Possible involvement of central cholinergic system in ameliorating effects of indeloxazine, a cerebral activator, on disturbance of learning behavior in rats

Selective antagonism at dopamine D3 receptors enhances monoaminergic and cholinergic neurotransmission in the rat anterior cingulate cortex

Recent neuroanatomical and functional investigations focusing on dopamine (DA) D(3) receptors have suggested a potential role of this receptor in psychiatric diseases such as schizophrenia and drug dependence. In line with the key role of the prefrontal cortex in psychiatric disorders, the present study aimed at assessing the effects of the acute systemic administration of the selective DA D(3) receptor antagonist SB-277011-A on the in vivo extracellular levels of monoamines (DA, norepinephrine (NE), and serotonin (5-HT)) and acetylcholine (ACh) in the anterior cingulate subregion of the medial prefrontal cortex. The in vivo neurochemical profile of SB-277011-A (10 mg/kg, i.p.) in the anterior cingulate cortex was compared with both typical and atypical antipsychotics including clozapine (10 mg/kg, s.c.), olanzapine (10 mg/kg, s.c.), sulpiride (10 mg/kg, s.c.), and haloperidol (0.5 mg/kg, s.c.). The acute administration of SB-277011-A, clozapine, and olanzapine produced a significant increase in extracellular levels of DA, NE, and ACh without affecting levels of 5-HT. Sulpiride also significantly increased extracellular DA, but with a delayed onset over SB-277011-A, clozapine, and olanzapine. In contrast, haloperidol failed to alter any of the three monoamines and ACh in the anterior cingulate cortex. These findings add to a growing body of evidence suggesting a differentiation between typical and atypical antipsychotic drugs (APDs) in the anterior cingulate cortex and a role of DA D(3) receptors in desired antipsychotic drug profile. Similar to their effects on DA and NE, SB-277011-A, clozapine, and olanzapine increased extracellular levels of ACh, whereas haloperidol and sulpiride did not alter ACh. The results obtained in the present study provide evidence of the important role of DA D(3) receptors in the effect of pharmacotherapeutic agents that are used for the treatment of psychiatric disorders such as schizophrenia and drug dependence.

Memory-related acetylcholine efflux from rat prefrontal cortex and hippocampus: a microdialysis study

To investigate the relationship between the prefrontal and hippocampal acetylcholine (ACh) systems and working memory, an in vivo microdialysis study was conducted. A group of rats was trained to perform a working memory task, delayed alternation, in an operant chamber for food reinforcement. The rats had to choose one of two response levers in an alternative manner in each trial, with a certain interval between trials. They had to remember which lever they chose in the previous trial without the assistance of external cues. Another group was trained to perform a reference memory task, cued alternation, in which the behavioral sequence was identical, but an external cue was provided. After stable behavior was established, a dialysis probe was implanted into the prefrontal cortex or the hippocampus of each rat. The extracellular concentration of ACh in the dialysates from the prefrontal cortex increased during performance of the delayed alternation task, while the hippocampal ACh showed a more distinct increase during performance of the cued alternation task. These results suggest that the prefrontal ACh is mainly related to working memory, whereas the hippocampal ACh is mainly related to reference memory.

Present imperfect: a critical review of animal models of the mnemonic impairments in Alzheimer's disease

This paper reviews the current literature on animal models of the memory impairments of Alzheimer's disease (AD). The authors suggest that modeling of the mnemonic deficits in AD be limited to the amnesia observed early in the course of the disease, to eliminate the influence of impairments in non-mnemonic processes. Tasks should be chosen for their specificity and selectivity to the behavioral phenomena observed in early-stage AD and not for their relevance to hypothetical mnemonic processes. Tasks that manipulate the delay between learning and remembering are better able to differentiate Alzheimer patients from persons with other disorders, and better able to differentiate effects of manipulations in animals. The most commonly used manipulations that attempt to model the amnesia of AD are reviewed within these constraints. The authors conclude that of the models examined, lesions of the medial septal nucleus produce behavioral deficits that are most similar to the mnemonic impairments in the earliest stage of AD. However, the parallel is not definitive and more work is needed to clarify the relationship between neurobiology and behavior in AD.