Adrenalectomy exacerbates stress-induced impairment in fear discrimination: A causal role for kynurenic acid?

Impaired activity of the hypothalamic-pituitary axis and reduced blood levels of glucocorticoids (GCs) are signature features of stress-related maladies. Recent evidence suggests a possible role of the tryptophan metabolite kynurenic acid (KYNA) in this context. Here we investigated possible causal relationships in adult male rats, using stress-induced fear discrimination as a translationally relevant behavioral outcome measure.

Postrhinal cortex contributions to the expression of auditory fear conditioning.

The postrhinal cortex (POR), the rodent homologue of the primate parahippocampal cortex (PHC), has been implicated in contextual and spatial processing. For instance, prior studies have demonstrated that permanent lesions of POR impair contextual fear conditioning. In contrast, permanent lesions of POR, specifically prior to training, do not impact auditory fear conditioning.

Retrograde amnesia of contextual fear conditioning: Evidence for retrosplenial cortex involvement in configural processing.

It has been suggested that contextual fear conditioning can be supported by either an elemental system, where individual features of the environment are associated with shock, or a configural system, where environmental features are bound together and associated with shock. Although the retrosplenial cortex (RSC) is known to be involved in contextual fear conditioning, it is not clear whether it contributes to the elemental or configural system. To isolate the role of the RSC in contextual fear conditioning, the current experiments examined the influence of RSC lesions on the context preexposure facilitation effect, a procedure known to produce conditioning to a configural representation of context.

Retrosplenial cortex damage produces retrograde and anterograde context amnesia using strong fear conditioning procedures.

Contextual fear conditioning relies upon a network of cortical and subcortical structures, including the hippocampus and the retrosplenial cortex (RSC). However, the contribution of the hippocampus is parameter-dependent. For example, with "weak" training procedures, lesions of the hippocampus produce both retrograde and anterograde context amnesia.

Retrosplenial cortex has a time-dependent role in memory for visual stimuli.

Although the retrosplenial cortex (RSC) is critically involved in spatial learning and memory, it appears to have more selective contributions to learning and memory for discrete cues. For example, damage to the RSC does not impair Pavlovian delay fear conditioning to a discrete auditory cue (e.g.

A functional circuit for the retrieval of remote cued fear memory.

Although the retrosplenial cortex (RSC) is necessary for the retrieval of remotely acquired fear to a discrete auditory cue, it is not necessary for the retrieval of recently acquired cued-fear memories. Thus, the RSC's role in memory retrieval for discrete cues is time-dependent. The purpose of the current experiment was to identify the larger cortical circuit involved in the retrieval of remotely-acquired auditory fear memories.

Increased sign-tracking behavior in adolescent rats.

An autoshaping procedure was used to test the notion that conditioned stimuli (CSs) gain greater incentive salience during adolescence than young adulthood under conditions of social isolation rearing and food restriction. Rats were single-housed and placed on food restriction during 10 daily training sessions in which a lever (CS ) was presented then followed immediately by a food unconditioned stimulus (US). A second lever (CS ) was presented on intermixed trials and was not reinforced.

Retrograde amnesia of contextual fear conditioning: Evidence for retrosplenial cortex involvement in configural processing.

It has been suggested that contextual fear conditioning can be supported by either an elemental system, where individual features of the environment are associated with shock, or a configural system, where environmental features are bound together and associated with shock. Although the retrosplenial cortex (RSC) is known to be involved in contextual fear conditioning, it is not clear whether it contributes to the elemental or configural system. To isolate the role of the RSC in contextual fear conditioning, the current experiments examined the influence of RSC lesions on the context preexposure facilitation effect, a procedure known to produce conditioning to a configural representation of context.

Intact renewal after extinction of conditioned suppression with lesions of either the retrosplenial cortex or dorsal hippocampus.

Extinction of fear to a Pavlovian conditioned stimulus (CS) is known to be context-specific. When the CS is tested outside the context of extinction, fear returns, or renews. Several studies have demonstrated that renewal depends upon the hippocampus, although there are also studies where renewal was not impacted by hippocampal damage, suggesting that under some conditions context encoding and/or retrieval of extinction depends upon other regions.

Higher-order conditioning and the retrosplenial cortex.

The retrosplenial cortex (RSC) is known to contribute to contextual and spatial learning and memory. This is consistent with its well-established connectivity; the RSC is located at the interface of visuo-spatial association areas and the parahippocampal-hippocampal memory system. However, the RSC also contributes to learning and memory for discrete cues.

Retrosplenial cortex is required for the retrieval of remote memory for auditory cues.

The restrosplenial cortex (RSC) has a well-established role in contextual and spatial learning and memory, consistent with its known connectivity with visuo-spatial association areas. In contrast, RSC appears to have little involvement with delay fear conditioning to an auditory cue. However, all previous studies have examined the contribution of the RSC to recently acquired auditory fear memories.

Cross-fostering differentially affects ADHD-related behaviors in spontaneously hypertensive rats.

Although both genetic and non-genetic factors are known to contribute to the occurrence of Attention-Deficit Hyperactivity/Disorder (ADHD), little is known about how they impact specific symptoms. We used a cross-fostering approach with an established animal model of ADHD, the Spontaneously Hypertensive Rat strain (SHR), to test the influence of genotype and maternal behavior on ADHD-related behaviors. SHRs and their normo-active genetic relative, Wistar Kyoto rats (WKY), were cross-fostered to an unfamiliar dam of either the same or different strain.

Exposure to Kynurenic Acid during Adolescence Increases Sign-Tracking and Impairs Long-Term Potentiation in Adulthood.

Changes in brain reward systems are thought to contribute significantly to the cognitive and behavioral impairments of schizophrenia, as well as the propensity to develop co-occurring substance abuse disorders. Presently, there are few treatments for persons with a dual diagnosis and little is known about the neural substrates that underlie co-occurring schizophrenia and substance abuse. One goal of the present study was to determine if a change in the concentration of kynurenic acid (KYNA), a tryptophan metabolite that is increased in the brains of people with schizophrenia, affects reward-related behavior.