Subchronic physostigmine pretreatment in guinea pigs: effective against soman and without side effects.

The behavioral and neurophysiological effects of the subchronically administered cholinesterase-inhibitor physostigmine (PHY) (0.025 mg/kg/h) either with or without the muscarinergic antagonist scopolamine (SCO) (0.018 mg/kg/h) were determined in guinea pigs.

Side effects of physostigmine as a pretreatment in guinea pigs.

To prevent incapacitation following nerve agent intoxications, it is proposed to replace pyridostigmine by the centrally active carbamate physostigmine (PHY). Behavioral and neurophysiological effects of PHY were determined and whether these effects would be counteracted by scopolamine. In addition, we compared them with the effects of another reversible cholinesterase (ChE) inhibitor ethyl-p-nitrophenylphosphoramidate (PNF) At similar levels of blood AChE inhibition, PHY caused a larger shuttlebox performance decrement than PNF, which was antagonized by scopolamine (0.

Effects of low doses of cholinesterase inhibitors on behavioral performance of robot-tested marmosets.

To investigate at which dose levels undesirable effects started, behavioural performance and several physiological parameters were measured in marmosets (Callithrix jacchus) after soman (1.75 and 3.5 micrograms/kg), sarin (3 and 6 micrograms/kg), physostigmine (10 and 20 micrograms/kg), and pyridostigmine (200 and 400 micrograms/kg).

Efficacy of HI-6 and HLö-7 in preventing incapacitation following nerve agent poisoning.

The therapeutic efficacy of the oximes HI-6 and HLö-7 (132.5 mumol/kg), in combination with atropine, in soman- or tabun-intoxicated guinea pigs was compared, particularly with respect to recovery of shuttlebox performance and electroencephalograms (EEGs). After 1.

A simple automated test to measure exploratory and motor activity of marmosets.

An automated device is described to test the exploratory and motor activity of common marmosets (Callithrix jacchus). The device consists of four boxes interconnected by PVC tubes. The presence of an animal in a box is detected by a photocell.

Search for a therapy against soman-intoxication.

This mini-review mainly describes a part of the pharmacological research carried out in our laboratory during the past decades, aimed at finding a therapy against intoxication by cholinesterase-inhibiting organophosphates, in particular against the nerve agent soman. In particular soman, because this is one of the nerve agents that consistently appears to be very resistant to treatment. Various experimental approaches are described.

Behavioral performance, brain histology, and EEG sequela after immediate combined atropine/diazepam treatment of soman-intoxicated rats.

It is known that rats poisoned with near-lethal doses of pinacolyl methylphosphonofluoridate (soman) develop brain lesions, particularly when convulsions are induced. When rats were intoxicated with a LD50 of soman and treated immediately thereafter with a combination of low doses of atropine and diazepam (LOW AS/DZ treatment), large decrements in performance of an earlier acquired shuttle-box task were found 6 days after intoxication. In contrast, no such decrements were found in soman-intoxicated animals treated similarly with a combination of high doses of these drugs (HIGH AS/DZ treatment).

Therapeutic efficacy of HI-6 in soman-poisoned marmoset monkeys.

The therapeutic efficacy of the oxime HI-6 against intoxication with the irreversible cholinesterase (ChE) inhibitor soman was tested in marmoset monkeys. Five out of six marmosets, intoxicated with 5 x LD50 soman and treated immediately with diazepam (0.2 mg.

Active avoidance behavior in guinea pigs: effects of physostigmine and scopolamine.

Behavioral training of guinea pigs by conventional methods, such as used for rats and mice, appears difficult. Hence, only a few behavioral experiments with guinea pigs have been described in the literature. An active avoidance technique in an automated two-way shuttlebox is described using sound as a conditioned (CS) and a tactile stimulus (a stream of air ruffling their fur) as an unconditioned (UCS) stimulus.

The isolated blood-perfused pig ear: an inexpensive and animal-saving model for skin penetration studies.

