Aims: 

The transient receptor potential vanilloid-1 (TRPV1) receptor of primary afferent neurons is considered as an integrator of noxious stimuli. TRPV1 receptors are also expressed in the brain, especially in the hippocampus and the cortex but their physiological role is unknown. Recent studies demonstrated reduced anxiety and conditioned fear in TRPV1 knock-out (KO) mice compared with wild type mice, as well as the absence of long-term depression in hippocampal brain slices from TRPV1-KO mice. Based on these data our present study is aimed at exploring the possible role of cerebral TRPV1 receptors in the hippocampus-dependent learning and synaptic plasticity.

Methods: 

Hippocampus-dependent learning was studied by the Morris water maze test and the Y-maze test on TRPV1-KO and wild type C57BL/6 Jax mice (n=12/group). The effect of an analgesic dose (30 mg/kg, p.o.) of SB-705498, a selective TRPV1 receptor antagonist, on the learning performance of male Wistar rats was also tested (n=10/group). Cortical spreading depression (CSD) in neocortical slices and long term potentiation (LTP) in hippocampal slices of TRPV1-KO and wild type mice (n=8/group) were elicited.

Results: 

No differences in hippocampus-mediated learning between TRPV1-KO and wild type mice were found. SB-705498 did not affect learning performance in rats. While in LTP studies TRPV1-KO mice showed significantly reduced neuronal excitability and synaptic plasticity, neocortical CSDs of TRPV1-KO and wild type mice did not differ.

Conclusion: 

In our rodent models, results on neuronal excitability appeared inconclusive, while behavioural performance was independent of TRPV1 function. Therefore, we suggest that TRPV1 receptors of the brain are probably not involved in the hippocampus-dependent learning and excitability properties.