The control of appetite and satiety is extremely complex and involves a balance between neurotransmitters and neuropeptides to stimulate and/or inhibit feeding behaviour. The effect of cannabinoids on food intake is well established, but little is known about the mechanism of action underlying their activity. In the present report, the effect of pharmacological manipulation of the cannabinoid receptor on the expression of hypothalamic neuropeptides is investigated. We used an immunohistochemical approach to examine the effect of intracerebroventricular administration of the cannabinoid receptor agonist WIN55,212-2 and the inverse agonist AM251 on neuropeptide Y (NPY) and the β-endorphin (β-end) neuronal hypothalamic systems. Double immunohistochemistry (c-fos/β-end) was used to assess the number of β-end neurons activated by the cannabinoid agonist. The present results showed that 1 μg WIN 55,212-2 increases β-end immunoreactivity within the arcuate nucleus while no significant changes were noted in the NPY-immunoreactive nerve fibres network in comparison to the control group. Injection of 1 μg AM251 decreases both NPY and β-end immunoreactivity within the arcuate nucleus. The number of β-end neurons exhibiting c-fos increased significantly in WIN 55,212-2 compared with the control group. These results suggest that cannabinoids affect the expression of hypothalamic neuropeptides, notably the NPY and β-end systems, which may have implications in the orexigenic action of cannabinoids.

The study was designed in order to gain a better understanding of whether the lack of competition stress and/or sampling time had an influence on circulating β-endorphin, adrenocorticotrophin (ACTH) and cortisol modifications after experimental showjumping sessions and to study the effects of fence height on hormone changes. Hormone levels were recorded before exercise in basal conditions and after warm-up, then 5 and 30 min post-exercise. Using a randomized crossover study design, six horses were studied during three experimental showjumping sessions over fences of different heights: 1.00 m (session 1), 1.10 m (session 2) and 1.20 m (session 3). The showjumping exercise did not modify plasma β-endorphin and serum ACTH concentrations after session 1, and tended only to maintain higher values than basal after both session 2 and session 3. The interaction fence height/time was not statistically significant for either β-endorphin or ACTH changes. Sampling time significantly affected both β-endorphin (F = 2.88; P < 0.04) and ACTH (F = 3.84; P < 0.01) changes. Serum cortisol levels were always higher than basal 5 min post-exercise, with levels falling at 30 min. The interaction fence height/time was not statistically significant, while sampling time significantly affected the results (F = 7.96; P < 0.0002). This study demonstrated no significant effects of fence height on β-endorphin, ACTH and cortisol changes. The sampling times adopted affected post-exercise changes in plasma β-endorphin, ACTH and cortisol and could have masked the effects of fence height on hormone modifications.