To overcome most of the disadvantages of current models to investigate percutaneous penetration of drugs or toxic substances, a model is proposed here based on the isolated pig ear, which is obtained at the slaughterhouse, and perfused with oxygenated blood from the same pig. To determine the viability of the preparations, we measured glucose consumption and lactate production as metabolic parameters, Na+ and K+ ions, as well as lactate dehydrogenase activity in blood as markers for cell damage, whereas vasomotor reactivity was assessed by administering noradrenaline and isoxsuprine. After 60 min of equilibration, only insignificant changes in these parameters were observed during the subsequent 3-hr test period (longer periods were not tested).

On the development of behavioral tolerance to organophosphates. IV: EEGand visual evoked responses.

Several earlier studies showed that, in contrast with DFP, repeated injections with soman did not lead to behavioral tolerance in rats. The reason for the difference between the effects of these two organophosphate cholinesterase inhibitors was not clear and a neurophysiological approach was undertaken. Four experiments (A, B, C and D) were carried out, each consisting of three groups of rats, SC injected with saline, DFP (600 micrograms/kg) or soman (60 micrograms/kg) respectively.

Some animal models and their probability of extrapolation to man.

A number of examples of experimental models are presented which are subdivided into models that provide results with a "high" or a "moderate" probability for (qualitative) extrapolation to man. Models with a high predictive value for man are those that produce results that can be directly verified in man or human organs, in contrast with models that have a moderate predictive value, where one has to rely on similarities or analogies of signs and symptoms between man and the animal model. Models with low probability should be rejected.

On the development of behavioral tolerance to organophosphates. III: Behavioral aspects.

As part of a study on the mechanisms underlying behavioral tolerance to cholinesterase-inhibiting organophosphates (OP's) the present investigation was focussed on behavioral procedures affecting the development of tolerance. The effects of chronic administration of the OP's DFP (600 micrograms/kg SC) and soman (60 micrograms/kg SC) were compared in rats. These doses do not cause detectable effects upon close observation of the animals.

On the development of behavioral tolerance to organophosphates. I: Behavioral and biochemical aspects.

The development of tolerance to organophosphates (OPs) was investigated by SC injections of saline and sublethal doses of DFP or soman three times per week or every other day for at least 4 weeks. Shuttlebox performance was tested 1 hr and 24 hr after the injections. Notwithstanding a progressive inhibition of AChE to very low values in various organs, shuttlebox performance was virtually normal 24 hr after the OP injections.

Side effects of therapeutic drugs against organophosphate poisoning.

The possible side effects of therapeutic drugs against organophosphate poisoning were investigated. First, dose-effect curves were obtained with atropine sulphate (AS), P2S, obidoxime, aprophen, N-methylatropine nitrate and HI-6. The first three drugs are currently used in the therapy of organophosphate poisoning, the others are potentially useful candidates.

Retention of soman in rats, guinea-pigs and marmosets: species-dependent effects of the soman simulator, pinacolyl dimethylphosphinate (PDP).

Whether the temporary retention of intact soman in the rat and its subsequent delivery from tissues into the circulation of the blood is also demonstrable in guinea-pigs and marmosets has been investigated as was whether the soman simulator PDP (pinacolyl dimethylphosphinate) prevented this retention. Electric eel AChE, intravenously injected 1.5 h after an intravenous soman intoxication into anaesthetized, atropinized and artificially ventilated guinea-pigs (150 micrograms kg-1 soman), marmoset monkeys (100 micrograms kg-1 soman) and rats (330 and 172.

The effects of topical foscarnet in a new model of herpes simplex skin infection.

Because of the lack of agreement about the effects of topically applied antiviral agents on herpes simplex virus (HSV) skin infections in humans and in animals, an in-vivo human skin model of infection was developed. Human skin was grafted on to congenitally athymic nude mice and the therapeutic effects of topically applied viral DNA polymerase inhibitor phosphonoformate (foscarnet) on the course of the disease were studied. Following infection with HSV, the human skin grafts developed herpes vesicles similar to those seen in human skin in situ.

Stereoisomers of soman (pinacolyl methylphosphonofluoridate): inhibition of serum carboxylic ester hydrolase and potentiation of their toxicity by CBDP (2-(2-methylphenoxy)-4H-1,3,2-benzodioxaphosphorin-2-oxide) in mice.

