Individual Differences in Spatial Memory and Striatal ChAT Activity among Young and Aged Rats

Individual differences in spatial memory among young and aged rats were assessed using memory tasks related to integrity of the hippocampus and the neostriatum. Relationships were then examined between measures of spatial memory and regional choline acetyltransferase (ChAT) activity, a marker for cholinergic integrity. Twenty-four-month-old Long-Evans rats were impaired in comparisons with 6-month-old rats on measures of place learning, working memory, reference memory, and perseveration in water-maze tasks. Aged rats that were impaired on one measure of memory, however, were not necessarily impaired on other measures. ChAT activity in the ventromedial and dorsolateral neostriatum of aged rats was significantly reduced in comparisons with young rats whereas no difference was found in the hippocampus. Aged rats with the most ChAT activity in the anterior ventromedial neostriatum performed best on the place-learning and reference memory tasks but also made the most perseverative errors on the working memory task. In addition, young and aged rats with the most ChAT activity in the anterior dorsolateral neostriatum were those with the least accurate working memory. No relationships were found between ChAT activity in the hippocampus and spatial memory. Thus age-related memory impairment has components that can be segregated by measuring relationships between cholinergic integrity in subregions of the anterior neostriatum and memory tasks with different strategic requirements.     

Amygdala circuitry in attentional and representational processes

The amygdala has long been implicated in the display of emotional behavior and emotional information processing, especially in the context of aversive events. In this review, we discuss recent evidence that links the amygdala to several aspects of food-motivated associative learning, including functions often characterized as attention, reinforcement and representation. Each of these functions depends on the operation of separate amygdalar subsystems, through their connections with other brain systems. Notably, very different processing systems seem to be mediated by the central nucleus and basolateral amygdala, subregions of the amygdala that differ in their anatomy and in their connectivity. The basolateral amygdala is involved in the acquisition and representation of reinforcement value, apparently through its connections with ventral striatal dopamine systems and with the orbitofrontal cortex. The dentral nucleus, however, contributes heavily to attentional function in conditioning, by way of its influence on basal forebrain cholinergic systems and on the dorsolateral striatum.