Impaired active avoidance learning in infant rats appears to be related to insufficient metabolic recruitment of the lateral septum

Imaging of Functional Brain Circuits during Acquisition and Memory Retrieval in an Aversive Feedback Learning Task: Single Photon Emission Computed Tomography of Regional Cerebral Blood Flow in Freely Behaving Rats

Active avoidance learning is a complex form of aversive feedback learning that in humans and other animals is essential for actively coping with unpleasant, aversive, or dangerous situations. Since the functional circuits involved in two-way avoidance (TWA) learning have not yet been entirely identified, the aim of this study was to obtain an overall picture of the brain circuits that are involved in active avoidance learning. In order to obtain a longitudinal assessment of activation patterns in the brain of freely behaving rats during different stages of learning, we applied single-photon emission computed tomography (SPECT). We were able to identify distinct prefrontal cortical, sensory, and limbic circuits that were specifically recruited during the acquisition and retrieval phases of the two-way avoidance learning task.

Comparing brain activity patterns during spontaneous exploratory and cue-instructed learning using single photon-emission computed tomography (SPECT) imaging of regional cerebral blood flow in freely behaving rats

Learning can be categorized into cue-instructed and spontaneous learning types; however, so far, there is no detailed comparative analysis of specific brain pathways involved in these learning types. The aim of this study was to compare brain activity patterns during these learning tasks using the in vivo imaging technique of single photon-emission computed tomography (SPECT) of regional cerebral blood flow (rCBF). During spontaneous exploratory learning, higher levels of rCBF compared to cue-instructed learning were observed in motor control regions, including specific subregions of the motor cortex and the striatum, as well as in regions of sensory pathways including olfactory, somatosensory, and visual modalities. In addition, elevated activity was found in limbic areas, including specific subregions of the hippocampal formation, the amygdala, and the insula. The main difference between the two learning paradigms analyzed in this study was the higher rCBF observed in prefrontal cortical regions during cue-instructed learning when compared to spontaneous learning. Higher rCBF during cue-instructed learning was also observed in the anterior insular cortex and in limbic areas, including the ectorhinal and entorhinal cortexes, subregions of the hippocampus, subnuclei of the amygdala, and the septum. Many of the rCBF changes showed hemispheric lateralization. Taken together, our study is the first to compare partly lateralized brain activity patterns during two different types of learning.

Infant avoidance training alters cellular activation patterns in prefronto-limbic circuits during adult avoidance learning: II. Cellular imaging of neurons expressing the activity-regulated cytoskeleton-associated protein (Arc/Arg3.1)

Positive and negative feedback learning is essential to optimize behavioral performance. We used the two-way active avoidance (TWA) task as an experimental paradigm for negative feedback learning with the aim to test the hypothesis that neuronal ensembles activate the activity-regulated cytoskeletal (Arc/Arg3.1) protein during different phases of avoidance learning and during retrieval. A variety of studies in humans and other animals revealed that the ability of aversive feedback learning emerges postnatally. Our previous findings demonstrated that rats, which as infants are not capable to learn an active avoidance strategy, show improved avoidance learning as adults. Based on these findings, we further tested the hypothesis that specific neuronal ensembles are "tagged" during infant TWA training and then reactivated during adult re-exposure to the same learning task. Using cellular imaging by immunocytochemical detection of Arc/Arg3.1, we observed that, compared to the untrained control group, (1) only in the dentate gyrus the density of Arc/Arg3.1-expressing neurons was elevated during the acquisition phase of TWA learning, and (2) this increase in Arc/Arg3.1-expressing neurons was not specific for the TWA learning task. With respect to the effects of infant TWA training we found that compared to the naïve non-pretrained group (a) the infant pretraining group displayed a higher density of Arc/Arg3.1-expressing neurons in the anterior cingulate cortex during acquisition on training day 1, and (b) the infant pretraining group displayed elevated density of Arc/Arg3.1-expressing neurons in the dentate gyrus during retrieval on test day 5. Correlation analysis for the acquisition phase revealed for the ACd that the animals which showed the highest number of avoidances and the fastest escape latencies displayed the highest density of Arc/Arg3.1-expressing neurons. Taken together, we are the first to use the synaptic plasticity protein Arc/Arg3.1 to label neuronal ensembles which are involved in different phases of active avoidance learning and whose activity patterns are changing in response to previous learning experience during infancy. Our results indicate (1) that, despite the inability to learn an active avoidance response in infancy, lasting memory traces are formed encoding the subtasks that are learned in infancy (e.g., the association of the CS and UCS, escape strategy), which are encoded in the infant brain by neuronal ensembles, which alter their synaptic connectivity via activation of specific synaptic plasticity proteins such as Arc/Arg3.1 and Egr1, and (2) that during adult training these memories can be retrieved by reactivating these neuronal ensembles and their synaptic circuits and thereby accelerate learning.

