Hippocampal levels of ChAT, PKA, phospho-PKA and phospho-CaMKIIα but not CaMKIIα positively correlate with spatial learning skills in rats

Evaluation of the Activity of Choline Acetyltransferase From Different Synaptosomal Fractions at the Distinct Stages of Spatial Learning in the Morris Water Maze

Accumulated data have evidenced that brain cholinergic circuits play a crucial role in learning and memory; however, our knowledge about the participation of neocortical and hippocampal cholinergic systems in spatial learning needs to be refined. The aim of this study was to evaluate the association of the activity of membrane-bound and soluble choline acetyltransferase (ChAT) in the synaptosomal sub-fractions of the neocortex and hippocampus with performance of the spatial navigation task in the Morris water maze at different temporal stages of memory trace formation. To identify distinct stages of memory formation, rats were trained using a 5-day protocol with four trials per day. The mean escape latency for each trial was collected, and the entire dataset was subjected to principal component analysis. Based on the Morris water maze protocol, there were three relatively distinct stages of memory formation: days 1-2, day 3, and days 4-5. The remotely stored memory trace tested in repeated and reversal learning beginning on day 19 (14 days after the end of initial learning) was associated at the individual level mainly with performance during the second trial on day 21 (the third day or repeated or reversal learning). The ChAT activity data suggest the participation of cortical cholinergic projections mainly in the first stage of spatial learning (automatic sensory processing) and the involvement of hippocampal interneurons in the second stage (error-corrected learning). Cholinergic cortical interneurons participated mainly in the stage of asymptotic performance (days 4-5). It is advisable to evaluate other signalling pathways at the identified stages of memory formation.

Possible effects of different doses of 2.1 GHz electromagnetic radiation on learning, and hippocampal levels of cholinergic biomarkers in Wistar rats

The present study evaluated whether short-term exposure to different doses of 2.1 GHz radiofrequency electromagnetic radiation (RF-EMR) has different effects on rats' behaviour and hippocampal levels of central cholinergic biomarkers. Animals were divided into three equal groups namely; group 1 was sham-exposed group, group 2-3 were exposed to 45 V/m and 65 V/m doses of 2.1 GHz frequency for 1 week respectively. Numerical dosimetry simulations were carried out. Object location and Y-maze were used as behavioural tasks. The protein and mRNA expression levels of AChE, ChAT, and VAChT, in the hippocampus were tested using Western Blotting and Real-Time PCR. The impairment performance of rats subjected to 65 V/m dose of 2.1 GHz RF-EMR in both object location and Y-maze tasks was observed. The hippocampal levels of AChE, ChAT, and VAChT, were significantly lower in rats exposed to 65 V/m dose of 2.1 GHz RF-EMR than others. The stronger effect of "65 V/m" dose on both rat's hippocampal-dependent behavioural performances and hippocampal levels of cholinergic biomarkers may be due to the stronger effect of "65 V/m" dose where rats' snouts were located at the nearest distance from the monopole antenna. Furthermore, the simulated SAR values were high for 65 V/m electric-field strengths. For the first time, we report the potential dose-dependent effects of short-term exposure to 2.1 GHz radiation on rat's behavioural performances as well as hippocampal levels of cholinergic biomarkers. Further studies are needed to understand the mechanisms by which RF-EMR influences the function of the central cholinergic system in the brain.

Effects of combined traffic noise on the synaptic ultrastructure and expressions of p-CaMKII and NMDAR1 in the hippocampus of young SD rats

In order to explore the effects of combined traffic noise (CTN) on learning and memory function, young Sprague-Dawley (SD) rats were exposed to CTN from highway and high-speed railway for 52 days, whose day-night equivalent continuous A-weighted sound pressure level (L_dn) was 70 dB(A) (corresponding sound pressure level was 80 dB). The synaptic ultrastructure and the expressions of phosphorylated calcium/calmodulin-dependent protein kinase II (p-CaMKII) and N-methyl-D-aspartate receptor 1 (NMDAR1 or NR1) in the hippocampus were tested by transmission electron microscopy (TEM) and Western blot, respectively. Results showed that there was no significant difference in the synaptic ultrastructure and the expressions of p-CaMKII and NR1 in the hippocampus of young rats between the experimental group and control group. Compared with single high-speed railway noise (HSRN) with L_dn of 70 dB(A), CTN had less influences on learning and memory function, which was closely related to smaller intermittency of CTN and less anxiety caused by CTN. In comparison with white noise with a sound pressure level of 80 dB, CTN had less impacts on learning and memory function, which was mainly associated with CTN's smaller R-weighted sound pressure level based on rats' auditory sensitivity.

