piperidines and physostigmine-heptyl

Cholinesterase inhibitors vary in their selectivity for acetylcholinesterase versus butyrylcholinesterase. We examined several cholinesterase inhibitors and assessed the relative role of acetylcholinesterase versus butyrylcholinesterase inhibition in central and peripheral responses to these medications. Donepezil and icopezil are highly selective for acetylcholinesterase, whereas tacrine and heptylphysostigmine demonstrated greater potency for butyrylcholinesterase over acetylcholinesterase. All four compounds increased acetylcholine levels in mouse brains. Dose-response curves for tremor (central effect) and salivation (peripheral effect) showed that donepezil and icopezil possess a more favourable therapeutic index than the nonselective inhibitors, tacrine and heptylphysostigmine. Co-administration of the selective butyrylcholinesterase inhibitor tetraisopropylpyrophosphoramide (iso-OMPA) potentiated peripheral, but not central, effects of the selective acetylcholinesterase inhibitor icopezil. The improved therapeutic index observed in mice with icopezil is due to a high degree of selectivity for acetylcholinesterase versus butyrylcholinesterase, suggesting that high selectivity for acetylcholinesterase may contribute to the clinically favourable tolerability profile of agents such as donepezil in Alzheimer's disease patients.

Topics: Acetylcholine; Alzheimer Disease; Animals; Brain; Butyrylcholinesterase; Cholinesterase Inhibitors; Donepezil; Dose-Response Relationship, Drug; Humans; Indans; Male; Mice; Physostigmine; Piperidines; Rats; Rats, Sprague-Dawley; Tacrine

We investigated the influence of increasing oral doses of second generation acetylcholinesterase inhibitors (AChEI) such as tacrine (0.25, 0.5, 1, 2, 3, 4, 10, and 20 mg kg(-1)), eptastigmine (0.5, 4, 8, 12, 20 and 40 mg kg(-1)) and E2020 (0.18, 0.25, 0.5, 1, 2, 3, 4 and 10 mg kg(-1)) on the distance travelled by a charcoal meal administered 30 min after each compound, in comparison with physostigmine (0.5, 1, 2, 4, 8 and 12 mg kg(-1)). An inverted U regression was observed with a significant parabola between the centimetres travelled and the log of the doses for all AChEI. The maximal stimulating doses (mg kg(-1)) were 2 for physostigmine, 4 for eptastigmine, 3 for tacrine and E2020, while the inhibitory doses were 12 for physostigmine, 40 for eptastigmine, 20 for tacrine and 10 for E2020. The stimulating and inhibiting effects on gastrointestinal propulsion were significantly reversed by 0.25 mg kg(-1)of scopolamine hydrobromide. A dose of scopolamine hydrobromide (0.06 mg kg(-1)) or methylbromide (0.25 mg kg(-1)), pirenzepine dihydrochloride (0.25 mg kg(-1)) and mecamylamine hydrochloride (0.5 mg kg(-1)), which per se did not affect gastrointestinal propulsion, antagonized both the stimulating and inhibitory effect of eptastigmine. Thus, the biphasic effect is peripherally mediated through both muscarinic (at least M(1)) and nicotinic receptors.

Topics: Administration, Oral; Animals; Cholinesterase Inhibitors; Donepezil; Dose-Response Relationship, Drug; Gastrointestinal Transit; Hydrocarbons, Brominated; Indans; Male; Physostigmine; Piperidines; Pirenzepine; Rats; Rats, Wistar; Receptor, Muscarinic M1; Receptors, Muscarinic; Receptors, Nicotinic; Scopolamine; Tacrine

Cannabinoids which impair rat working memory appear to inhibit hippocampal extracellular acetylcholine (Ach) release and reduce choline uptake through an interaction with CB1 cannabinoid receptors. Here we report that CP 55,940, a potent bicyclic synthetic cannabinoid analog, dose-dependently impaired rat performance, when given i.p. 20 min before an eight-arm radial maze test. The selective CB1 cannabinoid receptor antagonist SR 141716A, given i.p. 20 min earlier, significantly reduced the memory deficit Pretreatment with eptastigmine, a second generation cholinesterase inhibitor, given orally 100 min before the cannabinoid agonist, relieved the memory impairment without affecting CP 55,940-induced behavioural alterations such as reduced spontaneous motor activity, analgesia and hind limb splaying. These data suggest that cannabinoid-induced working memory impairment is mediated through a central cholinergic blockade.

Topics: Animals; Behavior, Animal; Cannabinoids; Cholinesterase Inhibitors; Cyclohexanols; Male; Maze Learning; Memory; Memory Disorders; Motor Activity; Physostigmine; Piperidines; Pyrazoles; Rats; Rats, Wistar; Rimonabant

