Behavioural parameters in aged rats are related to LTP and gene expression of ChAT and NMDA‐NR2 subunits in the striatum

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Abstract
Striatal parameters were assessed for their relevance to age‐related behavioural decline. Forty aged rats (28–30 months) were tested in the water maze and open field. Of these, seven superior and seven inferior learners were compared with each other in terms of levels of in vitro short‐ and long‐term potentiation (STP and LTP), and gene expression of choline acetyltransferase (ChAT) as well as of the NMDA‐NR2A‐C subunits assessed by quantitative RT‐PCR. Results revealed that the superior as compared with the inferior learners had higher levels of ChAT mRNA in the striatum. For the superior group, ChAT mRNA was correlated with escape on to the cued platform in the water maze, whereas level of LTP was predictive of place learning in the water maze and rearing activity in the open field. For the inferior group, expression of NR2A and NR2B was positively correlated with place learning and probe trial performance in the water maze. The results show that individual differences in various behaviours of aged rats were accounted for by variability in striatal parameters, i.e. LTP, ChAT and NMDA‐NR2 subunit mRNA. Notably, the correlations found were heterogeneous amid the groups, e.g. variability in place learning was explained by variability in levels of LTP in the superior learners, but in levels of NR2A‐B mRNA in the inferior group.