The interaction of C(+/-)P(+/-)-soman (pinacolyl methylphosphonofluoridate) and its individual stereoisomers with serum carboxylic-ester hydrolase and potentiation of their toxicity by a carboxylic-ester hydrolase inhibitor CBDP (2-(2-methylphenoxy)-4H-1,3,2-benzodioxaphosphorin-2-oxide) was investigated. C(+/-)P(+/-)-Soman and the individual stereoisomers all inhibited purified mouse serum carboxylic-ester hydrolase to different degrees. C(+/-)P(+/-)-Soman and the C(-)P(-)- and C(+)P(-)-isomers had Ki values of 30.

Further evidence for the effect of pinacolyl dimethylphosphinate on soman storage in muscle tissue.

Diaphragms isolated from rats 60 or 120 min after the intravenous injection of 6 X LD50 soman were incubated with electric eel acetylcholinesterase. As calculated from the enzyme inhibition, detectable amounts of P(-)-soman (1,2-dimethylpropyl methylphosphonofluoridate) were released from the diaphragm into the medium even 120 min post-injection. This release was reduced by additional pretreatment of the rats with pinacolyl dimethylphosphinate, providing further evidence that this compound prevents the storage of soman in diaphragm tissue.

Prophylactic and therapeutic efficacy of the soman-simulator, pinacolyl dimethylphosphinate.

Atropinized rats, intoxicated with 6 or 8 X LD50 soman and subsequently treated with the oxime HI-6 died several hours after intoxication. Oral or intravenous administration of the soman-simulator, pinacolyl dimethylphosphinate (PDP), given at progressively increasing time intervals before soman, appeared to be very active in preventing death and secondary failure of neuromuscular transmission that followed HI-6-induced recovery. Therapeutically, PDP was only effective when given immediately after soman intoxication and oxime treatment.

Residual behavioral incapacitation after therapy of soman intoxication: the effect of a soman simulator.

When rats are intoxicated with high doses of the cholinesterase inhibitor soman (5-8 X LD50), the compound is temporarily stored in a "depot" from which it is gradually released. Thus, despite an initially successful therapy with the oxime HI-6 and atropine, the released soman re-intoxicates the organism and death may ensue in several hours. Soman simulators, i.

The prophylactic efficacy of various simulators against intoxication with the organophosphate soman: structure-activity studies.

The effects were investigated of structural variations of the soman simulator pinacolyl dimethylphosphinate on its efficacy to prevent secondary failure of oxime-induced recovery of neuromuscular transmission and death after soman intoxication. The simulators were administered prophylactically to atropinized, HI-6 treated rats, dosed with 6 or 8 X LD50 soman. In these new simulators the pinacolyl moiety was varied, the phosphonyl oxygen atom was replaced by sulphur, or the phosphorous-bound methyl groups were replaced by ethyl or methoxy groups.

On the development of skin models for toxicity testing.

The extrapolation of the results of measurements of skin penetration or skin damage with current in vitro and in vivo animal models to humans is of questionable value. Therefore, the usefulness of two other models is being evaluated: human skin grafts on congenitally athymic mice and cultures of human epidermal cells. The results show that histologically and immunologically the human skin grafts retain their "human" characteristics for at least 6 months.

The automated analysis of coordinated hindlimb movement in rats during acute and prolonged exposure to toxic agents.

The effects of CNS-active drugs and neurotoxic agents on motor coordination in the rat were studied using a newly developed, automated technique. In this test, a tv/microprocessor-based system was utilized to detect and describe the movement and placement characteristics of one of the rat's hindpaws as the rat placed its paw from one rung to another while walking in a rotating wheel. In studies employing a wheel speed of 8.

New simulators in the prophylaxis against soman poisoning: structural specificity for the depot site(s).

The oxime HI-6 is effective as an antidote in the soman poisoned (6-8LD50) rat, however, successfully treated animals subsequently show a gradual relapse of signs of poisoning and eventually die after several hours. The relapse is caused by the reappearance of soman at specific sites, after having been elsewhere in the body. Diaphragms isolated from poisoned rats successfully treated with HI-6 also showed a 'secondary' relapse of poisoning.