Effects of chronic intraventricular infusion of heparin glycosaminoglycan on learning and brain acetylcholine parameters in aged rats

We reported previously that the glycosaminoglycan heparin (HP) has the facility to improve learning in adult rodents when administered into the nucleus basalis of the ventral pallidum. Here we gauged the effects of chronic intraventricular infusion of HP (20 ng per day over 28 days) in 26-month-old rats in terms of Morris water maze performance, habituation to a novel open field, retention of a step-through inhibitory avoidance task and changes in forebrain acetylcholine (ACh) levels. Control groups included vehicle-infused old and adult (3-month-old) rats. The chronic infusion of HP did not significantly influence the performance of the old animals in any of the learning and memory tasks employed. HP only slightly facilitated the retention of the inhibitory avoidance task and the rate of habituation in the open-field paradigm. In the water maze, the glycosaminoglycan did not counteract the navigation deficits observed for aged controls and even impaired performance during the initial place-learning trials. After behavioural testing, tissue levels of ACh were determined in frontal cortex, ventral striatum, neostriatum and hippocampus without detecting any obvious neurochemical differences between groups. The current results, together with our previous work, indicate that HP differentially affects learning and memory parameters in adult and aged rats. Thus, whereas the glycosaminoglycan proved effective in facilitating mnemonic functions in normal adult animals, no such a clear-cut beneficial effect was observed in behaviourally impaired old rats.