The in vitro and in vivo effects of the novel acetylcholinesterase inhibitors donepezil and NXX-066 have been compared to tacrine. Using purified acetylcholinesterase from electric eel both tacrine and donepezil were shown to be reversible mixed type inhibitors, binding to a similar site on the enzyme. In contrast, NXX-066 was an irreversible non-competitive inhibitor. All three compounds were potent inhibitors of rat brain acetylcholinesterase (IC50 [nM]; tacrine: 125 +/- 23; NXX-066: 148 +/- 15; donepezil: 33 +/- 12). Tacrine was also a potent butyrylcholinesterase inhibitor. Donepezil and tacrine displaced [3H]pirenzepine binding in rat brain homogenates (IC50 values [microM]; tacrine: 0.7; donepezil: 0.5) but NXX-066 was around 80 times less potent at this M1-muscarinic site. Studies of carbachol stimulated increases in [Ca2+]i in neuroblastoma cells demonstrated that both donepezil and tacrine were M1 antagonists. Ligand binding suggested little activity of likely pharmacological significance with any of the drugs at other neurotransmitter sites. Intraperitoneal administration of the compounds to rats produced dose dependent increases in salivation and tremor (ED50 [micromol/kg]; tacrine: 15, NXX-066: 35, donepezil: 6) with NXX-066 having the most sustained effect on tremor. Following oral administration, NXX-066 had the slowest onset but the greatest duration of action. The relative potency also changed, tacrine having low potency (ED50 [micromol/kg]; tacrine: 200, NXX-066: 30, donepezil: 50). Salivation was severe only in tacrine treated animals. Using in vivo microdialysis in cerebral cortex, both NXX-066 and tacrine were found to produce a marked (at least 30-fold) increase in extracellular acetylcholine which remained elevated for more than 2 h after tacrine and 4 h after NXX-066.

Topics: Acetylcholinesterase; Animals; Butyrylcholinesterase; Carbachol; Cholinesterase Inhibitors; Donepezil; Drug Evaluation, Preclinical; Humans; Indans; Indoles; Injections, Intraperitoneal; Isoquinolines; Logistic Models; Male; Physostigmine; Piperidines; Rats; Structure-Activity Relationship; Tacrine; Tumor Cells, Cultured

The potential of heptylphysostigmine tartrate (pyrrolo [2,3b] indol-5-ol, 3,3a,8,8a-hexahydro-1,3a,8-trimethylheptylcarbamate [ester, (3aS-cis)]) (MF201), a new second-generation cholinesterase inhibitor, to antagonize scopolamine-induced amnesia in rats was assessed in an 8-arm radial maze. Upon completing the training session, the rats were orally administered increasing doses of MF201 (2, 3, 4, 6 and 8 mg/kg) 60 min prior to a s.c. injection of scopolamine (0.25 mg/kg). 9-Amino-1,2,3,4-tetrahydroamino-acridine hydrochloride hydrate (tacrine) (0.25, 0.37, 0.5, 1 and 2 mg/kg), 1-benzil-4-[(5,6-dimethoxy-1-indanon)-2-yl]-methyl piperidine (E2020) (0.125, 0.18, 0.25 and 0.5 mg/kg) and physostigmine (0.15, 0.25, 0.5 and 1 mg/kg) were orally administered and rats were tested in the same task. As previously described, scopolamine induced an impairment in radial maze performance, measured in terms of total number of errors, total time taken to complete the task and the percentage of amnesic animals. The reversal of scopolamine-induced impairment was characterized by the presence of an inverted U-shaped dose-response curve. A significant antagonistic effect was achieved with a dose (mg/kg) of 0.25 for E2020, 0.5 for tacrine and physostigmine and 3, 4 and 6 for MF201, the latter manifesting a broader spectrum of activity (3-6 mg/kg). While the maximal active doses restored the scopolamine-induced modified pattern of arm entry, they were ineffective in reducing hypermotility, suggesting the drugs have a specific effect on cognitive function.

Topics: Amnesia; Analysis of Variance; Animals; Behavior, Animal; Cholinesterase Inhibitors; Donepezil; Dose-Response Relationship, Drug; Indans; Male; Maze Learning; Motor Activity; Muscarinic Antagonists; Physostigmine; Piperidines; Rats; Rats, Wistar; Scopolamine; Tacrine

In recent years muscarinic receptor agonists and cholinesterase inhibitors have been developed for the treatment of Alzheimer's disease. We have evaluated examples from both classes of compounds in rodent tests of reference and working memory, as well as tests that are sensitive to the side-effects of these compounds. Thus, three selective muscarinic receptor partial agonists L-689,660, (M1/M3), AF102B (M1/M3) and L-687,306 (M1) and two cholinesterase inhibitors, E2020 and eptastigmine, were compared in a mouse tail-flick (TF) test, a rat response sensitivity (RS) test, in rat tests of reference memory, passive avoidance (PA) or conditioned suppression of drinking (CSD), and working memory (delayed-matching-to-position, DMTP). In the TF test, all of the compounds tested, with the exception of L-687,306, (1.0-30.0 mg/kg) dose-dependently induced antinociception of which L-689,660 was the most potent (minimum effective dose (MED) = 0.03 mg/kg). In the RS test, all of the compounds, but again with the exception of L-687,306, (1.0-30.0 mg/kg), dose-dependently reduced response rates, of which L-689,660 was again the most potent (MED = 0.1 mg/kg). In the reference memory test, all the compounds reversed the effects of a scopolamine-induced deficit with L-687,306 being the most potent (MED = 0.01 mg/kg). By contrast, in the DMTP test, although both the cholinesterase inhibitors and L-687,306 reversed the effects of scopolamine-induced deficit, L-689,660 and AF102B were without effects. These results suggest that cholinesterase inhibitors and low efficacy M1 selective muscarinic receptor agonists can reverse the effects of a scopolamine-induced deficit in animal tests of reference and working memory at doses that do not induce the side-effects usually associated with cholinomimetics.

Topics: Animals; Avoidance Learning; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Cholinesterase Inhibitors; Conditioning, Classical; Discrimination Learning; Donepezil; Dose-Response Relationship, Drug; Indans; Learning; Memory; Mice; Oxadiazoles; Pain Threshold; Parasympathomimetics; Physostigmine; Piperidines; Pyrazines; Quinuclidines; Rats; Receptors, Muscarinic; Thiophenes