Introduction: Gastric vagal afferents (GVAs) relay signals to the hindbrain resulting in satiety and termination of a meal. Endocannabinoids regulate food intake via action at cannabinoid 1 (CB1) receptors and transient receptor potential 1 (TRPV1) channels. TRPV1 and CB1 are expressed on GVAs and the endocannabinoid anandamide (AEA) is expressed in the stomach. This study aimed to determine the relationship between TRPV1 and CB1 in mediating AEA effects on GVA satiety signalling.
Methods: Eight week male C57BL/6 murine (N=60) GVA responses to 3g tension were obtained using an in vitro GVA electrophysiology preparation. The effect of the stable analogue of AEA, methanandamide (mAEA; 1-100nM), on GVA responses to 3g stretch was determined in the absence and presence of a CB1 (rimonabant; 300nM)), TRPV1 (AMG9810; 30nM), protein kinase A (PKA inhibitor fragment (6-22) amide; 5nM), protein kinase C (bisindolylmaleimide II; 10nM), Gαi/o (NF023; 300nM), or Gαq (YM-254890; 100nM) antagonist.
Results: Low doses (1-10nM) of mAEA reduced whereas high doses of mAEA (30-100nM) increased tension sensitive GVA responses to 3g stretch. The inhibitory effect of mAEA (1nM) was lost and the excitatory effect of mAEA (100nM) was reduced in the presence of rimonabant. The inhibitory and excitatory effects of mAEA were lost in the presence of AMG9810. The PKA inhibitor fragment (6-22) amide or NF023 prevented the inhibitory effect of mAEA on GVA mechanosensitivity but had no effect of the excitatory component. Conversely, in the presence of bisindolylmaleimide II or YM-254890 the excitatory effect of mAEA was reduced or lost respectively whereas the inhibitory effect remained.
Conclusions: Activation of CB1, by mAEA, can activate or inhibit TRPV1 to increase or decrease GVA responses to stretch depending on the second messenger pathway activated. These interactions could play an important role in the fine control of food intake.
Funded by Diabetes Australia Research Trust