Lateral Parabrachial Lesions Disrupt Paraoxon-Induced Conditioned Flavor Avoidance

Screening of organic pollutants in pet hair samples and the significance of environmental factors

Organic pollutants (OPs) represent a wide range of chemicals that are potentially harmful for human and wildlife health. Many of these pollutants have been identified as endocrine disruptors that can alter hormonal balance producing adverse biological effects such as neurotoxicity, reproductive disorders, carcinogenicity and hepatotoxicity. For years, hair has been selected as a non-invasive source to assess levels of animal contamination. In the present study, a multiclass screening method for determining about 60 organic pollutants in pet hair was designed and validated for qualitative and quantitative purposes. Concentrations from different classes of organochlorine, and organophosphate pesticides (OCPs, and OPPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (NDL-PCBs and DL-PCBs), polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs) were identified in the selected pet hair samples from Ourense (NW, Spain). We detected most of these pollutants in the selected hair pets. The mean concentrations found ranged from 89 to 6556ng/g for OPEs, from 8.6 to 1031ng/g for PAHs, from 8.6 to 256ng/g for PBDEs, from 29 to 184ng/g for OPPs, from 0.29 to 139 for OCPs, from 0.30 to 59ng/g for NDL-PCBs and from 1.2 to 14ng/g for DL-PCBs. To our knowledge, this is the first study to document the presence of OPs in pets from North-West Spain and it could provide baseline information for future monitoring of OPs in the area.

Acute high dose of chlorpyrifos alters performance of rats in the elevated plus-maze and the elevated T-maze

Chlorpyrifos (CPF) is a broad spectrum organophosphate (OP) pesticide widely used in agriculture, industry and household. Several animal studies indicate emotional disturbances after CPF exposure, although the results are sometimes puzzling. Thus, both anxiolytic and anxiogenic effects of CPF have been reported in different animal models of anxiety [Sánchez-Amate MC, Flores P, Sánchez-Santed F. Effects of chlorpyrifos in the plus-maze model of anxiety. Behav Pharmacol 2001;12:285-92; Sánchez-Amate MC, Dávila E, Cañadas F, Flores P, Sánchez-Santed F. Chlorpyrifos shares stimulus properties with pentilenetetrazol as evaluated by and operant drug discrimination task. Neurotoxicology 2002;23:795-803; López-Crespo G, Carvajal F, Flores P, Sánchez-Santed F, Sánchez-Amate MC. Time-course of biochemical and behavioural effects of a single high dose of chlorpyrifos. Neurotoxicology 2007;28:541-7]. On the other hand, other behavioural effects of CPF are time-dependent [López-Crespo G, Carvajal F, Flores P, Sánchez-Santed F, Sánchez-Amate MC. Time-course of biochemical and behavioural effects of a single high dose of chlorpyrifos. Neurotoxicology 2007;28:541-7], raising the question that the effects of CPF could be task and post-administration time dependent. To test this hypothesis, three groups of rats were treated with a single high dose of CPF (250 mg/kg); one of the groups was tested on day 5 on the elevated plus-maze, to complete our previous study on day 2 [Sánchez-Amate MC, Flores P, Sánchez-Santed F. Effects of chlorpyrifos in the plus-maze model of anxiety. Behav Pharmacol 2001;12:285-92]. The remaining groups were tested on the elevated T-maze on days 2 and 5. CPF produced an increased open arm activity on the elevated plus-maze on day 5, an increased escape latency on the elevated T-maze on day 2 and an impaired inhibitory avoidance on day 5. Data are discussed taking together all studies carried out in our laboratory, confirming that CPF effects on emotional behaviour are dependent on both task contingencies and post-administration time.

Central Fos expression and conditioned flavor avoidance in rats following intragastric administration of bitter taste receptor ligands

G protein-coupled receptors that signal bitter taste (T2Rs) are expressed in the mucosal lining of the oral cavity and gastrointestinal (GI) tract. In mice, intragastric infusion of T2R ligands activates Fos expression within the caudal viscerosensory portion of the nucleus of the solitary tract (NTS) through a vagal pathway (Hao S, Sternini C, Raybould HE. Am J Physiol Regul Integr Comp Physiol 294: R33-R38, 2008). The present study was performed in rats to further characterize the distribution and chemical phenotypes of brain stem and forebrain neurons activated to express Fos after intragastric gavage of T2R ligands, and to determine a potential behavioral correlate of this central neural activation. Compared with relatively low brain stem and forebrain Fos expression in control rats gavaged intragastrically with water, rats gavaged intragastrically with T2R ligands displayed significantly increased activation of neurons within the caudal medial (visceral) NTS and caudal ventrolateral medulla, including noradrenergic neurons, and within the lateral parabrachial nucleus, central nucleus of the amygdala, and paraventricular nucleus of the hypothalamus. A behavioral correlate of this Fos activation was evidenced when rats avoided consuming flavors that previously were paired with intragastric gavage of T2R ligands. While unconditioned aversive responses to bitter tastants in the oral cavity are often sufficient to inhibit further consumption, a second line of defense may be provided postingestively by ligand-induced signaling at GI T2Rs that signal the brain via vagal sensory inputs to the caudal medulla.

Vulnerability of long-term neurotoxicity of chlorpyrifos: effect on schedule-induced polydipsia and a delay discounting task

INTRODUCTION

Chlorpyrifos (CPF) is a common organophosphate (OP) insecticide that has been widely used in extensive agriculture as a pesticide. The primary mechanism of acute toxic action of OPs is inhibition of acetylcholinesterase (AChE). However, targets other than AChE have been proposed to contribute to the acute lethal action and side effects of short- or long-term exposure to these compounds. Bekkedal et al. (Sci Total Environ 274:119-123;2001) showed that chronic administration of the OP trimethylolpropane phosphate (TMPP) reduces the number of schedule-induced polydipsia (SIP) sessions necessary to induce asymptotic drinking level.

MATERIALS AND METHODS

In the present work, rats were injected with 250 mg/kg CPF and 6 months later, its effect on schedule-induced polydipsia was evaluated. In addition, after stable levels of SIP, a pharmacological study was carried out to determine the implication of other systems in the long-term effects of OPs. Finally, these animals were evaluated in a delay discounting task, as a measure of impulsivity.

RESULTS

Results indicate that the CPF group gives more licks to obtain the same amount of water than control rats (VHC). Moreover, the administration of diazepam produces an increased water intake in the CPF without any observable effect in VHC rats. Data of the delay discounting task show that CPF rats prefer an immediate reward and show a major impulsive choice.

DISCUSSION

Taken together, our data confirm and extend the long-term behavioral effects of subcutaneous administration of CPF and point to a role for other systems that, besides AChE inhibition, contribute to the long-term neurotoxicity of CPF.