Behavioral and electrophysiological estimates of visual thresholds in awake rats treated with 3,3',4,4',5-pentachlorobiphenyl (PCB 126)

Divergence of dim-light vision among bats (order: Chiroptera) as estimated by molecular and electrophysiological methods

Dim-light vision is present in all bats, but is divergent among species. Old-World fruit bats (Pteropodidae) have fully developed eyes; the eyes of insectivorous bats are generally degraded, and these bats rely on well-developed echolocation. An exception is the Emballonuridae, which are capable of laryngeal echolocation but prefer to use vision for navigation and have normal eyes. In this study, integrated methods, comprising manganese-enhanced magnetic resonance imaging (MEMRI), f-VEP and RNA-seq, were utilized to verify the divergence. The results of MEMRI showed that Pteropodidae bats have a much larger superior colliculus (SC)/ inferior colliculus (IC) volume ratio (3:1) than insectivorous bats (1:7). Furthermore, the absolute visual thresholds (log cd/m(2)•s) of Pteropodidae (-6.30 and -6.37) and Emballonuridae (-3.71) bats were lower than those of other insectivorous bats (-1.90). Finally, genes related to the visual pathway showed signs of positive selection, convergent evolution, upregulation and similar gene expression patterns in Pteropodidae and Emballonuridae bats. Different results imply that Pteropodidae and Emballonuridae bats have more developed vision than the insectivorous bats and suggest that further research on bat behavior is warranted.

Coplanar Polychlorinated Biphenyls Activate the Aryl Hydrocarbon Receptor in Developing Tissues of Two TCDD-Responsive lacZ Mouse Lines

In utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can have an immediate impact on developmental processes that then lead to long-term deficits in function. To define the specific tissues affected by TCDD during development, we developed a lacZ-reporter gene mouse model driven by activation of the aryl hydrocarbon receptor (AhR). Exposure to TCDD on gestational day (GD) 14 results in strong activation of the lacZ transgene in numerous tissues including fore and hind paws, ear, and genital tubercle. Experiments were conducted to examine the ability of alternative AhR ligands to activate our model system. The coplanar polychlorinated biphenyl congeners 3,4,5,3',4'-pentachlorobiphenyl (PCB126) and 3,4,3',4'-tetrachlorobiphenyl (PCB77) both induced staining in fetal tissues identical to that observed following TCDD exposure. Exposure of fetuses to the PCB mixture Aroclor 1254 and the non-coplanar congener 2,3,6,2',5'-pentachlorobiphenyl (PCB95) did not result in any activation of the lacZ transgene. In addition to the testing of alternative ligands, another line of reporter mice was generated to determine the potential influence of the site of insertion of the lacZ transgene on the reported observations. Both TCDD and the coplanar PCBs induced a similar pattern of staining in the new line as compared to that observed in the original lacZ reporter mouse line. The ability of AhR ligands, other than TCDD, to activate the AhR-mediated transgene, in combination with the insertion-site independence of the response, strengthens the data previously derived from this model and increases the utility of this system for investigations examining AhR-mediated events during development.

Early Developmental Exposure to BDE 99 or Aroclor 1254 Affects Neurobehavioural Profile: Interference from the Administration Route

Among the most persistent and bio-accumulative environmental pollutants are the polybrominated diphenyl ethers (PBDEs), a class of chemicals widely used as flame retardants in plastics and textile coating, and the polychlorinated biphenyls (PCBs), previously used as coolants and lubricants in electrical equipment. Monitoring programs revealed high levels of both these classes of compounds in human breast milk, raising concerns for their potential noxious effects on infants. The aim of the present study was to investigate the neurotoxic effects of 2,2',4,4',5-penta BDE (BDE 99: 18mg/kg/day) or Aroclor 1254 (A1254, a PCB mixture: 10mg/kg/day) administration, from gestational day (GD) 6 to postnatal day (PND) 21, on neurobehavioral development in the CD-1 Swiss mouse. In addition, we investigated whether the administration route affects the emergence or the magnitude of the toxic effects of BDE 99 or A1254. In particular, we compared self-administration, consisting in letting the mouse drink spontaneously the compound dissolved in oil from a syringe, with gavage, consisting in force-feeding a substance by a tube inserted in the mouth and then into the stomach, a procedure reported to be stress-inducing. Both compounds induced hyperactivity, though BDE 99 affected activity profile only during adolescence and A1254 mainly at adulthood. Levels of total circulating thyroxine were decreased by both BDE 99 and A1254 administration, though only in the latter group the decrease was statistically significant. These findings suggest a different neurotoxic action exerted by PBDEs and PCBs. An effect of the administration route, independent from the compound administered, was found on thigmotactic behavior and gavage administration affected pup body weight gain only in the A1254 group, suggesting that the stress induced by gavage procedure may either affect results per se or modulate the detrimental action of selected compounds.

