Progressive cognitive impairment following chronic cerebral hypoperfusion induced by permanent occlusion of bilateral carotid arteries in rats

Subchronic intraventricular infusion of quinolinic acid produces working memory impairment--a model of progressive excitotoxicity

It has been proposed by Yamada et al. [Neurosci. Lett. 118: 128-131 (1990); J. Pharmacobiodyn. 14: 351-355 (1991)] that subchronic i.c.v. infusion of the NMDA receptor agonist quinolinic acid may serve as a model for some aspects of neurodegenerative dementia. In the present study, quinolinic acid (9 mM) was infused i.c.v. by ALZET osmotic minipumps for 2 weeks. This treatment produced a short-term working memory deficit in the T-maze (alternation) but no change in reversal learning in the same test. The working memory deficit in the T-maze was progressive i.e. seen after 14, but not 3 days of infusion and persisted for at least for 3 weeks after the termination of the infusion. Histological examination revealed a modest decrease in the number of cells in the nucleus basalis magnocellularis but not in the striatum, entorhinal cortex, or hippocampus. However, in most of the structures studied, morphological changes such as swollen somata and irregular shape were observed indicative of alterations in neuronal function. Autoradiography in the hippocampus revealed a decrease in [3H]hemicholinium and [3H]quinuclidinyl benzilate (QNB) binding to choline uptake sites and muscarinic receptors respectively. Surprisingly no change was observed in [3H]MK-801 binding to NMDA receptor channels in the hippocampus and cortex. The subchronic infusion of quinolinic acid may serve as a model of progressive deterioration of cognitive functions.

Preventive effects of bifemelane hydrochloride on decreased levels of muscarinic acetylcholine receptor and its mRNA in a rat model of chronic cerebral hypoperfusion

Changes in muscarinic acetylcholine receptor (mACh-R) binding and muscarinic cholinergic m1 receptor (m1-R) mRNA levels were determined in a rat model of cerebral hypoperfusion in which hypoperfusion was induced by permanent bilateral occlusion of the common carotid arteries. After 6 weeks of hypoperfusion, mACh-R binding activity was significantly reduced in the frontal cortex (79.0 percent, P <0.01), striatum (74.2 percent, P < 0.01) and hippocampus (78.6 percent, P < 0.01), and the m1-R mRNA levels in the frontal cortex (86.6 percent, P < 0.05) and striatum (89.4 percent, P < 0.05) compared with sham-operated control. Repeated administration of bifemelane hydrochloride (15 mg/kg/day, p.o., once a day from the day of operation for 6 weeks) prevented the hypoperfusion-induced loss of mACh-R binding and m1-R mRNA levels above described. Since the central cholinergic systems play an important role in learning and memory, these findings suggest that bifemelane hydrochloride is useful to treat and/or prevent vascular dementia which is closely related to cerebral hypoperfusion.

Chronic reduction of cerebral blood flow in the adult rat: late-emerging CA1 cell loss and memory dysfunction

Ten-month-old rats were subjected to permanent bilateral occlusion of both common carotid arteries (2-VO) to chronically but moderately reduce brain blood flow. 2-VO impaired Morris water maze acquisition as soon as 7 days post-surgery. 2-VO also caused a later-appearing impairment on the radial arm maze which did not reach significance until 63 days post-surgery. At 14 dats post-surgery there were no effects of 2-VO on hippocampal CA1 pyramidal cell number or density of glial fibrillary acidic protein (GFAP). Hippocampal choline acetyltransferase activity at 70 days was also unaffected by 2-VO. At 190 days post-surgery, however, the 2-VO rats showed loss of cells and increased GFAP density in CA1. The increased density of hippocampal GFAP correlated with radial arm maze but not Morris water maze impairment. It is suggested that 2-VO causes neuronal dysfunction which can be exacerbated by stress and thereby manifested on aversively motivated tasks such as the water maze. As well, CA1 neurons begin to degenerate after several weeks of the reduced energy availability caused by 2-VO and this impairs memory. Since reduced neuronal energy metabolism is associated with the progressive neurodegeneration that underlies disorders such as Alzheimer's, research should further explore the possibility that the effects of 2-VO may model age-related dementia.

