Memory modulation with peripherally acting cholinergic drugs

Physostigmine (PHYSO), in doses as low as 0.003 mg/kg IP, antagonized scopolamine (SCOP, 3 mg/kg) induced amnesia of step-through passive avoidance in mice. The peripherally acting acetylcholinesterase (AChE) inhibitor neostigmine (NEO) was also found to reliably, though less strongly, antagonize the SCOP induced amnesia at a dose of 0.03 mg/kg. The NEO antagonism of the SCOP amnesia could be reversed with SCOP (0.3, 1, and 3 mg/kg) and mecamylamine (MECA, 1, 3, and 10 mg/kg), muscarinic and nicotinic antagonists, respectively, which are active both peripherally and centrally, as well as with M-SCOP (0.3 and 1 mg/kg) and hexamethonium (HEX, 1 and 3 mg/kg), muscarinic and nicotinic antagonists, respectively, which are active only in the periphery. In contrast to the ability of these four compounds to attenuate the SCOP amnesia, only the centrally acting compounds SCOP (3 mg/kg) and MECA (10 mg/kg) induced an amnesia when administered alone. These findings suggest that the induction of amnesia of passive avoidance involves central cholinergic systems, whereas the NEO, and possibly PHYSO, reversal of the SCOP induced amnesia is mediated peripherally by both muscarinic and nicotinic receptors. It is hypothesized that the release of adrenal catecholamines, the influence of which on memory processes is well known, and secondarily glucose, may be responsible for the NEO antagonism of the SCOP amnesia.     

Anesthesia with 1.5 minimum alveolar concentration sevoflurane is not altered by physostigmine as measured by bispectral and clinical indices

STUDY OBJECTIVE: To evaluate the effect of physostigmine on 1.5% sevoflurane anesthesia and recovery. DESIGN: Prospective, randomized, double-blinded study. SETTING: Operating room of a university-affiliated, metropolitan hospital (Aretaieion Hospital and St Savas Hospital). PATIENTS: Forty female American Society of Anesthesiologists physical status I and II patients scheduled for breast biopsy. INTERVENTIONS: Patients were randomly assigned in physostigmine (PHYSO) and normal-saline (NS) group. Anesthesia was induced with sevoflurane 8% using a vital capacity breath technique, and rocuronium 0.6 mg/kg was given to facilitate Laryngeal Mask Airway (LMA) No. 4 insertion. Anesthesia was maintained with end-tidal sevoflurane 1.5 minimum alveolar concentration (MAC; 3% end-tidal concentration) throughout the procedure. MEASUREMENTS: After skin closure and under steady-state sevoflurane anesthesia 1.5 MAC, heart rate, blood pressure, and Bispectral Index (BIS) were recorded. Immediately after, the PHYSO group received intravenous 2 mg of physostigmine, whereas the NS group received equal volume of normal saline. Bispectral Index and hemodynamic measurements were recorded 5, 8, and 10 minutes after treatment. Anesthesia was then discontinued and the LMA was removed. Zero, 15, and 30 minutes after LMA removal, patients were evaluated for orientation, sedation, sitting ability, and the "picking up matches" test, as well as for nausea and vomiting. MAIN RESULTS: No difference was found in BIS (29 +/- 4, 32 +/- 6, 31 +/- 6, 30 +/- 7, 84 +/- 11 in the PHYSO group vs 29 +/- 6, 30 +/- 6, 30 +/- 5, 31 +/- 5, 86 +/- 7 in the NS group), hemodynamic parameters, or recovery parameters between the 2 groups at any time. No nausea or vomiting was observed in either group. CONCLUSIONS: Physostigmine did not influence BIS values or early recovery when administered to patients anesthetized with 1.5 MAC sevoflurane anesthesia.     

Acetylcholinesterase inhibitors ameliorate behavioral deficits in the Tg2576 mouse model of Alzheimer’s disease