Differential effects of wake promoting drug modafinil in aversive learning paradigms

Modafinil (MO) an inhibitor of the dopamine transporter was initially approved to treat narcolepsy, a sleep related disorder in humans. One interesting “side-effect” of this drug, which emerged from preclinical and clinical studies, is the facilitation of cognitive performance. So far, this was primarily shown in appetitive learning paradigms, but it is yet unclear whether MO exerts a more general cognitive enhancement effect. Thus, the aim of the present study in rats was to extend these findings by testing the effects of MO in two aversive paradigms, Pavlovian fear conditioning (FC) and the operant two-way active avoidance (TWA) learning paradigms. We discovered a differential, task-dependent effect of MO. In the FC paradigm MO treated rats showed a dose-dependent enhancement of fear memory compared to vehicle treated rats, indicated by increased context-related freezing. Cue related fear memory remained unaffected. In the TWA paradigm MO induced a significant decrease of avoidance responses compared to vehicle treated animals, while the number of escape reactions during the acquisition of the TWA task remained unaffected. These findings expand the knowledge in the regulation of cognitive abilities and may contribute to the understanding of the contraindicative effects of MO in anxiety related mental disorders.

Differential changes of metabolic brain activity and interregional functional coupling in prefronto-limbic pathways during different stress conditions: functional imaging in freely behaving rodent pups

The trumpet-tailed rat or degu (Octodon degus) is an established model to investigate the consequences of early stress on the development of emotional brain circuits and behavior. The aim of this study was to identify brain circuits, that respond to different stress conditions and to test if acute stress alters functional coupling of brain activity among prefrontal and limbic regions. Using functional imaging (2-Fluoro-deoxyglucose method) in 8-day-old male degu pups the following stress conditions were compared: (A) pups together with parents and siblings (control), (B) separation of the litter from the parents, (C) individual separation from parents and siblings, and (D) individual separation and presentation of maternal calls. Condition (B) significantly downregulated brain activity in the prefrontal cortex, hippocampus, nucleus accumbens (NAcc), and sensory areas compared to controls. Activity decrease was even more pronounced during condition (C), where, in contrast to all other regions, activity in the PAG was increased. Interestingly, brain activity in stress-associated brain regions such as the amygdala and habenula was not affected. In condition (D) maternal vocalizations "reactivated" brain activity in the cingulate and precentral medial cortex, NAcc, and striatum and in sensory areas. In contrast, reduced activity was measured in the prelimbic and infralimbic cortex (IL) and in the hippocampus and amygdala. Correlation analysis revealed complex, region- and situation-specific changes of interregional functional coupling among prefrontal and limbic brain regions during stress exposure. We show here for the first time that early life stress results in a widespread reduction of brain activity in the infant brain and changes interregional functional coupling. Moreover, maternal vocalizations can partly buffer stress-induced decrease in brain activity in some regions and evoked very different functional coupling patterns compared to the three other conditions.

Effects of muscarinic receptor antagonism in the basolateral amygdala on two-way active avoidance

The aim of the present study was to investigate whether the blockade of muscarinic receptors (mRs) in the basolateral amygdala (BLA), which receives important cholinergic inputs related to avoidance learning, affects the consolidation of two-way active avoidance (TWAA). In Experiment 1, adult male Wistar rats were bilaterally infused with scopolamine (SCOP, 20 μg/site) or PBS (VEH) in the BLA immediately after a single 30-trial acquisition session. Twenty-four hours later, avoidance retention was tested in an identical session. Results indicated that scopolamine in the BLA did not affect TWAA performance measured by the number of avoidance responses. Experiment 2 was conducted to test whether such a negative outcome might be due to the occurrence of overtraining during acquisition, which may indeed have a protective effect against scopolamine-induced memory deficits. In this experiment, rats were infused with scopolamine in the BLA immediately after a brief 10-trial acquisition session and tested 24 h later in a 30-trial retention session. The SCOP group showed significantly more avoidances and inter-trial crossings in the retention session than the VEH rats. Together, these results reveal that mRs blockade in the BLA does not disrupt TWAA consolidation and may even enhance avoidance performance when infused after a low number of acquisition trials. Performance factors, such as locomotor activity in the shuttle-box, may account, at least in part, for the facilitative effects of muscarinic antagonism in the BLA.

Cognitive training during infancy and adolescence accelerates adult associative learning: critical impact of age, stimulus contingency and training intensity

A growing body of evidence supports the hypothesis that juvenile cognitive training shapes neural networks and behavior, and thereby determines the adult's capacity for learning and memory. In particular, we have shown that infant rats, even though they do not develop an active avoidance strategy in a two-way active avoidance task, show as adults accelerated learning in the same learning task. This indicates that a memory trace was formed in the infant rats, which most likely is recruited during adult training. To identify the learning conditions, which are essential prerequisites to form this memory trace in infancy or adolescence, we investigated the critical impact of: (i) age, (ii) CS-UCS contingency, and (iii) pre-training intensity on this facilitating effect. We observed: (i) an age-dependent improvement of avoidance learning, (ii) that the beneficial impact of infant or adolescent pre-training on adult learning increases with the age at pre-training, (iii) that CS-UCS contingency during infant pre-training was most efficient to accelerate adult learning, (iv) that pre-training intensity (i.e. number of pre-training trials) was positively correlated with the pre-training induced acceleration of adult learning, and (v) that infant rats, compared to adolescent rats, need a higher training intensity to show learning improvement as adults. These results indicate that infant rats develop a goal-oriented escape strategy, which during adult training is replaced by an avoidance strategy, facilitated by the recruitment of the CS-UCS association, which has been learned during infant training. Based on these results the future challenge will be to identify the specific contribution of prefronto-limbic circuits in infant and adult learning in relation to their functional maturation.