on avoidance performance of vagal stimulation during previous fear conditioning in rats.

Attempted to determine, from experiments on 5 groups of 10 male albino rats each, whether parasympathetic stimulation given coincidentally with electric shock in a fear-conditioning situation would alter later performance on an avoidance conditioning task. 10 Ss were implanted with a small chronic electrode around the cervical vagus. During preconditioning, consisting of 8 trials of tone followed by inescapable shock, 1 group of Ss received stimulation of the vagus at the time foot shock was delivered. During subsequent avoidance conditioning, these Ss performed the avoidance task significantly better than Ss that received the same preconditioning without vagal stimulation and as well as Ss that had received no preconditioning shock trials. (PsycINFO Database Record (c) 2010 APA, all rights reserved)