Rationale Acetylcholinesterase inhibitors are widely used for the treatment of patients with Alzheimer’s disease (AD). However, the relationship between the capacity of such drugs to ameliorate the symptoms of AD and their ability to alter the underlying disease process is not well understood. Transgenic mice that overexpress the human form of amyloid precursor protein and develop deposits of β-amyloid (Aβ) and behavioral deficits during adulthood are useful for investigating this question. Objectives The effects of administration of two acetylcholinesterase inhibitors, physostigmine and donepezil, on Aβ plaque formation and memory-related behaviors were investigated in the Tg2576-transgenic mouse model of AD. At 9–10 months of age, Tg2576-transgenic [Tg(+)] mice develop Aβ plaques and impairments on paradigms related to learning and memory as compared to transgene-negative [Tg(−)] mice. Methods Beginning at 9 months of age, increasing doses of physostigmine (0.03, 0.1, and 0.3 mg/kg), donepezil (0.1, 0.3, and 1.0 mg/kg), or saline were administered over 6 weeks to cohorts of Tg(+) and Tg(−) mice. Performance on tests of spatial reversal learning and fear conditioning was evaluated at each drug dose throughout the period of drug administration. After drug administration was completed, the animals were sacrificed and Aβ plaque number was quantified. Results Administration of physostigmine and donepezil improved deficits in contextual and cued memory in Tg(+) mice so that their behaviors became more similar to Tg(−) mice. However, administration of physostigmine and donepezil tended to improve cued memory and deficits in spatial learning in both Tg(+) and Tg(−) mice. Physostigmine administration demonstrated more prominent effects in improving contextual memory than donepezil, while donepezil was more effective than physostigmine in improving deficits in the acquisition of the spatial memory paradigm. Administration of neither drug altered the deposition of Aβ plaques. Conclusions These studies suggest that acetylcholinesterase inhibitors can ameliorate memory deficits in Tg(+) mice without necessarily altering the deposition of Aβ plaques. Tg2576 mice may be useful as an animal model to further investigate the mechanisms by which aceytlcholinesterase inhibitors improve cognitive deficits in patients with AD.     

The effects of certain H(1)-antagonists on visual evoked potential in rats

The present study was undertaken to clarify the effects of certain H(1)-antagonists on visual evoked potential (VEP) in rats. Pyrilamine (5 and 10 mg/kg), diphenhydramine (5 and 10 mg/kg) and chlorpheniramine (10 and 20 mg/kg) caused a significant reduction in the amplitude of late VEP components (P(3)-N(3), N(3)-P(4)), although these drugs showed no significant changes in early VEP components (P(1)-N(1), N(1)-P(2)). Cyproheptadine caused a slight enhancement of late components of VEP at a dose of 20 mg/kg. On the other hand, epinastine caused no significant effect on late VEP components even at a dose of 20 mg/kg. The reduction in the late VEP components induced by pyrilamine and diphenhydramine was significantly antagonised by pre-treatment of histidine (200 and 500 mg/kg), but not by physostigmine even at a dose of 0.01 mg/kg. The effect induced by cyproheptadine was significantly potentiated by histidine (500 mg/kg), and significantly reduced by DOI (2 mg/kg). These results indicate that an inhibition of the late VEP components induced by H(1)-antagonist pyrilamine, diphenhydramine and chlorpheniramine may be due to an inhibition of specific sensory system relating the histaminergic mechanisms. In addition, slight enhancement of these components induced by cyproheptadine may be attributable to its anti-serotonergic effects.     

Effect of physostigmine and atropine on acetylcholine turnover in mouse brain

Summary The effect of physostigmine salicylate (0.5 mg/kg, i.p.) alone and in combination with atropine sulfate (25 mg/kg, i. p.) on levels of acetylcholine (ACh) and choline (Ch) and turnover of ACh has been studied in whole brain and striatum of mice. The animals were killed by focussed microwave irradiation and the turnover of ACh was studied after i.v. injection of deuterium labelled Ch by employing mass fragmentography. Physostigmine increased the levels of ACh in whole brain from 24.5–28.0 nmol/g (P<0.001) whereas there was no significant increase in striatum. The levels of Ch were also increased. The turnover rate of ACh was decreased in whole brain from 15.4 to 8.4 and in striatum from 52.9 to 24.4 nmol/g · min. Physostigmine given before or after atropine did not completely block the ACh lowering effect of atropine. When atropine was given before physostigmine the turnover rate of ACh in whole brain was increased to 24.2 nmoles/g · min. The results seem to indicate that there is no clear cut relation between the turnover rate and level of ACh in vivo. The increase of the turnover rate induced by atropine is masked unless a cholinesterase inhibitor is given to protect the newly synthesized labelled ACh released by atropine.A preliminary account of this work was reported at the Symposium on Current Topics in Drug Research, held October 19–21, 1977, at Uppsala, Sweden     

Tetrahydrocannabinol and acetylcholinesterase

Recent evidence suggests that the psychoactive effect of delta-9-tetrahydrocannabinol (Δ⁹-THC), the major psychoactive constituent of marihuana, may be mediated through an alteration of cholinergic neurotransmission. One possible mechanism by which Δ⁹-THC could have its effect is by affecting acetylcholinesterase (AChE) and there is evidence that has suggested that this may be an important mechanism. The results reported in the present study have shown that there is no physiologically important interaction between AChE and Δ⁹-THC or its metabolites that could explain its psychoactive effects or the profound clinical depression observed when human marihuana users are administered the cholinesterase inhibitor physostigmine.     

