Learned suppression of stereotypy in amphetamine-treated rats: implications for understanding tolerance to amphetamine 'anorexia'

The purpose of this study was to determine whether amphetamine-treated rats can learn to suppress stereotyped movements in order to feed. Rats implanted with cannulae were reinforced with intraoral infusions of milk for holding their heads stationary within a narrow area of space defined by intersecting photobeams. Four of six rats given chronic injections of amphetamine (2mg/kg) learned the response. The amount of milk ingested as a result of the infusions increased over trials at a rate that was comparable to that of rats given milk in bottles. Despite the development of such 'tolerance', analysis of the temporal distribution of photobeam interruptions revealed residual effects of the drug. Specifically, amphetamine-treated rats had longer latencies to initiate infusions and displayed a more fragmented pattern of responding than did saline controls. These results demonstrate that rats can learn to inhibit amphetamine-induced sterotypy and support the view that tolerance to amphetamine 'anorexia' involves learning to suppress stereotyped movements that interfere with feeding. Parallels to the suppression of involuntary movements in humans are noted.

The scavenging of hydroxyl radical(.OH) by a prostacyclin analogue, taprostene.

A possible mechanism by which prostacyclin (PGI2) analogues provide beneficial effects including improved survival in shock experimentally induced by endotoxin, polytrauma or hypovolemia was studied. Since several studies have implicated oxygen free radical-mediated tissue damage, we investigated whether PGI2-analogues exert their 'cytoprotective' effects by inhibiting overproduction of oxygen free radicals. For this reason, the efficiency of Taprostene to scavenge hydroxyl radicals (.OH) and to possibly prevent the subsequent formation of reactive oxygen species was studied. Competition experiments were performed in which the .OH generated by H2O2/Fe2+ abstracted a hydrogen from Taprostene (CG-4203) [5Z,13E, 9,11,15S)-2,3,4-trinor-1,5-inter-m-phenylene-6,9-epoxy-11,15-di hyd roxy-15-cyclohexyl-16,17,18,19,20-pentanor-prosta-5,13-dieno ic acid sodium salt], and the resulting carbon-centered radical was trapped with the spin trap 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO). This spin trap reacted with .OH to yield an M4PO-OH spin adduct observable by Electron Paramagnetic Resonance (EPR) spectroscopy and resulted in the rate constant, k2 = 1.5 x 10(10) M-1s-1, for the reaction between .OH and Taprostene. The results show that Taprostene is an efficient .OH scavenger. In addition, reactions of hypochlorous ion (-OCL) with hydrogen peroxide (H2O2) in the presence of Taprostene were monitored using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and M4PO dissolved in deuterium oxide.

Successful pretreatment/therapy of soman, sarin and VX intoxication.

Chemical pretreatment is effective against a 2 LD50 challenge of soman, sarin or VX or a 5 LD50 challenge of tabun. Chemical pretreatment followed by post challenge therapy should be effective against greater levels of agent. Such tests in guinea pigs are reported here; pretreatment regimens (PRGs) consisted of physostigmine (0.15 mg/kg, im) and an adjunct. The adjuncts [mg/kg, im] used were aprophen [8], atropine (AT)[16], azaprophen (AZA)[5], benactyzine [1.25], benztropine (BT) [4], scopolamine [0.08] and trihexyphenidyl [2]. Pretreatment was given 30 min before, and atropine (16 mg/kg, im) and 2-PAM (25 mg/kg, im) therapy (T) at one min after, 5 LD50s of agent. Results indicate that, all of the PRG+T regimens, except BT-not tested with T, prevent lethality by soman; trihexyphenidyl and scopolamine (the only adjuncts used therein) regimens each prevent lethality by sarin and VX. Against soman, all PRG+T regimens (vs PRG only) may shorten the median recovery time to 2 hrs or less. Even without therapy, the PRGs containing AT, AZA or BT prevent lethality by 5 LD50s of soman; however, used alone, only the PRG containing AZA reduces the incidence of convulsions at this level of soman.

Pharmacokinetics and pharmacodynamics of oximes in unanesthetized pigs.

The pharmacokinetics and cardiovascular pharmacodynamics of two oximes were studied in unanesthetized pigs. Effects of 2-[(hydroxyimino)methyl]-1-methylpyridinium chloride (pralidoxime chloride; 2-PAM Cl; 50 mumol/kg) were compared with those of 1,1-methylene bis[4(hydroxyiminomethyl) pyridinium] dichloride (methoxime; MMB-4; 100 mumol/kg). Cardiopulmonary parameters were monitored and plasma concentrations of oximes were determined from arterial blood samples taken at intervals over a period of 5 hr postinjection. Plasma concentrations for both oximes were fitted to standard pharmacokinetic models using the computer program PCNONLIN. Average pharmacokinetic parameters were determined for each oxime. Only mild to moderate physiological side effects were detected following intramuscular administration. 2-PAM Cl was more rapidly absorbed and distributed in the blood than MMB-4. Although the latter had a slight lag time to attain detectable levels in the blood, retention time was longer than that of 2-PAM Cl.

Hairless guinea pig bioassay model for vesicant vapor exposures.

