Hyperactivity and impulsiveness in rats fed diets supplemented with either Aroclor 1248 or PCB-contaminated St. Lawrence river fish.

We examined whether exposure to polychlorinated biphenyls (PCBs) around puberty would produce hyperactivity and impulsiveness in adult Sprague-Dawley rats. Randomly assigned groups consumed food containing environmental concentrations of Aroclor 1248, PCB-contaminated St. Lawrence River carp, or corn oil (control). All received operant training to a final multiple (mult) 120-s, fixed interval (FI), 5-min extinction (EXT) schedule. Pressing rates of both exposed groups for drops of water averaged more than 1.5 times that of controls, especially toward the end of the 120-s interval. This overactivity included bursts with short (< or =0.5 s) interresponse times (IRTs), behavior characteristic of hyperactive boys and genetically hyperactive rats. The exposed groups also overreacted to the decreases in reinforcement density associated with transition to the final schedule. The results were interpreted in terms of the possible alterations in the animals' reinforcement mechanisms and the possible neurotoxic effects of PCB exposure.

Aroclor 1242 inhalation and ingestion by Sprague-Dawley rats.

PCBs have been considered to be almost nonvolatile and insoluble in water. However, recent studies have shown the importance of their slight solubility in water and capability to enter the atmosphere and disperse throughout the global environment. This preliminary study was designed to measure uptake and observe any physiological changes in Sprague-Dawley rats. The PCB product Aroclor 1242 is the major pollutant of the Hudson River, NY, and New Bedford Harbor, MA. The rats were exposed for 30 d to 0.9 microg/m3 via inhalation and 0.436 microg/g (ppm) in the food. The inhalation of PCBs gave a greater PCB uptake than ingestion. Both routes of administration caused significant serum thyroid hormone elevations. Histopathologic changes were observed in the urinary bladder, thymus, and the thyroid after both exposure regiments. Rearing and ambulation were significantly decreased in both exposure regiments in an open field behavior test.

Sex differences in operant discrimination behaviour in an animal model of attention-deficit hyperactivity disorder.

The present study was aimed at determining whether the behaviour of the spontaneously hypertensive rat (SHR), an animal model of attention-deficit hyperactivity disorder (ADHD), showed sex differences parallel to those seen in ADHD children. The experimental protocol contained an operant discrimination task, a two-component multiple (mult) 2-min fixed interval (FI) 5-min extinction (EXT) schedule of water reinforcement, a reliable behavioural paradigm for testing activity levels, discrimination behaviour and impulsiveness. The results indicated that both male and female SHRs show some of the most important behavioural traits of ADHD. Both were hyperactive and showed discrimination problems in terms of a behavioural extinction deficit towards the end of the EXT component. Still their behaviour differed markedly, which was probably due to quite different underlying mechanisms. The behavioural characteristics of the female SHRs may be compatible with an attention-deficit interpretation, whereas the behavioural characteristics of the male SHRs may be due to a shorter than normal delay-of-reinforcement gradient. The present study strengthens the position of SHR as an animal model of ADHD for future studies that may elucidate details in the underlying neurobiological deficits and for testing various treatment strategies.

A quantitative cytochrome oxidase mapping study, cross-regional and neurobehavioural correlations in the anterior forebrain of an animal model of Attention Deficit Hyperactivity Disorder.

