Dietary conditions and highly palatable food access alter rat cannabinoid receptor expression and binding density

Abstract

Endogenous cannabinoid signaling, mediated predominately by CB1 receptor activation, is involved in food intake control and body weight regulation. Despite advances in determining the role of the CB1 receptor in obesity, its involvement in the driven nature of eating pathologies has received little attention. The present study examined CB1 receptor alterations as a consequence of dietary-induced binge eating in female Sprague Dawley rats. Four control groups were used to control for calorie restriction and highly palatable food variables characterizing this behavioral model. All groups were kept on their respective feeding schedules for 6-weeks and were given a uniform 33% calorie restriction (~22 h food deprivation) prior to sacrifice. Our findings indicate regional CB1 mRNA and density were influenced by dietary conditions, but were not specific to the dietary-induced binge eating paradigm used. An increase of approximately 50% (compared with naive controls) in CB1 receptor mRNA levels in the nucleus of the solitary tract as measured by in situ hybridization was found in animals receiving continuous access to a highly palatable food (i.e., vegetable shortening with 10% sucrose). This group also had a significant increase in body weight and adiposity. An approximate 20% reduction in CB1 mRNA was observed in the cingulate cortex (area 1 and 2) in animals that were exposed to intermittent schedule of feeding, compared with groups that had ad libitum feeding schedules (i.e., continuous access and naive controls). Receptor density as measured by [3H] CP55,940 autoradiography, was reduced by approximately 30% in the nucleus accumbens shell region in groups receiving repeated access to the highly palatable food. Taken together, these findings indicate dietary conditions can differentially influence CB1 receptors in forebrain and hindbrain regions.

Enhanced Glutamatergic Synaptic Plasticity in the Hippocampal CA1 Field of Food-Restricted Rats: Involvement of CB1 Receptors

“…Such alteration induced by FR may depend, in turn, on the reduced Food restriction and synaptic plasticity in rat hippocampus G Talani et al surface expression of CB1Rs as indicated by western blot analysis that revealed a reduction in CB1R protein level in a hippocampal-enriched membrane preparation. These results are also in line with previous studies showing a decrease in CB1R mRNA levels in the cingulated cortex as a result of FR or palatable food consumption in rats (Bello et al, 2012). In our experimental condition, CB1R protein expression appears independent on the time point relative to food presentation, and in fact its levels were decreased at all tested times.…”

“…Expression of CB1R protein has been found to be markedly affected by specific dietary schedules (Dazzi et al 2014;Bello et al, 2012). In the present study, immunoblot analysis revealed that the amount of CB1R protein in the whole hippocampus was significantly decreased in FR rats killed at different time points with respect to food presentation when compared with CTRL animals (one-way ANOVA and Newman-Keuls test: F (6,50) = 5.038, Po0.001; Figure 3a and b).…”

Exposure to a Highly Caloric Palatable Diet during the Perinatal Period Affects the Expression of the Endogenous Cannabinoid System in the Brain, Liver and Adipose Tissue of Adult Rat Offspring

“…Furthermore, hypercaloric diets have been linked to alterations in the expression and density of several components of the ECS in the brain and peripheral tissues. Thus, access to a highly palatable diet could modify the expression and density of CB1 receptors in specific brain regions [32]. It has been also demonstrated that a chronic high-fat diet exposure alters the levels of endocannabinoids and their metabolic enzymes in the pancreas and adipose tissue [33].…”

Blockade of CB1 receptors prevents retention of extinction but does not increase low preincubated conditioned fear in the fear incubation procedure

“…Thus, either species differences, task differences, or differences in feeding conditions could account for the different effects of a CB1 receptor antagonist on fear extinction. Notably, food restriction can affect the levels of endocannabinoids and CB1 receptors (Hanus et al , 2003; Bello et al , 2012), and this may change the effects of a CB1 receptor antagonist at the CB1 receptor. It is unclear which feeding conditions more closely resemble the human condition, although it is possible that the normal function of CB1 receptors in humans maintaining stable body weights more closely resembles that seen in our food restricted rats.…”