The distribution and regulation of vanilloid receptor VR1 and VR1 5′ splice variant RNA expression in rat

doi:10.1016/S0306-4522(01)00373-6

Neuroscience

Volume 107, Issue 3, 23 November 2001, Pages 373-381

https://doi.org/10.1016/S0306-4522(01)00373-6 Get rights and content

Abstract

The vanilloid (capsaicin) receptor, VR1, is expressed in dorsal root ganglion and mediates the sensory response to vanilloids and other noxious stimuli. There is evidence for VR1 expression in CNS regions as well, but its function in these tissues is unknown. The identification of a rat VR1 5′ splice variant and the rat stretch inhibitable channel, which are also expressed in dorsal root ganglia and CNS, raises the possibility that these and/or other VR1 variants may regulate VR1 activity. We have used a quantitative ribonuclease protection assay to characterize the central and peripheral expression of VR1 and VR1 variant RNA in the rat. The data confirm that VR1 is widely expressed in CNS, with highest RNA levels found in cerebral cortex, hippocampus, and cerebellum. VR1 RNA expression in dorsal root ganglia is approximately 28 times greater than in any other tissue sample studied. VR1 5′ splice variant RNA is expressed at levels 12 times lower than VR1 in dorsal root ganglia, but at similar levels to VR1 in all other tissues examined. A VR1-related RNA expressed at high levels in kidney was detected, and was distinct from VR1 or stretch inhibitable channel. Our results also show that peripheral inflammation does not change VR1 RNA levels in rat dorsal root ganglia. Systemic resiniferatoxin administration, however, decreases VR1 expression in dorsal root ganglia by 65–80%, an effect that persists for at least 2 months.

This study demonstrates that VR1 is expressed at high levels in dorsal root ganglia relative to other tissues and that VR1 5′ splice variant is expressed at low levels in dorsal root ganglia compared to VR1. VR1 gene expression in dorsal root ganglia is regulated in response to systemic resiniferatoxin but not peripheral inflammation.

Section snippets

Animals and nociceptive treatments

Male Sprague–Dawley rats (225–300 g; Charles River Laboratories, Wilmington, MA) were used for all experiments. Animals were handled in accordance with the Neurogen Animal Care and Use Committee. All efforts were made to minimize animal suffering and the number of animals necessary for reliable scientific data. For tissue distribution studies, tissue samples were rapidly dissected from CO₂-asphyxiated rats and frozen on dry ice.

For the CFA experiment, 100 μl of a 1:1 emulsion with saline was

Results

The distribution of VR1 RNA expression in DRG, CNS regions, and several peripheral tissues was examined with quantitative RPAs. Since several VR1 variants have been reported (Fig. 1), VR1 RNA was first measured with a probe that discriminates VR1 from all other reported variants by protecting a 606 nucleotide fragment of the rat VR1 RNA, nucleotides 410–1015 of rat VR1 (Fig. 2A). With this probe, high levels of VR1 expression were detected in DRG and relatively lower levels in the CNS,

Discussion

These experiments confirm that VR1 RNA is expressed in CNS and in several peripheral tissues at levels much lower than in DRG. Similarly, VR1 5′sv RNA is also expressed in CNS and in DRG, although at levels much lower than VR1 in DRG. RPA analysis with a VR1 3′ coding region probe reveals evidence for a novel VR1-like RNA in kidney, the functional significance of which remains to be defined. VR1 RNA expression in DRG is decreased by systemic RTX treatment but does not change in response to

Acknowledgements

The authors thank Tong Zou, Rita Patel, Mary Kay Lescoe, Amy Peck, Michele Kinrade, and Stephen Waters for technical assistance and Kathy Grant and Linda Boran for help with manuscript preparation.