The aim of this study was to trace by molecular imaging techniques the neural substrates of attention deficit hyperactivity disorder (ADHD) using the spontaneously hypertensive rat (SHR) as animal model. Adult SHR and Wistar-Kyoto (WKY) controls were used throughout this study. In experiment 1, naive male SHR and WKY were used, whereas in experiment 2 SHR and WKY rats of both genders were trained on a multiple fixed interval (FI (120 s for water, 5-min extinction)) paradigm and sacrificed 6 months later. In both experiments coronal sections of the anterior forebrain were processed for quantitative cytochrome oxidase (COase) histochemistry by the method of Gonzalez-Lima. Optical density values were transformed into actual enzyme activity units by using tissue-calibrated standards. In experiment 1, non-trained male rats of the SHR line showed lower COase activity in the medial and lateral prefrontal cortices, compared with WKY controls. In experiment 2, there was a line x treatment interaction effect in the pole of the nucleus accumbens (ACB). Regional correlative analyses revealed that: (i) under basal conditions, SHR are more synchronized than WKY rats in the COase level of different brain regions; and (ii) the training desynchronizes COase activity in the WKY, further synchronizes it and increases the cross-talk between hemispheres in male SHR only. Neurobehavioral covariations between behavioural scores and metabolic capacity in the medial and lateral prefrontal/frontal cortices, the caudate-putamen complex (CPU), the pole, core, and shell of the accumbal complex (ACB), and the ventral pallidum (VP), indicated that, in the WKY rats, the frequency of lever pressing covaried positively with the COase activity in the CPU, whereas in the SHR covaried with both medial and lateral prefrontal/frontal cortices. The bursts of activity during the 1-1.33-s segment was positively correlated, in the WKY rats only, with the core and shell of the ACB, and with the VP. Finally, the correlative profiles showed significant gender differences with effects in male SHR only. Thus, the results lend support to the involvement of the cortico-striato-pallidal system in ADHD.

Plasma glucose levels and leverpress avoidance versus escape behaviors in rats.

The relationship between performance in an avoidance conditioning paradigm and the plasma glucose levels of Sprague-Dawley rats was examined in two experiments. In Experiment 1 we investigated whether glucose levels varied with the animal's relative success at acquiring the avoidance task. Results indicated that animals classified as avoiders (60% avoidance and above) had lower glucose levels than animals classified as escapers (30% avoidance and below). In Experiment 2 we looked at whether glucose levels showed within-subject changes with avoidance acquisition. Results demonstrated that glucose levels showed reductions if an animal learned the avoidance response. Subjects that did not learn the response showed no such reduction. Such results suggest that the physiological response to stress is attenuated by acquisition of successful coping behaviors that exercise control over the onset of aversive events.

Contrasting lever-press avoidance behaviors of spontaneously hypertensive and normotensive rats (Rattus norvegicus).

Lever-press avoidance performances of Spontaneously Hypertensive (SHR) and Wistar-Kyoto (WKY) rats were observed in two experiments. The first compared them at shock intensities of 1 or 2 mA. The SHRs had the highest percentage of avoidances, made the most coping responses (avoidances plus escapes), and received the fewest shocks (ps less than .05). They also had shorter avoidance and initial-escape latencies (ps less than .05). In the second experiment these strains were trained with signal-shock intervals that produce good (60 s) or poor (10 s) avoidance acquisition. Analysis of the Strain x Conditions x Blocks interaction showed that SHRs performed better with the longer interval (p less than .05), whereas WKYs' performance was similar with both (p greater than .05). Thus WKYs differed from all other strains previously exposed to these conditions. The findings are interpreted in terms that emphasize the SHRs' tendency to move, compared with the WKYs' tendency to freeze in response to aversive stimuli, rather than characterizing SHRs as hyperreactive.

Effects of stress and ovariectomy on the plasma cholesterol, serum triglyceride, and aortic cholesterol levels of female rats.

Female Sprague-Dawley rats were either ovariectomized or sham-operated prior to puberty. As adults, they were maintained on a cholesterol-supplemented diet and subjected to either predictable, controllable shock; unpredictable, uncontrollable shock; or no shock for 30 days (51-min daily sessions). Sham-operated rats had higher plasma cholesterol levels than ovariectomized rats, but neither group showed an effect of stress treatments. For both groups, serum triglyceride and aortic cholesterol levels were lower in stressed than nonstressed rats. Additionally, the ovariectomized rats had higher levels of serum triglycerides than sham-operated controls.

Effects of stress and exercise on plasma corticosterone, plasma cholesterol, and aortic cholesterol levels in rats.

