Prenatal trace elements mixture is associated with learning deficits on a behavioral acquisition task among young children

Children are exposed to many trace elements throughout their development. Given their ubiquity and potential to have effects on children's neurodevelopment, these exposures are a public health concern. This study sought to identify trace element mixture-associated deficits in learning behavior using operant testing in a prospective cohort. We included 322 participants aged 6-7 years recruited in Mexico City with complete data on prenatal trace elements measurements (third trimester blood lead and manganese levels, and & urine cadmium and arsenic levels), demographic covariates, and the Incremental Repeated Acquisition (IRA), an associative learning task. Weighted quantile sum (WQS) regression models were used to estimate the joint association of the mixture of all four trace elements and IRA performance. Performance was adversely impacted by the mixture, with different elements relating to different aspects of task performance suggesting that prenatal exposure to trace element mixtures yields a broad dysregulation of learning behavior.

Learning by subtraction: Hippocampal activity and effects of ethanol during the acquisition and performance of response sequences

Learning is believed to be reflected in the activity of the hippocampus. However, neural correlates of learning have been difficult to characterize because hippocampal activity is integrated with ongoing behavior. To address this issue, male rats (n = 5) implanted with electrodes (n = 14) in the CA1 subfield responded during two tasks within a single test session. In one task, subjects acquired a new 3-response sequence (acquisition), whereas in the other task, subjects completed a well-rehearsed 3-response sequence (performance). Both tasks though could be completed using an identical response topography and used the same sensory stimuli and schedule of reinforcement. More important, comparing neural patterns during sequence acquisition to those during sequence performance allows for a subtractive approach whereby activity associated with learning could potentially be dissociated from the activity associated with ongoing behavior. At sites where CA1 activity was closely associated with behavior, the patterns of activity were differentially modulated by key position and the serial position of a response within the schedule of reinforcement. Temporal shifts between peak activity and responding on particular keys also occurred during sequence acquisition, but not during sequence performance. Ethanol disrupted CA1 activity while producing rate-decreasing effects in both tasks and error-increasing effects that were more selective for sequence acquisition than sequence performance. Ethanol also produced alterations in the magnitude of modulations and temporal pattern of CA1 activity, although these effects were not selective for sequence acquisition. Similar to ethanol, hippocampal micro-stimulation decreased response rate in both tasks and selectively increased the percentage of errors during sequence acquisition, and provided a more direct demonstration of hippocampal involvement during sequence acquisition. Together, these results strongly support the notion that ethanol disrupts sequence acquisition by disrupting hippocampal activity and that the hippocampus is necessary for the conditioned associations required for sequence acquisition.

Estradiol administration to ovariectomized rats potentiates mephedrone-induced disruptions of nonspatial learning

Mephedrone (4-methylmethcathinone) has been found in several over-the-counter products that are abused by humans, but very little is known about its behavioral effects and abuse liability. The present study examined the effects of mephedrone (1-10 mg/kg) on learning in female rats, as well as its interaction with the ovarian hormone estradiol. More specifically, female rats were trained to respond under a multiple schedule of repeated acquisition and performance of response sequences and then ovariectomized. Following ovariectomy, mephedrone dose-effect curves were obtained during periods of 17β-estradiol administration and periods without estradiol administration. Unlike mephedrone, which was administered acutely (i.p.) before the experimental sessions, 17β-estradiol was administered via subcutaneous Silastic capsules containing 25% 17β-estradiol and 75% cholesterol. In general, mephedrone produced dose-dependent rate-decreasing and error-increasing effects in the acquisition and performance components of the schedule in all subjects. However, when estradiol was present, three of the four rats were more sensitive to the rate-decreasing effects of mephedrone, and all of the subjects were more sensitive to its error-increasing effects. These data indicate that estradiol can potentiate the disruptive effects of mephedrone on both the acquisition and performance of complex behavior in female rats.

Effects of 3,3'-iminodipropionitrile on acquisition and performance of spatial tasks in rats

3,3'-Iminodipropionitrile (IDPN) has been reported to disrupt learning and memory in rats (24). The present work addressed the effects of IDPN on tasks requiring the use of spatial information. Separate groups of male rats were dosed with IDPN (IP, in 1 ml/kg saline) for 3 consecutive days and tested in the following procedures: (a) step-through passive avoidance conditioning (0, 100, 150, and 200 mg/kg/day); (b) Morris water maze (MWM) acquisition and retention (0, 125, 150, 175, and 200 mg/kg/day); (c) radial arm maze (RAM) acquisition (0, 100, 200, and 400 mg/kg/day); (d) RAM steady-state performance (0, 200, and 400 mg/kg/day); (e) repeated acquisition in the RAM (0, and 200 mg/kg/day). The vestibular toxicity of IDPN resulted in alterations in spontaneous behavior or swimming deficits in 5 of 8 rats treated with 175 mg/kg/day and in all the animals dosed with 200 or 400 mg/kg/day. IDPN increased step-through PA latencies at 200 mg/kg/day but not at lower doses. In the MWM, no performance deficits were observed at the dose levels preserving the swimming ability of the animals. In both the acquisition and the steady-state RAM tasks, IDPN (400 mg/kg/day) induced an increase in both choice errors and perseverative errors. In the RAM repeated acquisition paradigm, IDPN (200 mg/kg/day) induced performance deficits that included a decreased rate of within-session reduction in errors. The present data show that IDPN disrupts performance of tasks requiring spatial learning and memory and indicate that these deficits can be in part caused by an acquisition deficit.