Relationship between the hippocampal expression of selected cytochrome P450 isoforms and the animal performance in the hippocampus-dependent learning task

Despite very extensive studies on the molecular mechanisms of memory formation, relatively little is known about the molecular correlates of individual variation in the learning skills within a random population of young normal subjects. The role of cytochrome P450 (CYP) enzymes in the brain also remains poorly understood. On the other hand, these enzymes are known to be related to the metabolism of substances important for neural functions including steroids, fatty acids, and retinoic acid. In the present study, we examined the potential correlation between the animals' performance in a place learning task and the levels of selected CYP isoforms (CYP2E1, CYP2D1 and CYP7A1) in the rat hippocampus. According to their performance, rats were classified as "good" learners (percent error/number of trials to criterion ≤ group mean - 3SEM) or "poor" learners (percent error/number of trials to criterion ≥ group mean + 3SEM). The CYP enzyme levels were determined by Western Blot at the early, intermediary and advanced stages of the task acquisition (day 4, day 8 and after reaching a performance criterion of 83% correct responses). In this study, as expected, CYP2E1 and CYP2D1 isoforms have been found in the rat hippocampus. However, a putative CYP7A1 isoform was also visualized. Hippocampal expression of these enzymes was shown to be dependent on the stage of learning and animals' cognitive status. In "good" learners compared to "poor" learners, significantly higher levels of CYP2E1 were found at the early stage of training, significantly higher levels of CYP2D1 were found at the intermediate stage of training, and significantly higher levels of CYP7A1-like protein were found after reaching the acquisition criterion. These findings suggest that the differential expression of some CYP isoforms in the hippocampus may have impact on individual learning skills and that different CYP isoforms may play different roles during the learning process.

Comparison of spatial learning in the partially baited radial-arm maze task between commonly used rat strains: Wistar, Spargue-Dawley, Long-Evans, and outcrossed Wistar/Sprague-Dawley

Strain-related differences in animals' cognitive ability affect the outcomes of experiments and may be responsible for discrepant results obtained by different research groups. Therefore, behavioral phenotyping of laboratory animals belonging to different strains is important. The aim of the present study was to compare the variation in allothetic visuospatial learning in most commonly used laboratory rat strains: inbred Wistar (W) and Sprague-Dawley (SD), outcrossed Wistar/Sprague-Dawley (W/SD), and outbred Long Evans (LE) rats. All rats were trained to the arbitrary performance criterion of 83 % correct responses in the partially baited 12-arm radial maze allowing for simultaneous evaluation of both working and reference memory. In the present study, testing albino versus pigmented and inbred versus outcrossed rats revealed significant strain-dependent differences with the inbred SD rats manifesting lower performance on all learning measures compared to other strains. On the other hand, the outcrossed W/SD rats showed a lower frequency of reference memory errors and faster rate of task acquisition compared to both LE and W rats, with W rats showing a lower frequency of working memory errors compared to other strains. In conclusion, albinism apparently did not reduce the animals' performance in the allothetic visuospatial learning task, while outcrossing improved the spatial learning. A differential effect of strain on the contribution of each error type to the animals' overall performance was observed. The strain-dependent differences were more pronounced between subpopulations of learning-deficient individuals ("poor" learners), and generally the reference memory errors contributed more to the final behavioral output than did the working memory errors.

The effects of preweaning manganese exposure on spatial learning ability and p-CaMKIIα level in the hippocampus

BACKGROUND

The effects and mechanisms of preweaning Manganese (Mn) exposure on cognitive dysfunction remain unclear.

OBJECTIVE

This study evaluated the effects of preweaning Mn exposure on spatial learning and memory as well as the protein expression of CaMKIIα and p-CaMKIIα.

METHODS

We treated neonate rats with Mn(2+) doses of 0 (control group), 10, 20 and 30mg of Mn(2+) per kg body weight (Mn-exposed groups) over postnatal day (PND) 1-21 by intraperitoneal injection. The ability of spatial learning and memory was tested on PND 22 using the Morris water maze (MWM), while the protein expressions of CaMKIIα and p-CaMKIIα in the hippocampus were evaluated by Western blotting. The levels of Mn in the blood and hippocampus were measured by inductively coupled plasma-mass spectrometry (ICP-MS).

RESULTS

The rats in Mn-exposed groups showed a significant delay in spatial learning ability on the third day of the MWM without dose-dependent differences, but there was no effect on the spatial memory ability. p-CaMKIIα, but not CaMKIIα protein expression significantly reduced in the Mn-exposed group.

CONCLUSION

These findings suggested that the inhibition of p-CaMKIIα could be one of the mechanisms involved in the occurrence of Mn-induced cognitive impairments.