Rats, fed a 1% cholesterol diet, were subjected to either predictable, controllable shock; unpredictable, uncontrollable shock; or no shock for 30 days (51-min daily sessions). Half of the rats in each condition were allowed access to a running wheel for 3 hr immediately after each stress session except for the final stress session. Immediately following the final stress session, animals were sacrificed and blood and aorta samples were taken. Stressed animals allowed to run showed lower plasma corticosterone levels than stressed animals not allowed to run. Overall, stressed animals had lower levels of aortic cholesterol than nonstressed animals. Whereas running resulted in decreased levels of plasma cholesterol, aortic cholesterol levels were higher for the running animals than for the nonrunning animals.

The effects of differential psychological stress and infantile handling on plasma triglyceride and aortic cholesterol levels in rats.

The effects of differential psychological stress on serum triglyceride and aortic cholesterol levels were investigated in two experiments. In the first, rats with an unknown infant handling history purchased as adults from a standard supplier were subjected to predictable, controllable shocks; unpredictable, uncontrollable shocks; or the apparatus or their home cages with no shocks, for 30 days. All were maintained on a cholesterol-supplemented diet except during the daily 51-min stress sessions. The amounts eaten were equated among the groups. The results that the shocked rats had significantly lower terminal levels of serum triglycerides, and those receiving unpredictable, uncontrollable shocks had significantly less aortic cholesterol, than the nonshocked groups, which did not differ from each other in either measure. In the second experiment, rats born in this laboratory were either handled or left undisturbed in infancy and were exposed to a diet and differential stress conditions as adults. Animals handled in infancy had significantly lower aortic cholesterol than nonhandled animals across all stress conditions. In addition, those exposed to unpredictable, uncontrollable shocks had lower aortic cholesterol than those exposed to predictable, controllable shocks, and both had lower aortic cholesterol than the nonshocked group. Similar differential stress effects across stress conditions were seen in all the rats' serum triglyceride levels in Experiment 2. The effects of infantile handling did not interact with the stress effects, and neither could be accounted for by group differences in amount of the diet eaten or weight gained.

The effects of differential psychological stress on plasma cholesterol levels in rats.

The plasma cholesterol concentrations of rats receiving either lever-press escape or avoidance training, exposure to unpredictable, uncontrollable grid shocks using a yoked procedure, or no shocks, were compared in two experiments. All were fed a cholesterol-supplemented diet prior to and during the 30 days of exposure to these differing stress treatments. The results of both experiments showed that yoked groups had higher terminal levels of cholesterol than their experimental counterparts in the escape or avoidance group even though they received the same amounts of aversive stimulation and ate the same amounts of the diet. Both were higher than the nonshocked groups when the amount of food intake for all was matched in Experiment 2. The type of level-press training had no effect.

Rapid acquisition of discrete-trial lever-press avoidance: effects of signal-shock interval.

Acquisition of discrete-trial lever-press avoidance learning was studied in three experiments. Experiment I compared a new training procedure, which produces rates of lever-press avoidance learning comparable to those obtained in shuttle boxes, with a "conventional", less efficient training procedure. A factorial design was used to compare continuous versus intermittent shock and a long-variable versus a short-fixed signal-shock interval. Learning was best in the groups trained with the long and variable interval and poorest in those trained with the short and fixed interval. Type of shock had no effect. Experiment II separated the effects of duration from those of variability of the signal-shock interval. Fixed and variable intervals of 10 and 60 sec were tested and duration was the only significant factor. Experiment III addressed the effect of the differential opportunity to avoid provided by long signal-shock intervals by varying this interval from 10 to 60 sec in 10-sec steps. Only the 10-sec group showed slow acquisition relative to the others. Analysis of avoidance response latencies showed that the distributions for all groups were positively skewed and that skewness increased with increasing duration of the signal-shock interval. At intervals longer than 20 sec, the animals made progressively less use of their increased opportunity to respond. The data do not support the opportunity-to-respond interpretation of the effects of duration of signal-shock interval and suggest that some type of inhibitory process may block lever-press avoidance learning at intervals as short as 10 sec. The significance of these findings for species-specific defense reaction and preparedness theories was emphasized.