Disruption of temporo-entorhinal connections abolishes recognition memory-enhancing effect of angiotensins in rats.

In our laboratory, the positive influence of angiotensin II and its 3-7 fragment on learning and memory processes was found to be mediated by excitatory amino acids, because it was abolished by N-methyl-D-aspartate (NMDA) receptor antagonists. The purpose of the present study was to investigate whether bilateral disruption of glutamatergic temporo-entorhinal connections may have an influence on the facilitatory effect of both angiotensin peptides on recognition memory. The bilateral transections of temporo-entorhinal connections were made in 32 male rats 10 days before testing the effect of intracerebroventricular AII or AII(3-7) injection on the recognition of objects evaluated in an object-recognition test. Thirty additional rats served as sham-operated controls. The final analysis was based on 29 lesioned and 26 sham-operated animals. AII and its 3-7 fragment significantly improved object recognition in the sham-operated groups of rats. Bilateral disruption of temporo-entorhinal connections totally abolished the facilitatory effect of both angiotensins on object recognition. Moreover, bilateral disruption of temporo-entorhinal connections significantly attenuated crossings of squares and rearings, without affecting bar approaches and defecation evaluated in an open-field test. These results may suggest that the facilitatory recognition memory effect of AII and AII(3-7) requires a reciprocal glutamatergic connection between the lateral entorhinal cortex and the temporal cortex.