An indirect cholinesterase inhibitor, metrifonate, increases neocortical EEG arousal in rats

Eptastigmine restores the aged rat's normal cortical spectral power pattern

We studied the ability of eptastigmine, a second-generation acetylcholinesterase inhibitor (AChEI), to reverse the age-related increase of electroencephalogram (EEG) mean cortical spectral power in slow-wave delta activity and decrease in fast-wave alpha and beta activity. The relative basal spectral power profile evaluated for 50 min of the old (27-30 months) in comparison to young (4-6 months) awake rats was consistently different, showing a significant increase in delta(0.2-4.0 Hz) frequency and a significant decrease of alpha(8.2-13.0 Hz) and beta(13.2-25.0) bands. When 0.5, 1, 2, 4 mg kg(-1)of eptastigmine were administered orally as single increasing doses for old and young rats 2 h prior to the EEG recordings, lasting 2 h, the relative mean spectral power difference (Delta%) showed a linear log dose-related decrease in delta activity and a progressive increase in alpha and beta activity in old rats. Compared to vehicle, in young rats, the eptastigmine dose of 0.5 mg kg(-1)produced a significant decrease in delta activity and an increase in beta activity. The spontaneous motor activity, evaluated through cumulative horizontal and vertical counts for 30 min in old rats was significantly decreased when compared to young rats. Single oral treatment with eptastigmine (0.5 mg kg(-1)for young and 2 mg kg(-1)for old rats) given 2 h before the test did not significantly change motor activity in comparison to vehicle group of the same age. These results suggest a possible strategy to alleviate the severe slowing of neocortical EEG accompanying the cognitive decline.

Chronic, low-level exposure to the cholinesterase inhibitor DFP. II. Time course of behavioral state changes in rats

Rats were repeatedly administered with low doses of diisopropylfluorophosphate (DFP; 0.2 mg/kg/day, SC), an irreversible cholinesterase (ChE) inhibitor. Control rats received a daily injection of oil vehicle or of saline. Recordings of the sleep-wake states were obtained in the 6 h following 1, 3, 6, 9, 13, 17, and 21 injections, as well as 2, 4, and 19 days after 9-day treatment. DFP administration increased waking at the expense of slow-wave sleep (SWS), but not of paradoxical sleep (PS); as a result, the PS/SWS ratio was strongly enhanced. These changes developed across days, were maximal after six to nine injections, and were then maintained at that level until cessation of treatment. This time course of behavioral state alterations paralleled the time course of ChE inhibition in the mesopontine cholinergic nuclei and the pontine reticular formation described in the companion article. In contrast, after DFP withdrawal, behavioral states returned to control values more rapidly (in 2-4 days) than did ChE activity. These results are discussed regarding the promoting role of cholinergic neurotransmission in brain-activated states.

Effects of subchronic administration of metrifonate on cholinergic neurotransmission in rats

The effects of subchronic oral administration of metrifonate, a long-acting cholinesterase (ChE) inhibitor, on cholinergic neurotransmission were assessed in young adult male Wistar rats. Animals were treated twice daily with metrifonate. In a pilot study testing a 100 mg/kg dose of metrifonate for up to 14 days, ChE activity was found to steadily decrease to reach maximum inhibition levels of about 55%, 80% and 35% in brain, erythrocytes and plasma. Steady-state inhibition levels were attained by the 10th day of treatment. When metrifonate-treatment was discontinued, ChE activity in plasma returned to control levels within another day, while erythrocyte and brain ChE activity took more than 2 weeks to recover. In subsequent dose-response studies, metrifonate treatment was given for 3 and 4.5 weeks at doses of 0, 12.5, 25, 50, and 100 mg/kg, to different groups of animals, respectively. Correlation analysis indicted that brain ChE inhibition was more accurately reflected by erythrocyte than by plasma ChE inhibition, although all effects were highly correlated. The changes in ChE activity were not paralleled by changes in other parameters of the cholinergic neurotransmission, such as acetylcholine synthesis rate or acetylcholine receptor binding. It is therefore concluded that repeated administration of metrifonate to rats induces a long-lasting inhibition of ChE activity in a dose-related and predictable manner, which is neither subject to desensitization nor paralleled by counterregulatory downregulation of muscarinic or nicotinic receptor binding sites in brain.

