Behavioral and neurochemical modifications caused by chronic alpha-methylparatyrosine administration

Behavioral and neurochemical effects of a chronic choline-deficient diet in the rat

Chronic administration of a choline-deficient diet for 20 days caused no modification in ACh levels in the cortex, hippocampus and olfactory system of the rat and an increase in the density (Bmax) of the muscarinic receptors in the hippocampus. The choline-deficient diet caused no modification in noradrenaline levels and a reduction in the density of alpha1-adrenoceptors in the cortex, hippocampus and olfactory system. This paper discusses the possibility that these neurochemical effects are correlated with the reduction in spontaneous memory decay which was observed in the staircase maze after 20 days of a choline-deficient diet.

Behavioral and neurochemical effects induced by chronic L-DOPA administration

L-DOPA, in combination with benserazide, in the ratio 4:1 (w/w), was administered orally to rats. In the staircase maze test a low dose of L-DOPA (3 mg/kg/day) reduced the increase in errors caused by 20 days interruption of daily training, while a higher dose (30 mg/kg/day) was ineffective. A decrease in levels of dopamine in the olfactory system and DOPAC in the striatum was seen at all tested doses of L-DOPA, while an increase in 5-HT levels was seen in the hippocampus and in the striatum. 5-HIAA levels did not change. Levels of ACh in the olfactory system were reduced at all doses of L-DOPA, while in the hippocampus this effect was seen only at the dose of 90 mg/kg/day. The density of muscarinic receptors was not altered. All tested doses of L-DOPA caused norepinephrine levels to fall in the hippocampus and increase in the striatum. The density of alpha 1-adrenoceptors was reduced only at the two lower doses of L-DOPA. A comparison of the neurochemical results with the behavioral modifications seen in the staircase maze test suggests that the catecolaminergic systems are implicated in the memory process.

Action of caffeine, L-PIA and their combination on memory retention in the rat

Rats were trained to run in a staircase and to stop on the 3rd, 6th, 9th and 12th steps. The increase of errors (arrest on any other step) after 2O days of interruption of the daily training was evaluated after a chronic administration (15 days) of L-PIA (N6-(L-phenylisopro-pyl)adenosine) 1 mg/kg/day; caffeine 15,45,8O mg/kg/day and of the combination of L-PIA 1 mg/kg/day with 15, 45 and 80 mg/kg/day of caffeine. In the controls and after caffeine administration, the interruption of the daily training caused a reduction of correct responses. After L-PIA alone or in combination with caffeine there was no reduction of correct responses after 2O days of no daily training. These results indicate that in the behavioral situation of our experiments there was no antagonism between caffeine and L-PIA.

Action of chronic choline administration on behavior and on cholinergic and noradrenergic systems

Chronic administration of low doses (0.2-0.8 g/kg/day) of choline caused in the rat an increase of errors evaluated in the staircase maze after 20 days of interruption of daily training. An analogous pharmacological treatment caused no modification of the acetylcholine (ACh) and norepinephrine (NE) levels and no consistent modification of the density of muscarinic and alpha 1-adrenergic receptors. Only at higher doses (2.5 g/kg/day) did chronic administration (20 days) of choline cause in several sections of the CNS, an increase of ACh and NE levels and of the muscarinic receptor density. These observations indicate that only at high doses of choline are there consistent modifications of the central cholinergic systems, suggesting that the behavioral modifications observed at low doses of choline are not determined by an upregulation of the central cholinergic system.

The action of scopolamine on retrieval and memory storage in rats evaluated in the staircase maze

Rats were trained to run on staircase stopping on the 3rd, 6th, 9th, and 12th steps (correct responses). Stopping on any other step was considered an error. The acute administration of scopolamine (1.5 mg/kg) 20 min before the trial caused a reduction of the correct responses. An interruption of the daily training for 20 days caused, in the controls, a 24% reduction of correct responses. A chronic administration of scopolamine, at doses over 10 mg/kg in the first 15 days of the no-training period, nullified the behavioral deterioration observed in the controls. The interpretation of these results is that scopolamine damages the retrieval process and blocks the spontaneous decay of memory, as was observed in the controls after 20 days of interruption of the daily training.