The attention set-shifting test is sensitive for revealing sex-based impairments in executive functions following developmental lead exposure in rats

Abstract

The literature on lead (Pb) exposure has focused in large part on hippocampal-based learning and memory deficits, although frontoexecutive dysfunctions are known to exist in Pb-exposed humans. This study examined the effects of perinatal (PERI) and early postnatal (EPN) developmental low-level Pb-exposures in rats on frontoexecutive functions, using the Attention Set-Shift Test (ASST). Control males and females performed the ASST similarly. Male EPN rats had difficulty with simple discrimination (SD) of odors and failed to complete the compound discrimination (CD) stage of the ASST. All other Pb-exposed rats completed the training and testing. Male PERI rats performed worse on the SD, intradimensional (ID), and intradimensional-reversal (ID-Rev) ASST stages when compared to male Control rats. Female EPN rats performed similar to Controls on the ID-Rev rats, whereas PERI rats performed better the trials-to-criterion on the ID-Rev than EPN and Control rats. Pb-exposed female rats had significant difficulty performing the ED/ED-Rev stages, with the number of trials-to-criterion double that required by Pb-exposed and Control male rats and Control female rats. Together, the ASST results showed that developmental Pb-exposure induces frontoexecutive dysfunction that persists into adulthood, with different sex-based vulnerabilities dependent upon the time-period of neurotoxicant exposure.

Keywords: Attention set-shifting test; Cognitive flexibility; Developmental lead exposure; Dimensional shifts; Dysexecutive functions; Frontoexecutive functions.

Figure 1

Male (white bars) and female (grey stippled bars) Control rats ASST performance for trials-to-criterion (TTC). Control male and female rats were able to form attention sets evidenced by solving the ID stages with less trials and errors than the ED stages. Control male and female ASST test performance was not significantly different from one another, yet a trend was observed that female rats tend to require more trials in learning the ID-Rev stage. Data are presented as the mean ± SEM, with α = 0.05, and CI of 95%.

Figure 2

Control, PERI, and EPN male (A-solid bars) and female (B-stippled bars) trials-to-criterion (TTC) in ASST training when learning simple discriminations of odor (OD) and digging medium (MD). EPN exposure caused a learning deficit only in male rats when associating odors during training evidenced by increased the TTC (p < 0.01^##) in the OD. Legend: (^#) = Treatment Effect. Data are presented as the mean ± SEM, with α = 0.05, and CI of 95%.

Figure 3

Control and PERI male rats (A) and Control and PERI female rats (B) trials-to-criterion (TTC) in the ASST. PERI male rats showed delays in learning the SD, ID and ID-Rev conditions, yet solved the ED and ED-Rev stages similar to Control males (A). This data suggests male PERI rats has deficits in forming attention-sets. In contrast, PERI female rats (B) were able to form attention-sets like Control female rats, but had significant learning delays in the ED and ED-Rev conditions. This data suggest that PERI females have different frontoexecutive dysfunctions than PERI males despite the same developmental Pb-exposure, and, females required nearly twice the amount of TTC to complete the ED-ED-Rev conditions than males. Legend: (*) = Test Condition Effect; (^#) = Treatment Effect; (^†) = Test Condition X Treatment Interaction. Data are presented as the mean ± SEM, with α = 0.05, and CI of 95%.

Figure 4

illustrates the comparisons of the Control and PERI male rats (A) in Experiment 2, the Control and PERI female rats (B) in Experiment 3, and the Control, PERI, and added on EPN female rats (C) in Experiment 3 + EPN female rats. Male PERI rats (A) exhibit different frontoexecutive dysfunctions than female PERI rats (B), when compared to Control male and female rats. Further, female PERI rats exhibit different frontoexecutive dysfunctions than female EPN rats, when compared to Control female rats (C). The data suggest that dependent upon the developmental time-period of Pb-exposure and sex that different types of frontoexecutive dysfunctions may occur within the prefrontal cortex in rats that persist across the lifespan. Legend: (*) = Test Condition Effect; (^#) = Treatment Effect; (^†) = Test Condition X Treatment Interaction. Data are presented as the mean for each test condition of the ASST.

Figure 5

illustrates the Control (white) and PERI (dark grey) male rats ID-ED abilities from Experiment 2 (A) and the Control (white), PERI (dark grey), and EPN (light grey) female rats ID-ED shift abilities from Experiment 3 + EPN female rats add-on (B). The data revealed no significant differences in Control and PERI male rats ID-ED shifting abilities. In contrast, the data revealed a significant ID-ED shift difference in female EPN (p < 0.001***) and female PERI rats (p < 0.001***), when compared to female Control rats (B). The data suggest that females rats when Pb-exposed had more deficits in ID-ED shifts than Control female rats, regardless of the developmental time-period of exposure. In addition, Pb-exposed female rats have more deficits in ID-ED shifts than male Pb-exposed rats. Thus, female Pb-exposed rats exhibit sex-based differences in ID-ED frontoexecutive dysfunctions. Legend: (^#) = Treatment Effect. Data are presented as box plots with the solid black line as the median, the lower line, lower box, upper box, and upper line serving as quartiles 1, 2, 3, and 4, respectively.

Figure 6

Control and PERI male rats (A) and Control, PERI, and EPN female rats (B) ASST re-acquisition outcomes. Control and PERI males revealed a significant Treatment effect across the CD and ID re-acquisition conditions (p < 0.01^##) (A). In contrast, the Control, PERI, and EPN females showed no significant differences in the CD and ID re-acquisition conditions (B). The data suggest that PERI male rats have difficulty with learning re-acquiring prior learned information after already having learned an attention-set, yet PERI female rats do not have such problems. Legend: (^#) = Treatment Effect. Data are presented as the mean ± SEM, with α = 0.05, and CI of 95%.