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Preclinical evidence suggests that the endocannabinoid and endovanilloid system within the brain are important neuronal substrates involved in emotional responses to stress. Specifically, the Transient Receptor Potential Vanilloid 1 (TRPV1) is a member of the Transient Receptor Potential (TRP) superfamily, within the brain regulate anxiety and depression behaviors through its interactions with the endocannabinoid system. However, little is known about the cellular mechanisms that regulate these receptors’ interactions across the brain and their impact in neuropsychiatric disorders. Previous studies provided evidence of a functional cross talk between TRPV1 and CB1R in regulating anxiety and depression-like behaviors triggered by stress within specific brain regions related to emotional processes using rats as animal model. These findings contribute to a better understanding of the functional link between endocannabinoid receptors and endovanniloid receptors within the central nervous system as it relates to emotional disturbances associated to psychiatric disorders such as general anxiety and major depression.
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Citation Excerpt :
As a result, the contextual stimulus comes to elicit fear response during the expression phase, in the absence of the unconditioned stimulus (Curzon et al., 2009; Pezze and Feldon, 2004). Studies show expression of CB1 and TRPV1 in several brain regions involved in fear response, including thalamus, cortex, amygdala, and hippocampus (Herkenham et al., 1991; Mezey et al., 2000; Roberts et al., 2004; Sanchez et al., 2001; Toth et al., 2005; Tsou et al., 1998). In agreement, the administration of cannabinoid or vanilloid drugs modulates emotional and cognitive processing (for review, see Moreira and Lutz, 2008).
Studies suggest that the endocannabinoid and endovanilloid systems are implicated in the pathophysiology of schizophrenia. The Spontaneously Hypertensive Rats (SHR) strain displays impaired contextual fear conditioning (CFC) attenuated by antipsychotic drugs and worsened by pro-psychotic manipulations. Therefore, SHR strain is used to study emotional processing/associative learning impairments associated with schizophrenia and effects of potential antipsychotic drugs. Here, we evaluated the expression of CB₁ and TRPV1 receptors in some brain regions related to the pathophysiology of schizophrenia. We also assessed the effects of drugs that act on the endocannabinoid/endovanilloid systems on the CFC task in SHRs and control animals (Wistar rats – WRs). The following drugs were used: AM404 (anandamide uptake/metabolism inhibitor), WIN55-212,2 (non-selective CB₁ agonist), capsaicin (TRPV1 agonist), and capsazepine (TRPV1 antagonist). SHRs displayed increased CB₁ expression in prelimbic cortex and cingulate cortex area 1 and in CA3 region of the dorsal hippocampus. Conversely, SHRs exhibited decreases in TRPV1 expression in prelimbic and CA1 region of dorsal hippocampus and increases in the basolateral amygdala. AM404, WIN 55,212-2 and capsaicin attenuated SHRs CFC deficit, although WIN 55,212-2 worsened SHRs CFC deficit in higher doses. WRs and SHRs CFC were modulated by distinct doses, suggesting that these strains display different responsiveness to cannabinoid and vanilloid drugs. Treatment with capsazepine did not modify CFC in either strains. The effects of AM404 on SHRs CFC deficit was not blocked by pretreatment with rimonabant (CB₁ antagonist) or capsazepine. These results reinforce the involvement of the endocannabinoid/endovanilloid systems in the SHRs CFC deficit and point to these systems as targets to treat the emotional processing/cognitive symptoms of schizophrenia.

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¹: Present address: The School of Arts and Sciences, University of Bridgeport, Bridgeport, CT 06601, USA.

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The distribution and regulation of vanilloid receptor VR1 and VR1 5′ splice variant RNA expression in rat

Abstract

Section snippets

Animals and nociceptive treatments

Results

Discussion

Acknowledgements

Life Sci.

Anal. Biochem.

Neuroscience

Cell

Neuroscience

Neurosci. Lett.

J. Biol. Chem.

J. Biol. Chem.

Neuroscience

Neurosci. Lett.

Brain. Res.

Neuron

Mechanical and heat sensitization of cutaneous nociceptors after peripheral inflammation in the rat

J. Neurophysiol.

The capsaicin receptor: a heat-activated ion channel in the pain pathway

Nature

Impaired nociception and pain sensation in mice lacking the capsaicin receptor

Science