Resumo

Introduction. The hippocampus modulates learning/memory and anxiety processes. A relative contribution of its dorsal and ventral poles has been demonstrated: whereas the dorsal hippocampus (DH) has a key role in the former, the ventral hippocampus (VH) is preferentially involved in the latter. The neurochemical mechanisms supporting the regional functional dissociation within the hippocampus still remain to be investigated. As a functionally active population of transient receptor potential vanilloid type 1 (TRPV1) channels occurs in the rat hippocampus, the present study sought to investigate whether the pharmacological blockade of TRPV1 channels interferes with the acquisition and/or retrieval of the spatial memory of rats exposed to the water-maze task. Methods. Male Wistar rats were bilaterally-implanted with guide cannulas aimed at the DH or the VH. One-week after surgery, each animal was infused with vehicle (VEH; phosphate buffered saline containing 15 % of dimethyl sulfoxide) or the TRPV1 channel antagonist capsazepine (CPZ; 1.0 or 3.0 nmol in 0.2 μL per side) 10-min before training or testing in the water-maze. The behavioral measure scored during training was the total time spent to find a hidden platform (TFHP) in 5 consecutive trials while in the test session it was the time spent swimming in the target quadrant (TSTQ), i.e. the one where the hidden platform was located during training. The experimental design aforementioned was approved by the local Ethical Committee in Animal Research (23080.013799/2009-01/CEUA/PRPe/UFSC). Results. Repeated measures analysis of variance followed by Newman Keuls test (p<0.05) revealed that rats infused into the DH with 1.0 nmol of CPZ before testing exhibited a poor spatial memory retrieval, characterized by a reduction in TSTQ relative to controls [VEH (mean ± SEM) = 32.0 ± 3.0 s; CPZ 1.0 nmol = 24.0 ± 1.0 s; CPZ 3.0 nmol = 30.0 ± 2.0]. CPZ infusion into the VH, however, did not affect (p>0.05) this parameter scored on testing. With regard to CPZ effect on training, neither the DH nor the VH infusion of this TRPV1 channel antagonist interfered with TFHP when compared to controls. Discussion. The present results suggest the DH, but not the VH, TRPV1 recruitment during the retrieval of spatial memory. Therefore, our findings substantiate the idea that cognitive and emotional processing is regionally dissociated within the hippocampus.