Gut-to-brain signalling has a pivotal role in the regulation of food intake and energy balance. Vagal afferent neurons (VANs) integrate a wide range of signals from the proximal intestine to stimulate or inhibit appetite. Gut hormones and intestinal endocannabinoids (eCBs) are key peptides that act on the vagus nerve and transmit signals to the brain, responding to the food digestion or food deprivation. Enteroendocrine (EE) cells sense nutrients and release gut hormones that regulate food digestion and appetite. I-cells are a subtype of EE cells, primarily localized in duodenum, that secrete the classic satiety hormone cholecystokinin (CCK), mainly in response to fat. Post-prandially, CCK suppresses appetite via vagal CCK-1 receptors and also down-regulates the expression of the orexigenic-signalling associated cannabinoid receptor CB1 in VANs, to inhibit food intake. CB1 receptor is up-regulated during fasting, when CCK levels are low and intestinal eCBs levels are increased, to promote stimulation of appetite. Intestinal eCBs levels can also selectively increase after a fatty meal, a response that is dependent on the orosensory properties of the meal. Elevated eCBs levels further induce fat intake by activating CB1 receptor. Although it is accepted that CB1 receptor is expressed in VANs, it remains unknown if it is expressed in the duodenal epithelium. The aim of our study was to investigate if CB1 receptor is expressed in the duodenal mucosa and specifically in I-cells. We used the (Cck-EGFP)BJ203 transgenic mouse model to isolate I-cells by using fluorescence activated cell sorting (FACS). 5000-10000 I-cells were isolated by FACS in each experiment. Semi-quantitative RT-PCR analysis of total unamplified RNA prepared from sorted I-cells (eGFP+ cells) and equal number of non I-cells (eGFP- cells) revealed that I-cells are highly enriched in CB1 receptor mRNA transcript in comparison with non I-cells (epithelial cells). RT-PCR analysis was repeated on amplified RNA/cDNA samples from I-cells and non I-cells confirming that CB1 receptor mRNA transcript is specifically expressed in I-cells and cannot be detected in non I-cells. We then examined if the CB1 receptor mRNA levels are regulated by energy intake. We compared CB1 receptor mRNA levels using duodenal mixed cell populations from 3 different groups of mice (fed ad libitum, fasted for 16 hours and fasted for 16 hours/re-fed for 5 hours). Semi-quantitative RT-PCR indicated that CB1 mRNA is upregulated during fasting. Re-feeding of fasted mice down-regulates the expression of CB1 mRNA transcript. Our results suggest that I-cells contain mRNA transcript encoding CB1 receptor and that its expression is upregulated during energy restriction, similarly with VANs. The presence of CB1 mRNA transcript in I-cells may suggest that eCBs directly inhibit CCK release to promote stimulation of food intake.