Learning deficits induced by chronic intraventricular infusion of quinolinic acid--protection by MK-801 and memantine

The NMDA receptor agonist quinolinic acid (9 mM) was infused i.c.v. via ALZET osmotic minipumps for 2 weeks. This treatment produced a persistent, short-term memory deficit in the T-maze. Autoradiography revealed a decrease in the density of choline uptake sites in the hippocampus. Parallel s.c. infusion by another minipump of the uncompetitive NMDA receptor antagonist memantine (1-amino-3,5-dimethyladamantane, 20 mg/kg per day) or (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate ((+)-MK-801, 0.31 mg/kg day) prevented the learning deterioration induced by quinolinic acid. The treatment with memantine resulted in steady-state serum levels of 1.2 mu M which, based on in vitro data, should assure inhibition of NMDA receptors and are similar to levels seen in the serum of demented patients treated with this agent. In naive animals this treatment had no effect on either learning or on ex vivo induction of long-term potentiation, indicating that under chronic conditions it is possible to obtain neuroprotective effects with NMDA receptor antagonists without negative effects on memory processes. This contrasts to some acute insults (e.g. ischaemia) where high doses of NMDA receptor antagonists that produce side effects are required.

Neuronal damage and decrease of central acetylcholine level following permanent occlusion of bilateral common carotid arteries in rat

The neuronal damages and the changes in central acetylcholine (ACh) and choline (Ch) contents following permanent occlusion of bilateral common carotid arteries (2VO) of rats were investigated 1 and 4 months after the operation. Two types of neuronal damages were observed in the rats with permanent 2VO. The first type was the infarctions observed in the cerebral cortex and striatum. The infarction in the cortex and striatum was observed in 28.6 and 42.9% of the animals examined 1 month after permanent 2VO, respectively. These ratios did not change even when examined 4 months after permanent 2VO, suggesting that this type of neuronal damage is due to acute ischemic attacks. The second type was progressive neuronal damages observed in the hippocampus and white matter: the neuronal loss in the CA1 subfield appeared 4 months but not 1 month after permanent 2VO and the rarefaction of white matter which was observed 1 months after permanent 2VO and markedly increased 4 months after the operation. Moreover, ACh level significantly decreased in the striatum but not in the cortex, hippocampus or hypothalamus 1 month after permanent 2VO, while the ACh levels in the cortex, striatum and hypothalamus, and Ch levels in all the regions tested significantly decreased when tested 4 months after the operation. These changes did not accompany necrosis. These results suggest that the progressive neuronal degeneration and cholinergic dysfunction following the permanent 2VO are in part involved in chronic cerebral hypoperfusion-induced long-lasting cognition deficits in rats.

Tetramethylpyrazine improves spatial cognitive impairment induced by permanent occlusion of bilateral common carotid arteries or scopolamine in rats

Effects of tetramethylpyrazine (TMP), a major constituent of Ligusticum chuanxiong, on spatial cognitive impairment induced by permanent occlusion of bilateral common carotid arteries (2VO) and scopolamine were investigated using 8-arm radial maze performance in rats. Permanent 2VO produced a severe learning deficit in non-pretrained rats. Daily administration of TMP (3-10 mg/kg, i.p.) from the 3rd day after permanent 2VO significantly improved the learning deficit. TMP did not influence the impairment of the retention task in the pretrained permanent 2VO rats, but it tended to reduce the number of errors elevated by 3-min delay interposition in these rats. In the scopolamine model, scopolamine (0.3 mg/kg, i.p.) significantly decreased the initial correct response and increased the number of errors. Single administration of TMP (1-3 mg/kg, i.p.) dose-dependently reversed the scopolamine-induced impairment of the maze performance. These results suggest that TMP has therapeutic potential for the treatment of dementia caused by cholinergic dysfunction and/or decrease of cerebral blood flow.