Animal models for assessing the neurobehavioral impact of airborne pollutants

Impact of the Aversive Effects of Drugs on Their Use and Abuse

Drug use and abuse are complex issues in that the basis of each may involve different determinants and consequences, and the transition from one to the other may be equally multifaceted. A recent model of the addiction cycle (as proposed by Koob and his colleagues) illustrates how drug-taking patterns transition from impulsive (acute use) to compulsive (chronic use) as a function of various neuroadaptations leading to the downregulation of DA systems, upregulation of stress systems, and the dysregulation of the prefrontal/orbitofrontal cortex. Although the nature of reinforcement in the initiation and mediation of these effects may differ (positive vs. negative), the role of reinforcement in drug intake (acute and chronic) is well characterized. However, drugs of abuse have other stimulus properties that may be important in their use and abuse. One such property is their aversive effects that limit drug intake instead of initiating and maintaining it. Evidence of such effects comes from both clinical and preclinical populations. In support of this position, the present review describes the aversive effects of drugs (assessed primarily in conditioned taste aversion learning), the fact that they occur concurrently with reward as assessed in combined taste aversion/place preference designs, the role of aversive effects in drug-taking (in balance with their rewarding effects), the dissociation of these affective properties in that they can be affected in different ways by the same manipulations, and the impact of various parametric, experiential, and subject factors on the aversive effects of drugs and the consequent impact of these factors on their use and abuse potential.

Toxicologic considerations in workplace exposures

The evaluation of a potential toxic exposure requires a detailed patient evaluation in addition to consideration of the specific chemical substance, route of exposure, duration and intensity of exposure, and documentation of the pathologic consequences.

Function in neurotoxicity: index of effect and also determinant of vulnerability

1. In neurotoxicity, functional indices may be the only available measures of effect, as many potent neurotoxic agents produce no morphological change. Examples of these are strychnine, dieldrin and pyrethroids, which produce excitation but no pathology, and barbiturates, xylene and lithium, which produce depression but no pathology. 2. In other cases where both functional and morphological effects are seen, functional measures often produce the most convenient, if not always the most specific, indices of toxicity. Appropriate functional measures can be highly sensitive, both in humans and in experimental animals, and can also give vital mechanistic information. However, it is essential that functional measures are reproducible and interpretable (some behavioural measures are not) and also provide a reasonably exacting test of function (passive observation of resting behaviour can miss many effects). 3. In addition to their use as an index of toxicity, changes in function, even within the normal range, can themselves influence susceptibility to toxins. Tissue perfusion can determine delivered dose and is influenced by function, while metabolic transformation is modified by nutritional state. Nutritional state can also influence absorption, with anaemia enhancing manganese toxicity and calcium deficiency enhancing lead toxicity. Functional activity can influence target susceptibility directly: thus, noise exposure enhances the ototoxicity of carbon monoxide, toluene or aminoglycoside antibiotics; noise, motor activity or anaesthesia all influence the central neurotoxicity of dinitrobenzene or metronidazole; motor activity enhances the peripheral nerve toxicity of lead or thallium; and nerve regeneration enhances the toxicity of hexane. These functional factors can be very important in determining individual susceptibility.

Potential animal model of multiple chemical sensitivity with cholinergic supersensitivity

Multiple Chemical Sensitivity (MCS) is a clinical phenomenon in which individuals, after acute or intermittent exposure to one or more chemicals, commonly organophosphate pesticides (OPs), become overly sensitive to a wide variety of chemically-unrelated compounds, which can include ethanol, caffeine and other psychotropic drugs. The Flinders Sensitive Line (FSL) rats were selectively bred to be more sensitive to the OP diisopropylfluorophosphate (DFP) compared to their control counterparts, the Flinders Resistant Line (FRL) rats. The present paper will summarize evidence which indicates that the FSL rats exhibit certain similarities to individuals with MCS. In addition to their greater sensitivity to DFP, the FSL rats are more sensitive to nicotine and the muscarinic agonists arecoline and oxotremorine, suggesting that the number of cholinergic receptors may be increased, a conclusion now supported by biochemical evidence. The FSL rats have also been found to exhibit enhanced responses to a variety of other drugs, including the serotonin agonists m-chlorophenylpiperazine and 8-OH-DPAT, the dopamine antagonist raclopride, the benzodiazepine diazepam, and ethanol. MCS patients report enhanced responses to many of these drugs, indicating some parallels between FSL rats and MCS patients. The FSL rats also exhibit reduced activity and appetite and increased REM sleep relative to their FRL controls. Because these behavioral features and the enhanced cholinergic responses are also observed in human depressives, the FSL rats have been proposed as a genetic animal model of depression. It has also been reported that MCS patients have a greater incidence of depression, both before and after onset of their chemical sensitivities, so cholinergic supersensitivity may be a state predisposing individuals to depressive disorders and/or MCS. Further exploration of the commonalities and differences between MCS patients, human depressives, and FSL rats will help to elucidate the mechanisms underlying MCS and could lead to diagnostic approaches and treatments beneficial to MCS patients.