Amiridine (NIK-247) and cerebrocrast in the alleviation of cholinergic lesion-induced learning deficit in male rats

Effects of selective catechol-O-methyltransferase inhibitors on single-trial passive avoidance retention in male rats

The effects of new selective catechol-O-methyltransferase (COMT) inhibitors entacapone (mainly peripheral effect) and tolcapone (acting also in the brain) on normal and impaired cognitive functions were studied in aversively motivated inhibitory avoidance using a single-trial passive avoidance paradigm in young adult rats. Passive avoidance retention latency was shortened by either scopolamine (1.0 mg/kg) or bilateral lesions to nucleus basalis magnocellularis (NBM) caused by infusions of ethylcholine aziridinium (AF64A). Entacapone (30 mg/kg) administered once before training or before the retention test, 24 h after training, prevented the effect of scopolamine but did not alter extinction in these rats. However, entacapone (30 mg/kg) prolonged lag time when given during the extinction process to intact rats after training. Tolcapone administered once before training (10 mg/kg) counteracted the effect of scopolamine. It prolonged retention latency of the intact rats when given after training (10 mg/kg). Tolcapone (3 mg/kg) also prolonged lag time when given during extinction to rats bearing NBM lesions. The effect of scopolamine on extinction and retrieval was not prevented by tolcapone. Only entacapone improved memory storage. Collectively, the present results indicate that COMT inhibitors prolong retention latencies in a single-trial passive avoidance test assessed at several memory phases.

Effects of bilateral cholinotoxin infusions on the behavior and brain biochemistry of the rats

We examined behavioral and biochemical specificity and the general usefulness of the proposed rat model of Alzheimer's disease. Bilateral infusions of ethylcholine aziridinium (AF64A) into the basal magnocellular nuclei caused a deterioration of learning in passive and active avoidance tests, increased emotional reactivity, and decreased motoric activity. Choline acetyltransferase activity was decreased by 22% in the frontal cortex but increased by 8-10% in the hippocampus and hypothalamus. Noradrenaline and dopamine levels in the frontal cortex were decreased by 20%. In striatum, dopamine and its metabolites were strongly suppressed (by 50-60%). Also striatal noradrenaline (-48%) and 5-hydroxytryptamine (-34%) were significantly decreased. Hypothalamic 5-hydroxytryptamine was increased (+25%). Bilateral AF64A lesions decreased significantly (by 14-20%) activities of prolyl endopeptidase, dipeptidyl peptidase II and IV in hippocampal and frontal cortical brain homogenates. These results show that AF64A can be used to induce long-term learning deficits in the rat. However, striatal amine levels are also strongly suppressed, and are reflected as hypomotility and increased emotional reactivity. These changes may limit the usefulness of the rat model. Universally decreased peptidase activities offer interesting views regarding the role of peptidase inhibitors in amnestic disorders.