The Absence of the Transient Receptor Potential Vanilloid 1 Directly Impacts on the Expression and Localization of the Endocannabinoid System in the Mouse Hippocampus

Abstract

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective ligand-gated cation channel involved in synaptic transmission, plasticity, and brain pathology. In the hippocampal dentate gyrus, TRPV1 localizes to dendritic spines and dendrites postsynaptic to excitatory synapses in the molecular layer (ML). At these same synapses, the cannabinoid CB1 receptor (CB1R) activated by exogenous and endogenous cannabinoids localizes to the presynaptic terminals. Hence, as both receptors are activated by endogenous anandamide, co-localize, and mediate long-term depression of the excitatory synaptic transmission at the medial perforant path (MPP) excitatory synapses though by different mechanisms, it is plausible that they might be exerting a reciprocal influence from their opposite synaptic sites. In this anatomical scenario, we tested whether the absence of TRPV1 affects the endocannabinoid system. The results obtained using biochemical techniques and immunoelectron microscopy in a mouse with the genetic deletion of TRPV1 show that the expression and localization of components of the endocannabinoid system, included CB1R, change upon the constitutive absence of TRPV1. Thus, the expression of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) drastically increased in TRPV1−/− whole homogenates. Furthermore, CB1R and MAGL decreased and the cannabinoid receptor interacting protein 1a (CRIP1a) increased in TRPV1−/− synaptosomes. Also, CB1R positive excitatory terminals increased, the number of excitatory terminals decreased, and CB1R particles dropped significantly in inhibitory terminals in the dentate ML of TRPV1−/− mice. In the outer 2/3 ML of the TRPV1−/− mutants, the proportion of CB1R particles decreased in dendrites, and increased in excitatory terminals and astrocytes. In the inner 1/3 ML, the proportion of labeling increased in excitatory terminals, neuronal mitochondria, and dendrites. Altogether, these observations indicate the existence of compensatory changes in the endocannabinoid system upon TRPV1 removal, and endorse the importance of the potential functional adaptations derived from the lack of TRPV1 in the mouse brain.

Environmental Enrichment Rescues Endocannabinoid-Dependent Synaptic Plasticity Lost in Young Adult Male Mice after Ethanol Exposure during Adolescence

“…Recent evidence indicates that the lack of TRPV1 alters the main 2-AG and AEA degrading enzymes, as well as CB1Rs localized to excitatory and inhibitory terminals in the outer 2/3 DGML. Thereby, a crosstalk between TRPV1 and CB1R has been proposed [63]. In this scenario, our findings support a switch from MPP-LTD to MPP-LTP when EE is applied.…”

Lack of the Transient Receptor Potential Vanilloid 1 Shifts Cannabinoid-Dependent Excitatory Synaptic Plasticity in the Dentate Gyrus of the Mouse Brain Hippocampus

“…However, although CB 1 receptors located on the glutamatergic synapses are tightly coupled to G protein signaling (Steindel et al, 2013), basal activation in the hippocampus could not only correspond to CB 1 receptors as Gi/o proteins are also coupled to other metabotropic receptors besides the CB 1 receptor (Conn and Pin, 1997). In addition, a drastic increase in the cannabinoid receptor-interacting protein 1a (CRIP1a) was detected previously in TRPV1-/-hippocampus (Egaña-Huguet et al, 2021). CRIP1a reduces the agonist-stimulated CB 1 receptor internalization and attenuates CB 1 receptor signaling, thus increasing neurotransmitter release (Booth et al, 2019;Oliver et al, 2020).…”

“…Seven-/eight-week-old male TRPV1-/- mice ( n = 43) and their WT littermates (TRPV1+/+) ( n = 21) were used. The TRPV1-/- mice were derived from heterozygous breeding pairs as described previously in the study by Egaña-Huguet et al ( 2021 ). Mice were housed in pairs or groups of maximum three littermates in standard Plexiglas cages (17 ×14.3 ×36.3 cm), and before the experiments were conducted, they were allowed to acclimate to the environment for at least 1 week.…”

“…Conversely, high-frequency stimulation (HFS) of the lateral perforant path (LPP) triggers a CB 1 receptor-dependent longterm potentiation (LTP) that requires post-synaptic N-methyl-D -aspartate (NMDA) receptors, metabotropic glutamate receptor 5 (mGluR5), and mobilization of the endocannabinoid 2arachidonoylglycerol (2-AG) (Wang et al, 2016). Anatomically, the constitutive absence of TRPV1 in mice alters the principal degrading enzymes of 2-AG and anandamide (AEA, the other main endocannabinoid), as well as modifies CB 1 receptors Abbreviations: ACSF, Artificial cerebrospinal fluid; AEA, Arachidonoylethanolamine or anandamide; AMPA, D -Amino-3-hydroxy-5-methyl-4isoxazole-propionic acid; BSA, Bovine serum albumin; CA1, Region 1 of Cornu ammonis; CB 1 receptor, Type I cannabinoid receptor; CRIP1a, Cannabinoid receptor-associated protein 1a; DAGL, Diacylglycerol lipase; DMSO, Dimethyl sulfoxide; eCB, Endocannabinoid; ECS, Endocannabinoid system; eCB-eLTD, Endocannabinoid-mediated long-term depression of excitation; eLTD, Longterm depression of excitation; FAAH, Fatty acid amide hydrolase; fEPSP, Field excitatory post-synaptic potential; FIJI, Fiji is just IMAGE J; LFS, Low-frequency stimulation; LPP, Lateral perforant path; LTD, Long-term depression; LTP, Long-term localized to the excitatory and inhibitory terminals in the outer two-third of ML, the termination zone of the perforant path (Egaña-Huguet et al, 2021). However, the functional impact of these adaptive changes on synaptic plasticity is currently unknown.…”

“…Conversely, high-frequency stimulation (HFS) of the lateral perforant path (LPP) triggers a CB 1 receptor-dependent long-term potentiation (LTP) that requires post-synaptic N -methyl- D -aspartate (NMDA) receptors, metabotropic glutamate receptor 5 (mGluR5), and mobilization of the endocannabinoid 2-arachidonoylglycerol (2-AG) (Wang et al, 2016 ). Anatomically, the constitutive absence of TRPV1 in mice alters the principal degrading enzymes of 2-AG and anandamide (AEA, the other main endocannabinoid), as well as modifies CB 1 receptors localized to the excitatory and inhibitory terminals in the outer two-third of ML, the termination zone of the perforant path (Egaña-Huguet et al, 2021 ). However, the functional impact of these adaptive changes on synaptic plasticity is currently unknown.…”