Cannabinoid-Induced Hyperphagia is Mediated by Increased Meal Frequency and the Orexin-1 Receptor in Male Rats

Abstract

Exogenous cannabinoids have long been known to promote eating. However, the underlying mechanisms have not been completely elucidated, which is critical to understanding their utility. The orexin/hypocretin (OH) system of the lateral hypothalamus (LHA) has known anatomical, biochemical, and physiological interactions with the endocannabinoid system, and has an established role in promoting appetitive behavior; yet, it is still unknown if the OH system mediates food intake following cannabinoid administration. Herein, we validated an oral method of cannabinoid receptor agonist, CP55940, administration via gelatin-based edibles, showing that voluntarily consumed cannabinoid-containing edibles produce acute hyperphagia via an increase in meal number in male rats. Following cannabinoid administration, rats displayed an upregulation in the immediate early gene c-Fos in OH neurons compared to vehicle-treated animals. We further employed a within-subjects design to investigate whether orexin-1 (OX1) receptor signaling was necessary for cannabinoid-induced hyperphagia by coadministering a subeffective dose of an OX1 receptor antagonist, SB334867, with the cannabinoid-containing edible. Data were collected from metabolic monitoring cages, simultaneously capturing chow intake, locomotor activity, and metabolic variables. Results showed that the OX1 receptor antagonist blocked cannabinoid-induced hyperphagia and the transient increase in locomotor activity following cannabinoid administration. Furthermore, both the edible cannabinoid receptor agonist and the OX1 receptor antagonist individually reduced energy expenditure several hours following administration. Taken together, we conclude that the OX1 receptor is required for the hyperphagic response to exogenous cannabinoid administration.

Keywords: CB1; c‐Fos; foraging behavior; hypocretin; locomotor activity; meal patterns; microstructure.

FIGURE 1

Edible cannabinoid receptor agonist CP55940 acutely promotes eating behavior via an increase in meal number (n = 7/treatment). Male rats increased standard chow intake over the first 2 h of the dark cycle (A). Meal pattern analyses revealed hyperphagia was mediated not by an increase in meal size (B) but by an increase in meal number (C). However, over the course of 24 h, there were no differences in overall chow intake (D), meal size (E), or meal number (F). Data were analyzed by paired two‐tailed Student's t‐test and are means +/− SEM; *p < 0.05, **p < 0.01.

FIGURE 2

Edible cannabinoid receptor agonist CP55940 increases c‐Fos expression in orexin neurons (n = 5/treatment). Representative images from each treatment are shown in (A) with vehicle‐treated in the left column and CP55940‐treated in the right column. There were no differences in total orexin‐A + cell number (B), but there was an increase in doubly labeled c‐Fos + orexin‐A + cells in the cannabinoid‐treated group (C). The percentage of c‐Fos + orexin‐A neurons was calculated for each animal showing that the cannabinoid‐treated group had a higher percentage of orexin‐A neurons expressing c‐Fos compared to vehicle‐treated animals (D). The scale bars are 100 μm. Data were analyzed by unpaired two‐tailed Student's t‐test with Welch's correction applied only to the number of OH+ neuron counts due to unequal standard error of the mean and are means +/− SEM; *p < 0.05.

FIGURE 3

OX1 receptor antagonist SB334867 blocks cannabinoid‐induced hyperphagia (n = 8/treatment). Chow intake by the hour is shown in (A) up to 6 h following the return of food access. Two‐way repeated measures ANOVA and post hoc analyses with uncorrected Fisher's LSD of food intake 2 h following food access revealed that CP55940 increased chow intake that was blocked by SB334867 (B). Microstructural meal analysis after 2 h following food access showed no differences in meal size (C), but increased meal number in the cannabinoid‐treated conditions (D). There was a trend toward SB334867 (coadministered with the vehicle edible) decreasing meal number, but this did not reach significance. The red box in A is indicating the time point at which the two‐way cross‐sectional meal analyses were conducted, and the resulting data are displayed in B, C, and D. Data are means +/− SEM; *p < 0.05, **p < 0.01, ***p < 0.001.

FIGURE 4

Changes in locomotor activity and energy expenditure following cannabinoid receptor agonist CP55940 and OX1 receptor antagonist SB334867 (n = 8/treatment). Locomotor activity in meters is shown over the first 6 h following the return of food access in (A). Two‐way repeated measures ANOVA and post hoc analyses with uncorrected Fisher's LSD of activity 2 h following food access revealed that CP55940 increased ambulation that was attenuated, but not completely blocked, by SB334867 (A, enclosed in red square). Energy expenditure (EE) in kcal/h is shown for up to 6 h over the first 6 h following the return of food access in (B). Two‐way repeated measures ANOVA and post hoc analyses with uncorrected Fisher's LSD of EE 2 h following food access revealed that only SB334867 decreased EE at this time point (B, enclosed in red square). Red boxes on the larger graphs are indicating the time point at which the two‐way cross‐sectional analyses were conducted, and the resulting data are enclosed in the adjacent red square. Data are means +/− SEM; *p < 0.05.