EFFECTS OF AGING AND LONG-TERM OPERANT-CONDITIONING ON BEHAVIOR AND PRESYNAPTIC CHOLINERGIC AND DOPAMINERGIC NEURONAL MECHANISMS IN RATS

Presynaptic events in the brain, such as neurotransmitter synthesis an d release, may change during ageing or by performance of an operant be havior. Therefore, we measured the acetylcholine synthesis and release , and the dopamine release in brain tissue from different groups of ra ts. Male Sprague-Dawley rats, 4-5 or 16-17 months old, were housed ind ividually under identical conditions; one group of the older rats was maintained under an operant conflict procedure for 8 months. Striatal and cerebral cortex slices were preincubated with [H-3]dopamine and [H -3]choline, respectively, superfused and stimulated electrically. Diff erent Ca++ concentrations were used and, in [H-3]dopamine experiments, 0.1 mumol/l of apomorphine was added. Hippocampal slices were incubat ed with [H-3]choline, and H-3-uptake and [H-3]acetylcholine synthesis were measured. Gross behavior was not different between the groups as regards duration of exploration, defecation rate or spontaneous motili ty. Uptake of [H-3]choline and synthesis of [H-3]acetylcholine tended to be lower in the aged rats but did not differ significantly in the g roups. The [H-3]dopamine release was significantly reduced by 20 % in aged rats as compared to young or aged, trained rats. The effect of ch anges in Ca++ concentration and the response to apomorphine on the rel ease of [H-3]dopamine were similar in all groups, indicating a lack of age-related changes of the N-type Ca++ channels and presynaptic D-2 r eceptors. Thus, ageing coincided with an impaired striatal dopamine re lease which was prevented by the operant conditioning.