Sulfur mustard (HD; 1,1'-thiobis[2-chloroethane]) induces fluid-filled blisters in man but not in conventional laboratory animals. An animal model is needed to emulate both cytotoxic (vesicant) and vascular (irritant) responses of human skin to HD exposures. An acceptable model must permit reproducible comparisons of uniformly graded and dose-related HD control responses with reduced responses that may follow antivesicant treatments. Hairless guinea pigs were evaluated by exposing six or eight dorsal skin sites 12 mm in diameter to similar HD vapor concentrations for graded intervals (1-16 min). HD vapor was delivered under occlusive caps holding 10 microliters of HD in filter paper located 5 mm above the skin. Four-minute exposures induced moderate erythema, slight edema, and microblisters in 1 of 39 sites. Eight-minute exposures induced severe erythema, moderate edema, and microblisters in 31 of 40 sites. Gross blistering was not seen after use of vapor cups, but damage to basal cells resembled lesions of vesicant injury in man. The hairless guinea pig model, with graded HD vapor exposures, provides acceptable comparisons of responses. Exposures of both 4- and 8-min durations were used to show the feasibility of using this model to bioassay antivesicant topical protectants. These methods may be useful for measurements of irritant and cytotoxic responses of skin to other toxic vapors.

Decreased brain pathology in organophosphate-exposed rhesus monkeys following benzodiazepine therapy.

Two benzodiazepine compounds, midazolam and diazepam, were administered as adjunctive treatment to soman-exposed rhesus monkeys to evaluate their effects on acute soman intoxication. Monkeys were pretreated orally with pyridostigmine, exposed to soman, and treated i.m. with atropine, pralidoxime chloride (2-PAM), and with midazolam, diazepam or sterile water (control). All monkeys that received the benzodiazepines recovered sooner and exhibited no convulsions. Neuronal degenerative and necrotic lesions were decreased or eliminated in the entorhinal cortex, caudate nucleus, and hippocampus of those animals that received benzodiazepine therapy. These findings support the continued evaluation of drugs with anticonvulsant activity as standard adjunct therapy for soman intoxication.

Effect of lithium chloride-induced aversion on appetitive and consummatory behavior.

The effect of lithium chloride-induced conditioned taste aversions on appetitive and consummatory behavior was determined. Rats were given access to a 0.1% saccharin solution for 15 min either in bottles or by infusion through an intraoral cannula. Bottle-fed rats given postprandial injections of lithium chloride showed greater aversion to saccharin than cannula-fed rats. During extinction, cannula-fed rats gradually recovered to control levels of intake, whereas bottle-fed rats continued to avoid the saccharin. These results suggest that lithium chloride affects appetitive behavior to a greater extent than it affects consummatory behavior.

A possible role for taurine in osmoregulation within the brain.

Intracranial microdialysis was used to measure changes in extracellular amino acids within the rat brain during local osmotic alteration of the extracellular microenvironment or during systemic water intoxication. Increased cellular hydration produced by either of these methods was accompanied by a marked increase in extracellular taurine levels without affecting the other amino acids measured. With local osmotic alteration, this increase was osmolarity dependent and reversible. The specificity, sensitivity, and reversibility of the increase in extracellular taurine strongly suggest a functional role in osmoregulation in the brain under normal as well as pathological conditions.

Changes in extracellular amino acids during soman- and kainic acid-induced seizures.

Extracellular amino acid levels in the rat piriform cortex, an area highly susceptible to seizure-induced neuropathology, were determined by means of intracranial microdialysis. Seizures were induced by systemic administration of either soman (O-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase, or the excitotoxin kainic acid. Extracellular glutamate levels increased in animals with seizures shortly after administration of either convulsant, but this change was statistically significant only in the case of soman-treated animals. Extracellular taurine levels increased markedly, reaching two- and fourfold baseline levels during the second hour of soman- and kainic acid-induced seizures, respectively. Taurine levels did not increase in the subpopulation of soman-treated animals without seizures, a finding indicating that elevation of extracellular taurine level is seizure related. Thus, we propose that taurine efflux may be a physiological cellular response to neuronal changes produced by excitotoxic chemicals, either directly or as a consequence of seizures.

Induction of metallothionein in a human trophoblast cell line by cadmium and zinc.

The induction of metallothionein (MT) in a cell line derived from a malignant trophoblastic tumor (JAr cells) was demonstrated using the Cd/heme radioassay following exposure to Cd or Zn. Cd at an optimal concentration of 1 microM produced a 30-fold increase in MT following a 24 hr incubation. Induction by Cd was both time and dose dependent, with a significant increase in MT noted as early as 3 hr, with levels continuing to increase up to 24 hr. Zn was also quite effective in inducing MT synthesis in this cell line. Exposure to 80 microM Zn for 24 hr produced a 70-fold increase in MT. Although Cd was a more potent inducer of MT, exposure to Zn resulted in a greater magnitude of induction. The magnitude of MT induction in JAr cells was much greater than that seen in cultured trophoblasts from term chorion laeve. The degree of induction seen in this cell line makes it an interesting model for the study of MT's role in trophoblast function. MT induction in trophoblasts may reflect a protective mechanism against heavy metal toxicity and/or an integral aspect of normal zinc homeostasis.