Strain differences and the role of AT(1) receptor expression in anxiety.

This study investigated strain specific differences to the anxiolytic response to losartan focusing on genetic variation that may influence such responses. This included: AT(1) receptor sequence variation, angiotensin II receptor associated protein (ATRAP) and receptor expression between strains. Sequencing of exon 3 of AT(1a)R revealed no differences between BKW mice (n=6) and C57 and DBA(2) strains (n=3). Comparisons of AT(1) expression do show significant differences, whereby BKW mice showed the highest levels of expression and DBA(2) mice intermediate levels when compared to the C57 strain. Sequencing of sections of the Angiotensin receptor associated protein (ATRAP) identified a non-synonymous point mutation- (T/C) transversion (position 109-161) (SNP id = rs13467517) resulting in a Valine → Alanine (V157A) amino acid change in the BKW and DBA(2) strains. Our results indicate that the previously reported strain dependent effects are not due to variation in AT(1a) receptor sequence. Differences in AT(1)gene expression levels between strains, which mirror their anxiety phenotype, are observed. This is coupled with a non-synonymous single nucleotide polymorphism in ATRAP, a negative regulator of AT(1) signalling.

Strain differences in the effects of angiotensin IV on mouse cognition.

Angiotensin IV has been shown to improve learning and memory in rodents. Strain dependent variation in murine behaviour, aminopeptidase activity and inhibitory effect of Angiotensin IV, structural variation in insulin regulated aminopeptidase (IRAP) and aminopeptidase N (ApN) and expression of the encoding genes were explored. Strain differences in the behavioural response to Angiotensin IV were observed, where CD mice were refractory. All strains showed inhibition of aminopeptidase activity by Angiotensin IV but CD mice displayed reduced endogenous aminopeptidase activity. No differences in the coding sequence of IRAP or ApN were found. RT-PCR analysis showed no difference in IRAP expression between strains but an increased expression of ApN was observed in CD mice. The lack of cognitive response of CD mice to Angiotensin IV cannot be explained through variation within IRAP sequence nor expression but the results highlight a potential role for ApN in the effects of Angiotensin IV.