Alterations in the emotional and memory behavioral phenotypes of transient receptor potential vanilloid type 1-deficient mice are mediated by changes in expression of 5-HT1A, GABA(A), and NMDA receptors.

ABSTRACT

The transient receptor potential vanilloid type 1 channel (TRPV1) receptors are expressed in various regions of the brain. Much less is known about whether TRPV1 receptors affect higher brain functions. In the present study, we demonstrated that TRPV1-knockout (TRPV1KO) mice showed antidepressant-like behaviors in a novelty-suppressed feeding test and forced swim test when compared to wild-type (WT) mice. Additionally, TRPV1KO mice exhibited increased aggressiveness and reduced social interactions in a social dominance test and social interaction test. TRPV1KO mice showed reduced short-term memory and normal long-term memory in a novel object recognition test and passive avoidance test versus WT mice. Based on these behavioral data, we investigated changes in specific receptors related to depression, anxiety, and memory in the brains of TRPV1KO and WT mice. Binding of [(3)H]-8-OH-DPAT was significantly higher in the frontal associated cortex (FrA), nucleus accumbens (NAc), and the cingulate cortex (CC) of TRPV1KO mice than WT mice, while the expression of 5-HT(1A) receptors was higher in the FrA, NAc, and cortex of TRPV1KO mice than WT mice. [(3)H]-flunitrazepam binding was also significantly higher in the FrA, striatum (CPU), and the CC of TRPV1KO versus WT mice. In contrast, [(3)H]-musicmol binding in the FrA, CPU, NAc, CC, and the dentate gyrus (DG) was significantly lower in TRPV1KO mice than WT mice. The expression of GABA(A)γ(2) was higher in the NAc, CPU, and cortex of TRPV1KO versus WT mice, whereas the expression of GABA(A)α(2) was lower in the FrA, CPU, NAc, and cortex in TRPV1KO mice than WT mice. Finally, [(3)H]-MK-801 binding was decreased in the CPU and CA1 of TRPV1KO versus WT mice. The expression of NR2A was lower in the hippocampus of TRPV1KO versus WT mice. These data suggest that the loss of TRPV1 results in antidepressant-like, anxiolytic, abnormal social and reduced memorial behaviors due to changes in expression of 5-HT(1A), GABA(A,) and NMDA receptors. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.