The acetylcholine release enhancer linopirdine induces Fos in neocortex of aged rats

'When an old rat smells a cat': A decline in defense-related, but not accessory olfactory, Fos expression in aged rats

Comparisons were made between young (3-6 months) and aged (20-30 months) Wistar rats on locomotor activity, emergence, social interaction and cat odor avoidance. Aged rats were less active and spent less time in the open field during the emergence test than younger rats. Older rats also showed fewer contacts with a novel conspecific in the social interaction test, although total duration of interaction did not differ. There were very few behavioral differences between male and female rats. Older rats were less reactive than younger rats in a test of cat odor avoidance. However, they expressed similar amounts of cat odor-induced Fos in the posterior accessory olfactory bulb, a critical region for processing the predator odor stimulus. Older rats had reduced Fos expression in several defense-related brain regions that are normally activated by predator odors such as the medial amygdala and dorsal premammillary nucleus. These results indicate that aged rats are less reactive than younger rats to predator odors due to decreased responsiveness in defense-related but not necessarily olfactory circuits.

Cholinergic involvement in the cortical and hippocampal Fos expression induced in the rat by placement in a novel environment

Placing rats into a series of novel environments induced vigorous c-fos expression in the infralimbic, anterior cingulate and retrosplenial cortices, and in the hippocampus. Pretreatment with the antimuscarinic drugs scopolamine and atropine was able to greatly suppress novelty-induced Fos expression at these sites. Placement into the novel environments also induced Fos expression in the habenula and the paraventricular thalamic nucleus, but the response at these sites did not appear to be sensitive to cholinergic blockade. These findings suggest that cholinergic mechanisms play an important role in ability of behavioral events to influence cortical and hippocampal immediate-early gene expression and are consistent with the possibility that some of the effects of anticholinergic drugs on placticity and learning may be mediated through alterations in the expression of these genes.