Signal detection behavior in humans and rats: a comparison with matched tasks

Animal models of human cognitive processes are essential for studying the neurobiological mechanisms of these processes and for developing therapies for intoxication and neurodegenerative diseases. A discrete-trial signal detection task was developed for assessing sustained attention in rats; a previous study showed that rats perform as predicted from the human sustained attention literature. In this study, we measured the behavior of humans in a task formally homologous to the task for rats, varying two of the three parameters previously shown to affect performance in rats. Signal quality was manipulated by varying the increment in the intensity of a lamp. Trial rate was varied among values of 4, 7, and 10 trials/min. Accuracy of signal detection was quantified by the proportion of correct detections of the signal (P(hit)) and the proportion of false alarms (P(fa), i.e. incorrect responses on non-signal trials). As with rats, P(hit) in humans increased with increasing signal intensity whereas P(fa) did not. Like rats, humans were sensitive to the trial rate, though the change in behavior depended on the sex of the subject. These data show that visual signal detection behavior in rats and humans is controlled similarly by two important parameters, and suggest that this task assesses similar processes of sustained attention in the two species.

Flash-, somatosensory-, and peripheral nerve-evoked potentials in rats perinatally exposed to Aroclor 1254

Pregnant Long-Evans rats were exposed to 0, 1 or 6 mg/kg/day of Aroclor 1254 (A1254; Lot no. 124-191), a commercial mixture of polychlorinated biphenyls (PCBs), from gestation day (GD) 6 through postnatal day (PND) 21. At 128-140 days of age, male and female offspring were tested for visual-, somatosensory- and peripheral nerve-evoked potentials. The evoked responses increased in amplitude with larger stimulus intensities, and gender differences were detected for some endpoints. In contrast, developmental exposure to A1254 failed to significantly affect the electrophysiological measures. A subset of the animals were tested for low-frequency hearing dysfunction using reflex modification audiometry (RMA). An elevated threshold for a 1-kHz tone was observed, replicating previous findings of A1254-induced auditory deficits [Hear. Res. 144 (2000) 196; Toxicol. Sci. 45(1) (1998) 94; Toxicol. Appl. Pharmacol. 135(1) (1995) 77.]. These findings indicate no statistically significant changes in visual-, somatosensory- or peripheral nerve-evoked potentials following developmental exposure to doses of A1254 that produce behavioral hearing deficits. However, subtle changes in the function of the visual or somatosensory systems cannot be disproved.

Specificity of cognitive impairment from Pfiesteria piscicida exposure in rats: attention and visual function versus behavioral plasticity

Pfiesteria piscicida is a toxic dinoflagellate that has caused massive fish kills in estuaries along the East Coast of the United States, and exposure of humans to toxic Pfiesteria has been associated with cognitive impairment. A visual signal detection task was used to determine the possible importance of attentional and visual processes in Pfiesteria effects on cognitive function. Adult female rats were trained to perform the signal detection task. After training, the rats were injected subcutaneously with fish culture water containing toxic Pfiesteria (35,600 or 106,800 cells of Pfiesteria/kg of rat body weight) or with (control) fish culture water containing no Pfiesteria. Effects of toxic Pfiesteria on maintenance of signal detection behavior were assessed for 2 weeks after treatment. Then, the signal-response contingencies were reversed. After the discrimination was reestablished on the reversed levers, the rats received a second dose of toxic Pfiesteria. The rats were again tested for 2 weeks, after which a second reversal was imposed. Pfiesteria did not affect behavior in the signal detection task during 2 weeks of prereversal testing after either exposure. However, a significant Pfiesteria-induced deficit emerged when the signal-response contingencies were reversed. These findings suggest that Pfiesteria-induced deficits emerge during periods of behavioral transition and not during performance of previously learned tasks.

Comparing cognitive and screening tests for neurotoxicity. Effects of acute chlorpyrifos on visual signal detection and a neurobehavioral test battery in rats

It is often assumed that cognitive function is more sensitive to neurotoxic chemicals than are the unconditioned behaviors employed in neurobehavioral screens; however, direct comparisons of the sensitivity of these test methods are lacking. The present studies were conducted to compare the effects of the widely used cholinesterase-inhibiting insecticide, chlorpyrifos (O,O'-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothionate, CPF), on a visual signal detection task (SDT) with its effects on a neurobehavioral test battery. Adult male Long-Evans rats were trained to perform the SDT, dosed with CPF, and then assessed with both test instruments. Oral CPF (50 mg/kg) impaired signal detection for 8 days, and subcutaneous CPF (250 mg/kg) did so for 4 weeks. CPF (30 and 50 mg/kg po and 250 mg/kg sc) also lowered activity in the test battery for up to 18 days. Thus, CPF impaired attention and altered behavior in the test battery in the same dose ranges under two very different dosing scenarios.