Effects of metrifonate on radial arm maze acquisition in middle-aged rats

The efficacy of metrifonate, a well-tolerated cholinesterase (ChE) inhibitor, in attenuating the normal aging- and corticosterone-induced impairments of radial maze performance of rats was compared. Middle-aged Fischer 344 rats were screened for their spatial orientation performance in the Morris water escape task. Good and bad performers were selected: good performers (N= 22) were treated with subcutaneous sustained-release corticosterone pellets, resulting in hippocampal cell damage and impaired spatial orientation in the radial maze; age-induced bad performers (N = 20) were tested without additional pharmacological intervention. Metrifonate (MFT), administered daily during radial maze testing, 30 min before training, at a dose of 15 mg/kg p.o., facilitated the acquisition of the task in age-impaired rats, but not in corticosterone-impaired rats.

Effects of combined chronic nimodipine and acute metrifonate treatment on spatial and avoidance behavior

The present experiment was designed to elucidate whether chronic dietary treatment with nimodipine (3 months, 1000 ppm) enhances water maze spatial navigation, passive avoidance behavior and locomotor activity, and whether such a treatment with nimodipine would interact with the therapeutic effect of acute metrifonate treatment. In young medial septum-lesioned rats, nimodipine had no effect by its own on cognitive or motor behavior, and did not enhance the water maze and passive avoidance behavior improving action of metrifonate (3 and 10 mg/kg. p.o.). Nimodipine treatment of aged rats did not markedly affect the deficit in motor performance. Single and combined nimodipine and metrifonate (3 and 10 mg/kg, p.o.) treatment of aged rats resulted in shorter escape distance values to the hidden water maze escape platform compared to those of control aged rats. The passive avoidance performance of aged rats was more effectively facilitated by a combined nimodipine and metrifonate treatment than by either of the drugs on their own. Following a washout period of 2.5 months the rats that were treated previously with nimodipine no longer performed better than aged controls in the water maze test. Furthermore, after the washout period metrifonate 10 mg/kg was no longer effective in improving the water maze behavior of the now 26-month-old rats irrespective of their chronic pretreatment. Taken together, these findings indicate that chronic nimodipine and acute metrifonate treatment may more effectively stimulate cognitive functioning than either of the treatments on their own.

The ability of THA treatment to increase cortical alpha waves is related to apolipoprotein E genotype of Alzheimer disease patients

In a previous study, we reported that Alzheimer disease (AD) patients with an apolipoprotein E (APOE) epsilon 4 allele (+ APOE4) show more severe loss of nucleus basalis (NB) cholinergic cells than patients without epsilon 4 alleles (-APOE4). The present study investigates the effects of a single oral administration of THA 25 or 50 mg on cortical spectral EEG activity in + (five APOE4/4, six APOE4/3) and -APOE4 (eight APOE3/3) AD patients. THA 25 mg had no significant effect on EEG activity in any AD patients. However, THA 50 mg increased alpha activity and alpha/theta ratio in -APOE4 patients. In contrast, THA 50 mg had no effect on EEG activity in + APOE4 patients. This result tentatively suggests that in AD patients APOE genotype may affect the response of cortical electrical arousal to cholinergic therapy that enhances the efficacy of presynaptic NB axons.

Effects of combined nimodipine and metrifonate on rat cognition and cortical EEG

The present study investigated if short-term treatment with an L-type Ca2+-channel inhibitor, nimodipine, can stimulate cognitive functioning and cortical electroencephalograph (EEG) arousal, and potentiate the effect of a cholinesterase inhibitor, metrifonate. Pretraining administration of nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on water maze and passive avoidance behavior of young neurologically intact controls, or water maze and passive avoidance performance failure induced by scopolamine pretreatment (i.p.; 0.4 mg/kg during the water maze and 2.0 mg/kg during the passive avoidance study), medial septal lesioning, or aging. Furthermore, nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on the improvement by metrifonate (10 mg/kg, p.o.) of the water maze and passive avoidance failure induced by scopolamine pretreatment or medial septal lesioning, nor did it affect the potential of metrifonate (30 mg/kg. p.o.) to improve the water maze or passive avoidance behavior of aged rats. Finally, nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on spontaneously occurring thalamically generated neocortical high-voltage spindles or spectral EEG activity of young controls, nor did it alleviate the spectral EEG abnormality induced by scopolamine (0.2 mg/kg, i.p.) administration. Also, the combination of nimodipine 3 or 10 mg/kg and a subthreshold dose of metrifonate 10 mg/kg could not suppress high-voltage spindles or scopolamine treatment-induced spectral EEG activity abnormalities. According to the present results, short-term treatment with nimodipine does not stimulate cognitive functions or increase cortical EEG arousal, and does not block or potentiate the propensity of metrifonate to improve cognitive performance of rats.