Interaction between cholinergic and catecholaminergic agents in a spontaneous alternation task

Spontaneous alternation was examined in a free running Y-maze task after various pharmacological manipulations. Whereas scopolamine reduced alternation to chance levels, d-amphetamine in some doses resulted in alternation significantly below chance (perseveration). Physostigmine treatment increased levels of alternation whereas reserpine was without effect. Concurrent administration of drugs revealed that reserpine effectively reversed the effects of scopolamine, while the perseveration induced by d-amphetamine was antagonized by physostigmine. When animals were pre-exposed to the Y-maze the effects of d-amphetamine were enhanced, but effects of scopolamine were not modified. Finally, scopolamine treatment augmented the perseverative effects of d-amphetamine. It was suggested that cholinergic agents modify alternation by effects on habituation. On the other hand d-amphetamine produces genuine perseveration without effects on habituation per se. Alternation performance and perseveration were suggested to be mediated by the interaction between the distinct behavioral effects of cholinergic and catecholaminergic activity.     

Effects of physostigmine and scopolamine on operant brightness discrimination in the rat

Performance in an operant brightness discrimination was facilitated through the mid-range of training by injections of 0.3 mg/kg physostigmine. Performance was facilitated, compared to saline injected controls, due to lower response rates during S^Δ while S^D response rates were not affected. Injection of 0.5 mg/kg scopolamine suppressed both S^D and S^Δ response rates proportionally and thus did not affect discrimination performance as reflected in the discrimination ratio. The facilitation of discrimination performance produced by physostigmine was interpreted as due to facilitation of inhibitory precesses and as consistent with the hypothesis of a central cholinergic inhibitory mechanism.     

Effects of physostigmine,scopolamine, and mecamylamine on the sleeping time induced by ketamine in the rat

Male Sprague-Dawley rats weighing 116–241 g were injected i.p. with ketamine hydrochloride, 80 mg per kilo of body weight. Immediately after loss of righting reflex, scopolamine, physostigmine, and mecamylamine were administered i.p. to different groups of rats. Control animals received sterile saline by the same route. The ketamine-induced sleeping time was significantly prolonged by physostigmine and scopolamine, but not by mecamylamine. After the delayed injection of physostigmine, the ketamine sleeping time was longer. These results, although too preliminary for a mechanistic interpretation, suggest that multiple neurotransmitter systems, probably including the cholinergic system, are involved in the mechanism of action of ketamine-induced narcosis.     

An analysis of the mode of action of carbachol on the chick biventer cervicis nerve--muscle preparation.

The mechanism of contracture evoked by carbachol in the isolated chick biventer cervicis nerve--muscle preparation was studied. At concentrations lower than 11 muM, carbachol progressively induced contracture at a rate much slower than did acetylcholine. A spontaneous increase of the response to carbachol, but not to acetylcholine, was observed 2-4 hr after isolation of the muscle. By contrast, no change of the response occurred in the denervated muscle. Anticholinesterase treatment shifted the dose-response curve for carbachol markedly to the left as far as the contracture attained after 4-6 min incubation was concerned. The shift was much less marked for the dose-response curve plotted against the initial rate of response defined as the contracture obtained after 1 min incubation. No enhancement of response was detected by inhibition of acetylcholinesterase in the denervated muscle. beta-Bungarotoxin which blocked neuromuscular transmission within 30 min, caused a transient enhancement of the response to carbachol. After 2-3 hr treatment, however, the spontaneous increase of response to carbachol was counteracted by the toxin. No potentiation of the response by anticholinesterase agents was observed after toxin treatment. When added in the presence of physostigmine or echothiophate, beta-bungarotoxin reduced the response to carbachol to the control level in 2 hr. The response to carbachol in the muscle treated with alpha-bungarotoxin and washed subsequently was also not potentiated by anticholinesterase treatment. Repetitive nerve stimulation in the presence of hemicholinium-3 caused a neuromuscular blockade but did not appreciably antagonize the response to carbachol more than that to acetylcholine either in the absence or presence of physotigmine. When calcium ion in the medium was decreased from 2.7 to 0.54 mM, ther response to nerve stimulation was nearly completely inhibited, but the response to carbachol was not affected and could still be potentiated by anticholinesterase. It is concluded that carbachol has both direct and indirect effects on the chick biventer cervicis muscle. At a low concentration, particularly in the presence of an anticholinesterase and if sufficient time of incubation is allowed, the indirect effect caused by release of acetylcholine may become more prominent than the direct action on the post-synaptic receptor. Both the mechanism and the store of acetylcholine for this indirect action appear to be different from those for the nerve impulse.